Help me understand...passive preamps

[Alan]

Hi everyone, hope this isn't too boring for you, but I'd appreciate some of your experience. I'm currently Bi-amping some NVA monos, and I'm very happy. Most of my listening is done at low to medium levels (small house, small children), so what type of passive pre would you advise, and why?

The P50 I currently use is single cermet volume pot. As I understand it, with Bi amping I need to look at left/right volume control.

If I use a better quality pre, say a twin volume stepped attenuator, there must be improvements to be had in terms of imaging etc, right? But won't those resistors be an issue at low volume? I already note that I need a certain volume, above what is often possible at home, to really have the music open out, and for the bass to extend nicely. Admittedly this depends on the recording, but I'm no bass-head really.

So then, what about a TVC? If I've understood what I've read correctly, the principle benefit would be maximum efficiency at lower volumes, with such benefits diminishing the higher the volume goes. Am I right?

Glasshouse TVCs, although single control, are quite reasonable, but Promitheus audio (malayia) seem to be astonishingly cheap, confusing as their website is. The exchange rate makes this seriously worth considering, if nothing else.

I guess the nub is this: Better a decent twin stepped attenuator pre like the NVA P90sa (see ebay), or a cheaply specced (possibly) TVC from Malaysia?
I look forward to your thoughts and experiences, thank you for your time in helping me understand. Forums such as this are invaluable for those of us on tight budgets.

[Filterlab]

Well until I changed my system around I was using a passive pre-amp which consists of two Intact Audio autoformers (one for each channel) mated to a single volume control which is basically two 24 position stepped switches. It is consistent at every volume setting, certainly I've never noticed any change in the sound quality at the different levels.

Each system has its own merits, but there is no greater judge than you and your lugs. I tried a few passives but the one I settled on did it for me. If you want to have a go with it you're welcome to borrow it and try it out, it's a single stereo input/output but then who wants source switching getting in the way?

Have a look at the advert in the for sale section for pictures and a bit of info. Let me know.

[Filterlab]

It should work very well with your NVA power amps btw.

[Mike]

Richard wil no doubt be along shortly!

[Marco]

Wil no boubt?

Aye, boubt de doubt indeed!

Ish tat de lingo where yew come from?

Marco.

[Filterlab]

He knows a thing or two about passives.

[Filterlab]

No boubt?

Aye, boubt de doubt indeed!

Ish tat de lingo where yew come from?

Marco.

As you posted I corrected the spelling.

[WikiBoy]

Hi everyone, hope this isn't too boring for you, but I'd appreciate some of your experience. I'm currently Bi-amping some NVA monos, and I'm very happy. Most of my listening is done at low to medium levels (small house, small children), so what type of passive pre would you advise, and why?

The P50 I currently use is single cermet volume pot. As I understand it, with Bi amping I need to look at left/right volume control.

If I use a better quality pre, say a twin volume stepped attenuator, there must be improvements to be had in terms of imaging etc, right? But won't those resistors be an issue at low volume? I already note that I need a certain volume, above what is often possible at home, to really have the music open out, and for the bass to extend nicely. Admittedly this depends on the recording, but I'm no bass-head really.

So then, what about a TVC? If I've understood what I've read correctly, the principle benefit would be maximum efficiency at lower volumes, with such benefits diminishing the higher the volume goes. Am I right?

Glasshouse TVCs, although single control, are quite reasonable, but Promitheus audio (malayia) seem to be astonishingly cheap, confusing as their website is. The exchange rate makes this seriously worth considering, if nothing else.

I guess the nub is this: Better a decent twin stepped attenuator pre like the NVA P90sa (see ebay), or a cheaply specced (possibly) TVC from Malaysia?
I look forward to your thoughts and experiences, thank you for your time in helping me understand. Forums such as this are invaluable for those of us on tight budgets.

The single volume control pot (potentiometer) in the P50 is two volume controls attached to a single shaft, it is called dual ganged (stereo).

The twin volume control pots in the P90 are two volume controls attached to seperate shafts, it is called single ganged (mono) but there are two of them.

Advantage is seperation. Any electrical component creates a field and to have two in close proximity carrying seperate signals that field will crosstalk between them.

In the case of tvc then field generation is even more so as that is the primary function of a transformer, to use field generation and transmission between two dissimilar windings to (in this case) lower volume.

A stepped attenuator is better than a pot because it doesn't have a track as the resistive element. Track generates more field and doesn't have the accuracy of signal transistion as a pair of resistors. An sa is just discrete resistors wired accross a multi position switch. Now the other beauty of a stepped attenuator is you can use higher quality resistive material (resistors) than you can get in a pot track. The best pot track is cermet (ceramic metal) most are plastic film, which means a resistive metal oxide film is *printed* onto that plastic film which is then used to make the track of the pot. I was dubious about these claims for high quality resistors until I tried Shinko resistors in dual mono switches as used in the P90sa, but then I was convinced.

So in my opinion, and I make the P50 and P90, the Shinko sa in the P90sa is better than any TVC I have heard. I have tried three sets of transformers for TVC operation, I was even going to make one, but withdrew it in dissapointment. I have tried the Malaysian ones, some US ones and the Stevens and Billington ones. The Shinko sa is better.

PS - P50sa doesnt use Shinko it uses Holko resistors which are good but not as good.

[Marco]

And I freakin' edited my response again to take into account his other typo!!

You just cant get the staff these days, can you?

Marco.

P.S Bloody ace avatar of Richard's there, Rob!

[Mike]

There is nothing wrong with my spelling ability you clowns!

However, if we are talking typing skills then that's a different matter altogether !!!

I will take criticism from Marco when he learns how to use a soldering iron.