ultra newb question. monitor controller.

[chopstickkk]

i'm currently using a pair of tannoy monitors that have no volume control. i recently upgraded to a soundcard that has only line outputs so i'm looking to implement a realllly simple single potentiometer stereo volume control.

and also i figure it'll be the ideal entry point to the diy world (get me used to soldering, making measurements etc.)

i would like it to be balanced. i've been lurking here for a while, reading craig anderton's book and the radio shack books and am wondering...

do i need to unbalance the signal on input and run it through the pot and then rebalance on output? (apologies if that sounds really stupid!)


also i have the option of buying a...

'Dual / Stereo Potentiometer with a low noise conductive plastic track. 6mm shaft. PCB pins. Can be PCB or panel mounted.
10k linear 1.85

10k log 1.85

47k linear 1.85

47k log 1.85'


what resistance and curve type will be suitable for a monitor controller operating on line level?




thanks in advance and any other info that you guys could offer would be great.
john.

 

[abbey road d enfer]

i'm currently using a pair of tannoy monitors that have no volume control. i recently upgraded to a soundcard that has only line outputs so i'm looking to implement a realllly simple single potentiometer stereo volume control.

and also i figure it'll be the ideal entry point to the diy world (get me used to soldering, making measurements etc.)

i would like it to be balanced. i've been lurking here for a while, reading craig anderton's book and the radio shack books and am wondering...

do i need to unbalance the signal on input and run it through the pot and then rebalance on output? (apologies if that sounds really stupid!)


also i have the option of buying a...

'Dual / Stereo Potentiometer with a low noise conductive plastic track. 6mm shaft. PCB pins. Can be PCB or panel mounted.
10k linear 1.85

10k log 1.85

47k linear 1.85

47k log 1.85'


what resistance and curve type will be suitable for a monitor controller operating on line level?




thanks in advance and any other info that you guys could offer would be great.
john.

First, I think we'll exclude the use of transformers. Why, because they won't give you adequate performance, unless you use very expensive transformers, which I reckon is not commensurate with the goal to achieve.
In all cases, you'll use a dual potentiometer of the lowest value compatible with the output capability of your soundcard.

Why the lowest value?: because when you turn down the volume, the output impedance increases, making the signal prone to interference and loss of high frequencies.
Why compatible with your soundcard's output capacity?: because the output of the soundcard is loaded by the potentiometer in parallels with the amp's input impedance. Most soundcards use output devices of average performance, intended for loads not lower than 2 kohms. A value of 2.2kohms for the potentiometer is the minimum. 5k will work too, if the output cable is not too long.

Is your soundcard balanced? If not, there's no way your volume control will be really balanced.
Well, anyway, you have several options:
Fully unbalanced (if your card is unbalanced), then use a 2x5k pot
Pseudo-balanced or balanced, you must use a quad pot of 4x1k or 4x2.2k.
There is an alternative solution, using the pots as variable resistors in a double L-pad

 

[chopstickkk]

First, I think we'll exclude the use of transformers. Why, because they won't give you adequate performance, unless you use very expensive transformers, which I reckon is not commensurate with the goal to achieve.
In all cases, you'll use a dual potentiometer of the lowest value compatible with the output capability of your soundcard.

Why the lowest value?: because when you turn down the volume, the output impedance increases, making the signal prone to interference and loss of high frequencies.
Why compatible with your soundcard's output capacity?: because the output of the soundcard is loaded by the potentiometer in parallels with the amp's input impedance. Most soundcards use output devices of average performance, intended for loads not lower than 2 kohms. A value of 2.2kohms for the potentiometer is the minimum. 5k will work too, if the output cable is not too long.

Is your soundcard balanced? If not, there's no way your volume control will be really balanced.
Well, anyway, you have several options:
Fully unbalanced (if your card is unbalanced), then use a 2x5k pot
Pseudo-balanced or balanced, you must use a quad pot of 4x1k or 4x2.2k.
There is an alternative solution, using the pots as variable resistors in a double L-pad

thanks a million for your quick thorough reply and schematic it's excellent!

yes my soundcard output is definitely balanced (http://www.roland.com/products/en/FA-101/specs.html)
and the amp input in the speakers is rated at 'Input = 32 kΩ balanced on combined XLR/jack'. does that sound correct?
(http://www.tannoy-speakers.com/products/165/uman_RevealActive.pdf)
cabling will be kept to about 3 metres in total trs-type between soundcard output and active speaker input.

i think i'll go for the dual L pad design as then i can use one dual pot for stereo and retain the balanced operation.

is a 10k dual pot okay? the company i'm buying from doesn't have a resistance lower than that in dual (http://www.bitsbox.co.uk/resistors/potentiometers.html scroll down for the dual/stereo pot section)

should i double the two 1k resistors to two 2k resistors since it's a 10k? (sorry if that sounds silly, i'm reading about L pad's now as i'm still not fully clear on why this works)


also i forgot to mention that i'd like to have two rca unbalanced inputs going into the same pot also, so that i can have my ipod hooked up to my monitors.
will this change the circuit drastically??
or can i just pretend that the pot isn't hooked into anything and add an unbalanced circuit between the sockets and pot? (again, sorry if this is silly! i'm very new to this, but i figure the best way to understand is to do!)

thanks again you've been very helpful,
john.

 

[abbey road d enfer]

First, I think we'll exclude the use of transformers. Why, because they won't give you adequate performance, unless you use very expensive transformers, which I reckon is not commensurate with the goal to achieve.
In all cases, you'll use a dual potentiometer of the lowest value compatible with the output capability of your soundcard.

Why the lowest value?: because when you turn down the volume, the output impedance increases, making the signal prone to interference and loss of high frequencies.
Why compatible with your soundcard's output capacity?: because the output of the soundcard is loaded by the potentiometer in parallels with the amp's input impedance. Most soundcards use output devices of average performance, intended for loads not lower than 2 kohms. A value of 2.2kohms for the potentiometer is the minimum. 5k will work too, if the output cable is not too long.

Is your soundcard balanced? If not, there's no way your volume control will be really balanced.
Well, anyway, you have several options:
Fully unbalanced (if your card is unbalanced), then use a 2x5k pot
Pseudo-balanced or balanced, you must use a quad pot of 4x1k or 4x2.2k.
There is an alternative solution, using the pots as variable resistors in a double L-pad

thanks a million for your quick thorough reply and schematic it's excellent!

yes my soundcard output is definitely balanced (http://www.roland.com/products/en/FA-101/specs.html)
and the amp input in the speakers is rated at 'Input = 32 kΩ balanced on combined XLR/jack'. does that sound correct?
(http://www.tannoy-speakers.com/products/165/uman_RevealActive.pdf)
cabling will be kept to about 3 metres in total trs-type between soundcard output and active speaker input.

i think i'll go for the dual L pad design as then i can use one dual pot for stereo and retain the balanced operation.

is a 10k dual pot okay? the company i'm buying from doesn't have a resistance lower than that in dual (http://www.bitsbox.co.uk/resistors/potentiometers.html scroll down for the dual/stereo pot section)

should i double the two 1k resistors to two 2k resistors since it's a 10k? (sorry if that sounds silly, i'm reading about L pad's now as i'm still not fully clear on why this works)


also i forgot to mention that i'd like to have two rca unbalanced inputs going into the same pot also, so that i can have my ipod hooked up to my monitors.
will this change the circuit drastically??
or can i just pretend that the pot isn't hooked into anything and add an unbalanced circuit between the sockets and pot? (again, sorry if this is silly! i'm very new to this, but i figure the best way to understand is to do!)

thanks again you've been very helpful,
john.

You may increase the resistors to 2k, the HF loss will be ok for 3meters of shielded cable. With this arrangement (L-pad), there is always aresidual attenuation, even with the pot at max level, here it's ca. 3dB. Reducing the resistors to 1k will reduce the attenuation to ca. 1.5dB, but the volume vs. rotation won't be that good.
You may connect the RCA inputs according to the revised schemo

 

[chopstickkk]

seriously, thanks a million for all of this. you've been a great help.

3db att is fine as the monitors are way too loud anyway. thanks for the new schematic.