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Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sun Mar 29, 2020 12:28 pm
by wackyraces
I would like to know the ideal formula for matching an NVA passive preamp as close as possible in terms of selecting the right pot?
The general consensus is that for a solid state power amp 10K is generally the right choice (I don't know why however).
However I have a Croft 7 power amp which is a valve / mosfet hybrid (I am currently in the process of finding out the input impedance) - but I suspect that 10K is not the right match for this amp.
I currently own an NVA P50sa with a 10K pot - and it does sound good in front of the Croft 7 power but, if I could get a better sound with a closer match I should consider changing.
I don't really know the maths - but I am sure you can help me out here.
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sun Mar 29, 2020 12:38 pm
by savvypaul
What value do Croft recommend?
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sun Mar 29, 2020 12:54 pm
by wackyraces
I'm not sure yet - but generally is there a mathematical rule I can work with?
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sun Mar 29, 2020 12:57 pm
by savvypaul
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sun Mar 29, 2020 2:24 pm
by wackyraces
Ok reading between the maths the conclusion seems to be: ..as long as its maximum resistance does not exceed the input resistance on the target (input of power amp) it makes absolutely ferk all difference.
Well the output voltage of most digital sources are 2V - and the input impedance of a Croft Power amp seems to be 470Kohms (not sure if that's high or low - might as-well say 470 elephants to me).
Also interesting is that fact that 10K specced pot design means that it's 10K when fully turned down to minimum volume - but when the volume is fully up (open) that 10K is irrelevant - it then comes down to the direct relationship between the output of the source and input impedance of the power amp when fully open. So the 10K bit (or 50K or 100K) is the spec when the pot is at minimum - so must change as the volume is turned up.
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sat Apr 04, 2020 1:07 pm
by wackyraces
Because I swap between solid state power and valve power - is it possible to make an NVA preamp with selectable 10k and 100k ?
If not - I use the Croft power the most so - an upgrade from my 10k to a 100k might be in order.
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sat Apr 04, 2020 1:47 pm
by savvypaul
Did Croft say why it needs to be 100k?
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sat Apr 04, 2020 2:41 pm
by wackyraces
Actually Glen just replied 'Pre-amp pot value doesn’t matter with matching to the power amp.'
I wonder why that is when many others are saying that 100k is the right fit?
Obviously Glenn knows best - but to say it doesn't matter surprises me nonetheless.
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sat Apr 04, 2020 2:47 pm
by savvypaul
Only the things that matter, matter.
Re: Which pot for NVA passive? 10K, 50K, 100K ??
Posted: Sat Apr 04, 2020 3:07 pm
by wackyraces
Well - when I've saved up a little more I will probably get my current NVA P50sa upgraded to a higher end pot and silver wiring etc.