MAdbean Rabbit Hole Help !

[pedalbob]

Hi All-

Built a Madbean Rabbit Hole (small 1590A build of a Big Muff Circuit) and getting absolutely nothing when I engage effect. Built with 2N5088 transistors and to the Creamy Dreamer spec (as listed in build document) which replaces the resistors to ground off the emitters with jumpers and tweaks a few of the cap values like most bigg muff mods.
I've attached pictures of front and back from a few days ago. I've since reflowed all joints and replaced a bunch of components with no change.
Issues I've identified so far :

With Signal Probe I get good signal coming through 1st resistor and then it drops in half (loudness) coming out of downstrean leg of resistor and goes to zero sound coming out of the capacitor after the resistor (i.e the signal never gets to the 1st transistor Q1).  I've replaced the resistor, capacitor and Q1 with no change.

Measured voltages at Q2 and Q3 look healthy (about 4 volts at collectors and lower at emitter and base and match the build document and my stock OEM EHX Big Muff).  Voltage at collector of Q1 is twice as high as it should be (about 8.5 volts) and nothing at emitter.  Voltage at Q4 collector is lower than it should be (about 1.5 volts).  Tracing the Power coming in looks fine until it hits R6 (connected to Q1 collector) but upstream of R6 looks fine (coming from resistor that goes to Q2 collector R12).

Voltages at the 4 clipping diodes looks fine.  Voltage at the electrolytic cap C14 fine. Voltage on the 3 pots looks consistent with my EHX muff.

I'm Not great at circuit analysis but seams to me the high Voltage at Q1 is my issue I just can't figure out what is causing it.

Any thouhts from you big muff experts





  ?       

[PRR]

...voltages at Q2 and Q3 look healthy.....  Voltage at collector of Q1 is....

Which schematic are you using? This one?
https://www.madbeanpedals.com/projects/_folders/1590A/pdf/RabbitHole2020.pdf

I bet Base of Q1 is shorted to ground. Q1 turns off, collector goes way high. Can you find base of Q1?

In the pictures, IMHO the solder is too generous. More solder is NOT better. I would try to remove all but a trace.

[pedalbob]

Thanks for the reply.  Yes that is schematic although my PCB is the revision earlier than that but schematic is same.
I'll check base of Q1 again ... I replaced Q1 as part of my earlier troubleshooting because I was unable to socket the transistors in this tight 1590A build and was worried I had damaged it soldering it in but replacing it didn't fix the problem.  Maybe the board has a defect (?) although I've only had that happen once with the 50 or so pedals I've built... but your explanation is the best I've been offered so far.

Thanks again.

[Matthew Sanford]

Looking at the 2016 schematic for the board you have, Q1 is an n channel mosfet, but I didn't compare the values around it. Maybe they are different when there's a BJT there?

[duck_arse]

please - post the board layout that matches YOUR built board.

[pedalbob]

Here is parts list for Creamy Dreamer i used from build doc


Here is schematic from build doc.

[pedalbob]

 Hold on not sure why my images aren't uploading ...

[pedalbob]

Creamy Dreamer Parts List



Schematic

[url="https://www.dropbox.com/scl/fi/26k1c63sua3nih44b9q9n/RabbitHole.jpg?rlkey=e7dbezrqolb19fa99elaj8dif&dl=0"]

[R.G.]

Go here, read the thread:
https://www.diystompboxes.com/smfforum/index.php?topic=29816.0
It's specifically intended for situations like you find yourself in.
The short form is:
> get the accurate parts list and schematic (and post them in your request for help, if you later need to ask)
> use your voltmeter and measure all the pin voltages of the active devices
> do some reasoning; in order to be an amplifier, a bipolar NPN has to have 0.5 to 0.7V from its base to its emitter, and the collector must be higher than the base or emitter, usually by a few volts at least. If any two pins have the same voltage, then they are probably shorted together, or both are open.
If that process leaves you confused, post your schematic, parts list, and measured voltage back to the forum.

[pedalbob]

 PRR thanks for the suggestion and comments looks like you may have been correct about Q1 base being shorted to ground.

I checked continuity between Q1 base and ground and was only getting a few ohms.  Also found that only had a few ohms across R3 (which is 82K) when measured in situ.  I pulled R3 and it measured 82K uninstalled but now getting over .5 meg ohm between Q1 base and ground (with R3 empty) and also from non ground pad of R3 (.56 mega ohm). Not sure what was causing short but I will poke around some more and install new R3 and see if that works.

[PRR]

I just got lucky. Do what the smart guys are telling you!

please - post the board layout that matches YOUR built board.

> get the accurate parts list and schematic...
> use your voltmeter
> do some reasoning;

[pedalbob]

PRR just following up ...

Changed R3 with a new resistor (from different stock even) and was extremely careful soldering it in ... even soldered the leg connected to Q1 base first and then rechecked resistance with Ground leg unconnected ... lol
Anyway it fired right up.
I sincerely appreciate you answering my specific direct question from my initial post ... I get the drill of post the schematic , a bunch of pictures and all of that but considering this was a Big Muff clone the schematic is pretty well known and doesn't vary much ... and I had eliminated most of the voltage discrepancies from those in the build document and from measuring back to back with my real Big Muff which I said in the post ...  I don't ask for help until I've already done a bunch of troubleshooting and "reasoning" ... I try to boil it down to a simple question with my initial post so anyone who is trying to help isn't starting from scratch ... but i guess that rubs some people wrong

Thank-you so much again ... you are awesome