Cable construction for CV's in and out of the 9700?

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stevebryson
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Cable construction for CV's in and out of the 9700?

Post by stevebryson »

Hi all - I'm unclear about what to do about ground when using the 9700 to send CV's to other synths or when sending CV's to a 9700 module, even after reading the documentation. Should my patch cable connecting a 9700 module to the outside world have the ground hooked up at both ends?

I understand about not connecting the ground for patches within the 9700, but...
Billb3
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Re: Cable construction for CV's in and out of the 9700?

Post by Billb3 »

there needs to be one ground connection between devices.

for another external device ie. another synth you should use a grounded connection. if both devices use a 3 prong plug there is a chance they are already ground connected.

for connections between modules within the device you dont need it as the devices are already ground connected through the power supply.

having multiple ground connections on audio usually causes hum.

having multiple ground conections on CV may not be noticeable. I am not sure about this though

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Re: Cable construction for CV's in and out of the 9700?

Post by Kyhotay »

I'm not sure how big an issue this is. All patch cables that came with my Voyager XL and MS-20 are all grounded. I have grounded patch cords going between and within various synths and modules. I don't think I've run across manufactured patch cords that weren't grounded. Ground loops has not been an issue. To me the bigger problem is not having enough cords the right length!
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Re: Cable construction for CV's in and out of the 9700?

Post by stevebryson »

Scott wrote me that "When connecting with external equipment, a patch cable which joins or establishes a ground between the devices is needed, ie just a standard patch cable with tip to tip and sleeve to sleeve wiring between the plugs." so I guess that's that.

My experience with other synths says that everything needs to be grounded to the same circuit, otherwise I get hums. That's how I avoid ground loops.
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Re: Cable construction for CV's in and out of the 9700?

Post by toneman »

stevebryson wrote:Scott wrote me that "When connecting with external equipment, a patch cable which joins or establishes a ground between the devices is needed, ie just a standard patch cable with tip to tip and sleeve to sleeve wiring between the plugs." so I guess that's that.

My experience with other synths says that everything needs to be grounded to the same circuit, otherwise I get hums. That's how I avoid ground loops.
I'll have to disagree with Mr Lee here:
I don't think the patch cable should establish the ground.

I'll agree with U that everything needs to be grounded to the same point
to reduce/eliminate gnd loops and hum.

I recall that SERGE synths use[d] banana jacks and non-shielded banana cords for patching CVs.. I think SERGE also did signal paths with non-shielded banana cords[?] I've always liked banana plug patching because U can stack the plugs on the jacks.
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PAiA-Scott
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Re: Cable construction for CV's in and out of the 9700?

Post by PAiA-Scott »

Within a P9700S, the modules all share a power supply.

The VCO, VCF, and VCA modules tap power from the MIDI2CV8 and thus share "ground" / 0VDC / circuit-common.

A single wire from any output in the system will carry the voltage signal to any input on the system.

A cable wiring the tip to tip of mini-phone plugs can be used for patching outputs to inputs within the system. So too, can a cable with the tip to tip and sleeve to sleeve; however, the single wire cable is preferred (and easier to make). The shielding afforded by a two wire cable is not such a concern with the high-level voltage signals.

To go from the P9700S to some other external equipment such as an amp/speaker, etc., the cable must have two wires with one carrying the voltage and the other joining the grounds.

It is possible two separate pieces of gear can be joined with a single wire, but this is only if each device has its ground tied to the wall outlet "earth" ground prong -- not always the best or cleanest ground though.

Yes, banana style connectors are great for making the single wire patch and the ability to stack them is a plus. A way to realize this with the mini-phone connectors on the P9700S is to make a bunch of plugs with a small bare wire loop extending out the end and put one in the desired patch points and use test-lead-hooks/alligator-clips to make single or multi-point quick-connect patches.
Scott Lee
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Re: Cable construction for CV's in and out of the 9700?

Post by Kyhotay »

And just to add to this I suspect the pre-made patch cables PAiA sells are tip-tip, shield-shield. Right, Scott?
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Re: Cable construction for CV's in and out of the 9700?

Post by PAiA-Scott »

Yes, the PCA series patch cords are wired tip-tip and sleeve-sleeve, but they've since become unavailable.

The 9791 patch cord kit from the P9700S is listed on our site catalog.

9791
http://www.paia.com/proddetail.asp?prod=9791

The 9791 instructions are a part of the P9700S Overview.

9791 instruction page
http://paia.com/manuals/docs/P9700Sovrvw_200.pdf
Scott Lee
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