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Thought on OTL tube amps

Just curious....how do these sound/perform compared to tube amps with transformers? Why do you prefer one or the other? Any particular brands of OTL amps you would recommend listening to? You can see my system on my tag here...listen mostly to rock and roll with a smattering of jazz and a bit of classical once in a while. The next stop on my amplifier adventure is an OTL model, and I have no intention of trading it for either SET I currently have, as I'm very happy with both. One of the ways I enjoy experimenting with different "sound" is by switching up the amps. Just trying to solicit some opinions, of which I know there are many strong ones here at A-Gon. Thanks in advance!
afc
xonex77
42 posts
 
Using the Zero nullify an OTL status.You already get rid of transformer then put new Transformer?Whats happening? going in circle?
wolf_garcia
6,712 posts
 
I'm convinced…I'm immediately removing the output transformer from my amp…those wire cutters are around here somewhere...
ct0517's avatar
ct0517
2,041 posts
 

bsimpson

Perhaps I should put my $0.02 here from an end-user perspective.

I have owned at least seven (7) different OTL tube amps, some are big brands, some are DIYs from experienced (10+ yrs) tube amp hobbyists with extensive engineering experience.

IMHO, OTL tube amps are reliable if you understand their operation limitation first. I found that:

1) OTL tube amps do not work well under 4 ohm or less speakers. Even some transient passages at 2 or 3 ohms may blown the tubes. This is not specific to the tube type.

2) OTL tube amps are much less tolerant to wide impedance swing. The more stable the speaker's impedance, the better.

The best sound I got from OTL amps is when I use them to drive impedance-friendly monitors, with the aide of quality subwoofers covering 180Hz-250Hz and below.

Hope this helps.

This is a good summary bsimpson. And that's quite the experience with so many different OTL's, although you don't list the brands amps/speakers. Thanks for sharing. I particularly take note of your last comment - aide of quality subwoofers 180hz - 250hz. Very difficult to do going this high in the frequency range, even in a dedicated space. 


atmasphere's avatar
atmasphere
11,861 posts
 
I use the Classic Audio Loudspeakers model T-3.3 at home. It goes down to 20Hz. A set of our M-60s has no troubles driving them to very high volume levels with very satisfying bass (shakes the house). M-60s are full power down to 2Hz. 

Like **any** other amp, if you want to hear what its really capable of, its a good idea to put it on a speaker to which it is well-suited.
almarg's avatar
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almarg
9,670 posts
 
Using the Zero nullify an OTL status.You already get rid of transformer then put new Transformer?Whats happening? going in circle?

Xonex77, your question is a logical one, but there is a good answer to it.  From the FAQ at the website for the Zero:
What is the difference between the ZEROs autoformer and a typical tube amplifier's transformer?

The ZEROs have a few advantages over "typical" tube amp transformers:

A) The music comes out on the same winding wire that it goes in on so the music does not have to pass from a primary winding to a secondary winding.

B) There is no DC current to contend with. When a transformer is made to accommodate a DC field, its audio transparency is compromised.

C) The impedance ratio is very small (16 ohms to 4 ohms, compared to a few thousand ohms to 4 ohms). This simply means that it is much easier to achieve things like, frequency response extremes, than with a "typical" tube amp transformer. The ZEROs sport a frequency response of 2 Hz to 2 MHz.
All transformers (and autoformers) are not created equal!

Regards,
-- Al
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