In article <kk4i24t13io43j65n6jgmbjnpbr7juna56@[EMAIL PROTECTED]
>,
flipper <flipper@[EMAIL PROTECTED]
> wrote:
>
> Btw, the OTL doesn't 'require' the 120 ohm resistor and it works just
> fine as a 'low impedance' output.
>
> You could just remove the 120 ohm, and then adjust the FB resistor for
> the changed Vo, but there's also a nice trick can be played. Instead
> of the FB R and blocking cap. as shown, put a 12ohm under the existing
> Rk on V2A and take the headphone return to that junction. That
> eliminates the DC blocking cap.
If I am following your description of this mod correctly, doesn't that
convert the negative feedback from voltage feedback to current feedback,
with the expected effect on source impedance?
> With low impedance headphones there's a teensy improvement in
> distortion because, without the 120 ohm, output swing is less but
> it's negligible with 300 ohm headphones.
>
> Like I said, plenty of room for tweaking ;) But the basic topology
> looks good and 6CY7s are rather cheap.
>
> You felt the 6AW8s looked 'gloomy'. Well, lemme tell ya, the 6CY7s are
> anything but and those suckers glow like Christmas tree lights.
>
> Oh, something I noticed after posting everything. When I compromised
> with 200V on the phase splitter I forgot to readjust the R3 current
> soak resistor. It's there just to suck up the idle current V1A puts
> onto the output rail, and at 200V it's less than at 300V, so R3 should
> be more like 250k. Doesn't really matter all that much, though.
I was wondering about that, I had assumed that the 120k value shown on
the schematic was for the 200 volt supply feeding the phase inverter on
the "breadboard", and wondered why you hadn't also shown the correct
value to use with the intended 300 volt supply, now I see that I had it
sort of backwards.
Regards,
John Byrns
--
Surf my web pages at, http://fmamradios.com/
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