Bit odd - I have built this pedal before with no trouble but this time drew up my own layout so I could fit it into 20 columns, therefore squeeze it into a 1590B. I copied a fair bit of the layout from one I had done for a Honey Bee previously (which works perfectly!)
Can anyone see why this layout might cause the M pot to squeal when turned fully CCW, ie to full bass? It's sort of not a problem because I never use it with the M control fully CCW but I think it might be useful to know why it is doing this. The pedal works perfectly otherwise and I really like it. :-)
That M control is new to me and a bit puzzling, but it looks like a dual purpose variable high pass filter, 1 side before the distortion, and the other after the output buffer.
I cant reason out how that control can cause squealing as the frequency ranges on both sides seem somewhat low.
With the M control maxed, the control is grounding out the 4k7 on lug 3. I would probably check and see if any thing else grounds out when that control is maxed.
But looking at your layout, the only things likely would be the 3130 pin 6 or the 9v supply, neither of which would cause sqealing.
Or try this, disconnect lug 3 of the M control and see what happens when maxed. Then reconnect it and disconnect lug 1 and see what happens with it maxed. The symptom should most definitely change with one of those lugs disconnected. That should tell us something.
1978 Gibson Les Paul Standard, Cherry Sunburst, Nickel Tone Zone & Air Norton Pickups, Sweet 16 wiring
Thanks MAO! I hadn't seen the schematic before - I based my layout on Rockett's. I will definitely change the resistor to output just because it should be right.
The M control is a Bjorn specialty, very much like a Nature control on a Honey Bee. I guess the idea is to increase bass one way, increase treble or mids the other. In the past I have split the control to two pots to create a more conventionally operating treble and bass. But it seems to work ok in this pedal.
Coming from an amp-building background I was wondering if I have somehow created a parasitic oscillation or something. I will try disconnecting pins 1 and 3 and see what happens. Disconnecting pin 3 might not even do much!
After posting last night I went back and read through the posts about the Sparkling Yellow OD and it appears that I had the same exact problem when I first built it from a different layout! I had forgotten - I build so many of these things... So it's likely not the layout unless by some freakish coincidence the same thing happens in two different layouts.
And when I turn everything down to listen to the noise it makes when Nature is turned to the bassy extreme it is not quite a conventional squeal (!) but is more like a high-pitched purring sound. Almost like high-pitched motor-boating. Weird. I'm almost inclined to leave it alone because under normal use it's all fine and sounds damn good in fact.
I don't have an audio probe. Up until now I've never found the need for one.
Have you tried a buffer in front of it? I've made a few dirt pedals, including the EQD Talons, Boss HM-2 and Chunk Systems Black Dog which squealed on certain settings. A Klon-type buffer cured the Talons and HM-2, though the only thing that would stop the Black Dog from howling was hooking up a another, buffered pedal in front of it!
Maybe worth a try.
That's probably a very good idea, Lasermonkey. Thing is, under normal use it's not an issue so I don't think I can be bothered! Terrible I know.
I did change the resistor to Volume 3 to 4K7 from the 47K I had and I think it has probably made the pedal a tiny bit louder - it sounds great! So the only real mod I have done is to increase the value of the input cap from 22uF to 47uF, and i really like that change. It's not night-and-day different, just a little fatter.
So weird that you are making a Model G, MAO. I just made one today having got all the bits together last week. I wanted to build it again because I remember liking it last time but couldn't work out what the C control was supposed to do. So I've made it again and if the trace is right it does next to bugger all, just like when i made it before. It seems to shift the frequency of the mid peak a little but it's very subtle. I think it could be handier to measure the pot where I like it and stick a resistor on the board to do that job and use the available spot for a treble control. It's just a hair too bright for me.
So I built another Sparkling Yellow OD today and it got me thinking about this squeal again - because the new one squeals exactly the same. When i look at the Model G the 4u7 going to Nature doesn't connect directly to pin 2 of the chip. It connects to pin 2 (and Gain) via a 1K resistor which also goes to a 220n to Vref . There is a 1K in the Sparkling Yellow which also goes to a 220n from pin 2 but this time the 220n goes to ground. Still, I suspect that if I connect the 2u2 nature cap to pin 2 via that 1K I might avoid the squealing.
Could it be that a slight error crept into the trace? It would only be a tiny mistake but it might be the answer. I will test and report.
Fixed! Yup, moving where the Nature cap connects fixed the problem. So here is a completely working layout. If you want completely stock use a 22n input cap. I have changed it to 47n because it works better with a Strat like that. :-)
Not really. It might reduce the effectiveness of the Nature control a tiny bit but not enough to worry about. I have a feeling that this is really how the circuit should be. It sounds a lot how I remember my original sounding, as far as memory of sound is reliable!