I'm stuck: Passive 25k volume + 500k tone, what happens? - Jemsite
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post #1 of 9 (permalink) Old 01-19-2015, 06:45 PM Thread Starter
 
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I'm stuck: Passive 25k volume + 500k tone, what happens?

Learning a few things about pots and pickups atm.

I've got this guitar in my hands that has been fiddled with.

it is a HH 3 switch 1 tone 1 volume passive situation with a 25k (not 250 indeed) volume + 500k tone, and turning the tone know has no effect whatsover. I was breaking my head over this, but I starting to think that is totally logical.

25k's are supposed to be for active elements, whereas 250-500-1M are supposed to be for passives.

Can someone confirm my phenomenon (the tone pot not having any effect) and/or explain ? Would be a great help.

Thanks!
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post #2 of 9 (permalink) Old 01-19-2015, 07:19 PM
 
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Re: I'm stuck: Passive 25k volume + 500k tone, what happens?

You are probably correct on your assumption... I think the majority of the guitar signal is taking the "path of least resistance" and bypasses the tone pot completely. Typically you should use a 500k volume pot with the 500k tone.
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post #3 of 9 (permalink) Old 01-19-2015, 07:37 PM
 
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Re: I'm stuck: Passive 25k volume + 500k tone, what happens?

25k are for active and as you said 250k 500k and 1 meg can be used for passive. The value of the pot deals with the frequency sweep of the pot and how much resistance is between the terminals of the pot. Think of the middle lug of the pot as output and in the other two lugs as input. As you turn the pot the resistance lowers between output and input letting more signal bleed between the lugs. In the case of the volume pot this is how much signal is bleeding off to the ground.

the 25 k pot is lower resistance because the pickup system has the addition of a battery. The active circuit doesn't ground to the guitar. The 25k value is controlling the response of the preamp built inside the pickup whereas with passive you are controlling the actual AC voltage generated by the vibrating string inside a magnetic field.
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post #4 of 9 (permalink) Old 01-20-2015, 01:59 AM Thread Starter
 
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Re: I'm stuck: Passive 25k volume + 500k tone, what happens?

Thx for the input! So J.arledge, would you agree with FireEagle's statement about the bleed in your elaboration?
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post #5 of 9 (permalink) Old 01-20-2015, 09:50 AM
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Re: I'm stuck: Passive 25k volume + 500k tone, what happens?

Nice parallelisms from fireagle and arledge above. In literature basically you will find the vol pot referred to as "voltage divider" : http://en.wikipedia.org/wiki/Voltage_divider where Z1 and Z2 vary from 0 to max resistance (nominal resistance of the pot). The extreme cases are in 0 (Z1=nominal max, Z2=0) and 10 (Z1=0, Z2=nominal max).

In theory any pot would work for vol, but there is the concern of the treble bled, hence the 250, 500 KOhm values on passive pups. In actives, the impedance is less, hence the smaller pot values in KOhm.
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post #6 of 9 (permalink) Old 01-20-2015, 05:31 PM Thread Starter
 
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Re: I'm stuck: Passive 25k volume + 500k tone, what happens?

So I swapped the 25k pot with the 1M pot I had lying around and the duncan in the bridge gives lot more beef now. The tone pot has clearly more effect now, although not tremendously.
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post #7 of 9 (permalink) Old 01-20-2015, 10:43 PM
 
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Re: I'm stuck: Passive 25k volume + 500k tone, what happens?

the value of the pot will determine how much treble bleed off there is . Lower value higher bleed off. 1 meg pots are considered no load pots because almost no treble is lost. They sound much brighter. Great for dark pickups not so great with something like an evolution.

With tone pots the value of the capacitor will determine how much effect the tone pot has on overall sound. Most guitars have .22 micro farad ( abbreviated uf only with the u being the lower case greek MU.)

You can change this value. The smaller the value the more high end stays in the signal path. The larger, the more high end is taken away. This is also why some guitars have a high pass cap. When the volume is rolled back you loose some high end. The high pass cap lets the highs stay in the signal by bridging the ground and input terminals.
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post #8 of 9 (permalink) Old 01-21-2015, 01:33 PM Thread Starter
 
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Re: I'm stuck: Passive 25k volume + 500k tone, what happens?

Thanks J! Learning a lot here. Very cool.

So I'm that is how the high pass works on a JS when you pull the volume pot?
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post #9 of 9 (permalink) Old 01-21-2015, 09:58 PM
 
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Re: I'm stuck: Passive 25k volume + 500k tone, what happens?

Yeah the js line's high pass cap works the same way. It bridges the two lugs (output and ground) and in doing so the small value cap lets some high end frequencies back in to the signal flow.

This makes the volume pot more about turning the volume down instead of altering the tone when turned down.
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