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In Reply to: RE: Penny wise posted by Tre' on December 14, 2014 at 17:40:13
"Can you give me details of each driver stage?"
Thanks, but some other time. I'm done.
Big speakers and little amps blew my mind!
Follow Ups:
OK but understand that if the 6sn7 circuit is working correctly then the distortion you hear must be coming from your preamp or source. Not the 6sn7.
A proper 6sn7 driver stage will not distort driving a 2a3 to full power.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
One can argue that any properly designed driver will not distort driving any following stage.
I'm confused by what Mr_Steady is reporting and I'm only trying to say that a 6sn7 stage should drive a 2a3 to full power (which he doesn't need with his speakers) without distorting noticeably.
A 6sn7 with a reasonably high load impedance running 12ma at around 200 volts plate will swing a lot more that 90 volts peak to peak with very little distortion.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre'
I searched the web regarding gain structure. Mostly had to do with recording. Found the following in regard to tube based gain stages, but even it was on a guitar gear site;
"Gain structure is the concept of relative amounts of signal or voltage gain from one stage of a chain to another. If you have three devices capable of voltage gain (lets say each can create a gain of 10%), and you need an overall gain of 17%, the gain structure would be how you allocate the gain between the stages. If you set up the first stage to generate a gain of 10%, the second stage to create a gain of 6% and the third to create a gain of 1%, that would be one method of structuring the gain. Alternatively, you could set it up so that the first stage has a gain of 5%, the second has a gain of 5%, and the third has a gain of 7%. You have change the gain structure but not the overall amount of gain.
By definition, one voltage-gain-inducing device by itself cannot have a "gain structure."
Picture this: in an amp with a master volume and a preamp volume you are juggling gain staging. You can set it up so that you have a lot of gain in the early stages (which often causes distortion in the later stages) or you can set it up so that most of your signal gain comes in the later stages, keeping the overall signal less distorted. This would be more akin to "proper" gain staging in the audio (i.e. concerned with fidelity) world.
The short answer to your question (now that i've finished my little semantic rant) is that "mu" = "gain.""
Maybe you have an opinion about the above? Somewhere I picked up that you should get all the gain you could in the early stages.
Do you know any good books or articles regarding the proper gain structure of a series of voltage amplifiers in audio? Maybe with an emphasis on tube amps? A tip here would be greatly appreciated.
Jamie
Big speakers and little amps blew my mind!
"Gain structure is the concept of relative amounts of signal or voltage gain from one stage of a chain to another. If you have three devices capable of voltage gain (lets say each can create a gain of 10%), and you need an overall gain of 17%, the gain structure would be how you allocate the gain between the stages. If you set up the first stage to generate a gain of 10%, the second stage to create a gain of 6% and the third to create a gain of 1%, that would be one method of structuring the gain. Alternatively, you could set it up so that the first stage has a gain of 5%, the second has a gain of 5%, and the third has a gain of 7%. You have change the gain structure but not the overall amount of gain."This is a rather misleading paragraph. The total gain of multiple stages of amplification is equal to the product of the gain factors for each individual stage. If one really wants to express the gain of each stage in percentage terms, as in the paragraph above, then the total gain is not given by adding the percentages together. It becomes a reasonable approximation if the percentages are small (as in the examples above), but even there, the errors are non-trivial. The overall gain in each of the two cases above is closer to 18% than 17%. But the whole example seems rather bizarre; who would seriously build a three-stage amplifier where the stages had gain factors like 1.05, 1.05 and 1.07? (i.e. about 0.4dB, 0.4dB and 0.6dB.)
Of course, if one uses dB rather than talking of multiplicative gain factors then the process of combining the effects of multiple stages is indeed additive, since the dB scale involves taking logarithms. In fact, the paragraph above would make much more sense if one assumed that the writer had intended those numbers to be dB of gain, rather than percentages. An overall gain of 17dB is something worth talking about, whereas the writer's three-stage amplifier achieving a grand total of about 1.4dB of gain is not!
Having said all this, when Tubewrangler uses the term "gain structure" it appears that the word "structure" is superfluous. Since he quotes just a single figure (or range of figures, like 18-20 dB), he appears to mean simply the overall voltage gain of the amplifier. It seems to me the word "structure" would be better omitted in what he is saying.
Chris
Edits: 12/18/14
There's not many well designed amps out there. I keep looking at my stash of 2B6's and wondering how to use these to best advantage. Weird tube that looks like class B even single ended. It's not, but it looks like it. I'd like to have the knowledge to design an amp around these tubes.
I've got a hunch.
Quasimodo.
Have you read this?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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