On May 10th, 2013 Paul Joppa posted a schematic and parts list for a parafeed build of the M91 amp....this was following some interest in the M91 article documenting the build by Joe Roberts in Sound Practices (Summer 1992)....Paul's schematic can be found here - http://tinyurl.com/ncdphjpI already had all the iron needed....Magnequest PGP-8.1 ps, TFA-2004 OPT (cobalt), EXO-003 plate chokes and BCP-16 GC HN grid chokes....actually I had most of the parts with the exception of diodes, resistors and a couple of capacitors....
my build started with a lot of enthusiasm, progressed until Dec 2013 and then came to a halt....unhappy with my layout and having ideas of improving it, I repurchased diodes, and some resistors with thoughts of taking it all apart and starting over....instead I just boxed everything up tabled it....
last week, looking at a stretch of vacation, I decided to finish it....working on the amps for about 30hrs+ in 4 days they were brought over the finish line....yesterday, with the gracious help of triode_kingdom (Jack) and his co-worker, Richard, they were powered up the first time....quite remarkable to me, the only issue was a floating ground, which was jumper-ed and the voltages were with in range....Jack said "these are ready to make music"....what an understatement....
got home, corrected the ground issue and fired them up....amazing....truly amazing....its all there....detail, bass, very "involving sound"....
thank you to Paul Joppa....so willing to share his knowledge with the community....Paul, when you read this please contact me with your email if you don't mind....another thank you to Mike LaFevre for the heart of the amps....I am fortunate to have a pair of the rare cobalt TFA-2004 OPT's....and to triode_kingdom for the start up....this guy knows the whats what and I am so thankful for his help....and also a shout out to Doc and the Bottlehead crew as these guys got my interest started in parafeed amps....
testing and some glamour shots above....when I turn them off I could post some shots from under if there's interest....
best
Al
Edits: 12/24/14 12/24/14 12/24/14 12/24/14Follow Ups:
- thanks for the comments.... - awsjr 04:16:32 12/26/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
the PS transformers bells, the tubes socket and binding post accents and amp back plate were all made from the same chunk of bubinga rosewood to match the amp base.... there is one single plate inside the amp clamping the (4) big capacitors in place and the hum pot is mounted flush to the top plate.... I wanted a clean looking build but take no credit as these ideas were combined from seeing other builds....
it is always subjective with terminology to describe how an amp sounds.... I have (2) 45, (2) 2A3, and (2) 300B amps for reference.... and my speakers are Onken 360L bass w/ GPA 515LF, Oris 200 w/ AER MD3 and Fostex 900T....
while listening to the W91, its the first time my wife has ever sat down and starting making requests to hear certain songs.... I looked over and she was mesmerized listening with her eyes closed.... it obviously made an impression on her.... me too....
the OPT's are very special.... I do have a pair of TFA-2004 nickel pin stripe I may swap in sometime to get a perspective.... then there's the mix of stuff - capacitors - the 3 PS caps are 22uF Obligato film and oil, the bypass caps are 16uF Mundorf aluminum and oil and ASC 45uF motor run, parafeed cap is a 10uF Mundorf silver w/ oil, the screen bypass is an 8.2uF Jantzen red and the .1uF is a RelCap TFT.... resistors - Dale, tantalum, Caddock and Mills.... most of the wire is 20awg silver.... been said its like baking a cake as all the ingredients add to the taste (sound)....
thanks again for the comments....hope everyone had a nice Christmas
best
Al
- RE: thanks for the comments.... - mqracing 00:15:24 01/12/15
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- In Reply to: RE: thanks for the comments.... posted by awsjr on December 26, 2014 at 04:16:32
Great job Al. My hat's off to you!!!
Builder of MagneQuest & Peerless transformers since 1989
- RE: thanks for the comments.... - mqracing 00:15:24 01/12/15
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- Some people.... - Frihed89 01:17:28 12/26/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
Like to look at schematics. Some people look at measurements. Some people like to look at the insides, others the outsides. Some people like to sit in chairs and murmur words of wisdom. Some people even write about what they hear. Some people like to listen.
How do they sound?
This is NOT a criticism. I'm afraid of electricity. I've never heard about, or even heard, an M91, and I envy people who can do some of the above, but i love the sound of recorded music and love it even more when it comes in as lovely a package as this amplifier.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
- Lovely craftsmanship. - 91derlust 16:26:26 12/25/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
I like the pentode-drives-SEDHT topology. Please let us know how the sound and your experience of it evolves over the next month or so.
Regards,
91
P.S. I'd like occasional access to a workbench like that. Of course, I would need to know what to do with it!
- RE: M91 Derivative Paul Joppa Parafeed build - Garg0yle 08:48:40 12/25/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
That is a nice build. Nice touch with the burled wood power transformers.
It is cool to see you were able to get together with a couple of other members, as I believe it helps add context to audio when all we can do is read about it for the most part.
I'm always interested in more pictures.
_
- RE: M91 Derivative Paul Joppa Parafeed build - D Mike 04:09:56 12/25/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
Great looking build. But, I'm lusting for the work bench.
- RE: M91 Derivative Paul Joppa Parafeed build - Paul Joppa 19:58:38 12/24/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
Sweet! Thanks for posting, sometimes I never find out if my posts are actually read :^) you can get me at bottlehead dot com, under my first name.
Please post reactions as they break in!
- RE: M91 Derivative Paul Joppa Parafeed build - Triode_Kingdom 17:39:28 12/24/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
It was a real privilege watching those amps light up for the first time. The quality of workmanship could put a lot of commercial products to shame. Great job Al!
--------------------------
Buy Chinese. Bury freedom.
- RE: M91 Derivative Paul Joppa Parafeed build - amioutaline? 10:19:58 12/24/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
Love the wooden tube socket escutcheon.
Hw'd you do the woodgrain on the PT?
At the request of the Moderators,
This space has been deleted
- RE: M91 Derivative Paul Joppa Parafeed build - Garg0yle 09:09:46 12/24/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
That is a nice build, I like the use of wood accents, even what appears to be burled wood transformers!
It is inspiring.
Its cool that a few of you guys were able to get together for the launch.
.
- RE: M91 Derivative Paul Joppa Parafeed build - johnsonad 07:29:26 12/24/14
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- In Reply to: RE: M91 Derivative Paul Joppa Parafeed build posted by awsjr on December 24, 2014 at 05:45:00
Beautiful builds Al! Congrats!
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