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Old 4th February 2008, 10:48 PM   #1
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Default Heavy Metal distortion.

So, it takes alot of gain, and alot of tube stages to work well it seems. I'm after a sound like the Peavey 6505/5150 head which uses 6 12ax7's and 4 6l6's. For cost cutting i'd like to cut that down to two or three 12ax7's and two 6l6's (other tube suggestions?)

18w to 30w is all thats needed. I don't need a clean channel, just distorted. So, a pre level, tone controls, and a master volume. Perhaps a bright or boost switch which is easy enough.

I was thinking i could use an opamp stage to drive the tube stages. If i didn't get carried away with the opamp stage gain it wouldn't add anything to the signal, just boost it. That would give some extra clean gain to drive the tubes into distortion. How much gain should i use in the first stage?

Since i'm pretty comfortable with solidstate electronics i can build the opamp stage easily enough, but I'll need a good schematic for the tube stuff. Can anyone point me in a direction?

I'm thinking the block diagram would be:

Guitar > opamp stage > 12ax7 > tone controls > 1/2 12ax7 > master vol. > 1/2 12ax7 > 6l6's.

Thanks everybody.
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Old 5th February 2008, 06:54 PM   #2
Minion is offline Minion  Canada
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Maybe something like this is what you want:

http://www.diystompboxes.com/smfforu...?topic=18369.0


It is a starved plate design with an Opamp overdriveing a Tube, If you have the proper power transformer you could run the tubes off of High voltage and use a seperate power supply for the Opamp....

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Old 5th February 2008, 08:39 PM   #3
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Looking at your block diagram, I suggest you lose the opamp and add another 12AX7 instead. You will not save that much from one tube and having an all tube signal path is well worth the effort and cost, esp. when it comes to guitar amplification.

For metal sounds you need at least four gain stages or two 12AX7s, plus another 12AX7 for the phase inverter ....equals a total of three preamp tubes ....a common block diagram looks something like.... guitar > 1/2 12AX7 > drive > 1/2 12AX7 > 12AX7 > tone stack+volume > 12AX7 (PI) > 6L6s

There are tons of schematics out there within that 3 preamp tube limit.

Good luck! V.
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Old 5th February 2008, 10:17 PM   #4
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I listened to a few clips over at AX84.com and it seems the P1 Extreme or the HiOctane amps would do well enough. They seem to have plenty of gain. Both of these amps only have two gain stages (one 12ax7) before the output tube. I guess if i just built a P1x i could experiment with that.

Are there any other designs i should consider?
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Old 6th February 2008, 02:21 AM   #5
el`Ol is offline el`Ol  Germany
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x/sqrt(1+x^2) gives a good digital distortion. Is that possible with analog OPs?
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Old 6th February 2008, 10:40 AM   #6
teemuk is offline teemuk  Finland
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This comes very close. It clips higher input signals a tad smoother but I'm sure that if I would spent few more minutes tweaking I could nail that transfer function perfectly. Real-life device parameters would skew the final result somewhat anyway.
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Old 7th February 2008, 09:49 AM   #7
el`Ol is offline el`Ol  Germany
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Im totally puzzled, Teemuk. How did you do that?
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Old 7th February 2008, 10:52 AM   #8
el`Ol is offline el`Ol  Germany
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BTW, asymmetry is no issue. It has to be asymmetrized anyway by adding a constant voltage before distortion. Otherwize one would have too much compression and only odd harmonics.
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