Solid State Guitar Amp Forum | DIY Guitar Amplifiers

U3 and all those caps are the chorus clock circuit, they are not in the audio path.

U2, U7 Q6, Q7 are the chorus path.  MAybe Q5 too but I doubt it.  Turn chorus on, you get hiss.  Power off, remove U2, power on.  His still there?  You won't get a chorus signal with U2 gone but we are looking for the noise now.  Still noise?  Remove U7, same question?

Make SURE not to install ICs backwards.

It is fun to try to tweak an amp for tone, but remember, no matter what you do to a hamburger, you will never make it taste like a lobster.

A guy brings me a 1969 Corvette with a flat tire.  I put a brand new Goodyear (or Michelin or whatever) on it, balance up fine, car drives fine.  Now do I check to make sure the guy doesn't have his heart set on an actual 51 year old tire for it?

Those voltages look fine for idle DC levels, but they don't tell us if the parts can conduct current well.

You can probably find 2SC2233, or the common TIP41C would likely work fine too.

Just noticed a drawing error.  The two output transistors are drawn wrong, they have swapped base and collector connections.

Quite possible one of those two parts is bad.

OK, that tells me the output stage cannot provide the current the load demands.

You have 8v instead of 7.5 on the supplies, well close enough, it is just a guitar amp, not lab equipment.

verify the two 0.5 ohm 5w resistors associated with the output transistors.  And for that matter, the 150 ohm and 22 ohm resistors associated with the drivers.

From the speaker on the schematic, follow the output line to the left and you come to 10 ohm R124.  Is it open or burnt?

Perfectly normal for the two 330 ohm resistors to get hot.  Hopefully there is about 7.5v across each of the two diodes.

You say it sounds OK through headphones, but does it still sound OK through the phones with the speaker also connected?  Oh wait, you say the phones makes the speaker silent?  The schematic does not show a cutout, but we can deal.  With speaker connected, how does the line out sound?  Run that to some other amp.  Does the line out sound change when speaker is connected or removed.

You soldered some stuff and it came to life then failed again.  SOunds like you have a bad connection or cracked copper trace somewhere.  Not so much a bad part.  Transistors don't generally die and heal themselves.

Sounds like someone already uploaded a file with the same name as you want to use.  Try renaming your file first., or resave your file under a new name and upload that.