[ProAudio] Transformer color revisited -- DC injection

[Bob Katz]

Hi everyone. Hope you're still around!

I'm finally getting to finding time to build my "ultimate transformer 
color box".

Back in January, 2022, Bill Whitlock wrote:

"Yes, increasing series R on the drive side will exaggerate magnetic 
non-linearities of the core material (i.e., THD).  If you want to shift 
the mix of odd to even order harmonics, add a few mA of DC on the 
primary side (say 0 to 30 VDC through a 10 k-ohm resistor directly to 
the primary side."

My box contains a pair of WE111 and a pair of UTC A-20. Two sets of 
transformers with distinctly different saturation characteristics. It 
uses a couple of Wayne Kirkwood mastering insert relay boards to 
optionally insert a variable series resistor, and to switch in one or 
the other transformer.

Attached is a schematic for those who are interested. Simple stuff, but fun!

I wasn't planning on having a DC injection circuit, then it occurs to me 
I have a spare pair of relays. I'm trying to keep the box totally 
passive, so the question is how to handle the DC injection. We don't 
know what the source will be as it could be from any of my mastering 
gear, which is typically an active balanced output. With relays I could 
insert a large series capacitor to keep the DC injection from back 
feeding into the balanced source. block the DC injection from 
contaminating the source, plus the variable DC injection into a 
transformer primary. How does that idea sound to you?


Next question: Should I worry about the DC injection circuit permanently 
magnetizing the core of a transformer?


Best wishes,



Bob

-- 

If you want good sound on your album, come to Bob Katz 407-831-0233 
DIGITAL DOMAIN MASTERING STUDIO Author: *Mastering Audio* Digital Domain 
Website <https://www.digido.com/> No trees were killed in the sending of 
this message. However a large number of electrons were terribly 
inconvenienced.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://bach.pgm.com/pipermail/proaudio/attachments/20230722/450fe9f9/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Mastering_insert switcher ver 3.png
Type: image/png
Size: 4479139 bytes
Desc: not available
URL: <http://bach.pgm.com/pipermail/proaudio/attachments/20230722/450fe9f9/attachment-0001.png>