Oh, those 12AU7s again... - diyAudio
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Old 21st July 2009, 01:05 AM   #1
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Default Oh, those 12AU7s again...

Okay, let's try this: You have a drum machine/sequencer/software/whatever and you want to make the drums sound a little less synthetic. You don't want to have to buy a whole analog tape machine to track them onto tape and then back into computer files.

So you figure, if what I want to do is mess up the sound a little bit in a tubelike way, why not build a row of 12AU7 stages and run the drum tracks through them?

Comments, criticisms, childish insults?

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Old 21st July 2009, 03:09 AM   #2
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Default Re: Oh, those 12AU7s again...

Quote:
Originally posted by Bamalama
...what I want to do is mess up the sound a little bit in a tubelike way...
That's what a tenth octave graphic equalizer is for. (I know, not what you want to read.) Just adding tubes per se' probably won't give you what you're after. I'm not totally sure what that is either, but think I have an idea. Altering the transfer function by filtering might. This could be as simple as a cheap 1:1 transformer. A basic R/C or L/C network. How about a wa-wa pedal? (Just kidding...?)

Cascading several unity gain stages (in total) with perhaps some feedback and capacitive filtering would be an interesting experiment. Why don't you try it and let us know how it goes.
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Old 21st July 2009, 03:33 AM   #3
JoshK is offline JoshK  Canada
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I know how they measure but I have to say I've heard them in amps that don't suck. I wouldn't pick them for my design, but I've heard them and didn't think they sucked.
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Old 21st July 2009, 03:45 AM   #4
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This is just conjecture on my part submitted for it's discussion value only.

After having several different tube and solid state components in my system, I postulate that it is the tube output stage and speaker interaction that gives the "Tube Sound" more than any solid state or or tube components upstream.

Stated differently, the tube, transformer, and speaker transfer function MAY be beyond replication in a simpler manner. No other circuitry other than possibly DSP could simulate the "Tube Sound"
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Old 21st July 2009, 11:28 AM   #5
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Hmm.

Adding transformers seems like a good idea, but this isn't going to be an expensive project and the few cheap transformers I've had experience with didn't have a very attractive sound...

The idea of the 12AU7 of course is that it is held to be one of the funkier sounding tubes, but funky in a way that might be just right for this application...

I'm not thinking series but rather two tubes (four sections) simultaneously processing four tracks.

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Old 21st July 2009, 11:33 AM   #6
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Quote:
Originally posted by dshortt9
This is just conjecture on my part submitted for it's discussion value only.

After having several different tube and solid state components in my system, I postulate that it is the tube output stage and speaker interaction that gives the "Tube Sound" more than any solid state or or tube components upstream.

Stated differently, the tube, transformer, and speaker transfer function MAY be beyond replication in a simpler manner. No other circuitry other than possibly DSP could simulate the "Tube Sound"

I fully agree. It's the interaction between the output iron and the speaker that gives the "tube sound."
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Old 21st July 2009, 01:14 PM   #7
Merlinb is offline Merlinb  United Kingdom
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It sounds like a reasonable idea to me, especially if you use low-value loads on the 12AU7s, to maximise the 2nd harmonic. Maybe use variable cathode bypassing to control the amount of harmonic distortion too?
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Old 21st July 2009, 05:32 PM   #8
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The studio guys use transformers for this sort of sound tuning. And, fortunately for you, it sounds like the sort of tuning you want is what you get from less expensive transformers. Take a look at Edcor steel core input transformers. They will cost you ~$10 each http://edcorusa.com/Products/ShowProduct.aspx?ID=287
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Old 21st July 2009, 07:33 PM   #9
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Quote:
I fully agree. It's the interaction between the output iron and the speaker that gives the "tube sound."
To that I would add the power supply which generally has a more audible effect in a lower feedback amplifier such as most tube amps.
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Old 21st July 2009, 07:56 PM   #10
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Y'know, I was thinking about using a deliberately soft power supply. Maybe even tuning its recovery time somehow.

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