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passive preamps

post #1 of 24
Thread Starter 
I'm looking for a killer passive preamp design that is as simple as possible (less crap in the signal path to degrade the sound). I figure a good circuit in addition to a quality stepped attenuator and premium resistors will pass on the resolution to the amp with the sound unaltered (transparent).
post #2 of 24
A&M, I haven't really audition these products personally, but from what I read in AudioAsylum, these seems to your description.

http://www.placetteaudio.com/

http://www.ftaudio.com/
post #3 of 24
I don't know much about circuit design stuff, but I have been using Adcom's "Straight Line Controller" SLC-505 as a passive preamp. I had always noticed some background noise with even high quality preamps. It wasn't much but it was there. With this design, there is nothing at all. They don't make this product any more but I have seen them on Audiogon in the $100-$125 range (I think they were $150 new). Their new audiophile preamp, the GFP-750 (I think that's the number) is a preamp that can be switched to a fully passive signal path.
post #4 of 24
http://www.bentaudio.com/



Passive preamp using Stevens and Billington transformer volume control.
post #5 of 24

Make transformer volume control

Transformer volume controls (TVC) are better than any other passive design. The trick is that no energy is wasted as a heat.

I made one last year, and I am very satisfied. To me sounds better than any other preamp I have ever heard, passive or active.



More pictures you can find here.

There are two manufactures so far:

Sowter and
Stevens & Billington

I used Sowter units with great success.

For details, search at Audioasylum.com.

Mirko
post #6 of 24
I wish I could give advice based on experience. But I've never used a passive preamp.

I've read good reviews of the Channels Islands VPC-1 and at $249 it seems to be reasonably priced.

http://www.ciaudio.com/vpc1.html
post #7 of 24
Thread Starter 
I don't care for Adcom gear. =\
tim and mirk, thanks for the suggestion, but all that wiring inside scares the hell out of me, I can't help but think that I'd lose dynamics and resolution.

Now the VPC-1 is almost exactly what I'm looking for. I wonder if I can order that with a stepped attenuator, that'd be awesome. What I originally had in mind was perhaps building a passive pre using a DACT CT2 stepped attenuator and Audio Note tantalum or Vishay VSH or S102 resistors.

Gallaine - thank you so much, I am going to see if I can get this in kit form, or if I can get one modded.
post #8 of 24
Found on http://www.uhfmag.com/MiscAccessories.html:

Passive preamplifiers

Designers go to a lot of trouble to make preamplifier circuits sound neutral, but what if you could skip the circuitry altogether? You can...with a passive preamplifier, which doesn't actually amplify.
The Antique Sound Lab T1DT is different from any we've ever seen. Instead of using a conventional volume control, it uses a pair of transformers, with multiple taps that are selected for different volumes. Because it has a low impedance output (below 1 kilohm at most settings) it works with all amplifiers, and is less sensitive to cable characteristics than other passives. It is full-sized, with four inputs plus a tape loop. At $575 it will outperform most preamps costing three or four times as much.



See also: http://www.divertech.com/passiveti.html
post #9 of 24
Thread Starter 
VPC-1 suits my purpose just right, gonna rip that pot out and replace it with a goldpoint stepped attenuator.
post #10 of 24
Don't be in such a hurry! How about that?:

http://www.audio-consulting.ch/sr_pot.htm
post #11 of 24
Thread Starter 
Look how simple this is:
http://www.hometheaterhifi.com/volum...el-2-2002.html

It's precisely what I had in mind.
post #12 of 24

Re: passive preamps

Quote:
Originally posted by Audio&Me
I figure a good circuit in addition to a quality stepped attenuator and premium resistors will pass on the resolution to the amp with the sound unaltered (transparent).
I had the LW-1 in my old system. Theory and so called transparency is one thing, and real system synergy is another. Sometimes a good gainstage will compliment a system quite well.
post #13 of 24
Thread Starter 
http://www.goldpt.com/vcb.html
even better. No need to swap out the volume control.
SA-3 w/ ladder type vishay stepped attenuator.

pigmode, of course, if it doesn't work out, I can always sell it on audiogon. I can get my eta42 modded to a preamp if need be,
post #14 of 24
That's what I did (audiogon). The Fi X 2A3 amp I have now has built in passive controls. I'm looking for a complimentary linestage since I am running low gain 45 type DHTs.
post #15 of 24

Wiring is very simple

All those wires above are just multiple outputs. What you have is transformer with one input and multiple outputs. Sowter 9335 have 26 outputs, from -50 dB to 0 dB in 2 dB steps.

Wiring is very simple.

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