DIY Effects

[LukeFRC]

argh... something's wrong here! any tips on how to debug?

[JackLondon]

pic of the board with wiring?

[Alien]

[quote name='dudewheresmybass' post='762446' date='Mar 3 2010, 12:32 AM']this is pretty much what i'm after.

how would i supply the signal to the unit without losing my signal totally? i know i' said i'm thinking of a 'side chain' but how could i build that?[/quote]

Has your amp got a line/tuner out jack? If so, there's your sidechain. Shouldn't affect your sound at all as these outputs are usually buffered.

A

[LukeFRC]

like this?


thing that confuses me is that it was working, abet with a fault.
i tried to fix the fault. put the right cap in the 0.033 nF slot (the first one after the in, second nearest the in on the board) and spotted the 0.01 cap on the out side wasnt there.
Fixed them and it didn't work, went back a stage or two and it still doesn't work... :S


EDIT: should add.

+v linked to battery red
pot's wired in correctly (they did work when it did work)
ground and battery black on the sleave of the in jack.
tip of jack to in
tip of out jack to out
sleeves linked

Edited March 8, 2010 by LukeFRC

[LukeFRC]

oh and bypassing the 0.033 cap stopped the noise, but didn't make it work...

[dudewheresmybass]

thanks for that alien, i came to the same conclusion today. mind you i'm still going to toy with the idea of a stomper to switch it on

cheers for all of the useful advice chaps

[umph]

[quote name='LukeFRC' post='768591' date='Mar 8 2010, 10:09 PM']like this?


thing that confuses me is that it was working, abet with a fault.
i tried to fix the fault. put the right cap in the 0.033 nF slot (the first one after the in, second nearest the in on the board) and spotted the 0.01 cap on the out side wasnt there.
Fixed them and it didn't work, went back a stage or two and it still doesn't work... :S


EDIT: should add.

+v linked to battery red
pot's wired in correctly (they did work when it did work)
ground and battery black on the sleave of the in jack.
tip of jack to in
tip of out jack to out
sleeves linked[/quote]

check all the caps are in the right way round, also check and double check all the components. If that fails get a magnifying glass and check to make sure there aren't any hairline bridges or cracks in the traces.

[Al Heeley]

make a simple audio probe and follow the signal path round the circuit.
go here for info on audio probe and step by step debugging.
[url="http://www.diystompboxes.com/pedals/debug.html"]http://www.diystompboxes.com/pedals/debug.html[/url]
you cant buikd pedals and keep your sanity without an audio probe to help out

[escholl]

[quote name='LukeFRC' post='768591' date='Mar 8 2010, 10:09 PM']like this?


thing that confuses me is that it was working, abet with a fault.
i tried to fix the fault. put the right cap in the 0.033 nF slot (the first one after the in, second nearest the in on the board) and spotted the 0.01 cap on the out side wasnt there.
Fixed them and it didn't work, went back a stage or two and it still doesn't work... :S


EDIT: should add.

+v linked to battery red
pot's wired in correctly (they did work when it did work)
ground and battery black on the sleave of the in jack.
tip of jack to in
tip of out jack to out
sleeves linked[/quote]

Would you be able to provide some clear pics of the other side? Other than to say check and double check that any multipin and polarized components are in the right way round, there is not much I can say seeing only one side of the board.

[LukeFRC]

thanks guys! a long time of checking coming up I think. I think i know which end of the circuit board the problem is, its just tracking it down....

[LukeFRC]

okay... audio probe is brilliant idea, thanks- this is what i was looking for, some way for me to test my circuit
rigged one up and it works a treat. I'm actually going to look forward to going over the sft cuircit just to see what everything does!

but I think I've found my problem....no signal is getting through the opening 0.033 nF cap. you can hear the bass in the input arm of it, but on the output one not at all, just a popping noise. why would it do that?

I'm not sure why this is happening but i guess it would be usefull to check all the correct power from the battery is getting to the right places at the right voltages. That's for tomorrow, in my testing ive managed to break the battery clip!


EDIT: sorry my moans are overtaking this thread... anyway, found a wrong cap in a place that may affect it.... also unsure it was there when i had it working.... more cap shopping tomorrow..... remember kids this is a pedal building morality leson!

Edited March 10, 2010 by LukeFRC

[escholl]

[quote name='LukeFRC' post='769573' date='Mar 9 2010, 07:00 PM']but I think I've found my problem....no signal is getting through the opening 0.033 nF cap. you can hear the bass in the input arm of it, but on the output one not at all, just a popping noise. why would it do that?[/quote]

0.033 nF, or 33 pF, seems awfully small for a cap in this position in the circuit -- are you sure that is the right value? If it was 0.033 uF, which is 33 nF, that would make more sense given the typical input impedance and bandwidth requirements of these types of input stages.

[LukeFRC]

[quote name='escholl' post='770154' date='Mar 10 2010, 10:50 AM']0.033 nF, or 33 pF, seems awfully small for a cap in this position in the circuit -- are you sure that is the right value? If it was 0.033 uF, which is 33 nF, that would make more sense given the typical input impedance and bandwidth requirements of these types of input stages.[/quote]



yes, i think you're right! I was just following my plans which were confsing me, I've just looked up the baja version on freestompbox and it's way clearer! Oddly I had ordered the right pieces, just thought i had them wrong.... lets start again.
The good news is that I have now worked out enough of what each bit is doing that I pinpointed the 2 problems!

[LukeFRC]

I get to wear the bass chat dunces hat for a bit though

[LukeFRC]

so wired together in hopefully properly... and I have a pedal that amplifies and does a nice fuzz sound! with a phasing thing in the background. not what i was aiming for but progress!



EDIT:


ARRRGGHHH!!!! Whats gone wrong this time? the chorus is there in the background its just something is turning it into a fuzz pedal. Im guessing either the 4558 chip or one of the transistors??

Edited March 10, 2010 by LukeFRC

[LukeFRC]

sorry to bother you all again...
tracked down the problem I think. The 4558 chip seems to be funny.
On the [url="http://www.tonepad.com/getFile.asp?id=97"]schematic[/url] it works as two seperate units (op amps???) IC1a seems to be fine, everything doing what it should.
Ground is ok, as is the voltage into this chip. On the IC1b part however we seem to have a wierd fuzzy loudness. input 6 is fine, the signal from the bass, the output 7 however comes out all distorted. IS there a reason it would do this or have i broken the IC somehow?

[LukeFRC]

sorry to bother you all again...
tracked down the problem I think. The 4558 chip seems to be funny.
On the [url="http://www.tonepad.com/getFile.asp?id=97"]schematic[/url] it works as two seperate units (op amps???) IC1a seems to be fine, everything doing what it should.
Ground is ok, as is the voltage into this chip. On the IC1b part however we seem to have a wierd fuzzy loudness. input 6 is fine, the signal from the bass, the output 7 however comes out all distorted. IS there a reason it would do this or have i broken the IC somehow?

[escholl]

[quote name='LukeFRC' post='771092' date='Mar 10 2010, 11:21 PM']sorry to bother you all again...
tracked down the problem I think. The 4558 chip seems to be funny.
On the [url="http://www.tonepad.com/getFile.asp?id=97"]schematic[/url] it works as two seperate units (op amps???) IC1a seems to be fine, everything doing what it should.
Ground is ok, as is the voltage into this chip. On the IC1b part however we seem to have a wierd fuzzy loudness. input 6 is fine, the signal from the bass, the output 7 however comes out all distorted. IS there a reason it would do this or have i broken the IC somehow?[/quote]

The 4558 is indeed two separate op-amps. Check that pin 5 is definitely at 4.5 volts, and check that there isn't any sort of broken track or dry joint on the 33k feedback resistor (the one just above the 6.8k in the diagram). If everything is in order, but the output of pin 7 is still not what you expect, pull the IC out of it's little socket and then connect your audio probe to pin 6 of the socket. If the input is exactly what you expect to hear on the output, just quieter, then you will need to replace the IC.

Don't worry, it's not that uncommon a fault -- I've done it myself by accident. In case for some reason you can't find the 4558, you can also use an NE5532 in it's place, which is technically a better op amp. Either will work however and they are both cheap (under a quid from Maplin).

If, however, the input at pin 6 with the chip removed is not what you'd expect to hear on the output, then your problem lies elsewhere, and the IC is simply amplifying the problem. From what you've said however, that would seem not to be the case.

[LukeFRC]

[quote name='escholl' post='771133' date='Mar 10 2010, 11:56 PM']The 4558 is indeed two separate op-amps. Check that pin 5 is definitely at 4.5 volts, and check that there isn't any sort of broken track or dry joint on the 33k feedback resistor (the one just above the 6.8k in the diagram). If everything is in order, but the output of pin 7 is still not what you expect, pull the IC out of it's little socket and then connect your audio probe to pin 6 of the socket. If the input is exactly what you expect to hear on the output, just quieter, then you will need to replace the IC.

Don't worry, it's not that uncommon a fault -- I've done it myself by accident. In case for some reason you can't find the 4558, you can also use an NE5532 in it's place, which is technically a better op amp. Either will work however and they are both cheap (under a quid from Maplin).

If, however, the input at pin 6 with the chip removed is not what you'd expect to hear on the output, then your problem lies elsewhere, and the IC is simply amplifying the problem. From what you've said however, that would seem not to be the case.[/quote]


thanks so much for the reply!

voltage at 5 is 4.5v, 33k resistor is fine. I can't take it out to test (no signal will get through to the second op-amp without the first! but putting the probe on the input on the right hand side and the signal was there.
Checking the 33k resistor and there seems to be a gap on the icb there so no signal gets to either the 33k or .01 cap. Easily fixed.
So ill go buy a new chip tomorrow! Thanks folks

[LukeFRC]

[quote name='escholl' post='771133' date='Mar 10 2010, 11:56 PM']The 4558 is indeed two separate op-amps. Check that pin 5 is definitely at 4.5 volts, and check that there isn't any sort of broken track or dry joint on the 33k feedback resistor (the one just above the 6.8k in the diagram). If everything is in order, but the output of pin 7 is still not what you expect, pull the IC out of it's little socket and then connect your audio probe to pin 6 of the socket. If the input is exactly what you expect to hear on the output, just quieter, then you will need to replace the IC.

Don't worry, it's not that uncommon a fault -- I've done it myself by accident. In case for some reason you can't find the 4558, you can also use an NE5532 in it's place, which is technically a better op amp. Either will work however and they are both cheap (under a quid from Maplin).

If, however, the input at pin 6 with the chip removed is not what you'd expect to hear on the output, then your problem lies elsewhere, and the IC is simply amplifying the problem. From what you've said however, that would seem not to be the case.[/quote]


thanks so much for the reply!

voltage at 5 is 4.5v, 33k resistor is fine. I can't take it out to test (no signal will get through to the second op-amp without the first! but putting the probe on the input on the right hand side and the signal was there.
Checking the 33k resistor and there seems to be a gap on the icb there so no signal gets to either the 33k or .01 cap. Easily fixed.
So ill go buy a new chip tomorrow! Thanks folks

[LukeFRC]

no! it works i think! too late to try out loud now but it seems to work!!!!

[escholl]

[quote name='LukeFRC' post='771146' date='Mar 11 2010, 12:18 AM']I can't take it out to test (no signal will get through to the second op-amp without the first![/quote]
Doh! I knew that. Honest.

[quote]Checking the 33k resistor and there seems to be a gap on the icb there so no signal gets to either the 33k or .01 cap. Easily fixed.[/quote]

That'll be the problem then. Without those feedback resistors in the circuit, primarily the 33k one, the gain of the op-amp is left at whatever its open loop gain is, probably around 100. In this circuit, it looks like it's supposed to have a gain of about 3 (and not 100), so, that's where your distortion was coming from. With that pcb gap fixed, the problem should be sorted, assuming there are no other issues with the board.

Now to play!

[LukeFRC]

Yay! It works!



I tested it with a 0.015 on the input last night. It clearly wasn't letting the bass through. So I've stuck a 0.1 on the input rather than the 0.033. It probably isnt the same sound as the original but it works fine for me, makes sure there's a bottom end to it (I know idealy you would have some kind of wet dry mod but I havnt got space on the enclosure for another pentometer!

There is a fair volume drop though... would I be right in guessing from what you said that if the 33k resistor in the output op amp was less than 33k it would be louder?

[escholl]

[quote name='LukeFRC' post='771985' date='Mar 11 2010, 07:08 PM']Yay! It works!



I tested it with a 0.015 on the input last night. It clearly wasn't letting the bass through. So I've stuck a 0.1 on the input rather than the 0.033. It probably isnt the same sound as the original but it works fine for me, makes sure there's a bottom end to it (I know idealy you would have some kind of wet dry mod but I havnt got space on the enclosure for another pentometer!

There is a fair volume drop though... would I be right in guessing from what you said that if the 33k resistor in the output op amp was less than 33k it would be louder?[/quote]


A larger input cap shouldn't affect the sound in a detrimental way, it will simply lower the cutoff frequency of the high pass filter that is effectively created by that cap -- in fact, as the pedal was designed for guitar, 0.1 uF is probably a good value to put in for bass, instead of the original. It is a good choice.

You've got the right idea that the 33k resistor affects the volume, however it works in the opposite way. So, if you wanted a louder volume, increase the value of that resistor. This is why when the connection to that resistor was broken, effectively raising the resistance very high, the gain was increased and the distortion occurred. By calculating a ratio of the input resistor (in this case 10k) to the feedback resistor (33k) the gain of the op-amp stage can be calculated, in this case the gain is roughly 3. If you want to increase it, you could try a 39k resistor in place of the 33k, for a gain of roughly 4, or a 47k resistor, for a gain of about 5. You could also try, say, a 47k pot in series with a 10k resistor, which would give you a variable output level.

In case you are wondering, the 6.8k resistor in series with the 0.01 uF cap is there to prevent that gain stage from amplifying too much high frequency noise above the usual audio spectrum, so that can stay as it is and does not need to be adjusted, although it could be if you felt like playing about with the high frequency response.

Also, if you are curious and did want a wet/dry mod, stick a 47k linear pot in place of where the 22k and 20k resistors are next to points A and D on the schematic. Not really needed though, I don't think.

[radansey]

I've just finished housing my A-B switching box.

[attachment=44655:DSC_6978.JPG]

I originally built this way back in 1984 from a project in Guitarist magazine - it uses a CMOS chip for click-free operation with LED's to show the active channel.

1984 to 2010 - you can tell I don't like to rush things!!

Ross