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Music Student in Need of Help

Hi everyone,

I wish to replace the analog Pots in my distortion pedal with digital
equivalents so as to control it in real-time from a computer. To
achieve this, I have purchased 1-wire Maxim Digital POTs -

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2934

The package I have purchased is a 6-pin TSOC.

The pedal I'm modifying is called a Turbo RAT -

http://www.diystompboxes.com/pedals/ratmod.gif

I have built a few amplifier circuits before, designing and
constructing PCBs for them in the Electronics department in my college.
If I remember correctly, the package type of the amplifiers I used was
called DIP. When building these circuits, I used a socket for my
amplifiers so that I didn't have to solder on the opamps directly. This
way handy if the opamp was damaged later on.

http://uk.farnell.com/productimages/farnell/standard/42266199.jpg

I'd like to do the same again with the TSOC chip but I cant find any
sockets on Farnell for this package. What would you suggest? Also, do
people actually solder these devices onto pcb boards by hand? The 6
pins are so small...

Also, my plan for the digital POTs is to build a little PCB for each of
them. I can then suspend each little PCB above the pedal PCB in place
of the analog POTs. This will give me flexibilty so that I can easily
remove a POT and attack it to a different pedal - or whatever. The
1-wire master communicates with the POTs via a RJ-11connection, so I
will also place RJ-11sockets on each POT PCB. In addition, I will need
2 terminals on my POT PCB for power and I will also need to include
drilled holes so that I can wire the 3 POT pins to Pedal PCB. In other
words, the POT chip will sit in the center of its little PCB board and
the tracks will run out to the edges as required. How does that sound?
Is it a good approach?

Thanks for your help,

Barry.
 
A

Abstract Dissonance

Jan 1, 1970
0
Hi everyone,

I wish to replace the analog Pots in my distortion pedal with digital
equivalents so as to control it in real-time from a computer. To
achieve this, I have purchased 1-wire Maxim Digital POTs -

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2934

The package I have purchased is a 6-pin TSOC.

The pedal I'm modifying is called a Turbo RAT -

http://www.diystompboxes.com/pedals/ratmod.gif

I have built a few amplifier circuits before, designing and
constructing PCBs for them in the Electronics department in my college.
If I remember correctly, the package type of the amplifiers I used was
called DIP. When building these circuits, I used a socket for my
amplifiers so that I didn't have to solder on the opamps directly. This
way handy if the opamp was damaged later on.

http://uk.farnell.com/productimages/farnell/standard/42266199.jpg

I'd like to do the same again with the TSOC chip but I cant find any
sockets on Farnell for this package. What would you suggest? Also, do
people actually solder these devices onto pcb boards by hand? The 6
pins are so small...

Also, my plan for the digital POTs is to build a little PCB for each of
them. I can then suspend each little PCB above the pedal PCB in place
of the analog POTs. This will give me flexibilty so that I can easily
remove a POT and attack it to a different pedal - or whatever. The
1-wire master communicates with the POTs via a RJ-11connection, so I
will also place RJ-11sockets on each POT PCB. In addition, I will need
2 terminals on my POT PCB for power and I will also need to include
drilled holes so that I can wire the 3 POT pins to Pedal PCB. In other
words, the POT chip will sit in the center of its little PCB board and
the tracks will run out to the edges as required. How does that sound?
Is it a good approach?

Why would you want to manually have to change the pots each time? Are you
trying to get both analog and digital control of the pedal?


You could easily make an interface that converts the pedal to allow for
digital control by using the digital potentiometers with a microcontroller
and have an digital output interface(even make it midi compatiable if you
wanted) to control the pots and switches digitally. The problem would
mainly be that you would have to make an enclosure that will be able to
whole the new circuitry if you want it to look professional.

The way to do it would be to use a pic and its built in ADC's to sample the
pots on the pedal and use them to control the digital pots if it is in
"analog" mode else to get the info from the computer. Conceptually its not
that hard

1. Replace analog pots with digital pots.
2. Use a MC to interface the computer or the analog pots to the digital
pots.
3. Write software.
4. Create new enclosure for circuitry.


You could even create your own little "midi" like control language so you
could daisy chain pedals. Note that your power requirements would increase
though.


What I'd suggest, if you want to get more into it, is simply design a new
circuit that includes the circuit of the pedal with the new digital
circuitry and implement it all on a new PCB. It would be much more fun and
more professional. You might even be able to sale the pedals if you wanted.

You could also add a lot of "extra" features such as allows for additional
controllable circuit elements. For example, in the clip circuitry of an
distortion pedal you could use relays to add or subtract more diodes for
addition clipping effects or even asymmetric clipping. You could do the
same with digitally selecting different op amps, etc... You could get real
crazy and have tons of controllable features(which means tons of new sounds)
in a single pedal.


Jon
 
Abstract said:
Why would you want to manually have to change the pots each time? Are you
trying to get both analog and digital control of the pedal?


You could easily make an interface that converts the pedal to allow for
digital control by using the digital potentiometers with a microcontroller
and have an digital output interface(even make it midi compatiable if you
wanted) to control the pots and switches digitally. The problem would
mainly be that you would have to make an enclosure that will be able to
whole the new circuitry if you want it to look professional.

The way to do it would be to use a pic and its built in ADC's to sample the
pots on the pedal and use them to control the digital pots if it is in
"analog" mode else to get the info from the computer. Conceptually its not
that hard

1. Replace analog pots with digital pots.
2. Use a MC to interface the computer or the analog pots to the digital
pots.
3. Write software.
4. Create new enclosure for circuitry.


You could even create your own little "midi" like control language so you
could daisy chain pedals. Note that your power requirements would increase
though.


What I'd suggest, if you want to get more into it, is simply design a new
circuit that includes the circuit of the pedal with the new digital
circuitry and implement it all on a new PCB. It would be much more fun and
more professional. You might even be able to sale the pedals if you wanted.

You could also add a lot of "extra" features such as allows for additional
controllable circuit elements. For example, in the clip circuitry of an
distortion pedal you could use relays to add or subtract more diodes for
addition clipping effects or even asymmetric clipping. You could do the
same with digitally selecting different op amps, etc... You could get real
crazy and have tons of controllable features(which means tons of new sounds)
in a single pedal.


Jon

I will be removing the analog POTs so I wont be controlling the pedal
manually - no anlog control in other words. I will be controlling the
pedal via my computer and using a C program (interfacing to MAX/MSP via
MIDI) to adjust the pedal settings in real-time in order to apply
analog effects to my sound. I hope to use this pedal in a composition
I'm writing for my thesis. Thanks for you suggestions! For now though,
I wan't to keep things simple because I need to establish if my idea is
going to work or not. If it doesn't, I'll need to look into
alternatives.

Anyway, any suggestions regarding my question about TSOC sockets? How
does my design sound? I'd like to build my own pedals, but I'll wait
untial after my thesis deadline when I'll have more time to do so.

Thanks again for your help,

Barry.
 
A

Abstract Dissonance

Jan 1, 1970
0
I will be removing the analog POTs so I wont be controlling the pedal
manually - no anlog control in other words. I will be controlling the
pedal via my computer and using a C program (interfacing to MAX/MSP via
MIDI) to adjust the pedal settings in real-time in order to apply
analog effects to my sound. I hope to use this pedal in a composition
I'm writing for my thesis. Thanks for you suggestions! For now though,
I wan't to keep things simple because I need to establish if my idea is
going to work or not. If it doesn't, I'll need to look into
alternatives.

If you just want to be able to control the effects electronically why not
use a simple motor that hooks up to the analog pot(sorta like a gear). By
using a microcontroller you can supply power to the motor(a servo would work
best). This would be the quickest way IMO to do what you want and wouldn't
require messing with the internals of the pedal. The hardest part about this
would mechanically interfacing the analog pot with the motor. You could just
"glue" and it might work or you could do it a little more advanced. Most of
the software to do this can be downloaded and you only have to do a little
tweaking and write the computer to controller interface(and midi would
probably be the easiest because you won't have to worry about the software
on the computer but just implementing a simple midi interface with the MC).
Anyway, any suggestions regarding my question about TSOC sockets? How
does my design sound? I'd like to build my own pedals, but I'll wait
untial after my thesis deadline when I'll have more time to do so.

I'm not sure if they make sockets for the TSOC. The only ones I have seen
are SOIC, PLCC,DIP, and there variants. Have you thought about "bending"
the pins down to make it dip like or seeing if it could work in a dip
socket(some have "shoulders" that might work if the ic is the correct size
but it might not get a good connection). Or you could just by some extra's
and try to soilder them. It is possible and shouldn't be that hard if you
have a decent iron with the right tip.
 
P

Paul E. Schoen

Jan 1, 1970
0
Abstract Dissonance said:
I'm not sure if they make sockets for the TSOC. The only ones I have seen
are SOIC, PLCC,DIP, and there variants. Have you thought about "bending"
the pins down to make it dip like or seeing if it could work in a dip
socket(some have "shoulders" that might work if the ic is the correct
size but it might not get a good connection). Or you could just by some
extra's and try to soilder them. It is possible and shouldn't be that
hard if you have a decent iron with the right tip.

Silicon Laboratories has a good tutorial on hand soldering SMT parts:
https://www.mysilabs.com/public/documents/tpub_doc/anote/Microcontrollers/en/an114.pdf
You might need to set up a free account to access this.

They have a tiny 28 lead part that has 0.5 mm (0.02") lead spacing. The
TSOC is 0.05".
I have hand soldered this type of part and it wasn't too difficult.

Also, check DigiKey or Mouser for "Surfboards", which have SMT pads and can
be used as adapters to SIP or DIP.

The sockets I have found for fine pitch SMT parts are very expensive and
usually used for testing and burn-in purposes.
http://www.plastronicsusa.com/

Paul
 
V

vic

Jan 1, 1970
0
Hi everyone,

I wish to replace the analog Pots in my distortion pedal with digital
equivalents so as to control it in real-time from a computer. To
achieve this, I have purchased 1-wire Maxim Digital POTs -


Wouldn't the "steps" of the digital pot pose a problem for an audio
application ? There will probably be an audible click at each move of
the wiper.

vic
 
L

Luhan

Jan 1, 1970
0
Hi everyone,

I wish to replace the analog Pots in my distortion pedal with digital
equivalents so as to control it in real-time from a computer. To
achieve this, I have purchased 1-wire Maxim Digital POTs -

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2934

The package I have purchased is a 6-pin TSOC.

The pedal I'm modifying is called a Turbo RAT -

http://www.diystompboxes.com/pedals/ratmod.gif

I have built a few amplifier circuits before, designing and
constructing PCBs for them in the Electronics department in my college.
If I remember correctly, the package type of the amplifiers I used was
called DIP. When building these circuits, I used a socket for my
amplifiers so that I didn't have to solder on the opamps directly. This
way handy if the opamp was damaged later on.

http://uk.farnell.com/productimages/farnell/standard/42266199.jpg

I'd like to do the same again with the TSOC chip but I cant find any
sockets on Farnell for this package. What would you suggest? Also, do
people actually solder these devices onto pcb boards by hand? The 6
pins are so small...

Also, my plan for the digital POTs is to build a little PCB for each of
them. I can then suspend each little PCB above the pedal PCB in place
of the analog POTs. This will give me flexibilty so that I can easily
remove a POT and attack it to a different pedal - or whatever. The
1-wire master communicates with the POTs via a RJ-11connection, so I
will also place RJ-11sockets on each POT PCB. In addition, I will need
2 terminals on my POT PCB for power and I will also need to include
drilled holes so that I can wire the 3 POT pins to Pedal PCB. In other
words, the POT chip will sit in the center of its little PCB board and
the tracks will run out to the edges as required. How does that sound?
Is it a good approach?

I've used the Microchip MCP41010 256 step digital pot that comes in a
DIP-8 package. They come in 10k, 50k, and 100k versions and have the
standard I2C interface.

Luhan
 
vic said:
Wouldn't the "steps" of the digital pot pose a problem for an audio
application ? There will probably be an audible click at each move of
the wiper.

vic

Yeah I've been thinking all along that this might be a problem. This is
the circuit I'm hoping to modify -

http://www.diystompboxes.com/pedals/ratmod.gif

You can see the 3 pots on it. I'm not really worried about the volume
pot because I can control that on the PC. But couldn't I low-pass
filter the stepped POT voltage? I don't have any real electronics
background but I'm familiar with the concept of a RC lowpass filter.
I'm not sure though how to do this for the circuit above because its
simply too complex for my limited knowledge.

Anyway, I'd appreciate any advice you could give me.

Barry.
 
V

vic

Jan 1, 1970
0
Yeah I've been thinking all along that this might be a problem. This is
the circuit I'm hoping to modify -

http://www.diystompboxes.com/pedals/ratmod.gif

You can see the 3 pots on it. I'm not really worried about the volume
pot because I can control that on the PC. But couldn't I low-pass
filter the stepped POT voltage? I don't have any real electronics
background but I'm familiar with the concept of a RC lowpass filter.
I'm not sure though how to do this for the circuit above because its
simply too complex for my limited knowledge.

Anyway, I'd appreciate any advice you could give me.

Barry.

I'm not sure ... What is the spectrum of a single straight voltage
increase or decrease ? Probably something centered around 0Hz so you may
be able to filter most of it using a high pass filter with a low cut
frequency (below what the human ear can detect). I really need someone
to check this :)

The best thing to do would be to use a zero-cross detect circuit. I know
some digital pots include one, but not the one you have in your
possession it seems.

vic
 
R

Rich Grise

Jan 1, 1970
0
If you just want to be able to control the effects electronically why not
use a simple motor that hooks up to the analog pot(sorta like a gear). By
using a microcontroller you can supply power to the motor(a servo would work
best). This would be the quickest way IMO to do what you want and wouldn't
require messing with the internals of the pedal. The hardest part about this
would mechanically interfacing the analog pot with the motor. You could just
"glue" and it might work or you could do it a little more advanced.

A piece of rubber tubing over the shafts. RC servos are easier than a
rat to control, but I don't know if you can get one with 270 degree
rotation.

Good Luck!
Rich
 
Rich said:
A piece of rubber tubing over the shafts. RC servos are easier than a
rat to control, but I don't know if you can get one with 270 degree
rotation.

Good Luck!
Rich

I've actually bought the digital POTs and a USB interfaxce to work with
them so if any can offer my advice on using these POTs to control this
circuit then I'd be very grateful -

http://www.diystompboxes.com/pedals/ratmod.gif

Digital POT -

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2934

Thanks,

Barry.
 
T

TuT

Jan 1, 1970
0
[snip]
A piece of rubber tubing over the shafts. RC servos are easier than a
rat to control, but I don't know if you can get one with 270 degree
rotation.

Good Luck!
Rich

I've actually bought the digital POTs and a USB interfaxce to work with
them so if any can offer my advice on using these POTs to control this
circuit then I'd be very grateful -

http://www.diystompboxes.com/pedals/ratmod.gif

Digital POT -

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2934

Thanks,

Barry.

The pots used in the pedal are log, whilst the Maxim part you indicate is
linear, which will cramp all the adjustment at one end and also compromise
adjustment resolution.

Have a look around the Maxim website - they do some log versions.
 
TuT said:
[snip]
A piece of rubber tubing over the shafts. RC servos are easier than a
rat to control, but I don't know if you can get one with 270 degree
rotation.

Good Luck!
Rich

I've actually bought the digital POTs and a USB interfaxce to work with
them so if any can offer my advice on using these POTs to control this
circuit then I'd be very grateful -

http://www.diystompboxes.com/pedals/ratmod.gif

Digital POT -

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2934

Thanks,

Barry.

The pots used in the pedal are log, whilst the Maxim part you indicate is
linear, which will cramp all the adjustment at one end and also compromise
adjustment resolution.

Have a look around the Maxim website - they do some log versions.

Not yet. Anyway, I'm not too worried about that issue. I can see how it
works when I build the circuit. The stepping though is of concern to
me. Any suggestions?
 
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