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 Forum index » DIY Hardware and Software
How does this potentiometer work ?
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Sat Feb 15, 2014 6:24 am    Post subject:  How does this potentiometer work ?
Subject description: a stereopot with 2x 5 connections
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I'm retracing an old passive tonecontrol circuit I once took out of an amplifier (I think it was one of those radio/tapedeck/record player combos), and there
is a potentiometer on the PCB which has 2x 5 connections. I think it's used as a volume control with loudness but I'm wondering how the potentiometer
works. I tried to measure it and it seems like it has fixed resistors build in on each end, but I'd have to desolder it to be sure. So maybe someone knows Question

and another question,. what's the value of the capacitor on the 3rd pic; 150nF/100V, 100nF/150V, 150pF/100V, 100pF/150V ? (I don't think it's one of the last 2 options)


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PostPosted: Sat Feb 15, 2014 10:04 am    Post subject: Reply with quote  Mark this post and the followings unread

sometimes tone control pots would have fixed taps ... and i've seen ganged pots being used too ... maybe google Baxandall ... if I spelled that correctly ...
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PHOBoS



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PostPosted: Sat Feb 15, 2014 10:46 am    Post subject: Reply with quote  Mark this post and the followings unread

yeah I figured it would be a Baxandall tonecontrol (you spelled it correctly Very Happy) but never saw those pots before.
So it could indeed be fixed taps, thanks!

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analog_backlash



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PostPosted: Sat Feb 15, 2014 5:11 pm    Post subject: Re: How does this potentiometer work ?
Subject description: a stereopot with 2x 5 connections
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My guess (for what it's worth) would be 150nF/100V, as I've only seen that type of capacitor with DC ratings of 63V, 100V, 250V, 400V... and they're usually in the nF range. I think that they're the SilverCap™ type of metallized polyester film and I really dislike them as it's so easy to break the contact wires off Evil or Very Mad

Gary






accidental edit by PHOBoS (oops I have to get used to these new buttons)


No worries - I wondered what had happened there Laughing

Last edited by analog_backlash on Sun Feb 16, 2014 4:19 am; edited 1 time in total
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delayed



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PostPosted: Sat Feb 15, 2014 6:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Fender used center tapped pots in some of their designs also.
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PHOBoS



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PostPosted: Sat Feb 15, 2014 6:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
My guess (for what it's worth) would be 150nF/100V, as I've only seen that type of capacitor with DC ratings of 63V, 100V, 250V, 400V... and they're usually in the nF range. I think that they're the SilverCap™ type of metallized polyester film and I really dislike them as it's so easy to break the contact wires off Evil or Very Mad

Thanks Gary, 150nF was my guess too. And you're correct about those wires breaking off. Before ordering online I always went to the shop
with a list of parts which I would hand over. And I never really knew what i would end up with. Always hated it when I got those caps. Didn't really
have anything in stock back then (apart from some desoldered stuff) so it really sucked when a contact broke off.


delayed wrote:
Fender used center tapped pots in some of their designs also.

Thanks, those were the magic words. Laughing
I found this:
Quote:
Another common use for tapped controls was on a specially compensated volume control, called a Loudness control. In general, it allowed increased bass response with decreasing volume control settings, to compensate for the human ear's nonlinear response with respect to sound pressure level (Fletcher-Munsen curves). You'll find a button on the front panel of your home stereo to engage the additinal circuit components attached to this "loudness tap" on the volume control. There do exist multiple tapped volume pots for precision loudness tracking, but the normally encountered single tapped version has a tap at the physical center of the resistance track, which is at 10%/90% electrical resistance point on the audio taper volume pot.

here

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