Darlington output topology

[porifera]

Anyone know amplifier topology and it's outputs?

I have a no-name dual monoblock amp that was Zed built and i'm having an issue with output.

Runs fine but, at mid to high volume it puts out considerable distortion.

I noticed a "common" coming from both channels that traces back to the power supply rails.

Any help would be most appreciated, as i can explain further on this.

[Boon]

Eeer, Darlington, hooray.

What is it, TIP41C and TIP42C pairs or something? Can't remember really. Old Soundstreams were built this way.

Ugly output is easy. Get your scope out and trace the output back from the terminals to the source, find where it goes from looking nice to being ugly. My money is on one or more of the output transistors being a bit leaky, or a bad drive/preamp transistor that isn't driving them properly. Maybe, just maybe, bad resistor in the drive circuit somewhere.

Or could be a bad biasing resistor.

If you don't have a scope, you're pushing wet sh!t uphill with a rake.

[porifera]

Eeer, Darlington, hooray.

What is it, TIP41C and TIP42C pairs or something? Can't remember really. Old Soundstreams were built this way.

Ugly output is easy. Get your scope out and trace the output back from the terminals to the source, find where it goes from looking nice to being ugly. My money is on one or more of the output transistors being a bit leaky, or a bad drive/preamp transistor that isn't driving them properly. Maybe, just maybe, bad resistor in the drive circuit somewhere.

Or could be a bad biasing resistor.

If you don't have a scope, you're pushing wet sh!t uphill with a rake.

Lol, i don't so up the hill with something slippery and moist in push-tow i guess.

They are TIP147 2-pair and TIP142 2-pair. 2 sets of 2 pair each on both channels. So 8 per channel.

I found something though. The audible distortion went away when i used the "common". What is this common you say? Funny you should ask because i didn't know either.

Each channel has a common lug in between the pos and neg lugs. Hooking a driver to the pos and neg lugs amounts to driving all 8 of the TIP's and then up the gains and the distortion is there. (more like an over-modulation as it's not crackly and poopy) Fast-forward to running a driver on the common and the POS, and only 4 of the 8 TIP's drive, and said over-modulation disappears. Run a driver on the NEG and common, the other 4 TIP's drive and the same result, no distortion.

So, below is my new question (thanks for your reply by the way, helpful to my thinking).

The common lug is *ahem, common. Common to that channel. Once i drive IT and an adjacent lug, i get 50% total output for THAT channel. If i drive without that common, i am essentially bridging that channel and get 100% available output. I am not aware of, any other build that, you can bridge an already mono block rail.

Make sense? Not to me! Thoughts?