Finished my 8 channel HTPC amp

[V-bro]

That is quite a spiders web man! Or should I say a storks nest?

Well anyway, I can't make chocolate from what's happening in there from these pics indeed...

So the AC voltage are two separate windings from the transformer? I think the hum you have is induced by unsimilarities in the grounds of both amps. The fact that the source grounds are meeting makes it even worse...

I never built an amp like that with dual board, so I can only give some advises based on what I think you should try...

You can try to feed them both the same DC voltage.

You can try if this helps at low power by the following method. Just only feed one amp from the transformer, then pull two (thin) wires from the DC voltage of this amp to the AC input of the other amp. This way the one amp will run at slightly lower voltage than the other, but at least they'll be at the same ground potential (especially AC potential!!)

When this helps I'm afraid you should parallel the transformer outputs, use one single rectifier and go from there...

What could also help is pull out the ferrite choke that connects the AGND and PGND on one amp. Then connect the PGNDs of both amps together and connect the AGNDs of both amps together...

[l'eletto]

before making all these changes I think I do as I had thought, then I will follow your advice ...
thanks anyway

[more10]

Sorry for not observing your question l'eletto. I have hum in my amp too, but it is so low that I don't bother that much. The noise from my HTPC is louder. I have other problems with my setup that I also need to take care of but havn't found the time for that yet. For example the 41hz soft start doesn't work, the fuses trip 3 of 4 times.

I have a 650 VA toroidal transformer with two secondary windings. The two amps have separete secondary windings.

I don't use insulating silica between the chip and the case since I thought the chip was insulated internally. Maybe I am wrong.

I suspect ground loops on the input through my soundcard. Maybe balanced inputs/outputs as described here Balanced Line Driver & Receiver by Elliot will solve the issue, but that is a lot of extra electronics.

[V-bro]

I don't use insulating silica between the chip and the case since I thought the chip was insulated internally. Maybe I am wrong.

It's not isolated, but connected to PGND. Using no insulation can work well, but then only when this is the only ground connection. Then still the versatility of the amp and the possibility to solve ground problems is thrown in the bin. Having everything isolated (I learned the hard way!) is always a good starting point...

[l'eletto]

@more10:
somebody else besides me having trouble to build a 5.1, we can join forces to eliminate the problem !!!
the class T amplifier have the ground conformation different from normal class A/B amp, for this reason, it create buzz Although there isn't ground loop ! (when two input of different amplifier are connect together) If you have loops is even worse !
I am studying engineering and I'm doing everything possible to finish as quickly as possible while having no time...
I'm completing the last change, if all goes well I put in the forum all the hard work of my months and months of testing !!!

[more10]

Well, since I have finished the amp15 I have been working with for the last year, I will get my hands dirty on this project.

I have the same transformer for both apms, using separarte secondary windings. I will make shure that both secondary windings are connected the same way to both amps, never thought about that before. Then I will of couse put in insulation between the heatsink and the chip.

I also have to look into the problem with the soft start, maybe the problems are dendant of each other.

[l'eletto]

I have deleted the buzz, connecting the PGND (as V-BRO said ) together at both the amplifier, and using the instruments amplifier for separated the FR and FL input between two amplifier. When I have time, put all the schematics on forum !

[krilli]

Good news

[V-bro]

Great news! Thanks for posting this and taking the trouble to do some pioneering!!

[l'eletto]

here are the pictures:
lpf.jpganti bump circuit.jpgsatellite 2.jpght amplifier.jpgsatellite ht.jpg