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Buchla with CVGT1 grounding
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author Buchla with CVGT1 grounding
amnesia
Just got 2x Synovatron CVGT1 installed into my euro system but when in use I get a slight hum. I need to ground the euro / Buchla combo.

To anyone who has the CVGT1, did you have to ground yours? How, where?

thanks
amnesia
Do I need to run a cable from the CVGT1 ground out to the Buchla Ground at the back of the 24wls?
tIB
^ yes.
Kent
Try it. Does it make the symptom go away?
chrisso
I'm just sticking mine into any unused banana socket on the main Buchla.
My ground banana is a long way from the CVGT1
amnesia
seems to do the job either way, took me a couple of seconds to understand that the metal jack on the CVGT1 was actually a banana cable. Never seen a metal banana jack before.
tIB
If you don't want to ground the module then ground to the euro power supply instead.
komputerbrown
there's also ground in every tini-jax in the Buchla and in every 1/8" on the euro, so any 1/8" audio cable between the systems will be ground enough (at least the tip top stack cables work well with tini-jax plugs, do NOT use tini-jax in the euro)
synthomaniac
amnesia wrote:
seems to do the job either way, took me a couple of seconds to understand that the metal jack on the CVGT1 was actually a banana cable. Never seen a metal banana jack before.

Very sorry I meant to send you the user manual which would have explained the metal banana jack. Here it is below, you need the Rev 1.2 version:-
amnesia
Thanks!
exeterdown
I thought the silver bannana was weird too.
I have two of the blue bannana leads stacked to make one long enough to reach. Mr. Green
sytnax
Sorry for bumping this old thread...

If I need to use two CVGT1 modules from the same rack in a patch with a Music Easel, should I ground both of them? Is it ok to stack on top of the grounding jack on the Easel?
makrel
No.
Ideally, 2 devices should have a single point of contact for chassis ground connection - not more not less.
However, modular synths are unique beasts in the sense that the whole idea is to connect patch cables all over the place - this is not ideal, but it is ok, because otherwise, modular synthesis would not exist.
Every time you connect a normal patch cable from one cabinet to another, you implicitly make a chassis ground connection (via the cable shield / jack plug sleeve).
However banana patch cables are an exeption, because they contain only a single conductor and no shield.
Guess what, that's why banana based synths (usually) have a dedicated chassis ground connector.
Again, you can choose to use that connector or you can choose to ignore that connector, provided that you have chassis ground connected via at least one normal patch cable.

I hope this helps
synthomaniac
I agree! Exactly as @makrel has ably explained. Both CVGT1 grounds are connected internally to the same common ground point so either will do just fine, you don't need to connect both.

BTW nothing wrong in resurrecting old threads in my view and thanks for buying two CVGT1s applause
kbrush
this was very timely for me, about to install a pair cvgt's and hadn't considered the grounding issue. thank you!!
sytnax
Thanks @makrel for the detailed explanation!

@synthomaniac I only have one CVGT1 at the moment but plan to get more to pair with the Easel. The module is very useful thumbs up
Graham Hinton
makrel wrote:

Ideally, 2 devices should have a single point of contact for chassis ground connection - not more not less.


Each device should have that and be grounded. That is different from establishing a common 0V between two unbalanced devices. Both have to be dealt with properly together otherwise the 0V is established by non-ideal connections and that's why you get hum and bleed.

Quote:

However, modular synths are unique beasts in the sense that the whole idea is to connect patch cables all over the place - this is not ideal, but it is ok, because otherwise, modular synthesis would not exist.


The only thing unique about modulars is that most do not conform to professional audio grounding practise. Most manufacturers blindly copy bad 1970s practises and have never heard of AES48.
This causes problems when connecting to equipment that does conform to AES48--like a professional mixer.

Quote:

Every time you connect a normal patch cable from one cabinet to another, you implicitly make a chassis ground connection (via the cable shield / jack plug sleeve).


That should be the case, but it isn't. Most modules do not have a chassis ground and the jack screens are connected to the internal 0V. When you patch between two such modules you are creating a path between their two 0Vs in parallel with the one that exists in the power distribution and the signal currents split according to the admittance (1/resistance) of each path.

Quote:

However banana patch cables are an exeption, because they contain only a single conductor and no shield.


With unshielded cables the signal return path has to be via the power distribution. With shielded cables the shield should be connected to chassis ground hence extending an equipotential layer around the whole system. This layer should not be carrying any currents (otherwise it is no longer a screen), but it will if it connects to 0V.

When modules incorrectly use 0V as the cable screen the way to reduce the problems is to provide a lower resistance power distribution to divert most of the current. A reduction by a factor of ten will reduce unwanted signals by 20dB and a factor of a hundred by 40dB. This means connections with a resistance of a few milliohms and that rules out pcbs.

Quote:

Guess what, that's why banana based synths (usually) have a dedicated chassis ground connector.
Again, you can choose to use that connector or you can choose to ignore that connector, provided that you have chassis ground connected via at least one normal patch cable.


Unfortunately this connector is usually at the wrong place, on the PSU, and the PSU may not even be grounded. The correct place to join two unbalanced systems (balanced systems do not require a signal common) is directly between the 0Vs of each power distribution and you need something orders of magnitude less resistance than a single banana lead or audio cable. The PSU supply cables should not be in this path because of voltage drops along them.

Putting a grounding banana of a Eurorack module panel is less than ideal too. There is no chassis ground in Eurorack, and often no mains Ground either, and the path to 0V is via pcbs and ribbon cable.

The commonly given advice repeated above does not take in to account the resistance of the wiring and that is the most important factor. All modular synthesizers should be grounded to mains Earth for safety as well as having their 0Vs commoned by a much lower resistance.
What I am recommending now for 0V Commoning between systems is a Dinse connector with 25mm^2 welding cable. These are low cost and readily available worldwide from welding suppliers, electronic/electrical distributors don't tend to stock them. The sockets have an M8 bolt on the inside and battery cables with 8mm terminals may be used internally. That is battery as in truck, not PP3.

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