Eight Channel Differential Receiver

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atavacron

Well-known member
Joined
Jan 28, 2009
Messages
126
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.)
 

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MidnightArrakis

Well-known member
Joined
Sep 25, 2015
Messages
106
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: THAT Corporation 1240-series Balanced Line Receiver ICs

(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.)
GREETINGS!!! --- I actually replied to your posting around 12-hours ago (my time) and I am just now finding out that my reply didn't post here!!! So, that's a first!!!

I am - NOT - a circuit designer by any stretch of the imagination, but I - AM - an "electronic equipment designer", so perhaps I may be able to assist you in your endeavor here. All that I need from you is 1) A fully completed and finished schematic, 2) either a Digi-Key or Mouser "BOM" file and, 3) either a nicely drawn hand-sketch and/or a highly-detailed written description of what you are looking for mechanically. From there, I could design both the mechanical chassis or enclosure - AND - the PCBs necessary for your project. Sound like a plan???

I am guessing that a 32-Channel unit would require at least a 4U rack-chassis and that amount of rack-space would be primarily just for the connectors. I could design a "Surface-Mount" PCB if you are looking for something that would be fabricated in multiples of, or I could design a "Thru-Hole" PCB of the same thing, if you would want to offer this item as a "kit" for DIY'ers to build for themselves.

I am not completely clear in my understanding of what it is that this unit accomplishes, but I am guessing that it takes balanced XLR-inputs and converts it over to either unbalanced 1/4-inch phone-jack and/or RCA-connector outputs. Maybe??? Or, how about balanced XLR-input over to a DB-25 connector where you then use a "DB-25 to 1/4-inch" breakout snake cable instead? My "ancient" MACKIE SDR-24/96 Digital Recorder has 3 DB-25 connectors on its rear-panel (24-Channels) where I have connected 3 "DB-25 to 1/4-inch" breakout snakes that feed 24 or the 32-Channels on my MACKIE 32*8 console. Just a thought!!!

[Two ground planes would be nice] -- This can be accomplished by either using 2 "Copper Pours" on the outer-layers (i.e. TOP and BOTTOM) or (and, be more of a "true" GROUND PLANE), they could be 2 inner-layers.....creating a 4-layer board. However, if going that route, then it would actually make more sense to place all of the routing on the inner-layers and the 2 GROUND PLANES on the outer-layers. I have done this lots of times for "RF" PCB layouts.

[there could be a little double-throw DIP switch next to each IC to make things easy] -- Or, a couple of "header-jumpers" next to each IC. Since these parts are - almost - a "set and forget" item, then using "header-jumpers" would be cheaper than DIP-switches.

[using a metal or nylon standoff at one corner] -- I have certainly seen this done before, but.....it is basically a one-time "either/or" thing. Meaning, you either use "this" or "that".....PERIOD!!! There is NO going back to change it to the other later on. However, the alternative would be to use a metal standoff that is connected to the PCB by means of an isolated pad and then it is connected to CHASSIS GROUND or not by using another "header-jumper". Then, if there is a hum and/or ground-loop problem, you have the choice of connecting the chassis to your GROUND PLANE or not through the "header-jumper".

So.....your task Mr. Phelps, should you accept this mission.....is to completely design a working schematic that accomplishes the task as you wish for it to operate - AND - to create either a Digi-Key or a Mouser "BOM" that will also be used as the basis for all of the PCB footprints. And, of course.....should you be caught red-handed swapping out IC's in your circuit.....your entire existence will be disavowed forever!!! This message will self-destruct whenever the entire Internet ceases to exist!!!

Keep me posted, OK???

Some Of My Equipment & Systems Designs

Specific Rack-Mount Equipment & Rack-Systems Designs

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atavacron

Well-known member
Joined
Jan 28, 2009
Messages
126
Thanks all. I've moved on from this project actually. And in the intervening time JLM has released the Palpigrade (as Ian noted), which would certainly do the trick.
 
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