[fine]

Hi!
I need some thoughts from you guys....
I want to build a line preamplifier and my option will be:

1-Tribute inductive volume control.
http://www.tribute-audio.nl/
Tribute volume control is wound as an autotransformer, which means that a single, tapped coil is used.
2-Bent audio TX-102 transformers.
3-Django Silk transformers.
4-Dact attenuator follow by BUF634T buffer stage with serious power supply.
5-active preamp based on single tube....something like Euridice preamp:
http://www.fortunecity.com/rivendell/xentar/1179/projects/euridice/Euridice.html

All this because I have more than 1 meter of interconnect cable (aprox.3meters) and I can't go with single Dact or similar attenuators?
What do you think?
Thanks in advance.

[*Scotty*]

fine, My vote would be to try option no.4,Dact attenuator follow by BUF634T buffer stage with serious power supply.
I am biased toward this option because it is the least expensive project listed and I am using something similar for my preamp a Superphon RevIII
which is a discrete Class A buffer. See link http://superphon.com/
 If the BUF634T chip sounds good you could beat the other alternatives on your list by a healthy margin.
Good luck with your decision.
Scotty

[fine]

Thx. Scotty.
I read a little about some "mark" made by TVC's.Is really hard to choose the right direction.
The BUF634T like any other buffer could bring me fiss or also mark-mudding to Dact.



Also have anyone hear about this guys?
German quality...

http://www.silvercore.de/index.php?produkte_de

[refmedia]

No affiliation but these guys make a couple of passive pre amps that seem cool! They are proaudio though.
www.smproaudio.com

[richidoo]

fine
Maybe audition or borrow some good quality active pres before committing to passive, just to get an understanding of what they can do. Many sources really don't have enough clean fast power to properly buffer cables and low impedance amp inputs by themselves. If signal passes through a load with insufficient current it will be changed, and cannot be restored by stout power stages later in the chain. The low level signal preservation is the most critical thing and having plenty of current buffering around helps more than pristine silver wire, teflon caps blablabla, none of which can source current, they only mitigate losses. You need both for high end audio quality, clean signal path, and fast current sources. The best preamps have enormous power supplies to get enough headroom to buffer low level signals with no transient distortion at all. Few sources have that kind of fast power supply. An active preamp is gives an easy load to those wimpy source buffers to prevent signal loss on the way to the preamp, and then provide enough juice to drive anything that might come after without distortion. Active preamp is essential to me, but the best are very expensive. The best actives are better than any passive solution. The mid priced active preamps often pervert the signal audibly while buffering it which is why the passive craze has taken off, it is price driven, and gives a better sounding attenuation than pots used in mid priced active pres. But building your own active preamp can tilt the money/quality equation in your favor. A great quiet circuit like Aikido with lightning fast battery or Paul Hynes regulated power supply, and Goldpoint or LDR attenutation and some thoughtful shielding can get you into the $5000+ preamp category for <$1000.
Rich

[KT]

I like Scotty's idea of trying out the attenuator with buffer first. It'll give you a good baseline of sound for not a ton of money. You may even like it well enough to use it as your long-term preamp.

In case you haven't already read it, here's a link to Corey Greenberg's Buffered Passive Preamp article from 1991 Stereophile: http://www.stereophile.com/reference/54/index.html

I has a lot of good recommendations, like using the high speed rectifier diodes (now common, but this is the first time I saw it recommended in a DIY article), star grounding, and independent dual channel rectification. The preamp is built around the discontinued BUF-03, but it's essentially the same idea. A good read if you're interested in building the buffer.

There are also a lot of articles on the web for building a pre based on the OPA627 followed by a BUF634. I modified an old Adcom GFP-565 preamp to this configuration and it sounds really good! Definitely not a tubey sound, but clear, engaging, and musical.

If you do want a slightly warmer sound for the buffer, you might look at the PEC molded carbon pots. Last time I looked, Digikey carried them. Great sound, but hard to get one that tracks both channels accurately.

Good luck,
KT

[fine]

Yes I read Aunt Corey' article some time ago.Also on diyaudio about OPA + Buf634T and PEC problems.
There are weaks and strengths.I want to compare straight with a wire.This is pure sound from an preamp.Not a muddy one or something "similar".With tubes is very difficult to reach that.
I have two monoblocks pp tubes (something totaly transparent and definitely not tubby gear sound) and also solid state with laterals mosfet's.Also an active cross only for bass-dipole-Eminence Alpha 15A.Open baffle speakers -Supravox-Fostex T925A.
I like the neutral sound....probabily don't exist such thing.....

http://forum.audiofil.ro/index.php?topic=571.0
http://forum.audiofil.ro/index.php?topic=569.0
http://forum.audiofil.ro/index.php?topic=566.0

In all this system I need a selector source and a good passive-active preamp to drive my 3 meters of interconnect cables.
Also I'm thinking into ladder attenuator (with Shallco or Grayhill-military switch) folow by a buffer but I need something with "zero" noise....and two separately psu ..I have high spl on speakers and BUF-03 is not a proper noiseless buffer for my speakers.
I don't want to build another preamp soon and your guidance is appreciated.


KT
Please compare OPA+BUF with a straight wire and tell us the results.Listen that with a very short interconnects cables between output of your preamp and input of the amp.
What Buf634 do you have used?....634T?

[Gordy]

Fine, are you familiar with this stepped atten/source selector?  http://www.vaneijndhoven.net/jos/switchr/design.html

[fine]

Gordy
Do you,or others,know more about this implementation:
-T or bridget-T into audio "passive" topology?

http://www.diyaudio.com/forums/showthread.php?postid=1361130#post1361130

[Steve Eddy]

Do you,or others,know more about this implementation:
-T or bridget-T into audio "passive" topology?

Problem with those is that the input impedance and output impedance are the same. So if you want the input impedance to be 10k ohms in order to provide an easy load for the source component, you also have a 10k ohm output impedance, compared to a simple 10k ohm potentiometer which will give you a 10k ohm input impedance and a worst case 2.5k ohm output impedance.

se

[fine]

Steve...I know you have some experience in using 1:1 transformers folow by a pot. or stepped attenuator.Electraprint have some products:
http://www.electra-print.com/pva.php
What do you think it will be the weakness of this design comparing with attenuator + buffered option?
 

[fine]

There is some time...but I finished my preamp.
I used a 41 steped attenuator TKD model 2P65CS + BUF03AJ (MIL.),ultrafast diode,silver connects,Elma switch,etc.

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=1627



..2 pages.