Amp Camp Amp - ACA

I hope I'm on the right thread.

I need your help because I have a problem with the bias on one of the channels. The potentiometers do not influence the voltage on PIN 2 of Q1.

Does anyone have any idea what the problem is?

Thx

You are on the right thread.
85% of faults are poor solder connections as 6L6 says.
Getting components in the wrong places or the wrong way round is next most likely. (Capacitors and transistors Have to be in the right way round.)
So double check your soldering and make sure everything is in the correct place and the right way round. Check that both Q1 and Q2 get hot on the faulty channel.
Look at Step 56 of the build Guide for typical resistance and voltage checks.

Post some clear pictures of your build so we can take a look too.

Alan
 
You are on the right thread.
85% of faults are poor solder connections as 6L6 says.
Getting components in the wrong places or the wrong way round is next most likely. (Capacitors and transistors Have to be in the right way round.)
So double check your soldering and make sure everything is in the correct place and the right way round. Check that both Q1 and Q2 get hot on the faulty channel.
Look at Step 56 of the build Guide for typical resistance and voltage checks.

Post some clear pictures of your build so we can take a look too.

Alan

I'll re-check all the welds in this case. I must have done something wrong.

Q1 and Q2 are hot when I turn on the amplifier.

If it still doesn't work after that, I'll post pictures.

Many thanks for your help
 
amp camp 1.6 can't set bias low enough

I hope I'm on the right thread.

Have amp camp 1.6. It was working fine until I disassembled to add more filter
capacitance. Put it back together, but now bias pot will not enable the bias to be set properly. The bias creeps up on turn on, climbing past 13 volts, before I shut it off. Rail voltage is around 21-22 volts. Resistance checks are ok, but afraid to leave it on more than 30 seconds in fear that it will damage mosfets.
What would you check component wise as a start?
I"m baffled. Both channels are the same behavior. I notice C2 is only rated 16 volts, but could it have failed. I just followed the receipe, not a tech, but any help would be swell.

Thank you,
Den
 
I hope I'm on the right thread.

Have amp camp 1.6. It was working fine until I disassembled to add more filter
capacitance. Put it back together, but now bias pot will not enable the bias to be set properly. The bias creeps up on turn on, climbing past 13 volts, before I shut it off. Rail voltage is around 21-22 volts. Resistance checks are ok, but afraid to leave it on more than 30 seconds in fear that it will damage mosfets.
What would you check component wise as a start?
I"m baffled. Both channels are the same behavior. I notice C2 is only rated 16 volts, but could it have failed. I just followed the receipe, not a tech, but any help would be swell.

Thank you,
Den

Most likely bad solder joints around the pots.
Re-flow the solder joints there and try again.
As you are at it check all other solder pads for suspect cold joints.
Good luck.
 
I will do that, but I did notice that on the resistance checks where it shows
335K resistance at the end of R10, I only get around 72K
That is way off, but its odd that the amp worked fine before, and both
of the channels zonked out together.
If the reflow doesn't work, I will post pictures when I have it apart.
Thx
 
Amp working fine now. Problem turned out to be the substitution of a different input cap, and the way I implemented it by jumpering C3 position on the board, and putting the new

cap directly off of the input jack. That made the circuit go nuts, unable to set bias at all.
Went back to default cap on board with a polystyrene by-pass added, and all is A-OK!
 
I finally finished my ACA. I set the initial bias to 12V, screwed the bottom cover on and layed the top cover on. Then played some music for 30 minutes or so and reset the bias to 12V again (it hadn’t drifted more than 0.1V). The heat sinks get warm, but I can easily hold my hands on it for 10 seconds and I have wimpy hands Lol. I didn’t see anything in the 1.6 build guide about letting it warm up but assumed it would change. Do I need to check it again? I seldom get to listen for more than an hour at a time, fwiw.
 
Well I am nearly finished. The process has not been without tribulations.

My multimeter’s leads fell apart at the start, requiring a haphazard soldering. My multimeter can’t get close to measuring the large resistors.

One transistor refused to solder properly, especially one leg. It cold soldered repeatedly for no apparent reason. I was worried all that heat would harm the transistor... then I saw how much heat the transistor puts out when powered up.

Both potentiometers kept cold soldering too.

The LEDs barely seat in holes; I made the leads too short.

I bent the legs on one transistor the wrong way, initially.

Putting the chassis together is something of a Rubik’s cube. Shift one part one way and you block another.

The pinnacle of issues might be what occurred at the very end. I was re-tightening all chassis screws when I snapped the head off a screw holding bracket onto heat sink. Anybody got an extra heatsink, ha! I have the capacity to over tighten like no other. I could leave it. But I would bet that I take that side apart and drill out the remaining shaft.

I’m guessing I’m 12+ hours into it. I would test the amplifier... but I don’t have any speakers currently. True. Hopefully it turns out well in the end.

Pics attached. I went off book with some wire color choices.
 

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Well I am nearly finished. The process has not been without tribulations.

My multimeter’s leads fell apart at the start, requiring a haphazard soldering. My multimeter can’t get close to measuring the large resistors.

One transistor refused to solder properly, especially one leg. It cold soldered repeatedly for no apparent reason. I was worried all that heat would harm the transistor... then I saw how much heat the transistor puts out when powered up.

Both potentiometers kept cold soldering too.

The LEDs barely seat in holes; I made the leads too short.

I bent the legs on one transistor the wrong way, initially.

Putting the chassis together is something of a Rubik’s cube. Shift one part one way and you block another.

The pinnacle of issues might be what occurred at the very end. I was re-tightening all chassis screws when I snapped the head off a screw holding bracket onto heat sink. Anybody got an extra heatsink, ha! I have the capacity to over tighten like no other. I could leave it. But I would bet that I take that side apart and drill out the remaining shaft.

I’m guessing I’m 12+ hours into it. I would test the amplifier... but I don’t have any speakers currently. True. Hopefully it turns out well in the end.

Pics attached. I went off book with some wire color choices.


Are you applying the soldering advice offered in the build guide?
Amp Camp Amp V1.6 Build Guide - Step 8 Solder Resistors
As I explain in the guide's comments, I built my ACA with a soldering temperature too low. It worked but I may have put excess heat into components. There going strong so far but may check out early in life as a result.


I probably made it through ok because I sourced eutectic solder for the job. See the guide for relevant advice.


I'd expect if you follow the guide for temperature and solder you won't go wrong. I got myself a magnification head band + lamp arrangement. Inspecting the quality of your own work is an easy way to pick up issues and fix them before they become a real problem.