I am looking for 4-band Baxandall tone control, with Bass, Lo Mid, High Mid and Treble controls. Does anyone have a schematics for this (passive only), or I must try to figure out how to modify standard 3-band to 4?
passive will only give you grieve: the idea sounds nice, but... :icon_eek:
rather look up the eq from the soundcraft 200b desk it´s very simple and is 4band semiparametric :icon_idea:
see if you can find some Gallien Krueger amp schems
they did a passive 4-band tonestack I believe
Seems like you might get more control and more opportunity to mod (easier) if you were to do 4, or 5, EQ stages. Just my 2 cents.
I have an old amp and I want to upgrade it's preamp section. It already has 4-band EQ, but it is transistor based and I want a tube preamp, and I need some simple 4-band tone stack (not parametric) so I can replace it without changing the front panel.
How about doing a 3 band stack, and use 'pre' and 'post' gain controls for your preamp? ;)
I include them in my tube preamps (mostly), and like their functionality. You can really dial in some sweet tones that way, a lot like having a gain control and master volume....
Quotet already has 4-band EQ, but it is transistor based and I want a tube preamp, and I need some simple 4-band tone stack (not parametric) so I can replace it without changing the front panel.
Maybe an inductor based EQ like the Mesa-Boogie.
Here's another way to approach it, split into multiple bands then add back together.
This one needs second order active filters:
http://el34world.com/charts/Schematics/files/sunn/sunn_coliseum_bass.pdf
This one is the poor mans passive version:
http://www.next.gr/uploads/52/5-channel-graphic-equalizer-by-bc548-transistor.jpg
I'm not endorsing the second one. I suspect you will need to modify it so ensure the output is flat when the bands are set flat. The second issue it to have equal boost cut on all bands. It might even work better with a log or audio taper pot; more boost.
What OP is searching for might not exist.
Three controls (B/M/T) is just about the maximum one can cram into "Baxandall" circuit without controls starting to interact with each other too much.
Common scheme is therefore simply to use two Baxandall circuits, one configured for usual bass & treble, second one configured for low and higher mid-range. Sometimes you see three "Baxandall" stacks in series. I think some of those Gallien-Krueger amps should indeed be very good examples.
Passive configuration seems senseless to me. You can't fit any more controls to it than you could to active version.
"Baxandall" circuit (though Baxandall really refers to active version of the circuit) is very lossy in passive form. In addition, the more range you need for the controls the greater the insertion losses are. When you start to cascade the circuits in order to implement more controls the losses of each circuit add up.
Even if you build a passive circuit you will need to introduce gain anyway, basically just to recover the huge signal attenuation. At that point SNR has already degraded. So why not implement that gain to the tone control stages? That's the whole ingeniosity behind the Baxandall circuit: No considerable signal losses to recover and noise levels kept in a leash. Why purposefully downgrade the design by going passive and then amplifying to recover immense signal losses?
+1 Agree with Teemuk.
For 4 bands, you really need to be looking at an active circuit for exactly the reasons given.
I hadn't thought of cascading two two-band baxandall circuits, but that seems like a simple way to go, and you could do the whole thing with just one dual op-amp. Otherwise, you could do some 4-band graphic EQ based on gyrators or whatever.
If you want it all tube-based, that's not my area of knowledge, but I'm sure there's stuff out there.
Tom
Why does it have to be tubes? For an active EQ, you need noiseless, linear amplification, that doesn't"color" the tone. Modern opamps are the obvious choice. The Carvin X100B is a very interesting solution.
Quote from: rankot on October 28, 2017, 06:48:00 PM
I have an old amp and I want to upgrade it's preamp section. It already has 4-band EQ, but it is transistor based and I want a tube preamp, and I need some simple 4-band tone stack (not parametric) so I can replace it without changing the front panel.
what's the old amp?
Quote from: Derringer on October 29, 2017, 09:51:30 AM
what's the old amp?
Čajavec GA185B. Made in ex-Yougoslavia. :icon_mrgreen:
Any chance you can post a schematic for it? I'm wondering if you could copy its tonestack design and implement it with tubes.
Otherwise though, I mis-spoke about the GK tonestacks. They are 4-band, but they are active.
like this one http://gallienkrueger.mivamerchant.net/wp-content/uploads/400rb.pdf (http://gallienkrueger.mivamerchant.net/wp-content/uploads/400rb.pdf)
A cool tube-driven tonestack that's worth checking out it the one found in Ampeg V-4s and their like (v-2, vt-40 etc.)
It's a passive James stack with an active mid circuit that allows the user to boost or cut at 400hz, 1000hz, or 3000 hz.
Although you'd need to hunt down or wind your own inductor (there are directions somewhere online where someone did wind their own inductor for one of these)
If I were you, I'd just do a passive 3-band stack or a passive James-stack with a mid shift and build in an effects loop where I could run a 2 band parametric EQ. ;)
EQD Talons is a Guv'nor with a 4 band EQ. First is a Rat-like "presence" control leading into an active 3 band Baxandall section.
QuoteČajavec GA185B. Made in ex-Yougoslavia.
So it was Bass and Treble then HI and LO ?
I was thinking you were replacing a graphic EQ.
From what I can see the HI and LO filters don't match-up to give a flat response. The LO is lower than the HI and this leaves a gap in the mid to give the amp a scooped voicing. The Fender tone stack does this. If you replace it with a flat response EQ you know it will sound midrangy?
For Bass & Treble, why not use a Fender type Bass/Treble or a 2-band passive Baxandall (which you could match the old circuit or do your own).
For Hi & LO maybe use a simpler passive version of what was there. Go here and about 1/2 way down there is a muff with a tone control that has separated low and high frequencies:
https://www.premierguitar.com/articles/Electro_Harmonix_Russian_Big_Muff_Pi_Pedal_Mods
Another way to approach is to use a 2-band passive Baxandall tone control for Bass/Treble but change the meaning of HI and LO. You could for example make LO a variable frequency high-pass filter that cuts the bass, and HI a variable frequency low-pass filter that cuts the treble. It usually works best with second order filters but you could do it with a first order. A fender tone stack will give you the scooped mids but the bass control on that works kind of like a variable low-cut so having two low-cuts will be redundant.
Ask yourself you do what some mid-scooping and what would you like the controls to do. Something that would be useful to the sound you want.
Thanks a lot, Rob, this post explains many things! I didn't like it's original preamp because it was too noisy, and too loud - Volume pot was unusable after 9 o'clock. So I built a FET preamp based on a schematic I found somewhere here (Alembic Ripthorn), and added op amp based parametric 4-band EQ. It works fine, but sound is a kind of boring.
Fortunately, while changing the preamp, I also added a jack for external preamp input, so I can experiment. I also built a pedal using Acoustic 220 preamp schematic, and it works really nice, has a real bass sound, but it has 3-way tone stack done with inductors. So I wanted to try something completely different, and built Alembic F2-B with 12AX7 and it really kicks ass, but it also has only 3 pots for tone control. Which brings us to this discussion - I wanted to make a simple one-tube-preamp with 4 pots for tone (to fill all the holes). I will loosely keep this Alembic design, but I will choose another tube so I can run it on 40V (which is available in amp's power supply).
I will try with the third schematic from BMP page, to see what happens if I add this to 2-band passive Baxandall.
Original preamp schematic can be found here: (http://i67.tinypic.com/14sjpdc.jpg)
Maybe I could try this combination - Baxandall bass/treble and two mid notch filters taken from Marshall JCM 800 preamp?
(http://i66.tinypic.com/2dr9l4x.jpg)
There's a lot of options!
Honestly, you don't want to go backwards. If you think the F-2B was the best sound you shouldn't compromise from that just because of a few pot labels.
I've been trying to think of a way to stay with the F-2B and to use the extra pot to *add* more flexibility. The trick is how to "redefine" the meaning of the amp controls in a way that still makes sense.
If it were mine I would try this. Keep the F-2B but make one mod.
- Bass = F-2B Bass control
- Treble = F-2B Treble control
- LO = F-2B Mid control; re-interpret "LO" as LO-MIDs
- HI = added Upper Mids control; re-interpret "HI" as HI-MIDs
Now, the implementation of the Upper mids control mod is very simple:
- Connect the "Upper Mids" pot maybe 1MEG in series with a capacitor say 470pF.
- Then connect that combination in parallel with the 250pF treble cap on the F-2B.
- When you vary the pot it kind of varies the value of the treble pot adding more upper mids as the pot resistance is reduced.
You might have to play with the HI MID pot value and taper to make the control feel natural to use.
The downside is the effect of that pot will be quite subtle. Is that a problem if it lets you keep the good F-2B sound?
[The other way around is to put a pot in there for the 100k slope resistor and call this LO and use HI for the mid control].
--------
[Edit: adding whole mid ckt a bit like you suggested but before the tone control
https://images.talkbass.com/attachments/traynor-bass-ts50b-amplifier-schematic-png.2385807/
]
I will try it, seems to be quite simple addition so I can use existing PCB for that. I will need to check how does it perform with available 50V B+, because I don't want to add another transformer or PS. Thanks!
Not a baxandall but it has your bass, lo mid, high mid and treble controls and it's easy to implement...
http://milas.spb.ru/~kmg/files/schematics/Engl/530/1/530_full.gif
Quotebass, lo mid, high mid and treble controls and it's easy to implement.
Good find.
It's a bit like call HI a low-pass filter.
Maybe better to morph it into a Fender stack (like the F-2B) for bass?
> "Baxandall" circuit (though Baxandall really refers to active version of the circuit) is very lossy in passive form.
Baxandall's paper is for an *active* plan-- that was the whole point.
The bass/treb boost/cut passive tone control comes together in a paper by James, and has been called "James tone control", though it was not original with him.
The James (nearly all "passive" stacks) MUST have center-knob loss equal to the maximum "boost" you get at knob extreme. Passive can only cut, not boost. To get "boost effect" it must cut-down everything, then un-cut to give "boost". Also the action is limited by available pots. An "audio" taper naturally gives 20dB "boost", really up-to 20dB loss. A linear taper can be bodged to about 5dB "boost" and only 5dB loss, but that is not much boost.
That GA185B plan looks "poor" to me. It is all unity-gain through buffer, B/T Bax, and a couple filters. The first gain stage has 150K input resistor. The hiss level will be much higher (2X to 3X) than really necessary.
However if you are not annoyed by the hiss, add some more unity gain tone controls in front. Personally I would try to find one of the old graphic EQ pedals and put it in front. Using mostly boost positions, you get more level into the GA185B and therefore a better signal/hiss ratio; meanwhile 5 or 8 sliders gives many tonal possibilities.
I posted original schematic just for curious, but I already wrote that I intend to use tube preamp instead, and one of the main reasons for this was that I didn't like original preamp because of it's hiss (or noise).
So I decided to try with tone stack from Alembic F-2B, and to add fourth pot instead of switch for "Deep", like this:
(http://i67.tinypic.com/33a7vhi.jpg)
The rest is standard Alembic F-2B topology, followed by MOSFET booster stage at the end.
You have a 26V transistor amplifier. You want over 100V to run tubes well, and a high-current heater supply too. Do you have all that worked out?
I know that, but I have also 50V from main amp PS, so I will use that and adjust tube resistors for that scenario. Or I can try using another tubes, for lower B+. I will build this one and see what happens, then adjust. ;)
QuoteSo I decided to try with tone stack from Alembic F-2B, and to add fourth pot instead of switch for "Deep", like this:
I think you have done well coming up with that. It fits the front panel labels and you haven't lost any of the F-2B sound you like.
QuoteBaxandall's paper is for an *active* plan-- that was the whole point.
Very true.
Baxandall = Active Bass and Treble.
James = Passive Bass and Treble.
Unfortunately the passive often gets called Baxandall.
I believe the band-pass version of the Baxandall (often used for mid controls), and the 3-band Baxandall, should be attributed to Bohn (of Rane).
QuoteSo I decided to try with tone stack from Alembic F-2B, and to add fourth pot instead of switch for "Deep", like this:
R2 doesn't do anything because of the short from R3 to C16.
Is the schematic correct?
Quote from: Rob Strand on November 02, 2017, 09:10:03 AM
QuoteSo I decided to try with tone stack from Alembic F-2B, and to add fourth pot instead of switch for "Deep", like this:
R2 doesn't do anything because of the short from R3 to C16.
Is the schematic correct?
You're completely right, this was a mistake when redrawing schematic. I have uploaded correct one right now. :-[
> should be attributed to Bohn
I dunno, I wasn't there (or can't remember). It has been around a long time, in Nat Semi notes and maybe in Jung. BiAmp mixers had a very low-cost 4-band EQ, but my notes are packed away.
Quotedunno, I wasn't there (or can't remember). It has been around a long time, in Nat Semi notes and maybe in Jung. BiAmp mixers had a very low-cost 4-band EQ, but my notes are packed away.
I believe it started here, the nat-semi audio handbook,
http://www.worldcat.org/title/audioradio-handbook/oclc/8249960
Look what have I found this morning: http://music-electronics-forum.com/attachments/33067d1425320675-all-tube-bass-preamp.jpg
At least one good thing arrived from waking up at 4 am :(
I will try this schematic, too. :)
QuoteAt least one good thing arrived from waking up at 4 am
The weird thing is I had that come in the last two days as well.
These things have very low Q's. The 3-band barely works so I wouldn't get my expectations up :icon_razz:
I also found a Mesa Dual rectifier with a Presence which was part of the tone control.
What you have is probably more useable. If you want you could play around with the cap values to fine to it to how you like it.
The only think that might be worth considering is a single band active band-pass EQ placed around a free tube ie. somewhere where it won't load the guitar or the tone control.
FMV tone stack with additional band pass EQ after the last tube sound as a good idea. I'll try that too.
OK, this is what I ended up with, I will try with this tube (I have few of them), and combine NE5534/5532 for Low Mid EQ (I have centred that at 250Hz) and output amplification. Amplification levels are balanced, so my new Low control's volume range is close to the old Mid (now called High, since it is somewhere around 900Hz) tone stack's pot. Now I need to build this and see what happens :)
(http://i68.tinypic.com/5z14s2.jpg)
QuoteLook what have I found this morning: http://music-electronics-forum.com/attachments/33067d1425320675-all-tube-bass-preamp.jpg
That's very interesting but do you know what the frequencies are ?
Alf
Here is the url where it came from :
The second post mentions a lot of mistakes in the schematic !
http://music-electronics-forum.com/t38956/ (http://music-electronics-forum.com/t38956/)
I saw that there are errors in that schematic, but I thought that I could use it's 4-band tone stack. However, I decided to go without it, just use FMV 3-band tone stack with additional band pass filter with op amps at the end, as Rob proposed.
> the nat-semi audio handbook,
This is interesting.
It is in Jung Audio 1975 -- here's a scan from the 1978.
(https://s1.postimg.org/1y180hwm97/Jung-_Mids-1975.gif) (https://postimg.org/image/1y180hwm97/)
(Apology for ugly image; I do not want to flatten my copy on scanner.)
The '78 has references (general, not specific to each idea) which mentions Nat Semi Audio 1977 and editor "D. Bonn"{sic}. I do not have NatSemi 1977. I have a reprint of the 1980 issue, which lists Giles as editor and "Dennis Bohn" as mere contributor. (May be some company politics there.) I can not find the bump tone control in NS 1980 (cite?).
QuoteThe '78 has references (general, not specific to each idea) which mentions Nat Semi Audio 1977 and editor "D. Bonn"{sic}. I do not have NatSemi 1977. I have a reprint of the 1980 issue, which lists Giles as editor and "Dennis Bohn" as mere contributor. (May be some company politics there.) I can not find the bump tone control in NS 1980 (cite?).
Extremely cool find. Thanks for looking it up by the way.
I don't have the 1977 NS Audio Handbook only the 1980. However I did copy those sections from a friend's book when I was a teenager. I still have the photocopies. I do not know what edition he had. For what I remember and what I was doing at the time it would have been 1979 or 1980 but I also remember he had that book before I borrowed it. So I would put my money down that it wasn't the 1980 copy. In fact I'm now sure of it ...
For the photocopies. The 3-band appears as fig 2.14.18 on page 2-46. Whereas the 1980 copy has the 3-band as fig 2.14.18 on page 2-49. The band-pass equalizer appears in the section about the 10-band graphic equalizer. On my photocopy it is fig 2.17.12 and 2.17.13 on page 2-55. That section in the 1980 copy has gyrators and one opamp band-pass filters. So it's obvious my photocopies don't come from the 1980 edition.
The 10-band equalizer using the band-pass "baxandall style" equalizer wasn't very good because it used a parallel structure which produced some weird responses. Perhaps they decided to dump it, despite the fact the single equalizer section was quite useful on its own.
So I guess we can't know what book had it first until we can find an old Jung.
[Edit]
Hey cool, I found a 1976 (matches my photocopy)
https://archive.org/details/bitsavers_nationaldaAudioHandbook_17103876
> The 3-band appears as fig 2.14.18
Indeed it does; the Index sucks.
The note about expanding it to 4 bands sure sounds like Dennis.
References at the end of the section are not specific (Fletcher-Munson, Baxandall).
So we have Jung 1975 and Bohn(?) 1977. Neither presents it as a New Invention. I suspect the idea had been around a while. Perhaps in tubes, but the cost was too far on the slippery slope to L-C tanks and rows of tubes. The <$1 opamp made it practical.
QuoteNeither presents it as a New Invention. I suspect the idea had been around a while..
Well it did cross mind it might have been known before then. I've never seen it before the NS Audio handbook but that doesn't mean it wasn't known. (FYI, some of Bohn's Rane papers show the LC version but I've never traced the references to see where the trail stopped.)
(pls see edit of previous post.)
OK I think this is it, see the second paragraph, Bohn pretty much says it,
http://www.rane.com/pdf/constanq.pdf
Ref [1] is NS Audio 1976
Ref [2] is a well known paper which analyses that one-opamp band-pass equalizer (and other stuff).
IMHO, the 10/27-band EQs are a long step past the BMT Bax.
It is fascinating that three dudes came to about the same answer in the same year (like I designed and built a very low cost spectrum analyzer the month before PopElectroncs published 98% the same thing).
Quotet is fascinating that three dudes came to about the same answer in the same year (like I designed and built a very low cost spectrum analyzer the month before PopElectroncs published 98% the same thing)
Sometimes it's quite freaky but it happens a lot. You see this in scientific journals, two guys come up with the same *obscure* stuff within months of each other. My thinking is in a given era there are certain problems that arise and certain technologies and ideas that exist. If you put two of the right people on the job there's a strong chance they will come-up with similar solutions. Years ago I came up the the idea of (analog) speaker crossovers with *different orders* that add-up to |LPF+HPF| = 1. It seemed pretty obscure, then I found a paper by Malcom Hawksford (well know AES guy) pretty much come-up with the same thing some time before me. So ... bin that!
I couldn't resist adding this to the thread,
Marshall 9001
http://www.tremolo.pl/Firmowe/MARSHALL/9001.gif
The ancients are always stealing our inventions.
The rarer case is independent simultaneous inventions. A bad example is Bell and Gray. Nobody ever heard of a "telephone" then two guys show up to file the same day. Battery and wires, talk at a distance. Bad because both were very flawed: Bell's was lame and Gray's just would not carry speech. Newton and Leibniz, calculus, another murky tale. E=MC^2 wasn't as novel as we now think. But get into steel plows, everybody was inventing those (John Deere not even in the first wave).
...and Tesla and Marconi for radio invention amongst many others...
Did anyone had time to take a look at my preamp schematic? No comments yet :(
Quote from: PRR on November 06, 2017, 02:45:17 AM
The ancients are always stealing our inventions.
....
Yep them bastards. Why can't they just rest in their graves? Shame on them.
I've built this on a breadboard, still w/o tone controls, but preamp works really fine. Have some hiss, but that is expected for BB.
(http://i64.tinypic.com/24n1n9i.jpg)
I have also tried version with triode first, but it does oscillate. OK if one wants constant vibrato 8)
> take a look
Pentodes (and similar) usually want a bypass cap on screen grid.
Sequential stages with shared cathode bypass caps do oscillate at bottom of audio band.
If that pentode stage worked well, it is gain of 50, which is a LOT for a 50V supply. It will clip strong guitar.
I'd stick with simple low-gain triode like 12AU7.
I thought that I don't need so much amplification (times 50), so I didn't put screen bypass capacitor to have some negative feedback, thus reducing amplification and maybe achieving better sound. And having in mind that I will use passive tone stack, I believe that I need lots of amplification before it?
QuoteThe ancients are always stealing our inventions.
Proof of time travel.
QuoteNewton and Leibniz, calculus, another murky tale
That one's is a good one.
QuoteDid anyone had time to take a look at my preamp schematic? No comments yet
I though it you were just going to try it.
If I had to comment I'd say the gyrator is loading down the tube. It also makes cut a lot more than boost.
You already have an extra opamp stage. You could move the the gyrator to the next opamp. That will isolate it from the tube. Another way is to use a gyrator around the tube stage but connected like the Acoustic 220 EQ. Noise will probably be worse.
I wanted to try this preamp without tone stack first, now I did and I like it, so I will try it with TS now, but thanks for that idea with opamps anyway!
Quote from: Rob Strand on November 06, 2017, 08:36:51 PM
If I had to comment I'd say the gyrator is loading down the tube. It also makes cut a lot more than boost.
You already have an extra opamp stage. You could move the the gyrator to the next opamp. That will isolate it from the tube. Another way is to use a gyrator around the tube stage but connected like the Acoustic 220 EQ. Noise will probably be worse.
Rob, what is the trouble with loading down the tube? I have tried few combinations, also tried to put op amp unity gain follower right after triode, and then to put gyrator EQ stage, but then gyrator is reducing a tone very little, and boost is huge (at least in simulation, I can't check it really cause I don't know how to measure frequency response in a real circuit). I'm puzzled...
QuoteRob, what is the trouble with loading down the tube? I have tried few combinations, also tried to put op amp unity gain follower right after triode, and then to put gyrator EQ stage, but then gyrator is reducing a tone very little, and boost is huge (at least in simulation, I can't check it really cause I don't know how to measure frequency response in a real circuit). I'm puzzled..
If you are having trouble with a buffer there I suspect you have left off the input resistor. Have a look at this circuit.
http://ethanwiner.com/spect-5.jpg
Note the 10k feedback resistor, but also the 10k resistor in series with the input. You need both for this type of EQ to work. Usually both input and feedback resistors are the same value. With the tube the output impedance is high enough to act like the input resistor. The "problem" I mentioned is the tube impedance is very high compared to your feedback resistor and in fact the impedance of the Gyrator outside of the resonant zone, so I was thinking it might not work as planned. A buffer after the tube has to work!
There used to be free software you could generate a tone and measure. Some could even measured frequency response and others had options for sine or "noise" excitation. There's quite a few precautions you need to take to get a good result. The main one is to keep the signal generator level below the clip level of both the device and the PC sound-card input. 100mV to 200mV pk would be a safe starting point. Clipping generates harmonics which stuffs up the frequency response measurement.
I have a small variable signal generator I built myself, so I can try to compare input and output signals on oscilloscope, that will show if there is amplification in some frequency range or not.
QuoteI have a small variable signal generator I built myself, so I can try to compare input and output signals on oscilloscope, that will show if there is amplification in some frequency range or not.
That will work. You can use on oscilloscope or even a multimeter on AC. For measurements over 400Hz you might need to correct the measurements. Some meters will be OK to 2kHz and costly ones possibly upto 100kHz. What happens is the signal generator output might be flat (equal at all frequencies) but the meter is not. If you just measure the output you end up measuring the circuit response cascaded with the meter response. It can be quite bad on some meters.
First get an idea of how flat the meter is.
- Record the signal generator level measured by the meter at say 100Hz (50 to 200Hz OK)
- With the meter connected, change the frequency and note at what frequencies the reading differs from that in (a); say 5% or 10% for 0.5dB to 1dB accuracy.
When you do your response measurements, correct the measurement in the dodgy frequency regions by measuring the input level and scaling the measure output level (in dB that means adding an offset),
V_out_corrected = (V_in_100Hz / V_in_measured) * V_out_measured
After a while you will know what frequencies to trust your meter and when you don't have to bother correcting the measurements.
Measuring the levels with a sound card is often easier as it has a wide bandwidth.
Check this out,
http://audio.rightmark.org/download.shtml
I only checked loopback but it looks OK.
At least it works.
[EDIT: Some tips]
http://nwavguy.blogspot.com.au/2011/02/rightmark-audio-analyzer-rmaa.html