s36572u@puukko.hut.fi (Karl R. Tigerstedt) (09/24/90)
I just purchased the SID II, assembled it - it didn't work.
When I tried to record, the only sound I could get was a very
high-pitched tone. Looked at the thing with an oscilloscope, the
A/D chip was receiving this signal - so the problem had to be
somewhere around the filter unit (the TL064 or was it TL084, not important).
Anyway, I changed one of the 1 uF capacitors (the one that is
sort of fed back around the first op. amp.) to 820 nF, and the problem
was gone. No more high frequency tones, that block all else.
But, now when I record, the sound quality is very poor, even
at a sampling rate of 22khz. It seems that the bass tones are completely
cut off, maybe due to the change I made. When I played back the
"welcome to SID II from Cedar Technologies" -recording, I was amazed
how nice it sounded compared to the mumble I get.
My question is: What is really wrong with my SID?
Which component(s)?
P.S Sorry, but I don't have schematic right now, but I'll look it up
more precisely, if needed.
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"I have only come here seeking knowledge.
Things they would not teach me of in college" - The Policemikec@allspice.lcs.mit.edu (Mike Ciholas) (09/24/90)
In article <1990Sep24.112557.2941@santra.uucp> (Karl R. Tigerstedt) writes: > I just purchased the SID II, assembled it - it didn't work. >When I tried to record, the only sound I could get was a very >high-pitched tone. Looked at the thing with an oscilloscope, the >A/D chip was receiving this signal - so the problem had to be >somewhere around the filter unit (the TL064 or was it TL084, not important). > Anyway, I changed one of the 1 uF capacitors (the one that is >sort of fed back around the first op. amp.) to 820 nF, and the problem >was gone. No more high frequency tones, that block all else. > But, now when I record, the sound quality is very poor, even >at a sampling rate of 22khz. It seems that the bass tones are completely >cut off, maybe due to the change I made. When I played back the >"welcome to SID II from Cedar Technologies" -recording, I was amazed >how nice it sounded compared to the mumble I get. > My question is: What is really wrong with my SID? > Which component(s)? Since other's may have this problem I posted. Here's the scoop: That capacitor you changed is part of the precision anti-aliasing filter in front of the analog-to-digital converter. Changing its value to 820 pF (it was supposed to be 1.0nF, which is .001uF, not 1uF, so I hope you put in a 820pF, not 820nF in there) substantially altered the filter's pass band performance, but it did stop the oscillation. I suspect that you have one of the following problems: 1. You swapped or installed badly one of the precision resistors (the blue ones) or capacitors (silver can ones) which will cause the circuit to oscillate badly. 2. One of the components in the filter part is bad (rare, but possible). I would suggest you concentrate on 1. Check the value and location of every part north of the TL064. If there are all correct, then your best bet will be to send it back to me, and I will track down the problem. If I can't fix it, you will get a new one. Mike Ciholas mikec@lcs.mit.edu PS: The "welcome" message is me :-) (and it was made with the built-in microphone !)