Hey,
So my next project is going to be a phase 45. Started doing the Jfet matching using this:
(https://i.postimg.cc/HrPBBw0j/29761826-5-F2-A-4411-BDFF-9-C87-D6-DB0-DC1.png) (https://postimg.cc/HrPBBw0j)
I can't help but feel like I'm doing something wrong here. I decided not to use the switch and just remove the 100 ohm resistor, and jumper from the gate to ground. It looks to me like that is all the switch is doing. Which then makes sense that my two reading are very similar.
Within a few mV.
(https://i.postimg.cc/hXrb599V/C3-EE005-E-ACD4-4-BDE-A2-D8-D321718047-BC.jpg) (https://postimg.cc/hXrb599V)
Lastly if this is correct how close am I aiming for here. I'm assuming two at 1551mv and 1554mv would be considered matched. But would 1538 and 1547?
Thanks again, you all have been super helpful in me getting started in this.
Oh the switch makes it so it by passes the 1M resistor I think.
Ok that makes more sense now. My two best out of 8 are 1558mv with an idss of 19.2ma 1556 mv with an idss 18.8ma. I'm assuming those are close enough.
I just completed a 45 a month ago.
I purchased a matched set of 5485's from General Guitar Gadgets.
Here is a quote from their site.
"2N5485 Matched set of 2 JFET transistors that are matched to within one-tenth of a volt. They are tested, matched and sorted by hand. A very good set of Fairchild transistors for use in a Phase 45 or other 2-stage phase shifter."
1/10 seems like alot. But if that is what is needed then I am not the one to comment on that issue.
I have seen articles on how to match them not much on what is "matched". At .1v I'd have 7 of 8 being able to be called matching, haven't done the idss on all of those yet as I just took took my two best.
QuoteI have seen articles on how to match them not much on what is "matched". At .1v I'd have 7 of 8 being able to be called matching, haven't done the idss on all of those yet as I just took took my two best.
Less than 50mV is excellent. 100mV is very workable, in fact that's what Ibanez/Maxon use as worst case.
It's a good idea to connect a 470nF to 1uF poly cap across the source and gate to check if noise isn't affecting the measurements. The measurements with the cap is likely to be more correct.
Quote from: Rob Strand on August 01, 2022, 09:23:13 PM
QuoteI have seen articles on how to match them not much on what is "matched". At .1v I'd have 7 of 8 being able to be called matching, haven't done the idss on all of those yet as I just took took my two best.
Less than 50mV is excellent. 100mV is very workable, in fact that's what Ibanez/Maxon use as worst case.
It's a good idea to connect a 470nF to 1uF poly cap across the source and gate to check if noise isn't affecting the measurements. The measurements with the cap is likely to be more correct.
Good to know, I'll re measure with that. The impression I was getting was I'd be lucky to get a pair from 8. Only 1 is more than 100 mv off I've got four within 10 of each other.
QuoteThe impression I was getting was I'd be lucky to get a pair from 8. Only 1 is more than 100 mv off I've got four within 10 of each other.
Sometimes that's not far from the truth!
The people that sell the matched sets have the luxury of buying a whole stack from the *same batch*. The large sample size and the same batch greatly improves the chances of matching.
When you buy stuff from your local electronics store you could get JFETs from three different batches. If you buy 10 the chances getting a match can be quite low! Even if you get some from the same batch the chances of a match is reduced due to the low sample. That's where it can be more economical to just buy matched ones. Parts from larger supplies are likely to come from the same batch.
Ah. I got these from small bear or pedal parts. I'd have to look, I bought jfets from both last time I ordered. I rarely by at my local store because it's ridiculously expensive. And they don't have a lot for pedal purposes.
Quote from: Rob Strand on August 01, 2022, 09:23:13 PM
QuoteI have seen articles on how to match them not much on what is "matched". At .1v I'd have 7 of 8 being able to be called matching, haven't done the idss on all of those yet as I just took took my two best.
Less than 50mV is excellent. 100mV is very workable, in fact that's what Ibanez/Maxon use as worst case.
It's a good idea to connect a 470nF to 1uF poly cap across the source and gate to check if noise isn't affecting the measurements. The measurements with the cap is likely to be more correct.
Is it a good idea as well to have a power filtering cap on the positive and ground rails? Had it initially and took it off as I was disconnecting power when I changed jfets, and discharging every time made it annoying.
QuoteIs it a good idea as well to have a power filtering cap on the positive and ground rails? Had it initially and took it off as I was disconnecting power when I changed jfets, and discharging every time made it annoying.
It doesn't hurt that's for sure but normally you can get away without it because the power rails have a low impedance.
I've done experiments which check the measurement consistency on different setups. I've also checked touching the various leads in the test set-up to make sure there was minimal effect from noise.
- I powered from battery and a number DC adaptors. It is definitely true that power supplies which connect to the mains are more susceptible to noise than battery power. Some supplies are worse than others. With the 470nF/1uF cap usually the measurements are OK.
- Adding caps across the power wasn't very effective at fixing noise issues. (kind of expected)
- Adding caps across the
drain source and gate were very effective. You need at least 470nF, 1uF preferred.
The cap needs to be a film type to ensure the leakage is low.
(Junk can get in from the relatively long meter leads.)
- Some JFETs oscillate in the test jig, especially the low Rds_on/high Yfs types. A 1k resistor in series with the gate was very effective at preventing such oscillations. Power supply caps less effective. (With the 1k present I think I had the 1uF cap across the DMM terminals and not the gate as such).
- Measuring VP (Vgs off) at higher currents is less susceptible to noise than at low currents. That means a lower Rgs resistor. However, testing at higher currents means the Vgs measurement is somewhat less than the VP (Vgs_off) JFET parameter. The Vgs measurement is OK for matching but not for parameter measurement. I don't mean crazy high test currents, maybe 100uA max. I still test at low currents.
Other stuff:
- the 1k gate resistor give added protection to the test jig if the JFET is inserted incorrectly.
- it's a good idea to keep 100 ohms in series with the power rail to help prevent frying the JFET if the JFET is inserted incorrectly.
I think I drew a diagram of this set-up a year or two back but I can't find the posts. The schem has a kharki/olive background.
FWIW, I don't think I ended up drawing a complete schematic. I drew a schematic explaining some technical issues and mentioned the cap later on.
Thanks again,
Added the items you mentioned definitely saw more stability in the readings than I did before.
Now I'm debating if I want to make the 90 instead. My readings for the 8 were (I didn't do the IDSS) yet.
In mV
1501
1471
1247
1535
1548
1544
1544
1571
4-7 there should be pretty solid I'd think.
QuoteNow I'm debating if I want to make the 90 instead.
Why not!
Quote4-7 there should be pretty solid I'd think.
Those look quite good.
QuoteMy readings for the 8 were (I didn't do the IDSS) yet.
For a phaser IDSS is unimportant compared to VP (Vgs_off).
If you use the same part numbers matching VP will pretty much guarantee the other parameters
are close enough.
QuoteAdding caps across the drain source and gate were very effective.
FWIW, I actually added the cap across the source and gate.
Quote from: Rob Strand on August 02, 2022, 08:11:14 PM
QuoteAdding caps across the drain source and gate were very effective.
FWIW, I actually added the cap across the source and gate.
Yea I put it between source and gate, I don't even know if I really took in the typo. I just put it there as that is where I figured it would go I guess? Anyways realized I didn't have any 15u caps or a 5.1 zener they will be here Friday so I decided to move stuff around in my pedal board to make some room for a few of these I've made in the last couple weeks and broke the batter snap off on my Black Russian big muff. Guess I found what I'll be doing tonight lol.
QuoteAnyways realized I didn't have any 15u caps or a 5.1 zener
The 5.1V zener should be a 500mW typ if you use a 1W type the voltage
will be a little low. I think you end-up with around 4.8V across the zener
when you use the correct 5.1V 500mW and an ill-defined 4.0V if you use
a 5.1V 1W. If you can only get 1W zeners you might be better off with
a 5.6V 1W. There's quite a few posts on this forum which elaborate
on the precise voltages.
Darn it! Didn't realize the wattage on them mattered. Little confused by the product description in stompboxparts
(https://i.postimg.cc/ygq6fXyF/8-B64172-B-E6-ED-4-EF4-93-F8-3-B9969-EA2324.png) (https://postimg.cc/ygq6fXyF)
Product description notes the 5239, but then says 5.1v. Didn't even look at that when I ordered. Guess I'll see what I get
QuoteProduct description notes the 5239, but then says 5.1v. Didn't even look at that when I ordered. Guess I'll see what I get
I think you might end-up with 1N4733A's 5.1V 1W.
It will still work but you lose a bit of head-room and the LFO doesn't quite work the same.
No an enormous problem.
If you really want you can reduce the 10k between +9V and the zener. Probably needs to be about 2.2k or so.
That will bump the zener voltage up a bit. Another way is to leave the 10k and put a 1N4148/1N914
silicon diode in series with the zener. That will bump the voltage up by 0.6V. The zener "points up" and
the 1N4148/1N914 "points down".
quote author=Mark Hammer link=topic=82132.msg681143#msg681143 date=1265331970]
He's right, of course. The zener is there simply to stabilize the voltage supplying the bias circuit in the face of an everchanging battery voltage. If you use an external PS, then all those pesky battery-related issues simply vanish.
[/quote]
Reading this from a previous makes me wonder if the diode is necessary? I use power supplies that always give the 9.3v. You bias it off the 250k trim pot, correct. Wouldn't just a 78l05 be a better way of doing this?
Quote from: Locrian99 on August 03, 2022, 01:03:19 AM
Quote from: Mark Hammer on February 04, 2010, 08:06:10 PM
He's right, of course. The zener is there simply to stabilize the voltage supplying the bias circuit in the face of an everchanging battery voltage. If you use an external PS, then all those pesky battery-related issues simply vanish.
Reading this from a previous makes me wonder if the diode is necessary? I use power supplies that always give the 9.3v. You bias it off the 250k trim pot, correct. Wouldn't just a 78l05 be a better way of doing this?
It's largely correct but not 100% correct. If you have an unregulated external supply the voltage doesn't stay the same. If you have a nominal 9V regulated supply it could be anything from 8.5V to 10V. Each individual supply consistently stays at it's own voltage but different supplies may have slightly different voltages. If you use a zener it keeps the *local* "5V" rail relatively constant. When you set-up the phaser it is adjusted relative to this local "5V" rail, so it should stay in adjustment for the life of the product.
In principle the 78L05 would work. You might need to add a small dummy load because in-circuit the LFO can feed current *back into* the regulator. The main reason the zener is used is because the MXR circuit originate back in the days before 3-terminal regulators were common and they weren't that cheap. The 78L05's actually draw more current than the zener circuit. So for battery operation it's a consideration but not so much when using external supplies. The regulation of the 78L05 is much better than the zener.
If you think about, if you match your JFETs to 50mV you might expect the JFET adjustments need to be within say 100mV. And from that point of view it would be good if the 5V rail could be kept within 50mV to 100mV over the range of DC supply voltages.
The thing that puts a spanner in the works is the LFO is powered from the 9V rail, so if your DC supply voltages vary from say 8.5V to 10V you are going to see variations at the output of the LFO anyway. In other words there's a point where the LFO variations swamp any good intentions from better regulation on the 5V rail.
K I'm thinking I'm at least getting the gist of this. Reading the electro smash article as well. Plenty of it flies over my head, but getting an bit of understanding from it.
Quote from: Locrian99 on August 03, 2022, 02:14:19 AM
K I'm thinking I'm at least getting the gist of this. Reading the electro smash article as well. Plenty of it flies over my head, but getting an bit of understanding from it.
Electrosmash have some very good articles. There's a lot to take in.
The stuff I mentioned about varying voltages and adjustments is beyond that! These are fine details that are never addressed. I've never seen it mentioned in any articles. The issues really only show up in phasers which use JFETs. If you can get to the point where you can see the stuff I mentioned *could matter* then you have done extremely well.
So my diodes came in. Set up the little breadboard test. Basically just a 1k resistor between the power rail and the diode. I'm getting 4.85v with the 4 I tested. Should this be good?
QuoteSo my diodes came in. Set up the little breadboard test. Basically just a 1k resistor between the power rail and the diode. I'm getting 4.85v with the 4 I tested. Should this be good?
Yes it will work fine.
The down side of using 1k is there is 4.2mA going down the zener. Whereas the original had 0.42mA, somewhat less battery drain. With 2.2k you only use 1.9mA. The voltage will be a little lower but it's good trade-off in terms of current. Ideally you want at least enough current to keep the zener voltage in the 4.5V to 5.0V region. With a 10k and 5.1V 1W you start to loose out as the voltage is 4.0V or even lower in some cases.
Cool I'll check out some slightly larger resistors see where it gets me.
Hey if you have a second to take a look at this layout, is this circled 10k r15 from the schematic? Only one I see coming off the 9V source so I figure it's got to be, just seems odd it's heading straight to the source strip on the jfets.
(https://i.postimg.cc/mhQGVbxz/43940-B3-F-82-A8-49-F9-9-A7-D-D220-C6979-E95.png) (https://postimg.cc/mhQGVbxz)
(https://i.postimg.cc/fSjnbv7j/A6-BE947-B-62-BE-41-BC-A394-2-AD697-E94-DF4.jpg) (https://postimg.cc/fSjnbv7j)
QuoteHey if you have a second to take a look at this layout, is this circled 10k r15 from the schematic? Only one I see coming off the 9V source so I figure it's got to be, just seems odd it's heading straight to the source strip on the jfets.
Looks like the resistor to me. All the sources wire back to the zener (Vref, 5.1V). It's the only 10k resistor between +9V and Vref.
Cool found some .5 watts on eBay going to socket the diode and resistor. Thanks again for answering my questions. You've been extremely helpful as I try and figure this stuff out.
Well it's built and working. Biasing this thing is harder than in anticipated. I'll have to try to dial it in tomorrow.
Hi:
I completed this 45 and it works. Maybe it can work better.
Reading this interesting topic has lead me to a question(s).
First, I added a 1N4001 "protection" diode to the circuit, is this ok on this build ?
(See picture)
Second, What should the voltage be at D1 ?
My battery is 9.23 v and at D1 to ground is 3.51.
D1 is a 1 watt 1n4732A from Small Bear. I have lots of 1n914.
Should I try that in series with D1 ?
Thanks in advance..
(https://i.postimg.cc/wy9VSZwv/PHASE-45-QUESTION.jpg) (https://postimg.cc/wy9VSZwv)
> D1 to ground is 3.51
Let's peek at 1N4732A specs.
(https://i.postimg.cc/dDvDDgsx/Phase45-Bias.gif) (https://postimg.cc/dDvDDgsx)
This is a One Watt part, test for 4.7V at 53mA. Here it is used at 0.4mA, 0.02 Watts. We would expect voltage drop to be less. The other data is 500r dynamic resistance at 1mA. That would be a half-Volt different, and we are significantly under 1mA. And low-Volt "Zeners" are really soft knees. 3.5V is less than I expect but not unreasonable. Yes, if I thought I needed to be closer to 4.7V I'd try a couple '914s.
But does it have to be a specific voltage? I think it needs to be "mid-way", on a varying battery, and steady (actually tracking JFET Vgs). 3.5V may be a little tight on the downswing but if you are not clipping there may be no "better" here.
There is another plan which uses a JFET for bias, actually two, plus a trim. Looks better in theory but seems to be a pain in practice.
Ah, real-like curves.
(https://i.stack.imgur.com/hNCuk.jpg)
This seems to be a smaller series than your 1N4732A; note that the "4.7" part hits 4.7V at like 7mA (blue dots). The "4.3" part seems closer to 1N4732A spec showing 4.7V (purple dots) @ ~~50mA (which may be out of bounds). It shows 3.3V in P45 circuit.
(https://i.postimg.cc/4783DNDH/47-VZener-Curves.gif) (https://postimg.cc/4783DNDH)
LEDs are good regulators. The several colors are several innate voltages, and also vary with current. Three IR LEDs at low current may be awful close to 4.5V, but you can't know if it is "on". (g)
QuoteSecond, What should the voltage be at D1 ?
My battery is 9.23 v and at D1 to ground is 3.51.
D1 is a 1 watt 1n4732A from Small Bear.
The correct voltage is about 4.8V with the correct zeners.
The correct zener is 1N5231B, 5.1V 500mW; see attached schem.
In the phase90/phase45 circuit, with a 9V supply and 10k, it produces about 4.8V.
Problem 1: What happens in the DIY world is someone measures the voltage at 4.8V, then they assume the
zener voltage is the measured voltage ie. 4.7V. But it's not a 4.7V zener, it's a 5.1V operating at a low current.
Problem 2: People don't realize 1W zeners and 500mW zeners are different.
A 5.1V 1W zener will produce a lower voltage than a 5.1V 500mW zener for the same current.
What's happened with some of the Phase 45/Phase 90 builds is an accumulation of errors
from these two problems: The first means sometimes the zener voltage is incorrectly specified
at 4.7V zener. The second means some people buy a 1W zener and not 500mW and net
result is the 4.7V 1W zener in the phase45/Phase90 circuit ends up way down at 3.6V!
What the means is the pedal has lost 1V of headroom because the wrong zener is used,
not great for a 9V pedal. If you can bias Vref for 4.5V to 5.0V the headroom will return.
The exact voltage is not important as the trimpot has enough adjustment to set the
JFET bias.
PRR' first graph shows the first problem, however it doesn't show the second problem.
You will also notice PRR's curves doesn't quite match-up with the 1N5231B, 5.1V 500mW
zener in the Phase 90/Phase45 since it's showing about 4.4V at 400uA whereas
the voltage should be about 4.8V. Those curves only apply to a specific model of
zener.
Each model zener has it's own set of curves, even if it has the same power rating.
Unfortunately those detailed curves are rarely given, so you
have to eyeball what's going on for a specific zener by making it pass through
a known point (from the single point in the datasheet for *your* zener.)
For problem 2 the curves for a 1W zener will have lower voltages for the *same
current*. It's sort of like the curves for the 1W zeners are like a 500mW zener with
a lower voltage rating *but* that's technically not true - since it's the current axis which is
changed. When we want to compare a 1W and 500mW at the same current we are forced to
compare voltages.
(https://i.postimg.cc/BX4hvdwz/phase45-original.jpg) (https://postimg.cc/BX4hvdwz)
When you can only get 1W zener's you can either use a higher voltage and/or use a higher current,
https://www.diystompboxes.com/smfforum/index.php?topic=129436.msg1251001#msg1251001
https://www.diystompboxes.com/smfforum/index.php?topic=129436.msg1251103#msg1251103
However, if you raise the current on your 1W 4.7V zener it will help but since the voltage is wrong
the voltage is always going to be low - you would be better off changing it to a 5.1V 500mW.
typos fixed!
Thanks Paul and Rob. Fortunately resistors don't follow the same quirks as zeners, lol. Valuable info from both, thanks. Not knowing I guess I thought a Dollar General 5.1v zener was the same as a Dollar Store one. Thanks for the help and support. Chalk this up to lessons learned. Shall find correct zener.
Hmm. Shouldn't the lfo be causing the voltage of the fete to be jumping around?
Just get a good voltage, not a magic Zener. 1N914 shims are perfectly valid. The exact voltage does not have to be as exact as the line down the center of the road. (You know what I mean.)
Quote from: Locrian99 on August 05, 2022, 09:22:14 PM
Hmm. Shouldn't the lfo be causing the voltage of the fete to be jumping around?
The opamps are biased to Vref, which is set by the zener. That is a fix voltage. It is desirable to set the voltage so the opamps can swing symmetrically for maximum headroom. That occurs when Vref is about half the supply voltage.
The zener is also used to set the bias point of the JFETs. The bias voltage is *between* the source and gate. That's set by the trimpot, so as far as the JFETS go the exact Vref voltage isn't important (although you want it to be fairly stable and the adjustment must match the JFETs).
The LFO modulates the gate voltage. The actual gate voltage is a combination of the bias trimpot and the LFO voltage. The two are mixed together where the 470k resistors and 3M9 (or 3M3) resistors meet.
I'll go through it again I've got audio fine and when I play and Kobe the trimmer in what I hear a phase kikeneffect. Leave the trimmer be there is none. And I don't see any voltage movement at the fets or anywhere else. after the kids go to bed I'll play with it some more. I accidentally plugged it into my test box backwards for power (reversed polarity) wondering if I fried one of the op amps. I'll play around with some more, only thing that struck me as odd was pins 5/6 of the bottom op amp were 0 when I did my quick check through.
Tiny little solder bridge where the 15u cap was connecting to ground was grounding out pin 6 and the LFO. Works great now, now to to play with the bias and resistors feeding that diode. Tomorrow I've got some coming which will have a 5.6v 1w I'll try. Had to get the 5.1 1/2 watt from eBay so hopefully sometime next week. Will wait to box this up and call done until then. Now to remember the chords to lightning crashes lol.
Quote from: Locrian99 on August 05, 2022, 11:55:32 PM
Tiny little solder bridge where the 15u cap was connecting to ground was grounding out pin 6 and the LFO. Works great now, now to to play with the bias and resistors feeding that diode. Tomorrow I've got some coming which will have a 5.6v 1w I'll try. Had to get the 5.1 1/2 watt from eBay so hopefully sometime next week. Will wait to box this up and call done until then. Now to remember the chords to lightning crashes lol.
Good one!
Quote from: Rob Strand on August 05, 2022, 11:57:56 PM
Quote from: Locrian99 on August 05, 2022, 11:55:32 PM
Tiny little solder bridge where the 15u cap was connecting to ground was grounding out pin 6 and the LFO. Works great now, now to to play with the bias and resistors feeding that diode. Tomorrow I've got some coming which will have a 5.6v 1w I'll try. Had to get the 5.1 1/2 watt from eBay so hopefully sometime next week. Will wait to box this up and call done until then. Now to remember the chords to lightning crashes lol.
Good one!
I've screwed up enough of these vero builds now I'm starting to know what to look for lol.
Couple things of note.
Using the 10k resistor despite the voltage loss is a better way to go IMO, and this could I imagine have to do with the jfets as well? It took me all the way down to 3.58, but the effect was much more pronounced than when I went with a smaller resistor.
Using the 1n4148 in series while using the 10k was the best choice given what I have. That got me up to 4.14 and I could get a more pronounced phase than without and not get distortion (seems like the most pronounced phase on the bias adds distortion to my ears)
Will have to see just for experimenting sake what if anything would bump it up by a 1V see how that sounds. Does make me think the 5.6v zener at 1w isn't going to do it.
I also realized I bought some 5952s and put them in with my other transistors I am going to go through those and see if I have a set that matches and compare, also I have a bunch of 4558's with no real project in mind for them. Think I'll try those in here as well.
QuoteI've screwed up enough of these vero builds now I'm starting to know what to look for lol.
All part of the deal with electronics.
QuoteUsing the 10k resistor despite the voltage loss is a better way to go IMO, and this could I imagine have to do with the jfets as well? It took me all the way down to 3.58, but the effect was much more pronounced than when I went with a smaller resistor.
Not 100% sure what's going on there. What happens when the Vref is low the on an off times for the LFO become unequal. Maybe that's the sound you want/like?
There a tweak where you can reduce the 3M9/3M3 resistor to get a wider sweep. There's nothing stopping you playing around with that.
Quote1N914 shims are perfectly valid.
Sounds like shimming is the best plan since my builds are "open air" (no board).
Another thought, I have parts for the Rebote 2.5.
How about using a 78L05 ?
Either way saves postage to buy a 22 cent item unless I order stock, which we all like to have hanging around.
[
QuoteUsing the 10k resistor despite the voltage loss is a better way to go IMO, and this could I imagine have to do with the jfets as well? It took me all the way down to 3.58, but the effect was much more pronounced than when I went with a smaller resistor.
Not 100% sure what's going on there. What happens when the Vref is low the on an off times for the LFO become unequal. Maybe that's the sound you want/like?
There a tweak where you can reduce the 3M9/3M3 resistor to get a wider sweep. There's nothing stopping you playing around with that.
[/quote]
Interesting I'll check that out. I'm not sure I just played around with the different resistors and diodes until I found which gave me the sound I thought was best and that's where I ended up. Right now I've got it so the 10k resistor and diode are socketed with jumpers leading to a breadboard so I can play around with them. I'll try the 5.6v 1 watt tonight As well as a 6.2, from what I'm seeing i think the 6.2 will end up in that 4.5 range. Plenty to tweak with before I box it up.
Quote from: Phend on August 06, 2022, 07:46:59 AM
Quote1N914 shims are perfectly valid.
Sounds like shimming is the best plan since my builds are "open air" (no board).
Another thought, I have parts for the Rebote 2.5.
How about using a 78L05 ?
Either way saves postage to buy a 22 cent item unless I order stock, which we all like to have hanging around.
I thought the same thing with the 78L05. Rob touched on that earlier in this thread.
Well, shimmed it up 3 x 914 and getting 5.07 v.
Sounds quite a bit better.
My continued tinkering I think I ended up about using the same idea. A 1n4733a in series with two parallel 1n4148 I get 4.97, and good results. Now to tweak that 3.9M.
Been searching on how to increase the depth control now. Will continue..
The best way to increase the depth of a Phase 45 is to build a Phase 90... :icon_wink: :icon_mrgreen:
(sorry, couldn't help it — proceed...)
So it isn't as simple as changing a pot. (Probably not)
I'm only 23 from 90.
In principle the 78L05 would work. You might need to add a small dummy load because in-circuit the LFO can feed current *back into* the regulator. The main reason the zener is used is because the MXR circuit originate back in the days before 3-terminal regulators were common and they weren't that cheap. The 78L05's actually draw more current than the zener circuit. So for battery operation it's a consideration but not so much when using external supplies. The regulation of the 78L05 is much better than the zener.
This intrigues me for future use more than anything. What would the small dummy load need be?
QuoteThis intrigues me for future use more than anything. What would the small dummy load need be?
For this circuit, 10k should do it.
QuoteWhat happens when the Vref is low the on an off times for the LFO become unequal. Maybe that's the sound you want/like?
FWIW, that trick/effect doesn't apply to the phase 45, only the phase 90. If you look at the LFO circuit the phase 45 has a voltage divider (2x150k) to the + input on the opamp. There's a few ways you can change the on/off ratio on those LFO's.
I was thinking if the trimpot requires very fine adjustments then it's not hard to make small changes and hear an effect, when in reality if you could adjust the trim more finely you would end-up with a similar result.
I'm really happy now with how mine is sounding with the 3.3M (had 3.9 in) and the vref sitting at 4.97. I'm not sure why but when using the smaller resistor and just the 5.1 1w I felt like the depth was lowered. It might have just been my perception. Anyways, I'm curious to see where I end up with the 5.6 or 6.2. Looking at the graphs prr posted I think the 5.6 will be too low and the 6.2 too high. We'll see though.
QuoteI'm really happy now with how mine is sounding with the 3.3M (had 3.9 in) and the vref sitting at 4.97. I'm not sure why but when using the smaller resistor and just the 5.1 1w I felt like the depth was lowered. It might have just been my perception. Anyways, I'm curious to see where I end up with the 5.6 or 6.2. Looking at the graphs prr posted I think the 5.6 will be too low and the 6.2 too high. We'll see though.
The 3M3 change will increase the depth "by design" so to speak. Small tweaks to the voltage are likely to produce indirect and subtle changes.
If you want to try something you can add a second fine adjustment pot to the JFET bias trimmer.
- Lift the ground leg of the 220k/250k trimpot, now place a smaller value trimpot between ground and the now hanging lead on the 220k trimpot. You need to use the wiper and one of the other leads of the trimpot. Use say 20k, although 50k might do.
- Set the added pot to the center.
- Adjust the 220k pot as best as possible sound.
- Use the added pot for fine adjustment.
There's many ways to do this but this method has minimal parts and gives you an idea of what finer adjustments can do. (It's also possible add fixed resistors in place of the main trimpot for coarse adjustment and only have a fine trimpot. OK for a one-off build.)
Quote from: Rob Strand on August 06, 2022, 07:46:13 PM
Quote
If you want to try something you can add a second fine adjustment pot to the JFET bias trimmer.
- Lift the ground leg of the 220k/250k trimpot, now place a smaller value trimpot between ground and the now hanging lead on the 220k trimpot. You need to use the wiper and one of the other leads of the trimpot. Use say 20k, although 50k might do.
- Set the added pot to the center.
- Adjust the 220k pot as best as possible sound.
- Use the added pot for fine adjustment.
There's many ways to do this but this method has minimal parts and gives you an idea of what finer adjustments can do. (It's also possible add fixed resistors in place of the main trimpot for coarse adjustment and only have a fine trimpot. OK for a one-off build.)
Funny I was thinking of toying around with the idea of making an actual bias pot was thinking 10k would be good but I would have to play around with it. My only thought on this was much like my first vero build a four knob fuzz face I found one of the knobs to be quite unnecessary, I won't go so far as to say useless but pretty close. But I constantly second guess where is the sweet spot or think if I could just get it a little better this might be the answer. Only other trim I have at the moment is 10k though.
QuoteFunny I was thinking of toying around with the idea of making an actual bias pot was thinking 10k would be good but I would have to play around with it. My only thought on this was much like my first vero build a four knob fuzz face I found one of the knobs to be quite unnecessary, I won't go so far as to say useless but pretty close. But I constantly second guess where is the sweet spot or think if I could just get it a little better this might be the answer. Only other trim I have at the moment is 10k though.
The idea of the added pot is only do a more accurate set-up and get around the coarseness of the single trimpot - not really a front panel pot. However, I did see a phaser recently that had some sort of bias pot on the front panel - it was one of those boutique type units.
Quote from: Rob Strand on August 06, 2022, 10:15:27 PM
Quote
The idea of the added pot is only do a more accurate set-up and get around the coarseness of the single trimpot - not really a front panel pot. However, I did see a phaser recently that had some sort of bias pot on the front panel - it was one of those boutique type units.
Yea, there was talk of it on the the thread for this build if I remember correctly. The fine tuning I think could be huge as barely turning the pot can go from phasing pretty good to nothing. I'll probably mess around with it some, I'm inclinded to find the coarse setting and hopefully its near a typical value resistor that I have on hand (wouldn't that be phenomenal) and wire it in series (I somehow picture myself trying to get to 163.3k with a 150k, 12k, 1.2k, and 100 ohm in series lol, I realize it wouldn't need to be that exact) with the fine tuning trim pot.
Something tells me this might be sitting on the bench for awhile getting poked, prodded and fine tuned before it hits a box. But I do have a couple LDR based projects I'm itching to try as well.
So the diodes I got in from Amazon today, was a pack of a bunch of different values. The 5.1 actually sits at 5.12, 2nd one I tried 5.18. I feel like I get some minor clipping both at the 4.97 and 5.12v settings. Does this make sense (silly question I know). Would there be any drawback to upping that resistor to get the voltage down a bit. I don't hear any by upping it to 22k which gets me down around 4.9 but I've never claimed to have golden ears either.
Just settled on using a 4M1 (as measured) in the place of 3M9. I tried down to 3M and everything in-between. This is a 45 with Modifications for Vibrato and Univibe. Like it. Maybe the Depth isn't as deep but it is there. I'm good.
Finally got around to trying out 1n5231 diodes the 500mw 5.1v. Results are great, going with this one. Took a bit to get there but pretty happy with this now.
I should have mentioned it before, but there is nothing "magic" about the 5.1V zener. The thing is that the bias voltage applied to the FETs is divided down from the supply voltage. When players mostly powered their pedals with batteries, the challenge was to provide a *fixed* bias voltage, even as the battery voltage began to drop. The zener assured that as the battery dropped, the bias would be derived by dividing down a stable 5.1v.
My guess is that, in an era when most pedals are externally powered, one could comfortably omit the zener, although the trimpot setting would be different because you're dividing down 9v.
There are probably more things we perceive as critical or necessary, which were based on the presumption of battery power.
Quote from: Mark Hammer on August 13, 2022, 07:53:21 AM
I should have mentioned it before, but there is nothing "magic" about the 5.1V zener. The thing is that the bias voltage applied to the FETs is divided down from the supply voltage. When players mostly powered their pedals with batteries, the challenge was to provide a *fixed* bias voltage, even as the battery voltage began to drop. The zener assured that as the battery dropped, the bias would be derived by dividing down a stable 5.1v.
My guess is that, in an era when most pedals are externally powered, one could comfortably omit the zener, although the trimpot setting would be different because you're dividing down 9v.
There are probably more things we perceive as critical or necessary, which were based on the presumption of battery power.
Yea i had read your thoughts on that on a previous post. Actually quoted it earlier in this thread around when the 78l05 got brought up as well. It may just have been in the biasing but I noticed at or maybe just perceived some clipping as it drifted further from the 4.5v when it was biased with the trim setting at where I felt it was doing the max phasing.
QuoteI should have mentioned it before, but there is nothing "magic" about the 5.1V zener.
The 5.1V zeners biases the opamps for best swing. A higher voltage will increase the swing of the BJT stage - which hasn't got a great swing to start with.
The choice of zener voltage should be for clipping as the trimmer can take up the slack for the JFETs.
On average the 5.1V zeners have the lowest low drift of all the zeners.
QuoteActually quoted it earlier in this thread around when the 78l05 got brought up as well. It may just have been in the biasing but I noticed at or maybe just perceived some clipping as it drifted further from the 4.5v when it was biased with the trim setting at where I felt it was doing the max phasing.
That sounds a bit odd unless the clipping wasn't clipping it might be some of the JFETs are getting cut-off.
Measure the 5V rail when you first power up the pedal, then play the pedal to see if it is clean. What about 10mins
then see if you can hear any "clipping" and remeasure the 5V rail.
The 78L05's can drift as they warm up. I'm a little surprised you could detect it on a phaser though. On some measuring equipment I've replaced 78L05's with TO-220 packages LM7805 to reduce power-up drift - even though the circuit was only pulling 10mA or so.
For general drift the 78L05 should beat pulling a random 5.1V zener out of the box and using it for a phaser but the zener might win on *warm-up* drift.
Maybe look elsewhere or take some measurements of the 5V rail before going down the drift rabbit hole.
I am not using the 78l05, I was referring to earlier in the thread it was mentioned instead of the zener. With the different zeners I was referring to when they weren't supplying in the ballpark of the 4.7 I noticed some clipping, well at least what I perceived to be clipping who knows, it sounded best to me with the 500mw 5.1 compared to the other 4 ways I tried it.