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Old 19th November 2012, 04:01 AM   #1
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Default Want to make a tube preamp

I am a total newbie to tubes and would like to make a tube preamp. I was planning to make a headphone amp first, but due to output transformers availability (or rather lack of), its probably going to be delayed.

I dont need gain as I mainly use cd players and sound cards. No vinyl yet. My amp right now is a topping tp20 and yammy 663. I will probably replace the tp20 with myref revc in near future, and someday maybe a tube amp. This is going to be mainly for my desktop system. I already have a pass B1 for my other system.

I have the following tubes with me. If there is a very good design without these, i could try to get some other different tubes, but would prefer if I could manage with some of these.
ECC81, ECC82, ECC83, ECC88, 12AU7A, 5751, ECL86, PCL86, ECL82, PCL805. I have some more, will list those later.

For rectifier, I could get my hands on some of these - gz34, 5au4, ez81, PY88, 5U4, 5y3

For power transformers, it will be difficult to get a ready made trafo, I could get one custom wound. I could easily get my hands on an isolation trafo (230v) or a step down to US voltage trafo (230-110v). For heater, i can easily get a separate trafo of integer voltages 5,6,7,8... volts. I also saw one company making 6.3v upto 3A, so might try that. Pre built ones will be EI, but for custom wounds, i can go with any of EI, torroidal, R-cores. Any special care needed to use multiple power transformers? Which ones are recommended.

I would also prefer a simple design. I have a problem doing layout of complex p2p circuits, these very quickly become a mess and get out of hand. I need more experience.

Please suggest some design that can fit these needs. I would also need a power supply design to go with these.
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Old 19th November 2012, 05:20 AM   #2
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As you stated, you don't need gain. A "unity" gain buffer will do the job. In tubed circuitry, what's needed is a cathode follower in each channel. High transconductance (gm) makes for good cathode followers.

Among the types you listed, the 6DJ8/ECC88 has the highest gm. That type operates with approx. 90 V. on its plate. "Best" results with cathode followers are obtained with a bipolar PSU and constant current sink (CCS) loading. As long as a DC offset is not present at the I/P, the only capacitor in the signal path is at the circuit's O/P. Forget about vacuum rectification. A power trafo with a 125-0-125 rectifier secondary and 4X 600 PIV Schottky diodes takes care of the bipolar PSU. Add some electrolytic caps. and a couple of chokes and you're in business.

BTW, the 6GW8/ECL86 is scarce. You can sell them to fund part of the cost of this 1st project.
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Old 19th November 2012, 08:03 AM   #3
aeandm is offline aeandm  Ukraine
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Hi, I made an amplifier for mobile phones
on 6F12P (Soviet lamps) triode and pentode,
triode with a gain of 100 (0.25 X100)
pentode as a cathode follower, the output
any power transformers (220) rated at 10 watts, with
output voltage of about 10 volts.
The power transformer capacity of at least 20 watts,
two windings, 6.3 (1.2 A) and 250 (0.05 A), the rectifier
semiconductor, power supply, a separate unit,
no background at all, superb sound (CBS-15)
look for the scheme, have to drive somewhere.
Success, aeandm
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Old 19th November 2012, 08:34 AM   #4
Gost22 is offline Gost22  Bolivia
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Hi all!
What is best for the amplifier with LM3886 for i to get the tube/valve sound ?
Preamp (line-stage) or buffer with PCC88?
thank you!
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Old 19th November 2012, 12:38 PM   #5
DF96 is offline DF96  England
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Haven't you already asked this question in another thread?
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Old 19th November 2012, 06:14 PM   #6
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Quote:
Originally Posted by Gost22 View Post
Hi all!
What is best for the amplifier with LM3886 for i to get the tube/valve sound ?
Preamp (line-stage) or buffer with PCC88?
thank you!
For the best "tube sound" buy a guitar pedal .
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Old 19th November 2012, 06:35 PM   #7
TheGimp is offline TheGimp  United States
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This is a general question and not aimed at the OP or anyone else. Why do people build preamps?

I have a tube amp that can be driven from my cd player, tape deck, TV, etc .

I understand the utilitarian nature of a selector for this purpose. If the tube amp input impedance were low I could see a buffer might be necessary if the sources could not drive the amp. And possibly buffers might be useful to reduce noise pickup from the selector signal inputs (although I'm not sure on even this).

Unless gain is needed, why build a preamp at all (either tube or SS)?
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Old 19th November 2012, 06:41 PM   #8
SY is offline SY  United States
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A preamp is rarely needed these days, and when it is, generally unity gain is sufficient. I use a buffer (a real buffer, not a badly designed gain stage) to get me high common-mode rejection and the ability to drive multiple inputs from multiple sources that a simple potentiometer and switch won't allow.
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Old 19th November 2012, 06:43 PM   #9
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by TheGimp View Post
Unless gain is needed, why build a preamp at all (either tube or SS)?
I have tried it a couple of times , in the past
and have to say, a very simple and cheap tube pre/buffer could do wonders, or almost
to do the same with SS pre in those days would have been almost impossible, or very expencive to buy
but today ? I'm not sure
how about 'Juma's sit trioda' ?
that said, a tube pre can also screw up things
you need to make sure your load impedances are up to it, meaning high enough
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Old 19th November 2012, 06:48 PM   #10
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by SY View Post
A preamp is rarely needed these days, and when it is, generally unity gain is sufficient. I use a buffer (a real buffer, not a badly designed gain stage) to get me high common-mode rejection and the ability to drive multiple inputs from multiple sources that a simple potentiometer and switch won't allow.
you are not using passive att pot, are you ?
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