anyone help convert dual volume to single? - diyAudio
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Old 8th December 2010, 06:36 AM   #1
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Default anyone help convert dual volume to single?

This tube pre has independent l and R volumes. My power amp also has dual volumes so I'd rather just convert this pre to a single volume setup. Can anyone take a look at this pic and guide me towards this end?

thanks in advance.

fyi, this circuit is basically a marantz 7c
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Old 8th December 2010, 06:47 AM   #2
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Remove both single potentiometers and replace them with a double one of the same resistance and slope (logarithmic , I guess ) .
Put a red neon lamp to cover the hole of the lost pot .
Is it a joke ?
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Old 8th December 2010, 11:46 AM   #3
Loren42 is offline Loren42  United States
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Originally Posted by picowallspeaker View Post
Remove both single potentiometers and replace them with a double one of the same resistance and slope (logarithmic , I guess ) .
Put a red neon lamp to cover the hole of the lost pot .
Is it a joke ?
The second hole is where the balance control goes. So, he needs to understand how to add and wire up a balance control to the circuit.

There are two ways to do that. One is using a dual ganged pot. The ganged pot is wired similar to the ganged volume control, with one side grounded and the other connecting to the signal in. The wiper is the signal out. The ground side of the ganged pots are mirrored so that when you turn the pot one direction it increases volume of one channel and grounds the signal in the other. They make special tapers for these pots if you want to get exotic.

The other is a single pot with the wiper tied to ground and each end tied to the signal of the left and right channels. This pot needs to be a linear taper.
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Old 8th December 2010, 12:55 PM   #4
Loren42 is offline Loren42  United States
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Here are some ideas on rewiring your amp.

All pots are considered UP to be turning the pot clockwise in the schematic.

Dashed lines indicate a dual ganged pot.

Lin = Linear Taper, Log = Logarithmic Taper, and S = S Taper.

There are other ways to do this, but this will get you started.

Click the image to open in full size.
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Old 8th December 2010, 01:25 PM   #5
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Just to make this clear - balance control is not needed to convert to single pot. Post #2 is what I would do, balance controls are useless and you have the ability to change relative levels on the power amp in this case anyway.
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Old 8th December 2010, 01:33 PM   #6
mikje is offline mikje  United States
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Just to make this clear.... Post #2 is what I would do...
If you want to keep it simple, I wouldn't worry about a balance pot. Just go with a dual ganged volume pot such as this one Partnumber=023-650 from Parts Express. Not sure what value you would need, but PE has other values as well. You can also get one at Radio Shack.
Mike
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Old 8th December 2010, 07:47 PM   #7
tomchr is offline tomchr  United States
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Originally Posted by richie00boy View Post
Just to make this clear - balance control is not needed to convert to single pot. Post #2 is what I would do, balance controls are useless and you have the ability to change relative levels on the power amp in this case anyway.
A balance control would cover up the hole in the faceplate nicely, though...

~Tom
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Old 9th December 2010, 01:07 AM   #8
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The current pots are 250k. So I should get a dual 250k and wire it up the same as it is now? including the jumpers on the left tab(s)

No balance needed as my power amp serves this function. thanks

I have two 500k dual pots handy. Would one of these work? One reads D500k and the other A500k. The current pots read B250k. I assume the A and D mean something? Not sure if either of these dual pots are log or audio.......?

Last edited by awangotango; 9th December 2010 at 01:12 AM.
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Old 9th December 2010, 01:27 AM   #9
mikje is offline mikje  United States
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I would try to get a 250K, but you can use a 500K for now. Yes, wire it up like it is now.
Enjoy your amp!
Mike
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Old 9th December 2010, 02:05 AM   #10
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Wow, no problem! Your on-hand parts are perfect.

Here's Rod Elliot's take on volume + balance control: ESP - A Better Volume Control

Dual pots, both 500k will make a parallel pair of 500k loads makes 250k!. . . if you use one for balance and one for volume.
The A500k is the volume pot.
The B500k is the balance pot (one channel reversed on the pot itself makes balance pot--simply linear pot and when one channel turns up the other channel turns down).
Together, they make a 250k load. Well, I'm excited!

Its awesome that you already have the needed parts on hand.
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