Why does gating happen and how can i fix it?

[BuddytheReow]

I'm not talking about a noise gate. I'm talking about when you hit a note or chord and the output from the effect gets almost quiet at first until the input signal drops below a certain threshold and the circuit works fine after that. I'm trying to understand why this happens and how I can fix it. Is it an impedance thing? I'm trying to work something up on my breadboard and am running into this problem. Currently modding a heavy spider circuit.

 

[Big Monk]

I'm not talking about a noise gate. I'm talking about when you hit a note or chord and the output from the effect gets almost quiet at first until the input signal drops below a certain threshold and the circuit works fine after that. I'm trying to understand why this happens and how I can fix it. Is it an impedance thing?

Which circuit?

 

[BuddytheReow]

Which circuit?

Edited my OP. The heavy spider, but I did notice the same thing when breadboarding the El Sol (386 based) a few months ago

 

[benny_profane]

Buddy's Breadboard and Circuit Design Notes

Will definitely read the bias pdf tonight when I have some time. Maybe my definition of "bias" is incorrect You're right that the this sets the bias for the op amp so the virtual ground is 1/2(supply voltage) (i.e., Vref). The resistor provides a path from the buffered voltage divider...

forum.pedalpcb.com

Edit: I misunderstood your problem at first. It sounds like you're driving Q2 into saturation. Can you measure the voltages and post them. It may be a biasing issue.

 

[BuddytheReow]

Buddy's Breadboard and Circuit Design Notes

Will definitely read the bias pdf tonight when I have some time. Maybe my definition of "bias" is incorrect You're right that the this sets the bias for the op amp so the virtual ground is 1/2(supply voltage) (i.e., Vref). The resistor provides a path from the buffered voltage divider...

forum.pedalpcb.com

Edit: I misunderstood your problem at first. It sounds like you're driving Q2 into saturation. Can you measure the voltages and post them. It may be a biasing issue.

Yea, I remember this. I have to fool around with the circuit a bit more. I understand the crude noise gate in this circuit but I don't understand why when I barely play a note there is gating to the point of being unusable

 

[benny_profane]

I'm thinking that you might have a short somewhere. We'll know more when you get some measurements.

 

[BuddytheReow]

I'm thinking that you might have a short somewhere. We'll know more when you get some measurements.

What do you need? Voltages on the trannies?

 

[benny_profane]

What do you need? Voltages on the trannies?

Yeah, voltages for both would help out.

 

[Sturdag Lagernathy]

You may be driving the tranny hard enough(tee hee) it goes into passing essentially a DC signal. (Saturation)Try higher input resistors.

 

[Chuck D. Bones]

Various things cause gating. Sounds like what you're describing is the bias shifting when BJTs are overdriven. When BJTs are driven hard, the base current becomes very asymmetrical which causes the coupling caps to charge up that in turn alters the bias.

 

[BuddytheReow]

Finally getting around to this again. It’s been a busy weekend with house projects.

Q1
C 7.45
B 0.6
E 0 - grounded

I’m ok with this one

Q2
C 0.6
B 0.6v
E 0 - grounded

The collector seems off. I’ve got a 4.7k resistor from the power source here. Is this where the short may be? I will also try adding a pre-gain pot to see if that leans it up. I don’t think it will since dialing back the volume knob doesn’t change anything

 

[BuddytheReow]

Here’s the problem area I think but not sure how this breadboard layout is causing it. Left to right is EBC. I’ve got 9v on the rails (actually 8.8 but close enough). Once it goes through the resistor it drops to .6