A wonderful diagram. Very helpful. The accompanying commentary is helpful although back-and-forth discussion to further clarify what's going on is always good.
It's an awareness exercise of all that goes on under the hood.
I hate to say it, but now I think maybe I like my amp in ultralinear mode versus triode
It's a Cary V-12; it features a dozen EL34s and each pair has a switch in between them that configures that pair to either triode or ultralinear. In full triode Cary listed in the specs that it makes 50 wpc and in full ultralinear 100 wpc. For most of the twenty three years that I have owned this amp I have always felt that I preferred triode except for the occasions that I wanted to full out blast (it has literally been many years since I've felt the need to full out blast).
However, today I experimented with a couple of things in my system, and after listening to the same "Jazz Essentials" (compilation) red book CD a couple of times all the way through, the next thing I experimented with was switching to full ultralinear.
Maybe there was more "PRaT"? (Which is a term I am still not sure that I completely grasp.) Maybe . . . but what I do feel I noted for sure was that the imaging (particularly the imaging in the center) had more weight (meatier?) and was presented more forward, which I actually like.
I put a few more hours in (one more time with Jazz Essentials, Holly Cole/It Happened One Night, Dave's True Story/Sex Without Bodies, selected tracks from Rebecca Pigeon/The Raven and Once Blue/self titled and Norah Jones/Feels Like Home) after switching to ultralinear. (No booze during this session, just coffee.) The jury is still out on this, but I do have some CDs in mind that I want to listen to over the next few days as I continue to evaluate.
- ...
- 122 posts total
When Ralph and others talk about "optimizing" the amp for UL or triode mode, one thing they’re talking about is maintaining appropriate levels of feedback for each topology (assuming the amp uses global negative feedback). Switching from triode to UL increases the gain of the output stage. Switching the other way, from UL to triode mode, will decrease the gain. This affects the level of negative feedback the input stage will see. Let’s say an amp is optimized for UL mode. If you switch to triode mode without changing anything else in the circuit, you *decrease* the amount of feedback. I think this is often why people hear an "improvement" when switching to triode mode. You’ve reduced the amount of feedback, resulting in a sense of "clarity." The problem is, you’ve also reduced the output impedance of the amp and thus reduced the amount of control the amp will exert on the speaker. So the other comment you get is that bass sounds "looser." Conversely, then, if an amp is optimized for triode mode, switching to UL mode will *increase* the feedback, and this may detrementally affect the stability of the amp as well as the sound. Some "switchable" amps will include a circuit that changes the feedback network for each mode, thus "optimizing" the feedback circuit either way. Whether the Cary amp does this or not is a question for Cary. But more to the OPs point, I have built amps both ways and have always preferred UL arrangements, sonically speaking. For those who want to understand a bit more about these different topologies, there is an excellent article geared for the layman here: https://oestex.com/tubes/ul.html And if you want to better understand the issues of "optimizing" an amplifier for various modes of operation, there’s a slightly more technical but superb overview offered by Dave Gillespie over at Audiokarma: https://audiokarma.org/forums/index.php?threads/regilding-the-gilded-lily-heaths-w-2m.767851/ Even if you stop after the short history of feedback amplifiers Dave provides, you’ll have a better grasp on how your own tube amplifiers work! The "Gilded Lily" Dave refers to is actually the amplifier I build for myself, using a modern copy of the original Peerless output transformer. This is where, for all intents and purpose, the "ultralinear" configuration is in every way preferable to triode operation--to my ears, anyway. ;-) |
I'll also add, in reference to "marketing," that IMHO a "tube-swappers dream" is definitely a marketing ploy, in that there is no way an amp like that can be truly optimized for each tube--as Ralph cogently points out. I don't believe there's any harm being done here, but anyone with a technical understanding of tube amplifiers (and I'm barely on the periphery of that circle) will shudder at the idea of a "one-size-fits-all" amplifier. ;-) |
@dogearedaudio , I just took a look at the specs listed in the V12 owner’s manual and under feedback it says "zero." I do remember on another "switchable" amp I referred to, the Mesa Baron, on the back panel there were knobs to adjust feedback. I do not recall playing around with that particular adjustment during the two days that I auditioned that amp. As far as "tube roller’s dream", I should clarify that I dredged that up from my memory (which is USUALLY pretty good) but since I cannot find the blurb for whichever amp it was, I probably should not be providing a designer/manufacturer’s quotes that I cannot find to reference back to. |
- 122 posts total