Django
1 post
Sep 13, 2016
10:54 AM
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Just wondering if anyone knows for sure if there is a going to be even a subtle difference in tone when using a 100k pot vs 200k pot vs 500k pot for a volume control with a MC element of around 1000 ohms.
I know the sweeps will vary but I know at least with an electric guitar whether it be Strat of Les Paul going from 250k pots to 500k pots makes quite a big difference. However the impedance of a guitar pickup is around 6k and up. With single coils changing only the volume pot from 250k to 300k makes a difference.
Even the tone pot values make a difference.
Are these differences similar in a harp mic with an MC element as stated above? (I would put push push pot in it with dbdt but it won't fit.)
I've searched everywhere on the net for days but can't find any definitive comments.
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Bugfan
53 posts
Sep 13, 2016
7:18 PM
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With an MC element I am not sure as I am not a techo but from what I understand as a layman.... it also depends on the amp input impedance. The impedance of both the element (or in this case the element plus the vol pot) in parallel gives the overall impedance/resistance loading .As far as I know the amp input impedance is governed by the grid leak resistor. It certainly affects a ceramic element tone and I have the written instruction from Astatic regarding their ceramic element that says - I quote: " a parallel resistance or gridleak resistor must be at least 5 meg ohms unless a decrease of low frequency response is desired". I know that impedance and resistance are different things but I believe they are the same thing effectively for what we are looking at here. I am guessing (just guessing) that this will apply to some degree for all elements and therefore there will be some effect dependant on the pot value but more dependant on the amp input impedance. Hopefully the techs can chime in on this to help our understanding.
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Django
2 posts
Sep 13, 2016
9:29 PM
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Thanks for the information. I did some research on grid leak resistors and I am only a little more clear on their function but here are my thoughts on that.
Would that not be more crucial if we were talking about different elements i.e. crystal where the impedance is much higher.
I'm guessing the added resistance of the 100k, 250k, or 500k pot would allow slightly more signal through the higher they are rated but not so much as to change the overall relationship the mic has with the amp.
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Bugfan
54 posts
Sep 14, 2016
4:05 AM
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Yes that's my thought too...it would probably be a lot less effect but not sure how much. I suspect a dynamic element wouldn't be affected. I know that the combination of the resistor values some how makes a voltage divider which then acts as a frequency cut.... But the maths of that eludes me! Also what I don't understand is how the effect will vary with the position of the vol pot. If you are at full volume then the pot resistance is nil and no effect. As you quieten the mic then it is adding resistance ,so then I guess it is progressively having an effect. If that's the case then any pot will work and you could avoid any low frequency loss by minimising the vol control? If that's the case and harp mic needs to be putting a strong as possible signal into the amp to drive it harder for the sound we like.... then why do all the mic sites recommend minimum of 1 Meg or higher fit even CM or CR elements.
I guess I am asking more questions than you now!
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markdc70
168 posts
Sep 14, 2016
10:46 AM
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When you have the volume turned down on the mic pot, it is making a voltage divider circuit to send some signal to ground, and some to the amp input. If you are using a larger than needed pot, then the resistance that the mic signal must travel through to get to the amp is high enough to deaden the higher frequencies, giving you a dull sound when turned down. This is the reason for the "bright" cap soldered onto some volume pots. Hopefully Greg Hueman will chime in as he is the resident expert here on all things mic related.
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Django
3 posts
Sep 14, 2016
2:57 PM
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That's true although I'm mostly curious as to how the tone is affected in different valued pots when they are on full and if there is a difference between the previously mentioned values. I know that there is a difference when there is no pot whatsoever as Greg Hueman has stated it before and I also know that he prefers 250K pots with CM elements. I wonder what the difference is especially tonally compared with 100k and 500k if at all.
It doesn't have to be a tech response as someone with a discerning ear might hear the difference.
There is a lot of talk on this in guitar circles and I have done my share of experimenting with pots, cap and resistor values and even what caps are made of. It is not as much an issue it seems in harp circles.
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1847
3690 posts
Sep 14, 2016
6:20 PM
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are you deliberately being vague on the exact mc element you are referring to?
astatic elements call for a minimum of one meg. preferably five meg.
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Django
4 posts
Sep 14, 2016
8:23 PM
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Hi 1847 I didn't think I was being vague and am not trying to be but I do realize after rereading my posts that I said MC element when I meant "CM" (99A86)element at around 1000 ohms.
That might make more sense now. Sorry about that fellas.
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Greg Heumann
3277 posts
Sep 15, 2016
12:53 PM
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Django - you are correct " added resistance of the 100k, 250k, or 500k pot would allow slightly more signal through "
Rule Number 1: The higher the ohms of the pot, the less output loss, but the more sensitive the pot will be. If you use a 500K pot all of the useful volume range will be compressed into the 1st 1/4 turn of the knob.
Rule Number 2: You can't always get what you want. Depending on where the pot is to be mounted, you may or may not have your choice of the "perfect" pot. You have to buy what the vendors stock, unless of course you can afford to order 10,000 at a time (the manufacturer's minimum order.)
Rule #3: There is no free lunch. There will always be SOME loss of output and hence tone. HOWEVER with a properly matched pot, the benefits far outweigh these losses, in my opinion.
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***************************************************
/Greg
BlowsMeAway Productions
See my Customer Mics album on Facebook
Bluestate on iTunes
Last Edited by Greg Heumann on Sep 15, 2016 12:53 PM
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Django
5 posts
Sep 15, 2016
6:59 PM
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Thank you very much for that Greg, that is exactly what I was trying to find out.
Sounds like it's generally the same as it would be in a guitar or most other things I suppose.
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