The input potential meter lowers the signal so then it's not as loud because it has to amplify it a lot due to how an LM 386 is. For the gain you might wanna look up the Ruby amp schematic and follow how they handle pins one and eight, or look at the LM 386 data sheet for the info.

Quote from: antonis on Yesterday at 09:04:47 AM

Quote from: Microtone on Yesterday at 07:06:56 AMI am considering using the little gem circuit as an overdrive circuit.
I simply want to put the circuit in a pedal, without changing any values, and use it between the guitar and an amp.
Will it maybe be too loud?

Loudness can easily be set by Master Volume pot setting..

Take into account that LM386 minimun gain allowed is about 9 (not compensated for gain of lower values..) so it should be a good idea to place a pot between IN and input capacitor to be flexible enough for signals of high amplitude and low gain combination..

Thank you for your reply. I fear I may have already waded in out of my depth! What exactly does minimum gain mean? And the same question to high amplitude low gain combination! Is that to do with the input signal?
I went ahead and built the circuit into a pedal and it seems to work nicely with a medium output single coil guitar as well as a higher output humbucker guitar.
But I'd love to understand the implications of the caveats you mentioned, to ensure it's versatile.
At the moment I don't have a gain control in the circuit, so it's always at full gain with just an output volume control. But if I were to include a gain control, what would I need to consider for the high amplitude low gain caveat? And how does a variable resistor on the input help that? Would that not just reduce the voltage of the input signal?

The green leads are connected to sleeve lugs. He's used a stereo jack for the input to switch the power to the battery (which is why the + of the battery clip is connected to the ring lug, so it connects to gnd when a mono jack is plugged in).

[/quote]

No wait, I'm wrong and Duck_Arse is right, I think.

If those aren't sleeve lugs the green leads are connected to, then there wouldn't be power to the circuit (as ring wouldn't connect to sleeve) but there would still be power to the LED! Those are switching lugs maybe? So they'd do the opposite and connect the power when the circuit was UNplugged...? Connect the green leads to the lugs actually touching the sleeves at the top of the sockets and all should be good (though I suspect the LED will stop working).

edited for nonsense (see below)

2 welcomes [cause antonis won't].

when I look at your jacks, I ask myself - why hasn't he wired the ground/sleeve lugs? how does he get a common connection without the sleeves?

you need to check your sleeves. you also need to be using mono jack plugs. please link us to those exact jack sockets that we might observe the pinouts.

Quote from: Jaden on April 23, 2024, 08:27:09 PMbut LED works

This is the smoking gun for me. As shown, the LED shouldn't work! It's connected from positive ground at the ring of the input jack to positive ground from the board/sleeves, via a current limiting resistor (which shouldn't, as shown, have any current to limit?)

Quote from: ElectricDruid on April 23, 2024, 02:37:59 PMNo, I've checked and you're right and I'm wrong. Sorry about that. The VCA itself doesn't invert, but the whole thing does. I had it back-to-front.

Quote45 degrees at the cutoff freq.

QuoteThat's true, but that one resistor value makes a big difference to the overall frequency response, as well as the phase!

Thanks for clarifying!

I drew up a few more examples with the goal of achieving self oscillation:
The first one is a low pass filter.  It is the same one as the first one I posted but with an extra all pass filter added in the resonance path to get the required 360 degree phase shift.  With this setup I would have a one/two pole low pass filter with second order resonance capable of self oscillating?


This one is the high pass version:


The last one is a one/two pole high pass filter with 4th order resonance that should still be capable of self oscillation:


The down side is it requires an extra VCA.  If I were to do a low pass version I think I would just use figure 32 from the application note.

I have a lot of experimenting to do.  There could be a more elegant or clever way of doing things but I want to make sure my head is at least a little bit in the right place.

Looking at the schematic, the 4570 chips might provide an improvement in noise specs, but don't seem at all necessary for normal functioning.  Were they used in the original?

My best recommendation here is to use an audio probe to trace progress of the signal through the circuit.  Audio probes can mimic the circuit-under-test "ending" at various points.  For instance, at pin 1 of IC1a or pins 3 and 1 of IC3a, as examples.  If you have audible signal at those points, then you know everything UP TO that point is functioning as it should, and any troubleshooting can safely ignore those parts of the circuit.

The probe itself is very simple.  It is just a regular patch cable, with whatever plug you need (1/4" or 1/8" phone) at one end and the other end consisting of an alligator clip to connect the shield to a suitable and convenient ground point, and the "hot" end terminated with a non-polarized capacitor; hopefully with a nice stiff and long lead that can be touched to various points on the circuit.  The lead does not have to be part of the capacitor.  Soldering one end of a standard voltmeter probe to the capacitor can work every bit as well, if not better.  Plug into an amp (with volume set low enough), turn the amp on, and with some signal source applied to the pedal circuit input, and the alligator clip secured to a ground point, touch the probe to various strategic points on the board, until you identify a place where the signal seems to just end abruptly.  That can also include the stompswitch.  Many forumites in past have overheated the solder lugs on a stompswitch, and caused the grease inside it to liquify, flow, and form an obstruction to signal.

Quote from: Microtone on Yesterday at 07:06:56 AMI am considering using the little gem circuit as an overdrive circuit.
I simply want to put the circuit in a pedal, without changing any values, and use it between the guitar and an amp.
Will it maybe be too loud?

Loudness can easily be set by Master Volume pot setting..

Take into account that LM386 minimun gain allowed is about 9 (not compensated for gain of lower values..) so it should be a good idea to place a pot between IN and input capacitor to be flexible enough for signals of high amplitude and low gain combination..

You could also look at the MC1495 or MC1496 analog multipliers produced by Motorola.  The MC1496 is commonly used as a multiplier for radio frequencies and the MC1495 has additional internal connections to make it work better at DC or audio frequencies.  These are linear multipliers so the log scale needed for audio should be applied to the volume control input voltage.  Motorola has schematics in their linear data book.