HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

Yes. Thanks Rex. That is indeed very helpful.

I’ve committed the heresy and increased the feedback level by means of the 10K conversion from 18K resistor.
It works fine and I’ll audition it later.

Killed the sound completely. I’ll put it back as it was. Boring, boring, boring. Flat as a fart I’m afraid.

interesting. I wonder if the circuit is now unstable with longer speaker cables attached. Oh well. Sorry i wasted your time.

No problem Rex. Read on.

Now then! I dug a couple of 18K resistors out of my parts boxes and thought why the hell don’t I just reroute the feedback path direct from the speaker terminals instead of via the PCB track?
Anyway I traced the PCB to make doubly sure I would be connecting like with like once I removed the resistor from the board.

After satisfying myself that I knew what was what, and what went where, I soldered my own 18K resistors, one to each of the red speaker terminals where they exited the amp chassis. From the other side of the resistor I took a wire to the transistor side of where the original feedback resistors had been.

I’d read decades ago in Practical Electronics magazine, that feedback is best taken from the speaker terminals; can’t remember why now. I also realise that in a production environment, doing this is not viable, you want it all on the PCB and indeed that’s where it is on the NVA boards, where it eases assembly and removes any margin for error.

The sound is fantastic. All the NVA qualities we know and love but subtly enhanced. The bass especially, goes deep and fast, but the whole of the spectrum has gained in solidity and definition.

OK this isn’t proper remote sensing because the feedback path is still within the amp chassis, not from right at the speaker end. I’m not going there. That’s far enough.

I wouldn’t say you’ve wasted my time at all Rex.

Thanks for sharing that idea Steve and good idea. Taking the sense point to the speaker would make speaker cables irrelevant as far as I can see. One extra cable to your speakers is all it would take. Are you sure you won't be trying it You could even put the resistor right at the drive unit but that would make swapping amps a pain in the arse.

Scrub that. On further investigation it is not as easy as I thought and there are dangers.

karatestu wrote: ↑Sat Feb 05, 2022 5:17 pm Scrub that. On further investigation it is not as easy as I thought and there are dangers.

That’s why I wont do it. Even with just a single driver like mine it looks distinctly dodgy.

For Stu, as i'm unable to send a pic in a PM.

Polystyrene caps are circled. They are 470pF.

I must be blnd, I can't see any circles