Author Topic: E,G and G+ summing and E and G channels with a E or G center section  (Read 5343 times)

amillar

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Re: E,G and G+ summing and E and G channels with a E or G center section
« Reply #15 on: October 01, 2017, 12:33:46 AM »
Hi,
Sorry JJ, all my fault, I designed the "Hanger" mod in 1985 or 86 (long time ago now!) to fix a huge hum problem we had in the SWF studios in Baden Baden. It's nothing to do with the G series, Paul Frindle and I didn't mess with the bus design when we did the G series tweaks. If you're still having problems and see this message I'll try and remember how it works! I think (and I may be wrong, it's late at night and I've had a couple of glasses of wine :) ) post 1986 channels (E or G) will work in pre 1985 desks, but pre 1985 channels will need a  resistor mod to work in post 1986 desks.

It was a real bodge, the 651 (luckily) already had balanced inputs, so I routed the 'cold' side of these, which had just connected to ground, to new "balanced" mix bus "cold" lines, which were just connected with resistors near the channel strips to ground - IIRC some resistors were on the backplane and some on the channel strip. I chose the resistors to give the same equivalent parallel resistance as 8 15k resistors per bay. This basically meant that the 651 was being fed with a balanced busbar (i.e. with the same impedance to ground on both sides) which cancelled out induced magnetic fields. The fact that only one of these buses was being fed with a signal didn't matter.

Hope that helps, message me if you need more and I'll dig my manuals out and remember it in less blurred detail!

Cheers,
Andy Millar
 
co-designer and project manager G series analogue 1987
channel strip designer J series 1992-93
design "caretaker" 4000/6000 1985-93
analogue team leader ARC/Bertha 1988-92

xmax

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Re: E,G and G+ summing and E and G channels with a E or G center section
« Reply #16 on: October 14, 2017, 06:44:31 AM »
Adding a resistor to the cold side created equal impedance on both legs,
for true common mode rejection on the buss ribbons?

Druhms

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Re: E,G and G+ summing and E and G channels with a E or G center section
« Reply #17 on: October 15, 2017, 09:38:35 AM »
Very interesting stuff. Thanks for the info. I've heard of the mod but never truly understood how or why it was needed.
Thanks again!
JJ
www.BoogieTracks.com