pots for aux send

[gnd]

Hi.
I'm making some additional aux sends on my mixer. Pots are 10k Log (one side signal, other side ground, middle is regulating level to aux bus), feeding aux buss through 22k resistor. I need 64 pots, four on each of 16 channels.

There is a chance that I get quite cheap, good quality pots, but there is no 10k log. But hey have 500k log and 1k log. They are both way off original 10k, I know, but would it work anyway?

1k may be ok for NE5534 output stage, is it? Or is it not enough? Should I put some additional resistors between ne5534 and 1k pot?

And 500k I could parallel with 10k resistor, and this would give me 10k pot, just log curve would change, is it? Or maybe I could just use 500k instead of 10k, without any parallen resistors? Would it work?

Is it that 500k would be much worse regarding noise, or is it just the same?


What do you recommend instead of 10k log? 1k log or 500k log?

thnx

 

[gyraf]

would it work anyway?

Probably not.

500K is too high a series resistance.

1K is too low a load to drive properly - remember that there are more than one pot to be driven..

Jakob E.

 

[gnd]

Probably not.

1. yes, I see why 1k is too low, per channel there would be 4 pots in parallel, and this would give 250 ohm load on ne5534 IC. But could I insert resistor between IC and pots, say 1k resistor? It would reduce level somewhat, but... Would this work? Maybe I could just reduce value of summing resistore on aux buss from 22k to 20k and thus compensate for loss on 1k resistor before pot?

2. How would 500k (too high series resistance) show in operation? Too much noise? Or pot wouldn't work properly, and would cut signal too quickly? Or something else?

thnx

 

[gyraf]

I don't think it'll be worth doing this with the mentioned pots - after all, you can get decent-quality pots from e.g. Taiwan-alpha at less than one euro a piece..

Jakob E.

 

[gnd]

I don't think it'll be worth doing this with the mentioned pots - after all, you can get decent-quality pots from e.g. Taiwan-alpha at less than one euro a piece..

No Taiwan-alpha here. Farnell has variety of pots, but are more expensive, and shipping/import cost is high, almost additional 50% catalog price. While I can get those 1k/500k pots locally for 0.7euro, which is very low comparing to usual pot price of 1.5-3 euro.

If you would absolutely have to decide between 1k or 500k, which would be your choice?

I will have to make separate aux out buffers anyway, and I can use dual NE5532 for that (same price as single 5534), and load each buffer with just two 1k pots. Load would thus be 500E per buffer, and I can connect pots via 220E resistor te reduce load a bit (5532 can take 600E load). Would this be fine? What is problematic with this?

On the other side, what will be wrong with using 500k pots? More noise? If I connect 4 pots 500k in parralel on single 5534, this will give 125k load. What is the problematic part, if I do this?

thank you

 

[Handcrafted Tone]

Go to Omeg (http://www.omeg.co.uk/) and request a quote. They'll get you exactly what you need, and they ship world wide. They'll probably quote you around $2/each

 

[PRR]

If you must....

Use the 500K, but re-design the mix-bus for 150K input resistors. Driver loading will be negligible, and pot-loading will be small. However the mix-bus impedance will be around 10K, or around 1uV of noise. I guess 5532 will be fine for a mix-amp. TL072 would work at slightly higher noise (and poor output drive).

> No Taiwan-alpha here. ....shipping/import cost is high,

Put your Location in your Profile. Helps prevent unhelpful answers from people who don't know where you are. Also, there might be somebody here who knows your local market and where the cheap 10K pots are hiding.

 

[gnd]

Use the 500K, but re-design the mix-bus for 150K input resistors. Driver loading will be negligible, and pot-loading will be small. However the mix-bus impedance will be around 10K, or around 1uV of noise.

Thank you for this info. Can I just ask what will 1uV of noise mean in practice? Is it like ne5534 has 3,5nV? How do I predict noise level?

Is it like this?... It will be 4 aux channels mixed together, that gives 4uV of noise, and max voltage is say 12V. s/n is then 20log(12/4uV) = 129dB. And with 200mV output it is 20log(200mV/4uV) = 94dB s/n. Is this calculation correct?

thnx