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Topic: arduino audio controller in *stereophile* magazine (Read 13321 times) previous topic - next topic


I've been working on various incarnations of audio and audio-related controllers (one is what we call the LCDuino-1).  it started out as an LCD backpack with a port expander, RTC chip and some user proto-holes.  it was meant as a building block for doing audio remote control systems (volume, on/off, sleep timer, i/o selector, etc).

later, we added a proper 8-bit relay R/2R resistor attenuator and a matching 8 port i/o selector.  my partner designed a motherboard for it and we had this to show for our effort:

then, in oct 2010, my partner and I took our DIY modules to an annual audiophile gathering called 'burning amp' (yes, really) in san francisco to show to the local audio/builder community.   there was a reporter from stereophile magazine there and he interviewed us.  here's our equipment - and yes, its all arduino-powered ;)

here's a better shot (my own photo) of the setup we brought to 'burning amp':

one way or another, people are going to hear about arduinos (and controllers, overall) ;)

just wanted to share my success using arduino.  


Awesome! I bet you're proud (and you should be)! That's a nice piece of equipment you've built.

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.


Jan 15, 2011, 07:45 am Last Edit: Jan 15, 2011, 08:33 pm by linux-works Reason: 1
thanks ;)

what I built was on-the-cheap.  I had a spare metal cover from a network router - I inverted it and made a bottom/side chassis for it.  (there is no top.  its always in perma-tinker mode).

but for an on-the-proper build, see what my partner, Ti, did:

semi expensive metal work and fairly expensive front/rear panels (CNCd).  all 8 ports are wired up (I only did a few on mine).

we measured these with audio test gear and the noise level and distortion was at our test gear level (130dB down at points).  no 'arduino computer noise' coming thru at all thru the analog line (you can see 2 very visible ground plane separations on the motherboard; for analog and for digital).


I was worried about backlight (pwm) bleedthru, but again, our test gear shows this to be noiseless andn flat from dc thru about a mhz or so (well beyond audio needs).

what that thing is, btw: its an audio preamp that selects 4 inputs and routes to 4 outputs (all assignable to in or out); along with a 'stepped attenuator' volume control using relays, resistors and 256 steps of half-dB per step.  the output of the attenuator board go into a pair of discrete (fet/bpl) buffer boards that give voltage gain and are nearly noiseless, with near zero output impedance.  that would go to your power amp or set of amps.

you control it via a learning remote (arduino learns your remote) OR you twist the knob to change volume.  if you use the IR remote, the knob is motorized and catches up (in the background) to the IR-set value.  in this respect, whether you use the IR remote or the knob, itself, it always 'points the right way' due to the motor and arduino controlling it.  ie, if you had used the IR remote to set the volume to halfway, then the knob will motor over to point to 50%.


Nice job. I do have a question about how you handled volume moves in your software. Did you use a 'linear' type ramp up/down, or did you try and simulate a standard audio log type taper? Is the motorized pot of linear or log taper?




hi lefty,

the two are decoupled, so that you can control either one.  the way the user talks to the vol-control engine (or subsystem) should be different from the actual way the analog signal is attenuated.

on the motor pot side, its a linear track.  simple obvious voltage divider going into an arduino a/d pin.  cap across signal and gnd to kill noise and settle some of the 'wander' that pot-driven inputs sometimes have.  in this config, no audio goes thru or even near this pot, its simply a *control device*.

I considered, for a short while, using log-tape motor pots and de-logging them (lol) in software.  I found the curves to not be very nice, in the real world, and so delogging would not be all that practical.  perhaps a painstakenly done data point lookup table to map the current pot you have.

but then you run into other issues; at one end, its very 'wide' and at the other, very compressed.  you can't get resolution to 'unlog' stuff like that with a cheap a/d that we have on the arduino.  it becomes impractical to delog (grin) things unless you have a lot of bits of precision.  so I gave up and just decided to limit the design to the assumption of a linear track motor pot.  digikey/mouser has alps brand for $15 or so, so its realistic to spec for that kind of thing.

as for the engine itself, it has no taper.  its 0db down to -127.5db in half db steps.  or, if you prefer, you run our cheap-n-dirty CGI web gui and pick your own!


pick the top 3 parameters and it will compute the rest.  order the parts, solder onto the blank boards and that takes care of the vol engine (2 channel attenuator).

if you are on a budget, don't use all 8 relays.  for a while, I was doing proto builds with 7 bits and that would give me 0-127db but in 1db steps.  saved me the cost of a $5 relay (lol) but it also is a little faster and less noisy (chattery) since only 7 relays (max) would have to change, and not 8.

there is no 'taper'.  if you want a value, you send that value and the complement of it to the 2 adjacent PE chips and they pulse the relays to get the dB value you wanted.  that's the scheme.


Jan 15, 2011, 09:24 pm Last Edit: Jan 15, 2011, 09:46 pm by retrolefty Reason: 1

Thanks for the explanation. I'm still somewhat interested in home stereo Hi-Fi stuff. About 20 years ago I started seriously checking the thrift stores and e-bay for vintage hi-gear, mostly those made in the 70s. The stuff was really well made and designed back then. Most worked fine, only needing pots and switch contacts cleaned well. Even those needing repair was not hard as schematics were usually obtainable and output transistors were still available if searched for. Lots of Marantz, Sansui, Kenwood, Pioneer, etc were being donated as people 'upgraded' to five channel and other BPS (black plastic sh#t) equipment. I would keep the best and sell off the others. Then things started to dry up as the rest of the world started wising up to how great that vintage stuff was and e-bay prices soared on the higher end items. Still have a nice silver Sony component set-up and haven't been able to want to part with the Pioneer SX-1980 (270 watts per channel!) receiver.



what I found is that analog stereo pots don't track well from left to right (esp. at lower volume levels) and also the high freq. response 'merges' (crosstalk) as the freq goes up.  its very measurable even with a $100 pc sound card.  but once you remove the cheap analog pot and put dual mono attenuators in, crosstalk is highly improved and you get essentially identical tracking if you use 1% resistors (don't really need .1%).

the weak spot is usually (imho) the preamp section.  if you disable that in your vintage gear (or bypass/jumper around it) and use an outboard preamp or attenuator, you get a combo that makes the best of both.

for amp sections, I'm using 'chip-amps' that cost about $15/channel to build and they give about 50w/channel.  very good cost/perf ratio.  good for bi- and tri-amping ;)


I hear you. However I could never 'bypass' my favorite preamp:




that preamp would be a fun one to gut and re-do as a control-plane front-end with a more modern back-end.

I do like the older analog GUIs (lol).  but the old electronics is rarely as good as what can be made, diy-wise, today.

there's probably even enough room in that chassis if you remove all but the front UI parts and put in arduino controlled stuff behind it.


Jan 15, 2011, 10:29 pm Last Edit: Jan 15, 2011, 10:37 pm by retrolefty Reason: 1
that preamp would be a fun one to gut

Your a heretic to even suggest such a thing.  ;)

Do you realize that this pre-amp uses 100% fets running at over 100vdc power rail? This, grasshopper, was the peak of analog engineering design back when electrons were not ordered to simply turn on or off, but rather gently caroused into audio blissful movements.

Seriously this thing is designed and built like a piece of expensive H.P. test equipment. It has a passive vertical mother board with about six plug in boards. Nasa would have no problem letting with go on board a space craft. Except maybe for the weight penalty.  ;) These can fetch to $400 or higher on E-bay at times.



I have not seen the schematic for that so I don't know it.  sounds interesting.

still, a LOT has changed in noise level, alone, over the years.  even what was 'pro level' in the 70's and 80's is far behind what we have for consumer playback systems, now.

modern things like quiet power supplies (toroidal, as well), very low noise fet-based op-amps adn not to mention elimination of the pots and mech switches.

I have no doubt that the specs can be significantly improved by gutting and re-doing.  I know its heresay to say that, but I *would* still keep the nice metal work and shiny knobs ;)

I would guess that there are probably also ugly caps in the audio path, too.

old is romantic but in so many cases, old IS surpassed by current state of the art parts.


Jan 16, 2011, 12:27 am Last Edit: Jan 16, 2011, 12:33 am by retrolefty Reason: 1
still, a LOT has changed in noise level, alone, over the years.  even what was 'pro level' in the 70's and 80's is far behind what we have for consumer playback systems, now.

I know its also hearsay to say that human hearing hasn't improved sense the 70's, but I really don't want to punch that bees nest called audiophiles golden ears.  ;D

Can't help myself, they still selling $100+ caps to those guys? How about those $300+ 300A Western Electric 7 watt tubes? $500 AC power cables? $50 Wood thingees to place on top of your speakers?



being serious - there are things that are easy to measure, even using simple spdif sound cards and good dacs and a/d's.

what costed a thousand dollars in the eighties may not even compete with stuff 1/10 the price, today.  the modern *decent* op-amp quality, alone, is shockingly good; you don't even have to go discrete to have studio-grade audio paths these days.

I'm not talking about magic capacitors; but just replacing all the (likely) carbon resistors and ceramic/electrolytic caps with film types.  not $100 caps but $5 caps at the most.  competant upgrades, not boutique stuff.


being serious - there are things that are easy to measure,

I was being serious, but I was talking about things one can hear, no matter if measured better or worst. Under double blind testing conditions of course. Of course the audiophiles distrust measurements, they will just say you are measuring the wrong things.  ;D



if you want to compare that ancient boat anchor to some modern gear, I'm up for it.  lets put both of them on the same test harness and see what the computer says.

shall we?

I have audio test suites and hardware that can measure down quite low (m-audio firewire a/d d/a box).  it will show - impartially - how the 'old classic' gear compares.

up for it?

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