SOLVED Delegate Compressor

ambusch85

New member
Is there a schematic for this available? Is the white led supposed to glow even with no signal going to it? I think there may be something wrong with mine, but not sure. I did use an ultra bright white LED. I did use supposedly the correct ldr. Ill take some measurements in a bit. It also seems like it has fairly low output.
 
It does change a little but not a whole lot maybe just my expectations would it would be fairly dim and get fairly bright while playing. I only notice it change a bit at the highest sustain settings.
 
So confirmed led is functioning correctly not sure if I got a bum batch of ldrs. They measure about 800k dark 5-7k light. Still seems like output volume is quite low. I did change the volume for audio taper cause that's all I had, but in general total available output seems low. Is that normal?
 
Thanks pedal PCB! It doesn't appear the build docs have updated yet, but look forward to reviewing the schematic to see if I can increase the output volume somewhere. Or maybe mine has a mistake somewhere!
 
Mine has really low output and the same issue with the led, it has been on the repair shelf for a while. I will take a look at it and see if I can help at all.
 
Hey jjjimi84,

When testing the led, put your attack and release all the way down. And place the sustain around the 12:00. The attack and release are fairly sensitive. I still have pretty low output, but I think there is an inverting stage that the volume controls. The 10k beside pin 6 i think can be lowered for more output. Will need to mess around with it a bit once I see the schematic. I found at least a partial schematic over at freestompboxes. I think the output section of this one is a little different using 1k prior to the 1uf coupling capacitor as opposed to 470ohm after the coupling capacitor. With a 100k output resistor, I don't think this will have a large difference in volume. But I think we can mod this a bit for more volume output without clipping since it should have an 18V-gnd rail. I do get a little clipping on some settings not sure where that's coming from but it's very minor. I believe the ratio at one of the extremes causes that stage to clip slightly. Hopefully this helps in some debugging/modifications.

If it's close, lowering the 10k is where I think I'll start experimenting for more volume output. Lowering it to 1k should make the output 10x bigger or 3dB louder. But that may be too much voltage gain before hitting the rails. I'll experiment a bit sometime this week and report back.
 
One thing to note, in the original the LED / LDR placement is a little different from how we usually do it.

The LED was installed flush with the PCB and the LDR was tilted over pointing at the side of the LED (rather than directly at the lens)
 
Thanks PedalPCB!

I may be being impatient, but any idea when the build docs on the site would be updated with the schematic? I think when troubleshooting/modifying the circuit, it would be a huge benefit. There appear to be some differences in all the schematics I've found online.

Looks like its updated now! Thank you so much!
 
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Thank you PedalPCB!

So I tried lowering the 10k to 1k. A little more volume but it also changed how the tone knob operated. Likely going to put that back.

After doing some more testing, I believe my ldrs I got from Amazon that may be the overall culprit, for all of the issues.
 
Thank you PedalPCB!

So I tried lowering the 10k to 1k. A little more volume but it also changed how the tone knob operated. Likely going to put that back.

After doing some more testing, I believe my ldrs I got from Amazon that may be the overall culprit, for all of the issues.
its not your week as far as quality components go
 
its not your week as far as quality components go
No kidding, the derailer ended up being awesome. Thank you for your help with that! Played in a live situation over the weekend and it was perfect "over the top" gain when the song required.

For this one, fairly sure the LDR is the culprit. Too low of a resistance and it will cut volume, also on mine, I believe the state change of my ldr was causing some distortion. Mine had very slow and seemingly erratic response to my dark room and flashlight tests.

I'll order a couple different ones to try and replace it and check back in.
 
So got the new ldr in there and the unity volume issue is fixed. It still has some light distortion narrowed down to the mpsa-18 buffer/splitter. Tried a different transistor, no change. I'll continue troubleshooting this, but as of right now if your having trouble with getting unity volume back getting the correct and functioning LDR worked for me. You may also want to back the ldr away from the LED a bit.
 
Some distortion in this circuit is unavoidable without a design mod. The Delegate is a clone of the EQD Warden, which is based on the DOD 280. These all have a common design deficiency: the peak detector circuit (Q1-Q3, D1 & D2) puts a non-linear load on the point in the circuit where the guitar signal passes thru. Looking at the schematic, the signal that feeds the TONE control is taken from the emitter of Q1. Q3 and D2 load the signal on Q1's emitter. D2 clips the negative excursions of the signal and if the ATTACK control is set full CCW, Q3 clips the positive excursions. A better place to tap off the signal is from IC1-1. If you have an audio probe, check it for yourself: distorted signal a1 Q1-E, clean signal at IC1-1. Ideally, there should be a resistor in series with C5, something like 1K. Why did they do it this way? I can only think of one reason: that's how the last guy did it.

If you want to make the mod, simply lift the + lead of C14 off of the board and wire C14+ to IC1-1.

One more thing: optical compressors depend on the LDR's slow response to smooth out any ripple in the LED current. With low freq content, especially bass guitar, the LDR will let some of that ripple pass thru and modulate the guitar signal, creating mostly 3rd harmonic distortion.
 
I did what you suggested. But used a film cap for spacing and tied one leg to r13 and the other pin 1 on the pot side of the board. Highly recommend doing that. On most settings this was much cleaner signal. On some settings the first gain stage could be too much causing some distortion, like max sustain and min ratio. Tweaking the controls I can tell it's working and the volume issue is definitely fixed. I think the gain at the first stage may be a little high at extreme settings but I suppose that's normal. Because I can get usable tones out of it, I'm boxing it up and calling it done to play around with. I may revisit this and tweak the 2.2M (r5) resistor or try resistor in parallel with the ldr to lower the gain of that stage so that any setting will all play nice since it has so many parameters. Interesting build and the fact the PCB has withstood many soldering, desoldering, and resoldering is a good testament to the quality of these pcbs. Just make sure you get the right LDR from a reputable source (like PedalPCB). If you use a different ldr just know you will need to tweak the pedal by either a resistor in parallel with the ldr or adjusting r5.

Oh I did end up destroying my one and only mpsa18 during troubleshooting, so I threw a 2n5088 in it's place. Figured it's a gain of ~+/-1 and shouldn't really make any difference. Even less so with the cap bypass mod. Would you concur?
 
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