Chinese JL Hood Class A - Joined L & R Input on PCB??

[Robbie010]

Afternoon all.

I've been tinkering with one of these cheap Chinese JL Hood Class A amps and I wanted to remove the volume pot to run it as a pure power amp.

I was looking at the signal wires trying to work out how to remove the pot and directly connect the inputs to the amplifier boards when I noticed that both the left channel and the right channel signal wires connect to both amplifier boards and then join together in to a single signal path.

The pot is an ALPS 100kA x2, so there are 3 wires at each stage, left / right / ground from input to the pot and then the same left / right / ground to each amplifier board, at which point the left & right signal appear to combine in to a single trace.

I'm struggling to understand why this is the way it is, is it some kind of feedback or some method of increasing the signal voltage by combining left & right signal?

 

[AnalogSteph]

LGND and RGND are going to be joined at the signal source anyway, and things are rather high-impedance throughout, so there is no acute reason for keeping them separate at this point. If the amp actually has its RCA jacks placed a million miles apart as drawn, that serves no purpose at all and is actually worse than having them right next to each other.

The interesting part will be how they handled their power grounds. Does every amp have a transformer or at least a transformer secondary of its own? I presume something like that being the case, since you don't mention anything about the amp being prone to hum... (Also, is it an IEC Class I or Class II device, i.e. is there a protective earth and if so where does that go?)

Ground routing in audio equipment is somewhat of a science (/ an art) by itself with lots of nuance to it.