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Old 25th June 2004, 02:46 PM   #1
lazyfly is offline lazyfly  Australia
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Default Low volume imbalance

Hi folks.

I've got a pair of 50W modules running and have used the 'Better Volume (and Balance) Controls' - Rod Elliott - ESP / Bernd Ludwig. http://sound.westhost.com/project01.htm

It's definately smoother than the 50kOhm log pot I was using but at very low volume levels there's a definate bias to the right channel (in a cheesy 1 - 10 scale, anything below 1 the right channel is clearly lourder!). Can anyone explain what's happening here. I'm an aspiring electronic buff novice or something.

The only clue I have in regards to the bias is - aside from a cheap pot! - the speaker outputs on the modules show different measurements. The left channel shows 24mV the right 28mV. Is this anything to do with it?

It's not noticable at normal listening levels but at night when folks are sleeping the < 1 (on that cheesy scale) is an ideal level... but for the bias!

Thanks in advance to any replies and just for reading.

Kendal.

p.s I made two volume controls and matched the resistors on both to as best I had. The bias was there regardless.
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Old 25th June 2004, 04:37 PM   #2
sreten is offline sreten  United Kingdom
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Add a -10dB or or -20dB pad switch to your volume control
so you never have to use below 1, will work a treat.

sreten.
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Old 25th June 2004, 04:54 PM   #3
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The problem is the cheap pot.
If you have some of those, measure them and use the pot that has smaller difference between channels.
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Old 26th June 2004, 02:37 AM   #4
lazyfly is offline lazyfly  Australia
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sreten... what?? eh? Keyword here is 'novice'

carlos, thanks, I'll try that but I've problem I didn't notice yesterday that is taking precedence over the bias thing. When changing music tracks there's a mild thud in the left channel, argh! The right channel doesn't make a sound but the left has this little 'skip track' - 'dink' - 'track begins' noise. It's like the noise of very briefly touching the source (input) terminal. Any suggestions as to what would/could be causing this?

Oh yeah, I tried a different volume pot to cure this but no luck there.

Thanks again fellas!

Kendal.
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Old 26th June 2004, 06:23 AM   #5
lazyfly is offline lazyfly  Australia
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Hi folks - ignore my last post as I found the culprit. A dodgy RCA socket
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Old 26th June 2004, 02:31 PM   #6
rabbitz is offline rabbitz  Australia
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If you need a balance control use the design from Rod's project 88. Works a treat and is not in the signal path...... nice and simple.

http://sound.westhost.com/p88-f3.gif

http://sound.westhost.com/project88.htm

Some of these pots are real crap. Bought one from Jaycar and was really scratchy. Ended up using an Alps from Farnell.

Cheers
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Old 26th June 2004, 07:33 PM   #7
anatech is offline anatech  Canada
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Hi lazyfly,
Almost all pots suffer from tracking problems at the lower end. A -10 / 20 dB switch is a realistic approach. The only other way to get around this is to use a switch with a audio taper resistor network. I will consider a DAC to be the same approach. Personally, I like a -20dB switch and good audio control.
Life is too short to get freaked about channel matching at really low levels.
-Chris
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