Author Topic: working out a buncha-knobs-want-presets kind of problem... digipots? vactrols?  (Read 6580 times)

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Eddododo

Hi there all

working on a little project- ill try to be succinct to get to the actual issue...

jazz bass- TRS out.
 neck pickup -> tip
bridge pickup -> ring

offboard is a module to process each pickup independently before blending them-
it will be high pass, low pass, both with variable resonance and freq, and then a parametric mid EQ/(switch)/bandpass section with Q, freq, and level for the eq.
**I will expand on this in the end**, but here is my current issue...

thats a LOT of knobs. I'm fine with amp-top or a pitcher's mound on the foor, but with this much tonal control, you would REALLY think presets would be necessary. Or at least a damn shame to do without...

my current thoughts
      -arduino comes to mind, mainly because i've heard of it. Im not a programmer or really a huge 'computer guy' but I am clever and mathy, and i did well in the here-and-there programming in school.. Seems like an easy way to read and store whatever form of topology's information.

      -digital pots-    i dunno... seems like they don't get much love around here, and I'm not as good as some of you with overcoming frustrating parts... my naivete perhaps

     -mechanized pots seem like something that i would... just @#$% up.  im the type where the last 5% of  a build is me stuffing wires in and slamming it shut like im trapping a mummy.

      -vactrols : THIS seems promising to me... using digital pots to control vactrols, the latter acting in place of the original potentiometers.... eliminates the issues of catering the signal to the digipots' needs.  are vactrols within a tight tolerance of eachother? will i be weeping trying to bias them all to a proper operating range? especially since i will A) have to configure some as voltage dividers instead of just rheostats, and  B) implement dual-gangs for the fiters. in fact...  i may be implementing dual-ganged voltage dividers in the bandpass... yikes


vactrols seem promising to me... arduino remembers the digipot setting, said resistance sets the LED, isolated controlled resistance badabing badaboom, albeit convoluted

 
Another thing to consider is that i will NEED (lol) dual ganged pots in a few spots, which complicated the idea of using


I suppose at this point, as presets are an issue of comfort and convenience, it comes to mind that to not stop short of a decent result, that i would need a few more features
: some sort of display.. preferably one that informs of the nature of the settings, not just a bank number. seems easy enough
: devise an algorithm to deal with adjusting presets RE: ''where does the pot pick up"
i'm not a believer in a preset that you cannot edit live, intuitively. I'll trust my mileage on that philosophy

It is ALSO worth noting that, because I have layed out such an exotic, and weirdly specific set of needs and goals that NO ONE GETS TO USE REASON with me and discourage this project in lieu of a readily-available project. 

**the point of the project overall is, at least partially, to use different tonal characters imparted onto individual pickups via filters, BEFORE the pickups are blended. this could be used to get your sound just right , or you could try to, say, emulate a Rickenbacker with your jazz bass. At its' most extreme you could have each pickup heavily affected by peaking resonance on both high and low pass filters, with a bump or scoop in the mids. At its simplest youd have 2 buffered pickups that you can blend together actively.

The mid section is interesting in that it is switchable between functioning as a parametric mid and as a Band pass, sharing the same state-variable filter.
The high and low pass are sallen-key 2nd-order types,  with resonance (q?) from peaking to very sub-bessell. still working out how far in each direction.**



Brisance

For some of these usages, might I suggest a FET as a voltage controlled resistor?

snarblinge

I don't understand why the vactrol is in there. I have a project on the bench which I hope to finish one day... Which has standard pot as encoder, into arduino and digital pot out, in my case the standard pot sets the rate of a wah pot curve which is output through the digital pot which lies in circuit.

If I ever get this one off th bench it may be the first in a few experiments with digi pots.

I bought the arduino mini or something with seperate USB board. Little bit cheaper but footprint is nice and small. In future I would buy just the chip and use the board I have to program that. Leaving the chip in circuit somewhere.
b.

snarblinge.tumblr.com

samhay

Two thoughts.

1. This is kinda what digipots are designed to do, so I think the vactrols will just lead you down the rabit hole - It's not easy to properly fake a potentiometer, as you have to have one resistance proportionally decrease while another increases.

Before we worry more about that,

2. Have you breadboard this (with all the pots) to get some idea of whether you actually need anywhere near all this control? You might be able to get away with a bunch of trimmers, and/or external switches.
I'm a refugee of the great dropbox purge of '17.
Project details (schematics, layouts, etc) are slowly being added here: http://samdump.wordpress.com

Eddododo

I don't understand why vactrol is in.there
I had been getting the impression through initial research that digipots were a bit of a bummer for audio.. Finicky about signal level etc... Id be happy enough if the answer there is 'no' :)

To expand/ clarify, the become V.C. Resistors and no audio goes through the pots


Two thoughts.

1. This is kinda what digipots are designed to do, so I think the vactrols will just lead you down the rabit hole - It's not easy to properly fake a potentiometer, as you have to have one resistance proportionally decrease while another increases.

Before we worry more about that,

2. Have you breadboard this (with all the pots) to get some idea of whether you actually need anywhere near all this control? You might be able to get away with a bunch of trimmers, and/or external switches.
1- it seems like a pain but it seems ... Understandable? Two vac biased to the same range being affected by the same (dc) signal of opposite phase

2- well I don't NEED  any of the pots :p      but really the flexibility is the whole point, and I'm just not the type to set a preset at home and assume that it will be perfect for my next gig .. Though i guess I'm 'pickup emulating' so it makes sense In a way. A few pots could be switches but that's the same problem anyway..

samhay

I had been getting the impression through initial research that digipots were a bit of a bummer for audio.. Finicky about signal level etc... Id be happy enough if the answer there is 'no' :)

Fair point - the headroom will be limited to the digipots supply voltage and it looks like the through hole options are getting limited, so you might struggle to find parts that can take 9V. You could re-scale the circuit to run everything on e.g. +5V and use rail-to-rail op-amps.
I'm a refugee of the great dropbox purge of '17.
Project details (schematics, layouts, etc) are slowly being added here: http://samdump.wordpress.com

Eddododo

Re:
« Reply #6 on: January 26, 2015, 08:41:37 AM »
Hmm that gets a little far off-message for me... Hell my basses all run at +18, and i was planning on +-12 or so in the 'unit' for noise floor and the headroom for peaking filters.. I disliked it at 9+ even.. But 5v??


I guess i didn't mention this but Im also eyeballing this to  be able to drive my power amp without another pre.. So supply voltage is either important or more important

amptramp

Have you considered using a multiplying DAC like a DAC0808 or DAC1208?  The audio input becomes the reference voltage and the DAC multiplies by a fraction of 0/256 to 255/256 for a DAC08 or 0/4096 to 4095/4096 for a DAC1208.  The digital inputs can be controlled by a binary counter or a PIC - you don't need anything as complicated as an Arduino although you could use it to calculate the multiplier as a decimal fraction.  In fact, you could use ordinary 74HC192 up/down counters and a bit of random logic and avoid programming altogether.

The data sheet is here:

http://www.ti.com/lit/ds/symlink/dac1208.pdf
« Last Edit: January 26, 2015, 10:54:11 AM by amptramp »

David

Edd:

1)  You might consider using rotary encoders for your dials.  Easy for a microcontroller to determine its position.
2)  If you are still considering what microcontroller to use, research using PICs.  The PIClist is a web site that has huge libraries of prewritten and pretested microcontroller code (written for PICs).

anotherjim

You could use Vactrols and have the LED's running from an Arduino's PWM outputs. Uno has 6 PWM outs. It also has 6 analog inputs to read 6 pots. Inside the Arduino is an eeprom to store presets in.

"So lets stay within the limit of sureness: lets consider the fuses you have available and lets see what you have to do to light them up..." Farfisa Partner 15 drum machine manual.

karbomusic

Quote
You could use Vactrols and have the LED's running from an Arduino's PWM outputs.

Yep...

« Last Edit: February 15, 2015, 11:32:31 PM by karbomusic »

deadastronaut

^ very cool...

i bit the bullet and just bought an arduino uno.....hence the old thread search..

but haven't a clue about using it at all, total utter noob with this stuff...but for a fiver i thought why not have a dabble :)..

should come in a few days,

any tips/links/cool audio/midi projects?....

the midi side of it interests me, especially building
midi drum stuff..ideally i'd like to make a basic midi drum brain for use in a DAW/triggering ezdrummer/percussion etc
and make my own piezo/pads/drums..

i'm guessing for the audio stuff you just need the usual buffer in/out setup with arduino between?...

as i said, total noob...so any advice is welcome.. 8)





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Beo

I had been getting the impression through initial research that digipots were a bit of a bummer for audio.. Finicky about signal level etc... Id be happy enough if the answer there is 'no' :)

Fair point - the headroom will be limited to the digipots supply voltage and it looks like the through hole options are getting limited, so you might struggle to find parts that can take 9V. You could re-scale the circuit to run everything on e.g. +5V and use rail-to-rail op-amps.

I have a circuit layout I've been working on for an AVR controlled preset interface using Analog Digital digipots. Haven't procured the digipots yet to try out my design, but they have the broadest selection... although most are surface mount. However, the one I was most interested in (AD5242 dual channel 1Mohm resistance, i2c interface) only supports +5.5V supply. To get 16.5V supply support, we're limited to 200kohm. I'm sure opamps or companders could manage signal level, but that's a lot more circuitry.

~arph


Beo

There are high voltage digipots available:

http://nl.mouser.com/new/semiconductors/digital-potentiometer-ics/microchip-mcp41hvx1-potentiometers/n-4c498Z20ryhm

Would be great if they came out with dual HV chips, i2c interface and 1Mohm range. I haven't experimented yet, but I suspect using a voltage divider to scale down signal before a 5V digipot may have undesireable effects for particular pedals/controls. Probably okay for LFOs but not sure about the added resistance for gain and tone controls.

samhay

I'm a refugee of the great dropbox purge of '17.
Project details (schematics, layouts, etc) are slowly being added here: http://samdump.wordpress.com

~arph

It's new.. I don't expect new products to be available in through hole anymore. I think we need to bite the bullet and find ways to handle these tiny packages

Beo

It's new.. I don't expect new products to be available in through hole anymore. I think we need to bite the bullet and find ways to handle these tiny packages

Adapter boards are a cool way to use SMD, and have them as modular plug-ins on a through hole board:
http://www.futurlec.com/SMD_Adapters.shtml

I plan on trying out some SMD soldering using a toaster oven:
http://www.freetronics.com.au/pages/surface-mount-soldering-with-a-toaster-oven#.VmCt3berTyM

~arph

Yeah, adapterboards are essential as we like to breadboard our stuff first ( I do ) but you still need the skill to solder the chip to the adapterboard. So there is no point in using adapter boards in final pcb designs

garcho

Quote
i bit the bullet and just bought an arduino uno.....hence the old thread search..
[...]
any tips/links/cool audio/midi projects?....

http://wiki.openmusiclabs.com/wiki/StompShield

http://bleeplabs.com/store/nebulophone/
did this with some copper tape on the "fretboard" of an old pipa I had and attached a metal bridge wired to the trigger, for a key-tar kind of thing

https://www.sparkfun.com/products/10587
« Last Edit: December 03, 2015, 10:52:36 PM by garcho »
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