Is this power supply 'sag'?

[saros141]

Been playing with my Rangemaster testbed... I alligatored my DMM to collector and ground, in order to keep a bias reading as I swap out xistors.  

I left the meter on once I got it set at -7.00V, and started to play a bit... and I found that when I hit a pretty hard chord or pop the wound E, the voltage drops temporarily... the lowest I could get it to read was -6.82, but my DMM's 'refresh' rate isn't that fast, so I'm guessing it probably drops lower than that on the transient... then it rises back up pretty quickly.

Is this 'sag' in the power supply?  

BTW I swapped in Alkaline and Carbon-Zinc and got about the same 'drop' for both (around 180mV).  I'm still trying to figure out if I can hear a difference between the two battery types.

[will]

Hi,

I doubt it is power supply sag; it’s a natural function of the circuit. The dc bias is set at 7 volts at rest. However when you are playing you are now superimposing an ac signal on top of the DC voltage. When playing really loud the top part of the AC signal is clipping and the bottom part is not. The DC signal is shifting up and down all the time. Your meter is averaging the DC signal. But with the clipping, the average voltage is now a bit less than the circuit at rest.

I don't think there will be much diff between the batteries, other than the Alkaline will last longer. This circuit is not hard on batteries. Over time with older batteries a lower input voltage will cause the circuit to clip sooner.

Regards,
Will

[petemoore]

Voltage Regulator on the battery and you can try lower voltages on the ckt...just a few parts and a pot...