Wondering what would be the tonal difference in a guitar amp circuit where the power amp section sags and reduces the preamp supply voltages?
Example, preamp supply voltage around 380V decreasing to say 330V.. Would there be an appreciable difference? Or would it be difficult to notice? Maybe lose a little edge and clarity/definition/note separation?
Thank you
Example, preamp supply voltage around 380V decreasing to say 330V.. Would there be an appreciable difference? Or would it be difficult to notice? Maybe lose a little edge and clarity/definition/note separation?
Thank you
I would have thought there would be little or no difference so long as the anode voltage isn't reaching the rail voltage.
I always separately decouple each 12ax7 stage well.
This stops feedback via the supply rail and possible oscillation.
Grid stoppers are advisable too.
I always separately decouple each 12ax7 stage well.
This stops feedback via the supply rail and possible oscillation.
Grid stoppers are advisable too.
When output stage sags, then main changes in distortion spectrum takes place also at the output stage.
The changes at voltage amplifying stage compared to that are minimal.
The changes at voltage amplifying stage compared to that are minimal.
The 50V PSU sag will increase the bias point of a 12ax7 in a typical common cathode stage with about 0,25V. If it's audible depends on many factors. Input voltage swing and stage design for example. A very warm biased common cathode stage might give an audible effect compared to a stiff PSU, but a typical cathode follower wouldn't.
It also would depend some on if the stage was fully bypassed on the cathode. The bias point would be more stable with situation. Sometimes the tube would have less headroom with lower plate voltage, but I don't think much difference would happen at these higher voltages(380-330v). Some vintage amps ran the plate at around 100v and a drop in voltage at this level would add more distortion and have less headroom. I agree with Nigel,mostly not much difference in your situation.
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Hi Guys
Generally, a reduction of preamp supply voltage will make the tone warmer, but it takes a significant voltage drop to cause this. Changes of 10-20V will make a "nuance" but 50-100V will be a "broad stroke".
You can hear these differences best if the output stage is not clipping or causing obvious distortion. You can do this by changing a single dropping resistor in the power supply. The value change will be significant, in the 10s to 100s of k not just single k.
Have fun
Generally, a reduction of preamp supply voltage will make the tone warmer, but it takes a significant voltage drop to cause this. Changes of 10-20V will make a "nuance" but 50-100V will be a "broad stroke".
You can hear these differences best if the output stage is not clipping or causing obvious distortion. You can do this by changing a single dropping resistor in the power supply. The value change will be significant, in the 10s to 100s of k not just single k.
Have fun
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