Background electric noise problem

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Graham Hinton
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Re: Background electric noise problem

Post by Graham Hinton » Fri Mar 20, 2020 6:21 pm

snakejaw wrote:
Fri Mar 20, 2020 4:05 pm
Would installing a module like the intellijel Audio I/O (in a case with an external wall wart PSU) and then connecting the inputs and output between the case and the mixer via the Audio I/O's balanced jacks "solve" the problem?
Not necessarily. The thing to understand here is that there are many different electronic balanced circuits and they don't all work the same. The only thing that can be guaranteed is a transformer and then that still depends on the wiring.

Whether a Eurorack module has a metal bushing jack or a plastic insulated one the one thing that you can be sure about is that the screen connection will be the pcb 0V because there is nothing else it can be and that will be at a different potential from the screen the other end which should be connected to chassis ground.

Beware of manufacturers who think that balanced lines are +4dBu signal level. A balanced line has no restriction on the signal level, the only limit is the maximum level that an input can take and that is usually over +20dBu, apart from some low end devices.
Or, would it just be preferable to, as suggest, just use a TS to TRS cable, that was previously referenced, from the case to the mixer, and use a TRS to TS cable, per below, for going from the mixer to the case?
Always try the TS->TRS cable first as it is the cheapest solution and works in most cases.

The second cable won't work with all balanced sources. Some balanced outputs can accept one side being shorted to 0V, others don't.

It really is a minefield and you have to treat all combinations of equipment individually. You will get a better insight if you draw the output and input circuitry rather than just the cable and then you'll be able to see the conflicts. There is no simple answer apart from make everything balanced.

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Re: Background electric noise problem

Post by snakejaw » Sat Mar 21, 2020 2:02 pm

Graham Hinton wrote:
Fri Mar 20, 2020 6:21 pm
The second cable won't work with all balanced sources. Some balanced outputs can accept one side being shorted to 0V, others don't.
Do TRS -> TS connections, generally, pose less of a problem than TS -> TRS?

I imagine a common balanced output to unbalanced input scenario would be with guitars. The guitar goes into the preamp via a Hi Z input, then from the preamp's balance output, what are the reasonable options for connecting to unbalanced pedals/fx units?

Would this be the kind of cable to use?
HXP-000_RGB_1800.jpg
Hosa Pro Unbalanced Interconnect
REAN XLR3F to 1/4 in TS
https://hosatech.com/products/analog-au ... s/hxp-000/
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Graham Hinton
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Re: Background electric noise problem

Post by Graham Hinton » Sat Mar 21, 2020 4:32 pm

snakejaw wrote:
Sat Mar 21, 2020 2:02 pm
Do TRS -> TS connections, generally, pose less of a problem than TS -> TRS?
Only if the output is designed to be shorted by a TS plug. In which case you would just use a TS-TS cable
I imagine a common balanced output to unbalanced input scenario would be with guitars. The guitar goes into the preamp via a Hi Z input, then from the preamp's balance output, what are the reasonable options for connecting to unbalanced pedals/fx units?
Use a guitar level output intended for that purpose.
Would this be the kind of cable to use?
No, for the simple reason that the wiring is not given which mean that the maker does not understand the problems either.

Consider a transformer output which could be either centre tapped or not. If it is centre tapped then connecting to TS will short half the winding and damage it, so you have to use a cable that does not connect to one half and accept a 6dB loss. However the same cable will not work with a non-centre tap because the winding end will be open circuit.

There are similar conflicts with transformerless electronic outputs.

For all balanced to unbalanced patching you have to know exactly the type of output and use the appropriate cable. Connection charts like Rane publish only tell half the story, this is the other half.

You are still trying to get me to tell you a simple answer when I've already explained that there isn't one.

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Re: Background electric noise problem

Post by snakejaw » Sat Mar 21, 2020 5:09 pm

Thanks, Graham. Actually, I'm not looking for a simple answer, at least not since I read your recent posts. Given what you'd already explained, my question about the Hosa cable really didn't need asking. You'd already provided the answer.

How about using a converter box?

Rolls:
Rolls DB24 Passive Stereo Direct Interface
https://rolls.com/doc/manuals/manual_DB24.pdf
Henry Engineering:
Matchbox HD Unbalanced +4dB Balanced Audio Interface Converter
https://henryeng.com/pdf_MANUALS/MHDM.pdf
ART:
CLEANBox
https://artproaudio.com/framework/uploa ... 6_V1.3.pdf

;) My city happens to be on lock down, so I have plenty of time to ask questions. But I'm also very curious to see if there's a way to mitigate the noise problems that sometimes come with Eurorack. I'm aware of the recommendation to buy a good power supply and proper case, have it professionally installed and, I imagine, have a knowledgeable tech set up properly configured balanced inputs and outputs on that case. However that won't help with the majority of other unbalanced gear and synths.

So far, I can probably improve things from the Eurorack to the balanced mixer and audio interface with a pseudo balanced cable. I'm going to solder up a few TS to TRS cables. If a $150 box would help in the other direction, that would be peachy.

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Re: Background electric noise problem

Post by Graham Hinton » Sun Mar 22, 2020 7:17 am

snakejaw wrote:
Sat Mar 21, 2020 5:09 pm
How about using a converter box?
Yes, but none of the ones you listed. The reason being that they are all designed for consumer level interfacing as evidenced by the RCA phono inputs.

A synthesizer running on +/-12V or +/-15V cannot kick out a signal greater than +21dBu. The nominal +/-5V of VCOs is about +14dBu. A passive box with RCA phono inputs is going to have a transformer that will completely saturate at levels below that. What you need is a Line Isolator and check the specs on its input levels.
But I'm also very curious to see if there's a way to mitigate the noise problems that sometimes come with Eurorack.
There are three sources of noise:

1) Noise created within the synthesizer by the modules themselves interacting. This is solved by better power distribution and that doesn't necessarily mean a better PSU. It does mean get rid of flying buses and/or pcb busboards.

2) Noise created by improper grounding. This is usually mains frequency related hum or buzz and does mean a better PSU and/or a Line Isolator. Avoid output modules with XLRs or 1/4" TRS jacks.

3) Noise created by external interference. That is what balanced cables and differential inputs are for. They cancel out interference picked up by the cables, but it won't do anything to noise that leaves the synthesizer which is part of the signal.
However that won't help with the majority of other unbalanced gear and synths.
Don't accumulate lots of unbalanced gear. Once you realise that you are serious and spending a lot of money on a synthesizer, spend some of it on better quality FX and interfaces with balanced I/O and internal mains PSUs. Don't waste money on unbalanced cabling between them. Don't cling to to low end gear you started with, sell it to help pay for better.
So far, I can probably improve things from the Eurorack to the balanced mixer and audio interface with a pseudo balanced cable. I'm going to solder up a few TS to TRS cables. If a $150 box would help in the other direction, that would be peachy.
If you can solder up a cable you can also solder up an isolating transformer in a box for less that $150. Transformers can also pick up interference from external magnetic fields so look for ones that have a mumetal can.

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Re: Background electric noise problem

Post by StillNotWorking » Sun Mar 22, 2020 11:13 am

Also worth taking notice of are that XLR connector do not always imply balanced signal where intended. I have a few vintage pieces where the XLR connector seem to be implemented only for the locking function and professional look.
looking for service manual for the Clavia ddrum AT or ddrum III

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Re: Background electric noise problem

Post by snakejaw » Sun Mar 22, 2020 3:13 pm

Graham Hinton wrote:
Sun Mar 22, 2020 7:17 am
If you can solder up a cable you can also solder up an isolating transformer in a box for less that $150. Transformers can also pick up interference from external magnetic fields so look for ones that have a mumetal can.
Sounds good. Do you have a preferred schematic and preferred transformers?

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Re: Background electric noise problem

Post by Graham Hinton » Sun Mar 22, 2020 6:13 pm

snakejaw wrote:
Sun Mar 22, 2020 3:13 pm
Do you have a preferred schematic and preferred transformers?
Here you go:
Line_Isolator.png
I would use one of these Sowter Transformers, but if you are in the US look at Cinemag or Jensen for an equivalent.

You can put a 1/4 jack on the input too if you like. I would mount it in a suitable diecast box with the input jacks either a plastic bushing type or mounted on a small plastic plate (like an XLR blank). The 4.7µ capacitor is non-polarised and is to prevent DC on the primary.

Note that although the output is balanced it can only drive a long line if the source can too. You don't get anything for nothing with passive designs. Although transformers are designated 10k or 600R they don't actually have that impedance, they transform the impedances they are connected to, so 600R means that it has thicker wire than a 10k one.

Also don't knock the mumetal can as that can degrade its screening properties. You could wrap it in rubber and use a big P-clip to mount it.
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Last edited by Graham Hinton on Sun Mar 22, 2020 6:15 pm, edited 1 time in total.

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Re: Background electric noise problem

Post by Graham Hinton » Sun Mar 22, 2020 6:14 pm

StillNotWorking wrote:Also worth taking notice of are that XLR connector do not always imply balanced signal where intended. I have a few vintage pieces where the XLR connector seem to be implemented only for the locking function and professional look.
The ARP Odyssey comes to mind. This was both incorrectly wired and pin 3 hot, but is easily converted to either a built in adapter or pseudo balanced output or you could put a transformer inside.

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Re: Background electric noise problem

Post by Blairio » Fri Mar 27, 2020 12:40 am

Graham Hinton wrote:
Sun Mar 22, 2020 7:17 am
snakejaw wrote:
Sat Mar 21, 2020 5:09 pm
How about using a converter box?
Yes, but none of the ones you listed. The reason being that they are all designed for consumer level interfacing as evidenced by the RCA phono inputs.
I have used an ART Cleanbox 2 for a few years now to solve a noise issue between a Nord and my mixer. The Cleanbox 2 is passive, has 1/4 inch jack sockets (not phono), and has little discernable impact on sound quality. Doubtless the transformers in it are bargain basement, but they do the job. It probably helps that Nord's have a healthy output signal level.

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