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OTL and Parallel tubes

Posted by Perseo on March 1, 2002 at 03:54:13

In Reply to: Bottlehead SETs vs OTL posted by tottman2 on February 28, 2002 at 05:03:59:

I can't tell you anything good or bad about the Transcendent amp. I can tell you what I found with my OTL headphone amp.

After building a Foreplay, I decided to build a similar preamp that could drive highish impedance headphones -- Sennheisers with 150 ohm impedance. The topology is really similar to Foreplay, and the power supply puts out 150 volts DC, quite like FP. Driver tube is 6SN7 class.

To get the output impedance down, I paralleled three 6SN7s. For a cathode follower, output impedance is approximately 1 divided by the transconductance for one tube, with paralleling tubes lowering it further in the way paralleling does. No output transformer, just like Foreplay.

Now I was able to hear single ended sound for the first time. But, like all of you guys, I kept on tweaking.

Doc suggested in a post that paralleling tubes can smear the sound. So, I switched the output from 3 6SN7s to a single 6BX7. The improvement was dramatic, not subtle, bringing up the detail and you are there quality of the music.

So, like those posting below, I am convinced that a single output tube OTL has a big edge over paralleled tubes.

Perseo

I was taste testing all kinds of NOS tubes as drivers, including 12liste

more than one tubed For the follower tube ( It's the Driver tube

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