hi folks,
I'm new to the forum, and hoping someone can help me out with a project. I'd like to wire up a passive stereo volume control with balanced line-level XLR or TRS 1/4" inputs and outputs.
I plan to use a dual-gang 10K Ohm log taper pot, but can't find any resources for wiring the balanced cable. How should I handle the second signal wire in the XLR connnector? I suppose I could connect it to ground, but that would negate the benefits of the balanced signal and add to the noise potential.
Any links to wiring diagrams or other help would be very much appreciated!
I'm new to the forum, and hoping someone can help me out with a project. I'd like to wire up a passive stereo volume control with balanced line-level XLR or TRS 1/4" inputs and outputs.
I plan to use a dual-gang 10K Ohm log taper pot, but can't find any resources for wiring the balanced cable. How should I handle the second signal wire in the XLR connnector? I suppose I could connect it to ground, but that would negate the benefits of the balanced signal and add to the noise potential.
Any links to wiring diagrams or other help would be very much appreciated!
Check out figure 17 in this article: Chapter 4
I use "configuration B" as a passive volume control in my system when I need one and it works fine. I use 5K series resistors and a 10K pot.
You can ignore the surrounding circuitry for your application - just connect pin 2 (or tip) to one input phase and pin 3 (or ring) to other phase. Do not ground either phase. Same for the outputs which go to the grids in the figure.
Dave
I use "configuration B" as a passive volume control in my system when I need one and it works fine. I use 5K series resistors and a 10K pot.
You can ignore the surrounding circuitry for your application - just connect pin 2 (or tip) to one input phase and pin 3 (or ring) to other phase. Do not ground either phase. Same for the outputs which go to the grids in the figure.
Dave
-- Sorry if this is a repeat post. My first attempt didn't seem to work! --
Thanks for the reply, Dave! I have a few questions about the configuration you linked to, if you don't mind answering:
If I understand the schematic, and that may be a long shot, you're suggesting that both + and - signals from the XLR input connect to the pot via their respective series resistors, the + phase to the wiper and + output, the - phase to the pot's input lug(?) and - output. Input and output grounds connect via common ground (or simply to each other? perhaps via the pot housing?). The ground lug on the pot remains empty, yes? My guess here is that the audible signal is attenuated by adding more of the inverse phase signal via the pot?
Thanks for the help and the series resistor values, too!
Thanks for the reply, Dave! I have a few questions about the configuration you linked to, if you don't mind answering:
If I understand the schematic, and that may be a long shot, you're suggesting that both + and - signals from the XLR input connect to the pot via their respective series resistors, the + phase to the wiper and + output, the - phase to the pot's input lug(?) and - output. Input and output grounds connect via common ground (or simply to each other? perhaps via the pot housing?). The ground lug on the pot remains empty, yes? My guess here is that the audible signal is attenuated by adding more of the inverse phase signal via the pot?
Thanks for the help and the series resistor values, too!
The following stage will be a balanced (differential amplifier) so if you reduce the variable resistor value to zero ohms the two outputs would be at the same potential (no difference) and you'd have zero output.
The circuit Dave mentioned is fine. The only recommendation I would make is to tie the unused potentiometer lug to the wiper so if the pot develops noise or intermittent contact it wouldn't create an open circuit.
Since you have a log-taper pot it will work differently depending upon which "direction" you wire it in the circuit.
Hope that makes sense.
Cheers,
Dave.
The circuit Dave mentioned is fine. The only recommendation I would make is to tie the unused potentiometer lug to the wiper so if the pot develops noise or intermittent contact it wouldn't create an open circuit.
Since you have a log-taper pot it will work differently depending upon which "direction" you wire it in the circuit.
Hope that makes sense.
Cheers,
Dave.
Hi Studiodog,
Yes, your supposition is correct as you have found by modeling it. Davey's point is well taken for the unused pin on the potentiometer.
One other thing - if the frame of the pot is metal, it should be grounded to the chassis. There may be a ground lug connected to the frame of the pot but this pin is not connected to the resistive element of the pot. The resistive element should not be connected to ground.
Dave
Yes, your supposition is correct as you have found by modeling it. Davey's point is well taken for the unused pin on the potentiometer.
One other thing - if the frame of the pot is metal, it should be grounded to the chassis. There may be a ground lug connected to the frame of the pot but this pin is not connected to the resistive element of the pot. The resistive element should not be connected to ground.
Dave
Fig17 confB will give an impedance balanced output.
ConfA will be virtually impossible to set to balanced output if the tracking of the pots varies even very slightly.
You could substitute a precision matched stepped attenuator, but that is either going to be very expensive or take you a very long time to match all the steps to <0.01%
ConfA will be virtually impossible to set to balanced output if the tracking of the pots varies even very slightly.
You could substitute a precision matched stepped attenuator, but that is either going to be very expensive or take you a very long time to match all the steps to <0.01%
Hi I am a newbie on DIY projects and am very interested to make a volume control for my balanced input amplifiers which have no attenuator. I have got myself a 5k stereo pot with 6 terminals. I had tried wiring the pin 2+ on 1 input and pin 3 on the other input. With no ground attached. There is no attenuation at all when I plug it into my system. Pls advise. Your help is most appreciated.
Hi Andrew,
Thank you for your prompt help. Forgive me of my ignorance, with reference to config B, there is a resistor from both Pin2(+) and Pin3(-) which actually joined in series with the stereo pot am I correct? if that is the case where should I tap my outputs? I had inserted a pic of my current wiring which do not work , kindly advise where i should insert the resistors and where I can tap the out put for my Balanced input of my amp.
Any help will be most appreciated by this newbie!!
Thank you for your prompt help. Forgive me of my ignorance, with reference to config B, there is a resistor from both Pin2(+) and Pin3(-) which actually joined in series with the stereo pot am I correct? if that is the case where should I tap my outputs? I had inserted a pic of my current wiring which do not work , kindly advise where i should insert the resistors and where I can tap the out put for my Balanced input of my amp.
Any help will be most appreciated by this newbie!!
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This is how i wired my pot in balanced configuration
http://www.diyaudio.com/forums/pass-labs/214522-wiring-attenuator-dual-channel-balanced.html#post3060481
the side with resistors is the "in" side
http://www.diyaudio.com/forums/pass-labs/214522-wiring-attenuator-dual-channel-balanced.html#post3060481
the side with resistors is the "in" side
A two track vol pot for a stereo signal must use one track for left and the other track for right.
Wire each track to operate as a variable resistor, not as a potentiometer.
Insert the series resistors, two for each channel (4 in total).
Insert the variable resistor (the vol pot wired as a VR) between Hot and Cold AFTER the series resistors.
Wire each track to operate as a variable resistor, not as a potentiometer.
Insert the series resistors, two for each channel (4 in total).
Insert the variable resistor (the vol pot wired as a VR) between Hot and Cold AFTER the series resistors.
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.!!!
PS: can someone explain what's the function of the two 5k resistors before the 10k pot? If it's a 50k pot, should the value of the series resistors change or remain at 5k?
PS: can someone explain what's the function of the two 5k resistors before the 10k pot? If it's a 50k pot, should the value of the series resistors change or remain at 5k?
The resistors set the input resistance/impedance seen by the Source.
The Source sees the Zin of the amplifier + the vol pot in parallel plus the resistors.
Caclulate the effective parallel resistance. Then add on the two resistors in series.
eg.
amp Zin = 100k
vol pot = 50k
effective parallel resistance = 33k3
Source see 5k+5k+33k3 = 43k3, when set to maximum volume.
gain = 33k3/43k3= 0.77 = -2.3dB
When you set the vol pot to minimum, it places a zero ohm across the amp input and now the Source sees 5k+5k+0k = 10k
gain = 0.0 = -infinitydB
You could measure your vol pot resistance at the 30degree rotation settings (from 0° to 270°) and calculate the dB attenuation for each setting.
This will tell you how the vol pot "feels" for sound output.
Different track law will give different attenuation, eg. linear, log, anti-log (anti-log ~ = log wired in reverse).
Different ratios of resistor to vol pot resistance will change the attenuation.
You could compile a spreadsheet to see what happens to the "feel" for different ratios and for different track laws.
We can't do that for you, you need to start measuring, either with a DMM, or your ears, to "feel" what all the different combinations will be like and which suits your style of listening.
The Source sees the Zin of the amplifier + the vol pot in parallel plus the resistors.
Caclulate the effective parallel resistance. Then add on the two resistors in series.
eg.
amp Zin = 100k
vol pot = 50k
effective parallel resistance = 33k3
Source see 5k+5k+33k3 = 43k3, when set to maximum volume.
gain = 33k3/43k3= 0.77 = -2.3dB
When you set the vol pot to minimum, it places a zero ohm across the amp input and now the Source sees 5k+5k+0k = 10k
gain = 0.0 = -infinitydB
You could measure your vol pot resistance at the 30degree rotation settings (from 0° to 270°) and calculate the dB attenuation for each setting.
This will tell you how the vol pot "feels" for sound output.
Different track law will give different attenuation, eg. linear, log, anti-log (anti-log ~ = log wired in reverse).
Different ratios of resistor to vol pot resistance will change the attenuation.
You could compile a spreadsheet to see what happens to the "feel" for different ratios and for different track laws.
We can't do that for you, you need to start measuring, either with a DMM, or your ears, to "feel" what all the different combinations will be like and which suits your style of listening.
So if i use 1 100k pot with 2 5k series resistor,
the gain would be as follows:
Amp input Imp = 200K
parallel resistance would be 1/100k +1/200K=1/0.015=66.7K
Max Resistance=5+5+66.7K=76.7K
gain therefore=66.7/76.7=0.87x3=-2.6
Am i correct? and is it ok to have a-2.6dB for this passive balanced attenuator?
the gain would be as follows:
Amp input Imp = 200K
parallel resistance would be 1/100k +1/200K=1/0.015=66.7K
Max Resistance=5+5+66.7K=76.7K
gain therefore=66.7/76.7=0.87x3=-2.6
Am i correct? and is it ok to have a-2.6dB for this passive balanced attenuator?
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