audio-talk

Nick wrote: ↑Tue May 24, 2022 1:23 pm The phase your are looking for (maybe) is coupling between the channels.

Thanks nick, I'd somehow missed your post.. another thing learnt today !

I think coupling between stages is just as important to avoid too

I think coupling between stages is just as important to avoid too

Well, it depends, normally you hope there is coupling from the input stage to the output stage

But yes, you can end up with unwanted feedback loops via the power supply rails.

I read the term forward feedback..

And wondered if that was related

It's effect is very much like out of phase positive feed back
But I'd guess being out of phase stops it being positive feedback

I'm back to this: It sounds the best of the two topologies. Wider stereo picture with far better height and depth. Better instrumental separation, better micro and macro dynamics, better pitch definition, longer reverb tails, better vocal infection, more insight into how instruments are being played, sharper focus, better pace, rhythm and timing, and the emotion and evocation is back.

Well, feedback can be positive or negative or anywhere in between depending on the delay and the frequency being fed back.

I think though you may mean feedforward as a form of error correction. The big difference is that the signal once mixed does not get a chance to be sent around the loop again. Though I guess you could apply a feedback loop around a feedforward stage.

Cressy Snr wrote: ↑Tue May 24, 2022 4:28 pm
It sounds the best of the two topologies. Wider stereo picture with far better height and depth. Better instrumental separation, better micro and macro dynamics, better pitch definition, longer reverb tails, better vocal infection, more insight into how instruments are being played, sharper focus, better pace, rhythm and timing, and the emotion and evocation is back.

In that case, maybe try changing the 150R for different values. If the difference is that profound, then the chances are, that the value you arrived at by chance is not the optimum.

Aye, it’s quite a step up in quality, or should I say it’s back to the way it was. I only discovered just how good it actually is by listening to the worse version of the music put out by the resistor-less version. Altering resistor values could be interesting.

I’m wondering if doing that will be altering two things at once, ie the B+ to both stages and the -3dB point of the power section filters. Those are currently set at 10.6Hz. How important or not that is, I haven’t the faintest idea, or whether I should be going up or down in -3dB frequency.

Cressy Snr wrote: ↑Tue May 24, 2022 5:15 pm Aye, it’s quite a step up in quality, or should I say it’s back to the way it was. I only discovered just how good it actually is by listening to the worse version of the music put out by the resistor-less version. Altering resistor values could be interesting.

I’m wondering if doing that will be altering two things at once, ie the B+ to both stages and the -3dB point of the power section filters. Those are currently set at 10.6Hz. How important or not that is, I haven’t the faintest idea, or whether I should be going up or down in -3dB frequency.

It will do, but does it matter? Changing the resistor will be simple and if you find the best value of that, maybe then try the cap. Doesn't have to be perfect, but it may be better.

So, I tried playing around with clip leads and resistor values. 220R, 120R, 100R and 75R were tried out before I lost the will to live.
The differences were there, but I found the process tiring: couldn’t decide which was good, better or best, and ultimately it felt a little purposeless. I don’t have the burning curiosity I once had. To cut a long story short, I reverted to the 150R setup and settled at that.

After a bit more thinking, I began to wonder WTF I was doing with such low value caps at the front of the power supply, when I was using a solid state bridge rectifier. I did a quick sim on PSUD, knocked the 20uF motor run out of its friction fit hole using a 16oz claw hammer and wood block to drift it free, removed the Sprague 40uF cap and fitted another JJ 100 + 100uF 500V can cap in the hole left by the motor run cap. I put the choke between the two halves.

The amp before had been virtually silent when idling. Now it is absolutely silent. When playing, all the attributes it possessed before were still intact, but the bass was better in terms of tightness and extension. That’ll do nicely.

Musically there is little to choose between the ‘Nostalgia’ amp and the NVA based job. The ‘Nostalgia’ gives me a few more of the emotional cues where the performance demands them. Deep soul through the ‘Nostalgia’ is capable of leaving this listener a gibbering wreck.The NVA boogies down with disco and rock music.They are both equally good with jazz, blues and chamber music. Big production classical favours the NVA, but the ‘Nostalgia’ holds up brilliantly on choral. Voces 8 and The Sixteen, sound quite gorgeous through it. As ever, it’s horses for courses and which set of compromises the individual wants to live with.

It all turned out nice in the end.