For Sale: Passive pre-amp.

**Filterlab** · 28-01-2008, 19:47

My gorgeous transformer based passive pre-amp as featured in the DIY thread.

Wonderful natural and clean sound, nice heavy control, one in one out. Simply not needed anymore.

PM me.

**Gromit** · 29-01-2008, 13:53

Looks gorgeous!

I'm being a typical technophobe here (please bear with me!) but how does a transformer-based passive pre work? I notice NVA are now building their pre's with transformer volume controls and wondered how they work.

Sorry for the thread hijack!

**Filterlab** · 29-01-2008, 14:12

Originally Posted by Gromit

Looks gorgeous!

I'm being a typical technophobe here (please bear with me!) but how does a transformer-based passive pre work? I notice NVA are now building their pre's with transformer volume controls and wondered how they work.

Sorry for the thread hijack!

Cheers!

Very basically:

At varying points of the transformer windings there are different attenuation values (increasing with the number of windings) and are accessed by the pins on the transformer housing.

These points are spurred off to the volume switch which is usually a 24 position switch and as each position is selected the attenuation is reduced and the volume increases.

This one certainly works very well indeed and is very natural and transparent. Its only requirement is a low impedance input (say 50 ohms from a source) and a high impedance input on the power amp (say 50 Kohms). The ratio should really be no lower than 100:1 but preferably closer to 1000:1.

**Gromit** · 29-01-2008, 15:16

Thanks for that - looks like a very elegant and clever way of doing things (and even I understood it).

Makes sense that it would sound good.

**Filterlab** · 31-01-2008, 21:44

**Filterlab** · 31-01-2008, 22:51

Any offer considered - no matter how daft!

Go on, have a go with it. You'll be amazed!

**Filterlab** · 06-02-2008, 14:21

Well I paid £350 for it last year, obviously I'm not looking for that much, around a couple of hundred-ish?

**pure sound** · 06-02-2008, 19:12

sounded considerably better than the MFA (silver) to my ears. Didn't ring either! (I borrowed briefly before Rob had it)

Sastus,

The original metal case was RS part No. 364-1632

http://uk.rs-online.com/web/search/s...duct&R=3641632

**Filterlab** · 06-02-2008, 21:38

Cheers matey! Sounds like you know more about it than me. LOL!

**Filterlab** · 13-02-2008, 12:22

Going up on eBay this weekend.

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