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digital attenuator


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Like i don't have enough projects going on at once :D

I'm tired of waiting for someone to release boards that do this right.

so here is mine in progress

http://gilmore.chem.northwestern.edu/attenuator2.jpg

Because i don't like any standing power on the relays, and i don't

like the resistive drive either, this had to be a bit bigger.

board is 3.4 x 10 inches.

stereo single board, or two for balanced.

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I found these (TX2SA-LT-5V-TH) SMD relays on Mouser. They are au+ag plated, dual coil latching relays and consume about 140mW, but only when switching. Not sure if you are interested, but could possibly do something using both sides of the board.

I know what you mean about too many projects :)

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I wouldn't be surprised if someone requests a position for a regulator to drop the 5v to 3.3v.

i'd certainly love an on-board 3.3v regulator. given how many practical preamp and dac uses there are for 5v, such an addition would save the trouble of adding in yet another little pcb

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Not going to happen. Managed to take .5 inch by getting the relays as

close together as possible. All the other relays are the same exact

physical size whether they are surface mount or not. Each relay

is 20mm width. I doubt i can rotate the relays, but will see.

If i rotate the relays, by the time i locate the resistors, there would

be virtually no benefit.

here you go on the tightest fit i can get.

http://gilmore.chem.northwestern.edu/attenuator3.jpg

Edited by kevin gilmore
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Thanks for looking at this. I know this is getting crazy now, but what if you flipped every other relay to the opposite side of the board and pull it in by .25". The resistors would then be spaced evenly. I agree that less people would be able to do this by hand.

EDIT: You can keep the signal path same as now if you also switched the pins on the flipped relays.

EDIT2: It might not be doable, but would be nice if it could be mounted inside 2" x 1" channel. Could probably do 2 1/2" x 1", but not sure about the control end.

Edited by Kerry
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latest

http://gilmore.chem.northwestern.edu/attensmt3.jpg

now what i could do is have 4 relays in series

then flip the other 4 relays to the back of the board.

That way the inputs and outputs are on the same side.

It would absolutely have to be a 4 layer board.

Not such a bad thing.

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I'm basing it on the total cost. If Kevin can put half the relays on the other side of the board, it would put the board somewhere around 10 sq. inches. I'm guessing you could do that for about $20 per board (so $40 balanced). The rest of the parts will cost much more by comparison.

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pretty good guess. This is exactly 5 inches x 2 inches x 4 layers.

not done yet, but the rest should be easy. My eyes hurt.

Ground planes both sides. All audio in and out on the one side.

http://gilmore.chem.northwestern.edu/attensmt4.jpg

Edited by kevin gilmore
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My eyes hurt just looking at it and trying to translate the two-sided-ness. :blink:

The original design had a nice symmetry to it.

I really like how the collective around here helps morph KG's designs

into advanced things of wonder. Brainstorming works!

Edited by livewire
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Now that is beautiful! :D

Thank you.

It would be nice if you could use some sort of ribbon cable on the digital side to connect it.

You can either mount them one on top of the other or two boards vertially depending on the spacing requirements. It seems that we can figure out a way to have this fit a T2, etc.

Do you see any value in trying to mount inside some aluminum channel?

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Alrighty then, now an even bigger headache

http://gilmore.chem.northwestern.edu/attenuator4.jpg

just barely room for the 4 mounting holes, unless i make

it bigger can't put mounting holes by the digital stuff.

No room for on board 3.3V regulator.

someone check for accuracy, the individual layers

http://gilmore.chem.northwestern.edu/attenuatorsmt5.pdf

Board is exactly 5 inches x 2 inches and 124 holes.

50 boards are $11.28 each plus $200 tooling charge from pcbnet.com

So about $15.28 plus shipping, someone else should do this so as

to avoid the 11% illinois state and local taxes.

I could change the digital connector to a 10 pin ribbon with each

pin doubled up.

I'm pretty sure this will in fact fit into the T2.

Need simplified single pot thing like the twisted pear to control

it for this application. This exercise is left to the viewer.

Edited by kevin gilmore
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