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Old 9th September 2004, 03:35 AM   #1
TobWen is offline TobWen  Germany
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Question 12AX7 sound ... going with the trend

Hi there,

I have read a lot of interested things in this forum.
Normally, I'm working with OPAs to get amplification (preamps etc.), but now I want to go with the trend and build a combination!

The problem is: In this forum, you're mainly discussing about power- or phono-amps ... I need something with LINE-level without amplification...

In detail:
Behringer (ugly, I know) has two models of solid-state based mic-preamps with tube-stages:

http://www.behringer.com/MIC100/index.cfm?lang=ENG
http://www.behringer.com/MIC200/index.cfm?lang=ENG

It's build on NJM4580-amplification with a 12AX7.
AFAIK the 12AX7 doesn't do any amplification - it only makes the tube-sound and distortion.
So you cannot call it a tube-amplifier, like Behringer does!

Does anybody have some schematics of the tube-effect only?
The input should be a line-signal and the output should be the same.

Is that the correct way to go?
http://www.dogstar.dantimax.dk/tubestuf/mchowit.htm

Best regards,
Tobias
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Old 9th September 2004, 04:23 AM   #2
Optical is offline Optical  New Zealand
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im interested in this stuff too, but nobody who is really into tubes has much to do with it unfortunatly

check this website out also

http://www.paia.com/tubestuf.htm

a tube compressor/limiter without the use of complicated hard to find transformers/led-ldr combos is what i would really like to see!
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Old 9th September 2004, 04:25 AM   #3
TobWen is offline TobWen  Germany
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I don't think that Behringer uses ANY kind of transformers ...
They never did and they never will :-)

The schematics are hard to get and I can't spend 50 EUR to buy this thing now :-(
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Old 9th September 2004, 05:30 AM   #4
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Quote:
Originally posted by Optical
im interested in this stuff too, but nobody who is really into tubes has much to do with it unfortunatly

check this website out also

http://www.paia.com/tubestuf.htm

a tube compressor/limiter without the use of complicated hard to find transformers/led-ldr combos is what i would really like to see!

Very interesting indeed!
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Old 9th September 2004, 05:36 AM   #5
TobWen is offline TobWen  Germany
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hehe ... interesting:
The 12AX7 is "powered up" with +45V only :-)

Standard is 245V, I think :-)
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Old 9th September 2004, 05:47 AM   #6
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Quote:
Originally posted by TobWen
hehe ... interesting:
The 12AX7 is "powered up" with +45V only :-)

Standard is 245V, I think :-)

There is a link in the site that says something like "Starving" the tubes. That maybe the reason for the +45V.
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Old 9th September 2004, 06:09 AM   #7
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"Starved plate" is a great way for fuzz, but also adding noise. Would you run a transistor thingy in your stereo line with 1 volt on the Vcc? 45Va is basically the same thing.

IMO, if you need line-level amplification, dump the 12AX7 and think 12AU7, 12AT7, 6DJ8 or my favorite, the Russian 6N1P
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Old 9th September 2004, 06:33 AM   #8
TobWen is offline TobWen  Germany
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Quote:
IMO, if you need line-level amplification, dump the 12AX7 and think 12AU7, 12AT7, 6DJ8 or my favorite, the Russian 6N1P
do you have some more information on that?

If I listen to the Behringer-thing, it isn't much noisy.
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Old 9th September 2004, 06:51 AM   #9
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12AX7 is a very high gain tube. The noise voltage induced could cause problems.

I found in my own experiments that the noise level is 10 to 20 dB higher with a Va below 60 or so volts and going to about 40dB higher at 25 volts.

I cannot comment on the Behringer because I have not listened to it, nor have I seen circuit configuration or chassis layout.

I do know for a fact though, that improperly dressed wiring or poor chassis layout can make the starved-plate noise moot, as I have seen countless times in tube guitar/bass pedals
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Old 9th September 2004, 07:34 AM   #10
TobWen is offline TobWen  Germany
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Can you tell me / show me the circuit of a solution, based on 12AU7, 12AT7, 6DJ8?

Watch the link of the MIC100/MIC200 I've posted at the start of this threat. As you can see, the chassis is VERY small.
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