Ok, I've done a search, but information on this issue isn't exactly definitive. Perhaps an exact solution is yet to be found? On the GEO Brassmaster, RG's layout, from GGG, the Brass selector switch produces no audible difference. There are a lot of threads that discuss changing the resistor values in the twin-T filter. It seems that one thread might have suggested that the labeling of the resistors in that area might be to blame. And that maybe the layout has some in the wrong position? I'm not sure. Does anyone have the answer to this problem? I built this for a friend, and the poor guy has been waiting for it forever. I just want to get it working right so I can give it to him. Can anyone help?
http://www.generalguitargadgets.com/index.php?option=content&task=view&id=144&Itemid=171 (http://www.generalguitargadgets.com/index.php?option=content&task=view&id=144&Itemid=171)
Its funny you should ask this question. I've spent the last week sick in bed with nothing to do but watch tv and look at schematics. Well I was looking at the brassmaster schematic(R.G. Keen's version) and decided to try and figure out why everyone seems to have problems with the filter/brass switch. It took me about two minutes to find the problem. The problem is not the resistor or cap values, its connection errors. Use Keen's schematic as reference so me explaination makes sense. First take the output of the filter drive and connect it the junction of C10 and R25. Next connect R22 and the .01 cap to ground. The filter switch should work great with these changes. The original schematic is wrong as is R.G. Keen's revision. I'm really suprised that no one has made these corrections already. Now of course any PCB's out there will need to be modified to accommodate these changes.
QuoteThe original schematic is wrong as is R.G. Keen's revision. I'm really suprised that no one has made these corrections already.
Hmmm... the original schematic is wrong? That would account for a lot of problems if I accurately reproduced an incorrect maker's schemo.
I always did think that setup looked screwy, but that's what the schemo said.
Do you have an actual device to compare it to?
Quote from: mountainking on April 25, 2007, 01:34:18 PM
First take the output of the filter drive and connect it the junction of C10 and R25. Next connect R22 and the .01 cap to ground. The filter switch should work great with these changes.
Thanks for the reply! But just to clarify. The "output of the filter drive", would that be the collector of the "FILTER AMP" on the schematic? So, at C12?
I would think that Q7 is the filter drive. So, like this... maybe??
(http://moosapotamus.net/untitled.gif)
~ Charlie
Quote from: MikeH on April 25, 2007, 02:21:18 PM
Quote from: mountainking on April 25, 2007, 01:34:18 PM
First take the output of the filter drive and connect it the junction of C10 and R25. Next connect R22 and the .01 cap to ground. The filter switch should work great with these changes.
Thanks for the reply! But just to clarify. The "output of the filter drive", would that be the collector of the "FILTER AMP" on the schematic? So, at C12?
No the "filter drive" is before the filter and the "filter amp" is after. Output of the filter drive comes from its emmiter/R18.
Quote from: R.G. on April 25, 2007, 01:52:01 PM
QuoteThe original schematic is wrong as is R.G. Keen's revision. I'm really suprised that no one has made these corrections already.
Hmmm... the original schematic is wrong? That would account for a lot of problems if I accurately reproduced an incorrect maker's schemo.
I always did think that setup looked screwy, but that's what the schemo said.
Do you have an actual device to compare it to?
No, I don't have an actual device to compare it to, but really all you need to know is that its a twin t filter and without the changes I mentioned it isn't really a twin t filter since it won't really do much filtering and most of the components a basically bypassed. R.G. your updated schematic did correct another thing that I think was a mistake that was also in the original schematic and you certainly made the filter circuit much clearer. I've seen other Maestro schems that had obvious mistakes on them so I guess who ever was in charge of drawing them wasn't paying very close attention to what he was doing.
Quote from: moosapotamus on April 25, 2007, 02:53:07 PM
I would think that Q7 is the filter drive. So, like this... maybe??
(http://moosapotamus.net/untitled.gif)
~ Charlie
You need to move the ground to the junction of R22 and the .01 cap.
and don't forget to reconnect R22 back to the two .005 caps.
never...
Quote from: mountainking on April 25, 2007, 02:56:58 PM
No the "filter drive" is before the filter and the "filter amp" is after. Output of the filter drive comes from its emmiter/R18.
Ahhh. I see. That's reading a schematic on a whole new level. As in, reading the actual words on a schematic :icon_biggrin: .
Like this?
(http://img230.imageshack.us/img230/423/brassfixhd7.jpg)
Yes, correct. Sorry for my lack of visuals, but I'm at work right now.
Quote from: R.G. on April 25, 2007, 01:52:01 PM
QuoteThe original schematic is wrong as is R.G. Keen's revision. I'm really suprised that no one has made these corrections already.
Hmmm... the original schematic is wrong? That would account for a lot of problems if I accurately reproduced an incorrect maker's schemo.
I always did think that setup looked screwy, but that's what the schemo said.
Do you have an actual device to compare it to?
I just built one of these today using your circuit board. I had the real thing back in the 70's. This is real close, but as you have noticed, the Brass 1 & 2 switch hardly does anything, and the Harmonic switch doesn't work like the original.
So I started looking though the two schematics to see if there was an error when the twin-T filter was rearranged. After drawing it out a dozen different ways, I couldn't find any difference, except that you are hooking up one resistor parallel to the other instead of switching them, and there is a missing connection on the schematic from the left side of C10 to the junction of R28 and C12, but it is on the circuit board.
So I was puzzled since your board is exactly what was in the schematic. Then I saw a post at TalkBass where the guy who makes the Barker Assmaster clone said
Quotei've built one, and i've compared it to a real brassmaster.
I will say this. The brassblaster, is based off of the Maestro Brassmaster schematic.
And the Maestro schematic is not a correct schematic for the Brassmaster.
So it makes sense now.
So now I'm going to try this mod and see if it's the right tone.
But I love my Brassblaster... I've been longing for my old Brassmaster and they go for a tone of money these days! Unfortunately I had the original circuit board until recently when a box of parts went missing when we moved. :( (it's a long story, but my Brassmaster stopped working one day, and I was never able to get it repaired)
Quote from: DavidRavenMoon on December 20, 2008, 11:00:53 PM
So now I'm going to try this mod and see if it's the right tone.
Do that. I'll update the schematic and layout if it's the right way.
... preparatory to which I dug out my originals and started looking at the schemo.
Which brought back my original concerns. I thought "Twin T" when I saw that too. I was in the process of digging out the ground point when I realized that the original circuit as drawn drives the "ground point" with the output of an emitter follower and uses the T as a feedback across a voltage gain transistor - just like a proper bootstrapped twin T.
The obvious thing to do was to plop it in a circuit sim and try it out, but as I remember (that being 11 years ago now) I didn't have a handy dandy simulator to plop it into.
That being said, it's probably drawn incorrectly and needs to be regrounded for a non-bootstrapped Twin T config. But I'd sure like to hear from someone trying it both ways.
Quote from: MikeH on April 25, 2007, 03:11:44 PM
Quote from: mountainking on April 25, 2007, 02:56:58 PM
No the "filter drive" is before the filter and the "filter amp" is after. Output of the filter drive comes from its emmiter/R18.
Ahhh. I see. That's reading a schematic on a whole new level. As in, reading the actual words on a schematic :icon_biggrin: .
Like this?
(http://img230.imageshack.us/img230/423/brassfixhd7.jpg)
I tried this mod, and although it does make the switch work better, and more like the real thing, I get oscillation when the sensitivity control is more than a third up and the brass switch is in the open position (I think... it's one of the positions).
Also it should be noted that the above schematic is wrong, as there is a connection between the junction of R28 and C12 up to the junction of C10/R25.
Has anyone does this mod and not gotten oscillations?
I think I just found the biggest problem with the Brassmaster schematic, and it's not necessarily the Twin T setup.
Take a look at the base of Q7. I believe that R29 should come off the T1 side of C13, not the Q7 side. It fouls the biasing of Q7 up tremendously to leave it as the schemo suggests.
I was plopping part in the simulator and when I got to there, the first question in my mind was "... and how does Q7 ever bias up?" It can't. With R29 as shown, very little signal gets through. Very different if you put it on the other side of C13.
It's an easy cut and patch on the PCB; alternatively, you can simply leave off R29 in the position shown and take a new "R29" off from the transformer or C13.
Of course, there can be other bugs in the Twin T setup, but clearing this one should make those easier to expose.
Quote from: R.G. on December 21, 2008, 10:54:06 AM
I think I just found the biggest problem with the Brassmaster schematic, and it's not necessarily the Twin T setup.
Take a look at the base of Q7. I believe that R29 should come off the T1 side of C13, not the Q7 side. It fouls the biasing of Q7 up tremendously to leave it as the schemo suggests.
I was plopping part in the simulator and when I got to there, the first question in my mind was "... and how does Q7 ever bias up?" It can't. With R29 as shown, very little signal gets through. Very different if you put it on the other side of C13.
It's an easy cut and patch on the PCB; alternatively, you can simply leave off R29 in the position shown and take a new "R29" off from the transformer or C13.
Of course, there can be other bugs in the Twin T setup, but clearing this one should make those easier to expose.
OK that sounds like you are onto something. I thought it odd that R29 is on that side of C13. Last night before I went to bed I switched everything back to the "stock" schematic version. The only thing I left was swapping R22 and R27, because they are indeed mislabeled on the component layout. They are correct on the schematic, but since I followed the layout when I populated the board, they were not installed in the right place. With those parts where they belong the Brass switch does something at least. It's very subtle, the original did more.
So this morning I plugged it in and played with it a bit. The biggest thing that stands out is the huge volume boost when I switch the harmonic switch. Yesterday I thought the lower volume tone was the correct one, but now I'm convinced it's more like the louder tone, since that has more octave harmonics, so saying that very little signal gets through the filter makes sense. I also notice that the harmonics come out better if I turn the volume on my bass down a bit (regardless of the Sensitivity control setting).
The mod that added the ground between R22 and C11 and also moved the connection of Q7's emitter isn't right either. While this does give more change when you switch the switches, it's way too buzzy and seems to have increased the gain through the fuzz. As I mentioned on one of the Brass settings I would have uncontrollable oscillations as soon as I connected the power, even with no bass plugged in. Turning down the Sensitivity would stop it, but that's not how the original is.
Speaking of the Sensitivity control I don't remember it turning all the way off. It's admittedly a long time since I played a real Brassmaster, but I seem to remember you could use the sensitivity control all the way down, and still have some fuzz signal. I might be wrong though, and it works fine this way too, as very low sensitivity settings often get cool tones.
I'm going to try moving R29 now. If that brings the filter signal level up to the lo harmonic setting, that might be the fix. (fingers crossed)
OK, I did the R29 mod. I lifted the one end out of its hole and ran a jumper from the T1 side of C13.
I think it made an improvement to the low Harmonic setting, i.e., with the switch closed. It's still louder than the high setting, but it has more of the envelope tone the Brassmaster does. I like it. The Brass switch still does pretty much nothing, slightly brighter in one setting.
I'm quite happy with the tone now, and if we never figure out the T filter issue, could live with this tone, as the Sensitivity control really gets a lot of variation.
Now I'd like to make one with tone controls for the clean and fuzz cannel... maybe a variable low pass filter. In the mean time I might change the Brass switch to work like a tone control to roll some highs off.
Ah, OK. It pretty much had to be that way. I can hypothesize a couple of different connections for the Twin T setup.
One is with the grounding rearranged and the Twin T filtering what goes into the amplifier. I'll go see about drawing that up.
Interesting stuff from simulation.
The filter transistor has its bias changed all over the map when the filter hi-lo switch is flipped. Q7's collector is isolated from the DC conditions on the base of Q6 by the T-capacitors, but the base of Q6 is connected to DC ground through the T, the 150K, and the 10K volume pot. This is somewhat ugly, putting DC across the pot as it does. The change from 47K+47K to 6.8K+6.8K when flipping the filter switch changes the transistor's biasing significantly as well. Moving the "forgotten connection" of the junction of R25 and C10 from the 150K side of C12 to the collector side of C12 helps, and in one of the filter switch positions produces a nice resonant peak in the response. What should happen, I think, is that you should get two resonant peaks, one lower and one higher in frequency. The biasing problems are keeping this from happening.
I have no problem making the circuit do that on my own, but not ever having seen a real one limits my ability to make it "authentic."
I may rework this into an opamp version. That would be far more predictable.
Here's what the real thing sounds like at various positions:
http://www.malekkoheavyindustry.com/index.php?page=b-assmaster
Personally I wouldn't mind having the filter work even if it's not "authentic."
It's funny you mentioned doing it with op amps, I was thinking the same thing today.
So do you have any idea how to make this version work? :icon_biggrin:
I told RG a couple of months ago I'd give him the proper schematic...
Quote from: malekko on December 22, 2008, 02:59:18 PM
I told RG a couple of months ago I'd give him the proper schematic...
:icon_biggrin:
That's very generous. I've been eyeballing your version for a while now... it's very cool.
Quote from: malekko on December 22, 2008, 02:59:18 PM
I told RG a couple of months ago I'd give him the proper schematic...
This would be fantastic. I've been wanting to build this but shying away from it because of the reported issues. RG?
I do remember something about that. A quick search of my mail logs didn't turn up the email though.
I don't remember how that ended up. Malekko, was that a simple donation?
It was a phone conversation, you are supposed to swing by Malekko (in Round Rock) so we can do some 1spot testing with our E600
feel free to call me again 431 5428
Josh
Quote from: R.G. on December 22, 2008, 05:44:43 PM
I do remember something about that. A quick search of my mail logs didn't turn up the email though.
I don't remember how that ended up. Malekko, was that a simple donation?
Ahah! That's it. I put that into the mental "pending" bin while I waited on the 1Spots.
They're here now. What are you doing next week?
Quote from: R.G. on December 22, 2008, 07:19:17 PM
Ahah! That's it. I put that into the mental "pending" bin while I waited on the 1Spots.
They're here now. What are you doing next week?
hanging out with you!
I have a picture of the component side, but I really need a picture of the trace side. DOes anybody have that???
That wack tone section seems like more trouble than its worth. IMO most of the sound must come from the way the transformer is used - the signal is crudely amplitude modulated by a half-wave rectified version of itself.
As RG hinted at, one problem is people think the twin-T circuit should be a notch but it doesn't have to be. The twin-T can be used as a band-pass also. Given the circuit was called a *brass*master you would think that the aim of the filter would be to emulate a brass instrument. Brass instruments tend to be more band-pass in nature so I suspect the filter should act as a band-pass. Some time back the Brassmaster came up and the conclusion was it was bandpass.
This original circuit shows a working connection along these lines:
http://files.muziq.be/schematics/maestro_bb-1_001.gif
The "original" circuit extracts shown earlier are actually modified drawings.
As far as the sound goes for the maestro_bb-1_001.gif I'm not so sure people will like it as it's a very exaggerated response. The savior, and perhaps the key, can blend.
So are the part values correct? (perhaps so see second post)
> but I really need a picture of the trace side. DOes anybody have that???
I've got a picture of the top side only and I can make out 2x47k, 1x6.8k, 0.05uF caps, 3-way switch, transistor near 1k + 1.5Meg + 47? resistors. With a stretch it looks like 3x 0.05uF caps and a larger one which could be 0.01uF. So many values seem to agree with the original schematic.
I think one definite problem is the connection of the 82k going to SW-2:
If switched on, together with the brass volume control it will shift the bias of Q4.
Therefore the 82k should be connected in any case before the 0.1µ capacitor directly at the transformer.
Maybe this could solve some problems ? ::)
For the rest, here are the results of the austrian simulation jury (using 2x 2N5088 as models):
Low-Filter plot (http://analogguru.an.ohost.de/temp/Maestro_BB-1_filter-low.gif)
High-Filter plot (http://analogguru.an.ohost.de/temp/Maestro_BB-1_filter-high.gif)
merry christmas,
analogguru
> Therefore the 82k should be connected in any case before the 0.1µ capacitor directly at the transformer.
It's very likely.
The issue came up in this earlier thread (this thread has the clear pcb pic)
http://www.diystompboxes.com/smfforum/index.php?topic=57420.msg446262#msg446262
Quote from: analogguru on December 23, 2008, 01:37:53 AM
I think one definite problem is the connection of the 82k going to SW-2:
If switched on, together with the brass volume control it will shift the bias of Q4.
Therefore the 82k should be connected in any case before the 0.1µ capacitor directly at the transformer.
Maybe this could solve some problems ?
Probably. See the earlier thread referred to and also reply #15, this thread.
There are other issues lurking in there as well, but the shift in bias issue is known.
Merry Christmas!
I suppose one thing to question is whether the diodes are actually connected to the transformer that way.
The traditional diode ring multiplier has the diodes connected in a ring with two centre-tap transformers. There are two input terminals and one output terminal.
The traditional frequency doubler has a single winding transformer on the input side, the diodes connected as a bridge rectifier, and a single-ended transformer on the output side. (There's also a traditional doubler which uses two diodes, like the tychobrae.)
The bm connection doesn't match either, and is assymetrical. That doesn't mean it is wrong, or that it can't work - it's just something to check. BTW, the phase-splitter on the bm doesn't have a centre-tap output to emulate the input side transformer of the ring multiplier.
The bm doubler seems to work ok, it provides clipping which shouldn't be an issue,
http://www.geocities.com/george_giblet/effects/bm_doubler.png
If you imagine the center tap of the transformer connected to ground, "rectifiying" for both half-waves will occur, resulting in frequency doubling.
analogguru
Delemna time.
I got all the bits & pieces,PCB together in preparation to do this over holiday period.
Should I wait for the updated correct schematic, or plough ahead with the build & mod in any changes at a later date? :icon_confused:
Would appreciate any advice.
From what I gather the Brassblaster in its original guise with all its foibles is still a pretty decent (albeit limited) bass fuzz(?)
Merry Christmas to all & all the best for 2009 to everyone
Nick
http://www.myspace.com/nickdawsonbass (http://www.myspace.com/nickdawsonbass)
Quote from: analogguru on December 23, 2008, 01:37:53 AM
I think one definite problem is the connection of the 82k going to SW-2: If switched on, together with the brass volume control it will shift the bias of Q4.
Therefore the 82k should be connected in any case before the 0.1µ capacitor directly at the transformer.
I rewired mine to have the 82K on the transformer side of the cap. It made an improvement to the tone of that Harmonic switch setting, but still doesn't fix the Brass 1 & 2 settings.
Hi all,
Just looking at the schematic, it seems likely to me that C12 might not be in the collector circuit of Q6 as shown, but belong in the base circuit so the bias doesn't go nuts, as in a coupling capacitor from the output of the Twin-T to the base of Q6. Make sense?
FWIW
Quote from: MR COFFEE on December 29, 2008, 02:30:21 AM
Hi all,
Just looking at the schematic, it seems likely to me that C12 might not be in the collector circuit of Q6 as shown, but belong in the base circuit so the bias doesn't go nuts, as in a coupling capacitor from the output of the Twin-T to the base of Q6. Make sense?
Kind of. Your premise that bias should not shift when switches are flipped is good, and that's what led me to note that C13 was shown incorrectly. However, C12 or some equivalent is needed for blocking the DC from the collector to the output; it may be that it ALSO needs another cap at the input to Q6, and that is one of the things I've been messing with. As soon as I get back from the holidays I'll have more info on that.
Quote from: R.G. on December 29, 2008, 12:38:43 PMAs soon as I get back from the holidays I'll have more info on that.
I'm going to call 2009 the Year of the Brassmaster! Chris Squire will be proud!
BTW over at another forum someone posted a photo of the trace side of the PCB, as well as a PDF of the board traces after it had been run though some software, and the board with the parts layout.
The guy that did the layout said he took the "incorrect" schematic and redrew it into Circuitmaker and was able to verify that the schematic is in fact correct, and matches the real pcb. He also said the Q1 supply is not marked, but it should be fed from the
8 volt supply.
This is all very exciting for this old Brassmaster fan. :icon_biggrin:
I've always missed my BB and my Univox Unitron (Mutron clone) and my script Phase 90, and my Guild Foxy Lady, and my... :icon_frown:
> BTW over at another forum someone posted a photo of the trace side of the PCB, as
I've checked the following:
- Traced parts overlay pdf and compared with the *original* schematic.
http://files.muziq.be/schematics/maestro_bb-1_001.gif
- Checked wiring of pots and switches matches *original* schematic and photos.
- Traced parts overlay pdf with top side photos, appears to agree but I can't see all the value.
Haven't fully checked:
- Traced parts overlay pdf with bottom side photo
- Pot values
At this point it appears the original is correct. So all the propaganda about the original schematic being wrong is crap!
Interestingly moosapotamus build one just like that,
http://www.moosapotamus.net/THINGS/brassmaster.htm
The sound samples don't sound like the b:assmaster samples, possible because of direct recording vs speaker or speaker emulation.
Note is Q5 is a darlington, and is therefore different to the other transistors. On the original schematic, the top view pin out picture for Q5 is wrong (the schem itself is OK) - the 2N5308 datasheet has the same pin outs as the 2N3392.
One thing which would be nice to know is the DC resistances of the transformer windings
- primary: center to outside1, center to outside 2 (need to measure with both meter polarities and take largest reading)
- secondary
I hope that you all will solve the mystery as soon as possible because i got the transistors and i will build one these days :)
Quote from: George Giblet on December 30, 2008, 02:36:57 PM
> BTW over at another forum someone posted a photo of the trace side of the PCB, as
I've checked the following:
- Traced parts overlay pdf and compared with the *original* schematic.
http://files.muziq.be/schematics/maestro_bb-1_001.gif
- Checked wiring of pots and switches matches *original* schematic and photos.
- Traced parts overlay pdf with top side photos, appears to agree but I can't see all the value.
Haven't fully checked:
- Traced parts overlay pdf with bottom side photo
- Pot values
At this point it appears the original is correct. So all the propaganda about the original schematic being wrong is crap!
It's interesting. I found the photos of the top and bottom of the PCB as well, and did my own tracing from that, to the extent possible from the photos. I also took the copied layout and parts overlay and compared that to the original schemo as well.
Net result - while I can't see all the detail, it does appear that the factory schemo could well match the photos I've seen. I also managed to get a sim to run on the whole forward path. When I finally got the simulation failures stomped out, it did seem to work, at least somewhat.
I did find that the bias points of the buffer and filter amp vary with switch setting, as I said. One of the brass positions gets really dull instead of peaky because of that. The response curves get more interesting if the changes to C12 I mentioned are put in, and more importantly a new cap inserted between the T networks and the base of the filter amp. But those do not appear to be in the original.
... if the photo is of an original, or is of an original that has the sound that we hear in samples.
I'm still hamstrung by not seeing a real one ever. And I'm getting paranoid (:icon_lol:) about photos as well as schematics.
Anyway, one day I'll find a real one and this will get solved. Shoot, the first layout I did may have accidentally been accurate, if unsatisfying. :icon_lol: :icon_lol:
I still hold some skepticism but after checking through those fairly clear photos it's diminishing rapidly :).
> I did find that the bias points of the buffer and filter amp vary with switch setting, as I said.
Yes they definitely do.
> ... But those do not appear to be in the original.
In the photo I checked that part of the circuit many times and it appears it's just like that.
With a darlington for Q5 the bias points are very poor, particular with the filter set to the 6k8/3k3 position. I'm seriously thinking all the transistors are alike. When Q5 is a normal (non darlington) BJT the bias points aren't too bad at all.
I've thought a few times about reducing that to modern (i.e. opamp) practice, and that would fix things.
See what happens in your sims when you move the C13 cap to the base side and insert a 1uF in series from the Twin T to the base of the filter amp. Now there is no more bias shift. The filter resonance give two nicely distinct peaks at about 700 and 2.5K. I thought for sure that was what was in the original, but it appears not.
Quote from: George Giblet on December 30, 2008, 02:36:57 PM
At this point it appears the original is correct. So all the propaganda about the original schematic being wrong is crap!
Interestingly moosapotamus build one just like that,
http://www.moosapotamus.net/THINGS/brassmaster.htm
The sound samples don't sound like the b:assmaster samples, possible because of direct recording vs speaker or speaker emulation.
He also says that the Brass switch doesn't really work. The only difference between the original schematic and RG's is the twin T filter, and they are functionally the same.
I built the same clone and the brass switch doesn't work. It sounds just like the one in the samples. It doesn't sound bad, just different.
The problem seems to be that in the
original schematic, Q1 does not have it's supply voltage listed, so the assumption is it is 9V, but the guy that reverse engineered it at the other forum says it should be 8V, and that's the only mistake. He says he has a pedal built from RG's layout and with that fix it works.
I'm going to get the details from him and give it a try after the New Year.
Quote from: DavidRavenMoon on December 30, 2008, 04:02:32 PM
The problem seems to be that in the original schematic, Q1 does not have it's supply voltage listed, so the assumption is it is 9V, but the guy that reverse engineered it at the other forum says it should be 8V, and that's the only mistake. He says he has a pedal built from RG's layout and with that fix it works.
I went back to my friend the circuit simulator.
(Here is the standard disclaimer for the circuit sim nay-sayers: yes, yes, I know that circuit simulators often lie. I'm familiar with the ways they lie, and some ways to avoid them. They are almost always deadly effective on things like DC bias and low frequency gain, though. Like I'm using it here.)
The input stage changes its collector bias voltage by 90mV when the supply voltage is changed from 8 to 9V. The forward gain at the collector changes from 21.68db to 21.81db in going from 8V to 9V and the "gain" at the emitter changes from -1.073 to -1.09db with an input of 100mV peak sine wave at 600Hz. The gain is substantially flat from 120Hz up to over 100kHz.
That is to say - except for the minor change in clipping voltage from the smaller supply voltage, it doesn't change in any noticeable way at all.
The change I suggested, moving C13 to the Q7 base side of R29 makes a much bigger difference in the sound, according to what you said, David, and in the direction of the way you remember it sounding. But the PCB info I have says it's not that way. The other change I suggested that's also not there, putting in a 1uF cap between the base of Q6 and the filter circuit makes a change that will be clearly audible too.
QuoteSee what happens in your sims when you move the C13 cap to the base side and insert a 1uF in series from the Twin T to the
If I keep Q5 (the filter-amp transistor) as a normal transistor I'm getting good bandpass filtering behaviour with the circuit *as is*. If I use a darlington the bias point almost turns Q5 off which is rubbish. With the non-shifting bias point mods I get the similar results. From a technical point of view I'm all for non-shifting bias points. The shifting bias points cause nasty "pops" when the switches are changed.
(BTW on the original circuit the filter-amp is Q5 on the geofex marking this has been changed to Q6.)
As far building an original clone we shouldn't have to mod the circuit, it should sound correct despite the technical issues.
The question is why doesn't it sound right! There's two assumptions which might be wrong:
- The transformer. We are assuming it's a 1:1 transformer. Maybe it's not, maybe the output side produces a hotter signal that would make the filtered signal and the harmonics switch more responsive.
- ceramic cap distortion.
- The filter switch wiring "looks" like it matches the original schematic, however, some switches have "funny" connections. IMHO, this is a possibility but an unlikely one.
QuoteThe problem seems to be that in the original schematic, Q1 does not have it's supply voltage listed, so the assumption is it is 9V, but the guy that reverse engineered it at the other forum says it should be 8V, and that's the only mistake. He says he has a pedal built from RG's layout and with that fix it works.
The change from 8V to 9V is going have a minor effect.
It's frustrating when everything looks correct but it doesn't sound correct!!!
Another assumption is the pot values.
If VR3 was higher, say 100k, the bias shifts change and the output of the filter would be hotter. This would have a noticeable effect on the sound. Also if this was done I'm not sure if Q5 should then be a darlington.
OK, this is where it gets weird... I just got done talking to the guy that posted the circuit board trace at the other forum. He's also the one that said Q1 is supposed to have the +8V supply.
He says that the schematic is correct, and that the Q1 issue is not that important.... notice that the B: Assmaster clone only uses 9V. He ran the schematic and the trace from the original board though circuit checking software, and that's where he found the Q1 issue, but everything else checks out.
He also went though and took readings on the carbon comp resistors in various parts of the circuit and found they were higher than stated, but he didn't think that was all that important, except that some Brassmasters he tried sounded better than others. He also thinks the diodes might have been matched.
What he thinks is going on is just the actual layout of the original, with the myriad wires, and all those ceramic caps close together. He says he modded a clone to sound like the original and also compared it on a scope to the real thing. Apparently it was done by using the original style parts and tweaking some values.
So based on this info he thinks the schematic is correct, it was a sloppy circuit design, and just happened to work well in the context of the original pedal.
He lives close to me so at some point I'm going to check out his clone.
So RG, unless you learn something new from Malekko, this is still a mystery. I'm curious what he thinks the change is.
Hi everyone. I'm the guy that did the copy of the original pcb layout. When I couldn't get a great sound out of my clone, a friend lent me his original. I was convinced that the schematic was wrong at the time, and that the problem was in the filter section. After the schematic and layout were input into the Traxmaker, the computer kept giving me an error between the two. When I went back to check against the schematic it was clear that the only error was Q1s supply. This really didn't make any difference in the tone of the unit or the function of the switches. I just wanted people to know that the schematic on the internet matched a brassmaster that I had in my possesion. It is entirely possible that there are other units revisions with circuit variations.
I modified my board with the 8 v supply on Q1, changed all the caps in the filter section to ceramic disc (as per original), and changed the resistor values to the actual values of the drifted parts in the original and it was right there. Here are those resistor values - 47k measured 54k (use 56k), 3.3k measured 3.9 k and 22k measure 24k. The final clone sounded just like the original. Oh yea, I also matched the diodes in the ring (these were 1n456 in the three units I had to examine).
I will be getting my hands on another one in about a week, and I will be able to measure the input and output impedances of the transformer. I will also try to get an fft analysis of the filter section.
I can take some voltage measurements off of the unit if anyone needs them, but I doubt the owner will let me unsolder transistors and things like that.
Quote from: gtrgeek1 on December 31, 2008, 12:16:32 AM
When I went back to check against the schematic it was clear that the only error was Q1s supply. This really didn't make any difference in the tone of the unit or the function of the switches. I just wanted people to know that the schematic on the internet matched a brassmaster that I had in my possesion.
Good bit of verification. I didn't think the voltage change would make much difference.
QuoteI modified my board with the 8 v supply on Q1, changed all the caps in the filter section to ceramic disc (as per original),
Ceramic is highly variable for most non-NPO forumlations.
Quoteand changed the resistor values to the actual values of the drifted parts in the original and it was right there. Here are those resistor values - 47k measured 54k (use 56k), 3.3k measured 3.9 k and 22k measure 24k. The final clone sounded just like the original. Oh yea, I also matched the diodes in the ring (these were 1n456 in the three units I had to examine).
Good data; thanks. I think this just affects the exact frequency and peak of the resonant filters, not the overall operations, but good to know.
QuoteI will be getting my hands on another one in about a week, and I will be able to measure the input and output impedances of the transformer. I will also try to get an fft analysis of the filter section.
I can take some voltage measurements off of the unit if anyone needs them, but I doubt the owner will let me unsolder transistors and things like that.
Actually, some additional good pictures and especially voltage measurements would make me happy. Ohm's law, some good photos and a little navel-staring make many circuits much clearer. Yes, please, voltages if it's possible for you to get them. DC to ground, all transistor pins.
On the transformer, input and output voltages with a sine wave drive should be plenty. The nominal impedances are not of all that much concern for this circuit.
Quote from: gtrgeek1 on December 31, 2008, 12:16:32 AM
Hi everyone. I'm the guy that did the copy of the original pcb layout. When I couldn't get a great sound out of my clone, a friend lent me his original. I was convinced that the schematic was wrong at the time, and that the problem was in the filter section. After the schematic and layout were input into the Traxmaker, the computer kept giving me an error between the two. When I went back to check against the schematic it was clear that the only error was Q1s supply. This really didn't make any difference in the tone of the unit or the function of the switches. I just wanted people to know that the schematic on the internet matched a brassmaster that I had in my possesion. It is entirely possible that there are other units revisions with circuit variations.
I modified my board with the 8 v supply on Q1, changed all the caps in the filter section to ceramic disc (as per original), and changed the resistor values to the actual values of the drifted parts in the original and it was right there. Here are those resistor values - 47k measured 54k (use 56k), 3.3k measured 3.9 k and 22k measure 24k. The final clone sounded just like the original. Oh yea, I also matched the diodes in the ring (these were 1n456 in the three units I had to examine).
I will be getting my hands on another one in about a week, and I will be able to measure the input and output impedances of the transformer. I will also try to get an fft analysis of the filter section.
I can take some voltage measurements off of the unit if anyone needs them, but I doubt the owner will let me unsolder transistors and things like that.
That's an interesting idea about revisions. I had a Brassmaster when they first came on the market, shortly after I heard that Chris Squire was using one... in the music store they even had one on display with a sign that said "Chris Squire's fuzz". Mine had the schematic glued to the bottom cover, and it's the same schematic that you find everywhere else. I even have a hand drawn copy I made back then.
But who knows if they changed stuff and left the drawing the same.
At some point I'll try changing parts and see what I get.
> just wanted people to know that the schematic on the internet matched a brassmaster that I had in my possesion.
Thanks a lot for your efforts and for sharing the info!
Getting some voltage measurements would be great, but you need to take note of the switch settings (since the bias points depend on the switches.)
I still think it would be a good idea to measure the transformer DC resistance as this would give some idea of the turns ratio.
On your clone, what type of transistor did you end-up using for the filter-amp transistor Q5? Darlington or the same as the others?
Interesting thread. Using this schematic that was posted before in this thread
http://files.muziq.be/schematics/maestro_bb-1_001.gif
Besides the filter and bias shift.
Q2 C to B resistor and the transistor hfe. What is the Collector operation point? Q2 sets Q3 operating points and Q3 is the phase splitter diode transformer driver. Q2 C to B resistor can make a difference depending were the collector "sits" and the resulting wave shapes and headroom.
Q6 operating points set Q7s again Q6 C to B resistor and Q6 hfe might make a difference
Q2,Q6,Q5 and maybe Q4 maybe need to be selected for hfe for good operating points because of the bias setup. As posted previously in the thread, DC voltages at all the transistor pins would be a help.
Maybe the transformer is not 1:1 etc like others have posted. If someone had a real BM one could find the ratio and the core size and winding resistance to make a closer clone.
Maybe the filter design is what the designer wanted?
has someone got a mouser number for the little xfmr??
i think i used a 42TM018 for my Lovetone RingModulator clone...
wonder if they would work here also(??)
it's weird how the centertap of the primary is fed back to the bridge(?)
this way, one diode appears across one of the primary halfs(?)
other octave-ups use the secondary for the recitification with only 2 diodes.
as for the "Twin T"....screwyist TT i've ever seen!!
Maybe **that's** the MOJO!! LOL!!! :icon_wink:
For a "true" (voltage controlled) TT, check out the ancient PAIA 2720-3b.
now it's said that "everything is correct"... ??
think i'll wait for the DVD LOL!!!
:icon_cool:
I've built these days a ZVEX Jonny Octane clone (which has the same "modulator driver" as Brassmaster) using an 42TM018 (1:1) transformer and it sounds very good for me.
Just finished a Brassmaster clone using R.G. Keen's layout (i waked up at 6AM on 01.01.09...i am a little crazy).
After looking carefully at the schematic and at the layout i saw that on the layout Q6 (my 2N5308 has the pinout as here: http://files.muziq.be/schematics/maestro_bb-1_001.gif (http://files.muziq.be/schematics/maestro_bb-1_001.gif)) is reversed, even the pins are written well.
I wired the "Sensitivity" trimpot as an external pot and the "Bass/Brass volumes" using a dual 10K liniar pot, as a blend pot.
I used the suggestions made by gtrgeek above about the resitors of the filter: 47k replaced with 56k, 3.3k with 3.9 k and 22k with 24k.
And...wooow...it sounds very well, both switches makes strong differences in the sound!
The only (possible) problem is that it sounds a gated with the Sensivity pot at maximum, but i will measure the voltages later to see if some of the transistors are misbiased...but after I re-listened to the clips of charlie (http://www.moosapotamus.net/THINGS/brassmaster.htm (http://www.moosapotamus.net/THINGS/brassmaster.htm)) i my clone sounds the same as his clone (my gated sound is the same as the sound of BB1guitWet.mp3).
Thx a lot all!
Quote from: toneman on December 31, 2008, 11:10:25 PM
has someone got a mouser number for the little xfmr??
42TM018-RC
XFMR 10KCT-10KCT
My voltages, using a 9.30V battery and both switches on (R.G. Keen's layout):
Q1: E=0.81 C=2.22 B=0.21
Q2: E=0.87 C=2.67 B=0.25
Q3: E=2.68 C=8.45 B=2.08
Q4: E=0.64 C=4.60 B=0.04
Q5: E=4.60 C=5.32 B=4.00
Q6: E=0.01 C=7.78 B=0.95
Q7: E=1.92 C=9.30 B=1.31
What do you think, are OK?
To me, Q6 seems very strange, but i rechecked it and the same result...
Thx a lot all!
Quote from: gigimarga on January 01, 2009, 03:33:50 PM
To me, Q6 seems very strange, but i rechecked it and the same result...
From reading the various Brassmaster threads on various forums, it's looking like Q6 is probably the culprit.
Quote from: DavidRavenMoon on January 01, 2009, 03:48:07 PM
Quote from: gigimarga on January 01, 2009, 03:33:50 PM
To me, Q6 seems very strange, but i rechecked it and the same result...
From reading the various Brassmaster threads on various forums, it's looking like Q6 is probably the culprit.
It does look funny. I wonder if the pinout issue is all there is.
Of course, I still don't like the bias funnies.
Q6's voltages look squiffy. It is possible that somehow the emitter is getting grounded?
I think you may also have E & B reversed when reporting the other voltages. They look "reasonable" -- just reversed.
Quote from: PerroGrande on January 01, 2009, 04:15:31 PM
Q6's voltages look squiffy. It is possible that somehow the emitter is getting grounded?
I think you may also have E & B reversed when reporting the other voltages. They look "reasonable" -- just reversed.
In the schematic the emitter of Q6
is grounded though a 1K resistor, and the output is coming from the collector. I'm not all that good with transistor circuits, but that looks kind of screwy without it having another transistor following it.
From simulation I get, by comparison, in parentheses:
Q1: E=0.81 (0.862) C=2.22 (2.25) B=0.21 (0.227) ( I believe you have base and emitter mixed up. What you're calling E is actually B and vice versa)
Q2: E=0.87 (0.945) C=2.67 (2.73) B=0.25 (0.307)
Q3: E=2.68 (2.73) C=8.45 (9.3) B=2.08 (2.1)
Q4: E=0.64 (0.684) C=4.60 (4.38) B=0.04 (0.061)
Q5: E=4.60 (4.38) C=5.32 (5.61) B=4.00 (3.71)
Q6: E=0.01 (0.04) C=7.78 (7.24 or 8.8) B=0.95 (1.05) (Q6 is a darlington here)
Q7: E=1.92 (2.06) C=9.30 (9.3) B=1.31 (1.41)
When I make Q6 be a 2N5088, not a darlington, I get collector voltages of 5.05 and 6.24V depending on the setting of the Brass hi/lo switch.
Q6 almost seems to need the base-current bleed through the Twin T resistors to bias better. Very strange. Very inconsistent.
Oh yeah -- Q6 is a Darlington -- my bad.
I can see, however, why the resistor network might get into the biasing equation. There is a DC path to ground via the selected resistors in the twin-T portion -- via the 150K resistor and the Brass volume control (10K). Every other path is AC coupled. At least when looking at this schematic: http://files.muziq.be/schematics/maestro_bb-1_001.gif
When I first looked at the circuit, I (incorrectly) thought that the bias problem might be related to the Hfe of the transistor. A quick run of the snippet through my sim cured me of that myth. However, my voltages were nowhere near what RG encountered... That is, until I added the twin-T network's path to ground, and now my values are very close.
I started replacing transistors with opamps.
I *think* I can get away with two dual opamps, and one transistor for the signal path. For the switching, I think it makes sense to replace that 3PDT switch with a CD4053 and the hi/lo switch with a P-FET to get the switching on the board and minimize the wiring.
By the way, the input impedance of this thing sucks treble, bad. The input impedance is about 17K. That may be a "feature". Anyway, it's easy to make it that bad if needed. :icon_biggrin:
Quote from: R.G. on January 01, 2009, 07:34:25 PM
By the way, the input impedance of this thing sucks treble, bad.
Well, it is a "BASS" Brassmaster! :D
~ Charlie
The biasing improves if Q6 (RG layout) is a non-Darlington.
What is right is unknown until gtrgeek1 posts his voltages.
Can we combine this thread and the one over at the other place? ;D
Thx a lot all!!!
R.G. you're wonderful!
I will try to replace Q6 with another 2N3392 and to see what's happening...i hope that the mistery will be solved soon :)
I just noticed something with mine. I decided to look up the pin layout on my particular 2N5308, since there had been some talk about it not matching the diagram on the original schematic. I hadn't thought to check it when populating the board, and just followed the layout for orientation.
So I looked up this particular Fairchild 2N5308 using the data sheet link at Mouser... and guess what? It's the opposite of the way it's marked on the layout, with the base going to R19. I can't be the only person this happened to, since I just assumed the orientation of the case matched the layout. I should have double checked it first. :icon_redface:
If I get a chance tomorrow I'll replace it with a new 2N5308 installed in the right direction and report back!
Quote from: DavidRavenMoon on January 02, 2009, 01:43:28 AM
...
So I looked up this particular Fairchild 2N5308 using the data sheet link at Mouser... and guess what? It's the opposite of the way it's marked on the layout, with the base going to R19. I can't be the only person this happened to, since I just assumed the orientation of the case matched the layout. I should have double checked it first. :icon_redface:
That's what i did...my 2N5308 must to be reversed according to the layout...but no good news...look a couple of posts above :)
I replaced 2N5308 with a 2N3392, but no major changes...it sounds less gated, but still too gated for my taste :(
Anyway, it's obvliously that when Hi/Lo it's on the volume increases a lot...and the action of the Brass 1/Brass 2 switch i think it's still too subtle (but i have no ideea about how the original sounded).
I posted a re-engineered version of the circuit at GEO - The Bass Ackwards.
Simulation says it runs, but simulators sometimes lie. I think it's a fruitful place to dig. In this version, the transformer/diode ring seems to give a fairly smooth doubling. We'll see.
I replaced the 3PDT with a 4053, used an LM386 for a bias generator, did a few other cleanup things. As soon as I can locate the breadboard, I'll hack one together.
Quote from: gigimarga on January 02, 2009, 04:25:05 AM
I replaced 2N5308 with a 2N3392, but no major changes...it sounds less gated, but still too gated for my taste :(
Anyway, it's obvliously that when Hi/Lo it's on the volume increases a lot...and the action of the Brass 1/Brass 2 switch i think it's still too subtle (but i have no ideea about how the original sounded).
The original has that gated tone also. In this version the louder setting on the harmonic switch is kind of like the original, but too thick, and the other setting is too thin... But you were supposed to mix some fuzz in with the dry signal, and the fuzz was bright and had that upper octave thing going on. It was never very useable with just the straight fuzz signal with no bass, unlike something like a Big Muff Pi.
The Brass switch was a higher or lower version of the fuzz. The Harmonic switch did something with the octave tone from what I remember. They were subtle changes, and some of the settings were very thin and fizzy. I remember I had
A good example of a vintage Brassmaster is the section in Close to the Edge about 6:01 right after one of the choruses. That's a typical Brassmaster setting... a thin envelopy type of thing. Close to the Edge (excerpt) (http://www.sgd-lutherie.com/media/close_to_the_brassmaster.mp3)
And from his solo album Fish out of Water, Hold Out Your Hand (excerpt) (http://www.sgd-lutherie.com/media/hold_out_your_brassmaster.mp3) and Silently Falling (excerpt) (http://www.sgd-lutherie.com/media/silently_falling_brassmaster.mp3). A reminder on why Squire is so great. :icon_biggrin:
So that's the sound there. It's a quirky little device, and certainly wasn't for everyone back then, or today even. Also I don't there were any effects for bass players, so who ever thought of the thing was being pretty radical at the time. That's pretty much what mine sounded like. The clone is close, except for the filter section.
Here's a funny story... when I heard about the Brassmaster I went looking to buy one. So I went to the 48th Street music store district in NYC, and to the famous Manny's Music. I talked to a salesman telling him what I was looking for. He was an older gent who was probably into jazz. He said to me "you don't want that thing! It sounds like thunder and lightning!" I said "yes! That's exactly what I want... thunder and lighting!" He refused to sell me one or even let me try it out! So I left Manny's and crossed to street.. maby to Rudy's or Gracin and Towne or something, and bought it untried!
Bass Ackwards thoughts
What kind of noise is at the output of the 386 used for bias? I did not see a RC filter.
Maybe make the 820K at the filter section a fixed min value and and pot to have fun with the gain.
Quote from: R.G. on January 02, 2009, 12:49:38 PM
I posted a re-engineered version of the circuit at GEO - The Bass Ackwards.
Simulation says it runs, but simulators sometimes lie. I think it's a fruitful place to dig. In this version, the transformer/diode ring seems to give a fairly smooth doubling. We'll see.
I replaced the 3PDT with a 4053, used an LM386 for a bias generator, did a few other cleanup things. As soon as I can locate the breadboard, I'll hack one together.
Cool! I'll have to try this one out soon. (scrounging though my parts bin)
Ah, so I was having trouble with my brassmaster clone and I stumbled on this really awesome thread you guys have going here. I, too, discovered the reverse pin arrangement for Q6 and reversed it promptly. I am having a bit of a rookie problem which led me to that discovery. I was given this RG's version of the board about a year ago perhaps...maybe more than that...by a friend of mine. I just now got around to getting all the parts and began putting it together. For some reason the clean bass works fine but there is nothing coming through the octave/fuzz section at all. I've checked all of the transistors and diodes. Would you suggest the next culprit to be T1? I've been over the schematic probably a few dozen times and all the other parts look correct (except the ones that you guys are finding I should change...definitely swapping the R29 location to be in front of C13). I've checked what I have the equipment to test on the transformer (which is basically just the resistance levels of the individual sides) although I have very little experience with these at this point. Any tips on things I should check out? I suppose it couldn't hurt to buy a new T1 and try it, although I can't get those anywhere nearby me that I know of. Also, were there perhaps any issues with an older version of the board? Mine says TUBA KING on it.
Keep up the awesome detective work. I'm learning a lot by reading your discussions/discoveries.
Quote from: airplanehuh on January 02, 2009, 09:35:47 PM
Ah, so I was having trouble with my brassmaster clone and I stumbled on this really awesome thread you guys have going here. I, too, discovered the reverse pin arrangement for Q6 and reversed it promptly. I am having a bit of a rookie problem which led me to that discovery. I was given this RG's version of the board about a year ago perhaps...maybe more than that...by a friend of mine. I just now got around to getting all the parts and began putting it together. For some reason the clean bass works fine but there is nothing coming through the octave/fuzz section at all. I've checked all of the transistors and diodes. Would you suggest the next culprit to be T1?
It's far more likely that there is some issue with soldering or wiring. Measure and post your transistor pin voltages. That's about the fastest way to find the bugs.
QuoteAlso, were there perhaps any issues with an older version of the board? Mine says TUBA KING on it.
An "R.G.'s" board with "Tuba King" on it? Hmmm... I'd sure like to see photos of the top and bottom of that board if that's at all possible.
You can get more drive out of the filter with the following mods:
- reduce on Q6 (RG layout) to say 68k
- increasing the cap 50nF that connects to this resistor to 100n
- reduce 1k resistor on the emitter of Q6 (RG layout) to 680R
Set the brass pot to 12 O'Clock to make it sound like full on the original.
QuoteA good example of a vintage Brassmaster is the section in Close to the Edge about 6:01 right after one of the choruses. That's a typical Brassmaster setting... a thin envelopy type of thing. Close to the Edge (excerpt)
I've always loved Chris Squire's sound and playing on that album - especially that part of the track.
Sorry to ask, I'm sure the answer is here, but there are so many suggestions and what not I'm a little overwhelmed - basically if I want to build this based on the re-worked "Bass Ackwards" schematic, could I still use the PCB at GGG? If so, what changes are made to how it's assembled? Again, I know the answers are probably here (though not sure if the old PCB image will work) but would be nice, if the PCB would work, to have it summarized in one posting how what you would change when assembling from that image.
Thanks!
Quote from: R.G. on January 02, 2009, 12:49:38 PM
I posted a re-engineered version of the circuit at GEO - The Bass Ackwards.
Simulation says it runs, but simulators sometimes lie. I think it's a fruitful place to dig. In this version, the transformer/diode ring seems to give a fairly smooth doubling. We'll see.
I replaced the 3PDT with a 4053, used an LM386 for a bias generator, did a few other cleanup things. As soon as I can locate the breadboard, I'll hack one together.
Quote from: fogwolf on January 03, 2009, 12:06:22 PM
if I want to build this based on the re-worked "Bass Ackwards" schematic, could I still use the PCB at GGG?
No. It's not practical IMHO. Sorry. Too many changes.
Of course, I just finished some touch ups to the new Bass Ackwards PCB layout. :icon_biggrin:
Quotewould be nice, if the PCB would work, to have it summarized in one posting how what you would change when assembling from that image.
I'll do that when we get to a conclusion. Right now, there's things still remaining to be checked out.
Gotcha - thanks!
Quote from: R.G. on January 03, 2009, 12:26:01 PM
Quote from: fogwolf on January 03, 2009, 12:06:22 PM
if I want to build this based on the re-worked "Bass Ackwards" schematic, could I still use the PCB at GGG?
No. It's not practical IMHO. Sorry. Too many changes.
Of course, I just finished some touch ups to the new Bass Ackwards PCB layout. :icon_biggrin:
Quotewould be nice, if the PCB would work, to have it summarized in one posting how what you would change when assembling from that image.
I'll do that when we get to a conclusion. Right now, there's things still remaining to be checked out.
Quote from: George Giblet on January 02, 2009, 11:49:45 PMI've always loved Chris Squire's sound and playing on that album - especially that part of the track.
Yeah, me too! That album made buy the Brassmaster! Listening to that album made me want to build a new one.
It's exciting that just when I got around to building one, and then searching for why mine wasn't working right, is happening just when some progress to that answer is being made.
Hey Guys,
I finally got the original Brassmaster on my bench and have the following info for your reference:
Transistors
The transistor designations follow the original factory schematic.
Q1,2,3,4,6,7 are 2N3392 factory marked 83930. All have an orange dot on the top, possibly matched or selected.
Q5 is 2N5308 factory marked 135 43C. Pinout matches 2N3392 not schematic pinout.
Maestro Bass Brassmaster Voltage Chart 01/03/09
V1 = 9.3V
V2 + 8.0V
E C B
Q1 193 mv 2.107V 0.793V
Q2 63.9mv 4.68V 0.656V
Q3 4.04V 5.16V 4.68V
Q4 H1 1.319V 9.34V 1.918V
Q4 H2 3.195V 9.34V 3.796V
Q5 H1B1 28.2mv 7.58V .907V
Q5 H1B2 61mv 5.88V .980V
Q5 H2B1 6.5mv 8.7V .816V
Q5 H2B2 40.8mv 6.92V .937V
Q6 267mv 2.986V .870V
Q7 2.391V 8.04V 2.987V
H1 = SW2 closed / 82K connected
H2 = SW2 open
B1 = 47K resistors selected in filter
B2 = 6.8K resistors selected in filter
Diodes
All Diodes 1N457A
Transformer (measured in circuit)
Primary = 680 ohm CT
Secondary 572 ohm
500 mv 1K sinewave into secondary, measured 500 mv on primary
The transformer on this particular unit is much smaller than others I have seen. Mounting tabs did not line up with pads in pcb and were folded flat.
Resistors
All 1/2 watt carbon comp
All pots 10k CTS with 1971 date code
Capacitors
.01, .005 (x2), .05 in filter are ceramic disc
.05 on base of Q3 is ceramic disc
Electrolytic as marked on schematic
All others mylar 100V
PCB
C.M.I. 980 018260
Since the owner paid a boatload for this thing, I am a little hesitant to unsolder anything for a more accurate measurement, but I did compare all voltages to a clone built on RGs layout and all voltages match.
Since I will have to return this treasure soon, please let me know if there is any other info needed.
Regards,
gtrgeek1
From listening to the posted excerpts, I think the Brassmaster can be de-composed and re-formulated.
The BM is a high gain preamp and less-distortion-s frequency doubler that feeds a resonant filter which can be set to one of two frequencies. The frequencies are about 700Hz and about 3kHz, and you only get to use one at a time. It wouldn't be all that hard to ditch the Twin-T setup and sub in a multiple feedback filter or a state variable and be able to set the resonance wherever you want it. Or shoot, put in two filters and mix to your heart's content.
The transformer based doubler is kinda nice from what I've seen so far, and that may be the big advance value of the design.
OK, I got it working! :icon_biggrin:
gtrgeek1 is correct... there seems to be nothing wrong with the original schematic (except for Q1's supply voltage being 8V and not 9V), and RG's PCB is correct.
So here's what I did... first there was the issue where on RG's layout sheet R22 and R27 are swapped. So I removed them and put them in the correct locations. That did little to help the Brass switch, but I at least heard something when I switched it. I had tried moving where R29 connected to C13, but I switched that back to the original location.
I decided to check Q6, since that was responsible for amplifying the output of the filter and sending it back to the circuit. I looked up the pin out for the Fairchild 2N5308.. voilà! I had it in backwards. It did match the layout as far as where the flat side was, but it had the emitter and collector swapped!
So I carefully unsoldered it and flipped it around.
Here's the results. First you hear the two settings of the Brass switch, then I flip the Harmonic switch, and then switch the Brass switch again. You go from very full to very thin, just like the real thing. The very thin setting is what Squire used a lot, as in the example I play from Close to the Edge, which has the dry signal mixed back in.
Brassmaster Fixed (http://www.sgd-lutherie.com/media/Brassmaster_fixed.mp3)
I don't have a real one in front of me to compare, but going from memory, this is pretty much nails the tones I remember using. :icon_biggrin:
Ok, great...I got mine working! It sounded great in the stock form (maybe I got lucky with the values). I tried comparing the new placement of R29 to the original schematic location and I definitely like the old (less obvious) harmonic switch because the tones in both positions, although slight, are packed with good tone and are more responsive to me than putting R29 before the cap. With it before the cap the tone seems much too brittle. Although I was only testing the differences through a small combo amp in my room and have yet to hook it up to the big svt rig or the traynor bassmaster. Brassmaster into the bassmaster running 2x15's could sound pretty good. What other mods to the original pcb layout would you guys suggest?
I like the possibility of the new design you are working on R.G. I may have to try that one sooner or later. Has everyone on here been using the millenium bypass with their bb-1s? Is anyone satisfied with the old-school true-bypass version? Are there any noticeable differences aside from the led option?
All right, I'll get the documentation straight.
So, using the layout as a reference, R27 as marked is 22K and R22 = 6.8K, correct?
And the actual Fairchild 2N5308s have B and E reversed from the pinout picture on the original schematic, which I then propagated?
The datasheet at both Fairchild http://www.fairchildsemi.com/ds/2N/2N5308.pdf (http://www.fairchildsemi.com/ds/2N/2N5308.pdf) and Central Semiconductor shows to match the 2N3392 pinout.
So the second bug was that the pinout on the 5308 was backwards.
Other than that, the evidence is that the layout works. Is that the net net, David (since you actually had one and remember it, as well as having recorded examples and a working board now)?
Hey RG,
Don't forget to connect Q1 to the 8V supply. I have the original on my bench right now and soundwise everything jives between the original and the clone on your board. If there is any other info you need to finalize this, just email me gtrgeek1@yahoo.com
Regards.
gtrgeek1, that's awesome!!!
Thanks for all your efforts deciphering the bm - no more speculation.
What is interesting is:
- the circuit was correct all this time (except for the minor 8V/9V thing)
- the suggested transformer MOUSER 42TM018 should be spot on
- Everyone should have *already* been building bm's cones (apart from those who had the wrong pinout).
Nothing has changed other than the knowledge in our heads.
Quote from: gtrgeek1 on January 03, 2009, 07:07:01 PM
Don't forget to connect Q1 to the 8V supply. I have the original on my bench right now and soundwise everything jives between the original and the clone on your board. If there is any other info you need to finalize this, just email me gtrgeek1@yahoo.com
Yep, got it. Here's the changes to the board:
1 - Changed Q1 to +8V (although this is viewed as unnecessary; 820R can be replaced by a jumper to make it all 9V)
2 - swapped nomenclature on R22 and R27 on the schematic
3 - swapped the direction of the darlington to match Fairchild's datasheet.
4 - added pads for separate resistors as in the original Twin T filter, as opposed to adding a resistor in parallel; no big difference, just a bit of "originality" for those who can't see far enough to calculate paralleled resistors
5 - added pulldown resistors on input and output; added polarity protection diode
6 - general cleanup; used standard sized box film caps instead of generic poly outlines; rotated all the transistors to face one direction; rotated all polarized electros to face the same direction; used new footprints with better accuracy; changed to a larger and more easily found outline for the sensitivity trimmer; moved every cotton-picking component at least once; kept the same outside dimensions and mounting dimensions.
Who's gonna do the checking pass? :icon_biggrin:
Gtrgeek, you and David are PERSONALLY responsible for this getting ironed out to its current state of flatness. You realize that don't you? :icon_wink:
Quote from: R.G. on January 03, 2009, 11:09:31 PM
2 - swapped nomenclature on R22 and R27 on the schematic
The schematic is correct, the parts layout and wiring diagram is wrong. Since people follow that to populate the board, the mixup happens. If they are building from scratch using just the schematic, that wont happen.
Quote
3 - swapped the direction of the darlington to match Fairchild's datasheet.
Same as the last comment... the schematic is correct, but the build instructions have the transistor facing the wrong way. Might be good to add a "B, C, and E" to the drawing.
Quote4 - added pads for separate resistors as in the original Twin T filter, as opposed to adding a resistor in parallel; no big difference, just a bit of "originality" for those who can't see far enough to calculate paralleled resistors
5 - added pulldown resistors on input and output; added polarity protection diode
6 - general cleanup; used standard sized box film caps instead of generic poly outlines; rotated all the transistors to face one direction; rotated all polarized electros to face the same direction; used new footprints with better accuracy; changed to a larger and more easily found outline for the sensitivity trimmer; moved every cotton-picking component at least once; kept the same outside dimensions and mounting dimensions.
Nice touches! I used box caps too, and I had to bend the contacts before I could fit them in the board.
One last thing, the Sensitivity knob would never be a trim pot.
Quote
Gtrgeek, you and David are PERSONALLY responsible for this getting ironed out to its current state of flatness. You realize that don't you? :icon_wink:
Cool! RG thanks for your effort to have this board out there in the first place. I just wanted the damn thing to work, no matter who and how often I had to bug people! :icon_wink: After I built mine and then went through the schematic several times comparing it to the PCB, and didn't find a problem, I figured let me see what others were saying. You probably only hear from people who built it and never checked which way to put Q6 in (like me) and can't get it to work. And since we didn't realize that the main issue with the filter amp was an improperly installed Q6, where do you look? Then once the idea is out there that the schematic is wrong, everyone starts looking in the wrong place.
And thanks to Gtrgeek for insisting the schematic was correct. We had a long conversation about his experiences with the circuit, which made me decide to open mine back up and take another look. He was very thorough in his comparison against the real thing.
You had to see me jumping up and down today when I made the change and plugged it in for the first time! It was a real eureka moment!
Hey RG,
I can double check the pcb if you like.
I'm glad that David had a problem and brought this issue back up! ;D I didn't want any more people in that state of misery - you know, removing parts so much the traces are breaking, transistor leads breaking, bad solder joints, cutting traces, second guessing, burning fingertips and still not knowing why it isn't working.
Feel free to use/post all of the data and voltages I pulled from the original as a troubleshooting tool.
I do have some questions about this design:however they are really for the original designer(s) of the circuit. I will post them anyway most are why some of the transistor operating points?
Q1 first gain stage was that designed for .193VDC at the emitter and 2.1VDC at the collector?
Q4 the emitter follower to the filter Why not offset the emitter more to +9VDC, for a few reasons. With an emitter follower with a resistor in the emitter leg the transistor can turn on and"pull" up harder than the resistor can "pull" down" for more equal drive that plus the bias shifting with the harmonic switch would seem to make more sense to have the emitter around 5VDC or so.
The output amp 2.98VDC at Q6 collector and 2.391VDC at Q7 emitter? Q6 is both a gain stage and a summing amp the two 10Ks from the volume controls are summed at the base junction of Q6 because of the DC bias and feedback gain control resistor 470K from collector to base forming a inverting summing amp.
Are the offsets on purpose or are they a result of different transistor hfe etc changing the operating points and this was just accepted?
I would guess Q1 is on purpose because that biasing is more predictable. Q2 Q6 that bias is not as predicable IMO.
8VDC looks like it was done as a power supply RC filter for the "cleaner" gain stage sections input and output circuits to help remove noise that might be generated from the other sections.
Q6 is both a gain stage and a summing amp the two 10Ks from the volume controls are summed at the base junction of Q6 because of the DC bias and feedback gain control resistor 470K from collector to base forming a inverting summing amp.
Maybe change the stock E 470 ohm and cap bypass it and/or the C 10K value it this can increase the open loop gain and let the 470k and other parts set the gain with a different collector voltage?.
@DavidRavenMoon: I can't download your soundclip with your fixed Brassmaster clone. Can you post it on another server?
QuoteI do have some questions about this design:however they are really for the original designer(s) of the circuit. I will post them anyway most are why some of the transistor operating points?
I suspect the Emitter resistors of the gain stages are tweaked to produce the desired gain. The voltage drops across the emitter resistors are so low that they don't really help with any bias predictability. [Edit: For got to mention because they wanted higher gains in the circuit that needed small emitter resistors relative to the collectors resistors. They probably didn't want to increase the component count by using larger bypassed emitter resistors, so they just put up with the poorish biasing - feedback biasing isn't too bad anyway.]
Regarding Q1, the low feedback resistor, while making the bias more predictable with the other 150k, is going the make the input resistance quite low and it will load the pickup - deliberately loading the pickup?
The tap off the emitter is obviously an attempt to get a free buffered (gain of 1) signal for the straight through path, but I suspect the fact the bias point is very marginal is an oversite.
The output mixer (Q6 and Q7) appears to be a standard Maestro building block. The same circuit appears on the Maestro Octave Box, however the C-B resistor is larger (1.5M) on that one and produces a better bias point. Presumably that was to adjust for different transistor gain but maybe not: 1.5M vs 470k is a factor of 3 and it is unlikely the gains would vary that much!
Regarding the bias shifting - that is strange. I can only guess it's an oversite, or something disregarded.
Regarding the generally "poor" biasing - who knows, oversite vs. deliberate sound shaping?
BTW: Using gtrgeek1's voltages I've estimated the hfe of the non-darlingtons to be about 130.
Quote from: George Giblet on January 04, 2009, 01:13:11 PM
I suspect the Emitter resistors of the gain stages are tweaked to produce the desired gain. The voltage drops across the emitter resistors are so low that they don't really help with any bias predictability. ...
The tap off the emitter is obviously an attempt to get a free buffered (gain of 1) signal for the straight through path, but I suspect the fact the bias point is very marginal is an oversite.
...
Regarding the bias shifting - that is strange. I can only guess it's an oversite, or something disregarded.
Regarding the generally "poor" biasing - who knows, oversite vs. deliberate sound shaping?
One of my favorite quotes is from Napoleon: "Never ascribe to malice, that which can be explained by incompetence."
At the time of the design, good EEs were snapped up by military contractors, and in short supply. Component sensitivity was still a research issue.
QuoteRegarding Q1, the low feedback resistor, while making the bias more predictable with the other 150k, is going the make the input resistance quite low and it will load the pickup - deliberately loading the pickup?
Yeah, see my note from earlier in the thread. It's about 17K to 18K input impedance, and loads the daylights out of the incoming signal. Of course, as David said, it is a bass effect.
See Gus's Octave Up Sick Box for an earlier example of an op amp based phase inverter in a pedal.
I have the new doco package up at GEO for checking.
For checking...
If you have a hankering to, (please, David and gtrgeek) please look at the new layout and schemo and let me know where my typical absent mind has missed something.
QuoteThe transistor designations follow the original factory schematic.
Q1,2,3,4,6,7 are 2N3392 factory marked 83930. All have an orange dot on the top, possibly matched or selected.
Q5 is 2N5308 factory marked 135 43C. Pinout matches 2N3392 not schematic pinout.
Uhh...according to the factory schematic, Q6 is the 2N5308. Am I missing something? I've been following this thread very closely anticipating a resolution (ie, new pcb layout). I've hacked my pcb so many times that I need to etch another one, so I want this to be correct as well if I am to start over from scratch. ;D
DOH! You beat me.
Quote from: R.G. on January 04, 2009, 05:01:06 PM
I have the new doco package up at GEO for checking.
For checking...
If you have a hankering to, (please, David and gtrgeek) please look at the new layout and schemo and let me know where my typical absent mind has missed something.
Will do!
I replaced the diodes from 1N4148 to Schottky (1N5817) as R.G. suggested and it sounds less gated obviously (all 4 diodes matched around 160mV).
But when i connected the Q1's collector from 9V to 8V it started to oscillate very strong, so i gave up and went back to 9V.
I tested it on a Squier guitar, not on a bass guitar (i liked the clips with B:assmaster used on guitar...)
@DavidRavenMoon: After a lon battle I downloaded the clip...
Thx a lot all!
Quote from: gigimarga on January 04, 2009, 06:41:58 PM
@DavidRavenMoon: After a lon battle I downloaded the clip...
Are you on a dial up connection, or was there a problem downloading the file?
> Component sensitivity was still a research issue.
Actually that's a good point. What we see as obvious today probably wasn't in those days (hence all the dodgy early designs). Transistors were new strange beasts at the time.
From our era it's like switch mode power supplies. Once mystical beasts studied by researchers, now throw-away items that come with your mobile-phone.
> Uhh...according to the factory schematic, Q6 is the 2N5308. Am I missing something? I
You have to watchout what the Q designators are in this thread. Some posts are using RG's mark-up because it matches the layout most people have built, others use the original schematic (which is that maestro bb-01 link that appears a few times in the thread).
The original schematic had no part numbers for the resistors and capacitors, only transistors and some of the controls. The version I did that's being sold by GGG has numbered parts; I back-annotated the factory schematic with part numbers matching my PCB layout - getting one pair of them reversed in the process.
I have redone the layout, and the schematic. This has yet a third, different set of part numbers.
Part numbers have no meaning outside the context of the schematic and/or PCB to which they refer or link together.
So yes, you must be scrupulously careful about which schematic and/or PCB or both you refer to when referencing part numbers.
Quote from: DavidRavenMoon on January 04, 2009, 07:21:37 PM
Quote from: gigimarga on January 04, 2009, 06:41:58 PM
@DavidRavenMoon: After a lon battle I downloaded the clip...
Are you on a dial up connection, or was there a problem downloading the file?
No, i have a good cable connection...but IE cann't open the file...only with Firefox using a proxy :)
Quote from: gigimarga on January 05, 2009, 12:27:50 AM
Quote from: DavidRavenMoon on January 04, 2009, 07:21:37 PM
Quote from: gigimarga on January 04, 2009, 06:41:58 PM
@DavidRavenMoon: After a lon battle I downloaded the clip...
Are you on a dial up connection, or was there a problem downloading the file?
No, i have a good cable connection...but IE cann't open the file...only with Firefox using a proxy :)
That's odd... it's just an MP3 file. I'm on a Mac and I can play it from the browser on both Firefox and Safari.
MS sure likes to complicate things. :icon_confused:
Few people appreciate the extents to which microsoft went to protect digital media rights in Vista. Many are not apparent in any way except "gee, that sure is a funny way for that to (not)work."
If Vista is involved, it may be working as designed.
I use Windows XP, so no Vista here :D.
I think i have some problems with the Internet provider (some security settings) because i can open http://topopiccione.atspace.com (http://topopiccione.atspace.com) only using an proxy server (and the same thing for analogguru's site and another DIY site).
Thx both of you!
Little off topic but take this
http://www.diystompboxes.com/pedals/ousb.gif
10uf and to to the right remove increase the 270 ohm resistor value and add
the 2.2ks, diodes and transformer from the Bass Ackwards and a volume control at the output of the transformer
Bass Ackwards looks like it might be a fun build.
O.k., since it's oh-so-bitter-cold outside and I had to wait half an hour I could not resist to play around with the Brassmaster circuit... just more or less random mods with possible errors in thinking and drawing thrown in for free. Anyway I'd call it food for thought and occupational therapy ;D. Well, no - I seem to have nothing better to do, but thanks for asking... be gentle with a fool in the cold.
(http://i95.photobucket.com/albums/l155/fotofix/Elektrik/BrassDisaster.png)
Quote from: majormono on January 07, 2009, 08:11:14 AM
O.k., since it's oh-so-bitter-cold outside and I had to wait half an hour I could not resist to play around with the Brassmaster circuit... just more or less random mods with possible errors in thinking and drawing thrown in for free. Anyway I'd call it food for thought and occupational therapy ;D. Well, no - I seem to have nothing better to do, but thanks for asking... be gentle with a fool in the cold.
Interesting... I like the improved input impedance. I was thinking of doing that to mine, though I'm probably going to build a second unit and mod that. Just so I have a unit fairly stock.
Two thoughts though, the Sensitivity control shouldn't be a trim. They shouldn't have called it Sensitivity either, it should have been labeled "Drive". It's key to some of the tones you can get from this pedal. I often have it almost off, and then sometimes all the way up, or half way.
I'm not sure a blend control would work well either, since some of the fuzz settings are much quieter than others. So sometimes you have to really crank the fuzz while keeping the dry signal about the same. A blend would probably need a master volume control.
The input impedance isn't improved all that much. I found experimentally about 17kohm input in the stock circuit. It's up some, as the voltage-feedback nature of the first transistor circuit lowers input impedance with increasing voltage gain.
The input impedance is the lower 150K|| upper 150K divided by the voltage gain || base impedance of Hfe*390 (ignoring Shockley resistance). At frequency, the Ccb gets into it too. The voltage gain is lower than expected because of the 10K sensitivity pot loading and any loading from the second stage depending on the pot position.
I would either drop in an opamp, which is simple; or use a JFET in front of the first transistor in a similar circuit but using the JFET's high impedance as the buffer. But there are a million or more different ways to do this.
R.G I was drawing up a input with 8.2K collector R and a 2.2K emitter maybe run it at about 1/2 ma Ic set the base at about 1.7VDC gain <x8. Maybe a voltage divider input 100K and 470K (429k from math) common resistors. The 2.2K emitter R kind of big for the 10k bass volume pot but it might be OK. Input R hfe x 2.2K || 100K || 470K maybe a MPSA18
1/ 2pi * 17 x10^3 *.1 x10 ^-6 = stock HP input Might even want to move the input filter turnover frequency depending on the bass used
Like you posted many different ways to change things.
QuoteI'm not sure a blend control would work well either, since some of the fuzz settings are much quieter than others.
i have mine wired with a dual linear 10K as blend, and the output of the circuit is followed by a 100K vol pot. works the same, u just have to choose different blend settings according to switch settings, then adjust vol to taste.
btw, thanks everybody who contributed to the final solving of the puzzle. i flipped the darlington yesterday, and now all the switch settings produce pronounced results. 2 settings were useable before (the very meaty and the very thin setting), but now there´s two more !
for the swapping of the resistors, i have to thank myself as well, as i posted that info more than one year ago, but nobody seemed to care really (or understand what i mean - except meanderthal). but, who cares, now everything is good. :icon_cool:
cheers,
lowstar
Quote from: lowstar on January 07, 2009, 11:09:40 AM
QuoteI'm not sure a blend control would work well either, since some of the fuzz settings are much quieter than others.
i have mine wired with a dual linear 10K as blend, and the output of the circuit is followed by a 100K vol pot. works the same, u just have to choose different blend settings according to switch settings, then adjust vol to taste.
With a master volume I could see it working. The thing can get loud, so that was my one concern. I like blend controls in my basses, so maybe I'll try that at some point.
Quotebtw, thanks everybody who contributed to the final solving of the puzzle. i flipped the darlington yesterday, and now all the switch settings produce pronounced results. 2 settings were useable before (the very meaty and the very thin setting), but now there´s two more !
for the swapping of the resistors, i have to thank myself as well, as i posted that info more than one year ago, but nobody seemed to care really (or understand what i mean - except meanderthal). but, who cares, now everything is good. :icon_cool:
Well someone posted about the resistors... I hadn't even noticed that until I read it here, or somewhere. Maybe it was you?
I was determined to get this thing working! I spend an afternoon putting it together, so the switch dysfunction didn't sit well with me. :icon_lol:
Thanks for the info R.G. Maybe I'll stick a jfet in the front. I have a bunch of those laying around.
QuoteI like blend controls in my basses
same here, i only have one bass that is vol/vol, and i really cannot get into liking that config. it´s faster to just turn the blend knob if you want to change sounds mid-song, as opposed to having to tweak two knobs.
other people swear by the vol/vol, though.
tastes are different, sad the old woman and ate the
moco.
cheers,
lowstar
built a circuit fragment as a test. I did not have a 470K and a mpsa18 so I used a 47K and 10K and a lower hfe 2n3904
Bias
47K, +9 to base of a 2n3904
10K Base to ground
8.2K +9 to collector of 2n3904
2.2K emitter to ground
9VDC power 5.53VDC at the collector, .931VDC at the emitter
Gain about 8.2/2.2
Adjust the input cap to the base and take the outputs from the emitter and collector. Use a 470K and 100K bias string with a high hfe transistor like a mpsa18
So is the new pcb layout waiting to be verified, or is everyone just updating with the old layout? I'd like to make another attempt at this pedal, but if there will be a new layout with pulldown resistors and such, I'll gladly wait. I had the last one running, but after all the swapping of parts and the like, the traces are starting to come up. :(
The new layout's posted at GEO. David and gtrgeek were going to check it for my normal forehead slapping errors and give a yea or nay.
David - you want a JFET buffer in front on the new PCB?
Quote from: Plinky on January 12, 2009, 08:09:27 PM
So is the new pcb layout waiting to be verified, or is everyone just updating with the old layout? I'd like to make another attempt at this pedal, but if there will be a new layout with pulldown resistors and such, I'll gladly wait. I had the last one running, but after all the swapping of parts and the like, the traces are starting to come up. :(
I just swapped R22 with R27 and turned Q6 180° around. It works just dandy. To me it sounds just like the real thing, just with better parts. ;)
But I'm going to make another one with the new layout (and goodies), which brings me to...
Quote from: R.G. on January 12, 2009, 08:15:52 PM
The new layout's posted at GEO. David and gtrgeek were going to check it for my normal forehead slapping errors and give a yea or nay.
David - you want a JFET buffer in front on the new PCB?
I will be digging into it more closely this week. I haven't talked to gtrgeek yet to see what he's up to.
Yeah, a jfet buffer would be great. I'm using mine with an active bass, but if I bypass the preamp or use another bass you can tell the difference.
Being that I haven't used one of these in about 20+ years, I can see room for improvement in the clean channels tone. At the time, that's what it sounded like, and it was just a quirky pedal.
I think a buffer would be a good place to start. If I were to design an ultimate version I'd also include tone controls for each channel and maybe even a second output jack that would split the fuzz and dry channels when used. But that's probably overkill. Tone controls would be cool though. Certain sounds are better with the highs removed from the bass channel, and sometimes the fuzz could use to have the top end tamed a bit.
BTW, just for fun, here's what it sounds like with guitar:
Guitar 1 (http://www.sgd-lutherie.com/media/Brassmaster_with_guitar.mp3); various settings.
Guitar 2 (http://www.sgd-lutherie.com/media/brassmaster_with_guitar2.mp3); sensitivity almost all the way off, and volume on guitar half way off.
Lots of sick and twisted fun!
Quote from: DavidRavenMoon on January 12, 2009, 09:59:29 PM
I just swapped R22 with R27 and turned Q6 180° around. It works just dandy. To me it sounds just like the real thing, just with better parts. ;)
So did I, and it does sound like the original per some friends of mine that have owned/played one, but I'm not getting any difference in the switching. A little is noticed on the SPST switch, but nothing on the 3PDT switch. I noticed the wiring to the switches is a bit different on the new layout. Will this make a difference? Sorry for sounding like a noob but I honestly never heard about this pedal until a friend asked me if I could make one for him. Little did I know of the pit I was about to fall into. :icon_biggrin:
Someday I'm going to try to use this triple pot to make a brassmaster with a continuously variable filter to replace the two position switch. It's a triple 25K. I just have to replace two of the wafers with 50K's.
(http://homepage.mac.com/sonicvi/ctstriplepot.jpg)
Quote from: Plinky on January 13, 2009, 10:35:06 AM
Quote from: DavidRavenMoon on January 12, 2009, 09:59:29 PM
I just swapped R22 with R27 and turned Q6 180° around. It works just dandy. To me it sounds just like the real thing, just with better parts. ;)
So did I, and it does sound like the original per some friends of mine that have owned/played one, but I'm not getting any difference in the switching. A little is noticed on the SPST switch, but nothing on the 3PDT switch. I noticed the wiring to the switches is a bit different on the new layout. Will this make a difference? Sorry for sounding like a noob but I honestly never heard about this pedal until a friend asked me if I could make one for him. Little did I know of the pit I was about to fall into. :icon_biggrin:
Check Q6. That was the problem with the switching. If you follow the layout Q6 will be in backwards and wont work correctly. Double check which pins are which on your particular transistor. Mine was a fairchild and needed to be flipped around. Don't fry it when you make the change either. If in doubt put a new one in. It should sound like this on the four switch settings:
Brassmaster Fixed (http://www.sgd-lutherie.com/media/Brassmaster_fixed.mp3)
R.G.'s new layout is switching between two resistors instead of switching in a parallel resistor. But I doubt it makes a huge difference. But that's the way the original is. My clips are using the original GGG PCB.
Quote from: DavidRavenMoon on January 13, 2009, 12:26:37 PM
Check Q6. That was the problem with the switching. If you follow the layout Q6 will be in backwards and wont work correctly. Double check which pins are which on your particular transistor. Mine was a fairchild and needed to be flipped around. Don't fry it when you make the change either. If in doubt put a new one in. It should sound like this on the four switch settings:
I have. I flipped it around and it made no difference. I get a very subtle difference with the harmonic switch, but nothing compared to your sound clip. I'll compare some voltages when I get a chance. I'll try to get this one working before I etch a new pcb.
Well, some of my voltages are considerably off from what gtrgeek posted (sounds ok, just not switching), so I'm gonna etch a new pcb and start all over. To me this board has been abused too much to try and debug. Hopefully I can get this done this weekend.
http://www.aronnelson.com/gallery/main.php/v/gus/bminput.GIF.html
Two fragments for a BJT input. Not built yet. I would look for about 1 VDC at the emitter. The value shown are a starting point.
Gain from the collector should be about X3.7 and inverted and from the emitter just under 1 noninverted
First input resistance hfe X 2.2K || 100K || 470K. Second is a bootstrapped input
I would use high hfe like a MPSA18.
Well, I finally finished my new pcb for this and this one works, including the switches (sounds just like DRM's soundlclip). I don't own a bass amp, but I can still get some interesting tones on my crummy Peavey bass through a SS guitar amp.
One question though - was it normal on the original BMs for the bass volume to be low? I'd like to blend in a bit of the fuzz tone with the bass tone, but the clean bass signal is a bit low when compared to the bypassed bass signal.
Quote from: Plinky on January 27, 2009, 12:33:48 PMOne question though - was it normal on the original BMs for the bass volume to be low? I'd like to blend in a bit of the fuzz tone with the bass tone, but the clean bass signal is a bit low when compared to the bypassed bass signal.
No, it's not normal. I get a bit of a boost on mine with the clean level all the way up.
Quote from: DavidRavenMoon on January 27, 2009, 12:48:42 PM
Quote from: Plinky on January 27, 2009, 12:33:48 PMOne question though - was it normal on the original BMs for the bass volume to be low? I'd like to blend in a bit of the fuzz tone with the bass tone, but the clean bass signal is a bit low when compared to the bypassed bass signal.
No, it's not normal. I get a bit of a boost on mine with the clean level all the way up.
Okay. Back to tweaking. 8)
So has the PCB image and BOM/layout been corrected at Geofex? Sorry, there's just been so much back and forth and posts about tweaking what's there what's not there I'm not totally clear. I'm looking for is an easy "just go get the updated PCB image here and follow the new wiring diagram here" :icon_lol:
Quote from: fogwolf on January 27, 2009, 01:13:08 PM
So has the PCB image and BOM/layout been corrected at Geofex? Sorry, there's just been so much back and forth and posts about tweaking what's there what's not there I'm not totally clear. I'm looking for is an easy "just go get the updated PCB image here and follow the new wiring diagram here" :icon_lol:
Yeah. I wish I would have waited, but I didn't know what I was getting into. ;) I haven't seen any updates to RG's site regarding the new BM layout. I went and redid the old one with the new info and other than a little clean up on my part it works great.
If someone could summarize in 1 message what those all those exact changes/fixes are and how to build this project correctly with the existing PCB image, what to change in the parts layout/wiring exactly and any parts that need to be changed (or if there's an updated BOM and layout file to follow to apply to the old image) that would be greatly appreciated. Sorry, I'm just lost in both a few people trying to work it out and others wanting to add mods and adapt other circuits into it and I would simply like to be build a working clone as was originally intended.
Thanks!
Quote from: fogwolf on January 27, 2009, 02:11:57 PM
If someone could summarize in 1 message what those all those exact changes/fixes are and how to build this project correctly with the existing PCB image, what to change in the parts layout/wiring exactly and any parts that need to be changed (or if there's an updated BOM and layout file to follow to apply to the old image) that would be greatly appreciated. Sorry, I'm just lost in both a few people trying to work it out and others wanting to add mods and adapt other circuits into it and I would simply like to be build a working clone as was originally intended.
Thanks!
RG's update to the BM is at the top of the GEOFex (http://www.geofex.com/) site. The .pdf file lists the fixes for the old pcb layout that's sold by GGG (http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=62&Itemid=26).
Great - thanks!!
Quote from: Plinky on January 27, 2009, 02:23:30 PM
Quote from: fogwolf on January 27, 2009, 02:11:57 PM
If someone could summarize in 1 message what those all those exact changes/fixes are and how to build this project correctly with the existing PCB image, what to change in the parts layout/wiring exactly and any parts that need to be changed (or if there's an updated BOM and layout file to follow to apply to the old image) that would be greatly appreciated. Sorry, I'm just lost in both a few people trying to work it out and others wanting to add mods and adapt other circuits into it and I would simply like to be build a working clone as was originally intended.
Thanks!
RG's update to the BM is at the top of the GEOFex (http://www.geofex.com/) site. The .pdf file lists the fixes for the old pcb layout that's sold by GGG (http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=62&Itemid=26).
Not to keep beating a dead horse here...but...
I got my brassmaster working great. I love this pedal for bass. I need to add a sensitivity knob to the outside of the box as well as a switch to change the input impedance for use with different guitars and basses. This brings me to my question: Would changing the input impedance help me regain the lost high frequencies through the dry channel specifically? I haven't noticed a lowpass filter in the circuit to mess with. What component would be best to try different values with in order to bring back the highs? Even for bass I find the high roll off to be a bit too drastic compared to the sound when bypassed. If the highs were brought back in would that reduce the lows?
Quote from: airplanehuh on March 10, 2009, 09:42:39 PM
Not to keep beating a dead horse here...but...
I got my brassmaster working great. I love this pedal for bass. I need to add a sensitivity knob to the outside of the box as well as a switch to change the input impedance for use with different guitars and basses. This brings me to my question: Would changing the input impedance help me regain the lost high frequencies through the dry channel specifically? I haven't noticed a lowpass filter in the circuit to mess with. What component would be best to try different values with in order to bring back the highs? Even for bass I find the high roll off to be a bit too drastic compared to the sound when bypassed. If the highs were brought back in would that reduce the lows?
The Sensitivity knob is supposed to be on the outside. It's key to getting many cool tones!
Yes, increasing the input impedance would help. Or run your bass into something that will buffer it first. My bass is active so it doesn't cause that dulling effect.
However, I used to love putting an EH Mole bass booster before the Brassmaster. So I'd have a thick slab-O-bass from the clean channel with the bright fuzz on top of it.
Yes I agree, I've been running a DOD Meatbox into the BB-1 and that makes for one really thick bass sound. I just sort of want a switch that will add more clarity for use with guitar too.
Would raising both C1 and R1 increase the impedance or just R1.
...I totally forget everything that I learned about impedance in college. I'll have to look up impedance info on the web.
Oh yeah, the mole(hog's foot) sounds great in front of this thing... I stuffed my brassmaster in a big enclosure with one, and a flipster also... it's screwed down on my pedalboard in pre-fixed filter version... one of these days I oughtta mod it to get it workin right, but even 'wrong' it's got a permanent place on my pedalboard... thanks for figuring this out guys!
Quote from: airplanehuh on March 11, 2009, 12:20:03 AM
Yes I agree, I've been running a DOD Meatbox into the BB-1 and that makes for one really thick bass sound. I just sort of want a switch that will add more clarity for use with guitar too.
Would raising both C1 and R1 increase the impedance or just R1.
...I totally forget everything that I learned about impedance in college. I'll have to look up impedance info on the web.
Go back a page in this thread and read what Gus wrote:
Quote from: Gus on January 07, 2009, 11:05:37 AM
R.G I was drawing up an input with 8.2K collector R and a 2.2K emitter maybe run it at about 1/2 ma Ic set the base at about 1.7VDC gain <x8. Maybe a voltage divider input 100K and 470K (429k from math) common resistors. The 2.2K emitter R kind of big for the 10k bass volume pot but it might be OK. Input R hfe x 2.2K || 100K || 470K maybe a MPSA18
1/ 2pi * 17 x10^3 *.1 x10 ^-6 = stock HP input Might even want to move the input filter turnover frequency depending on the bass used
Like you posted many different ways to change things.
At the very least you can tack on a JFET buffer stage before the main circuit. There are plenty of those circuits around.
Finally got around to debugging my BM clone - had R13 & R14 crossed. It now has more of a level boost like DRM mentioned when the BM is set for a clean tone.
Now to tweaking.
The friend I'm building this for made one observation and I'm thinking this would work, but I thought I'd run it by the experts.
I'm at work so I don't have the pedal with me, so bear with me. I can't remember which pot controls the amount of fuzz in the circuit (brass volume?). The adjustment is very touchy, so it's easy to add too much fuzz. All the pots are 10k linear. Would changing this pot to log taper (or other taper) make it so the change from no fuzz to all fuzz is a bit more gradual instead of almost immediate? He likes the tones out of it, but it's hard to dial in a subtle amount of fuzz.
Quote from: Plinky on April 08, 2009, 02:37:49 PMbut it's hard to dial in a subtle amount of fuzz.
Check your wiring, it shouldn't be that touchy. I dial in the clean bass tone, and then turn up some fuzz. You can get a small amount of fuzz with no trouble.
Quote from: DavidRavenMoon on April 08, 2009, 02:51:08 PM
Quote from: Plinky on April 08, 2009, 02:37:49 PMbut it's hard to dial in a subtle amount of fuzz.
Check your wiring, it shouldn't be that touchy. I dial in the clean bass tone, and then turn up some fuzz. You can get a small amount of fuzz with no trouble.
I'm still quite foreign to using this pedal (not a bass player). What are your settings for clean tone, just to make sure we're on the same level?
Quote from: Plinky on April 08, 2009, 06:07:32 PM
Quote from: DavidRavenMoon on April 08, 2009, 02:51:08 PM
Quote from: Plinky on April 08, 2009, 02:37:49 PMbut it's hard to dial in a subtle amount of fuzz.
Check your wiring, it shouldn't be that touchy. I dial in the clean bass tone, and then turn up some fuzz. You can get a small amount of fuzz with no trouble.
I'm still quite foreign to using this pedal (not a bass player). What are your settings for clean tone, just to make sure we're on the same level?
If you turn the "brass" (fuzz) down, and turn the bass up, that's more-or-less the clean signal. I'm getting a little fuzz bleeding into my straight signal, but that's probably something to do with the layout of the wires. But the clean signal is not totally pristine on a passive bass due to the imput impedance not being high enough.
So start with the straight signal, and then mix some fuzz into it. Also the sensitivity control is important for different effects. Turned up it's a lot of fuzz, and turned almost all the way down gives you more of a grunty tuba fuzz with less sustain.
The Brass and Harmonic switches change the tone of the fuzz, from fuller to thin, and with more of an upper octave tone.
That's about how I had it set, and I'm not having any problems dialing the brass in. I'm thinking it's being nitpicky more than anything. I just don't know a lot about these pedals, so it's hard to explain to someone who says they know what it should sound like. It switches quiet, the clean setting sounds very close to bypass IMO, and every control makes a smooth transition back and forth (at least that's what I hear).
If he doesn't like it, I'll keep it for myself. I've spent enough time with this for parts money, and I haven't even started on the enclosure.
I had to look at this stuff for a recent post. I've got these notes which tried to summarize the final results.
This one took ages to resolve partly because the original circuit has some dodgy things which throws everyone off the trail. Luckily gtrgeek1 had a real unit to help decipher the final circuit.
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Thread Summary
Maestro BB-1 Bass Brass Master
Pot tapers (linear) missing on all but the original schematic.
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Thread started 2007, revived 2008, resolved 2009
gtrgeek1, RG, George Giblet, DavidRavenMoon
https://www.diystompboxes.com/smfforum/index.php?topic=56690.0
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Thread Re: GGG Brassmaster: Does anyone know the correct resistor values?
DavidRavenMoon: 29 December 29, 2008
The guy that did the layout said he took the "incorrect" schematic and redrew it into Circuitmaker and was able to verify that the schematic is in fact correct, and matches the real pcb. He also said the Q1 supply is not marked, but it should be fed from the 8 volt supply.
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Thread: Re: GGG Brassmaster: Does anyone know the correct resistor values?
page 5
gtrgeek1: 03 Jan 2009
Hey Guys,
I finally got the original Brassmaster on my bench and have the following info for your reference:
Transistors
The transistor designations follow the original factory schematic.
Q1,2,3,4,6,7 are 2N3392 factory marked 83930. All have an orange dot on the top, possibly matched or selected.
Q5 is 2N5308 factory marked 135 43C. Pinout matches 2N3392 not schematic pinout.
Maestro Bass Brassmaster Voltage Chart 01/03/09 (03 Jan 2009)
V1 = 9.3V
V2 + 8.0V
E C B
Q1 193 mv 2.107V 0.793V
Q2 63.9mv 4.68V 0.656V
Q3 4.04V 5.16V 4.68V
Q4 H1 1.319V 9.34V 1.918V
Q4 H2 3.195V 9.34V 3.796V
Q5 H1B1 28.2mv 7.58V .907V
Q5 H1B2 61mv 5.88V .980V
Q5 H2B1 6.5mv 8.7V .816V
Q5 H2B2 40.8mv 6.92V .937V
Q6 267mv 2.986V .870V
Q7 2.391V 8.04V 2.987V
H1 = SW2 closed / 82K connected
H2 = SW2 open
B1 = 47K resistors selected in filter
B2 = 6.8K resistors selected in filter
Diodes
All Diodes 1N457A
Transformer (measured in circuit)
Primary = 680 ohm CT
Secondary 572 ohm
500 mv 1K sinewave into secondary, measured 500 mv on primary
The transformer on this particular unit is much smaller than others I have seen. Mounting tabs did not line up with pads in pcb and were folded flat.
Resistors
All 1/2 watt carbon comp
All pots 10k CTS with 1971 date code
Capacitors
.01, .005 (x2), .05 in filter are ceramic disc
.05 on base of Q3 is ceramic disc
Electrolytic as marked on schematic
All others mylar 100V
PCB
C.M.I. 980 018260
Since the owner paid a boatload for this thing, I am a little hesitant to unsolder anything for a more accurate measurement, but I did compare all voltages to a clone built on RGs layout and all voltages match.
Since I will have to return this treasure soon, please let me know if there is any other info needed.
Regards,
gtrgeek1
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Thread: Re: GGG Brassmaster: Does anyone know the correct resistor values?
page 5
George Giblet: 03 Jan 2009
What is interesting is:
- the circuit was correct all this time (except for the minor 8V/9V thing) ***
- the suggested transformer MOUSER 42TM018 should be spot on
- Everyone should have *already* been building bm's cones (apart from those who had the wrong pinout).
Nothing has changed other than the knowledge in our heads.
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Thread: Re: GGG Brassmaster: Does anyone know the correct resistor values?
page 6
George Giblet: 04 Jan 2009
Regarding the bias shifting - that is strange. I can only guess it's an oversite, or something disregarded.
Regarding the generally "poor" biasing - who knows, oversite vs. deliberate sound shaping?
BTW: Using gtrgeek1's voltages I've estimated the hfe of the non-darlingtons (2N3392) to be about 130.
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*** "The minor 8V/9V thing" is that Q1 should get power from the +8V rail.
It is unclear or unspecified on the original schematic.
Schematics Summary
Maestro BB-1 Bass Brass Master
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Schematics
Maestro_BB-1_Bass_Brass_Master.pdf / maestro_bb-1_001.gif
Original
Identifying feature: parts table in top left
Shows pot tapers as Linear
R & C have no designators
Bugs:
- Q1 connection to +V unmarked. It should go to +8V.
Maestro_BB-1_Bass_Brass_Master.jpg
Some changes but they are wrong
Identifying feature: parts table replaced with notes, mentions filter redrawn for clarity.
Changes:
Filter redrawn
R & C designators added.
Bugs:
- filter is drawn incorrectly (missing connection to C12)
- filter switching incorrect, uses SPDT switch paralleling resistors
- Pot tapers missing
ggg_brassm_sc.pdf
Close to original, but modernized slightly
Identifying Feature: (17 Nov 2009 JD Sleep)
Changes from original:
- 1M5 on input added
- 1M5 on output added
- Reverse polarity diode added
- 2N3391 transistors
- The true-bypass wiring is different to the original
- LED added
Bugs:
- post taper missing should be linear
- shows 2N3391 transistors, should be 2N3392 as per original schematic
(The 2N3391s have higher gain. George Giblet said gtrgeek1's measurements
match hFE = 130, which is more like the 2N3392.)
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The ever-hanging issues which were resolved:
(rg) The voicing is a band-pass filter.
(gtrgeek1 measurements) The bias does change when the switches are in different positions.
The original schematic was correct (except for Q1 connection to +8V)
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Parts
- Transformer 1:1 with centre tap,
DC Resistance primary 680 ohm + ct,
DC Resistance secondary 572 ohm
42TM018 very close match (10k:10k)
- Q gains (2N3392, hFE approx 130)
- original diodes were 1N457A despite schematics showing 1N4148/1N914
- pots should be linear taper
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