Hello all.
I'd really appreciate some help with my build please, if possible. I have followed the troubleshooting steps in the FAQs but nothing seems to have had any effect. This is my first build with a PCB rather than a veroboard which I though would be more straightforward. That was certainly the kiss of death!
The kit is the Supreme Compressor from Effect Pedal Kits. It is based on the Engineer's Thumb, with 4 control knobs.
A lot of fuzz-like distortion is being produced when the input signal is higher, i.e. when a string is played hard. Sounds ok when played gently. Exhibits the behaviour with both humbuckers and single coils. Can be reduced by playing with the vol and ratio pots but not removed entirely. Sounds as though when trying to compress it is distorting instead. Bypass works fine.
Schematic is shown below.
No modifications to circuit or parts subs.
Battery voltage 9.02V
Voltage at the circuit board end of the red battery lead = 8.88V
Voltage at the circuit board end of the black battery lead = 0V
For the following, vol, attack and threshold turned fully clockwise, ratio turned fully anticlockwise.
Q1
C = 1.08V
B = 4.80V
E = 4.41V
U1
5.23V
4.45V
3.98V
0V
4.17V
4.43V
4.43V
8.83V
U2
1.08V
30mV
4.42V
4.42V
4.44V
0
0
0
100mV falling
0
8.82V
0
0
0
0
0
U3
4.46V
4.45V
3.98V
0
4.21V
4.45V
4.86V
8.83V
D1
A = 4.21V
K = 4.45V
D2
A = 4.46V
K = 4.46V
D3
A = 4.84V
K = 4.45V
Grateful for any assistance!
(https://i.postimg.cc/234cW5BV/Supreme-Compressor-Schematic.jpg) (https://postimg.cc/234cW5BV)
Sounds like you should add the two LEDs at the input, which seem to be missing from the kit schematic (D6/D7 in my circuit). They're used for pre-clipping, to stop the rest of the circuit being driven to overload, which is not pleasant.
(http://valvewizard.co.uk/Engineers_Thumb_Schem_ISS4.jpg)
Thank you Merlin, I shall certainly give that a try.
Seems like an odd omission if it does turn out to be the issue!
I built a "Thumb Sucker" from PedalPCB. It has 5 knobs and a bright switch, but else very much the same.
I have the problem when I go to Ratio passed noon or 3 o'clock, and Threshold turned down to noon to 9.
My friend built an Engineer's Thumb (different kit) and he can set to 3 and 9 without distortion. Or oscillation. Bad sound anyway.
I have tried several things and traced with a probe. Got many good tips in PedalPCB forum (https://forum.pedalpcb.com/threads/thumb-sucker-compressor-scrapy-sound.10516/ (https://forum.pedalpcb.com/threads/thumb-sucker-compressor-scrapy-sound.10516/)) but none helped.
Eventually I did re-solder every joint and every wire. Swapped around the 8-pin ICs and I think I even rotated in a third one.
So although the help I got said it would not be the LM13700, that is what remains for me to try.
I'll see my friend over the weekend, So I plan to swap LM13700 with his Engineer's Thumb to see if that is the issue. If not, I am at a loss and might give up on it for good. But really would like it to work...
Not sure if this helps you in any way, but with all the help I have gotten in this forum I feel I must pay back whatever I can when I can.
Thanks. Good to know I'm not alone if nothing else!
My issue seems pretty similar to the one in your posted sound file, although min is more of a "crackle" than a "scrape" I would say...
Currently having a bit of a play with the pre-clipping LEDs. So far it's having an effect (at least I think it is) but it still doesn't take much effort to get the distortion back, particularly on the lower strings.
Desoldering/re-soldering may be on my list of next steps, but I think I'll wait until you've had a play with an alternative LM13700 first!
Quote from: Wook22 on May 24, 2022, 05:56:09 PM
Thanks. Good to know I'm not alone if nothing else!
My issue seems pretty similar to the one in your posted sound file, although min is more of a "crackle" than a "scrape" I would say...
Currently having a bit of a play with the pre-clipping LEDs. So far it's having an effect (at least I think it is) but it still doesn't take much effort to get the distortion back, particularly on the lower strings.
Desoldering/re-soldering may be on my list of next steps, but I think I'll wait until you've had a play with an alternative LM13700 first!
Cool, I'll report back.
Have a scan trough the tips I got in the other thread.
I first verified that my components could handle 18V then tried that. And it reduced the problem but did not fix it.
Quote from: Wook22 on May 23, 2022, 10:56:23 AM
A lot of fuzz-like distortion is being produced when the input signal is higher, i.e. when a string is played hard.
Based on that description, my first thought is rectifier distortion. This would be possible if you had diodes D4/5 or electrolytic caps C4/5 reversed or otherwise installed incorrectly, or if the resistors on those components aren't right. That type of problem wouldn't show up in your stable voltage readings, but would be immediately obvious if you scoped or audio-probed the C5/opamp junction and saw/heard half-wave distortion.
Quote from: merlinb on May 24, 2022, 11:31:26 AM
Sounds like you should add the two LEDs at the input, which seem to be missing from the kit schematic (D6/D7 in my circuit). They're used for pre-clipping, to stop the rest of the circuit being driven to overload
what (other) comp/limiter design needs diode/LED clamps at the input to work cleanly ? ... that's a red flag right there
and, what are LED's going to do to single-coil pickup signals ?
... even played hard, pretty much nothing or not much anyway
I mentioned too many times already the author has no real understanding of what can go wrong with his invention
I provided many hints for his wizardship to take a second look and have a chance to fix this ...
thanks for all the insults so far bud
---
I mentioned very clearly from the get-go that some people would randomly run into the problem posted here
which I'll explain later once we get confirmation of a potential deviation/correction in performance
(something that's easily recreated on the simulator)
https://www.diystompboxes.com/smfforum/index.php?topic=105610.msg1203643#msg1203643 (https://www.diystompboxes.com/smfforum/index.php?topic=105610.msg1203643#msg1203643)
I even suggested where to look for a solution ... but, I'm an asshole right ?!
---
well, I knew eventually someone would pipe up about it ...
so, I'm glad to say matopotato and wook22 are finally at the threshold of a big discovery here
(and it doesn't just apply to this circuit)
I will offer one suggestion, try out a bunch of 13700 IC's to compare ... and hopefully you're only using one of the two OTA
two OTA's makes the problem worse, as I also pointed out
like, if you have several of them tell us how many IC's you tried and how many made the circuit work clean or not ...
leaving everything else the same, and the front LED's out of circuit
---
eventually, the next question will be the following : whether or not there is a fix that precludes having to "hand select" the offending part
let's leave that for part B of my reply even though I showed everybody where to look too many times already
Quote from: Keppy on May 24, 2022, 06:43:51 PM
Based on that description, my first thought is rectifier distortion. This would be possible if you had diodes D4/5 or electrolytic caps C4/5 reversed or otherwise installed incorrectly, or if the resistors on those components aren't right. That type of problem wouldn't show up in your stable voltage readings, but would be immediately obvious if you scoped or audio-probed the C5/opamp junction and saw/heard half-wave distortion.
Thanks Keppy. I believe D4 and D5 equate to D1 and D2 on my layout.
I have added images of the layout from the plans and my board. R2 and C1 are on the veroboard I am using to play around with clipping diodes and I have swapped out R1 to be the same value as Merlin's plans to see if it makes a difference. I think I've "idiot-checked" it to the point that I'm happy that components are all correctly oriented, but would be very happy to be proven wrong!
(https://i.postimg.cc/jDXDNbcy/Supreme-Compressor-PCB-Layout.jpg) (https://postimg.cc/jDXDNbcy)
(https://i.postimg.cc/8fMRgYSw/IMG-4070.jpg) (https://postimg.cc/8fMRgYSw)
Building an audio probe is on the to-do list, I now suspect it should have been further up!
Quote from: Eb7+9 on May 24, 2022, 07:18:52 PM
let's leave that for part B of my reply even though I showed everybody where to look too many times already
I appear to have inadvertently walked into an on-going conversation.
I'm not sure I have much to contribute other than trialling any suggestions and reporting my findings and as my electronics knowledge is fairly limited!
Yes, I felt the same. I have learned also to try and listen to all suggestions, but also with my limited knowledge it takes a while and some study hours to check all out. Here I am a newbie to the functional schemas as well as other stuff.
I was a bit puzzled on a "higher level": if (in my case) the Thumb Sucker was made into a PCB, and sold to several people and most have no issues ( I seem to be the distortion exception rather than norm) then how can the design/schematic be the main culprit?
I would think my bad soldering, orientation mistakes, or my own goofs first. Then unlucky bad component.
Anyway, will try LM13700 as planned, but with less hope now and see.
Probe: quite easy to build. Just google or aske me again.
Very useful tool to help follow the signal. You need a looper or tone generator to send in a signal.
That and a decent DMM to check "beep-connectivity"
Thanks again Matopotato.
There seem to be positive reviews for the kit I have too, therefore my first instinct was that I'd ballsed something up, which may still be the case!
I have a plan ready for a probe, just need to get on with it...
Quote from: Wook22 on May 25, 2022, 05:28:25 AM
I appear to have inadvertently walked into an on-going conversation.
Ignore the troll
Sorry, totally missed it :icon_redface::
@Wook22: Very welcome to the forum!
;D :D :)
Thank you!
So, I have concluded that whilst the addition of the LEDs to the front end does make a difference, it hasn't got rid of the issue. This leads me to 3 possibilities:
1. Builder error (most likely)
2. Component fault.
3. An issue with the PCB or design (least likely).
If no one can spot anything obvious from the image I posted (component orientation for example) then I think the next step is the sound probe route to see if I can zone in on where the problem may lie.
Managed to get an old oscilloscope and ditto tone generator. And we tested around a bit this evening. Really cool to see the effect and also with guitar. It gets very obvious when the distortion happens. Remains to figure out where.
One thing I noticed though is that the Ratio pot does not deliver expected values. Could be because of its context, but also a bad pot. A1M that read 19k in full CW feels a bit off. So now I gave to things to try.
Which beats zero things by far. ;)
Quote from: matopotato on May 26, 2022, 04:55:51 PM
One thing I noticed though is that the Ratio pot does not deliver expected values.
Sounds like you are trying to measure the pot resistance while it is in the circuit. You cant do that in this case. You should disconnect it (or at least one of the two used pins) from the circuit in order to measure it. Pot is probably OK.
Quote from: DrAlx on May 26, 2022, 09:17:23 PM
Quote from: matopotato on May 26, 2022, 04:55:51 PM
One thing I noticed though is that the Ratio pot does not deliver expected values.
Sounds like you are trying to measure the pot resistance while it is in the circuit. You cant do that in this case. You should disconnect it (or at least one of the two used pins) from the circuit in order to measure it. Pot is probably OK.
Ok, thanks.
Yes wasn't sure. Circuit is not powered and no signal fed either. The other 4 pots check out.
But your point is what I was debating with myself as well.
Quote from: Wook22 on May 23, 2022, 10:56:23 AM
U1
5.23V
4.45V
3.98V
0V
4.17V
4.43V
4.43V
8.83V
U1 pin-1 seems abnormally high. Could your output cap C3 be leaky? Do you measure any DC across the VOL pot?R6 should be 220R, it looks like you have installed 10k.
U1 pin 7 = 4.43V which is the bias voltage. Looks correct.
U1 pin 3 and U3 pin 3 are both at 3.98V.
Looking at schematic I would think they should be at bias voltage also (they connect to the bias voltage via the threshold pot).
I assume measured voltages are reported OK so what am I missing here?
Could it be measurement error because of multimeter impedance?
Good spot on the build error BTW.
Quote from: DrAlx on May 27, 2022, 04:10:20 AM
Could it be measurement error because of multimeter impedance?
Yes, your meter pulls the voltage down, it's normal.
Reporting back @Wook22: I tried with the other LM13700 and expectedly (?) and sadly it was not the culprit. So no change on my Thumb Sucker, and just great in his Engineer's Thumb. He has a TL074 and me 2xTL072, but just can't see how this would matter. So something else is wrong in my case.
Will try the A1M pot. But I am at a loss nearing the end if my efforts. Last is to go through each component...
Or scrap for parts. Not sure if I should get another kit or just get something off the shelf.
Any progress on your side, @Wook22?
Quote from: Keppy on May 24, 2022, 06:43:51 PM
Quote from: Wook22 on May 23, 2022, 10:56:23 AM
A lot of fuzz-like distortion is being produced when the input signal is higher, i.e. when a string is played hard.
Based on that description, my first thought is rectifier distortion. This would be possible if you had diodes D4/5 or electrolytic caps C4/5 reversed or otherwise installed incorrectly, or if the resistors on those components aren't right. That type of problem wouldn't show up in your stable voltage readings, but would be immediately obvious if you scoped or audio-probed the C5/opamp junction and saw/heard half-wave distortion.
Thanks for this @Keppy. I think you set me on to some new discoveries.
I did probe around with a 1-ch scope. It shows a clearly cut top peak when turning the Ratio to the area where the audio gets distorted in my case.
I noticed that only the top of the wave was flattened, and the bottom didn't get flattened until more or less diming the Ratio pot. (Not 100% sure the scope wave was "levelled", so the signal might have been floating a bit above "zero" which might be a reason if the top got flattened first. But I could be totally wrong as well. Of course.)
But I didn't think much of it as far as troubleshooting goes until I went back and re-read your comment.
So if one of them diodes is clipping too soon, or in a faulty/bad fashion, that could count for the flat top of the signal. At least made sense to me. In my head.
So I went over and the 4148's check out and are connected as should be along with the surrounding resistors.
But I realized I have gotten two 1uF MKT Film caps, but the schematics call for polarized ones. I trusted the kit assembler, but maybe I shouldn't have.
So I plan to replace them with electrolyte caps.
I have 1uF/50V and 1uF/100V. Does the max voltage matter? The sizes are similar so no issue there.
The build I have has a 100k + B1M pot for Release, while original and some other versions have 470k fixed for Release. I guess this does not matter (that my total R is 100k to 1100k), although a B500k might have been enough in my case.
I understand you are focusing on the section where the 4148's are located.
My own first clipping suspicion went to the red LEDs I have in my build close to the input. Like some sort of hard clipping, but very early on.
Anyway, I measured them and they do show the same value (less than expected from red LEDs, so I assume that is part of being in the circuit context), but one of them keeps fluctuating a lot. From the 0.728mV-ish to OverLoad, while the other is constant 0.728mV. So I am suspecting the dodgy one not being sound and plan to change it.
In my limited understanding it is a diode, doing clipping, so why not potentially part of my distortion problem?
So I will go ahead and try changing the dodgy red LED and the two 1uF (C5, C6 ?).
EDIT:
PS. I noticed that the transistor does not seem to do much. We even pulled it out during testing and there was no change imho to the sound, flaws and all...
Quote from: matopotato on May 29, 2022, 04:28:47 PM
So I went over and the 4148's check out and are connected as should be along with the surrounding resistors.
But I realized I have gotten two 1uF MKT Film caps, but the schematics call for polarized ones. I trusted the kit assembler, but maybe I shouldn't have.
So I plan to replace them with electrolyte caps.
Don't bother. You can use a non-polarised cap anywhere a polarised cap would do. The only reason polarised caps exist is that they tend to be cheaper/smaller for large uF values. The kit assembler knew this and sent equivalent parts.
Good spot, but this is not the problem.
Quote
The build I have has a 100k + B1M pot for Release, while original and some other versions have 470k fixed for Release. I guess this does not matter (that my total R is 100k to 1100k), although a B500k might have been enough in my case.
Just leave the pot a little bit less than centered and it's all the same!
Quote
I understand you are focusing on the section where the 4148's are located.
My own first clipping suspicion went to the red LEDs I have in my build close to the input. Like some sort of hard clipping, but very early on.
Anyway, I measured them and they do show the same value (less than expected from red LEDs, so I assume that is part of being in the circuit context), but one of them keeps fluctuating a lot. From the 0.728mV-ish to OverLoad, while the other is constant 0.728mV. So I am suspecting the dodgy one not being sound and plan to change it.
In my limited understanding it is a diode, doing clipping, so why not potentially part of my distortion problem?
The red LEDs will provide clipping *but only if the input rises above their forward voltage*. For typical red LEDs that might be 1.5V to 2V or so. So while your guitar signal stays under +/-1.5V, the LEDs won't do anything at all. They're there to provide a hard limit to the size of the signal that the rest of the pedal can see, because distortion from the rest of the circuit apparently sounds worse than LED clipping!
If one of them was somehow faulty or had a much lower forward voltage, then it's possible that you could get distortion. EXCEPT that in that situation, the distortion wouldn't be affected by the controls, since it would be happening before any of the controls have a chance to take effect.
So, again, good idea, but this is not it.
Quote
PS. I noticed that the transistor does not seem to do much. We even pulled it out during testing and there was no change imho to the sound, flaws and all...
That transistor is an essential part of the current source that drives the OTA, so if it's same with it out or in, something is wrong here. That fits with what Keppy thought - that the distortion is coming from the sidechain. Check the transistor and check the pinout. This might be the problem.
Quote from: ElectricDruid on May 30, 2022, 10:53:02 AM
Quote from: matopotato on May 29, 2022, 04:28:47 PM
So I went over and the 4148's check out and are connected as should be along with the surrounding resistors.
But I realized I have gotten two 1uF MKT Film caps, but the schematics call for polarized ones. I trusted the kit assembler, but maybe I shouldn't have.
So I plan to replace them with electrolyte caps.
Don't bother. You can use a non-polarised cap anywhere a polarised cap would do. The only reason polarised caps exist is that they tend to be cheaper/smaller for large uF values. The kit assembler knew this and send equivalent parts.
Good spot, but this is not the problem.
Quote
The build I have has a 100k + B1M pot for Release, while original and some other versions have 470k fixed for Release. I guess this does not matter (that my total R is 100k to 1100k), although a B500k might have been enough in my case.
Just leave the pot a little bit less than centered and it's all the same!
Quote
I understand you are focusing on the section where the 4148's are located.
My own first clipping suspicion went to the red LEDs I have in my build close to the input. Like some sort of hard clipping, but very early on.
Anyway, I measured them and they do show the same value (less than expected from red LEDs, so I assume that is part of being in the circuit context), but one of them keeps fluctuating a lot. From the 0.728mV-ish to OverLoad, while the other is constant 0.728mV. So I am suspecting the dodgy one not being sound and plan to change it.
In my limited understanding it is a diode, doing clipping, so why not potentially part of my distortion problem?
The red LEDs will provide clipping *but only if the input rises above their forward voltage*. For typical Red LEDs that might be 1.5V to 2V or so. So while you guitar signal stays under +/-1.5V, the LEDs won't do anything at all. They're there to provide a hard limit to the size of the signal that the rest of the pedal can see, because distortion from the rest of the circuit apparently sounds worse than LED clipping!
If one of them was somehow faulty or had a much lower forward voltage, then it's possible that you could get distortion. EXCEPT that in that situation, the distortion wouldn't be affected by the controls, since it would be happening before any of the controls have a chance to take effect.
So, again, good idea, but this is not it.
Quote
PS. I noticed that the transistor does not seem to do much. We even pulled it out during testing and there was no change imho to the sound, flaws and all...
That transistor is an essential part of the current source that drives the OTA, so if it's same with it out or in, something is wrong here. That fits with what Keppy thought - that the distortion is coming from the sidechain. Check the transistor and check the pinout. This might be the problem.
Many thanks,
A touch disheartened that my ideas probably have no bearing. Will probe with scope to try and understand where the peak gets cut down.
Sidechain: is that among the 4148s? Thought I checked those Ds Rs and Cs in that area between OPAs.
The transistor I will measure to see what it shows and if those values make sense.
Again thanks.
Might swap the LED anyway just to have a functioning one.
Quote from: matopotato on May 30, 2022, 11:24:11 AM
A touch disheartened that my ideas probably have no bearing. Will probe with scope to try and understand where the peak gets cut down.
Don't get disheartened. I think you might be getting close. It only takes one part to have some little problem and the thing doesn't work right. But at the same time, find one little thing, and it might all be fine.
Quote
Sidechain: is that among the 4148s? Thought I checked those Ds Rs and Cs in that area between OPAs.
The transistor I will measure to see what it shows and if those values make sense.
Again thanks.
Might swap the LED anyway just to have a functioning one.
Yes, the sidechain is the whole section U3A to U3B to Q1. It measures the volume level of the incoming signal and produces a proportional current which is then fed to the OTA as VBIAS. Keppy initially suspected the rectifier (U3A and those diodes) because problems there might well turn up as distortion in the audio. But the problem could be a bit later in that sidechain section, like in the current source (U3B and Q1). So definitely check that transistor.
Quote from: matopotato on May 29, 2022, 04:28:47 PM
PS. I noticed that the transistor does not seem to do much. We even pulled it out during testing and there was no change imho to the sound, flaws and all...
The transistor is in parallel with a 1M resistor. If the transistor makes no difference, then that indicates that it is never turning on, and the OTA is unchangingly biased by the 1M resistor. The voltages you posted are wrong for a PNP transistor (base should be a few tenths below emitter, not above). I initially figured that it was because the voltages were taken without a signal to lower the base voltage, but now I'm not so sure.
Is that really a PNP transistor? If so, have you tried another?
What happens at the base of the transistor if you apply a signal at the input? You should see a drop in voltage at the base.
Thanks @ElectricDruid and @Keppy.
Sorry for the confusion, it is my bad. I should open a separate thread for my issues.
This is @Wook22's thread and I had similar problems. But trying to help has glided over to hogging the thread. So I was going to lay low until I find something.
So I should post my readings but in a separate thread.
OP seems to have disappeared, and it was just a wrong resistor value.
Have been away for a few days.
Will have a crack at checking that resistor and see where it gets me!
Thanks for all the help so far.
Alas, just checked R6 and it is indeed a 220R.
Was very hopeful it might be a simple fix!
Quote from: Wook22 on May 31, 2022, 07:34:54 PM
Alas, just checked R6 and it is indeed a 220R.
Not in your photo it wasn't?
I wonder whether we are talking about the same resistor?
I have removed R6 from the board and it's definitely 220R according to my multimeter - I find differentiating the reds and browns quite tricky by eye so I tend to go for this method.
(https://i.postimg.cc/XZJ0ydnG/IMG-4079.jpg) (https://postimg.cc/XZJ0ydnG)
From first picture it looks as if R2 has a cable to one of the eylets instead of the resistor. The other eyelet is empty. This is most likely covered somehow or there wouldn't be much of anything in the first place. Just curious.
Edit: Ignore, just read the early post. All is well.
Quote from: Wook22 on June 01, 2022, 03:47:56 AM
I have removed R6 from the board and it's definitely 220R according to my multimeter - I find differentiating the reds and browns quite tricky by eye so I tend to go for this method.
Hmm...colors sure do look like 10k to me
Quote from: merlinb on June 01, 2022, 09:51:20 AM
Quote from: Wook22 on June 01, 2022, 03:47:56 AM
I have removed R6 from the board and it's definitely 220R according to my multimeter - I find differentiating the reds and browns quite tricky by eye so I tend to go for this method.
Hmm...colors sure do look like 10k to me
You definitely have me doubting myself!
Just to clarify, we are talking about the resistor circled below?
(https://i.postimg.cc/4m9rRRgm/Inked-IMG-4070-LI-Updated.jpg) (https://postimg.cc/4m9rRRgm)
If so, definitely 220R
(https://i.postimg.cc/rzthKGYH/IMG-4080.jpg) (https://postimg.cc/rzthKGYH)
Quote from: Wook22 on June 01, 2022, 12:02:43 PM
Just to clarify, we are talking about the resistor circled below?
Yes. Which makes me wonder if any of your other '10k' resistors are actually 220R... I suggest you check them
I have re-checked every resistor value and they are all to spec.
Also checked that everything that should lead to ground according to the schematic does so, and no issues noted.
I decided to try to reduce the level of confusion, so I took my problem to a separate thread: https://www.diystompboxes.com/smfforum/index.php?topic=129225.0 (https://www.diystompboxes.com/smfforum/index.php?topic=129225.0)
Thanks all who helped me so far. Still some ways to go though.
Will follow this closely, @Wook22 and hope you eventually find out what is wrong. The pedal is promising IMHO.
Any luck on your side, @Wook22?
I left your thread to keep things more clean. I breadboarded the whole thing from scratch apart from the ICs and a pot, but same problem.
And I had already swapped the LM13700 with no change, so I am a bit at a loss.
Either buy the same kit again and try out fresh, or get the Engineers thumb and add some of the mods, including the bright switch since I liked that option in the Thumb Sucker as a way of adapting to single coils vs humbuckers. But now I am not so sure what another Thumb Sucker kit would do good.
Might look around for other alternative compressor builds. Did an optical (Zirconia) which is just fine.
Quote from: matopotato on June 06, 2022, 02:23:05 PM
Any luck on your side, @Wook22?
Not really!
I have fashioned an audio probe but that's not really shed any light as yet. I was also thinking of getting hold of a "normal" ET PCB and transferring parts / add new ones to see if perhaps there was an issue with the design of this one, but I have to say my enthusiasm is wavering a bit!
Quote from: Wook22 on June 06, 2022, 02:30:49 PM
Quote from: matopotato on June 06, 2022, 02:23:05 PM
Any luck on your side, @Wook22?
Not really!
I have fashioned an audio probe but that's not really shed any light as yet. I was also thinking of getting hold of a "normal" ET PCB and transferring parts / add new ones to see if perhaps there was an issue with the design of this one, but I have to say my enthusiasm is wavering a bit!
Yeah, I wish I was able to share some enthusiasm to get your hopes up. (Sometimes that is enough to break on through...) But I felt I reached som sort of thicker wall today.
How far did your probe give you clean sound?
I got to the Threshold/first IC and after that distorted.
see eh la bas ma`s latest thread ...
https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new (https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new)
:icon_question:
Quote from: puretube on June 07, 2022, 05:16:09 AM
see eh la bas ma`s latest thread ...
https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new (https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new)
:icon_question:
Thanks, I shall give that a try!
Quote from: matopotato on June 06, 2022, 04:04:53 PM
How far did your probe give you clean sound?
I got to the Threshold/first IC and after that distorted.
Same for me.
Was interesting playing with the input level on my loop pedal to see what effect it had on the distortion.
Quote from: Wook22 on June 07, 2022, 05:27:29 AM
Quote from: puretube on June 07, 2022, 05:16:09 AM
see eh la bas ma`s latest thread ...
https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new (https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new)
:icon_question:
Thanks, I shall give that a try!
Unfortunately it doesn't appear that either pin 8 or 9 are grounded on mine.
Quote from: Wook22 on June 07, 2022, 07:21:41 AM
Quote from: Wook22 on June 07, 2022, 05:27:29 AM
Quote from: puretube on June 07, 2022, 05:16:09 AM
see eh la bas ma`s latest thread ...
https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new (https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new)
:icon_question:
Thanks, I shall give that a try!
Unfortunately it doesn't appear that either pin 8 or 9 are grounded on mine.
Hmmm... I was hoping for some magic here. Will try anyway since it is on breadboard anyway
"Hoping for magic" is pretty much where I am at too!
Quote from: Wook22 on June 07, 2022, 07:21:41 AM
Quote from: Wook22 on June 07, 2022, 05:27:29 AM
Quote from: puretube on June 07, 2022, 05:16:09 AM
see eh la bas ma`s latest thread ...
https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new (https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new)
:icon_question:
Thanks, I shall give that a try!
Unfortunately it doesn't appear that either pin 8 or 9 are grounded on mine.
oops, that`s a fourth different schematic - hadn`t seen that close-up yet ...
sorry it didn`t help - I thought I had found the culprit. :icon_sad:
(but in that schemo, pins 7 & 10 (unused buffer inputs) are NOT grounded ...)
Quote from: puretube on June 07, 2022, 07:39:08 AM
oops, that`s a fourth different schematic - hadn`t seen that close-up yet ...
sorry it didn`t help - I thought I had found the culprit. :icon_sad:
No worries. Thanks for the pointer anyway. Hopefully it will help on the other builds!
Quote from: puretube on June 07, 2022, 07:39:08 AM
Quote from: Wook22 on June 07, 2022, 07:21:41 AM
Quote from: Wook22 on June 07, 2022, 05:27:29 AM
Quote from: puretube on June 07, 2022, 05:16:09 AM
see eh la bas ma`s latest thread ...
https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new (https://www.diystompboxes.com/smfforum/index.php?topic=129237.new#new)
:icon_question:
Thanks, I shall give that a try!
Unfortunately it doesn't appear that either pin 8 or 9 are grounded on mine.
oops, that`s a fourth different schematic - hadn`t seen that close-up yet ...
sorry it didn`t help - I thought I had found the culprit. :icon_sad:
(but in that schemo, pins 7 & 10 (unused buffer inputs) are NOT grounded ...)
So in summary, OTA pin 8 and 9 are better off lifted away from ground. And pin7 and 10?
I also have 6 and 16 to ground. But I assume at least 16 should go?
If lifting 6 7 8 9 10, should the be connected to eachother or left "in the air"?
As I understand it, the 1k resistor on the emitter of the PNP is what converts the control voltage from the rectifier stage into a control current for the OTA.
According to the datasheet for the OTA (if I understand it correctly) the peak transconductance can be from 6700 to 13000 (umho). So practically a factor of 2.
So is it possible that the 1k resistor is too small a value for some OTAs but OK for others ?
i.e. it lets through too much control current for some OTAs but not others.
If i was going to play with things, I would add a 1k trimmer in series with that 1k resistor on the emitter of the PNP (so you can vary the total resistance from 1k to 2k) and see how things behave with increased resistance there.
pin 6 = "power ground" (V-): MUST ground.
pin 7 = "buffer input": ground.
pin 8 = "buffer output": not connected.
pin 9 = "buffer output": not connected.
pin10 = "buffer input": ground.
pins 12 & 13 connected together (shorted). Not going anywhere else.
pin14 (non-inverting input of unused half: should connect to Vref (4.5V). Not left open!!!
https://www.ti.com/lit/an/sboa204a/sboa204a.pdf?ts=1654522163497&ref_url=https%253A%252F%252Fwww.google.co.uk%252F (https://www.ti.com/lit/an/sboa204a/sboa204a.pdf?ts=1654522163497&ref_url=https%253A%252F%252Fwww.google.co.uk%252F)
I`m not sure about pin 16 (Vbias of the unused half).
Since I don`t know whether there is an internal offset-voltage on this pin,
I`d rather ground it through a 27k resistor instead of directly. But that`s just a guess ...
I'll see what happens if I ground 7 and 10, then have a play with the resistor value at R9.
Thanks both!
Quote from: DrAlx on June 07, 2022, 08:55:07 AM
As I understand it, the 1k resistor on the emitter of the PNP is what converts the control voltage from the rectifier stage into a control current for the OTA.
According to the datasheet for the OTA (if I understand it correctly) the peak transconductance can be from 6700 to 13000 (umho). So practically a factor of 2.
So is it possible that the 1k resistor is too small a value for some OTAs but OK for others ?
i.e. it lets through too much control current for some OTAs but not others.
If i was going to play with things, I would add a 1k trimmer in series with that 1k resistor on the emitter of the PNP (so you can vary the total resistance from 1k to 2k) and see how things behave with increased resistance there.
Thanks, good idea. I was just thinking about try to measure the current. Trimming around will be similar but by ear.
Seems we are gravitating around the OTA and how to make it feel at home. Seems sensitive though or are we just the three unlucky ones among an ocean of happy compressor diy kit builders and owners perhaps...
Conscious that there are now parallel threads on broadly the same topic, just thought I'd note that I have tried the suggestions listed above and so far the "magic bullet" evades me.
Quote from: Wook22 on June 12, 2022, 03:15:12 PM
Conscious that there are now parallel threads on broadly the same topic, just thought I'd note that I have tried the suggestions listed above and so far the "magic bullet" evades me.
Thanks for the update. I had some limited success, but hope for some magic in July. Next week travelling so no testing.