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Christian Ottow 29th January 2011 02:22 PM

Mic Preamp + Sunt Regulator a la E. Borbely
I built a six channels preamp around the E.Borbely 213 mic pre and his Super Shunt (kits are no longer online...:( ). I made pcbs to fit the mic pre & regulators on one board. Pres, relays and I+O transformers are installed in a 2HE & 450mm deep rack.
Frontpanel picture:

I set up a little website for it with a PDF containing some details here>
In case anyone is interested or has suggestions...

Thanks for this great forum. Best whishes,

Christian Ottow 29th January 2011 07:58 PM

shunt reg ...
not sunt....

johnferrier 29th January 2011 08:35 PM


Originally Posted by Christian Ottow (
not sunt....

Super Shunts for line amp/headphone amp here. Glad I put the Choke Power Supplies in a seperate enclosure because the chokes seem to emit a strong field.


Christian Ottow 29th January 2011 10:08 PM


Originally Posted by johnferrier (
Super Shunts for line amp/headphone amp here. Glad I put the Choke Power Supplies in a seperate enclosure because the chokes seem to emit a strong field.

I do not really understand how this relates to my post... :confused: but yes, I also seperated the power supply. Decided against (series) regulation before the onboard shunt regs and for a "star" point for audio power rails and grounds. In this (rare) case power ground is signal ground.
In the near future, I plan to install a cap multiplier before the shunts.

Gordy 30th January 2011 11:59 PM

You have clearly put much effort into the project, congratulations Christian.

Christian Ottow 15th April 2011 01:00 PM

Thank you very much Gordy!
Sorry for the late reply, I was travelling in India for some time.
Yes, it has been quite a task for a newbie like me.... :trapper:
The unit's technical performance is currently beeing assessed. So that the LUMUS II will improve over the existing one.

I am working on another, more compact device incorporating Erno's line/phone and mic preamps. It will be a small all fet DAW frontend. Featuring recording, monitoring, summing, phones amp and monitor controller. Stay tuned....

Thanks, regards,

AUDIODH 16th April 2011 01:04 AM

Dear Christian,
although I didn't have a chance to see the schematic. I must say the design goes beyond most anything one could purchase. I'm very impressed with your attention to detail. I have used and love the Lundahl LL1517 transformers. I've used those in past designs. The overall sound of the preamp should be very smooth and have a fairly low distortion for a transformer-coupled design (which I love). I would enjoy looking over the schematic of the entire system, if you have one to share....if not, that;s alright. Nice job on the power supply too!

Christian Ottow 19th April 2011 11:28 AM

Thanks for your reply AUDIODH! :)
Yes the LL1517 can be quite nice for tracking certain instruments.
I was investigating incorporation of the mixed feedback design in order to decrease distortion further but it turned out to be overkill for this project. Partly because the outformer can be switched in and out of the signal path.

A thourough distortion measurement has not been done yet but will happpen soon. Yesterday, we have checked for freq. response and drive capability as well as the behaviour at various input impedances....:hypno2:

Which part do you want the schematic for? The preamps are based on E.Borbely's designs . I ll have to ask him before I can post them.... Meters, relay drivers, grounding and PSUs are pretty much standard.


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