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maxw 9th September 2010 01:58 PM

My Preamp Project: Arduino, I2C, relay selector+attenuator, tube stage
 
1 Attachment(s)
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.

Leon08 9th September 2010 02:54 PM

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.

maxw 9th September 2010 03:01 PM

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!

Leon08 9th September 2010 07:04 PM

I recomend this here RelaiXed -- Balanced pre-amplifier
if you want something special.

maxw 9th September 2010 10:00 PM

Quote:

Originally Posted by Leon08 (Post 2298009)
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!

wabun 13th September 2010 01:11 AM

Quote:

Originally Posted by Leon08 (Post 2298009)
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..

maxw 14th September 2010 12:33 PM

3 Attachment(s)
Here are some pics of the PCBs

maxw 14th September 2010 12:35 PM

1 Attachment(s)
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

maxw 14th September 2010 12:36 PM

Quote:

Originally Posted by wabun (Post 2301177)
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.

qusp 15th September 2010 10:06 AM

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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