EHX The Silencer (2014 new version) troubleshooting

[tootsMcgee]

I don't know if this is the right forum for repair work? But I thought you guys might like to see.

Patient: EHX The Silencer (2014 version)
Problem: no/very weak signal in both buffer and active mode
Schematic: none found

The new Silencer is a noise gate that can operate inline but also switch an effects loop in and out. Send is always active, Receive gets mixed in based on the input from the guitar. You can also use it as a rich man's splitter. No true bypass; it's always on.

Almost all components are SMD except for the electrolytics, pots, and jacks. Ribbon cable footswitch on its own little PCB (probably reusable). The enclosure quality is REALLY nice. The Soul Food feels like a contractor's electrical box. This feels like an actual guitar pedal. I'm a sucker for good powder coating.

If you find one of these busted, at the very least you could salvage the enclosure, four enclosed jacks with switched terminals, and footswitch PCB. Power might be interesting since it is board-mounted, but it's a standard Boss-style barrel.

ICs:

TLC2262C dual op-amp (I/O buffer)

LM324A quad op-amp
MC33079 low noise quad op-amp
LM393 comparator
HEF4066B switch (for switching between bypass and active signal)

Interestingly, unlike the original Silencer, I haven't spotted any JFETs. The actual switching and volume adjustment must be happening inside one of the opamps or the 4066.

The crown jewel IC:
THAT Corporation 4315 "Pre-trimmed Low-voltage Low-power Analog Engine® IC"

I think this is a modern low-power replacement for something like the NE570 and surrounding circuitry. All of the application notes look like they're related to noise reduction, compression, etc. I'm going to save all these, they look interesting! Check out the "One Knob Squeezer" in particular.

Analysis (pics to follow in a future post once I get it cleaned up)

I traced the signal from the input jack to Pin 3 of a small opamp tucked near the bottom of the board, and observed no signal coming out. Pin 2 (inverting, I think) had DC bias but no AC signal on it. Pin 1 had the same bias but no AC signal. Pin 3 was similarly biased.

I checked all the ICs to ensure they had ~9V going to them. All good.

My gut said it was the buffer opamp and I think I was correct. We'll know for sure when I get my TLC2262Cs in from Mouser.

[ElectricDruid]

Signal going into pin 3 would imply a non-inverting op-amp stage, probably the typical buffer. Bias ok but no signal coming out does sound like maybe the op-amp is dead.

Since the THAT chip includes a VCA, I'd guess that's the part that's doing the gating. It's got an RMS detector for envelope following too, so it's a good chip for the job. Using a VCA rather than the 4066 switch for the gating allows you to do a soft-fade in or out, to prevent clicks.

HTH,
Tom

[tootsMcgee]

Signal going into pin 3 would imply a non-inverting op-amp stage, probably the typical buffer. Bias ok but no signal coming out does sound like maybe the op-amp is dead.

Since the THAT chip includes a VCA, I'd guess that's the part that's doing the gating. It's got an RMS detector for envelope following too, so it's a good chip for the job. Using a VCA rather than the 4066 switch for the gating allows you to do a soft-fade in or out, to prevent clicks.

HTH,
Tom

Yeah, the wild jumpers above to a working TL072 makes the effect come to life. I wonder how the buffer got zapped? Voltage spike coming along the input? It has to go through a few resistors capacitors to get there though including a 100n input cap (one of the few box caps on the board).

I noticed the soft fade in/out when playing with the controls. In fact one of the knob lets you go from 8ms to I think 4 seconds of fade out. Definitely a more complex circuit than the original Silencer, but that's some nice quality of life stuff.

Also, and the manual even mentions this, you can actually boost the noise instead of reducing it. No idea why you'd want to do that but it's an option.

[tootsMcgee]

Verdict: bad op-amp. The 2262C on the top (control) side of the board next to the LED wasn't letting any signal past the first stage.

New 2262C arrived today, patiently soldered in place (SMD)...pedal came to life.

I can't think of what would have killed the old one without taking out the rest of the pedal.

Don't mind all the probe marks..this was the old chip before I removed it.

Be careful about C28. I knocked it off and had to solder it back. That didn't fix the original opamp though. The cleaner pic is after I tried touching up the solder.