Eight Channel Differential Receiver
« on: June 27, 2019, 06:52:06 PM »
Has anyone thought about – or made – an 8 channel input PCB for the THAT 1200 or THAT 1240 series? I could see it being a useful tool for people making active summing mixers and small consoles and such. It would be tiny if one went surface mount. I'm not sure there's really an advantage to swapping ICs, but there is a DIP8 version of each chip, and through hole soldering would be easier for people still learning.

Currently, I need to get 32 balanced inputs into a matrix mixer. I could use four 8-input cards, and spares might be useful for other things. I am not a PCB designer, but it seems like a pretty straightforward design that would benefit folks, so maybe someone would like to collaborate. I could make a Mouser BOM, surely. The only commercial alternative is the single-channel SparkFun THAT 1206 InGenius Breakout, with a TRS that would be more of an inconvenience for most folks. Also it's $15 USD.

You're dropping the shield before you hit the card, so it would just be a 16-pin .100" header on the input, Hi/Lo x 8. Output could just be 8 x signal & the 0V reference (to which you would tie a shield), coming out to another 16-pin  .100" header. I like to keep things super obvious, thus female on the in and male on the out. Power could arrive via a 3-pin female header. Two ground planes would be nice. I like Jeff Steiger's approach to grounding/not grounding a board (as on the Inv-ACA) by using a metal or nylon standoff at one corner.

There is a recommended RFI circuit on the 1200 spec that would work on a card that was remote from the input, thus one would not have to be wiring sixteen little caps off of one's input DB-25 (or XLRs as the case may be). It is attached. I might have to check to see if the 1240 can drop in the same socket as the 1200 if that RFI circuit is in place, but there is a little sample layout in the spec that demonstrates the two series' interchangeability (and thus with the INA and SSM equivalents to the 1240) when it's just the simplest application drawn in the spec.

Also of note, because the chips can be set up for + or - gain on the 3dB and 6dB versions, and the board would want to accept all of these, there could be a little double-throw DIP switch next to each IC to make things easy.

THAT design note: http://www.thatcorp.com/datashts/dn140.pdf

1200 spec: http://www.thatcorp.com/datashts/THAT_1200-Series_Datasheet.pdf

1240 spec: http://www.thatcorp.com/1240-series_Balanced_Line_Receiver_ICs.shtml

(Sidenote, if you're wondering "Who is this person," I've been a member since 2008 but only recently got back into design. I run a recording studio.)
« Last Edit: June 27, 2019, 06:56:19 PM by atavacron »


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