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Old 27th March 2011, 02:48 PM   #1
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Default Yet another preamp...

Hi all...

I'm thinking of building some preamp based on Arduino.

The features i'd like to include:

Inputs (6 means 6 stereo, 12 mono):
- 6xAnalog IN (could do single "5.1" and 3 stereo, or 6 stereo inputs)
- 2xDigital IN (for different digital sources. maybe i should increase the count to 3 inputs - media streamer, TV set top box, CD, PC... well, i need at least 3... or 4?)
Probably i'll use the analog inputs as digital too (could be modified by different jumper wire configurations)

Outputs:
- 1x digital out (to external DAC. the DAC will send back the signal to the preamp)
- 3x analog out (for 5.1, or stereo. front channels will be used as main stereo output)

Volume control (off-board - the firmware will support them, but you'll have to use own PCB, the pre will just send a proper signals):
- Relay attenuator - both inverted and regular.
- Moto ALPS - both with feedback and just spinning motor circuit.
- PGA chips (maybe)

Display:
- Classic LCDs - 16x2, 20x4 etc.
- 7SEG leds (input number, volume level)
- Nixies (same info as 7SEG)

User input:
- Potentiometer
- Rotary encoder
- Pushbutton
- IR remote

Additional hardware:
- Power enable circuits, with delay (soft start, output relays, power-on etc)
- Power-on signal acceptance ?? (auto turn-on)



Well, quite a lot of control traces. I don't want to mess with signal itself, but it's routing.
It is going to be passive, arduino controlled system.
Maybe i should step off the basic arduino, and go for mega?


I won't put everything in single firmware - you'll have to use certain blocks of my code for specific functions. You'll program it yourself, i'll give the "drivers" for everything, and a sample code like this:




/* volume read block */
#vol=get_ir_volume(300);
vol=get_encoder_volume(300);
#vol=get_button_volume(300);

/* volume set block */
#set_relay_volume(vol);
#set_pga_volume(vol);
set_pot_volume(vol);

/* volume display block */
#show_lcd_volume(vol);
#show_7seg_volume(vol);
show_nixie_volume(vol);


etc. the example above uses potentiometer as volume input,spins ALPS motor to the desired value, and displays the value on nixies. All you have to do is uncomment the desired function and wire the hardware in appropriate way.


When will i bring this project to life? I don't know, but thinking of it is a good starting point.

Any input is welcome!

Thanks.

Last edited by s3tup; 27th March 2011 at 02:51 PM.
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Old 27th March 2011, 06:33 PM   #2
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definitely go for the mega. more pins available means you can upgrade it later without changing existing circuitry, or make it super modular. what do you intend to use this preamp for?
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Old 27th March 2011, 10:37 PM   #3
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Well, it's just a "basic" inputs selector/volume control/heart of system - controlling power on/off, input/output routing, volume...

- Squeezebox, CD, PC, tape , LPs...
- Various DACs
- Sooner or later i'll get 8-ch relay attenuator boards done. By now i have 6ch moto ALPS.
- I've got 3-way active crossover. One day i'll do digital one too.
- I need to put 6xLM3886 amps in enclosure with lots of caps and single transformer - i'll need soft start circuit and a way to turn it on (i don't want to put power button on the front panel, as i haven't found any push buttons that looks nice)
It would be nice to turn on the system and control it's volume via single remote.
It would be cheaper to have a single MCU controlling everything.
And i love nixies
http://s3t.it/data/uploads/Nixie_Vol.JPG

UPD: Gone with mega This makes my life much easier... Although i'll try to squeeze everything to Nano

Last edited by s3tup; 27th March 2011 at 10:54 PM.
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Old 28th March 2011, 12:02 AM   #4
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for the power button, you could do a flip-flop latch thingy, and still use a pretty-looking momentary or whatever. sorry im a little undereducated in digital electronics, im more of an analog guy , hence the use of the word thingy and the probably incorrect flip-flop configuration term. and i think everyone love nixies!
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Old 28th March 2011, 12:24 AM   #5
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Yes, JK, T flipflops will do the job. The main concern is "pretty-looking momentary or whatever". I have no metalworking skills - i need to shamefully cover every hole i create
I have to match the button to front panel surface/color, and to volume knob i put - it's quite impossible task

Lately i have found the solution - rotary power switch. Better selection of knobs over eBay + all holes covered

Ahh, the remote from Mac, uses NEC commands which are compatible with Arduino IR library.
Click the image to open in full size.
Review: Apple Remote Control (Aluminum) | Art of the iPhone
Just what i've been looking for. Simple, tiny, and perfect match to brushed aluminum front panels.
Too bad the "wheel" doesn't spin.
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Old 29th March 2011, 04:09 AM   #6
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Quote:
Originally Posted by s3tup View Post
Yes, JK, T flipflops will do the job. The main concern is "pretty-looking momentary or whatever". I have no metalworking skills - i need to shamefully cover every hole i create
I have to match the button to front panel surface/color, and to volume knob i put - it's quite impossible task

Lately i have found the solution - rotary power switch. Better selection of knobs over eBay + all holes covered
aha! pretty good idea. i typically use a rubber washer to hide any poorly drilled holes, but that wouldnt be kosher with your spiffy brushed aluminum! moving on, have you considered input and output buffering, isolation of inputs and outputs, and all that good stuff? the buffering can help a lot with preservation of tone and also provide some split inputs and sum multiple outputs, sans arduino processing
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Old 28th November 2011, 07:52 PM   #7
Tekmek is offline Tekmek  Canada
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S3tup, so what happenned with your in-14 & in-19 nixies? did this ever got forward?
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Old 29th November 2011, 09:41 AM   #8
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I'm kinda stuck between my other projects, and figured out that ALPS moto-pots are terribly SLOW...

As for nixies - it's an easy task to do - you need 180V psu
NIXIE TUBE POWER SUPPLY MODULE FOR CLOCK 2 OUTPUTS | eBay

Some decoder-nixie driver ICs, 74141

Each IC has 4 data input pins, so you need 8 outputs on arduino for 2-digit version.
Alternatively, you can throw a shift-register in between to use just 3 pins on arduino with some additional programming...
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Old 29th November 2011, 02:22 PM   #9
Tekmek is offline Tekmek  Canada
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I personally decided to go against moto-pots, but to try digital potentiometers; they aren't as linear but you can control them via microcontrollers.
Maybe I'll hate that, but that's the current plan.

I have in-14, in-19b and in-19v on order, will start experimenting soon. (however, I am a fan of using the atmel microcontrollers without arduino bootloader...)

P.S.: I fully understand about having too many projects... sometimes finishing something can take years, even if it really require a few hours of actual work.
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Old 29th November 2011, 03:23 PM   #10
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I'm going with relay attenuators ( Vol2 English ) myself, as i find it to be ultimate mix of digital and analog technologies.
I have 340 sweet NAIS TX latching relays anyway... Damn their latchiness (2 coils, 2x control wires)
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