PCB for differential line input

I'm wondering if there's anyone out there selling small PCBs for a "standard" differential/balanced line input circuit.  I know the real answer is "make your own", but I'm not really fluent with PCB design software yet, and it seems like the kind of thing that's gotta exist already. I need something designed for a single op amp (OPA604 to be specific), and something that is physically small.

Any ideas? I could always do it on strip board but I'll need many of them so a purpose-made board would be nice...

I could design this board for you if you need something small and a bunch of them. Send me a pm with the size, quantity, and circuit you want. Or I can just use the big standard one.

Sounds like your requirements may not be general purpose enough....the simplest way to do this is with a that balanced line receiver.

JLM audio do one. I think it is called the Dingo pup or something like that.

https://www.jlmaudio.com/shop/small-interface-kits.html

Cheers

Ian

Matt C said:

I need something designed for a single op amp (OPA604 to be specific), and something that is physically small.

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Is there a reason you need to do it with a single opamp? (besides space).  It will be suboptimal in terms of CMRR and noise compared to a single chip balanced line receiver like the THAT 1200 series - http://www.thatcorp.com/1200-series_High_CMRR_Balanced_Line_Receiver_ICs.shtml

ruairioflaherty said:

Is there a reason you need to do it with a single opamp? (besides space).  It will be suboptimal in terms of CMRR and noise compared to a single chip balanced line receiver like the THAT 1200 series - http://www.thatcorp.com/1200-series_High_CMRR_Balanced_Line_Receiver_ICs.shtml

Click to expand...

I was going to suggest the DIYRE 12xx etc board. DIYRE have discontinued it but the pcb is available as per link on their website:
https://oshpark.com/shared_projects/HDKs6y9c

ruffrecords said:

JLM audio do one. I think it is called the Dingo pup or something like that.

https://www.jlmaudio.com/shop/small-interface-kits.html

Cheers

Ian

Click to expand...

The Dingo Pup seems to be 'both ways' so maybe more than the OP is looking for although he may also need the Output ?

Was going to suggest SSM2141, Elektor did an article on these. It is likely they have a THAT equivalent (as the balanced driver SSM2142, is the same as THAT1646 and DRV134, I am assuming there are pin compatible equivalents for the receiveing end as well).

It will be powered with +-24VDC.  I haven't found any monolithic line receiver chips that can handle that high of a supply voltage. That's why I'm planning on using the OPA604. I only need the input/receiver circuit but if I found a really easy/cheap solution maybe I'd do the outputs too.

ruairioflaherty said:

Is there a reason you need to do it with a single opamp? (besides space).  It will be suboptimal in terms of CMRR and noise compared to a single chip balanced line receiver like the THAT 1200 series - http://www.thatcorp.com/1200-series_High_CMRR_Balanced_Line_Receiver_ICs.shtml

Click to expand...

You can add some local regulators to your PCB to take the ±24 down to something more sensible like ±17V. Otherwise, you are limited to exactly one IC suitable for audio with ±24V.

Monte McGuire said:

You can add some local regulators to your PCB to take the ±24 down to something more sensible like ±17V. Otherwise, you are limited to exactly one IC suitable for audio with ±24V.

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I thought of that idea, but I need to do this on 24 channels.  Doing local regulators on each channel seemed like overkill, and probably ends up being just as complicated (and maybe taking up more space).  The THAT chips might be "better" but I don't think I'd notice the difference.

There are some projects that used opamps for a receiver, GSSL perhaps? A bit of copying and pasting might be viable to make boards.

john12ax7 said:

There are some projects that used opamps for a receiver, GSSL perhaps? A bit of copying and pasting might be viable to make boards.

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Plenty of older gear used a single IC, the reasons not to are well documented but the lower performance may well be good enough as per the O.P.

A question for the group, I've seen people use diode drops to lower +/-18V rails to +/-15V.  Is there a reason we couldn't use a few LEDS to drop the 4V from 24V to 20 for some THAT 1200s?

ruairioflaherty said:

Plenty of older gear used a single IC, the reasons not to are well documented but the lower performance may well be good enough as per the O.P.

A question for the group, I've seen people use diode drops to lower +/-18V rails to +/-15V.  Is there a reason we couldn't use a few LEDS to drop the 4V from 24V to 20 for some THAT 1200s?

Click to expand...

Entirely my subjective opinion, but I've found that sometimes the all in one receiver chips aren't necessarily the best sounding for a given application.

For the voltage drop another option would a single diode for directionality (not entirely necessary) and then an appropriate zener.  With either approach I would think they would work fine provided you get the supply impedance low from the opamp perspective.

ruairioflaherty said:

A question for the group, I've seen people use diode drops to lower +/-18V rails to +/-15V.  Is there a reason we couldn't use a few LEDS to drop the 4V from 24V to 20 for some THAT 1200s?

Click to expand...

The problem with all op amps is their current draw is signal level related. Series LEDs would probably end up flashing in time to the music (cool?) and a zener would have to draw the expected maximum current when then the op amp is idle. A small fixed current zener plus an emitter follower might work.

Cheers

Ian

john12ax7 said:

For the voltage drop another option would a single diode for directionality (not entirely necessary) and then an appropriate zener. 

Click to expand...

You'd need a series resistor in there too.

ruffrecords said:

The problem with all op amps is their current draw is signal level related. Series LEDs would probably end up flashing in time to the music (cool?) and a zener would have to draw the expected maximum current when then the op amp is idle. A small fixed current zener plus an emitter follower might work.

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re LED voltage drop - There might also be a problem with the current required since LEDs tend to have lower current ratings than standard diodes.

Matt C said:

I thought of that idea, but I need to do this on 24 channels.  Doing local regulators on each channel seemed like overkill, and probably ends up being just as complicated (and maybe taking up more space).  The THAT chips might be "better" but I don't think I'd notice the difference.

Click to expand...

Can you regulate the +/-24V down to, say, +/-17V before it gets distributed to the channels ?

Matt C said:

...I need to do this on 24 channels.  Doing local regulators on each channel seemed like overkill, and probably ends up being just as complicated (and maybe taking up more space).  The THAT chips might be "better" but I don't think I'd notice the difference.

Click to expand...

my suggestion: http://www.douglas-self.com/ampins/balanced/balfig9.gif (http://www.douglas-self.com/ampins/balanced/balanced.htm)  should do the trick using the 604, probably add some decoupling, have someone here https://groupdiy.com/index.php?board=13.0 create a pcb, have the pcbs made to order. It should only cost a little bit of money, it would be a really simple and small pcb.

Michael

that's what I was thinking (using the line input circuit on pg 359 of his small signal audio book). I think I'd be better off doing that than mess around with modifying the power supply

Michael Tibes said:

my suggestion: http://www.douglas-self.com/ampins/balanced/balfig9.gif (http://www.douglas-self.com/ampins/balanced/balanced.htm)  should do the trick using the 604, probably add some decoupling, have someone here https://groupdiy.com/index.php?board=13.0 create a pcb, have the pcbs made to order. It should only cost a little bit of money, it would be a really simple and small pcb.

Michael

Click to expand...

Michael Tibes said:

my suggestion: http://www.douglas-self.com/ampins/balanced/balfig9.gif (http://www.douglas-self.com/ampins/balanced/balanced.htm)  should do the trick using the 604, probably add some decoupling, have someone here https://groupdiy.com/index.php?board=13.0 create a pcb, have the pcbs made to order. It should only cost a little bit of money, it would be a really simple and small pcb.

Michael

Click to expand...

That's the basics of the circuit . But you need to add decoupling as advised. Also consider whether you want a small resistor in the voltage lines to give RC filtering and Short Circuit protection for the supply if needed (Use non flammable NFR resistors). Also if you need overvoltage protection on the inputs. Any rfi countermeasures ? And, of course, the connection type detail...