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2011-07-24 by klosmon
While we're on the subject of Odysseys, I have one on the bench with a high-pass filter that has no response for 4/5ths of the slider travel -- then at the top position it finally cuts off. This is one of the most simple circuits in the world-- I've replaced the slider, cap & resistor with no effect. Can anyone with a Mark II tell me if this is normal, or is there something going on with this particular unit? Thanks. ~GMM
2011-07-24 by Malte Rogacki
> While we're on the subject of Odysseys, I have one on the bench with a > high-pass filter that has no response for 4/5ths of the slider travel -- > then at the top position it finally cuts off. > This is one of the most simple circuits in the world-- I've replaced the > slider, cap & resistor with no effect. > Can anyone with a Mark II tell me if this is normal, or is there > something going on with this particular unit? I personally find the HPF almost useless; and to make matters worse it even affects the sound slightly when the slider is in the bottom position (you can see this with an oscilloscope). Anyway, the important thing to keep in mind for the HPF is that it can only work on material that contains suitable frequencies. Compare it to the LPF: If the source material is reasonably "buzzy" you will always get some filtering result because the harmonics continue upwards anyway. With the HPF it's different: If you play a somewhat middle to high note the HPF will have nothing to pass for quite some time. So please test this once again with very low notes (transposition two octaves down) and check if the response now starts earlier.
2011-07-24 by klosmon
Interesting thought, thanks.
I personally find the HPF almost useless; and to make matters worse it even
affects the sound slightly when the slider is in the bottom position (you
can see this with an oscilloscope).
Anyway, the important thing to keep in mind for the HPF is that it can only
work on material that contains suitable frequencies. Compare it to the LPF:
If the source material is reasonably "buzzy" you will always get some
filtering result because the harmonics continue upwards anyway.
With the HPF it's different: If you play a somewhat middle to high note the
HPF will have nothing to pass for quite some time.
So please test this once again with very low notes (transposition two
octaves down) and check if the response now starts earlier.
2011-07-24 by Boddington
At the risk of stating the obvious, is there a chance that that slider is just worn or dirty? Do you a see a consistent change in ohms if you move the slider from bottom to top? I just wonder if the strip inside inside is worn out.
2011-07-24 by klosmon
It never hurts to state the obvious; in this case, I tried a couple of new 1M audio pots (both tested good with the ohmmeter). This whole thing is bugging me because, as a passive filter, it's SUCH a simple circuit (a total of three components, all of which have been replaced with tested new ones).At the risk of stating the obvious, is there a chance that that slider is just worn or dirty? Do you a see a consistent change in ohms if you move the slider from bottom to top? I just wonder if the strip inside inside is worn out.
2011-07-24 by Boddington
I'd start by taking a step back from it then. Firstly, just make sure the resistor and cap values are correct (again, another somewhat obvious statement but let's rule it out), then I'd move towards the VCF. Check the pins to see if they're working. Are you getting +/-15 V on pins 6 & 8? What does pin 10 tell you? Also - is the VCF still sealed?
2011-07-24 by klosmon
Again, no offense at stating the obvious. The cap and resistor values are correct (as contained in the statement "all three components were replaced with tested new ones").I'd start by taking a step back from it then. Firstly, just make sure the resistor and cap values are correct (again, another somewhat obvious statement but let's rule it out), then I'd move towards the VCF. Check the pins to see if they're working. Are you getting +/-15 V on pins 6 & 8? What does pin 10 tell you? Also - is the VCF still sealed?