sonolink

Amp with motorized pots
« on: January 10, 2020, 07:08:32 AM »
Hello everybody,

I'm looking for info on how to implement motorized pots on a guitar amp/pedal to recall presets via midi or a rotary encoder like this:
https://www.youtube.com/watch?v=_ZBpFZZ0QBk

My guess is that the knobs are motorized pots controlled via some digital thing (Arduino maybe?) but is this easy to implement?

All input is very much appreciated :)
Thanks
Sono
Why sleep when you can mix?
M.P.Stavrou


Martin Griffith

Re: Amp with motorized pots
« Reply #1 on: January 10, 2020, 10:08:51 AM »
Something like the Alps RK168 might do, but you might need to use at least 1 track for positional feedback to the controller board. You could use something  an Atmel mega48,that have up to 8 ADCs and simple programming wouldn't need to be too difficult. I wouldn't use a arduino, as getting a custom board is quite cheap these days. I'd probably use GCC and Atmel studio 7 in straight C rather than 'Duinos system

Martin,

buckethead

Re: Amp with motorized pots
« Reply #2 on: January 10, 2020, 10:17:15 AM »
Check out the Soldano X99 preamp. They did a nice implementation of motorized pots. It looks like they used some kind of stepper motors with conventional pots, which would make servicing the amp easier/cheaper.

For learning and quick prototyping/testing µC stuff Arduino is a nice and quick option, but programming AVRs in GCC isn't that hard and gives you kinda more control over hard-/software.

Best regards,
Mathias

Rocinante

Re: Amp with motorized pots
« Reply #3 on: January 10, 2020, 11:21:34 AM »
So I played around with this using a teensy. I bought a volume controller board/kit from eBay that had an Alps dual gang motorized potentiometer, then simplified and copied part of the design using 3 more Alps motorized pots. They are pretty cheap and can actually operate balanced which i would use later on but obviously not in a guitar amp.  Wiring the positive leg of the motor then to another junction board then to power and the teensy. 
Then onto the arduino forum to read hours upon hours upon hours of threads until I scraped together enough code to get it to work.  Lots of copy and paste cause I am a kiddie scripter at best.
It worked but it was slow.
I eventually just never used the features and scavenged all the motorized pots for some monitor controllers I was building. IMO amps don't have that many knobs to not remember. Its also pretty easy to take a pic and upload it to PT if you need recall. It was a great learning experience though and I believe I used the Elliot Sounds p27 amp design for my preamp and power amp sections and was really impressed with his simple but really good sounding design.
« Last Edit: January 10, 2020, 03:04:52 PM by Rocinante »
If there's a harder way to do this, I haven't found it yet.

pucho812

Re: Amp with motorized pots
« Reply #4 on: January 10, 2020, 03:10:31 PM »
I saw a video recently where a guy used what was part of a bicycle break system attached to a pedal  on one end and around the pot on the other calling it a volume control. it worked.  ;)
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

sonolink

Re: Amp with motorized pots
« Reply #5 on: January 10, 2020, 11:33:03 PM »
First of all thanks a lot to everyone for your input :)

But the thing is I don't really know s**t about this (I mean programming). I build totally analogue tube amps, 18w plexi kinda stuff and when I saw that amp I thought it was a great way to for instance use amp distortion: most guitar players nowadays have a clean amp and use pedals to get distorted sounds. I guess it's easier to stomp on a pedal than redialing knobs. So this looked to me like a great solution. One moment my gain is at 9-10 o'clock and the next it's way over 3 o'clock!! Same with EQ.

I THINK I understand the concept (a digital signal actuates the motors just like a low voltage signal actuates a relay sort of) but I need to learn how to make it happen, basically...

I have time, so maybe I should read some stuff before, or maybe there's some ready made templates? Any advice in that direction would be great. Thanks again for your time and help!

Cheers
Sono
 
Why sleep when you can mix?
M.P.Stavrou

Rocinante

Re: Amp with motorized pots
« Reply #6 on: January 11, 2020, 04:19:03 PM »
Go to the arduino forum. You'll find what your looking for, albeit it might be in bits and pieces.
I was an all hardware person myself not too long ago.
If there's a harder way to do this, I haven't found it yet.

sonolink

Re: Amp with motorized pots
« Reply #7 on: January 13, 2020, 01:00:27 PM »
I'm giving up on this. I can't find enough different values for the pots. For some reason it's always 5k, 10k, 50k, 100k. I need 25k, 250k, 470k, 500k, 1M. Anyway...

I was an all hardware person myself not too long ago.
I'm sorry you left us ;)

I saw a video recently where a guy used what was part of a bicycle break system attached to a pedal  on one end and around the pot on the other calling it a volume control. it worked.  ;)
I'm glad it did

Check out the Soldano X99 preamp. They did a nice implementation of motorized pots. It looks like they used some kind of stepper motors with conventional pots, which would make servicing the amp easier/cheaper.

For learning and quick prototyping/testing µC stuff Arduino is a nice and quick option, but programming AVRs in GCC isn't that hard and gives you kinda more control over hard-/software.

Best regards,
Mathias

Thanks for the input Mathias. I did check the X99 but I think Soldano had custom built pots for that unit.

Something like the Alps RK168 might do,

It would indeed Martin but I can't find proper values that match my amp's pots :(

Anyway, thanks again to all for your help and time ;)

Cheers
Sino
Why sleep when you can mix?
M.P.Stavrou

clintrubber

Re: Amp with motorized pots
« Reply #8 on: January 13, 2020, 04:18:45 PM »
Has the TERRORBOT been mentioned yet ?

If not:

http://trigonometrie.bplaced.net/blog/terrorbot/

It's on my to-DIY-list for some years now, but haven't started it yet.

sonolink

Re: Amp with motorized pots
« Reply #9 on: January 13, 2020, 04:23:29 PM »
Has the TERRORBOT been mentioned yet ?

If not:

http://trigonometrie.bplaced.net/blog/terrorbot/

It's on my to-DIY-list for some years now, but haven't started it yet.


I was hoping to create a more elegant and in the box solution TBH ;)
Why sleep when you can mix?
M.P.Stavrou


clintrubber

Re: Amp with motorized pots
« Reply #10 on: January 13, 2020, 04:47:37 PM »

I was hoping to create a more elegant and in the box solution TBH ;)

OK, the Terrorbot was known I understand.

But that's where 'Additional DIY' can come in: I had a look at how to implement this with everything internally, connecting the motor-spindles with the pot-shafts. A from scratch amp-chassis could accommodate this.

Rocinante

Re: Amp with motorized pots
« Reply #11 on: January 13, 2020, 05:24:05 PM »
Damn. Admittedly that Terrobot is pretty cool. I use arduino nano's and relays in all my amp builds now. Makes having a three channel amp (or two channel with an extra gain circuit) and with footswitch easier to implement via monetary illuminated switches. Plus you also know what channel is on.
If there's a harder way to do this, I haven't found it yet.

sonolink

Re: Amp with motorized pots
« Reply #12 on: January 13, 2020, 05:26:02 PM »
OK, the Terrorbot was known I understand.

But that's where 'Additional DIY' can come in: I had a look at how to implement this with everything internally, connecting the motor-spindles with the pot-shafts. A from scratch amp-chassis could accommodate this.

The thing is that the Terror Bot concept is to place it outside the amp/pedal. My idea is to implement it inside. I've been looking for motorized pots but I think the choice of values is a problem.

Next option would be a dual shaft miniature stepper motor (to place it between the pot and the knob, but I don't know how much hardware is necessary for that to work. My CNC and my laser have a microcontroller board and 3 drivers units. Fitting that into a pedal, even small sized ones can be a challenge...not to mention that it would make things more complex and more subject to problems.

So I'm still reading but I'm about to give up TBH...

Of course all input and suggestions are still always welcome :)

« Last Edit: January 13, 2020, 05:57:32 PM by sonolink »
Why sleep when you can mix?
M.P.Stavrou

clintrubber

Re: Amp with motorized pots
« Reply #13 on: January 13, 2020, 06:01:42 PM »
The thing is that the Terror Bot concept is to place it outside the amp/pedal. My idea is to implement it inside. I've been looking for motorized pots but I think the choice of values is a problem.

Say starting from that Terrorbot-template, that's indeed the first change I as well would try to implement: everything inside, for convenience and coolness as well.

It'd then be most likely be in the form of a mechanical challenge:

  correct-value pots with a 'back entrance' (these exist) and the driver inside, on-axis,

  or possibly by some other way of mechanical coupling

I was and am considering an amp chassis, wasn't considering pedal format as you do.

sonolink

Re: Amp with motorized pots
« Reply #14 on: January 13, 2020, 09:11:48 PM »
I checked the Soldano X99 as suggested by Mathias. It uses stepper/servos and looks pretty neat actually:

https://s20.photobucket.com/user/Anti-Idiot/library/x99?page=1

Those pots you mention, what are they called and where do you find them?

Cheers
Sino
Why sleep when you can mix?
M.P.Stavrou

CJ

Re: Amp with motorized pots
« Reply #15 on: January 14, 2020, 04:25:04 AM »
just get a line 6.   or not.

have you seen those auto tuners they have on guitars now? are we taking things too far ?

listen to the first Montrose album. it's a 58 sunbust into a 5E7  3-10  Bandmaster, that's it.

« Last Edit: January 14, 2020, 04:28:42 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

sonolink

Re: Amp with motorized pots
« Reply #16 on: January 14, 2020, 04:58:21 AM »
Line 6? Not in my lifetime, sir. Thanks.

Listen to The Dark Side of the Moon. Gilmour would use SIX Hiwatts alive in 1972, not to mention pedals, etc. So what? Was he taking things too far?


have you seen those auto tuners they have on guitars now? are we taking things too far ?

I have and I laugh at them. Do you honestly think those things were invented for real musicians?

Being able to program an analogue amp or pedal is not taking"things too far". Shall we ban flying faders and automation then? What about footswitches to change channel? Should we discard those too?

What does that have to do with digital emulations and silly gadgets? Honestly I don't get the point of your post...

Why sleep when you can mix?
M.P.Stavrou

Newmarket

Re: Amp with motorized pots
« Reply #17 on: January 14, 2020, 05:18:41 AM »
You don't need to get 'that much' digital / coding to implement a motorised pot or fader.
Really just need to set a DAC to give the 'target' voltage to an op amp based control circuit (PID type) to drive the motor to the target position.
You can try to read the position with an ADC (likely built into the microcontroller) and control the motor directly but be warned that there's a danger of essentially 'destroying' the pot track with short movements where the action is not 'smooth' enough.
Speaking from experience here having tried this at Penny & Giles in the past and reverting to analogue PID.

On pot values - yes - most available values for motorised pots are likely to be 10K etc.
Demand for high impedance tracks is likely to be very low so unless you custom order in quantity you're unlikely to get them.
Remember that realistically the 'feedback' track needs to be linear even if the 'audio' track has a log or audio taper etc.
Actually you can use a log or similar taper by using a log amp (as done on the DDA Profile mixing desk automation option) but you don't want to go there tbh :-)

sonolink

Re: Amp with motorized pots
« Reply #18 on: January 14, 2020, 05:27:28 AM »
Thanks for your reply Newmarket. I'm obviously not going to order custom motorized pots in quantity, so I'm getting more and more convinced that the way to go is with steppers. But the problem with that is space. I can't seem to find dual shaft miniature steppers (NEMA 8 ).
 :-[

Cheers
Sono
« Last Edit: January 14, 2020, 09:21:26 AM by sonolink »
Why sleep when you can mix?
M.P.Stavrou

sonolink

Re: Amp with motorized pots
« Reply #19 on: January 14, 2020, 03:12:55 PM »
Ok so I bumped into THIS:







https://www.youtube.com/watch?v=QhpGXC-5rOo

If I use a micro stepper instead of the 2nd pot that would solve all the problems: I wouldn't need a hard to find dual shaft motor, I could use the same pots I use in my builds and would have access to all the resistance values and wouldn't need a second gang.

Now I need to find:
1- Small motors with the ideal specs for this job (step resolution, torque, consumption, etc)
2- The smallest possible microcontroller
3- The smallest possible drivers
4- The code


I'm getting all excited again!!! :)
Why sleep when you can mix?
M.P.Stavrou


 

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