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Many thanks to Tark for troubleshooting my previous issues. A faulty sensitivity pot wreaked havoc on setting up my pedal. Alas, all is not well yet. There are 2 issues that currently make this pedal unusable which is not good since I have a gig on Saturday.

Issue 1: Substanstial volume drop when engaged (both in filter and auto modes). Not good when you're playing live.

Issue 2: this one is strange and I haven't been able to work through the obvious troubleshooting but maybe some of the smart ones could explain it in theory. When alone, pedal sounds great (minus the volume issue) in both modes. When placed in a chain, there is no output when in filter mode. It currently is after a Lovepedal Gen Echo, BYOC tremolo and BYOC chorus. I will play around with the order when the kids aren't asleep but this perplexes me.

Here are some pics and as always thanks for the help.

I have reflowed all the joints.

You really aren't having much luck with this pedal are you

The level drop is an odd one. The signal path through the pedal is pretty simple - through a cap and some input resistors, through a unity gain buffer - through half the LM13600 OTA - and out through another cap and resistor. The manual / auto switch part of the circuit goes nowhere directly near that. Flipping that switch should have no effect on volume other than that produced by the filter. If the filter is at one extreme or the other volume is of course reduced.

Possibilities - damaged / faulty ICs or the 1Ms at the input or the 100K at the output have got swapped around for much lower value resistor. Looking at your pictures of the PCB it does not seem that they have. Are the jacks wired OK - there were some other posts about some jacks going out that were riveted together in a different way such that the tag order was changed.

I am having no luck with this pedal! I swapped out the 8-pin IC and will Try to procure the other one tomorrow. Here is a picture of the jacks, let me know what you think. Thanks again for all the help.

It is a little hard to tell from the pictures if the jacks are OK particularly as I have never seen these supposedly changed jacks.
The output jack is probably OK as it only has 2 contacts - sleeve and tip - and the sleeve pretty obviously goes to ground. The input jack also looks OK but it is tricky to be sure that the tip goes to the circuit input and the ring goes to the power switching. The sleeve connection does seem to go to ground. Just looked at my jacks and they look the same and are wired the same as yours so I guess that theory is a goner.

This business of no output in filter mode only when in a chain sounds impossible.

It works when it is the first in line albeit quieter than it should be. There is clearly a gremlin in this pedal I just need to find it.

That sounds like some freakish ground wiring problem. The guitar 'floats' - that is to say it is only grounded by plugging it in to something else. Plugging the input of the Envelope Filter into other pedals connects its input to stuff which may not be floating. Or maybe there is a problem with the input capacitor on the Envelope filter.

The manual mode will work when placed later in the chain, not the envelope. No luck finding the other IC locally, I'll have to hit up Mammoth for another one. While I'm ordering more stuff which caps should I look at replacing? I swear I'll get this thing working if it's the last thing I do. It has even taken precedence over getting my taxes done!

That makes more sense. In auto mode the filter sweep is quite extreme to the point where with insufficient input signal it will close the filter down to a very low frequency. When the filter is shut down it acts a bit like a noise gate and wont let any signal reach the pedal output. This is related to your low level problem. It means that the full signal probably is not getting through the input buffer. This is likely all related to the problems you had with the sensitivity pot. I'd guess the op-amp is damaged although it could be a bad joint, short or bad component just in the input circuit. Tracing the signal through the circuit with an audio probe would really help pin this down.

Ok, I have finally been able to MacGyver a probe, not the best but workable. I hope that this info will solve this problem once and for all! Tracing the signal this is where I was able to get a signal:

R20 (1M) strongest signal on board this was "on the top" of the resistor (closest to the input jacks)
Pin 7 of the op-amp
D1 & D2
R22 (22k)
Right post of attack pot

I have marked the spots with yellow circles on the picture below




I hope this means something! Thanks again in advance.

That you have signal at pin 7 of the op-amp is a good sign - that means that signal in the envelope follower side path is reaching the diodes. The diodes should rectify the signal so if you hear something on the junction of the diodes it should sound distorted (one or other of the diodes might be dead). The rectified signal is supposed to charge C9 4.7uF through the Attack pot - at which point it should become a DC voltage that roughly follows the volume of the input signal. This voltage drives the base of Q1 which in turn feeds current (via the switch) into the control inputs of the dual OTA and sweeps the frequency of the state variable filter.

So - Remaining questions - do you have a voltage on the junction of R21, R22 ? it should be 1/7th of the 9V supply with pedal on but no input signal and the switch to manual. Does the rectified signal make it through the attack pot to the cap to be smoothed into DC. Does the signal pass through the transistor and does it get through the switch. Turn the pedal off and do a continuity check on the toggle switch to make sure it is making a connection centre pin to outer (the pin closest to the middle of the PCB) when switched to Auto. Check that that pin does connect back to the emitter of the transistor. Do a resistance check across the two outside pins of the Attack pot - turning the pot to its extremes to make sure you get close to zero resistance at full anti-clockwise and about 100K at clockwise. If the pot and switch are OK then that leaves the 4.7uF cap, the transistor and C10.

Right now I would suspect either a blown transistor, a faulty switch or our old favourites - open solder joints or shorts in that area.

In theory when all is working OK I suppose you might be able to measure the rising and falling voltage on C9 and at the emitter of the transistor as you play chords into the pedal. In practice changing voltages are hard to see with a digital multimeter and the meter will in any case place a load on that part of the circuit.

Good Luck!

Thanks Tark, I will get to that straight away as you Brits say. I don't know if this makes a difference but the signal on my audio probe was very weak. I could barely hear it even with the volume on my little practice amp cranked. I'm using a 1uF 50V capacitor and I know the diagrams call for a .1uF so I don't know if the two are related or nor. If they're not, it could possible explain the low output because the in-line signal is very quiet. Thanks again for all the help.

OK, here's what I've got. At the "top" of R21 & 22 I have 1.186 volts. At the "bottom" of R21 I have 9.3v and 0v at the bottom of R22. I have no signal at Q1 from any of the posts (I think the top post is the emitter). I have continuity at the switch and the proper values with the Attack pot. So in my non-scientific brain I'm thinking that my tranny is shot.

One other note, it seems that the signal is louder at R20 than at R21 & 22. But to my early post, it is barely audible at all. I will await further instruction!

If they would have told me there was science/engineering involved with rock 'n roll, I probably would have paid attention in school!

The voltages on R21 and R22 sound OK. There should be no audio signal as such around the transistor. At that point the idea is that the rectifying diodes and the time constant of the Attack pot and the 4.7uF have transformed the signal into a varying DC voltage that follows the instantaneous volume of the input note. However what you should see is (with the Attack pot turned up just a little) a rising and falling voltage at the + terminal of the 4.7uF each time you play a chord into the pedal. Unfortunately a digital multimeter wont show this very well, one of the old fashioned analogue types with a needle would do a better job. Probably the best place to look for this would be the emitter of the transistor (it connects to the switch) because this is a low impedance point and the meters own resistance wont load the signal too much.

As to signal level when tracing with your audio probe (BTW a 1uF will do fine providing it is a non-polarised cap - ie not an electrolytic) - you should find that the level at pin 7 of IC1 with the Sensitivity pot turned up is quite loud, it should be louder than the level you get straight off the input jack. At the junction of R21 and R22 (with the Attack pot turned up a bit) it should still be quite loud but I would expect it to sound distorted because at this point it has been rectified. Once you get past that point you won't get much audio because it has been converted to the varying DC that tracks the input note volume. You should get a thump every time you pick a note. In fact that might be a better way to check if you have any envelope signal out of the transistors emitter. Hang your audio probe off there, set the Attack pot to around 3 and the Sensitivity to max. You should get a healthy thump out of your monitoring amp every time you pick a note on the guitar. Watch out for the volume. If you don't get a thump there then - yup - the transistor is a good suspect.

Maybe it's just easier to replace the transistor without any further testing.

+1. Should be easy to find a replacement transistor, since that unity gain buffer can use pretty much any general purpose NPN transistor in the TO-92 form factor. This will work fine, if you don't have one on hand: http://www.radioshack.com/product/index ... Id=2062609

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The build from you know where seems to be resolved. I swapped out tranny and the output is now consistent across all settings, I just need to dial it in. A thousand thanks to Tark for taking it to DefCom 6! The only thing is the output volume is still lower than bypassed volume. I just don't know if I have it in me to try and troubleshoot this anymore. Thanks again!

OH my, I am so glad you got it to work, you must have thought I was really leading you around the houses. I'm sorry it took so long to put a finger on the transistor. I'm now wondering if there was anything wrong at all with the Sensitivity pot we homed in on earlier.

On my pedal I don't perceive any volume drop between bypassed and active, but it is hard to tell because the thing is a filter and as such it only lets some of the original signal through. Even standard Wah Wah pedals mess with levels. Maybe it won't sound that way once you have played around with it.

Good for you for having stuck with trying to fix it for so long.