Cary 805, deHavilland or Atma-Sphere? Anyone cares

Using an Speltz autoformer for speaker/amp impedance matching is defeating the purpose of OTL.

From the FAQ at Zeroimpedance.com:

12) 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 transparence 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 frequence response of 2 Hz to 2 MHz.

Regards,
-- Al

Dracule1,
I cannot comment on the M-60. I have the S-30 so my remarks are related to it.

You stated:

"First, speaker choices are limited to those that are 8 ohms or higher, which have been pointed out. Using an Speltz autoformer for speaker/amp impedance matching is defeating the purpose of OTL."

With all due respect, I don't find that using the Spelz Zeros with my S-30 and Joseph Audio Pulsars defeats anything at all. On the contrary. The sound actually improved when I put the Zeros in.

You stated:
"... the image specificity is more diffuse than other tube and solid stage amps. Bass can be loose, if you don't have the proper impedance matching."

With my S-30 the images are spot on and the bass is tight. With the right tweaks the sound is so realistic, it is uncanny. I could not be happier.

I have not had any tube noise or tube failures.

Al, point well taken. I stand corrected. Then perhaps Atmasphere should just have built in autoformers in their amps.

Hi Sabai, I'm glad your S30 worked out for you and your speakers. My OTL amp didn't work out in my system. OTLs are more finicky and speaker dependent compared to other amps I've owned.

"With all due respect, I don't find that using the Spelz Zeros with my S-30 and Joseph Audio Pulsars defeats anything at all. On the contrary. The sound actually improved when I put the Zeros in."
If you found no degradation in sound and actual improvement, why doesn't Atmasphere build autoformers into their amps? Sounds like win win for the customer and Atmasphere.

Why doesn't Atmasphere build autoformers into their amps?

I'd expect that the main reason is that it would add cost, size, and complexity to the designs, while being unnecessary with many speakers.

Also, provisions would have to be made to allow the user to select among different impedance transformation ratios, and to bypass the autoformer altogether if high impedance speakers are being used.

Finally, having a Zero close to the speaker, as opposed to within the amplifier, helps to reduce the sonic effects of the speaker cable, since it results in the resistance and inductance of the cable being proportionately less significant in relation to the increased load impedance that is presented at the end of the cable.

Regards,
-- Al