View Full Version : Help me understand...passive preamps
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?:confused:
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?:scratch:
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?:scratch:
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
28-03-2008, 16:09
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 (http://theartofsound.net/forum/showthread.php?t=52) for pictures and a bit of info. Let me know. :)
Filterlab
28-03-2008, 16:10
It should work very well with your NVA power amps btw. :)
Richard wil no doubt be along shortly!
Wil no boubt?
Aye, boubt de doubt indeed!
Ish tat de lingo where yew come from? :lol:
Marco.
Filterlab
28-03-2008, 16:47
He knows a thing or two about passives. ;)
Filterlab
28-03-2008, 16:47
No boubt?
Aye, boubt de doubt indeed!
Ish tat de lingo where yew come from? :lol:
Marco.
As you posted I corrected the spelling. :D
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?:confused:
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?:scratch:
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?:scratch:
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.
And I freakin' edited my response again to take into account his other typo!! :lolsign:
You just cant get the staff these days, can you?
Marco.
P.S Bloody ace avatar of Richard's there, Rob!
There is nothing wrong with my spelling ability you clowns!
However, if we are talking typing skills then that's a different matter altogether !!! :confused:
I will take criticism from Marco when he learns how to use a soldering iron. :lolsign:
Filterlab
28-03-2008, 16:59
P.S Bloody ace avatar of Richard's there, Rob!
His own work mate. :)
Filterlab
28-03-2008, 16:59
Apologies to Alan for slight thread hijack, please resume.
An adenda to my first post. Obviously my findings are with NVA power amps which are designed to be used with a passive pre. With power amps designed to be used with an active pre you may find the TVC better than pot or sa based passives. This is due to matching and interface considerations.
No problem & thanks for the response.
Richard, I am very interested in your reply (notwithstanding my limited understanding). I was sure I remembered seeing some TVCs in you ebay showroom, now I see why they aren't there now.
It certainly helps me try and weigh up whether a cheap TVC is worth a punt over a good stepped attenuator model. I wish I were in a financial position to weigh it all up for myself, but I'm not. So this is another vote for 'the new way' of buying Hi-Fi.
Regarding the response of my amps as the volume increases, I must stress it is just my perception. No-one else has ever commented on it. Perhaps bigger amps on the bottom?
Plenty to think about for now (thanks also Rob), will check in again tomorrow.
An adenda to my first post. Obviously my findings are with NVA power amps which are designed to be used with a passive pre. With power amps designed to be used with an active pre you may find the TVC better than pot or sa based passives. This is due to matching and interface considerations.
300 posts - congratulations! I may need to think of ditching the top amps to fund a nice P90sa, but I would then certainly want to add A80s in place of A70s.
However I am wary of losing any of the magic I enjoy at the moment, and I have no way of knowing how much of it is down to the Bi-amp configuration.:scratch::confused:
There is nothing wrong with my spelling ability you clowns!
Which is why I wrote:
And I freakin' edited my response again to take into account his other typo!!
Eejit! :lol:
I will take criticism from Marco when he learns how to use a soldering iron
You'll have a bloody long wait then!
:flasher:
Sorry, Alan, as you were...
Marco.
300 posts - congratulations! I may need to think of ditching the top amps to fund a nice P90sa, but I would then certainly want to add A80s in place of A70s.
However I am wary of losing any of the magic I enjoy at the moment, and I have no way of knowing how much of it is down to the Bi-amp configuration.:scratch::confused:
Ah! now I know who you are ;)
Most is down to bi-amp as I told you, what you have in bi-amp is better than two 80's, and better than just two 70's with P90sa.
Wait until you can afford to trade in the P50 for P90sa. Only then upgrade the amps as and when you want and can afford. Don't move away from bi-amp, retrograde step.
Anyway I am not here to promote NVA so any question for me then back channel please. Any others can comment at will.
300 posts 'struth, I should shut up more. :mental:
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