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Old 26th February 2017, 10:46 PM   #11
oltos is offline oltos  United States
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Default First Watt F7, Cascode and/or 300B P-P Amps for Quads?

Thanks to Sheldon for the feedback about the First Watt F4 p-p amp and SET amps, if only to rule them out for the Quads. Indeed, the only First Watt that seems to be a really safe bet is the F7, at least according to the ears of this reviewer. https://www.cnet.com/news/first-watt...-audiophiliac/

The F7 is a p-p Class A amp, 20 wpc, damping factor 100. Nelson Pass discusses the design and what he tried to achieve in the manual FIRST WATT F5 Again, like many p-p amps the F7 doubles its power into 4 ohms to 40 wpc, so I’d have to be sure that the Quads have the voltage clamping to protect the tweeters.

The “ideal” amp for the Quads seems to be the same as for probably most speakers: low output impedance and low and local (not global) negative feedback? But what about damping factor? More about this later.

Is anyone familiar with a rather strange high performance animal called a cascode amp? https://en.wikipedia.org/wiki/Cascode Gary Dahl built this ~ 20 wpc amp to drive his two way mains, which are 97db and 7 to 8 ohms. It’s a balanced input, direct coupled, local feedback, two stage cascode amp. It uses with Bud Purvine’s O-Netics Level 3 output transformers, presumably to reduce the amp’s high output impedance.

Gary says the sound is “fantastic”, though his speakers are very different from the Quads; Azura 425 horns/Radian 745 Neo Beryllium drivers atop sealed Altec 416 midwoofers, plus powered Acoustic Elegance subs with passive radiators.

In lieu of schematics, Gary said that this cascode amp uses local feedback. But what might this cascode amp’s output impedance be measured at its output transformers to thereby compute damping factor? https://en.wikipedia.org/wiki/Damping_factor

As for tube amps, I am aware that many find the Quads and 6BQ5/EL84 amps to be among the very best sounding combinations. But would most 300B p-p amps be a good or not so good choice for the Quads?

Before building the cascode amp, Gary’s built Lynn Olson’s Amity 300B p-p mono blocks. http://www.nutshellhifi.com/IT-Triode-Amp.gif However, Gary found that the Lundahl transformer interstage coupling was far less able to get his Azura/Radian beryllium diaphragms to produce highs and upper midrange as cleanly and strongly as does his solid-state cascode amp’s input stage-also a 20 wpc amp.

Again, his main speakers’ system sensitivity and impedance are 97db and 7 to 8 ohms; much different than the Quad 63s, and the 57s even more so. When last we chatted Gary was indeed upgrading his 300B p-ps. I hope to soon learn about those mods. Perhaps he removed the Lundahls and used some very high quality film or oil caps to couple the two stages.

But would 20 wpc 300B p-p mono blocks typically be a good or not so good choice to drive Quads, regardless of input stage design?

Would these amps’ 4 or 8 ohm output taps have low enough impedance and high enough damping factor to get the Quad 57s to deliver all of their bass, and robustly, down to 45Hz or so.

And without rolling off the highs or making them sound bright?

If yes or no, please explain why. Or would 6bq5/EL84 still be a better sounding choice for the Quads in every way?
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Old 26th February 2017, 10:52 PM   #12
oltos is offline oltos  United States
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Default Proper WPC and Damping Factor for Quad 57/63s?

Quote:
Originally Posted by lafish View Post
Currently driving my ESL 57's (rebuilt by Wayne Piquet) with a First Watt M2. Very sweet and detailed, but not as punchy as with my diytube st35, an el-84 amp. Try to hear them with Rodger Modjeski's RM-10, which was designed using them. They don't tend to like single-ended triodes.
Regarding the seemingly mysterious damping factor, OTL amp designers David Berning and Atmasphere’s Ralph Karsten caution that amps with relatively high damping factor tend to sound less than pleasing with high sensitivity speakers like Gary’s >96 db 7 to 8 ohm impedance system. Says Berning at his website “Higher damping is likely to give a tighter, dryer and more analytical sound, and low damping is likely to give a more open and resonant sound. The sonic attributes of damping show up most dramatically in the bass.”

I doubt that Gary’s build of Lynn Olson’s Amity 300B P-Ps have high damping, but one thing that I just found is that relatively high amplifier damping factor is apparently not essential to make the Quads sing. Indeed, lafish recommends the RM10MK2, which Roger Mojeski had voiced with the Quads. It too is an EL84 amp but its damping factor is only 12.5! Music Reference RM-10 Vacuum Tube Amplifer

How can that be? Isn’t it all but physically impossible to have low output impedance without getting high damping factor, at least with 300B or EL84 push-pull amps, compared to their SET counterparts?

So unless the Mojeski’s transformers and/or the EL84 p-ps tubes are as “magical” as the 300B p-ps-or more so when paired with the Quads-then provided the amp has low output impedance is damping factor irreverent?

But what about output power? What is the comfortable amount that the Quads need for best sounding full range response, regardless of average listening levels?

For solid-state, I googled Sheldon’s Classe 70 amp; 70 wpc 8 ohms/ 140 wpc 4 ohms. His Quad 99 amp delivers at least as much power Quad 99 stereo power amplifier Hifi Gear And his Quad 303 does ~ 45 wpc. https://www.hifiengine.com/manual_li...quad/303.shtml

For tubes, Art Dudley’s review has the Quad II’s push-pull paraphrase mono blocks driving his Quad 989s. Apparently he found everything wonderful except that Steeley Dan’s “Reelin in the Years” bass seemed noticeably slow (??). Quad II Classic monoblock power amplifier Page 2 | Stereophile.com Why might this be? The paraphrase circuitry? The selected tubes, none of which are EL84s? And/or that the Quad II mono blocks are only 15 wpc? Quad II Classic monoblock power amplifier Specifications | Stereophile.com

Or do the 989s need more power than the Quad 57s? But again note that while the Quad II monos have half the power of the RM10MK2, they both have the same very
low damping factor, ~ 12.
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Old 26th February 2017, 10:57 PM   #13
oltos is offline oltos  United States
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Default EL84 P-Ps Still Kings for the Quads?

Conclusions:

Even if a 300B p-p tube amp or solid-state cascode amp has suitably low output impedance, if they have more than 15 but less than 25 wpc, bass response to 45Hz or so may not happen with the Quad 57s?

EL84 p-p amps, which deliver at least 30 wpc are a much safer bet for all around performance than are 20 wpc 300B p-p amps for Quads?

And would the Quad 57s deliver better full range response with 30 wpc than 20 wpc, regardless of average listening levels and room size?

My room is 14 ft x 19 and average listening levels ~ 50 phons or ~ 80db at 70Hz (perhaps +/- 5 phons?), as per the revised 2003 curve shown here. https://en.wikipedia.org/wiki/Equal-loudness_contour

The RM10MK2 might well be a very cost-effective amp for the Quads. It would have been interesting if Srajan Ebaen, Art Dudley or Dick Olsher heard and wrote about such a listening session. 6moons audio reviews: Music Reference RM-10 MkII

As would have been a shoot out like this.
PrimaLuna DiaLogue Seven Monoblock Amplifiers (TAS 199) | The Absolute Sound

But I know that ct0517 was very happy with the RM10MK2. And I suppose that my pair of Rythmik 12" sealed servo subs would blend with the Quad 57s at least as well as his Dynaudio BM12s. https://forum.audiogon.com/discussions/review-quad-57
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Old 26th February 2017, 11:06 PM   #14
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Have a look to the tube designs of the Quad II amps, for a stable design driving ESL57.

The RM10 is an excellent choice, if you can find one. They're rare, second hand.

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Old 27th February 2017, 05:29 AM   #15
oltos is offline oltos  United States
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Quote:
Originally Posted by anji12305 View Post
Have a look to the tube designs of the Quad II amps, for a stable design driving ESL57. The RM10 is an excellent choice, if you can find one. They're rare, second hand.
While I am certainly tied to a budget, the latest RM10MK2 is under $2K.

But as there are clear advantages to OTL amps, are there any such models that you would especially recommend?
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Old 27th February 2017, 06:52 PM   #16
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I've never owned an OTL tube amp, and have only vague memories of them from the 1990's. My friends who owned them found them less than robust. As I mentioned earlier, the current Quad 909 is built to handle ESL and is an underappreciated bargain.

http://www.quadesl.org/index.php/har...an-steingruber

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Old 9th May 2017, 03:24 AM   #17
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Default QUAD ESL 57

must be 15 wpc class A amp.
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