Page 4 of 8
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Fri Jul 03, 2020 1:43 pm
by Geoff.R.G
Lurcher300b wrote: ↑Thu Jul 02, 2020 2:28 pm
Thus, although the current may not be large a high capacity PSU is required to prevent throttling (basically what is going on in the Phono 3)
Just think about that for a moment. The current is not being supplied from the transformers, but from the caps, the transformer then tops the caps up 100 times a second. The variation in current draw from the load will govern how much the capacitor discharges in each 100th of a second.
Not sure exactly what "throttling" means in this context (low load on the supply).
In the case of the power output stage then again the size of the cap and the output the load requires controls how much it is discharged. The size of the transformer controls how fast the cap is charges up, and if the transformer can't supply enough current in each 100th of a second to replace what the load draws in that time (and draws while its charging the cap), the the power supply will not get back to full voltage and will sag. But that should never happen with a load in the low ma range.
I was being lazy.
As you know the capacitors also smooth the output waveform and a larger capacity PSU may well just use larger capacitors. Clearly it makes a difference otherwise the Phono 3 wouldn't use a higher capacity power supply, well four different PSUs which is effectively a four times larger PSU.
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sat Jul 04, 2020 12:55 pm
by 29mile
Lurcher300b wrote
In the case of the power output stage then again the size of the cap and the output the load requires controls how much it is discharged. The size of the transformer controls how fast the cap is charges up, and if the transformer can't supply enough current in each 100th of a second to replace what the load draws in that time (and draws while its charging the cap), the the power supply will not get back to full voltage and will sag. But that should never happen with a load in the low ma range.
A niave question but using one transformer and capacitor bank with 2 feeds off the caps ie one for the front end and one the output stage - is this any better ( or worse ?) than using one transformer/caps supplying one board without splitting the front/output stages ?
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sat Jul 04, 2020 1:57 pm
by Geoff.R.G
29mile wrote: ↑Sat Jul 04, 2020 12:55 pm
Lurcher300b wrote
In the case of the power output stage then again the size of the cap and the output the load requires controls how much it is discharged. The size of the transformer controls how fast the cap is charges up, and if the transformer can't supply enough current in each 100th of a second to replace what the load draws in that time (and draws while its charging the cap), the the power supply will not get back to full voltage and will sag. But that should never happen with a load in the low ma range.
A naive question but using one transformer and capacitor bank with 2 feeds off the caps ie one for the front end and one the output stage - is this any better ( or worse ?) than using one transformer/caps supplying one board without splitting the front/output stages ?
The simple, and unhelpful, answer is "it depends". If both stages use the same rail voltage a designer may simply use one PSU but if they use different voltages there are a number of options. Sonically, Richard seems to have thought that powering the input stage separately from the output was worthwhile.
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sat Jul 04, 2020 2:17 pm
by karatestu
How about one transformer and two sets of rectifier & caps. Also there are available transformers with two centre tapped secondary windings. Saves a bit of space.
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sat Jul 04, 2020 5:18 pm
by 29mile
Yes lots of options but as Tom mentioned in his earlier post Richard had tried many permutations and in the end settled on 4 separate transformers. I am in no way qualified to argue with that so I will stick to the NVA way.
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sat Jul 04, 2020 6:20 pm
by karatestu
I agree 100%
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sat Jul 04, 2020 6:22 pm
by savvypaul
4 is the 'ultimate' NVA way...
The little A20 (one transformer) can sound fabulous with high efficiency speakers...
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sat Jul 04, 2020 6:31 pm
by karatestu
I have an AP20 in my kitchen diner and it never fails to amaze. Speakers are only 84 dB
and made by a company Doc didn't think much of.
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sun Jul 05, 2020 12:35 pm
by Lurcher300b
As you know the capacitors also smooth the output waveform and a larger capacity PSU may well just use larger capacitors
Yes, but the phrase "smooth the output" hides a lot of detail from a process that is far from simple involving the dynamic interaction of the transformer, rectifiers, caps an the load, so to simplify it in this way runs the risk of loosing something important.
Clearly it makes a difference otherwise the Phono 3 wouldn't use a higher capacity power supply, well four different PSUs which is effectively a four times larger PSU.
Yes. but there is a danger here of saying that X does something like is better. Y is something that fits in with my world view of how I think these things work, so X has used Y to provide the improvement. When in fact there is no link between X and Y.
Re: Dual mono or separate transformers for input- and outputstage?
Posted: Sun Jul 05, 2020 12:53 pm
by Daniel Quinn
Lurch, you know its making amps not political economy don't you
