Rabbit Hole Problem

[pedalbob]

 Hi-

Built a Rabbit Hole and having issue.  Built it to the Creamy Dreamer spec. in the build document so that is why you see some jumpers in the photo.
Anyway when effect engaged I get no sound.  When I probe it with my signal probe I get a considerable volume loss thru R2 (33k resistor) and then no sound coming out of C1 (110n cap).  No sound at base of Q1.
I checked my Actual Big Muff and the signal carries loud all thru the signal pass (iei no volume drop at R2 and signal on base of Q1 thru Q4).

Any thoughts ?

[zombie_rock123]

Howdy bob!

Think this would probs need a bit more info including a rear shot of the PCB and what transistors did you use? Something with reverse C & E (compared with 5088) could explain the killed signal so early on in the circuit. Could be worth double checking any values hidden by those huge disc caps too.

[pedalbob]

Thanks for the reply. I used 2N5088 just like the stock build of this pedal so pinout should not be issue . I checked each of the 4 with my PEAK analyzer beforehand as well because I wanted to check Hfe of them and everything else with them was fine.
The big ceramic caps are 50n per build instructions too. I have used others from the batch I have for a Nom Nom phasor build with no issue.
Here is back of board     
https://www.dropbox.com/scl/fi/k1mt8q6p33kv78h0f2pbi/Photo-Sep-14-2024-5-58-25-PM.jpg?rlkey=mk0u2sr56mux56d76sjys59b4&dl=0

Thanks for any suggestions. 

[mauman]

In your photo, there's not much solder on the north leg of R2, and the same with a lot of the other components.  I think I'd reflow each of your solder joints and add a bit more solder, there should be a small fillet around the legs of each component and many of them don't have that (R8, R5 jumper, etc), which could indicate cold joints = no connection.

[pedalbob]

Thanks.
Ok reflowed joints with no change.
Just for yucks I pulled the downstream leg of R2 and signal volume increased when I touched the loose leg so not a bad R2 resistor. Re installed and pulled C1 as well and also signal now passed to C2 (and it measeured ok with my analyzer) so not a bad C1 either.  So seams like it is feeling downstream circuit as a large impedence.

Also double checked the pinnout on the 2N5088's I used from the ones I had left (same batch) and fine.

Going to check some back to back voltages based on the stock EHX Big Muff I have unless anyone else has some beter idea.  I am getting good 9v from the Power connections and thru D5 etc.   

[jwin615]

Make sure you didn't mix up 100k and 100R resistors in the first stage?
I'm assuming you have an audio probe setup. Are you sure you're losing signal before Q1? I like the break up circuits for initial probing. So, I would probe the collector of each transistor.

Do your transistor voltages look similar to those in the build doc?

[pedalbob]

 Thanks jwin615

Unfortunately the build doc for this one has no voltages but I have my actual Big Muff apart and will check its voltages tonight.

Yes I was using a signal probe and getting no signal after C1 and just about 1/2 of the loudness going into C1 and coming out of R2.  When I probed my actual Big Muff I have signal all over the place (Q1-Q4, clipping diodes, etc.) so I know something is drastically wrong.

Will report back voltages if I find anything.

[jwin615]

https://www.madbeanpedals.com/projects/_folders/1590A/pdf/RabbitHole2020.pdf

Voltages in there

[pedalbob]

 Ha thanks ! ... I have a 2016 board so was using that build document (catching up on some that I never build and have been sitting around).

In the meantime I measured the voltages on my actual big muff and they are similar.

I think I'm getting close to my problem.  I have roughly 4+ volts at collectors on Q2-Q4 but the collector on Q1 is over 8 volts and 3 of the emitters are measuring 0 volts.

guessing something around R6/C2/R4 not right.  Will poke around some more and check values in the morning. 

[pedalbob]

Still scratching my head on this.

I'm not great at circuit analysis at all but hard to see how I can get 4.25 volts at R12 (going to collector on Q2) and 8.6 volts on R6 (going to Q1 collector) other than a simply Ohm's law thing and something downstream of R6 drawing twice as much current

I changed R6 and R4 in the process ... I know not likely a resistor goes bad (and I measured them all while I was populating board) but I was lifting a leg on each while pokong around and didn't want to risk heat damaging them with the desoldering.  Of course each measured fine when I got them off the board so I am still working on this.

Should I go after Q1 ?? or does anyone else have  any thoughts. I normally socket transistors but this build didn't have much headroom with the small enclosure and tight spacing so I couldn't bend them over. Soldered them pretty quickly and waited in between each leg so don't think I heat damaged them but you never know ...

[jwin615]

Triple check for solder bridges around Q1. A lot of your disc caps look like the insulation is going through the pad and a lot of joints didn't flow through the via. May be worth reflowing that first gain stage area if you haven't. The 0v reading could be due to your meter. Assuming it's capable of reading ~40mV, make sure it is ranged for mV.

[pedalbob]

Thanks but still nothing new...

Reflowed Q1 and inspected everything. Reflowed everything else around initial gain stage.  The legs on the ceramic caps are fine ... I had trimmed a little of the insulation coating before I installed ... hard to see in the photo but they are fine. I checked continuity with pads and bare spots on legs and nothing faulty.

The higher voltage at Q1 still not making sense to me when I get 4 volts at other transistors. 

[pedalbob]

Swapped out Q1 anyway and it wasn't that. Did C3 in the process too and it wasn't that either.
This one is about to go into the bin of unwanted PCB's. Unfortunately I had already drillesd the Pot holes in the enclosure before I soldered them to the daughter board so that I could make should they were lined up ok.  I'm sure I can find another 3 knob 1590A build to use the enclosure
Should have been a simple build ... I built one of the BYOC 1590A mini Muffs with 2N5088's a couple of years ago and it fired right up.
I was doing this one to see if I wanted to mod my actual Big Muff to the Creamy Dreamer and I had the Rabbit Hole board laying around ... seen lots of conflicting info on it online but I don't care for some of the other mods out there.