Dynamic contrasts lacking with 300B SETs - Plinius_Fan 23:08:28 05/14/13 (10)
 RE: Dynamic contrasts lacking with 300B SETs - Thorsten 23:26:08 05/24/13 (1)
 PS, maybe I am being obtuse... - Thorsten 08:10:36 05/25/13 (0)

...

Show full thread outline!

 Dynamic contrasts lacking with 300B SETs - Plinius_Fan 23:08:28 05/14/13 (10)
 RE: Dynamic contrasts lacking with 300B SETs - Thorsten 23:26:08 05/24/13 (1)
 PS, maybe I am being obtuse... - Thorsten 08:10:36 05/25/13 (0)
 RE: Dynamic contrasts lacking with 300B SETs - drlowmu 11:50:17 05/20/13 (1)
 RE: Dynamic contrasts lacking with 300B SETs - cpotl 13:16:29 05/20/13 (0)
 RE: Dynamic contrasts lacking with 300B SETs - Paul Joppa 11:34:41 05/15/13 (3)
 Nice tip in helping recognise IMD; noted! nt. - RC Daniel 15:24:53 05/15/13 (2)
 RE: Nice tip in helping recognise IMD; noted! nt. - charles1dad 21:36:34 05/17/13 (1)
 Shouting in agreement! nt. - RC Daniel 17:46:06 05/18/13 (0)
 RE: Dynamic contrasts lacking with 300B SETs - Larry I 05:43:08 05/15/13 (0)
 RE: Dynamic contrasts lacking with 300B SETs - RC Daniel 03:59:50 05/15/13 (0)
 RE: Sophia Electric 300B: neither. - Jamesbmay 08:51:02 05/14/13 (0)
 Western Electric 91A SET by Tube Audio Labs - Plinius_Fan 10:20:23 05/11/13 (8)
 RE: Western Electric 91A SET by Tube Audio Labs - RC Daniel 04:22:01 05/13/13 (1)
 Thanks a lot - Plinius_Fan 22:39:40 05/14/13 (0)
 RE: Western Electric 91A SET by Tube Audio Labs - Paul Joppa 23:46:41 05/11/13 (5)
 Here is the thing - Michael Samra 00:18:46 05/15/13 (0)
 Tube Audio Lab WE91A - Sebrof 06:27:53 05/12/13 (3)
 RE: Tube Audio Lab WE91A - drlowmu 13:01:54 05/12/13 (2)
 Uber Supply - Sebrof 19:39:59 05/12/13 (1)
 RE: Uber Supply - drlowmu 22:30:40 05/12/13 (0)
 Listening to the Allnic T1500 at the moment - Plinius_Fan 06:43:22 05/10/13 (0)
 RE: Sophia Electric 300B: 91-01 vs 91-05 - Johno 03:47:03 05/09/13 (0)
 RE: Sophia Electric 300B: 91-01 vs 91-05 - RC Daniel 17:11:21 05/08/13 (2)
 Another yes - Frihed89 02:19:22 05/09/13 (0)
 RE: Sophia Electric 300B: 91-01 vs 91-05 - Gerry E. 18:01:15 05/08/13 (0)
 Bad experience with Sophia Electric - Lord Soth 09:06:52 05/08/13 (4)
 I can't believe this didn't cause more outrage - Tre' 09:35:43 05/11/13 (2)
 100% agree with you Tre. - RC Daniel 14:15:07 05/11/13 (1)
 I burn in all new tube amps 24 hrs all the time - Lord Soth 01:35:27 05/12/13 (0)
 RE: Bad experience with Sophia Electric - Plinius_Fan 23:22:15 05/08/13 (0)
 RE: Sophia Electric 300B: 91-01 vs 91-05 - Chip647 07:52:01 05/08/13 (36)
 Is it better to use interstage transformers ? - Plinius_Fan 16:56:45 05/08/13 (35)
 The WE91 did not use interstage transformers - Frihed89 02:40:03 05/09/13 (15)
 Agreed! Nor does a "91" use cascaded 6sn7 halves. - RC Daniel 16:00:43 05/09/13 (14)
 A suitable modern "91" circuit ... - Paul Joppa 19:27:31 05/09/13 (13)
 Yep - that is the one that... - RC Daniel 20:20:44 05/09/13 (12)
 RE: Yep - that is the one that... - Paul Joppa 20:56:57 05/09/13 (11)
 M91 derivative - long! - Paul Joppa 13:47:14 05/10/13 (2)
 Thanks Paul. - RC Daniel 23:28:33 05/10/13 (1)
 RE: Thanks Paul. - Paul Joppa 23:58:07 05/10/13 (0)
 RE: Joppa M91 PF Derivative - awsjr 05:28:17 05/10/13 (6)
 RE: Joppa M91 PF Derivative - anystereo 07:13:39 06/27/15 (1)
 RE: Joppa M91 PF Derivative - awsjr 05:49:17 06/29/15 (0)
 RE: Joppa M91 PF Derivative - mach1 02:56:30 05/12/13 (2)
 RE: Joppa M91 PF Derivative - RC Daniel 15:06:58 05/14/13 (1)
 RE: Joppa M91 PF Derivative - Paul Joppa 19:18:05 05/14/13 (0)
 RE: Joppa M91 PF Derivative - RC Daniel 13:39:58 05/10/13 (0)
 Interested? Hell's yes... - RC Daniel 22:09:52 05/09/13 (0)
 RE: Is it better to use interstage transformers ? - drlowmu 20:42:44 05/08/13 (18)
 RE: Is it better to use interstage transformers ? - Plinius_Fan 23:23:02 05/08/13 (17)
 RE: Is it better to use interstage transformers ? - Frihed89 02:54:35 05/09/13 (15)
 DHT comparos (OT). - RC Daniel 18:24:56 05/09/13 (7)
 RE: DHT comparos (OT). - drummerwill 19:29:17 05/09/13 (6)
 Don Garber's approach seems to be different - Frihed89 02:51:27 05/10/13 (4)
 RE: Don Garber's approach seems to be different - drummerwill 08:15:12 05/10/13 (2)
 SET 801A - Roli 13:01:06 05/10/13 (1)
 Dadgummit! SHHHhhhhh..... ~nT - Cleantimestream 13:52:19 05/27/13 (0)
 RE: Don Garber's approach seems to be different - RC Daniel 03:30:57 05/10/13 (0)
 RE: DHT comparos (OT). - RC Daniel 22:14:52 05/09/13 (0)
 RE: Is it better to use interstage transformers ? - Sebrof 05:08:58 05/09/13 (6)
 Tell us more about the OPTs - Frihed89 07:45:02 05/09/13 (5)
 RE: Tell us more about the OPTs - Sebrof 10:35:00 05/09/13 (3)
 RE: Tell us more about the OPTs - awsjr 05:39:02 05/10/13 (0)
 RE: Tell us more about the OPTs - Palustris 13:50:38 05/09/13 (0)
 RE: Tell us more about the OPTs - RC Daniel 13:07:29 05/09/13 (0)
 RE: Tell us more about the OPTs - Palustris 08:13:17 05/09/13 (0)
 RE: Is it better to use interstage transformers ? - drlowmu 01:46:36 05/09/13 (0)

Personally, I leave Sophia well alone. I have read about some concerning Sophia experiences; I don't like their product marketing approach; and the photos of the amps I have seen suggest poor build quality. I also put very little stock in Jeff's review. I've no doubt he liked the amp, but considering it reads more like a marketing exercise and contains some dubious "facts", I feel that expectation effects were/are strongly at play. Anyone writing about these types of systems should also have been able to identify what I think is poor build quality.

Buyer beware.

Cheers.

Edits: Grammar; minor terminology changes; and a minor qualification.

"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki

May I suggest :

The best way to buy an amp is to listen to it for yourself, hopefully on your system, and you, and you alone decide if it is worth using. Its called YOU LISTEN and decide.

Jeff Medwin

• http://www.tubeaudiolab.com/

• http://www.hifiwigwam.com/forumdisplay.php?22-2-Channel-Deba

Thank you.

"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki

Gordon Rankin, Thorsten and IIRC Dennis Fraker have alluded to the difference in presentation between the different ratios...

Cheers.

Edits: minor changes to improve clarity.

"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki

My thinking though is that current 2A3s (mostly 2.5v 300B) and 300B at the 1:6 to 1:7 mA:volt operating point with 5k load can also sound much like (but not same) a 45... with more power.

I hope to be able to experience this first hand with my upcoming builds. Man, do I need to get cracking! The perfectionist in me is very resistant though... what, my first build is merely a learning experience and a bit of a shoehorning exercise of some parts I hve laying around... not good enough!

Cheers.

"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki

• http://www.audiocircle.com/index.php?topic=113472.0

Sue's response re: resting the amp after hours was so odd that when the owner posted her response, I misinterpreted his post and assumed the odd 5 hour limit WAS in the manual. The poster mentioned "page" or some such, which assumed referred to the manual; however, the poster was referring to the forum thread. How can an amp's warranty be voided by breaching some obscure condition that was not even stated in the manual?!

And irrespective of whether she thinks tube in amps in general are not designed to run for 24 hours (BS, to my mind!), there is a general expectation they should be able to run for more than 5 hours without rest.

Very, very poor form on behalf of Sophia.

Cheers.

"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki

• JE Labs WE91A Info

You wrote this :

"Paul and others may want to comment on it specifically (I'd sure like to read comments since this is what I'm listening to as I type)".

I will offer you my own thoughts of this amp you are listening to.

I would rebuild the supply. I have redesigned it as follows:

As it stands now, it uses a cap input filter, 10 uF, with a single 65 Ohm choke, and a power transformer whose secondary is 72 Ohms DCR ( either end to center tap ) and whose primary DCR is 2.8 Ohms ( Hammond 272DX, 123 VA ). All these power supply DCRs are certainly too high.

I have found, in more than thirty years of A-Bing such things, that choke DCRs to the Finals stage need to be in the order of 20 Ohms or less to get acceptable audio performance, the "line in the sand" so to speak.

Also, the 5R4 is a nice sounding directly heated tube rectifier, but it is TOO HIGH in Z for any audio amp, it may be OK for a preamp. Its a whimp for a amplifier. Use a 5V3A instead, also a directly heated rectifier. Some people like Sylvania brand 5V3s.

When I PSUD2 simulate your power supply to the Final 2A3 tube, and subject it to a 15% current step at 4.1 seconds, is seems to fully settle in 150 mS. and it drops 10.2 VDC in B+ with a current step of 18.7 mA. So, applying Ohms' Law, "I" express this above as 545 Ohm dynamic Z, powering the 2A3. ( 10.2 VDC divided by 0.0187 A. equals 545 Ohms )

My suggestion settles fully in 90 mS. and drops only 3 VDC with the same current step, which "I" will express as 160 Ohms. ( 3 VDC divided by .0187 A. equals 160 Ohms ) A 160 Ohms filter to 2A3 Finals will sound a HELL of a lot better in music play-back than a 545 Ohms one !! Its a reduction to one third !!

The power transformer becomes a Hammond 270HX, which is 176 VA. That transformer is rated 275-0-275 at 230 mA. and has a DCR for one half of its high voltage winding of 30 Ohms, and a primary DCR of only 1 Ohm. This is better, way better, and you will hear it as so !!

In place of one choke, you will use three smaller and much lower DCR chokes, placed below-deck. In every DIY amplifier I have built since 1982, I exclusively use two chokes in series to the Finals, rather than a single choke. This always sounds to me as a more "refined" audio presentation. I'll have it no other way, thank you !

L1 input choke is a Triad C-56U, which at just 0.8 Ohms DCR with a 2 A. current rating, so it will loaf. C1 is 20 uF. Next, the filter splits ( as a "Y" ) to a separate L2 / C2 for each 2A3. Use the EDCOR XC87-2HY-300 mA. 21 DCR chokes, with 50 uF for C2s, a L2 / C2 feeding each 2A3.

The 14K series resistors feeding the Input stage should likely provide adequate ripple reduction to the Input tube's B+ rail. Five hundred mVAC of ripple to the 2A3 finals will be of no consequence, and the trade off you have reaped in gaining speed and dynamic renderings of the music, will easily offset inaudible ripple "numbers" to the Finals when you listen.

If you build this supply, please let me know how it sounds to you. These changes will transform your amplifier and be on the par of what you heard when you went from the James to the custom EP output transformers. Actually it MAY well be a far greater improvement, and it will spoil you forever, like it has me. But you have to experience it directly to comprehend it and appreciate it. Enjoy.

Jeff Medwin

A lot of people own these amps and most love them; I’ll not argue with them. However, I feel that I should share my experiences and opinions and will try to be brief, balanced and reasonable.. but don't take this as fact.

Caveats: I only have experience with one of his kits and am yet to hear one of his amps. I have viewed closely his photos of builds and have been looking into these types of amps for a while. Make of that what you will.

I was well aware that the “kit” was collection of parts and contained minimal instructions; no problem. The chassis had badly burred and out-of-shape holes but more importantly had what I consider a rather sub-standard layout. I was not expecting boutique parts, but reliable tube sockets and appropriate selection of parts that are documented to be important to the overall performance should have been the minimum. Further, some hardware and wire were absent. For me, important requirements were simply not met, to the point I was questioning the long term safety of the amp. I aborted the build and now consider it to have been a great learning experience; I learned a lot and it has forced me to learn more!

I don’t know why Min supplied the kit like this. Many people claim to like the build and sonics of his amps. My guess is that he was busy and took less care than perhaps he should. Still, some of the mistakes would have been obvious to a competent DIYer. Min has performed a lot of builds; perhaps mine was an isolated experience? Perhaps my experience with this kit does not extend to his builds? It is a while since I have looked at the images of Min's builds on his site, but I recall thinking that his earlier builds are "better" than his more recent builds. That said, the photos generally show layouts and build quality I’d not be satisfied with and his component selection often leaves much to be desired. Thankfully, Min allows you to specify the components to be used and if he is building.

Which brings me to the things I would ask for if I were requesting a build from him. For simple reliability and safety: do not use the nasty Chinese-made ceramic tube sockets (I like the phenolic UX4 and UX6 that are available for a few bucks each); use grommets around the holes through which wires are routed; de-burr and cleanly finish all holes; and use a suitable location and method for attaching the safety earth-chassis connection (it needs to be a dedicated connection!). Layout and grounding are well beyond the scope of this post, but I’d ask him to use a larger chassis than absolutely required and to lay it out as optimally as he knows how, paying particular care to the grounding (rather than just “making it fit”). Components I would specify include a 2uF or greater PIO capacitor for screen-ground bypass; a coupling capacitor that voices the amp to your liking; spend the extra $ on Yamamoto grid caps for the 6C6; ElectraPrint 3K (primary load) output transformers (or the pricier Hashimotos); and a higher spec Hammond power PSU (for cooler running). If you wanted to go further, I’d suggest film caps for the PSU and cathode bypasses (you could get away with a cathode bypass of ~ 16 to 33uF for the 6C6, I think).

I have likely missed a few things, but that should get you a reliable and nice-sounding amp, if built well. There is a heap more that could be done to “improve” the circuit, but then it would not be the same amp.

Cheers.

Edits: vastly cleaned up to improve intelligibility.

"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki

Dynamic contrasts are something a well-sorted SET & high efficiency system can do well.

Cheers.

"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki

Speaker SPL @ 1m/1W =   90dB/W
Amplifier Power     = + 10dB/W
                     -------

Max SPL @ 1m        =  100dB

Stereo pair gain    = +  4dB
3m distance loss    = -  8dB
reverberant field   = +  2dB
                     -------

Max SPL @ list. Pos =   98dB

required SPL        =  105dB
                     -------
Surplus/Shortfall   =  - 7dB

http://www.audioasylum.com/cgi/vt.mpl?f=magnequest&m=11464

how something sounds is always subjective... to me they are excellent... minimal hum...

as far as cad files, they are in NX... attached jpg of the top plate... if you would like some others message me... thanks -Al