500 Series Pin 11 Buss Feed Connection

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Bobby Baird

Well-known member
GDIY Supporter
Jun 15, 2013
Austin, TX
I have e-mailed Radial service department to ask about the correct way to implement a Buss Feed connection, but I would like to ask here as well for any insight. I will update if I get a reply from they're service department. I am designing a HP/LP Filter Set, and I had a question on the proper method of connecting the output of the filter circuit to the Pin 11 Buss Feed edac gold finger. Would I tap the output of the filter after the coupling cap before the line driver to a series 4.75k resistor as in the attached schematic to pin 11, or should I tap the positive of the differential output of the 1646 line driver to series 4.75k resistor to pin 11?

This is an exert from Radial workhorse open source specification.

"Buss Feed
The BUSS FEED (Pin-11) connects to one of eight channels in the mixer section of the Workhorse. The module
designer may supply whatever signal they wish to this pin as long as there is a 4K7 or 4K75 resistor in series with
it. Isolation is not required as long a there is no DC on the signal output at this pin.
This output from the module is connected to the inverting (virtual earth) input of an op amp (in the mix section of
the rack) with a 4K75 feedback resistor. This is called a ‘Virtual Earth Mix Buss”. It is low noise and is less prone to
problems. We chose 4K75 because it tends to have lower noise than a higher value and because the Rupert Neve
Designs Portico series employs a 4K7 Mix Buss on all of their modules. This provides cross-compatibility between
Radial and Rupert Neve Designs."

Thank you in advance for any insight into the circuit design.



  • Pin 11 Buss Feed Connection.jpg
    Pin 11 Buss Feed Connection.jpg
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