Max

If you can't find spare boards then you could just add a 4th layer (like just duplicate the middle layer) then you could get new boards made quickly and cheaply at a place like https://oshpark.com Otherwise 3 layer is less commonly available and you might have to go to a more expensive PCB manufacturer.

The AMB attenuator is pretty good: http://www.amb.org/audio/delta1/ I've used the PGA2310 and the PGA2320. They are pretty good but I can never get them to be quiet, there always seems to be some noise.

Got mine today, thanks Kerry!

You can use pretty much any encoder with an Arduino. The code already posted will work with all "Incremental" encoders that are "2 bit Gray Code" or "2-bit quadrature code", such as the one linked to above. I do recommend going for a higher PPR (pulses per revolution) or CPR (cycles per revolution) as possible because this attenuator has 256 steps, so at 24 PPR you will need to rotate it many times to go from 0 to 256. Also, you get what you pay for, a cheap encoder will feel cheap and they can sometimes jump around between steps. If you want to splash out, I have both of these and they are really nice: http://ca.mouser.com/ProductDetail/Bourns/EM14R0D-M20-L064S/?qs=sGAEpiMZZMsWp46O%252bq11WaOTWrP7dyXBueE8zSLmq%252bw%3d http://ca.mouser.com/ProductDetail/Bourns/ENA1J-B28-L00128/?qs=sGAEpiMZZMsWp46O%252bq11WcqwRcNrfIIZ3fHa2t9hjOc%3d

Amazing work Kerry, much appreciated! Can't wait for it to arrive now.

Sweet, Paid. I included a bit extra as the paypal fee would be more with the extra postage.

OK I'll go for a single complete assembled board (I don't have any balanced gear). Does that $97.21 include the relays or is it just the board and resistors? ICs? Also, I clicked the USPS link but not sure how to calculate cost of shipping to the UK

I had this problem too. I actually settled on 24K to get closest values using Vishay SMM0204 range of resistors from Mouser but I bet you US folks have a better range to choose from.

Perhaps the process of exporting to PDF messes with the clearances? It looks like some clearances are inconsistent, example attached!

They look amazing but foil resistors are usually really expensive, for example: http://uk.farnell.com/vishay-foil-resistors-vpg/s102c-20k000-0-01/resistor-metal-foil-0-6w-20k/dp/1692579?Ntt=1692579

So you will have pads for both? Nice! That will depend on what people are using for sources and whether they are happing driving 10K. Folks could always use an input buffer though, or buy their own resistors! This calculator is handy for calculating values: http://www.amb.org/a.../delta1/r2r.cgi

And here I am! My code is here: http://nospecifictop...eamp-relay.html Feel free to use it! I don't claim to be good at coding though, I just learn enough to get what I need done. That was by design, not a mistake Interesting project! I'm curious why you chose that resistor package? Isn't it hard to get all the values right from the same range and make? I used 1206 sized which also fits MMA0204 (both pretty common) and it was still tough to get the right values all within one range/make! I settled for +/-2.5% of the correct value using 1% metal film resistors: Also someone mentioned using thick film resistors, wouldn't metal film be a better choice?