My Preamp Project: Arduino, I2C, relay selector+attenuator, tube stage - diyAudio
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Old 9th September 2010, 02:58 PM   #1
maxw is offline maxw  United Kingdom
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Default My Preamp Project: Arduino, I2C, relay selector+attenuator, tube stage

I thought I would detail my preamp project. I've had this idea for a while but only recently got around to starting it. Seen a couple of threads previously with similar intentions but looks like they never got finishedÖ

Iím going to use an Arduino for control because I really like open source hardware and its so easy to work with. The Arduino will control a passive, relay-based input selector and Attenuator via I2C using a rotary encoder/buttons/remote. Not sure if Iíll use an LCD display in the final design but I have one at the moment anyway. Not sure about the tube stage yet but Iím thinking a Low Voltage Aikido (Aikido LV)

Attached is a diagram showing the general layout.
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Old 9th September 2010, 03:54 PM   #2
Leon08 is offline Leon08  Germany
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I think it's unnecessary complicated with tubes and relay-based Attenuator.You can take an Op-amp and pga2310 instead and it will cost less and make better sound.
I know some people want something extravagant and very expensive, but it sounds not better then "cheap" things.
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Old 9th September 2010, 04:01 PM   #3
maxw is offline maxw  United Kingdom
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Yeah I was very undecided about using the PGA2310 vs relay attenuator for volume control but decided on the relay attenuator purely because it was more interesting to build.

But I think quite a few people would disagree with you about a PGA2310 and opamp sounding better than tube stage and pot!
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Old 9th September 2010, 08:04 PM   #4
Leon08 is offline Leon08  Germany
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I recomend this here RelaiXed -- Balanced pre-amplifier
if you want something special.
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Old 9th September 2010, 11:00 PM   #5
maxw is offline maxw  United Kingdom
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Quote:
Originally Posted by Leon08 View Post
I recomend this here RelaiXed -- Balanced pre-amplifier
if you want something special.
Yeah I've seen this design, its very good. My attenuator is pretty much the same schematic (also same as the Joshua Tree and Jos van Eijndhoven's work) except mine has double the amount of steps and its not balanced. I don't have any balanced equipment and I've never had any hum or interference so I don't really see the point of it. Mine also uses smaller relays and all SMD parts. I'll post schematics and layout soon!
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Old 13th September 2010, 02:11 AM   #6
wabun is offline wabun  United States
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Quote:
Originally Posted by Leon08 View Post
I recomend this here RelaiXed -- Balanced pre-amplifier
if you want something special.
I tried this, but it has bug, the rotary enoder need to debounce by 1uf capacitor
and the decrement has inconsistant result..
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Old 14th September 2010, 01:33 PM   #7
maxw is offline maxw  United Kingdom
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Here are some pics of the PCBs
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File Type: jpg IMG_6231.JPG (46.9 KB, 2683 views)
File Type: jpg IMG_6239.JPG (50.1 KB, 2601 views)
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Old 14th September 2010, 01:35 PM   #8
maxw is offline maxw  United Kingdom
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Some of the features are:
I2C controlled using an MCP23008
The I2C address can be set using small DIP switches
Surface mount components for shortest possible signal path
PCBs are small (100 x 50 mm) and stackable
Should work as single ended or balanced (need to one per channel)
Omron G6K relays - High quality, low power, very compact with gold alloy contacts
The input selector has 5 inputs and 1 output relay for muting to stop preamp pop or thump etc.
The attenuator has 128 steps + mute.

Here is a pic of the bottom of the attenuator board
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Old 14th September 2010, 01:36 PM   #9
maxw is offline maxw  United Kingdom
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Quote:
Originally Posted by wabun View Post
I tried this, but it has bug, the rotary enoder need to debounce by 1uf capacitor
and the decrement has inconsistant result..
That's a shame!

I'm working on my arduino code now but so far it just seems so easy! I'll post results soon.
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Old 15th September 2010, 11:06 AM   #10
qusp is offline qusp  Australia
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watching with interest. so has both attenuator and selector yes? or this is separate functionality from same board? will you have PCBs? I do not need tube stage, only balanced selector and attenuator, with buffer (I will just use IC or discrete diamond buffer)
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