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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
tubegroover
2,320 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
1,085 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
5,138 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
1,908 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. 
mikelavigne
2,147 posts
 

my OTL experience is now more than 10 years ago, but the OTL magic is still a guiding light in my sonic compass.

in 2001 i was moving away from Wilson WP6’s and top level Mark Levinson #32 and #33 mono blocks. i looking for a more involving and musical presentation and purchased Kharma Exquisite Reference 1D speakers and starting searching for an amp to go with it. tried a few and then had the opportunity to demo the Atma=sphere MA2 Mk2.2’s in my room and really liked it. i was ready to pull the trigger but then had another opportunity to try the Tenor 75 watt OTL mono blocks. ok; here was a modestly powerful amplifier but this one had a fire in the mid range and was linear top and bottom. it seemed like a direct connection to the music. so i purchased the Tenors and had a 3 year love affair.

like some other love affairs, it was painful too. the darn Tenor would explode on a regular basis and take out drivers in the Kharma’s. that direct sound and lack of transformers did have it’s dark side. so I ended my love affair.....but looked around for a something else that could be similar but was reliable.

i ended up with darTZeel NHB-108 solid state which combined that fire in the mid range and transparency of the Tenors, but also had the solid state attributes of lower noise, more authority, and reliability.

back to the Tenor OTL’s; eventually Tenor went bankrupt; but the good news is that another group bought the assets and raised it from the dead, and the 75 watt Tenor OTL’s got their design cleaned up and did become reliable......and i would strongly recommend a set if you can find one (and make sure it was built after 2005 or upgraded.

it’s a magical amplifier. or get a darTZeel solid state and never look back. i did.

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