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  #1  
Old 25th February 2014, 02:09 PM
colin.hepburn colin.hepburn is offline
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Default Balance pot for WAD CF Pre

Well the WAD CF is up and running and I like it
However, there is a problem with me not the pre and this is due to my odd ear canal differences, which is a pain in the **** for correct imaging

As it pools the image to the right of centre so will need to fit a balance pot to the CF, which needs to be a small pot to mount on front panel
There for a single pot would be best something like this see image but would it work correctly

The CF Alps pot is a 100k I have a single pot 47k and 50k one is a liner the other problem is the resistor values so as not to lose too much gain
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File Type: jpg Balance Cotrol.jpg (8.6 KB, 20 views)
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Old 25th February 2014, 03:27 PM
bob orbell bob orbell is offline
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Default Re: Balance pot for WAD CF Pre

That may well work Colin, some time ago I added a two gang linear pot to mine, as in the FAQ, just to see if it would be useful, but I lost far too much gain, so never fitted it in. BOB
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Old 25th February 2014, 05:46 PM
Richard Richard is offline
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Default Re: Balance pot for WAD CF Pre

Yes it looks elegant but I think you have to add on the vol control following to see what will happen.
The balance pot adds a parallel load to earth so lowers the input impedance usually set by the volume pot.
It also adds series resistance before the volume pot attenuating the output.
We need to keep R1 R2 RB high in order to keep input impedance reasonable but the higher we make them the more they will attenuate the volume pot following.
Example, using Col's 100K volume pot and the 50K linear balance pot with R1 R2 at 25K to keep attenuation as low as we dare go considering input impedance would be,
loss at balance pot mid position 25K/(25K + 25K) = X0.5 = -6dB
loss at volume pot max position 100K/(100K + 25K) = x0.8 = -2dB
total loss x0.4 = -8dB and input impedance 50K//100K = 33K fine for CD but less so/short cables for Phono 3.
It would probably work fine but (as Bob found and is mentioned in the FAQ) you'd need some gain in the pre unless the power amp is very sensitive.


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Old 25th February 2014, 06:52 PM
Guy Pettigrew Guy Pettigrew is offline
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Default Re: Balance pot for WAD CF Pre

Apologies for ignorance, but what's a WAD CF, please?

Thanks.

Guy
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  #5  
Old 25th February 2014, 06:55 PM
A Stuart A Stuart is offline
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Default Re: Balance pot for WAD CF Pre

Does no-one make coaxial-shafted separate potentiometers any more?
I mean, as found on old radios where you might have on the left volume on one control ring and tone on the other ring; and similarly on the right waveband selection and tuning as another paired control.
A very brief look on Google did not show anything.
I do not think I am inventing my recollection that Mission Cyrus amps around 1990 had a split volume knob, for L & R channels, so a cleaner path than a separate balance control followed by a volume control.
Note the earlier 1987 Cyrus1 only had a weedy miniature size Alps pot which rapidly wore out in my case, hugely improved by replacing with full size Alps Blue. So caution if looking for an old Cyrus to cannibalise.
Alastair
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Old 25th February 2014, 07:32 PM
colin.hepburn colin.hepburn is offline
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Default Re: Balance pot for WAD CF Pre

BOB/Richard
Thanks for the details Richard
I will try it later and report back

Alastair

No the mission amp was not slit L/R it was a single pot balance control on the volume pot shaft same as the above schematic
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Old 25th February 2014, 07:36 PM
A Stuart A Stuart is offline
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Default Re: Balance pot for WAD CF Pre

They do exist!
I should have looked up the word "concentric" potentiometer.
Apologies, I stand corrected on the Cyrus I just assumed that was how they worked from the pictures.
Alastair
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Old 25th February 2014, 08:00 PM
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Greg. Greg. is offline
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Default Re: Balance pot for WAD CF Pre

Quote:
Originally Posted by Guy Pettigrew View Post
Apologies for ignorance, but what's a WAD CF, please?

Thanks.

Guy
Hi Guy,

CF refers to the Cathode Follower alternative to Pre2/3 some of us prefer to use. See the FAQ.

http://www.world-designs.co.uk/forum...read.php?t=144

Greg
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Old 26th February 2014, 07:39 AM
bob orbell bob orbell is offline
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Default Re: Balance pot for WAD CF Pre

Quote:
Originally Posted by A Stuart View Post
Does no-one make coaxial-shafted separate potentiometers any more?
I mean, as found on old radios where you might have on the left volume on one control ring and tone on the other ring; and similarly on the right waveband selection and tuning as another paired control.
A very brief look on Google did not show anything.
I do not think I am inventing my recollection that Mission Cyrus amps around 1990 had a split volume knob, for L & R channels, so a cleaner path than a separate balance control followed by a volume control.
Note the earlier 1987 Cyrus1 only had a weedy miniature size Alps pot which rapidly wore out in my case, hugely improved by replacing with full size Alps Blue. So caution if looking for an old Cyrus to cannibalise.
Alastair

This is a very good idea, my Stax head phone amp has just this arrangement, all you need to do Colin is find such pot. BOB
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Old 26th February 2014, 02:08 PM
colin.hepburn colin.hepburn is offline
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Default Re: Balance pot for WAD CF Pre

Quote:
Originally Posted by bob orbell View Post
This is a very good idea, my Stax head phone amp has just this arrangement, all you need to do Colin is find such pot. BOB
BOB
Yes, it is a possibility to fit a concentric pot would save any drilling of front panel
My plan was/is to use the mini pot if it works ok to mounted it above the led not the easiest of tasks thou with just a hand drill or black in Decker
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