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My latest amp ...a push pull eventually

188.216.123.170

Here it is. Now playing. There is not much to say about it ... a couple of differential pairs direct coupled and stacked over a string of zener. That's something I made in other amps before this but, hey ... this is a push pull now after many many years in the deep dark side of single ended amps.
I'll shoot some measurements one of these days.

Edits: 10/13/12 10/13/12

Follow Ups:

RE: My latest amp ...a push pull eventually - dhsettim 23:55:16 10/22/12 (1)
Hi, could this be built with stacked power supplies rather than using the zeners?, regards, tim
- Yes, you can ... - gluca 10:56:28 10/23/12 (0)
  ... but you would toss more $$$ on the amp and you would not have any more what I like: the upped CCS+zeners kinda work as shunt regulated PSU for the lower differential pair.
  
  zeners can be a bit noisy but we are talking here of final stages in power amps and you can anyway bypass them with some film caps.
  
  gianluca
a few runs on my oscilloscope ... - gluca 01:37:04 10/20/12 (0)
Thanks Bas. I built the prototype in almost nothing ... maybe a couple evenings and all went OK at the first power up. Kinda scared at first turn on but it looks really stable and reliable so far. Probably the best sounding amp I built ... Initial idea was to use EL84 but I found those 4 VT52s.
Noise 0.8mVrms (AC filaments and a simple cLC filter ... not hoping to go that much low!)

Square 1kHz 3.28Vrms on 8ohm

1KHz tone at 2.40Vrms on 8ohm

FFT of the above signal. 3rd harmonic is at -44.8dB... now, my lecroy is a 8bit oscilloscope so FFTs are just for troubleshooting

FFT of 1kHz+3.3kHz to show intermodulation ... it's below 50dB

Edits: 10/20/12
I LIKE it.....will build something similar - Bas Horneman 06:08:42 10/19/12 (0)
...but with EL84.
To infinity and beyond!!!
details - gluca 10:59:45 10/13/12 (4)
Zeners are 15x16V each ... mind the wattage as they are heating quite a lot. I need to fix this bug, mine are boiling.

EXO99 is used as push-pull choke or as if it was a primary of a interstage transformer
EXO99 is also acting as a sort of grid choke for the following stage

You want to add a pot under the cathodes of 6CG7 (not shown and not yet implemented in my prototype) to fine tune the bias of the output stage.

VT52 are running quite balanced, there is kust 1.5mA of unbalanced current across the MQ565.

CCS' are cascoded depletion FETs (DN2540 or similar) as widely used nowadays.

The amp biases pretty stable and with no issues... I didn't check all the fail modes so maybe something catastrophic may happen if something goes pop ... there are very few parts and each of them is important.

AC on the filaments ... no problem whatsoever.

THe amp can easily be adapted with minor mods to 45, 2A3, 6A3 and all the puppies in that range of mu/Rp.

Very tight basses (better maybe of my PASS F4), sweet mids and all the highs you need. A no coming back (until the next amp)

Gianluca
- RE: details - Frank Mena 09:19:57 10/15/12 (3)
  Just curious... why did you use the MQ565 instead of perhaps say a S240 trans for the push pull?
  
  Looks fantastic.
  
  Cheers
  Frank M
  - RE: details - mqracing 19:13:56 10/20/12 (1)
    Hi Frank:
    
    The S-240 does NOT have screen taps--- so if someone were building an amp with EL-84's and wanted to go UL the 240 is not an option--- plus the 240's pri impedance is too low for most EL-84 apps that I've seen.
    
    Don't shortchange the orig dyna 565 design--- it's actually a pretty good design and one of the best for EL-84's if your building UL. Dyna actually ran the core conservatively and the UL taps have very good AC symmetry--- which a lot of other ul tapped outputs do not have as well.
    
    Norman Crowhurst wrote an article on optimizing an amp with UL taps and explains the need for AC symmetry btwn the two opposing taps.
    
    MSL
    
    Builder of MagneQuest & Peerless transformers since 1989
    - Thanks Mike.. - Frank Mena 07:14:57 10/22/12 (0)
      My confusion in Gluca's post was with the VT52 tube as I always thought it was only a pentode tube . However a little digging led me to seeing there are two different versions with the same name, one British (pentode) and the other American (triode). So that is why he could substitute tubes like the 2A3 in his circuit. Gluca's stuff is really facinating for me.
      
      In any event, I am still going to build the Baby Huey (link below) with the EL84 and your MQ565 which can use the UL taps. It will be my first scratch build and my thought was why not start off right with the really good stuff!! (MQ565)
      
      Cheers
      Frank M
      Baby Huey (Open in New Window)
  - RE: details - gluca 12:31:34 10/15/12 (0)
    the project started with EL84s and evolved towards VT52 as i found a nice quartet along the way

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