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What's your OTL tube amp experience and suggestion?

Are OTL amps in general much less reliable due to their nature, or due to the implementation quality, or both?

Perhaps this has been discussed a zillion times in the past.   Perhaps, however, makers have now improve on past experience?  So it could be worth re-visiting.

My past encounters with OTL tube amps are among the most negative: Wonderful (but never great) sound during the brief period that they work.  Otherwise, major fire hazard.  Overheating, red hot plates, sparks, consistently toasted fuses, burning smell, you name it.  My past OTL amps are like crying babies on an changing table - don't you ever walk away from an arm's distance.   The used market seem to reflect such as well --- way more 'as-is for parts' or 'totally refurbished' units than reliable 'used' units that rarely need service.

Beg your pardon if it's just my poor judgement that keep getting the lemons.   What's your experience, and tips to keep OTL amps up and running happily?


bsimpson
lancelock
625 posts
 
Look into David Berning's ZOTL designs built by Linear Tube Audio.
tubegroover
2,279 posts
 
Not too sure about the SA-4, I was always of the understanding that they were one of the problematic designs. Agree that Atmasphere is certainly dependable and at least in my experience the Transcendent T-8 I owned without a hiccup. The Berning ZOTL designs are very dependable as well but the design is not a purist OTL without risk of opening up that debate again. 
lancelock
625 posts
 
@tubegroover - agreed, no more debates needed since it's certainly not a traditional OTL.  I suggest only having a listen. My MZ2-S pre and ZOTL40 combo powering my Janszen electrostats is the finest sound I've experienced.
swampwalker's avatar
swampwalker
5,132 posts
 
bsimpson- I've owned amps by the 3 major players in the OTL game at one time or another.  Here are my thoughts:
Joule-Electra 80 wpc stereoblock- Big, somewhat warm sound, build quality of basic chassis (no idea about music block) not as robust as it could be.  I suspect that thaluza's problem w the hum/buzz was due to bad joint at the input jacks.  Tremendous amount of heat.  Not recommended for those w inquisitive children.  The most "fiddley" of the 3.  Somewhat cubersome power-up procedure.
Berning ZH-270- One of the Berning built amps, not the newer LTAs.  Not fiddley at all.  Auto-biasing and auto-dc offset nulling.  Tube life should be very long.  I found the sound not all that engaging, but then again, I used it w/o a pre-amp and I have found that the pre-amp is a critical part of a system.  Lightest weight and lowest heat output of the 3.
Atma-sphere- I have owned the M-60s and now the S-30.  Manual bias and dc offset.  No reliability issues at all so far.  More neutral sounding and "faster" than the Joule.  Best customer support imaginable.  UPgrade path available, which extends warranty.  One of my 2 "go to amps" (the other is a VAC Ren 30/30). 

pryso
1,501 posts
 
bsimpson, in case you may still be following your thread.

I've owned a pair of AtmaSphere monoblocs and spent time with a few different Joule Electras.  From that experience I can offer two considerations.

First is the appropriate match with speakers.  That is a question of both power and load impedance.  Proper mating with lower than 8 ohms can be problematic.

Second is the issue with heat.  More output tubes may be required per channel to drive lower loads with OTLs.  My AtmaSpheres had 10 outputs per channel to produce 100 watts which I attempted with 4 ohm speakers.  They put out more heat than similarly rated transformer coupled tube amps.  But with less demanding (i.e. complex) music at reasonable levels they were magical.

That was all some years ago and now I look forward to auditioning the ZOTL 40s that lancelock recommends. 
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