Questions & Answers

Silly question regarding mic. inputs on Presonus (and other's) mixers ?

+1 vote
asked Apr 27, 2018 in StudioLive Series Feature Requests by neilgledhill (230 points)
My Presonus RM32ai (and modern mixers from most vendors) presents a 1kΩ impedance to microphones. This makes it difficult to get a decent sounding signal from a dynamic mic.

i use the RM32ai both live (it's a handy light weight small rack case) when i want to record the performance and in the studio as a great sounding and easy to use I/O device.

Where i came across this problem was many years ago, trying to use the first pro mic i bought (a 1958 AKG D-12). It didn't sound right, i thought the magnet was wearing out with age so thought no further about it.

Later, having built a transformer-based step-up (using one of the Hammond 560's) things were improved, but not completely. The transformer worked perfectly but i was trying to match 200Ω into 600Ω when the actual load was 1000Ω.

Blah blah blah.

Back in the '70's and '80's, the standard mic input was 600Ω (centre-tapped, 300-0-300). Even back then it was wrong. Look at the tech spec sheet of the excellent old Shure SM57. It wants to see an impedance between 150Ω and 310Ω. The newer Beta 57 wants to see the same. My old D-12 wants 200Ω, my newer SE R-1 wants 100Ω.

i appreciate this circuitry was designed by youngsters trained in the earlies - higher impedance gets higher volts from source. However, this is not taking into account the mechanical, magnetic and electrical demands of the source. The whole doesn't work properly unless you are drawing enough current from the electrical bit.

Is it possible to lower the mic input impedance of the RM32ai ? Without invalidating any warranty ?

Silly question, Neil xx.

1 Answer

+1 vote
answered Apr 28, 2018 by AlexTinsley (735,370 points)
Best answer
Thanks for the detailed explanation, I'm sure others will find it very informative.

To answer your question, no it isn't something that can be easily changed.

The Input Impedance is fixed at 1K Ohm. You would void your warranty.

I have sent your question to the product team for consideration for future product designs.

Going to move this to feature requests.