Need help to debug this fuzz.. (Roland ad-50)

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hiorgos
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Post by hiorgos »

Hi. Nice to see this up and running again!

Got this Roland ad-50 built, but is not working, :?

I have checked that all the parts are correct, twice. I plug the guitar and I get the bypassed signal strong and clear. When I switch on the pedal the light is on.

I used an audio probe I made to test the circuit. Signal seems to flow from input to output, but the circuit emits just a bit of sound. No effect at all, just a bit of signal when the knobs are at max.

One question, when using an audio probe, should I be able to listen to the effect along as I go testing from the input to the output? Because I start on the input with a clear signal but when I move along the circuit I just hear the signal with less intensity, and no effect at all.


I used sockets for the transistors, but that should be fine, right?. The position  of sc1000 transistors is clear by their shape. No fuzz at all comes out of the pedal.

Diagram I draw, based on all the available ones, the actual circuit looks pretty much like that:

Image


Could it be the wiring? Are the pot lugs right? The signal is OK with the effect bypassed..

Wiring diagram.
Image

I don't know what else can I check,  I have been today again trying to find the problem, but cannot find anything! .. any ideas of what to check next? Should I desolder everything and start again?

I just bought a DMM yesterday, but still have no idea how to use it!


Thanks!
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DrNomis
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Post by DrNomis »

hiorgos wrote:Hi. Nice to see this up and running again!

Got this Roland ad-50 built, but is not working, :?

I have checked that all the parts are correct, twice. I plug the guitar and I get the bypassed signal strong and clear. When I switch on the pedal the light is on.

I used an audio probe I made to test the circuit. Signal seems to flow from input to output, but the circuit emits just a bit of sound. No effect at all, just a bit of signal when the knobs are at max.

One question, when using an audio probe, should I be able to listen to the effect along as I go testing from the input to the output? Because I start on the input with a clear signal but when I move along the circuit I just hear the signal with less intensity, and no effect at all.


I used sockets for the transistors, but that should be fine, right?. The position  of sc1000 transistors is clear by their shape. No fuzz at all comes out of the pedal.

Diagram I draw, based on all the available ones, the actual circuit looks pretty much like that:

Image

Could it be the wiring? Are the pot lugs right? The signal is OK with the effect bypassed..

Wiring diagram.
Image

I don't know what else can I check,  I have been today again trying to find the problem, but cannot find anything! .. any ideas of what to check next? Should I desolder everything and start again?

I just bought a DMM yesterday, but still have no idea how to use it!


Thanks!

When you use an audio-probe to trace a signal through the circuit, you should hear a steadily increasing signal level as you progress from the input to the output, this is the case if you have the tip of the audio-probe on the Collector of each transistor because each transistor produces a certain amount of "gain", so, if the signal is getting lower, you know that something somewhere in the circuit is causing signal loss, backtrack through the circuit till you regain signal level, and then progress through the circuit towards the output, note the position of the probe tip when you first notice a signal level drop, between that point and where you had good signal level is where the fault is most likely to be, hope that helps.... :thumbsup

Also, use a strong magnifying glass to closely examine all your solder joints to make sure they are okay, re-work those that look suspect.... :hmmm:

Also, try replacing the transistors with known good ones.... :hmmm:
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.
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hiorgos
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Post by hiorgos »

Thanks a lot..

When using the audio probe, the signal is strong just at the input, it starts to decrease after the first cap, and continues losing power at every stop, until is barely audible at the output. So there is something definitively wrong somewhere :lol:

Not sure if it's a silly idea, can be the ground line I put causing any trouble?

Why does the 470K resistor, the one with the blue doted line, end before the first transistor? Shouldn't go to ground?

Transistors are 2SC1000, which are supposed to be the ones that go in this pedal. They are Toshiba. Is there some link around to learn how to test transistors with a DMM? I mean, to know if they are actually working?
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