More output/volume from this circuit

[gutsofgold]

I've been trying to 'tweak' this build to sound best with my guitar and amp. One problem I had was to get it to unity gain, the volume on the pedal is often set to 75 - 85% just for it to be loud enough to match my amp when its off.



I tried a 50k pot for the volume (audio taper) and it seemed to help a little. Would 10k make that much difference? Or would I best to change that 10k resisitor .047 cap series before the pot?

[John Lyons]

CHanging the 10K will change the tone a bit as it's part of a low pass filter.
Try making it 4.7K and see if it helps. Not sure you will get much more level though

Making the vol pot smaller will reduce the output.
Adding a diode in series with one of the 4148s will give you a little more juice and make the clipping asymetrical.

The 1M resistor is setting the gain so there isn't much room to go up there. Since the clipping stage is at the end, the diodes limit the output of the circuit. If you need more level you may just have to tack on another stage to boost the level. The big muff last stage may work.

[johngreene]

Smaller value pots are only going to make it worse because of the 10k resistor. With an audio taper pot to ground, you will be able to attenuate the signal all the way down to zero at minimum and will have 91% of the output from the opamp available at full volume. The unity gain point is a function of max available output and pot taper. If you have enough max gain available, then changing the taper from audio to standard will lower the unity gain spot but the top end of the adjustment range will seem like it isn't doing much. You could also put a resistor between the pot and ground to raise the minimum level. If you are not getting enough max volume, the only way to increase that would be to add diodes to the two that are already there. As it is, you should have approximately 3 times the volume available than from the guitar alone because of the diodes limiting the output. If adding diodes changes the character too much, you can do as John Lyons suggested and add a bit of gain on the output.

--john

[Gus]

I would try a 100 ohm for the 10K at the output.

[gutsofgold]

I like the way it sounds I would like to leave the diodes as they are.

If the 0.047 cap at the end is the decoupling cap, what purpose does the 10k resister before it serve?

[Gus]

A series resistor in the output of a opamp can be for a number of things.

A way to protect the output of the opamp if something shorts the side of the resistor to ground or one of the rails the resistor can be sized to limit the max worse case current that might happen protecting the opamp.  In this case a min load of 10K with the volume up full and a short from wiper to ground etc.

The resistor can also be used to limit the max volume.  In this schematic the total load not connected to anything is 10K plus 100K volume for 10/11 max output compared to the signal at the output of the opamp before the resistor

Some opamps circuit can have problems driving cap loads a series resistor can sometimes help this.

Question what are you plugging into after the circuit? maybe it is loading down the output because of too low an input resistance, are you using an audio taper volume pot or a linear taper pot?.

[gutsofgold]

Right now its an audio taper pot (as dictated by the schematic) 100kA.
I'm plugging my guitar into this circuit only and then running it into a simple 15 watt tube amp.