DIY Transistor Amp Using NVA Boards

[Nick]

Imho you are thinking about valves with the bleed resistors. The output stage won't stop pulling current when the heaters are cold as there aren't any. But I agree the bipass caps are always a good idea

[Cressy Snr]

Imho you are thinking about valves with the bleed resistors. The output stage won't stop pulling current when the heaters are cold as there aren't any. But I agree the bipass caps are always a good idea

So do you think that all the bleeders are doing in this situation is to waste electricity? I put them in really, because the indicator LED was taking up to 5 minutes to go out after the amp was switched off. The LED is now across one of the 10,000uF caps rather than at the board end, which is probably why. I worked the resistor values out to give a 60 second discharge time.
I could swear the sound was fuller bodied and more authoritative with the resistors in than out. We all know about expectation bias (I’d never heard of it until somebody told me about it.)
Is there any mechanism involving bleed resistors that could have changed the sound.

With the bypasses however, there was no argument. There was a definite change for the better.

[Nick]

Well, its your amp your ears, but I guess it depends on what idle current the NVA amp is passing. The resistor is passing 30ma or so, so unless its very much a class B amp I would have thought would not be a large fraction of the idle current. Will be a different case for the input stage, that will probably be pulling bugger all current so the cap will take some time to run down.

Depends on what you are doing it for. If you want to get rid of the voltage in the caps then why not. You could consider a diode between the input stage supply and the output stage supply (both rails) so that once the output stage falls below the input stage it will start to pull that down as well. If you just want the indicator to go off when the power is off I would just put a diode in series with it and put it across the ac output of the transformer.

As to will it improve regulation, not sure how, all it will do is slightly increase the ripple on the rails unless I am missing something.

"The LED is now across one of the 10,000uF caps rather than at the board end, which is probably why." Not sure what difference that would make assuming the wire you are using conducts

And yes, we should all (IMHO) be aware of the assorted biases we live with all the time. Conformation Bias is another one that I find you have to work hard against.

https://en.wikipedia.org/wiki/List_of_cognitive_biases

Though to be fair "I’d never heard of it until somebody told me about it." is true of most things for just about all of us.

[steve s]

Looks good Steve.. I can see another mini meet brewing.

[Cressy Snr]

…If you just want the indicator to go off when the power is off I would just put a diode in series with it and put it across the ac output of the transformer.

Have done the above now. That’s that one solved.
Bleeders are out too. No feckin difference to the sound without them.
Improvements gained with the bypass caps still intact though.

[Cressy Snr]

Looks good Steve.. I can see another mini meet brewing.

Aye… should be good. Just PM or text when you get one sorted

[Daniel Quinn]

I have a serious problem with the use of confirmation bias to explain differences in what we here . Don’t wish to derail this thread so I just say ‘what a load of bollocks’

[pre65]

I have a serious problem with the use of confirmation bias to explain differences in what we here . Don’t wish to derail this thread so I just say ‘what a load of bollocks’

Dennis, are you saying there is no such thing ac "confirmation bias", or that it does exist but you are immune to it's effects ?

I think that if one does a "mod", and finds a difference (careful choice of word), then live with the difference for a while, then go back to the previous state and see if it sounds like you remember the pre difference sound.

*

[Nick]

I think that if one does a "mod", and finds a difference (careful choice of word), then live with the difference for a while, then go back to the previous state and see if it sounds like you remember the pre difference sound.

Though in that case confirmation bias can still get involved. Memory can be a problem.

https://en.wikipedia.org/wiki/Confirmat ... nformation

[Cressy Snr]

The main problem with all this confirmation bias/expectation bias stuff, is that acknowledging its existence invalidates any attempt to compare anything to anything else. I heard an improvement with the bleeder resistors, then I didn’t, so which is the correct response, both of them? Did I first expect a difference so duly heard one? Equally did I then expect not to hear a difference so duly heard none, after I had read Nick’s argument that the resistors were not really necessary and got influenced by that?

The ‘A compared to B question’ is irrelevant if the biases are present, rigour is absent, so why bother? We like what we like.

Here’s a statement then. “My NVA based amplifier and Mission 731i stand-mounted speakers, produce (on an extensive range of musical programme) a standard of music reproduction that, under the present circumstances, pleases me. Not very exciting, but an accurate statement nevertheless.
Trouble is the quality of the discourse is now at the dilution levels of a homeopathic medicine, and excitement, enthusiasm, awe and wonder has become

[Nick]

Yes, all the above yes, but its worst that that. Once you hear something, you cant rewind your brain back to the state it was in before you heard it, so before/after becomes problematic.

Its why I like to find some correlation between what I hear and what I measure, but that process of hearing and correlation finding is itself still as prone to biases and humanity.

[Daniel Quinn]

I have a degree in social theory . I could wax lyrical for hours on why confirmation bias deos not explain what we hear. But why spoil so many audiophiles fun .

And nick you are of course assuming there is a correlation but simple audio measurements and what you hear. If only it were that simple

[Cressy Snr]

…..But why spoil so many audiophiles fun….

But audiophilia is not fun; far from it. In fact it’s a fecking pain in the arse when all you wanna do is git on down.

[pre65]

I have a degree in social theory . I could wax lyrical for hours on why confirmation bias does not explain what we hear.

It would be a waste of your degree if you did not at least try to explain.

A forum is for the exchange of ideas ?

[Nick]

I have a degree in social theory . I could wax lyrical for hours on why confirmation bias deos not explain what we hear. But why spoil so many audiophiles fun .

And nick you are of course assuming there is a correlation but simple audio measurements and what you hear. If only it were that simple

Confirmation bias doesn't try to explain what we hear it just suggests that we can't trust what we hear if we hope to make progress.

I also didn't say simple measurement. But letting that pass I think is is very much that simple. It's just that in general people don't want it to be simple. Where is the chance of making money if it was that simple.

Given it's easy to show how you can't trust what you hear and see, and it's so easy to play to biases why would you assume that we can't measure some things perfectly well enough. It's just that most people want to believe that are more special than that.