Morris Slutsky
September 27th 09, 10:07 PM
On Sep 27, 5:06*pm, Morris Slutsky > wrote:
> Output stage schematic: *http://img14.imageshack.us/img14/8218/pseudootl.jpg
>
> Been playing around with this in SPICE. *This is sort of inspired by
> Brosie's single ended "power buffer" circuit, only it's push-pull.
> Maybe it's sort of like a McIntosh output stage, except that it
> doesn't use a separate feedback winding.
>
> What I like about this idea is that it seems like a very easy way to
> apply a bit of damping right at the output stage, without worrying
> about low-frequency rolloffs and phase shifts during preceding
> stages. *Might be an easy way to tame the low-frequency high-impedance
> resonance of a loudspeaker. *While it might be difficult to get
> sufficient drive with low-gain triode or beam tetrode tubes, it
> doesn't look like a difficult problem to drive this circuit using EL84
> or EL34 pentodes.
>
> It's also an elegant looking circuit - to actually hook a speaker
> right to the tube cathodes, almost looks like an OTL! *I could even
> pretend that some of the tube milliamps were directly driving the
> speaker, assisted by the transformer secondary.
>
> I wonder why I've never seen this circuit before. *Is there some
> reason that this hasn't been used?
>
> I'm a little concerned about stability, about high resonance
> frequencies where the transformer induces a 180 degree shift. *Any
> ideas how to be safe about this?
>
> Thanks, I look forward to any suggestions or advice.
I have drawn 4 and 16 ohm taps on the secondary, as I imagine that a 4
ohm tap would be a center tap between 0 and 16 due to the square law
of impedance. I hope this is correct.
> Output stage schematic: *http://img14.imageshack.us/img14/8218/pseudootl.jpg
>
> Been playing around with this in SPICE. *This is sort of inspired by
> Brosie's single ended "power buffer" circuit, only it's push-pull.
> Maybe it's sort of like a McIntosh output stage, except that it
> doesn't use a separate feedback winding.
>
> What I like about this idea is that it seems like a very easy way to
> apply a bit of damping right at the output stage, without worrying
> about low-frequency rolloffs and phase shifts during preceding
> stages. *Might be an easy way to tame the low-frequency high-impedance
> resonance of a loudspeaker. *While it might be difficult to get
> sufficient drive with low-gain triode or beam tetrode tubes, it
> doesn't look like a difficult problem to drive this circuit using EL84
> or EL34 pentodes.
>
> It's also an elegant looking circuit - to actually hook a speaker
> right to the tube cathodes, almost looks like an OTL! *I could even
> pretend that some of the tube milliamps were directly driving the
> speaker, assisted by the transformer secondary.
>
> I wonder why I've never seen this circuit before. *Is there some
> reason that this hasn't been used?
>
> I'm a little concerned about stability, about high resonance
> frequencies where the transformer induces a 180 degree shift. *Any
> ideas how to be safe about this?
>
> Thanks, I look forward to any suggestions or advice.
I have drawn 4 and 16 ohm taps on the secondary, as I imagine that a 4
ohm tap would be a center tap between 0 and 16 due to the square law
of impedance. I hope this is correct.