February 16, 2020 at 7:17 pm #20567
First off, build was a blast, no real problems except tired eyes. Initial calibration done to nominal specs for gain and Hi/Lo trim pots. All controls, LED, switches, function as they should except sound quality. No appreciable noise or hum but tremolo effect is faint and very distorted. Tone is very muddy and indistinct, no matter where controls are set at. I can hear depth, rate, shape, rate, etc, function but not the way they should. Sounds to me like the original signal is being over-driven before reaching the tremolo circuit. When on bypass, signal is good and sounds clean. Adjusting Hi/Lo trimmers 20+ turns either way by ear in calibration mode makes no real difference in Hi/Lo balance or tone.
For Fuzz effect it’s great but… This box is so funky I just have to get it to work.
Is normal operation Volume full left = Volume off?
Oh, I totally spaced and swapped red and green LED for Tap and Bypass?
Single coils with fender tube amps.
My sticker reads ZD3813February 17, 2020 at 8:38 am #20582
The good news is that you are getting at least some sound to pass through the circuit, so we know it seems to be working on some level. This problem sounds like a bad connection somewhere…like a bad solder joint in the audio path. The volume knob is off in the counter clockwise direction…is it behaving that way? I suggest you re-flow your solder joints again to make sure everything is connected the way it should be. Another possible cause could be the signal is partially shorting out somewhere, possibly against the back of one of the pots when the circuit board is installed in the chassis. Make sure the pieces of paper don’t have any holes in them and nothing is poking through.
-BrachFebruary 17, 2020 at 12:43 pm #20584
Thanks for getting back to me so soon. I double checked all solder connections before assembly but will do so again (third time a charm). I lost my flush-cut nippers and used regular diagonals and I did make an effort to cut all leads as close to the board as possible, even put a layer of tape over the paper next to the pots. It was a tight fit so leakage to signal ground is very possible. I will disassemble/reassemble and let you know. I’ll even change the LED’s to their proper position.February 17, 2020 at 5:08 pm #20586
Problem found, me thinks. All solder joints look OK, paper insulator not punctured so I was buttoning it back up and lo! The Triad in Q3 is backwards… I’m guessing this is not good for signal quality. I was going to make something up touting my diagnostic abilities but bottom line, I goofed. I’m not going to be able to remove and reinstall safely so please sir, can I have some more?
Let me know what I have to do to get another one. Thanks and for anyone reading this thread, you can’t check your work enough. Live and learn.
ScooterFebruary 18, 2020 at 9:21 am #20593
Yes, that would do it. Good job noticing it was backwards. That is a FET (field effect transistor) which is responsible for momentarily muting the audio signal while the relay is switching to keep the relay click out of audio path. Since it’s backwards it might be constantly keeping the signal muted, so that’s why everything is really quiet.
Email us at info “at” zeppelindesignlabs.com and we’ll explain how to get a new FET.
-BrachFebruary 25, 2020 at 3:12 pm #20724
Thanks for the FET Brach, That cleared up volume levels fine. Now I seem to be missing any signal from the HFO side of things. In calibration mode LFO sounds fine when Harmonic mix fully counter-clockwise to about halfway. Full clockwise gets nothing except at max gain a faint high-pitched pulse squeal, back to halfway then the LFO seems to cut back in and functions work well. Tempo LED works fine either way. Nothing I can do trim-pot wise makes any difference whatsoever. Case on or off, no difference either.
Ideas please? Test-points I can work with?February 26, 2020 at 8:19 am #20746
So that’s good that the FET fixed the no signal issue.
Now it sounds like something is wrong with the high frequency signal path. We need to know if the problem is with the digital control (as in the high optocoupler’s led isn’t lighting up) or if the problem is in the audio signal path.
With the depth knob at 0 (fully counter clockwise) what DC voltage do you get on the square pad of the high side optocoupler (opto1)…from ground (black lead on ground, red lead on the square pad)? It should be about 1.8V dc.
-BrachFebruary 26, 2020 at 10:58 am #20750
1.8 Vdc (roughly) on both square pads of HF & LFO LED side.
While I was in there, measured resistance on LSR side of both and there is major differences in values.
everything set in middle position (12:00) except volume
LFO pulses to ~ 1. Kohm
HFO pulses to 24 ~ 25. Kohm, would this value not allow any signal to pass or is this still part of the control path?February 27, 2020 at 8:27 am #20769
25K is not enough resistance to stop the signal from getting through the high frequency signal path. But you wouldn’t get an accurate reading anyway unless you unsoldered the jumpers…the dc voltage from opamp pins will skew the reading of your ohm meter. The most likely cause is a bad solder joint somewhere. Make sure everything is soldered correctly…including the jumpers. You can double check that the high frequency optocoupler led is being lit up by making a tiny incision with you xacto knife (about 1mm long) on the heat shrink on the back side of the led (close to the led’s leads). That way you can see if the led is actually bright when it’s supposed to be bright (when the depth knob is at 0, for example…or when in calibration mode on the high harmonic mix setting).
If the LED is turning on then the problem has to be in the high frequency signal path somewhere…most likely a bad solder joint. Use the schematic to trace out the components in the high frequency path and then look for bad solder joints in those areas.
Let me know what you find.
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