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prgdeltablues
Joined: Sep 25, 2006 Posts: 222 Location: UK
Audio files: 12
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Posted: Tue Sep 16, 2014 1:41 am Post subject:
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That's looking pretty good. Your ramp appears to be offset from 0, which may be part of the trouble for the triangle (and the sine is derived from the triangle of course). Try adjusting R5 to get the ramp/saw symmetrical about ground. Then adjust R7 as described to shape the triangle.
I'd also check component values around U4-C.
Peter |
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Europanaut
Joined: Apr 04, 2014 Posts: 46 Location: Nanaimo, BC, Canada
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Posted: Tue Sep 16, 2014 10:58 pm Post subject:
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Thanks Peter,
You were right. It was all about the adjustments. It's now showing good shapes.
I'll hit the scaling calibration tomorrow, and report back. |
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Europanaut
Joined: Apr 04, 2014 Posts: 46 Location: Nanaimo, BC, Canada
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Posted: Thu Sep 18, 2014 12:26 am Post subject:
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There are some challenges with the scaling calibration.
I can't seem to shrink the scaling down to proper octaves. Adjusting R16 doesn't seem to do the trick.
At 0v, the oscillator is tuned to 100hz. At 1v, the oscillator plays 218 hz. This is when R16 is set fully clockwise. When R16 is fully COUNTER clockwise, the range is 0v=100hz to 1v=217hz. So in both situations, the octaves are too stretched.
In his calibration description, Ray says "Adjust R11 so that you have the most resistance between its pin 2 and pin 3 and thus the least high frequency pitch correction. We will adjust this later as necessary." Pardon my newbyness, but if I measure across these pins while they are in situ, I don't get any activity on the MM at all. Is this normal(maybe the pot must be out of the circuit for measurements), or is the lack of readings on the MM indicative of a problem with the R11 hftrim pot/solder joints/etc?
Any suggestions?
Thanks! |
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prgdeltablues
Joined: Sep 25, 2006 Posts: 222 Location: UK
Audio files: 12
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Posted: Thu Sep 18, 2014 1:40 am Post subject:
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Hmm. sounds as if you may have a problem around the high frequency trim R11. Attempting to measure the resistance of a component in circuit is not usually a good thing, because there may be other resistances in parallel with it - what you are measuring is the sum of all paths between the two points. But it is a valid thing to do if you understand that point (I do it for instance to check that the resistance between say V+ and Ground is what I expect from the schematic.) You should always do this WITHOUT power applied to the circuit though.
When you say you don't get any activity on your DMM, what do you mean? [Check you've set it to measure resistance ] If it reads 0 Ohm, or Out of range, that suggests a problem. Try measuring from pin 1 to pin 3 of R11 - that should be 1MEG where-ever the pot is adjusted.
If R11 is faulty in some way, you'll not get R16 to adjust properly. But you could check what the voltage is at R16 pin 2. You're aiming for 18.6mV per 1V input if I recall correctly. R10/R24 voltage divider divides by 50, so the top end of R16/R19 - pin 1 of U1A should show 20mV for a 1V input. R16/R19 then act as a further voltage divider to trim that down to the proper value. (Start with R16 roughly midway).
Peter |
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Europanaut
Joined: Apr 04, 2014 Posts: 46 Location: Nanaimo, BC, Canada
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Posted: Sun Sep 21, 2014 8:34 am Post subject:
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Found the problem. R19 was 475k, instead of 475 ohms. All is working well now, the oscillator is working 100%, and is calibrated.
I'm hoping to finish two more this evening, then move on to the filters (and to a new troubleshooting thread topic!).
Thanks for the help! |
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_Shorty
Joined: Jul 07, 2014 Posts: 2 Location: Parksville, BC
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Posted: Sun Sep 21, 2014 11:17 am Post subject:
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Sweet! |
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Europanaut
Joined: Apr 04, 2014 Posts: 46 Location: Nanaimo, BC, Canada
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Europanaut
Joined: Apr 04, 2014 Posts: 46 Location: Nanaimo, BC, Canada
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Posted: Sun Sep 28, 2014 8:48 am Post subject:
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Update:
So something has changed. The triangle in osc 3 has become very shy. It's still there, but much quieter then the other waveforms.
Edit: Ok, so nothing changed. R22 was 100k instead of 1k. I must have been tired....yeah..... |
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