Does variable B+ for tube mics make sense sound-wise?

[rock soderstrom]

What do you think? Is it useful to implement a variable B+, with simultaneous static polarization voltage? I did some experiments with it and was surprised. My test circuit is without NFB and loosely based on a SELA T12/T24 mix. Voltage range was betwen ca. 70 and 140V.

 

[gyraf]

..would probably depend on the actual tube and biasing setup - but in e.g. the G7, I haven't been able to detect significant change in characteristics even over quite a large B+ range (as long as pol voltage was kept constant)

That said, going very-high tends to increase grid bias (that we don't want) and going very-low introduces (in the G7) early distortion in a imo non-flattering way.

/Jakob E.

 

[rock soderstrom]

..would probably depend on the actual tube and biasing setup - but in e.g. the G7, I haven't been able to detect significant change in characteristics even over quite a large B+ range (as long as pol voltage was kept constant)

That said, going very-high tends to increase grid bias (that we don't want) and going very-low introduces (in the G7) early distortion in a imo non-flattering way.

/Jakob E.

Thanks for your experience. Was NFB installed in your G7 test or without?

 

[gyraf]

..this was without the nfb, that I gave up on that early (it never made anything more interesting, only the opposite)

 

[kingkorg]

I experimented with variable cathode resistance and capacitance for different flavors. I liked it a lot, i also went crazy for extra crunchiness, room mics, special fx... Some members here thought it was plain stupid, as many think lowest thd is always the way to go. I say experiment and listen, you can always go back to clean setting.

 

[Gus]

If you are going to adjust B+ and capsule voltage another fun thing to do is to adjust the heater voltage

Zebra50 posted a build years ago IIRC that had variable capsule and heater voltage settings on the power supply.

When I build a triode plate out microphone I often adjust the capsule voltage and heater voltage at the last part of the build and this might change if the capsule is changed.

 

[rock soderstrom]

I experimented with variable cathode resistance for different flavors. I liked it a lot, i also went crazy for extra crunchiness, room mics, special fx... Some members here thought it was plain stupid, as many think lowest thd is always the way to go. I say experiment and listen, you can always go back to clean setting.

My experience is similar. I believe that a variable B+ voltage can make sense and soundwise fun! I was amazed at the differences after a short test.

The right dose of THD can give a signal exactly what is needed.

Low B+ can thicken a thin voice like mine quite a bit. An acoustic guitar sounds authentically 50's with the right amount of distortion. A reality fanboy will tend to hold the pot to the right stop for maximum headroom and lowest THD, I'm more of a K2 addict.

I will put this in my next PSU, the voltmeter will be modified with a LED afterwards and can then act as a big status light at the same time.

 

[rock soderstrom]

When I build a triode plate out microphone I often adjust the capsule voltage and heater voltage at the last part of the build and this might change if the capsule is changed.

Interesting! In my test setup I can also adjust everything. With a variable B+ I hear more differences than with the heater voltage.

At the polarization voltage I do not really dare, I'm afraid that the capsule collapses and dies.
Besides, Kingkorg has described elsewhere that changes of the polarization voltage (inbetween a small range) have little effect.
Therefore I keep it constant at 60V

 

[Delta Sigma]

Interesting! In my test setup I can also adjust everything. With a variable B+ I hear more differences than with the heater voltage.

At the polarization voltage I do not really dare, I'm afraid that the capsule collapses and dies.
Besides, Kingkorg has described elsewhere that changes of the polarization voltage (inbetween a small range) have little effect.
Therefore I keep it constant at 60V

But lowering the polarization will attenuate, won't it? So also useful as a pad?