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In Reply to: Haven't tried it but I've a theory that ... posted by Naz on February 19, 2007 at 23:01:52:
Hi,See link.
Refering to a Komuro design Thorsten concluded: "Of some interest is here the very distinctive distortion of an "unloaded" triode wired pentode, which has a very strong 2nd Harmonic cancelling some of the distortion of the output triode if designed correctly."
So, you're not alone with this line of thought...
Regards,
NC
Follow Ups:
Thanks NC, pity I seemed to get on the wrong side of Thorsten early on in the piece (my fault I’m sure) because I share many (but not all) of his views and have had some very similar experiences. I too tend to run drivers at lower currents these days, although I still like higher currents for OP tubes. I also like grid chokes and prefer mu follower to textbook SRPP.On the subject of mu followers, I've done a lot of testing of different circuits recently and I'm surprised by the very different sound I hear when taking drive from the cathode of the top triode (mu follower) vs the plate of the bottom triode (CCS). And the cause can't be the difference in OP impedance because a high impedance load was used in all cases. Mu follower is subjectively much stronger at the frequency extremes particularly bass, whereas CCS tends to favour clarity in the mids. I can see why so many don't like SRPP in general because of the apparent loss of mid range detail causing a kind of muddiness, loss of precision and depth, or as Thorsten describes it "opaqueness". Perhaps it’s simply a by-product of their strong bass/mid bass. Paradoxically, they can also suffer from sibilance. But all that said I can also see that their strength might be of great benefit to restoring tonal balance in systems that need what they have to offer.
Hi.From the link, I can see 6SL7 SRPP driver topology exhibits the smoothest overall HD profile from very lo to hi O/P power.
He also said about the operation conditions of SRPP to deliver good sound:
"Most circuit benefit from a stiff regulated PS, the SRPP & most
other half assed PP circuits really NEED them.""It (SRPP) is a very linear & good sounding topology for as long as you have it working with a FIXED load".
So constant O/P load is crucial for such topology.
I would agree with Mr. Konichiwa (Thorsten's moniker here) that smooth & even decending profile of least orders of HDs would deliver good sound to our ears.
c-J
Hi c-J,Before you 'jump into conclusions' as I did when I first saw these graphs, maybe it is good to read part of a private e-mail conversation I had with TL about this (which he told me I could share).
Thorsten wrote:
First the graphs from the above, the perspective makes it difficult to see, but the peak at the 5th Hamrmonic at lower power levels on 417A and EL84) is from output valve (not sure why it did that, but it sure did), so if you do not see a distinct peak-up to the 5th it means the driver produces more 5th than the output did.
The 6SN7 cascade always does more distortion even at high orders than the 300B, in effecting swamping out the 300B's distortion, but it adds some more of it's own at the 5th causing that peak in the 2.5W graph.
When comparing the spectra I felt that the EL84 (and C3m) provided the most evenhanded (and low high order) distortion overall, arguably the 6SL7 SRPP is second and IMHO better than the 417A (same trend with 437A) purely from a harmonic profile.
That said I liked the various pentode driven 300B Amp's I have build about equally well as the 417A/437A/6S45/E180F/E810F/D3a TWGC Amplifiers (TWGC - Triode With Gridchoke), all BTW using rather low anodic current, usually around and below 10mA in the driver, feeling they offered a similar overall performance levels.
No, they do not sound alike, either between Pentode or Triode nor among the different types, but they share some overall charateristics, with the Pentodes offering more "Tone" and "Delicacy" while the Triodes tend towards "Detail" but also directness and notably greater macrodynamic robustness (maybe gridchoke plays a role here, they are not easily used with pentodes).
Compared to that the 6SL7 SRPP (with or without gridchoke, also when connected as mu-follower which I thought best) seems a little "further away from the music" sorta like "through a glass, darkly", giving a certain sameness to varied music, more so than the others).
The 6SN7 cascade seemed to combine the worst of all worlds, managing to sound opaque, without variation in the music (making all sound the same) while giving me headaches with edgyness at the same time. Didn't care for that at all.
A cascade with 6072A & 5687WB sounded more balanced and had more immediacy and directness, but not quiet up to the single pentode or triode levels.
Not sure if any of this of use.
I'm currently working (extremely slowly) on a topology provisionally called "Bushido" which aims to combine the best sonic features of the pentode driven amplifiers (the "delicacy", "lightness of touch", "speed" (whatever we want to call it) and the nice "tone" with the macrodynamic cojones of the "TWGC", it might see the light of day at some point.
Ciao T
Hi.Yes, it was TL's email to me yesterday with the same texts.
On reading TL's 3-D HD spectrum charts alone without other supporting papers showing the HD spectrum of the 300B involved, & sonic comparison, I would still find 6SL7 SRPP shows "arguably" better than EL84 pentode in overall HD figures from 0.66W to 11W except its 4th order HD levels at 0.66W & 2.5W
One thing I would agree with Thorsten in general sonic characteristics triode vs pentode. A triode sounds more "detail" & "macrodynamic robustness" & less "tone" than a pentode. Given proper component mating, a triode amp can deliver "lightness of touch" & "speed" too.
Hi.Was it from you or directly from Thorsten in U.K.??
c-J
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