SOLVED Muffler Noise Gate - No Gate - Help

[BuddytheReow]

Hey guys.

just finished populating the board on a muffler noise gate. I have it alligator clipped to check. Signal comes through just fine. How do I check if the “effect” actually works? Rub my hand up and down the strings and turn the pot simultaneously?

 

[Chas Grant]

I double checked q1. Pin1 is 3.7 and pin 2 is 3.0. Does this mean that pin2 needs to be higher or pin 1 needs to be lower voltage?

Pin 2 should be about .6V higher than pin 1. If pin 2 is 3 and Pin 1 is 3.7 then something is wrong and the transistor is not conducting. If your multimeter has the diode check function on it, check Q1. Red lead to pin 2 and black lead on pin 3 then on pin 1. Like this you should see a diode both measurements

 

[Chas Grant]

Testing the resistance between the downstream of r103 (22k) and ground is about 300 ohms. Should it be? Seems very low

Way LOW!

 

[BuddytheReow]

Pin 2 should be about .6V higher than pin 1. If pin 2 is 3 and Pin 1 is 3.7 then something is wrong and the transistor is not conducting. If your multimeter has the diode check function on it, check Q1. Red lead to pin 2 and black lead on pin 3 then on pin 1. Like this you should see a diode both measurements

Diode mode works both sides based on your instructions.

 

[Chas Grant]

Check D1, that's my bet. But could also be C101 but not likely.

 

[Chas Grant]

OH SNAP is everything still socketed? If so pull D1 and check resistance to ground

 

[BuddytheReow]

OH SNAP is everything still socketed? If so pull D1 and check resistance to

D1 was the problem. Voltage drop both ways. Swapped it out with my last one. Rechecked resistance to ground and -1.2M ohms. Negative resistance? That problem is solved I guess. Now my signal is going through again.

Back to the original problem...

I decided to check the transistors again.

q1
Pin1 3.6
Pin2 3.0
Pin3 8.8

q2
Pin1 0
Pin2 0.1
Pin3 1.1

q3
Pin1 starts at 3.3 and slowly drops to 2.9 then I hear a hum and voltage goes back up
Pin2 4.5 steady
Pin3 starts at 2.2 then slowly to 1.8 the hum again and back up to 2.2

im thinking q3 2n5485 is a fake? Why could voltage fluctuate like that?

 

[Chas Grant]

D1 was the problem. Voltage drop both ways. Swapped it out with my last one. Rechecked resistance to ground and -1.2M ohms. Negative resistance? That problem is solved I guess. Now my signal is going through again.

Back to the original problem...

I decided to check the transistors again.

q1
Pin1 3.6
Pin2 3.0
Pin3 8.8

q2
Pin1 0
Pin2 0.1
Pin3 1.3

q3
Pin1 starts at 3.3 and slowly drops to 2.9 then I hear a hum and voltage goes back up
Pin2 4.5 steady
Pin3 starts at 2.2 then slowly to 1.8 the hum again and back up to 2.2

im thinking q3 2n5485 is a fake? Why could voltage fluctuate like that?

Do you have any other jfets

 

[BuddytheReow]

2n5485? I’ve got another, but there from the same eBay supplier and I’m waiting in a shipment from smallbear. 2n3904 I’ve got I think 3 more.

do q2 voltages seem right? The zero I get cuz it goes directly to ground.

 

[Chas Grant]

Honestly none of the transistor voltages seem right. They have me scratching my head. Have you removed the transistors and then apply power and check voltages? Q1 should have near 5 volts on pin 2, 8 to 9 volts on pin 3 and 0 volts on pin 1. Q3 should have about 5 volts on pins 1 and 2, pin 3 I’m not sure of but it will be 5 volts or less. Q2 should have near 5 volts on pin 3 and something less than 5 on pin 2. Something around 1 - 2 volts from quick guess looking at schematic

 

[BuddytheReow]

I'll circle back tomorrow with results.

I started checking the components starting with resistors. R101 and r102 should be 1M but when testing them they are around 5-600k each, yet they are in series. Shouldn't it be 2m? Seems like my issues are starting early on in the circuit.

 

[Chas Grant]

500 to 600K each is good. These are forming a voltage divider to give VREF_A at 4.5V with 9Vdc in. The reason the read lower is that they are in parallel with other components. Parallel resistors always lower the resistor value.

 

[BuddytheReow]

I’ve got 8.8v going in and just under 3v coming out of the voltage divider. Shouldn’t it be half (4.4v)?

 

[Chas Grant]

I’ve got 8.8v going in and just under 3v coming out of the voltage divider. Shouldn’t it be half (4.4v)?

Theoretically Yes, in Actuality No. When you measured R101 and R102 in the circuit, what were the values of each resistor?

 

[BuddytheReow]

R101 is 500k. R102 STARTS at 500k and slowly creeps up...

here are the voltages at each socket

q1
0.5
3.1
8.8

q2
0
0.4
3.7

q3
1.67
4.6
3.7

 

[Chas Grant]

R101 is 500k. R102 STARTS at 500k and slowly creeps up...

here are the voltages at each socket

q1
0.5
3.1
8.8

q2
0
0.4
3.7

q3
1.67
4.6
3.7

These don't look bad. I expected Q1 pin2 and Q2 pin2 to be higher, but quick calculations say they are close. Its either Q1 , still don't like the 3.7 volts on pin 1 when power is applied. Or Q3 is messed up. You can try replacing Q1. When you do, just put Q1 in, leave Q2 and Q3 out and measure the voltages on Q1. If pin 1 is lower than pin2 then Q1 will conduct, if pin 1 is still 3.7 and pin 2 is 3.1 then the circuit is designed like this( and I'm missing something in the schematic, like where the 3.7 volts is coming from). Next replace Q2 and Q3 and measure Q1 again, if the circuit still doesn't work after this, then go after the JFET.

 

[BuddytheReow]

FYI my whole board has been alligator clipped this whole time. Just to make sure I wired it up to 3pdt switch and output jacks. I’m still getting the same results even when replacing q1 and q2. Those came from Tayda. Q3 replacement I’m waiting for an order from smallbear.

I guess I gotta wait a few more days. Sometimes it’s better to walk away for a bit and go in with fresh eyes...

@Chas Grant you’ve been EXTREMELY helpful and I truly appreciate your help so far.

 

[BuddytheReow]

Who would know if those voltages should be correct as per the schematic? I have only basic electrical knowledge

 

[Chas Grant]

Who would know if those voltages should be correct as per the schematic? I have only basic electrical knowledge

The engineer who designed the circuit ! If some one has the original or a working circuit, then they could get them. I have electronics schooling and experience and that's what I'm going on. A lot of times there are paths that you don't see in the schematic, unless you stare at it a long time. In this circuit you have quite few parallel paths to figure out, then there is always the theoretical vs real values which is what you see on the voltage divider.

 

[Nostradoomus]

It’s most likely the eBay FET, just wait it out haha

 

[BuddytheReow]

Considering the number of HOURS I’ve put into this I guess I can wait a bit longer, haha. I guess I’ll start my next one. Should I do the thermionic distortion or sabbath distortion? Chicken or the egg, anyone? Lol