Which pot for NVA passive? 10K, 50K, 100K ??

All things NVA
wackyraces
Posts: 51
Joined: Wed Feb 24, 2016 11:06 pm
Has thanked: 0
Been thanked: 0
Great Britain

Which pot for NVA passive? 10K, 50K, 100K ??

Unread post 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.
System: AURALiC Mini - SPS DAC 3 - NVA P50sa / Croft 7 - Role Audio Enterprise

User avatar
savvypaul
Posts: 8634
Joined: Tue Oct 11, 2016 7:14 pm
Location: Durham
Has thanked: 1657 times
Been thanked: 2978 times
Contact:
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post by savvypaul »

What value do Croft recommend?
I am in the hi-fi trade
Status: Manufacturer
Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

wackyraces
Posts: 51
Joined: Wed Feb 24, 2016 11:06 pm
Has thanked: 0
Been thanked: 0
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post by wackyraces »

I'm not sure yet - but generally is there a mathematical rule I can work with?
System: AURALiC Mini - SPS DAC 3 - NVA P50sa / Croft 7 - Role Audio Enterprise

User avatar
savvypaul
Posts: 8634
Joined: Tue Oct 11, 2016 7:14 pm
Location: Durham
Has thanked: 1657 times
Been thanked: 2978 times
Contact:
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post by savvypaul »

I am in the hi-fi trade
Status: Manufacturer
Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

wackyraces
Posts: 51
Joined: Wed Feb 24, 2016 11:06 pm
Has thanked: 0
Been thanked: 0
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post 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.
System: AURALiC Mini - SPS DAC 3 - NVA P50sa / Croft 7 - Role Audio Enterprise

wackyraces
Posts: 51
Joined: Wed Feb 24, 2016 11:06 pm
Has thanked: 0
Been thanked: 0
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post 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.
System: AURALiC Mini - SPS DAC 3 - NVA P50sa / Croft 7 - Role Audio Enterprise

User avatar
savvypaul
Posts: 8634
Joined: Tue Oct 11, 2016 7:14 pm
Location: Durham
Has thanked: 1657 times
Been thanked: 2978 times
Contact:
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post by savvypaul »

Did Croft say why it needs to be 100k?
I am in the hi-fi trade
Status: Manufacturer
Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

wackyraces
Posts: 51
Joined: Wed Feb 24, 2016 11:06 pm
Has thanked: 0
Been thanked: 0
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post 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.
System: AURALiC Mini - SPS DAC 3 - NVA P50sa / Croft 7 - Role Audio Enterprise

User avatar
savvypaul
Posts: 8634
Joined: Tue Oct 11, 2016 7:14 pm
Location: Durham
Has thanked: 1657 times
Been thanked: 2978 times
Contact:
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post by savvypaul »

Only the things that matter, matter.
I am in the hi-fi trade
Status: Manufacturer
Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

wackyraces
Posts: 51
Joined: Wed Feb 24, 2016 11:06 pm
Has thanked: 0
Been thanked: 0
Great Britain

Re: Which pot for NVA passive? 10K, 50K, 100K ??

Unread post 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.
System: AURALiC Mini - SPS DAC 3 - NVA P50sa / Croft 7 - Role Audio Enterprise

Post Reply