The Alpha Big Boy with Buttah (ABBB) 52w Class A Amp GB

[xrk971]

Hi Josh,
Your diagram shows one of the primaries connected to earth ground. I assume that’s a typo. You should add an NTC (CL60 or 8D-20) in series with the line from the wall plug to the primaries. That will serve to be soft start and help reduce hum. Also, don’t twist the earth ground with the mains L and N lines. They will induce hum into the ground line.

Here is my sketch. I think you are already twisting the AC secondary wires?

[joshua43214]

Thanks for the really fast answer.

I assume that’s a typo.

Your are correct

I think you are already twisting the AC secondary wires?

Yes, you are correct again

I went ahead and unwound the earth from the mains, and added a CL-60 along the load line.

Sadly, it didn't help.

My mains power is pretty decent, so I am not too surprised. Winding the earth didn't affect my M2x, but I also use a mains filter on that and good wire. So who knows really...

Attached is a pic of the new set up.

Once again, I can't thank you enough for your help.
It is greatly appreciated.

Thanks,
-Josh

[xrk971]

You get no hum when playing from say your phone right? But hum when connected to the DAC that’s connected to the mains. This is a common problem. You may have a ground loop from your source - the shield wire on your RCA cable is the ground loop. Can you add to the diagram how the DAC/source is grounded and what it’s power supply is?

What is that diode bridge doing there with thick black and white wire?

[joshua43214]

Originally Posted by xrk971

You get no hum when playing from say your phone right? But hum when connected to the DAC that’s connected to the mains. This is a common problem. You may have a ground loop from your source - the shield wire on your RCA cable is the ground loop. Can you add to the diagram how the DAC/source is grounded and what it’s power supply is?

What is that diode bridge doing there with thick black and white wire?

One question leads to another, as they say. I am working on a proper answer, and a conditional matrix. I need to track a few things down first.

I will have your info this weekend.

Thanks,
-Josh

[joshua43214]

Originally Posted by xrk971

You get no hum when playing from say your phone right? But hum when connected to the DAC that’s connected to the mains. This is a common problem. You may have a ground loop from your source - the shield wire on your RCA cable is the ground loop. Can you add to the diagram how the DAC/source is grounded and what it’s power supply is?

What is that diode bridge doing there with thick black and white wire?

The diode bridge is for the 12V supply to the fan controller.

I want to thank you all for your help and patience.
To add to everything else, my mother had a minor stroke (she is fine), and a power surge seems to have killed my JVC RS25U projector

After spending much time trying different things, and building a conditional table, I found the problem.
During my efforts to maximally mis-handle everything, I damaged one of the traces on the board. I repaired the trace, and the amp is now essentially hum free.

I was able to listen to it for about 45 minutes the other night, and so far it seems very nice. If I had to use a single word to describe it, it would be "authority." The amp as authority.

OK, to move onto less interesting questions:

One of the amps runs much hotter than the other.
62C and 59C vs 57C and 54C
I monitor temps with thermistors attached to the heatsink copper die.
I run the fans at full speed, and do not use PWM.

Should I worry much about this? I expect the thermal paste also needs to cycle a few times before I get optimal contact.

I have a second question as well.
Is there any reason not to put a relay between the transformer and the board?
I'd like to have an auto-shutdown feature incase the amp overheats. I currently have a 120dB siren hooked up that will scream when the temp exceeds 95C.

Thanks again,
-Josh

[xrk971]

Hi Josh,
Sorry to hear about your mother - hope she recovers quickly!

Congrats on finding the problem! Glad that the amp sounds nice - autority of a 50w Class A is something I have noticed too vs a 100w Class AB.

The temps sound Ok - some differences result from different heatsink contact pressure and amount of thermal paste. Check your bias currents and if they are all identical, then should be similar temps. I have also seen 5 deg variations for temps on mine. Increasing the clamp bolt pressure can decrease the temps. etc.

No reason not to have a relay but make sure it can handle high currents. Good idea to connect it to a safety shutoff. You can also use those coffee pot thermal switches that disconnect when greater than some set temp lie 85C etc. But they reset so you would get recycling unless you use it to activate a latch.

Happy Xmas and enjoy your amp!