OTL amplifiers

I agree with Trelja that finding an OTL friendly speaker is the optimal way to go, but I did have exceptional results with the ZEROs and a previous set of speakers that, on paper anyway, were a good match for OTL amps (nominal 8 ohms that never dip below 6.5 ohms). I obtained these results by using an alternative 2X configuration that I understand involves using less of the windings in the autoformer. Using this configuration, I was able to retain the refinement of the Atma-Sphere M-60s, in the process though bass performance suffered. I then put a second pair of ZEROs, using standard 2X configuration, on the woofer binding posts and the overall performance of the system went through the roof. The whole spectrum was improved, bass performance was phenomenal, and the mids and highs benefited in major way as well. The resolution of the system improved enormously. I had strong expectations that by using the second pair of ZEROs I would get the bass performance back that was lost when switching to the alternative 2X setting. I ended up with performance that vastly exceeded the sum of the parts - making me a wildly enthusiastic believer in the ZEROs. I now use a pair of speakers that are rated at a 10 ohm nominal impedance and I achieve better results without the ZEROs.

Wellfed your points are well taken. I however agree with Trelja in my experience with the autoformers. I found the 1.37 setting the best. 2X was ok but anything above that the sound became whiter or more solid statish losing much of the natural sweetness intrinsic to the Transcendent amp I used it with. Indeed the bass was improved. It seems this device designed with the Atma-sphere in mind decidedly didn't do what I needed in my system. I liked it at first but found myself over time going back to direct most of the time. What I needed was more OTL power.

I feel the zero autoformer is a very well priced well designed product that will benefit some systems more than others but bear in mind that the character of the sound changes the higher the multiplier.

I have heard reports that OTL's like Tenors have been known to blow out speakers due to the lack of there being a (transformer, buffering factor?) Any truth to this?

Hi!
The Zero Autoformers have another great advantage: they won't alow that amps blow out your speakers. I believe that was one of the idea's when constructing the Zero's.
I agree that results with them vary, but do try them... I'd rather invest in them (because of their universality-they work even with solid state amps!) then in speaker cables of that price. But that's just my five cents...
Cheers!

The alternative 2X setting I refer to use the white and black leads attached to the speaker binding posts and the blue and yellow leads attached to the amplifer posts. This configuration brought back the "magic" OTL sound, but resulted in a small loss on the bass side of things. If I only had one pair of ZEROs or did not have bi-wire capability I would have easily, and happily settled for this setup and accepted the loss of bass output for the improvements gained elsewhere.

Not entirely content to leave it at that however, I contacted Paul Speltz and he suggested I try a second pair in standard 2X mode on the woofers and like I said before, the results were phenomenal. The best of both worlds and then some.

I don't know why Paul doesn't promote this setup more at his website. I don't know if my results would be achieved on other speaker models, but on N.E.A.R. 50Me II loudspeakers the gains were absolutely awesome.

One method I never tried, but would be curious to hear the results of, would be to bi-wire using just one pair of ZEROs.

On the N.E.A.R.s I would use the configuration described above on the high frequencies and another alternative 2X such as brown/green or gray/green on the low frequencies. If anyone tries this, you might as well try the reverse as well, brown/green or gray/green on the highs and white/black on the lows, to see if there are any gains.

Refer to Group 2 Configurations at the ZeroImpedance.com website to see a diagram of the alternative configuration options I refer to.

I know that this bi-wire with one pair of ZEROs is an option, but for safety, please check with Paul Speltz before trying.