Topic: Replace XLR with TRS

[Roger Gustavsson]

As I want to shrink my equipment, I am searching for a replacement for the large XLR connectors. Tested some 3.5 mm TRS (Tip Ring and Sleeve) like these:


There will be a short during inserting between left and right channels if you have a balanced connection. What happens if it is a 3-wire battery box like this? Will it hurt the electronics?


Roger
 

[Roger Gustavsson]

So it seems that I can use TRS connectors with this:


Here is the complete schematic of the preamp:




Of course, there should be a capacitor inside the microphone from +9V to ground in order to remove unwanted noise pickup.


Roger

[Chuck]

Cool, Roger. So, you are looking at running three wires to each mic now?
I'm very happy with the solution Jon made for me. I *lost* one of the PFA cables Jon made for me at Roger Clyne and the Peacemakers on Wednesday night. I was sick over it. So, I went back to look for it yesterday at the venue. Lucky me, I found it in a tangle of wires next to the SBD.

About the switch from the 1.2k to 4.7k resistor. I know it is supposed to make the mic be able to handle more SPL's without distortion. Ala Chris Church mod. But, doesn't it also cut the output some?

[Roger Gustavsson]

You can add a cap in the mic, the but the cap in your battery box is probably sufficient. 

By the way, it would be mighty tempting to mod that preamp by hanging a supply resistor (say 4k7, for a modest amount of gain) off the power rail to meet the incoming signal wire at the R101/C101 junction.  Next, wire the capsule as 2-wire (omit the signal wire from 2SK118 source). Then you wouldn't need a battery box

There are no battery box! The idea is to use the 10V already present in the mic preamp. Now, this preamp have 2 pole (mono) jacks that I would like to replace with 3 pole (stereo) jacks.

The original schematic of the microphone but without the balancing transformer and low cut switch is like this:

About the switch from the 1.2k to 4.7k resistor. I know it is supposed to make the mic be able to handle more SPL's without distortion. Ala Chris Church mod. But, doesn't it also cut the output some?

Chuck, this is just a typing error of mine. It is 4k7 in the schematic from Primo (the manufactor of the Nakamichi microphones). I think 4k7 would raise the output by about 3 dB and raise the output impedance too.

Maybe this could work too? At least it would improve the cable driving.





Roger

[Roger Gustavsson]

That's not a great idea with a supply of +1.5V, which these mics were designed for. 

No, they used 9V in the Nakamichi CM-300. The CM-100 used 1.5V and that drops the maximum SPL by 20dB. This can easily be corrected just by using a different battery in the CM-100. The CM-300 came with two capsules, omni and cardioid. The CM-100 with only cardioid.

Roger

[Roger Gustavsson]

I have converted my microphones like this:


As my mic preamp have a suitable supply voltage, I could then use it in place of a battery inside the microphone (but my chopped barrels still have room for internal batteries). The enclosure of the preamp is heavy and too large. It can be replaced by a far lighter and smaller one that can take a couple of batteries inside. All this just because I have these items! 

I am also playing with other ideas. That extra buffer is/was one of them. JFET vs. BJT, I was adviced by two Gurus, Erno Borbely and Scott Wurcer, that a JFET would be preferable because of its lower current noise. I am only a layman in electronics....     

I think we will have to discuss electronics in another thread. 


Roger