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Old 18th February 2003, 01:50 PM   #1
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Default Simple tube preamp...

I am looking for a very simple but good tube preamp. If possible, with only one tube per channel. No output transformer.
I would be happy if the preamp could be used as a headphone amp too.
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Old 18th February 2003, 03:10 PM   #2
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Default PREAMP.

Hi,

You can have a look at this one for instance:

JOEL'S ALL PURPOSE PREAMP

Cheers,
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Old 18th February 2003, 04:43 PM   #3
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Maybe this one will work?
Anyone having some PSU recommendations?


http://hjem.get2net.dk/aaholm_audio/schems/6dj8_1.htm
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Old 18th February 2003, 05:16 PM   #4
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Quote:
Originally posted by chrille
Maybe this one will work?http://hjem.get2net.dk/aaholm_audio/schems/6dj8_1.htm
Nope. If you want a line pre as well as a headphone amp, that one won't work. It's output Z = 4k8 and gain (into a high Z load) will be about 20. Probably fine as a line amp on it's own, though it wouldn't be my first choice. A headphone amp requires quite a lot of drive capability into low impedance loads. A single tube, without a transformer is too big an ask, esp if you want to drive something like Grado's (32 ohms?), and presumably want to have some gain in the stage.

Joel's schem Frank linked above would be better than the one you linked.
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Old 18th February 2003, 05:46 PM   #5
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Default HEADPHONE AMP.

Hi,

Quote:
If possible, with only one tube per channel
That is certainly possible.
The drawback is that you will have to use octal or novar types of dissimilar triodes such as a 6EW7,6GF7 etc.

One of the triodes can be used for voltage amplification and the other as the poweramp part.

If you need to keep things small then there is this one :

http://www.diyaudio.com/forums/showthread.php?s=&threadid=10984

Cheers,
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Old 18th February 2003, 06:14 PM   #6
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Frank,

You're right. I was thinking of a single triode/pentode per channel, not a dual in a single envelope. At a glance, the 6EW7 looks like a good possibility for a setup similar to Joels, ie CC->CF. Or what about a 6080 / 6AS7 SRPP? :-)

Cheers
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Old 18th February 2003, 08:21 PM   #7
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I think I give this circuit a trie
(I can build a headphone amp separate instead)

http://hjem.get2net.dk/aaholm_audio/schems/6dj8_1.htm

Its cheap and very very simple... perfect for a tube beginner like me.




BUT I dont know which PSU I am going to use?
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Old 18th February 2003, 09:09 PM   #8
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Years ago I made a little preamp...I call it my Experimenting Chassis because I have B+, heater and ground wires lead out externally for the breadboard...

Drives a 5k load fine...not too much gain overall though, not with the tone circuits in.

BTW if anyone was curious about the tone circuit in my 6L6GC SE amp, this is where I developed it.

Mods I recommend:
- Increased coupling caps.
- Seperate cathode bias, and more bias (1k per cathode), likewise smaller plate resistors (circa 100k).
- Higher voltage - a single, purpose-built transformer would function better than the current arrangement. If nothing else, a larger 2nd transformer and a voltage doubler.

DC filaments if you feel adventurous...maybe a cathode follower output instead...

Tim
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Old 18th February 2003, 09:44 PM   #9
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Default 6080.

Hi Brett,

Quote:
Or what about a 6080 / 6AS7 SRPP? :-)
A Sovtek 6AS7G could do, the others may cause trouble with cathode bias...

Either way, it won't have much gain to play with.

Cheers,


P.S. You are aware that most people want to burn off lots of gain,aren't you?
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