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Old 14th November 2003, 08:23 AM   #1
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Question Tube mic preamp

I have seen this schem on the web, but i've lost the original file (but i printed it, this is a scan) an where it was...!

- Is there anybody who know this schem ?

- How can I put a gain pot ao switch ?
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File Type: gif tubepre.gif (10.7 KB, 207 views)
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Old 14th November 2003, 10:36 AM   #2
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here's the link:

http://alterneo.free.fr/tubepre.GIF
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Old 14th November 2003, 12:28 PM   #3
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Hi,

Quote:
- How can I put a gain pot ao switch ?
You could replace the 1M gridleak resistors at the input with a 500K stereo volpot.

A switch to do what?
If it's for source selection you can fit it at the inputs as well.

Cheers,
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Old 14th November 2003, 12:44 PM   #4
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it's nice..pretty simple...but the voltage used is pretty high...
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Old 14th November 2003, 12:53 PM   #5
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Quote:
You could replace the 1M gridleak resistors at the input with a 500K stereo volpot.
...really, not after the first 12AX7 ?

Quote:
A switch to do what?
to switch the gain (ex: 6-12-18-24-... dB)
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Old 14th November 2003, 01:08 PM   #6
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Default I don´t think so...

Transformerless? 12ax7 cathode follower? no.... it´s not "nice" for a mic preamp. Use a transformer balanced circuit, like this one instead:

http://www.gyraf.dk/gy_pd/g9/g9pd.htm

Or, if you need to go transformersless, just use this one:

http://www.iclr-sch.com/results.aspx...%3fID=13749966

This one will give you a low impedance input!!!
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Old 14th November 2003, 01:20 PM   #7
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Quote:
http://www.gyraf.dk/gy_pd/g9/g9pd.htm
yeah, i know this one...

your 2nd link is dead...
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Old 14th November 2003, 01:36 PM   #8
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Hi,

Quote:
to switch the gain (ex: 6-12-18-24-... dB)
If you're using a stepped attenuator, go for a series type.
By doing so you keep the load constant and you can put it where you like: in front of the first stage or inbetween the two stages.

6 dB steps are quite coarse but that's up to you.

Regarding the CF at the output, you can easily convert it to use a different tube or even opt for a WCF.

Cheers,
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Old 14th November 2003, 02:45 PM   #9
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Default second link again

Yes. This is dead.

This is the right one:

http://dogstar.dantimax.dk/tubestuf/graphics/shroom.gif

...
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