Help with circuit for motorized faders

Hi all...

I have eight Alps motorized faders and I thought that I could use them in a mixer project I have, but I have no experience in using motorized fader and I have no schematic to compare how to control the motors.

The faders are all in very good condition but used. They are 509C/ 10kB (RSA0N11M9A0K)

If I can't find a proper solution how to use those motors I might sell them all here at the "Black market"

Best regards

/John

Another picture...

And finally the data sheet...

http://www.alps.com/prod/info/E/HTML/Potentiometer/SlidePotentiometers/RSN1M/RSA0N11M9A0K.html


Best regards

/John

johnheath said:

And finally the data sheet...

http://www.alps.com/prod/info/E/HTML/Potentiometer/SlidePotentiometers/RSN1M/RSA0N11M9A0K.html


Best regards

/John

Click to expand...

You can make a MIDI fader controller with Arduino and some H-bridge DC stepped motor driver.

http://blog.codyhazelwood.me/motorized-faders-and-the-arduino/

Hi
This fader is single track, linear taper, you can't do more than control surface (no log audio track for automated analog mixer)
PWM driver is the common way to drive those, arduino as already say or midibox/MIOS offer driver and code for this application.
There is other routes (analog PID driver), but not that cheap... I know it 
Best
Zam

Thanks both of you guys for your replies

All this talk about midi and all is a fair bit over my knowledge and perhaps not really what I have time to investigate at the moment... let's see if there are anybody who can use them better than myself... Black market it will be

Best regards

/John

Very easy in analog, with an opamp comparing the voltage from the servo track with the control voltage. The opamp needs be buffered for driving the motor.
When I did that for the BVE option on the Soundcraft 200B, I thought it would be tough to nail it, but it turned to be a piece of cake, worked right out. You just have to adjust the closed-loop gain to optimize the hysteresis, then there is no stability issue. Taking advantage of mechanical friction is key.

abbey road d enfer said:

Very easy in analog, with an opamp comparing the voltage from the servo track with the control voltage. The opamp needs be buffered for driving the motor.
When I did that for the BVE option on the Soundcraft 200B, I thought it would be tough to nail it, but it turned to be a piece of cake, worked right out. You just have to adjust the closed-loop gain to optimize the hysteresis, then there is no stability issue. Taking advantage of mechanical friction is key.

Click to expand...

Interesting !
I work quite a lot for an automated fader system, and I don't see how you combine speed and oscillation/overshoot-less without a PID driver ?
Best
Zam

zamproject said:

Interesting !
I work quite a lot for an automated fader system, and I don't see how you combine speed and oscillation/overshoot-less without a PID driver ?
Best
Zam

Click to expand...

The actual compromise is between transient response (which includes speed and overshoot control) and accuracy. You need PID if you want both.  IIRC I had about 1% accuracy with satisfactory speed 'about 50ms for full travel) and negligible overshoot. 1% accuracy results in about 0.5dB precision in the critical -20/+10 dB range. Indeed, below that range, there maybe several dB error; in most applications, that wouldn't matter practically.

Do affordable linear encoders exist? At what price point?

I saw some industrial 30 cm linear encoder recently. It's around 1.000 € a piece and too big.

If there are "encoding" faders, this github project offers the code to drive up to 16 of these, daisy chained over I2C:

https://github.com/Fattoresaimon/i2cencoder

Interesting?

cyrano said:

Do affordable linear encoders exist? At what price point?

Click to expand...

The faders in the OP are indeed linear encoders (with an audio track atteched), or do you mean binary-output encoders?

Hello

abbey road d enfer said:

The actual compromise is between transient response (which includes speed and overshoot control) and accuracy. You need PID if you want both.  IIRC I had about 1% accuracy with satisfactory speed 'about 50ms for full travel) and negligible overshoot. 1% accuracy results in about 0.5dB precision in the critical -20/+10 dB range. Indeed, below that range, there maybe several dB error; in most applications, that wouldn't matter practically.

Click to expand...

Ok, that make sense then.
With PID driver I ended at 0.05% precision...which is aprox 0.02dB step at nominal position.
Half a dB is a lot (I think) if you have 16 or more fader passing audio, mix and automation is unreliable if each element can have +/- 0.5 dB of unexpected level.

cyrano said:

Do affordable linear encoders exist? At what price point?

I saw some industrial 30 cm linear encoder recently. It's around 1.000 € a piece and too big.

If there are "encoding" faders, this github project offers the code to drive up to 16 of these, daisy chained over I2C:

https://github.com/Fattoresaimon/i2cencoder

Interesting?

Click to expand...

TKD (and certainly other) offer 100mm or 60mm fader encoder, I2C interface .

Best
Zam

abbey road d enfer said:

The faders in the OP are indeed linear encoders (with an audio track atteched), or do you mean binary-output encoders?

Click to expand...

No the OP fader are servo only, that's what the ref say (RSA0N11M), if you want dual track servo +audio you need RSA0N12M


I think Cyrano mean binary encoders ?

Zam

zamproject said:

With PID driver I ended at 0.05% precision...which is aprox 0.02dB step at nominal position.

Click to expand...

PID is an analog concept; no doubt an analog implementation could yield better precision than my crude circuitry.

zamproject said:

No the OP fader are servo only, that's what the ref say (RSA0N11M), if you want dual track servo +audio you need RSA0N12M

Click to expand...

You're right, I've been fooled by the cryptic diagram. Thus, they are intended to be used with either VCA's or DCA's.

zamproject said:

TKD (and certainly other) offer 100mm or 60mm fader encoder, I2C interface .

Click to expand...

Thx, zam, I'll see if I can chase those down.

Until now, the cheapest (industrial) ones I could find were something like 63$ a piece, with an order quantity of ten on TaoBao. But I haven't been looking into these for long.

The idea of building some sort of control surface isn't new to me, but I planned on using VCA's and faders like the alps ones in this thread.

Moving faders are the holy grail for WYSIWYG console interfaces.

A linear encoder makes the most sense as these rarely get audio passed through them.

As a thought experiment one could superimpose , DC or an above audio band HF sine wave on top of  an audio signal to run both through the same resistive element, just separate them apart at the output. (I AM NOT RECOMMENDING THIS).

Peavey sold a cheap midi interface with a bank of moving faders so knowing them there are probably used ones around.

JR

cyrano said:

I planned on using VCA's and faders like the alps ones in this thread.

Click to expand...

With care taken to design you can certainly use same DC signal that read servo track for motor fader position and feed VCA control input.

JohnRoberts said:

As a thought experiment one could superimpose , DC or an above audio band HF sine wave on top of  an audio signal to run both through the same resistive element, just separate them apart at the output. (I AM NOT RECOMMENDING THIS).

Click to expand...

Hopefully you don't recommand it !!!!
I don't see how this could work with good result regarding noise  :-\
And you will have an issue to scale signal, as you want linear taper for servo and log for audio.

IMO, If one want a "great" moving fader system, dual track fader is the way to go and no PWM, analog PID only...
That's the final route I take 3 years ago, after evaluating PWM driver  :-\

Best
Zam

cyrano said:

The idea of building some sort of control surface isn't new to me, but I planned on using VCA's and faders like the alps ones in this thread.

Click to expand...

Hi Cyrano

They are for sale in the "Black Market"

Someone said they are available on E-Bay for around 20€ each... I'll go lower than that since I got them for free (Super honest here )

Best regards

/John

zamproject said:

With care taken to design you can certainly use same DC signal that read servo track for motor fader position and feed VCA control input.

Hopefully you don't recommand it !!!!
I don't see how this could work with good result regarding noise  :-\
And you will have an issue to scale signal, as you want linear taper for servo and log for audio.

Click to expand...

Please don't say it can't be done.... I get sucked into more projects that way..  (like my drum tuner) 8)

IMO, If one want a "great" moving fader system, dual track fader is the way to go and no PWM, analog PID only...
That's the final route I take 3 years ago, after evaluating PWM driver  :-\

Best
Zam

Click to expand...

Yes back in the day when moving fader automation was added on top of analog consoles,  dual track faders were the logical way... IIRC the PG moving faders were something like $350 each in (1970s dollars).  Now for controlling VCA or digital multipliers, there is little reason to add an additional analog fader track... Those motorized alps faders were pretty inexpensive last time I looked at them in the 90s.

Speaking of noise why put a sensitive audio  path that close to an electric motor being stepped or ramped?

JR