Audio Trace Question

[djmiyta]

I recently built a Blackstone MOSFET O.D. that didn’t work plugging my guitar in. I input a 440 hz signal to trace throughout the circuit and got signal on the output and throughout the circuit.
So I plug the guitar moving knobs around and only if I hit the guitar strings really really hard does a very sputtery short sound come out of the amp. With the 440 hz signal it works perfectly. I’m confused why this would happen. Has anyone experienced this before or heard of this? Any ideas would be appreciated Thanks

 

[EGRENIER]

I recently built a Blackstone MOSFET O.D. that didn’t work plugging my guitar in. I input a 440 hz signal to trace throughout the circuit and got signal on the output and throughout the circuit.
So I plug the guitar moving knobs around and only if I hit the guitar strings really really hard does a very sputtery short sound come out of the amp. With the 440 hz signal it works perfectly. I’m confused why this would happen. Has anyone experienced this before or heard of this? Any ideas would be appreciated Thanks

What voltage is you tone generator producing ? Could it leak through a faulty part of your circuit and be strong enough for you amp ? While your guitar voltage is really low I think between 100-300 mV, it may all get sucked up...

Thinking out loud here... I would check your tone generator voltage to be sure it's not to high....

 

[djmiyta]

Thank you for the response. I’m using an app off my laptop that’s very primitive ( no bells and whistles just a test tone) and I don’t know how to test the voltage of it. Would trying a different signal source make a difference? Like playing an mp3 or a different tone other than 440? My knowledge of electronics is pretty limited wasn’t even aware there’s a voltage on a test tone

 

[djmiyta]

What is a good voltage number for test signals to be used ?For future reference.

 

[EGRENIER]

Thank you for the response. I’m using an app off my laptop that’s very primitive ( no bells and whistles just a test tone) and I don’t know how to test the voltage of it. Would trying a different signal source make a difference? Like playing an mp3 or a different tone other than 440? My knowledge of electronics is pretty limited wasn’t even aware there’s a voltage on a test tone

OK to you're taking the "headphone" output of your laptop, I think this would be at line out level. Here's what I find on the subject:

"Commercial line out specification is to be able to drive 1 milliwatt to a 600 ohm load. For a sine wave, this means a voltage of 0.77 volts RMS (2.2 volts peak-to-peak) and a current of 1.3 milliamperes RMS (3.6 milliamperes peak-to-peak)."

2.2 V is much louder than your guitar pickups.

You can probably still do your trace with that, but I recon you should see a volume drop somewhere on the circuit. The drop may not be perceivable by ears tho...

When tracing the audio, what I do is use my looper pedal, just hit the string once and loop it. Then that's my input and that's what I trace.

If you sending a signal from laptop to pedal, I assume you have a 1/8 jack to 1/4 jack cable. You can check the voltage by using your DMM on the 1/4 jack end while the computer is generating the tone. But this will just confirm my theory why you may have sound with the laptop and not the guitar.

 

[djmiyta]

Awesome thanks for sharing your wisdom. I’ve always used this method and it’s worked until now. So what is a good voltage reading to look for? And would there be a way to lower or raise the voltage from my laptop I think probably not but not sure. My next buy (or build if I can) is a looper pedal since I don’t have one. In the mean time got any other ideas I could do to trace this out?

 

[EGRENIER]

I should add that you should perform the standard checks first (check all resistor values, all caps values, all pot values, swap IC, etc...

Visual inspection of your soldering, reflow everything that looks suspicious, etc.

Then post pictures of both side of the PCB with the pots raised so we can see all the components and solder points. Make sure we see all the input/output/switch connections also...

 

[EGRENIER]

Awesome thanks for sharing your wisdom. I’ve always used this method and it’s worked until now. So what is a good voltage reading to look for? And would there be a way to lower or raise the voltage from my laptop I think probably not but not sure. My next buy (or build if I can) is a looper pedal since I don’t have one. In the mean time got any other ideas I could do to trace this out?

I wouldn't call that wisdom... I'm probably as new to all this as you...

Not sure if playing with the volume of you laptop can change the voltage, would have to test...

However, if I'm right and input voltage is what explain the sound making it, my first thought is that you have used a wrong value for one of of the resistors... did you check all you resistors and cap value to be sure you didn't make a simple mistake.

I know it's tedious but that really the first step of trouble shooting, checking all the values is very important before trying to trace the audio.

 

[djmiyta]

Yes I’ve triple checked components. Continuity ,grounds all good. The wiring due to the layout was (is ) tricky and I’m thinking that’s my issue. I just thought it strange using my way of signal tracing that works everytime to show the circuit to work and then not work with the guitar plugged in. Weird. You’re probably right about the voltages. What is a good voltage for a signal to be for tracing? Gonna check values one more time. Thanks again. And pics? It’s a real ratty looking mess if I can get some decent pics I’ll post them
Here’s the layout I worked from my problem was the input wiring.From what I got the input goes to the mode switch and the pcb board but I’m not sure

 

[EGRENIER]

Yes I’ve triple checked components. Continuity ,grounds all good. The wiring due to the layout was (is ) tricky and I’m thinking that’s my issue. I just thought it strange using my way of signal tracing that works everytime to show the circuit to work and then not work with the guitar plugged in. Weird. You’re probably right about the voltages. What is a good voltage for a signal to be for tracing? Gonna check values one more time. Thanks again. And pics? It’s a real ratty looking mess if I can get some decent pics I’ll post them
Here’s the layout I worked from my problem was the input wiring.From what I got the input goes to the mode switch and the pcb board but I’m not sure

Oh Vero board, you'll need someone else than me to help you on that... Sorry...

The only thing I would point out is the notice of the cut under R6 and R8, these would seem easy to forget...

 

[djmiyta]

Guess I should'a mentioned I redrew the vero to etch my own pcb. which I've done several with great results since I got a few copper boards it's easier for me this way. It's all good I'll get it figured out. by the way my signal I use for the tracing measured .772 V AC is that a number we're looking for for tracing?
Quick side note and FYI to myself raising the volume while using the tone generator would increase the voltage ...(which makes sense).

 

[EGRENIER]

Guess I should'a mentioned I redrew the vero to etch my own pcb. which I've done several with great results since I got a few copper boards it's easier for me this way. It's all good I'll get it figured out. by the way my signal I use for the tracing measured .772 V AC is that a number we're looking for for tracing?
Quick side note and FYI to myself raising the volume while using the tone generator would increase the voltage ...(which makes sense).

From what I understand, that would be 2.5 to 6 times louder than a single string strum. So that may explain why the tone is making it through. If you PC volume controls the voltage, it would be interesting to see if at .150 V AC you get it through to the amp...

To me what this suggest is that you have a component sucking up the tone at low voltage but letting it through at high voltage. Did you double check all your values ?

When you test with your tone, is the input louder than the output ?

 

[djmiyta]

From what I understand, that would be 2.5 to 6 times louder than a single string strum. So that may explain why the tone is making it through. If you PC volume controls the voltage, it would be interesting to see if at .150 V AC you get it through to the amp...

To me what this suggest is that you have a component sucking up the tone at low voltage but letting it through at high voltage. Did you double check all your values ?

When you test with your tone, is the input louder than the output ?

Thanks for the feedback. And I’m curious now too. I’ll check it out tomorrow and post what I find.

 

[giovanni]

+1 to all the above. I think you want at most 0.150V RMS to emulate the guitar level. Also the headphone output probably has a much much lower output impedance than a guitar which means it’s easier for the pedal to drive that signal. The two things together could explain why the test signal seems to be working. I think using a looper with a guitar loop is the best choice.

 

[giovanni]

This is a good article on the subject.

 

[djmiyta]

A good read with interesting tidbits thank you. After a 4th time go over I (ya know if these Gnomes and Idjets keep messing with my boards and don't stop fucking with my shit I'ma start getting pissed it's the 5th build this year !) I found a cap (specifically C10 ) going to pin 7 instead of pin 6. Whoops. After correcting that I get nothing. Maybe I fried the Tl072. I get signal to the TL072 in put pin but get nothing on the out put pin.
I've uploaded I wiring diagram minus the by-pass switch anybody mind looking it over for mistakes? I'm pretty sure it's the final draft.

 

[giovanni]

Could be yeah. If socketed, try replacing it? Or post pics and we can see if we can spot anything else?

 

[djmiyta]

Could be yeah. If socketed, try replacing it? Or post pics and we can see if we can spot anything else?

ewww that opens me up to .... criticism. It's rough and I know someone will say reflow the joints or at least think it having said that okay I'll get a pic or 2. Also know I had no 500k trimmers and used regular pots just to see if it'll work
here is my layout and the original I'll get some pics of my build in a few thanks for looking.

 

[djmiyta]

I’ll be amazed if somebody makes sense of my rats nest here’s pics of my non working blackstone mosfet O D I think Ive wired wrong but I haven’t swapped out possibly fried IC’s either .The schematic shows it wired for a by pass but the layout I worked off didn’t have one so the input goes to lug 1 of mode switch and input to the board?

 

[djmiyta]

Dont waste time on this ditching the board messed up the layout sorry fors wasting anyone and everyones time and all the rest of you. I re-did my layout and gonna give it a 2nd go in a few.