Active ribbon-mic

[clintrubber]

before the "Boom" of cheap Ribbon Mics

Not sure when the boom was the boomiest, but when I started this thread,
Thomann was already selling several T-Bone ribbons and I thought the container with the ACM-mass-order had left a Chinese harbor as well.

 

[Whoops]

In the next days I will build a couple of XLR barrels with the PRR circuit to try out.

It's a great idea, and thanks so much PRR and everyone for sharing this information.

 

[clintrubber]

I will build 2 with the PRR circuit to try out on some Ribbon mics.

After so many years that PRR showed the circuit is there anyone with some tips or improvments  over the original circuit?

I guess you'll like it as is, no changes needed despite being a circuit from a while ago.

Whether you need gain at all is of course depending on application & mic-type. Near-close micing might not need it.

 

[Whoops]

thanks clintrubber

did you build yours inside a box or an XLR barrel?

 

[abbey road d enfer]

Not sure when the boom was the boomiest, but when I started this thread,
Thomann was already selling several T-Bone ribbons and I thought the container with the ACM-mass-order had left a Chinese harbor as well.

Thank you for setting the record straight. After all, who am I to know?

 

[Whoops]

Old Thread that seems to predate the present tendencies....

Theres a lot of products in the market at the moment, did it all started in this thread?

No. FetHead and Cloudlifter started about 10 years ago.

Hi Abbey,
this thread started 14 years ago.

You were wrong Abbey,
there's no problem in admiting that and moving on...

 

[abbey road d enfer]

You were wrong Abbey,
there's no problem in admiting that and moving on...

What's my mistake? Saying about 10 years ago, when it was 14 actually. When you're as old a sme, 4 years is nothing.

 

[Whoops]

What's my mistake? Saying about 10 years ago, when it was 14 actually. When you're as old a sme, 4 years is nothing.

No need to go around in circles without setting the record straight.


I said this thread predated FetHead and Cloudlifter and similar products on the market (you were quick to disagree), but
is that a fact or not?


Is it possible that some of those products took inspiration of this thread started by clintrubber and PRR's circuit?
It's also possible that some of those products are actually just PRR's circuit?

there's reports of that:

"The cloud lifter was just lifted from PRR's FET version created here years ago...
I cracked one open and felt a little stupid for paying 150 bucks for a differential pair. "

 

[clintrubber]

thanks clintrubber

did you build yours inside a box or an XLR barrel?

I was/am interested in this topic mainly from a technical point of view. The Royer R-122 was out then, I was curious to what would be inside.

The funny thing is, I have the parts available, including 1 or 2  early Triton Audio barrels suited for XLR that they kindly sent me.

But somewhat surprisingly perhaps, mic-pre settings for ribbon mics tend to live at low settings here, so haven't had an urgent need to boost ribbon mics so far, even not after 14 years.

So soldering iron was pointed at other stuff so far.

 

[Whoops]

I just received a Trionaudio Fethead barrel for repair.

I was amazed by the low build quality. Really awful soldering job,  bad wiring stripping, no cleaning on the pcb.
The barrel itself is also one of cheapest XLR barrel models you can buy, they just put a "tritonaudio" logo ring around it.
For 70€ I would expect at least a good build quality.

The circuit itself is just 2 FET transistors (2SK170BL) and 4 resistors.

It was not working (said the previous owner) , but I didnt even test it. I cleaned it, replaced all the wiring and soldered everything properly. Tested in the end, it's working perfectly.

It does it job well, I tested it with a SHURE SM7 microphone, it's a dynamic mic with low output, and I enjoyed the gain boost.
I didn't make any frequency response or noise measurement with or without the Fethead, maybe I will do in the future.

here's the circuit for future reference in case someone needs to repair one:

 

[clintrubber]

Aha!  :

Thanks for sharing those pics

 

[abbey road d enfer]

The circuit itself is just 2 FET transistors (2SK170BL) and 4 resistors.

Could you trace the circuit? I can't see well enough the resistor values from the pix.
I believe the 68R are the source resistors. What are the others? 22k? If so, they must be the gate resistors.

 

[Whoops]

Could you trace the circuit? I can't figure out the resistor values from the pix.
I believe the 68R are the source resistors.

I was actually just drawing it in Eagle while you posted.
I Edited the post with the circuit now.

 

[clintrubber]

Thanks for the sch.

So they swapped source & drain (shouldn't be a problem).

Nice though that they paid attention to preserving signal polarity
(by crossconnecting the XLRs to compensate for the signal inversion of the JFETs)

 

[Whoops]

So they swapped source & drain (shouldn't be a problem).

I hope that's not my mistake.
I swapped S and D in the schematic in the top FET so it could be easier to draw the 68r resistors

 

[abbey road d enfer]

I was actually just drawing it in Eagle while you posted.
I Edited the post with the circuit now.

Thanks! It's how I figured it out. I've sim'd it in LTspice; there's no 2SK170BL in LTspice, but I used LSK170A, which seems to give adequate results. Not surprizingly, gain depends very much on the mic preamp's input impedance, which does not seem to be the case with the Rode and SE units.

 

[Gus]

I wonder if the 3 pairs of parts were matched?

CMRR

 

[abbey road d enfer]

So they swapped source & drain (shouldn't be a problem).

Oops! Didn't notice that... Maybe it explains the strange noise behaviour. Although FET's are supposed to be symmetrical, it has been mentioned somewhere that the g-d junction, being polarized with a higher voltage than ususal, may create noise issues.

 

[abbey road d enfer]

I wonder if the 3 pairs of parts were matched?

CMRR

CMRR is governed by the impedance of each leg, which is determined by the phantom-feeding resistors, which are in the mic preamp, not in the Fethead.
The other components act on the voltage balance of each leg, which is not an important factor.

 

[Whoops]

Oops! Didn't notice that... Maybe it explains the strange noise behaviour.

Please simulate it the other way around also, just in case when tracing I swapped pin1 for pin3 on the transistor.