Differential Input Module For My Analog Audio Test Gear

[grievousangel]

Due to external noise riding on my test leads and in general, I'm looking for external Diff Input Modules designed for low voltage analog audio applications. Many are very expensive. So I am looking kits and or ideas to build one. Signal levels range from ~ -70db to +4 to +24db. Typically I measure the resulting minimum CM noise for the adjustment procedure, like in 2-stage DOA line amps. My Pico USB scope is purpose built for audio analog precision low level signals, but only as single-ended input leads. I would also use the diff lead set for my precision RIGOL Benchtop DMM.

TI offers a kit version of an Instrumentation diff op amp design. You furnish all components (including a bipolar power supply (+/-16VDC) except for the TI PCB w/ surface-mount components mounted. It can be upgraded as well.

Anyone have suggestions or links?

Later, Billy

 

[radardoug]

Just buy a really good transformer.

 

[Bo Deadly]

I would make a PCB for a THAT1200 with solder jumps for different configs and pads in / out or mill max pin sockets so that you can insert some through hole resistors (parallel for precision) to make different pads.

Inevitably you will want different configs like sharing 0V or not for different scenarios like for a mic vs a guitar input.

The key to it all will be to make a power supply that is genuinely really good and quiet (which is a lot harder than most people think).

A transformer certainly has it's advantages in that it provides total DC isolation and does not require power.

But, in theory, the 1200 should actually perform better with bandwidth, THD, high frequency CMR, etc. If the power supply is truely great, the noise level might be comparable.

This is the sort of thing I could spend a month fiddling with though.

 

[fazer]

Some answers in this thread

Simple unbalancing and balancing line amp

Look at the Spark fun for low cost.

Hard to beat a bridging Jensen transformer.