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trustalbini 12th April 2003 09:45 PM

Tube Phono Preamp/Headphone Amp
Hi Everyone!

I'm new to the forum and have a question for all of the tube audio geniuses here:

I am in desperate need of a schematic for an amazing tube phono preamp with both RCA and headphone outputs.


-Warm sound
-Class A
-No Solid State circuitry
-Phono/RIAA optimized for a MM cartridge
-Zero Negative feedback
-dual mono operation (in one case)
-multiple tubes per channel
-1/4" Headphone Output w/impedence optimized for AKG 240M's
-Stereo RCA ins and outs
-2 BALANCED (3 conductor phone) 1/4" outs (line level)
-2 Volume controls (one for Main outs, the other for the headphone out)
-Standby switch
-Automatic bypass of "Main" RCA and 1/4" outs when headphone is inserted

I'm sorry for the endless list of requirements, but this is my "holy grail" DIY project and I'm thoroughly aware that this is probably the only place with the number of highly skilled tube enthusiasts required to create such a complex circuit. I hope you'll take on the challenge...

Good luck and thank you in advance!


paulb 13th April 2003 01:29 AM

Look for tube sites. The word bottlehead comes to mind. Or tubecad.

Joel 13th April 2003 02:51 AM

Re: Tube Phono Preamp/Headphone Amp

Originally posted by trustalbini
-Warm sound
What does "warm sound" mean? You mean you don't want the amplifier to be transparent? :confused:

trustalbini 13th April 2003 04:43 AM


What does "warm sound" mean? You mean you don't want the amplifier to be transparent?
-I'm simply implying that I would rather have a slightly higher level of THD than the absolute cleanest possible reproduction, as my power amp is very clean. I don't mind the distortion- I'm a guitar player who's used to hearing alot of hiss anyway:)

fdegrove 13th April 2003 11:32 PM



What does "warm sound" mean? You mean you don't want the amplifier to be transparent?
Hmmm, sounds a bit odd coming from Joel but maybe he made a u-turn after all.:clown:
Transparent SE designs a far and in between, most of them tend to be rather euphonic in nature.

When people refer to 'warm" sound they often refer to a distortion spectrum with predominantly even order harmonic content.

The harshness that's often heard when listening to transistor designs is mainly due to the predominantly odd harmonic content
of the distortion spectrum.
Add to that the fact that tubes tend to clip more graciously than transistors and you get the picture.


analog_sa 14th April 2003 08:27 AM


Tube enthusiasts or not i somehow doubt anyone will come up with the bespoke circuitry you're looking for. Why don't you split your pursuit into a RIAA stage and line/headphone amp and do the switching arrangement the way you want it?



Joel 14th April 2003 01:41 PM

Re: Tube Phono Preamp/Headphone Amp
Dan, I see no one's helping you out? You can find an RIAA stage schematic in any tube manual, and there are a few in the radiotron handbook.
As far as a class A headphone amp, well that's no problem. There are hundreds of schematics on the internet, and on this forum. I don't know what the impedance of your AKG's is, but any good design should drive almost any set. And actually there is very little difference between a "preamp" and a "headphone amp" - usually just the size of the output capacitor.

"Warm sound", I already covered. ;)
You'll rarely find a headphone amp with NFB.
Dual mono - this is a waste of money.
Multiple tubes per channel - this depends on the circuit, no?
Transformers? On the outputs you mean? Not necessary.
Balanced outputs - why?
Standy switch - this is a hi-fi son, not a guitar amp.
Getting a switching jack to short the RCA outs is easy, and cheap. Just tack it on to the schematic you choose.

You can rummage through,
or use Search here at the forum and look for schematics of headphones and preamps.

Hope that helps a little.


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