Blue shoe gai pan

[tallenosborne]

Built this circuit, this is my third one and for some reason the sweep and mid control have no audible effect. Isolated the dual gain pot, reflowed all my points on the pots, push works so the haunting mids circuit is working I'm just stumped. Everything on the pedal works. Fets are biased at 4.5v. Help please!

 

[giovanni]

Post pics of both sides of the board please!

 

[tallenosborne]

Post pics of both sides of the board please!

K got em up

 

[giovanni]

I see at least a couple potentially cold solder joints that you may want to reflow. Did you verify all component values?

 

[tallenosborne]

I see at least a couple potentially cold solder joints that you may want to reflow. Did you verify all component values?

Yes all component values are correct and the pedal sounds as it should as far as the push driving the gain stage of the superbolt circuit just no variance in mids and sweep

 

[tallenosborne]

Yes all component values are correct and the pedal sounds as it should as far as the push driving the gain stage of the superbolt circuit just no variance in mids and sweep

Update, I get no reading on lugs 1 and 2 on the dual gang pot, but 100k reading between 2 and 3 when turned all the way to the left. Dual gang pots aren't supposed to behave this way correct?

 

[tallenosborne]

Update, I get no reading on lugs 1 and 2 on the dual gang pot, but 100k reading between 2 and 3 when turned all the way to the left. Dual gang pots aren't supposed to behave this way correct?

I should be getting 100k between 1 and 2 when turned all the way to right I do believe

 

[swelchy]

Doesn't the blue shoe gai pan require 9V on the trimmer pots?

 

[jesuscrisp]

Doesn't the blue shoe gai pan require 9V on the trimmer pots?

Yup, I doubt that it actually works with the jfets biased to 4.5V.

Ia the first IC sitting in its socket correctly? Looks rather loose from the pictures even though it's sort of covered by the footswitch wire.

 

[jesuscrisp]

No reason to be mean now, but generally with these JFET preamps you bias to half the supply voltage, which is 18V, thus 9V on the drains of the JFETs should be correct. The point of the charge pump isn't to supply 4.5V, otherwise you wouldn't need a charge pump at all.
Lugs 1 and 2 of both halves of the pot are shorted together to work as variable resistors, so of course you won't get any reading between them.

 

[tallenosborne]

No reason to be mean now, but generally with these JFET preamps you bias to half the supply voltage, which is 18V, thus 9V on the drains of the JFETs should be correct. The point of the charge pump isn't to supply 4.5V, otherwise you wouldn't need a charge pump at all.
Lugs 1 and 2 of both halves of the pot are shorted together to work as variable resistors, so of course you won't get any reading between them.

I'm sorry, I'm frustrated and I obviously took it out on you so my apologies. I get what your saying so I'll give it a shot, its been my experience that the mid and sweep are prior to the jfets and push into them so I would think there would be an audible effect even with low bias

 

[tallenosborne]

I'm sorry, I'm frustrated and I obviously took it out on you so my apologies. I get what your saying so I'll give it a shot, its been my experience that the mid and sweep are prior to the jfets and push into them so I would think there would be an audible effect even with low bias

I biased at 9v and still no effect from mid and sweep

 

[swyse]

How are the voltages looking on IC2 (the IC near the mid control at the top)? I'd first check around that IC and then if that's good I'd check for continuity from mid pin 1 to IC2 pin 1 and I'd check if you have 22k ohms from mid pin 3 to pin 2 of IC2 to make sure all of those connections are good.

 

[tallenosborne]

How are the voltages looking on IC2 (the IC near the mid control at the top)? I'd first check around that IC and then if that's good I'd check for continuity from mid pin 1 to IC2 pin 1 and I'd check if you have 22k ohms from mid pin 3 to pin 2 of IC2 to make sure all of those connections are good.

Okay I'll get these readings and post back, might be an hour or more though

 

[giovanni]

I biased at 9v and still no effect from mid and sweep

Yeah that sounds like an unrelated issue.

 

[jimilee]

Interesting, and makes perfect sense. I wonder if I dialed mine at 4.5 not thinking. I never really liked the way it sounded, that may be why.

 

[tallenosborne]

How are the voltages looking on IC2 (the IC near the mid control at the top)? I'd first check around that IC and then if that's good I'd check for continuity from mid pin 1 to IC2 pin 1 and I'd check if you have 22k ohms from mid pin 3 to pin 2 of IC2 to make sure all of those connections are good.

IC2 voltages
1 5.10v
2 4.34v
3 4.34v
4 0v ground
5 4.29v
6 6.78v climbs slowly as I hold the meter on it
7 4.34v drops slowly as I hold the meter on it
8 9.20v

Continuity from mid pin 1 to ic2 pin 1
-87.4k (won't read with opposing probes) from mid pin 3 to ic2 pin 2

 

[tallenosborne]

IC2 voltages
1 5.10v
2 4.34v
3 4.34v
4 0v ground
5 4.29v
6 6.78v climbs slowly as I hold the meter on it
7 4.34v drops slowly as I hold the meter on it
8 9.20v

Continuity from mid pin 1 to ic2 pin 1
-87.4k (won't read with opposing probes) from mid pin 3 to ic2 pin 2

R9 is also reading at 87.4k

 

[tallenosborne]

Interesting, and makes perfect sense. I wonder if I dialed mine at 4.5 not thinking. I never really liked the way it sounded, that may be why.

Yeah give it a shot, I really like it at 4.5v

 

[giovanni]

R9 is also reading at 87.4k

I haven’t seen the circuit but measuring components in circuit doesn’t usually yield to nominal reading (because components are often in parallel with others).