Box of rock help plz

[Jay]

Hi all working on the aion megalith. No sound coming out of either channel. And the signal seems to stop after the transistors on both sides.

I have audio probed the circuit and found that there is signal coming off the gate of both q1 and q4, but at the pots nothing.
The first odd thing I have noticed is that the gain pot will emit some sound on pin 3 if the pot is turned all the way down. No such luck on the drive level.
The second odd thing is that I don't hear any signal on r3 at all, but that goes to 9v (i'm not sure if no signal is ok there, but it gets to the transistor).

I've replace R3 just in case, and the same thing happens, no signal there.

Any ideas on what to check next? Attaching the schematic so you don't have to dig for it.

[mauman]

At Q1-Q4, signal goes into the gate, and should come out the drain amplified. If you have signal at the gate and not the drain, the FET is the location of the problem, if not the source of the problem.

Some things I would check: What parts am I using for Q1-Q4?  Are they known good FETs or could one or more be faulty?   Do the pinouts match the PCB (D-G-S)? 

[Jay]

At Q1-Q4, signal goes into the gate, and should come out the drain amplified. If you have signal at the gate and not the drain, the FET is the location of the problem, if not the source of the problem.

Some things I would check: What parts am I using for Q1-Q4?  Are they known good FETs or could one or more be faulty?   Do the pinouts match the PCB (D-G-S)?

That was it. The docs were wrong about the way the transistors faced and it was printed incorrectly on the circuit board too. Put in sockets for all 4 after taking them out. Turned them around and everything worked. Thanks for the assist!


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[Aentons]

It has this in the build doc...

"MOSFET selection and pinouts
The original Box of Rock uses BS170 MOSFETs. These are identical in specification to the 2N7000, but
with the major difference that sometimes the pinout is different. Some manufacturers use D-S-G and
others use D-G-S, while the 2N7000 is always D-G-S. Therefore, it's recommended to use 2N7000 when
building this project."

[Jay]

I used the 2n7000s


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[Aentons]

I used the 2n7000s

Would you mind sharing where you got them from so others don't suffer the same fate? I'm building this one now and was about to place an order.

[Jay]

Tayda. But the docs for all 2n7000s are the same.


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[Aentons]

Ok, right. I see. The transistor package outline on the PCB is upside down. Thanks for the heads up.