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Buchla Quiet Vs Noisy Ground
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author Buchla Quiet Vs Noisy Ground
Does anyone know the difference between
Noisy Vs Quiet ground? seriously, i just don't get it

This is in relationship to the Buchla power supply:

1 Black: quiet ground
2 White: -15
3 Red: +15
4 Dark Green: +12
5 Orange: +5
6 Brown: noisy ground
7 polarizing key
8 Yellow: i2c clock
9 Green: i2c data
10 nc

Is noisy ground is for digital circuitry and LEDs and quiet ground is for
analogue signals ????
jondent wrote:
Is noisy ground is for digital circuitry and LEDs and quiet ground is for analogue signals ????

Noisy for digital circuitry and quiet for analogue + audio. This is what I have read yes and also noticed from all modules I have.
Thanks Batchas. thumbs up
Hi guys,

let me resurrect this thread and get into more detail.
i was looking at a couple of modules and i found more than those two cases for ground connections.
For example, opamps...they take a lot of power and run on the +-15V rails, +12V and also +5V sometimes.
Do they also go to brown (NGDN) only ?
What if you have a module that processes audio and CV like a 292 ?
The ground that rund on the front plate, is that black or brown ground ?
What if a 208 module is present in the rack ?
Its NGND and QGND are joined together .
+/-15V (red and white) are referenced to Q GND (black).
Q GND is the same as case ground, and is the same as the brick ground.
Busboards should connect Q GND to the case through their mounting posts (or otherwise). Every module using Q GND should connect it to the faceplate. All devices (op amps, etc) using +/-15V should be returning current via Q GND. In general, CV is running on Q GND.

12V is just the power from the brick, and is also referenced to Q GND because there is no difference between Q GND and the brick GND.

5V (orange) is referenced to N GND (brown). N GND connects to Q GND on the powered busboard only. Seems to me that it should not connect directly, but it should connect through an inductor only. I could be wrong about that.
So N GND floats through the entire case, connected to Q GND in only one spot on the powered busboard.

The trick is keeping these grounds completely separate in your module, and also not ever forcing +/-15V power to return via N GND and not ever forcing 5V power to return via Q GND. Seems many (most?) module designs fail in this regard. The 266e for example dumps a lot of digital noise onto Q GND.

In the 200e, the preset bus is referenced to 5V and N GND. Seems to me all LEDs, CPUs, knobs, switches, and ADC's should also be on 5V and N GND. DACs should be on Q GND with the digital signals kept clear of the analog return paths.

I suppose if you are digitizing CV or audio (why would you do that? ha ha) the ADCs should be referenced to Q GND and the digital signals kept clear of the analog return paths. Use of ADC's on the CPU in this case is problematic, so I am talking about a remote ADC, like a codec chip.
If I want to make a ground for my Buchla cabinet so I can patch it with my Eurorack which ground would I use? The ground reference for the 15v is what I assume but I want to double check before making an error.
If i'm not totally wrong both Grounds the quiet and noisy gnd are connected at some Point in the PSU... They are only separate like you won't have a few VCO'S sharing a power rail for Long distance bceause of Crosstalk or logic and VCO's for the same reason…

Guess you could measure this… that there should be only really, really small resistance between them… so my guess would be to get your gnd directly from the PSU and there it shouldn't matter when i'm Right and they go to the same Destination at the PSU....

This way you would also have the smallest resistance in the path between your both Systems gnd.

I'm re-arranging all my stuff in a few days because i fear my shelf were i staple all my cases will break some time under that weight and then will also include a thick Copper or Aluminium bar where i connect all PSU's gnd's.
Graham Hinton had one of his usual helpful Posts About this somehwere in These Forums...
Thanks Doug smile
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