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A Gainclone amplifier makes for a nice simple benchmark/monitor amp. It is a class AB linear amplifier capable of 20 W - 120 W of power, and is based on a monolithic amplifier chip such as the LM1875, LM3875, LM3886, or LM4780.

What different ways are there to add controllable even order harmonic distortion to its sound?

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    \$\begingroup\$ What is special about a Gainclone amp (no I'm not going to follow a link, you should state what is special about it for your application), and why does adding specific distortion dependent on it? Sounds like a job for a DSP. \$\endgroup\$ – Olin Lathrop Jul 3 '12 at 11:19
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    \$\begingroup\$ I think when we copy part of a Wikipedia article (or other external source), we at least should take the effort to remove the edit, [citation needed], [2], ... links. Also I think we should mention the source too as a respect to the original author. \$\endgroup\$ – jippie Jul 3 '12 at 16:26
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    \$\begingroup\$ @jippie I removed the plagiarism and summarized. \$\endgroup\$ – W5VO Jul 3 '12 at 18:08
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You ask about getting "tube sound" but then presume the answer by suggesting a specific method.

  1. In addition to what you suggest, try adding a small and variable amount of mains frequency signal to the output. This simulates heater hum, which is a low level but nearly unavoidable characteristic of AC heated filament* tube amplifiers. The ear/brain associates this sound with "tube amplifiers". This is NOT mentioned in the Wikipedia "Tube Sound" page but I have long ago heard it mentuioinbed seriously as a factor so it is well worth looking at.

  2. Even harmonics are referred to (by some) as Octave harmonics as they share a 1:2 ratio with the original, and then 1:4 etc. Processing which emphasises this effect will influence the "octave sound". There are many ways of doing this - or trying to. This remarkably good page A Musical Distortion Primer discusses the underlying principles and then proposes about 15 ways or variants of achieving such effects.
    one obvious is to use full wave rectification in a variety of ways. A full wave rectifier fed with the signal and with a portion of its output summed with the input AC will give even harmonic effects which may be deemed to be useful.

Wikipedia - Tube Sound provides an very extensive overview of the subject but with minimal circuitry.

Some useful user discussion is here

Of some use

http://www.geofex.com/effxfaq/distn101.htm


  • The large majority of tube amplifiers utilise AC heated filaments.
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    \$\begingroup\$ VG but small confusion here. Octaves are consecutive frequency doublings, i.e. power-of-2 harmonics. The other even harmonics such as 6th, 10th are not octaves and should not be referred to as 'octave harmonics'. \$\endgroup\$ – user207421 Oct 10 '12 at 4:31
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Amplifier genius Bob Carver was challenged once to make a solid state amp sound like a tube amp to prove that the tube vs transistor sound was not necessarily due to the active devices themselves but was due to the overall transfer function of the amplifying circuit. I believe he just added some output resistance (resistors) to the solid state amp and a panel of "golded ear" audiophiles could not reliably tell the difference between the two amps. Hope this helps !

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I have made solid state Amps sound Valvey by Using 2 Nchan mosfets in a SRPP class A using only a small amount of local negative feedback .The single ended nature of the SRPP gives lots of pleasant sounding even harmonics as does the square law characteristics of the FETs .The mimimal negative feedback means that there are not any TID problems and the output impedence is not too low .Poor damping factor is associated with tube amps and is sonicly pleasing to some .I found that the Amp sounded awesome on older music .

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There is no way to get "real tube sound" with any semiconductor in amplifying stage. I waste dozens of years to achieve this. If your question is not referred to instrument amplifiers, the best I've got is tubes in preamp stage and transistors at output but ONLY as voltage follower.

Instrument amplifiers are total different area, and there is no such thing to replace the tube on proper way to shape tone.

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    \$\begingroup\$ Isn't there anyone that has been able to classify the distortions? \$\endgroup\$ – Trygve Laugstøl Oct 12 '12 at 18:29
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    \$\begingroup\$ This is hardly a constructive answer. Saying that you weren't able to do it, without outlining the things you tried and the manner in which they failed, isn't useful information to anyone else. \$\endgroup\$ – Dave Tweed Oct 12 '12 at 19:51
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    \$\begingroup\$ I -1'd your answer for a few reasons. First, as @DaveTweed mentioned, just because you couldn't do it doesn't mean it's impossible. More importantly, though, I -1'd your answer because it's rubbish. "Real Tube Sound" is pretty well understood and the only people who seem to say it's impossible are the same people who also colour the edges of their CDs, use depleted oxygen cables and have hearing acuity well beyond the best instrumentation man can create. \$\endgroup\$ – akohlsmith Oct 13 '12 at 3:42
  • \$\begingroup\$ @Andrew, I have no time to explain something which is huge material to discuss about and psychoacoustics is such matter. Can you tell me why main top recording studio gear (and most valuable) is with tubes? How much of tube devices did you actually built: \$\endgroup\$ – Alex Oct 13 '12 at 6:14
  • \$\begingroup\$ (hi-fi amps, condenser tube mics, mic preamps, bass preamps, guitar amps, effects...)? If someone ask you can he get the "tube sound" for gainclone, you can freely say to him "no way, you can't do it". Well, maybe someone can. I am desperately seeking for such guru to enlight me, and I'll pay him a 15 days of vacation in any worlds destination. \$\endgroup\$ – Alex Oct 13 '12 at 6:33

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