[patricksalter]

I've recently had something come up where I need to power some speakers from an audio interface using Balanced XLR outputs.  I already have speakers that will do a perfect job for this task, but I need an amp to drive the speakers.  I have already ordered a couple of the TDA7297 based amps, and already have some of the capacitors to to upgrade them.  But I'm not sure this plan will work, because I was just thinking I would use an XLR - RCA cable to connect them.  However, something tells me I'm in for a world of hurt, dealing with hums, level issues, etc.  So, I would like to start looking into a plan B.  My needs are pretty straight forward for this amp: Balanced XLR input.  Mono is preferable if the price is low enough.  I'd love to be able to drive them off of batteries but that's not a requirement.  Trying to keep the budget ultra low, as this would be a temporary solution, hence posting this to the Cheap and Cheerful circle.   

I should also say that if somebody knows that a simple adapter from XLR to RCA to connect the source to the amp without issue, that would be ideal, as I've already ordered the amps. 

Thanks in advance. 

Patrick

[CurtisIIX]

I would be more worried about level issues than hum. However, the audio interface's routing software may be able to set the output to consumer level "-10 dbV". I know that my RME FireFace can do this with the TotalMix FX software.

For the balanced XLR output to unbalanced RCA input, I doubt you can get any common-mode noise rejection unless you use a pricey transformer on the RCA input side.

For cables, Benchmark Media recommends a shielded twisted-pair cable with XLR-female (pin 3 floating) to RCA.  I don't exactly know if/how this works better than an XLR to RCA adapter on the output side and using a regular RCA coaxial interconnect. Maybe someone else could chime in.

An alternate amplifier board would be a TPA3116 in BTL mode. There are some red boards on eBay from China for < $10. These boards have +/-/GND input connections. I don't think any of the Parts Express TPA3116 boards are configured this way, but maybe they could be modified if you are willing to look at datasheets and do some soldering.

[patricksalter]

Hi CurtisIIX, thanks for the feedback, very helpful.  The audio interface is an Apogee Ensemble Thunderbolt (I should have mentioned that).  It can output  +4dBu or -10 dbV, which makes me think my original plan, based on your feedback, may actually work. 

As far as looking at datasheets and soldering, that's exactly what I want to be doing.  Being stuck at home thanks to the pandemic, I'm all for the whole "roll up your sleeves and DIY" approach to this project. 

[Speedskater]

If you are building an amplifier and it has a ±15V DC supply, all you need is a THAT Corp op-amp for a balanced input.

[poseidonsvoice]

If you are building an amplifier and it has a ±15V DC supply, all you need is a THAT Corp op-amp for a balanced input.

Indeed, I use the THAT1200 quite a bit. When properly implemented (per the datasheet), it is sonically transparent. I use Tom Christiansen's THATRX designs when he still had them (you can search on diyaudio to see if anybody is willing to sell the boards). Tom's current Universal Buffer is a completely new design using the latest SMD's, fully built and has multiple options. The Universal Buffer is the best measuring unit of this type I have ever seen and several fellas are astonished by its performance as well.

Ti Kan's AMB Alpha 24 boards are available for full diy builds as well. I also have those boards, and they are also excellent.

The documentation provided by both of these fellas are very well done. From a subjective standpoint, I find them to be sonically transparent compared to transformer implementations by Lundahl, Cinemag or Jensen.

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

https://www.diyaudio.com/forums/vendor-s-bazaar/346956-universal-buffer-achieving-140-dbc-0-00001-thd.html

https://www.amb.org/audio/alpha24/

Best,
Anand.

[patricksalter]

Thanks for the input guys.  I think Im going to go with the AMB's b24 build.  This seems like the perfect solution for me. 

Indeed, I use the THAT1200 quite a bit. When properly implemented (per the datasheet), it is sonically transparent. I use Tom Christiansen's THATRX designs when he still had them (you can search on diyaudio to see if anybody is willing to sell the boards). Tom's current Universal Buffer is a completely new design using the latest SMD's, fully built and has multiple options. The Universal Buffer is the best measuring unit of this type I have ever seen and several fellas are astonished by its performance as well.

Ti Kan's AMB Alpha 24 boards are available for full diy builds as well. I also have those boards, and they are also excellent.

The documentation provided by both of these fellas are very well done. From a subjective standpoint, I find them to be sonically transparent compared to transformer implementations by Lundahl, Cinemag or Jensen.

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

https://www.diyaudio.com/forums/vendor-s-bazaar/346956-universal-buffer-achieving-140-dbc-0-00001-thd.html

https://www.amb.org/audio/alpha24/

Best,
Anand.