Wiring Attenuator for dual channel Balanced

[wengtech]

hi everyone,
i need to add a passive volume pots for my aleph 30 in balanced way.
i am planning to use 10k 24step ladder attenuator pots like this one :

An externally hosted image should be here but it was not working when we last tested it.

my question is:
how to wire this attenuator for dual channel balanced
using only one attenuator like in the picture.

thanks.
visit my blog here

 

[Zen Mod]

consider each phase (+ one , - another one ) as separate channel

edit : of course , that means that you need two of those for stereo , meaning - one per balanced channel

 

[wengtech]

zen mod,
do you mean i should use 2 attenuator for 2 channel balanced amp?
attenuator like in the picture only support (+in -in gnd, +out -out gnd) one channel.
so, to wire 2 channel i need 2 attenuator (+inR -inR gnd, +inL -inL gnd, +outR -outR gnd, +outL -outL gnd) is that true?

my friend said there should be a wiring technique which using only one attenuator
for 2ch amp, but i don't know yet how to do that.

 

[secanbj]

I did like this with an alps pot. i think you should be able to do the same with yours, but i might be wrong

picture only shows one channel

An externally hosted image should be here but it was not working when we last tested it.

 

[Frank Berry]

That method will work. I've used a similar circuit in the past.

 

[wengtech]

secanbj:
that is interesting, but can you explain which one IN and OUT?
and how about the result in sound, compared with using 2 pots.

 

[secanbj]

The side with the resistors is the "in". Regarding sound with one vs two pots i have no idea as i have only used this configuration

 

[Holger1975]

Don´t get the wiring

Hello Community,

tried to wire it like on the scrabble, but i don´t get it. Could somebody describe where to put which wire on the shown switch from photo ?

Thanks in advance!

 

[wuffwaff]

Hi,

you can´t use a normal 10klog pot for this. The resistor values for a "balanced" pot are completely different. I use one on the output of my X-BOSOZ.
I´ve got an excel sheet where you can calculate the resistor values depending on the two series resistors (here 5k). I can try to find it.

To wire it you have to put the switch after the two resistors. With this you change the resistance between the two output resistors. If the resistance is zero the output is shorted and more or less silent. Without a connection the output is only attenuated by the output resistors.

Depending on the volume set the output impedance of the control will change quite a lot (from almost zero to 5k diff. in this example)

William

 

[AndrewT]

With a balanced interconnection, the impedance on both the hot and cold are identical. If they are not identical then the interconnection is not balanced.

The attenuator must insert identical resistances into both the hot and the cold poles of the signal connection.

 

[wuffwaff]

With a balanced interconnection, the impedance on both the hot and cold are identical. If they are not identical then the interconnection is not balanced.

The attenuator must insert identical resistances into both the hot and the cold poles of the signal connection.

Yes that is true, and that is the nice thing about this balanced attenuator. It only switches one restistor between hot and cold (after the two series restistors) so it is always balanced perfectly.

William

 

[AndrewT]

...............so it is always balanced perfectly..................

Is it?
What is the channel matching tolerance?

 

[wuffwaff]

the chanel as such is balanced perfectly (you can match the two series resistors if you think 1% isn´t enough or use 0,1% as I did).

Between left and right channels you can get 1% when using 1% resistors. In dB that would not be very much.....

cheers,

William

 

[AndrewT]

between hot and cold.

0.1% is usually the biggest acceptable tolerance. That is half the tolerance of using +-1% resistors. Some would say you should be aiming for better than 0.01% for hot to cold channel matching.

I don't care if it's -30.02dB or -30.09dB

 

[wuffwaff]

Andrew,

I´m not sure we are talking about the same thing.

I´ll try to say it more precisely:

The attenuation by changing only one resistor (between hot and cold) won´t change the balance (between hot and cold) of this channel. It will stay as it is.

If the balance between hot and cold needs to be better than 0,01% I don´t know. This would mean using only precision resistors to set the gain and attenuation. Most preapms using 4-way pots and 1% resistors (at best) will never get near this value.

william

 

[AndrewT]

yes you have identified the problem.
Balanced requires precision matching of impedances.

Throw away precision and you throw away all the advantage that balanced brings.

 

[hschaser]

Hi all... Thank you for all ur precious advices . The attenuator now works fabulously. I used a 50k pot instead of 10k as recommended. I would also like to find out with this configuration can I use a 100k pot ? Also for both the 5K resistors is there any power rating or requirement? (I.e 1/4 watts or something with bigger values? Thank you once again you had been a fabulous people.!!!

 

[DaveFred]

I did like this with an alps pot. i think you should be able to do the same with yours, but i might be wrong

picture only shows one channel

An externally hosted image should be here but it was not working when we last tested it.

Do you have this image still?

 

[MAAC0]

With a balanced interconnection, the impedance on both the hot and cold are identical.

Should be identical, but most of them usually aren't.

More on this:

Balanced Interfaces