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-   -   12AX7 sound ... going with the trend (http://www.diyaudio.com/forums/tubes-valves/40657-12ax7-sound-going-trend.html)

TobWen 9th September 2004 03:35 AM

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

Optical 9th September 2004 04:23 AM

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!

TobWen 9th September 2004 04:25 AM

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 :-(

JojoD818 9th September 2004 05:30 AM

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!

TobWen 9th September 2004 05:36 AM

hehe ... interesting:
The 12AX7 is "powered up" with +45V only :-)

Standard is 245V, I think :-)

JojoD818 9th September 2004 05:47 AM

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. :D

Geek 9th September 2004 06:09 AM

"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 ;) :2c:

TobWen 9th September 2004 06:33 AM

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.

Geek 9th September 2004 06:51 AM

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 :rolleyes:

TobWen 9th September 2004 07:34 AM

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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