DIY Impedance Jumper cable

Hey all,

So I am wanting to make a jumper cable for a ribbon microphone. I worked on an SSL Duality that had a 10k High Impedance option for the micpre amps and LOVED it on ribbons.

Most mic pre amps are around 1.2k-2.5k though. I know this should be relatively simple to make happen. But I am new to the idea of it.

I don't want it to pad the signal, just change the impedance of the input on the Preamp. Similar to what the CL-Z Cloudlifter does.

I know Peterson used to make a kit like that too but it was 200-1k Ohms. I want something that will kick up the impedance to around 10k.

Near as my light searching can find i just need 3 resistors to do this? or am I wrong and just need 2, one on each signal wire in series?

impossible.  requires a mod to the preamp, if even possible.  anything else IS a pad. 

Impossible is right. You can put two resistors in series with the mike, 4300 ohms let's say, but the thermal noise (hiss) from those resistors will be stupendously large. And, you'll lose around 20dB of level. You won't notice the subtle improvement of your now higher load impedance.

Thanks gents.

So then i am curious. How does the CL-Z work then?

Blackdawg said:

So then i am curious. How does the CL-Z work then?

Click to expand...

"The Input amplifier is based on the circuit developed for the 'Classic Channel' with the addition of a High Impedance (10K) mode coupled to changing the impedance of the 20dB input PAD"

http://sslweb.solidstatelogic.com.s3.amazonaws.com/content/Duality-Delta/pdfs/docs/Duality_Drawings.pdf

[silent:arts] said:

"The Input amplifier is based on the circuit developed for the 'Classic Channel' with the addition of a High Impedance (10K) mode coupled to changing the impedance of the 20dB input PAD"

http://sslweb.solidstatelogic.com.s3.amazonaws.com/content/Duality-Delta/pdfs/docs/Duality_Drawings.pdf

Click to expand...

Thanks! that makes sense there.

However..

did this mean when Hi-Z was enabled that a 20dB pad was put on? I never had the pad switch on on our Duality and you could hear a very clear difference by just pressing the Hi-Z button.

And i guess my other question is how does this guy work then? Or is it just modifying the microphones output impedance really?  Or is it because it itself is active it can change the load that that microphone sees but has it's own output impedance the mic preamp sees as normal?

https://www.sweetwater.com/store/detail/CLZCloud

Thanks for the replies!

Blackdawg said:

Thanks! that makes sense there.

However..

did this mean when Hi-Z was enabled that a 20dB pad was put on? I never had the pad switch on on our Duality and you could hear a very clear difference by just pressing the Hi-Z button.

And i guess my other question is how does this guy work then? Or is it just modifying the microphones output impedance really?  Or is it because it itself is active it can change the load that that microphone sees but has it's own output impedance the mic preamp sees as normal?

https://www.sweetwater.com/store/detail/CLZCloud

Thanks for the replies!

Click to expand...

  That's a phantom preamp, kind of converting a passive mic to an active one, some gain before the preamp. For the impedance control, you design a an amp with high input impedance  and then shunt the input with a pot that changes is in a certain range. Then add a HPF with a switch and change the gain of the circuit with another and you are good to go.

  If I had to guess I'd go with something like this, R6 and R7 would be the phantom feeding resistors on your preamp, forget about R1B and R3, R13 and greater plus the OPA is your mic pre. You can harvest some voltage at the bottom for the biasing and use a current source there or just go with a well selected resistors as R8 and R9 and avoid the "negative rail" all together. R1A and R2 would increase the gain as it decrease in value.



JS

My Shure 565SD, a dynamic mic, has an impedance selector jumper that seems to do exactly what the poster was asking. SM57 and 58 also came with the same Z jumper, but that stopped at some point and now they're all low Z. When you set the mic to high Z and hook it to a low Z mixer, the volume level goes up, by a lot. I see a lot of people saying there's no way to up the impedance without padding the sound, but Shure seemed to do it in that dynamic, resulting in the opposite of a pad.

And yes, so much magnetic interference.