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Old 10th September 2014, 04:09 PM   #1
Ensoniq is offline Ensoniq  United States
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Default Line level / unity gain vacuum tube circuits

Looking for simple circuits with vacuum tubes at line level, not preamp or amplifiers just so I can integrate a tube circuit before an amp for line level signals and have audio pass thru it.
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Old 10th September 2014, 04:29 PM   #2
DF96 is offline DF96  England
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For unity gain you need a cathode follower. In all cases this will add a little noise and distortion. In some cases it may also reduce the driving ability of the source. Only in unusual cases will it enhance the source and increase driving ability - typically where the source itself ends with a poorly designed valve stage.
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Old 16th September 2014, 06:39 PM   #3
Bigun is online now Bigun  Canada
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A simply buffer can be very handy if using a low impedance volume potentiometer. A simple approach that is popular is the Nelson Pass B1, all JEFT. You could make a tube version. Ideally, you want to use tubes with high transconductance, such as the 6DJ8. If you want to get fancy then look up some of the circuits by Allen Wright(?) - some of them are ultra-low distortion and will be close to transparent.
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Old 17th September 2014, 03:01 PM   #4
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Don't wanna get fancy at all haha. Want as simple as possible
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Old 17th September 2014, 03:35 PM   #5
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The simple as possible is probably to build the PASS B1 buffer. Although I've never compared them I expect it will give up nothing in comparison with a tube buffer.
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Old 19th September 2014, 04:52 AM   #6
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What about this 6n3 based 'buffer'?
DIY Amp Board Tube 6N3 Buffer Audio Preamplifier Pre Amp Board HiFi Amplifier | eBay
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Old 19th September 2014, 03:02 PM   #7
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As simple as possible is to have no buffer. Some 'buffers' are actually signal degrader units.
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Old 20th September 2014, 03:06 AM   #8
ammel68 is offline ammel68  United States
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Quote:
Originally Posted by Ensoniq View Post
I would avoid most of those eBay tube buffers as most are trying to operate the tube at voltages that are much too low. As a result, the tube is trying to work outside its ideal operating range.
Like transistors, tubes have to be biased correctly to sound their best. I don't know of many tubes that are happy with 24V going to their plates.
Not sure if there's a certain tube that's best suited for a buffer, but I've gotten great sound from the low gain(or mu) 6CG7.

You might get more replies if you post in the Tubes/Valves section under amplifiers.

Good luck...
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Old 20th September 2014, 11:24 PM   #9
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Just use this a direct coupled feedabck free fet input BJT output that has 1ohm output impedance at 80ma Class A buffer, the BUF03 it's magic. And is short circuit protected and can even drive low impedance headphones as well.

Cheers George
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Old Yesterday, 07:15 PM   #10
Ensoniq is offline Ensoniq  United States
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Originally Posted by georgehifi View Post
Just use this a direct coupled feedabck free fet input BJT output that has 1ohm output impedance at 80ma Class A buffer, the BUF03 it's magic. And is short circuit protected and can even drive low impedance headphones as well.

Cheers George
Is there any schematic for it?
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