What potentiometer value to use for a volume control / attenuator?

The output from my audio interface is balanced, as are the inputs to my powered speakers.

To make a simple passive volume control, I just need a 4 channel pot to act as 2 pairs of voltage dividers, but I'm not clear on the effect of say a 50K pot vs a 200K one.

What's the safest, middle-of-the-road value to go for? (What happens at the extremes - say a 100ohm vs a 10Mohm? What happens to the audio?)

Normally balanced audio drivers have a impedance of 600Ohms. The input load impedance is normaly between 10k and 47k. The load impedance of a passive volume control has to be much higher than the driver and max the impedance of the load impedance of the input. So 4k7 or 10k would be a choice for starters. The lower the value the higher the load on the driver. The higher the value the more interaction with the input impedance. The latter can cause attenuation or uneven frequency response

Super - thanks!

h

Can get a reasonable quality one for good price:
http://www.thomann.de/gb/sm_pro_audio_nano_patch.htm

Works fine :slight_smile:

The "proper" ones are constructed using a dual gang stepped attenuator.
There are suppliers of just the switch/resistor assembly, last time I looked they were a couple of hundred Quatloos (GBP). Then you need to build and case the thing!

Certainly above the class of my speakers and into the realms of audiofoolery IMVHO.

Not worth trying to save a few quid, get the nanopatch, if chasing that ethereal last percentile of audio then DIY a stepped attenuator could be the way.

All the budget active ones I saw were not as clean as the nano, cheapo active ones are to be avoided!

Normally balanced audio drivers have a impedance of 600Ohms.

That's an old standard from when tubes & transformers were used. Most modern equipment is not "impedance-matched". The outputs have low source-output impedance and inputs have high input-impedance. I'm sure the monitor's input impedance is 10K or more.

How about just getting an interface with a volume control? Or, control the volume digitally before feeding it into your interface? :wink:

I just need a 4 channel pot to act as 2 pairs of voltage dividers,

Have you actually found a 4-channel pot? Is it expensive? Normally, the volume would be attenuated somewhere the signal is not balanced. i.e. before the balanced-output on the interface, or after the balanced-input on the monitors.

And, you'll get better left & right volume-tracking if you control the volume in the digital domain or with digitally controlled pots. Your project would probably be better & cheaper with 4 digital pots, but it would be more complicated to design & build, and it would require a power supply.

but I'm not clear on the effect of say a 50K pot vs a 200K one.

At maximum volume, there will be no difference. If the impedance of the pot is high relative to the speaker's input impedance, there will be more "drop" across the pot at low & mid volume-settings, so the volume will be lower.

BTW, make sure to get an "audio taper" or "logarithmic" pot, not a linear pot. Digital pots are linear, but you can compensate in software.

DVDdoug:
That's an old standard from when tubes & transformers were used.

I think he meant that the two pots would be matched.

Or the "balanced" part was misunderstood?
Balanced is a differential way of transmitting audio signals in the "pro" domain ("pro" be used loosely), that allows high, cleaner signal over longer runs and maintain a high noise rejection.

Can get a reasonable quality one for good price:
http://www.thomann.de/gb/sm_pro_audio_nano_patch.htm

I'm sure it works fine, but given the price, I'd be surprised if it's truly balanced (with 4 pots or 4 attenuators).

Balanced line and I think two gang stereo pot is used, but not sure and never looked.