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Post by wiz on Apr 2, 2016 19:08:44 GMT -6
 I have an existing pot, that I will wire as a variable resistor. The pot is 22KOhms I need it to cover a range of 10K to 82K (ish) Possible? I aint smart enough to work it out... x and y are just suggested idea for circuit cheers Wiz svart jimwilliams @smallbuttfine @anyone who is smarter than me... 8) |
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Post by acegunn on Apr 2, 2016 20:13:18 GMT -6
Did a page of resistance calculations, but only could solve the equations for that circuit with either y or x being negative.
Not sure getting a total range of 10K to 82K is possible with a 22K pot.
Maybe the smart guys on RGO know a clever circuit for this.
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Post by svart on Apr 2, 2016 23:11:06 GMT -6
The range is doable, but you didn't mention the law of the pot..
If that pot is linear, you're going to end up with a strange S shaped curve.
If it simply has to be 82k (a very uncommon value indeed), then you can get a 100k and put a divider network around it to preserve the law while changing value.
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Post by wiz on Apr 2, 2016 23:31:27 GMT -6
Thanks guys...
The pot is existing...it's an aux in my delta... I am toying with the idea of turning it into the variable part of a HPF.
So the pot value is fixed... The rang dis what sounds good in the circuit .... 40 Hz to 340hz
Cheers
Wiz
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Post by NoFilterChuck on Apr 3, 2016 10:37:59 GMT -6
You should ask this over on GroupDIY.com
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Post by wiz on Apr 3, 2016 15:51:13 GMT -6
You should ask this over on GroupDIY.com Good thought... those guys kinda scare me though 8) I was hoping someone here would help out... Here is the Delta HPF circuit  R26 is what I have been changing the value in the schematic yields a HPF of 86Hz 10K = 338Hz 22K = 135Hz 47K = 72Hz 82K = 41Hz Here is the circuit of the Aux on the Delta  I was thinking of stealing one of those Auxs, most likely aux 4. But I could just use the physical space and put any pot I need in there. I was looking at the Harrison Ford Filter Circuit Also I found a post from our own EmRR on GDIY where he posted this picture..I hope its okay to post it here..I think it is..  That is the schematic of a harrison filter. 20Hz to 200Hz. Looking at it I wonder about just replacing the AUX 4 pot in the Delta with a dual gang 47K pot from AML, and wiring it up like the schematic... thoughts? cheers Wiz |
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Post by wiz on Apr 3, 2016 15:52:44 GMT -6
Here are the two circuits on same page to make it easier to compare |
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Post by wiz on Apr 3, 2016 15:55:01 GMT -6
Did a page of resistance calculations, but only could solve the equations for that circuit with either y or x being negative. Not sure getting a total range of 10K to 82K is possible with a 22K pot. Maybe the smart guys on RGO know a clever circuit for this. thanks for doing that cheers Wiz |
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Post by jazznoise on Apr 3, 2016 16:12:59 GMT -6
A 75K pot with a 10K in series is the best way of getting that rough range of values. Remembers pots aren't precise and most are +/- anywhere up to 20%.
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Post by wiz on Apr 3, 2016 16:26:48 GMT -6
good thinking and I could make the 10K pot, smaller to go higher if I wanted.
what type of pot would be best?
cheers
Wiz
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Post by jazznoise on Apr 3, 2016 16:59:46 GMT -6
good thinking and I could make the 10K pot, smaller to go higher if I wanted. what type of pot would be best? cheers Wiz The circuit itself will usually have a preference - usually for audio stuff though, you want a log pot. For the record, I meant a single 75K pot and a fixed 10k resistor. You could have the 10K be a trim for adjusting the actual values, but I'd be much too lazy for that. |
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Post by svart on Apr 4, 2016 9:18:02 GMT -6
OK, sorry guys, I rarely visit here on the weekends..
But let me straighten out a few things..
Wiz mentions changing R26.. That's only ONE of the resistors that needs to change.. R27 needs to change, as well.
AND.. Wait for it.. These need to be reverse log pots.
So you'd need odd value, ganged, reverse log pots. Impossible to find.
The easiest thing to do is scale your cap values to align with a dual ganged reverse log pot values that you can purchase..
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Post by wiz on Apr 4, 2016 14:55:42 GMT -6
OK, sorry guys, I rarely visit here on the weekends.. But let me straighten out a few things.. Wiz mentions changing R26.. That's only ONE of the resistors that needs to change.. R27 needs to change, as well. AND.. Wait for it.. These need to be reverse log pots. So you'd need odd value, ganged, reverse log pots. Impossible to find. The easiest thing to do is scale your cap values to align with a dual ganged reverse log pot values that you can purchase.. Thanks for the reply svartI was wondering about R27.. is he what sets the Q? okay, so lets say I want to customize the HPF on a channel per channel basis.... eg, set channel 1 to HPF of 40z because thats always my kick drum channel etc Is there a ratio that needs to be maintained with those two resistors? Is 1 over 2pye RC how I calculate the freq? that seems to ring a bell in my noggin... 8) can you give me a quick example with existing cap values... what the two resistors would need to be changed to (R26 R27 ) for say 40Hz (ish) and 135Hz (ish) I was using this calculator online link
cheers Wiz |
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Post by wiz on Apr 4, 2016 15:53:57 GMT -6
Ok I am trying to work this out ... I am watching some op amp tutorial videos.. I am in real danger of learning something here... 8)
The delta is a non inverting amplifier....
that means the gain calculation is 1 + R2/R1
there fore
1 + 4K3/10K near enough to 1.5 or 3dB
cool...
I know how to work out the HPF freq with one cap and resistor but a bit flummoxed by the two 47nf caps and the resistor R27.. what does it do?
cheers
Wiz
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Post by svart on Apr 4, 2016 17:47:27 GMT -6
OK, sorry guys, I rarely visit here on the weekends.. But let me straighten out a few things.. Wiz mentions changing R26.. That's only ONE of the resistors that needs to change.. R27 needs to change, as well. AND.. Wait for it.. These need to be reverse log pots. So you'd need odd value, ganged, reverse log pots. Impossible to find. The easiest thing to do is scale your cap values to align with a dual ganged reverse log pot values that you can purchase.. Thanks for the reply svart I was wondering about R27.. is he what sets the Q? okay, so lets say I want to customize the HPF on a channel per channel basis.... eg, set channel 1 to HPF of 40z because thats always my kick drum channel etc Is there a ratio that needs to be maintained with those two resistors? Is 1 over 2pye RC how I calculate the freq? that seems to ring a bell in my noggin... 8) can you give me a quick example with existing cap values... what the two resistors would need to be changed to (R26 R27 ) for say 40Hz (ish) and 135Hz (ish) I was using this calculator online link
cheers Wiz What you have is a 12dB/decade 2 pole Sallen-Key filter.. The equations are quite a bit more complicated than the 1pole RC filter (1/(2piRC)) when picking the parts, but the general Fo is figured by the apparently resistance and apparent capacitance in a modified RC equation: 1/2piSQRT(R1C1R2C2).. I'd save yourself some pain and find a nice online calculator.. But you can find information and formulas here: www.linkwitzlab.com/filters.htmAnd of course, here: en.wikipedia.org/wiki/Sallen%E2%80%93Key_topologyThe Q is formed from the relationship between the caps and resistors and the poles they form with the feedback.. So yes, there is a good relationship between all R's and all C's, but the easiest way to change the Q is to change the relationship between the feedback resistor (R27) and the shunt resistor (R26). (you could put another pot (in rheostat mode) between the shunt pot and ground, so you can adjust the overall value of the shunt pot to ground, which would take the place of R26 in your original schematic.) Most designers will try a few cap ranges to find something that is either easily obtained, or gives a pot value that is reasonable for usage. A good calculator that both allows you to specify the frequency, caps AND the Q with the resulting resistor values is here: sim.okawa-denshi.jp/en/OPseikiHikeisan.htmBTW.. You were spot on with the 82K.. That's good work for such a complicated circuit. I'd personally move to 100n on the caps, which gives you a lower end at 35hz, and a 47K dual anti-log (reverse log) pots.. Those are used in a lot of things and would be much easier to get. |
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Post by svart on Apr 4, 2016 17:56:53 GMT -6
Ok I am trying to work this out ... I am watching some op amp tutorial videos.. I am in real danger of learning something here... 8) The delta is a non inverting amplifier.... that means the gain calculation is 1 + R2/R1 there fore 1 + 4K3/10K near enough to 1.5 or 3dB cool... I know how to work out the HPF freq with one cap and resistor but a bit flummoxed by the two 47nf caps and the resistor R27.. what does it do? cheers Wiz Yes that is correct. The slight gain is there to counter the loss in the filter network (all filters are lossy).. The equation is in the post above for the 47nF caps, R26 and R27. |
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Post by wiz on Apr 4, 2016 19:48:28 GMT -6
Thank mate
really appreciate it
cheers
Wiz
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Post by wiz on Apr 25, 2016 20:20:58 GMT -6
This is done... I have due to the help of joemalone, JLM Audio, now have 16 variable HPF from about 36hz to 360Hz on my delta console... they work a treat. I removed the pot for Aux 4, and replaced it. very cool thanks joe! cheers Wiz |
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Post by mulmany on Apr 25, 2016 21:38:04 GMT -6
pics, please!
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Post by tonycamphd on Apr 27, 2016 7:36:12 GMT -6
Joe Malone is a seriously knowledgable, and extremely helpful guy! I must buy many of his JLM la500's!
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Post by svart on Apr 27, 2016 7:50:12 GMT -6
This is done... I have due to the help of joemalone , JLM Audio, now have 16 variable HPF from about 36hz to 360Hz on my delta console... they work a treat. I removed the pot for Aux 4, and replaced it. very cool thanks joe! cheers Wiz So what was the final circuit? |
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Post by wiz on Apr 27, 2016 15:04:02 GMT -6
20K dual gang rev log pot, with a 2K2 resistors in series with the pot, caps changed to 220nf, sweeps from 36 to 360 @ 12dB per octave.
cheers
Wiz
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Post by svart on Apr 27, 2016 16:03:45 GMT -6
20K dual gang rev log pot, with a 2K2 resistors in series with the pot, caps changed to 220nf, sweeps from 36 to 360 @ 12dB per octave. cheers Wiz Cool. I take it you scaled the caps for the available pot values? |
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Post by wiz on Apr 27, 2016 16:22:45 GMT -6
20K dual gang rev log pot, with a 2K2 resistors in series with the pot, caps changed to 220nf, sweeps from 36 to 360 @ 12dB per octave. cheers Wiz Cool. I take it you scaled the caps for the available pot values? Well, I would like to take credit for that, Joe Malone.. did that for me 8) I am just the brawn.. he is the brains.. 8) cheers Wiz |
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