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Old 13th April 2006, 12:37 PM   #1
kepa1 is offline kepa1  France
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Question How to connect a pot balanced

Hello,

Visited the entire cyber space but could not find relevant information.

So I have a stereo ALPS and need to connect it before a balanced mono amplifier.

I suppose each row is a channel but where is In ant Out? There are 3 pins by row, numbered from 1 to 3, really!

Click the image to open in full size.

Thank you.
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Old 13th April 2006, 01:06 PM   #2
huguini is offline huguini  Argentina
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Maybe this helps...

http://diyparadise.com/charlize.html

Look at the bottom of the page.

regards
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Old 13th April 2006, 01:48 PM   #3
kepa1 is offline kepa1  France
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Thank you for this one Huguini, this helps a lot!

I see what was my mistake the last time I switch on my amp with a wrong wiring... In fact the ground must go through to pin 3 and then be connected to the amp...

But in a balanced set up there's only one ground for two signal cables, so does it mean that the ground must be divided in two, connected to R3 and L3 and then R3 and L3 connected to the amp signal ground?

Something like that?
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Old 14th April 2006, 12:08 PM   #4
Vidalgo is offline Vidalgo  Israel
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see picture
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Old 14th April 2006, 05:04 PM   #5
kepa1 is offline kepa1  France
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Sorry, it doesn't make sense as the dact attenuator has two pins only and that the ground is attached to both of them

Can't figure it out...
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Old 15th April 2006, 03:01 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi Kepa,
your 2channel (stereo) pot is intended for unbalanced use.

If you buy a 4channel pot you can control both the + & - of both channels at the same time. That is what the DACT 4deck is doing.

If you are prepared to use a stereo pot on each channel and control them independantly then you can use the ALPs you already have on one channle and buy another for the second channel.

Now go back to post4 and look again at the DACT 4deck connections. Using the wiring for deck 1 & 2 only you can wire up your ALPs to exactly match this to control one balanced channel.

Notice that ground is common all the way through. your ground will also do this and pick up one pin from the ALPs (either 1 or 3, because pin2 is the wiper). + in goes to the other unused 1 or 3. + out uses wiper (pin 2) and repeat for the - connections.
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Old 16th April 2006, 01:00 AM   #7
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You have a quality pot there, but I would not expect great performance from it in controlling a balanced source. Any mistracking of the resistance in the two halves (even if it is made for balanced operation) will result in poor common mode rejection (i.e. - noise), and they ALWAYS mistrack.

You'd be better off with an electronic attenuator chip or a pair of them, one for each channel. The on-chip matching is usually very good, and won't change after thousands of operations. A pot may start out OK, but after it is turned a few hundred times, it WILL mistrack and then you will lose the benefit of using a balanced line.

I_F
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Old 17th April 2006, 11:21 AM   #8
kepa1 is offline kepa1  France
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Ok I think I can do it now

In fact these pots will be controling 2 subwoofers that have balanced UCD amps.

Considering what you said, it should be a good idea to set the pots to let's say 12 o'clock and adjust the volume from the digital active filter (though I know I'll lose a bit of dynamics). Or else, I could connect them unbalanced...
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Old 21st April 2006, 10:33 AM   #9
kepa1 is offline kepa1  France
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Ok, so this ALPS pot set up has gone a little crazy, so I've decided to go with fixed attenuator of 30db.

I'll then use the digital XO gain to control volume; this supposedly means loss of dynamics and details but I don't care much because it will only happen in the bass region.

Well, my reading has taught me that I need 1 resistor on the hot and cold rails, and 1 resistor between them.

The issue is now to set their correct value, knowing that
the XO output impedance is 160 Ohms,
and the UCD180 amp input impedance is 100 kOhms.

Any idea?
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Old 21st April 2006, 11:07 AM   #10
EC8010 is offline EC8010  United Kingdom
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You can use your pot in a balanced system. You just need to add a couple of 0.1% resistors to avoid the imbalance problem mentioned earlier.
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