need help troubleshooting VCO/VCF..can hear clicks, VCF..
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Re: need help troubleshooting VCO/VCF..can hear clicks, VCF..

by Altitude on Sat Dec 29, 2012 7:30 am

make a headphone probe like described in the build docs, its the next best thing to a scope. You should be able to hear the saw and square waves at the wave switch, if you dont, that's where the problem is
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Re: need help troubleshooting VCO/VCF..can hear clicks, VCF..

by stinki2 on Mon Dec 31, 2012 8:47 pm

i don't think i know anyone with an oscilloscope.

yes i've already done the headphone test. it's very quiet, but when i touch to pin 1 of the switch i can hear the saw, randomly changing pitch as it should, in random mode..i can't hear the sqr at pin 3...i thought that was normal though..?

so the problem is definitely the VCO? it's not very many parts, i'm tempted to clip all the resistors i've got in the section and put in new ones...pretty frustrated..wish I could just check voltage at a few key points to narrow down the problem area though... If I hear the saw at pin 1, but the VCO doesn't seem to make it through the filter, does that narrow down the suspects/areas to check?

I did replace the Q39 K30A transistor at some point. Originally I had it in Q28, as the fab manual calls for one there, but my kits came with a K118 transistor which is in Q28 instead. So maybe there's something gone wrong with the K118..?

hmm
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Re: need help troubleshooting VCO/VCF..can hear clicks, VCF..

by MMM on Tue Jan 08, 2013 6:53 am

stinki2 wrote:so the problem is definitely the VCO? it's not very many parts, i'm tempted to clip all the resistors i've got in the section and put in new ones...pretty frustrated..wish I could just check voltage at a few key points to narrow down the problem area though...


There is a sticky thread at the top of this forum called "Analogue Section Reference Voltages" that could help.

I don't know if the VCO is the problem; if the saw oscillator is "very quiet" it could be that the output is too low to properly drive the saw-to-square conversion.
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Re: need help troubleshooting VCO/VCF..can hear clicks, VCF..

by synthplayer on Fri Feb 08, 2013 10:43 pm

stinki2 wrote:i don't think i know anyone with an oscilloscope.

yes i've already done the headphone test. it's very quiet, but when i touch to pin 1 of the switch i can hear the saw, randomly changing pitch as it should, in random mode..i can't hear the sqr at pin 3...i thought that was normal though..?

so the problem is definitely the VCO? it's not very many parts, i'm tempted to clip all the resistors i've got in the section and put in new ones...pretty frustrated..wish I could just check voltage at a few key points to narrow down the problem area though... If I hear the saw at pin 1, but the VCO doesn't seem to make it through the filter, does that narrow down the suspects/areas to check?

I did replace the Q39 K30A transistor at some point. Originally I had it in Q28, as the fab manual calls for one there, but my kits came with a K118 transistor which is in Q28 instead. So maybe there's something gone wrong with the K118..?

hmm


Have you tried the headphone test at these points,

SAW: Q28 connecting R105.
SQR: Q8 connecting R36.

The level will be quite high so you can hear it without wearing the headphone.
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Re: need help troubleshooting VCO/VCF..can hear clicks, VCF..

by stinki2 on Fri Apr 05, 2013 9:24 am

thanks for all the help guys, i finally figured it out by comparing the voltages between my working xox and the non-working one. that reference voltage chart would have come in handy too..oh well, i've got it now, thanks!

it was indeed the k118 in q28, one of the legs was broken but impossible to see...the voltages gave it away...

now it's almost fully working, i have a small problem with the envelope to figure out next..
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