vtl output louder than direct output

[Estebandito]

Hi all,
I have hooked up the output of an LM386 audio amp circuit to a switch that lets me choose to either send the signal directly to the output or have it go through two vactrols to mess with it before it hits the volume potentiometer. Strangely, I am experiencing a significant difference in output volume between the two. The direct output is much more quiet than the VTL output. I am wondering if this could be caused by the controls signals operating the vactrols even when the audio signal is not routed through them. I can’t think of any other explanation, however, the level of the more quiet output doesn’t vary; it’s consistently low.


Are any of you familiar with this phenomenon?

ps. Another suspect might be the 100k pull down resistor between the two vactrols, as the other channel does not have a pull down resistor, but I don’t know how this would affect either channels volume level.

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[dk]

Hi,

Ideally, most of your circuit should be before the LM386, but that aside, there are a few oddities in your circuit:

When you have signal going through A, the B side of your circuit is in parallel with the volume pot. Try using a DPDT switch that disconnects both the input (as you already have it) and the output of the B side (where the 1k resistors meet). You can theoretically also remove the 1k resistors. Another alternative is to have the signal always go through the B side, and just have switches between your CV inputs and a high signal for the control signals.

On the B side, the VTL which control 1 hooks up to forms a voltage divider with the 100k resistor to ground after it, but the VTL connected to control 2 does not. That one effectively becomes part of the volume knob at the end. You're better off either making 2 control voltage inputs to the same VTL, or put a second resistor to ground after the second VTL, but you will lose a bit of signal that way.

Referring back to my first statement, though, the LM386 is a power amp. It's meant to be directly connected to a speaker. While you can put stuff after it (guitar pedal builders often put pots after them so they can be overdriven), it's intended that you put a volume control before it. You'll probably get more predictable results if you put your A/B circuit with one of the modifications mentioned above in front of the LM386 instead of behind it.

[Estebandito]