Distortion circuit not functioning, need help identifying the issue.

Thread Starter

Aivaras Andrijauskas

Joined Aug 26, 2019
41
HELP!!!
I've built this pedal, and I cant identify what's wrong.
Black Arts Toneworks Revelation Super Bass.png
If both pre-gain and gain are turned up, a steady, fast ticking noise appears, or a loud high pitched whistle, depends on which one is turned up first, with no signal from the bass coming through. With both these knobs turned down, the signal can be heard, undistorted, quiter than when the circuit is bypassed. The bass signal could be heard with the volume turned down, but the before mentioned issues appear when the volume is up, so i just removed it until i solve the issue.
I've built an LTspice simulation to compare voltage values, and these are the main points:
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1.voltages before the collectors of Q1 and Q2 are identical in the simulation, 4.228.. , but it's 4.9 and 4.16 in my circuit
2. Voltages before and after the diodes are identical in the simulation, but it's 4.14 on on the side of Q2 and 3.99 on the side of C7.
3. After the 10uf output cap, voltage should be 42uv, but in my circuit, the value started at around 2.4V and is slowly droping, removing the multimeter leads, and then reapplying them, didn't reset the value, turning the power on and off didn't reset the value, it kept dropping, it was around 600mv last time, but when i meassured it now, it randomly jumped up to 1.4V and is now steadily decreasing again. There are no solder bridges or anything, like that. Should voltage even be able to travel through the cap?

These are the main clues to what could be wrong, I really need some guidance on how to figure out what's going on. I've built this circuit twice now, and the problems are identical this time as they were the first time. I'm new to this, so don't be afraid to suggest anything to basic.

I have no idea what to do next, and what to look for. I'm using a 9v battery,but the actual value of my battery is 9.5v
The firs template i used called for different diodes, that's why they're not the same as in the circuitboad diagram.
 

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1.voltages before the collectors of Q1 and Q2 are identical in the simulation, 4.228.. , but it's 4.9 and 4.16 in my circuit
It does not matter.

2. Voltages before and after the diodes are identical in the simulation, but it's 4.14 on on the side of Q2 and 3.99 on the side of C7.
C7 does not pass DC.

3. After the 10uf output cap, voltage should be 42uv, but in my circuit, the value started at around 2.4V and is slowly droping
The output capacitor, or ANY capacitor does not pass DC.

I'm using a 9v battery, but the actual value of my battery is 9.5v
that is normal and it does not matter.

The schematic in your simulation is a mess, but the simulation works fine. Here is the original hand-drawn schematic:
 

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Alec_t

Joined Sep 17, 2013
11,386
The voltage differences you found are due to tolerances in the transistor and diode etc properties. No two components are identical in the real world.
The dropping voltage is because the output cap was charging through the high input resistance of your multimeter.
The weird noises were probably due to spurious circuit oscillation if your circuit was built on a breadboard or involved straggly unscreened wiring.
 
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Thread Starter

Aivaras Andrijauskas

Joined Aug 26, 2019
41
Thank you for the information.

Regarding the wiring, yes, i did do it on a blank pcb board. Should i design and order a printed PCB board, and then just put the components on there? The circuit is enclosed in a shielded enclosure, so it shouldn't pickup interferance, or if it does, wouldn't it just result in an unclean signal, rather than no signal and the previously described noises?

I did use unshielded single wires to connect the jacks, pots, dpdt bypass switch. But it's in a shielded enclosure, are the components in the enclosure itself generating the electromagnetic interference, meaning if an unshielded wire comes close to a transistor or something, it starts picking up so much interferance it completely destroys the signal? How should i connect the components then? using shielded wire? Do i connect the wire shielding, at one end, to the ground of the circuit? But then wouldn't every single connection between every single component need to be shielded?

(Additional info - I can't get a stable resistance reading between any base of a transistor and the ground. The reading starts around 82 and is ticking up, while jumping back and forth by 0.01 kohm, but overall the value is increasing. Shouldn't i just immediatly get a reading of 100k? the resistors are definetly 100k. Waited for a while, the resistance reading between base of Q1 and ground seems to stabilizes or at least slow down to the point of almost stopping, at around 88.8 - 88.7, and is now fluctuating between these values. What could explain this? Is it because of multiple paths to ground?)
 

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I am sorry that I cannot say anything nice about your craftmanship.

Since you showed the circuit built neatly on a stripboard then I thought it was yours, BUT your wiring IS A MESS!
Why didn't you build it on stripboard like the original that you posted?

You cannot measure the base-emitter resistance of a powered transistor, instead you measure its voltage.
If you measure the base-emitter resistance of an unpowered transistor then the base-emitter diode might conduct then the measurement is of the diode and not of the resistance.

An unshielded input wire near an unshielded output wire causes feedback. Input parts of your circuit board near the output pot or output parts of the circuit board near the input pot will also cause feedback.

Did you use plumber's solder instead of electronics rosin-core solder? Or did you drip the solder down from a high place?
 

Alec_t

Joined Sep 17, 2013
11,386
If your measurements with a multimeter are unstable, that's a possible sign that spurious oscillation is occurring.
Instability can also arise if your battery is dying or has developed a high internal resistance.
 
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