[ProAudio] Transformer color revisited -- DC injection

[Bob Katz]

Thanks very much, Bill!

I'll post measurements when I'm done.



Best wishes,



Bob



On 7/22/23 2:00 PM, Bill Whitlock wrote:
> First, you'll get a lot more "effect" from el-cheapo transformers 
> (smaller cores) rather than better ones like the 111's.
>
> Second, the chances of any significant remanent magnetization depends 
> on many things. Higher DC current increases risk, of course, but 
> technically the width of the BH loop of the core material also has a 
> huge effect.  In general, steel has the widest and high-nickel alloys 
> (like Permalloy) have the narrowest. But then you may like the sound 
> of a magnetized core. It will have stronger even-order harmonics than 
> odd, which normally predominate.
>
> Cores can be demagnetized by driving them into saturation with AC and 
> then slowly reducing the AC amplitude to zero (over a period of 15 to 
> 30 seconds). Cores will, of course, saturate with the least voltage at 
> very low frequencies, say 10 or 20 Hz.  Only one winding need be 
> driven and you can tell you've reached saturation by looking for 
> flat-topping of the voltage output at any other winding. Always check 
> to be sure the driving source isn't clipping when you think you've 
> reached the saturation point.
>
> Bill Whitlock
> AES Life Fellow
> (from my new home in Chino, CA)
>
> Sent from the all new AOL app for Android 
> <https://play.google.com/store/apps/details?id=com.aol.mobile.aolapp>
>
>     On Sat, Jul 22, 2023 at 6:50 AM, Bob Katz
>     <bobkatz at digido.com> wrote:
>
>     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.
>
-- 

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.
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