Building a non-standard cable

[AudioHTIT]

I like to build my own cables when possible as they all are exactly the right length, and look more or less the same. This is pretty much limited to audio cables, and isn’t too difficult, but I want to try and use some balanced (2 wire) cable for an unbalanced (1 wire) application. These are simple RCA cables, except one is for my turntable, which works at low levels, is sensitive to capacitance, and hum can be an issue. As this cable will be short (around 18”) I don’t think the cable’s capacitance will be an issue regardless of my choice below, but for ‘academics’ I’d like to learn a bit from those who might know the answers.

So with three wires — signal 1 +, signal 2 -, shield/drain — and two connections on each end, I see four possible ways to wire the cable — I’ve made a simple drawing that I hope can be understood. I’m leaning toward #1, but what interests me most is:

1) Which option would have the lowest capacitance (as seen by the phono cartridge)
2) Which would have the best shielding, lowest noise / him

Bonus questions: Can the capacitance option on some multimeters measure something like this? How would you configure the cable to do that?



Edit:
Option 1: use the two conductors for the signal, add the ground to the ring terminal at the preamp only
Option 2: connect both conductors forming a single ‘hot’ and use the shield /drain as is typical for RCA cables
Option 3: same as 2 except use only one signal cable
Option 4: same as 1 except shield / drain connected at both ends

My normal resource doesn’t discuss this option www.ranecommercial.com/kb_article.php?article=2107

[ttocs]

I also use Rane as my reference for how to correctly make cables!

So if you look at 20A in the Rane information it shows RCA connectors at each end, the Signal wire, and the Shield is connected from end to end. Whether you use one or both internal wires available is up to the cable maker. It will result in lower resistance for the Signal wires, which I'm not sure what ramifications there might be but I've done this for many of my cables. What I really don't know is what this does to the overall capacitance, but I can measure that!

Using a regular multimeter for "Capacitance" is more for measuring capacitors. To measure Capacitance, as well as Inductance and Resistance, very accurately I use this: Hantek 1832C LCR Meter which I got from that rain forest place on the triple dub.

[KeithL]

If you're really determined to get into the finer details here there are a lot of them... not all obvious...

For example it's going to matter whether your two signal leads are parallel or are a twisted pair.
For another thing most phono cartridges have a recommended capacitance... the sum total of the cable and the input of the phono preamp.
However that recommended capacitance is not zero... and some cartridges actually specify a somewhat higher capacitance than others.
It's also worth mentioning that cable capacitance tends to matter quite a bit for Moving Magnet cartridges...
However, because Moving Coil cartridges operate with a much lower load resistance, they don't tend to care much about cable capacitance...
And, as to how well shielded a cable is, you're looking for things like "shield percent coverage" for braid shield... and whether a foil shield is included or not...
And, to be quite blunt, many turntables are grounded poorly, or not even wired properly at all.
And the grounding on both the turntable and your preamp will affect your results.

And, likewise, what you do with that separate ground lead will also sometimes make a major difference.
(Many turntables have a separate ground lead... some keep it separate, some tie it to the ground of one of the RCA connectors, and some don't have one at all.)

It's also worth pointing out that, in many cases, how you run your cables matters more than the cables themselves.
For example, especially with low level signals, you DO NOT want to run signal cables parallel to and near AC power cables.
You want to keep them as far apart as possible and, if they need to cross, try to make them cross at right angles.

I suppose it's also worth mentioning that you really want a continuous ground...
(So none of that odd stuff, where the shield is only connected at one end, and the drain only at the other, and there is no actual ground path between the ends.)

Personally, if I was making a cable, and it had a twisted pair of conductors, I would treat the twisted pair as a single wire, with both ends of both connected to the center pin...
Then connect the shield to the shield on both connectors.
(This gives you the equivalent of a single conductor and shield.)

I've seen lots of justifications for doing it one way or the other...
But I've never seen a clear consensus that any one of them is actually better in any significant way...

It's also worth mentioning that it doesn't always work out as you expect...
And both turntables and cartridges are sometimes not grounded in the standard way...
(I talked to one person recently who was getting hum... which entirely went away when he disconnected the separate ground lead.)

Jun 6, 2023 12:07:55 GMT -5 AudioHTIT said:

I like to build my own cables when possible as they all are exactly the right length, and look more or less the same. This is pretty much limited to audio cables, and isn’t too difficult, but I want to try and use some balanced (2 wire) cable for an unbalanced (1 wire) application. These are simple RCA cables, except one is for my turntable, which works at low levels, is sensitive to capacitance, and hum can be an issue. As this cable will be short (around 18”) I don’t think the cable’s capacitance will be an issue regardless of my choice below, but for ‘academics’ I’d like to learn a bit from those who might know the answers.

So with three wires — signal 1 +, signal 2 -, shield/drain — and two connections on each end, I see four possible ways to wire the cable — I’ve made a simple drawing that I hope can be understood. I’m leaning toward #1, but what interests me most is:

1) Which option would have the lowest capacitance (as seen by the phono cartridge)
2) Which would have the best shielding, lowest noise / him

Bonus questions: Can the capacitance option on some multimeters measure something like this? How would you configure the cable to do that?

View Attachment

Edit:
Option 1: use the two conductors for the signal, add the ground to the ring terminal at the preamp only
Option 2: connect both conductors forming a single ‘hot’ and use the shield /drain as is typical for RCA cables
Option 3: same as 2 except use only one signal cable
Option 4: same as 1 except shield / drain connected at both ends

My normal resource doesn’t discuss this option www.ranecommercial.com/kb_article.php?article=2107

[405x5]

Jun 6, 2023 12:07:55 GMT -5 AudioHTIT said:

I like to build my own cables when possible as they all are exactly the right length, and look more or less the same. This is pretty much limited to audio cables, and isn’t too difficult, but I want to try and use some balanced (2 wire) cable for an unbalanced (1 wire) application. These are simple RCA cables, except one is for my turntable, which works at low levels, is sensitive to capacitance, and hum can be an issue. As this cable will be short (around 18”) I don’t think the cable’s capacitance will be an issue regardless of my choice below, but for ‘academics’ I’d like to learn a bit from those who might know the answers.

So with three wires — signal 1 +, signal 2 -, shield/drain — and two connections on each end, I see four possible ways to wire the cable — I’ve made a simple drawing that I hope can be understood. I’m leaning toward #1, but what interests me most is:

1) Which option would have the lowest capacitance (as seen by the phono cartridge)
2) Which would have the best shielding, lowest noise / him

Bonus questions: Can the capacitance option on some multimeters measure something like this? How would you configure the cable to do that?

View Attachment

Edit:
Option 1: use the two conductors for the signal, add the ground to the ring terminal at the preamp only
Option 2: connect both conductors forming a single ‘hot’ and use the shield /drain as is typical for RCA cables
Option 3: same as 2 except use only one signal cable
Option 4: same as 1 except shield / drain connected at both ends

My normal resource doesn’t discuss this option www.ranecommercial.com/kb_article.php?article=2107

“non-standard cable“……??
Forgive me, but considering what’s out there, what is meant by this?

[KeithL]

A "standard unbalanced cable" would be:
- a pair of RCA connectors
- with a piece of standard single-conductor coax cable between them
- usually with a single layer braided shield with a high percentage of coverage
- with the center conductor of the cable connected to the pin on the connector at each end
- and the shield of the cable connected to the shield on the connector at each end

Incidentally, ignoring things like twisted pairs, and multiple conductors...
Capacitance of a cable increases as the surface area of the center conductor increases (its diameter gets larger)...
And DECREASES as the distance between the center conductor and the outer shield INCREASES... 
So, for lowest capacitance, you want a relatively fat outer cable, with a relatively thin center conductor, and a large gap between them...
The dielectric also matters... and those can include things like Teflon and polyethylene as well as things like foamed polyethylene...
And some interesting things... like the conductor riding in a piece of tubing with a spiral thread to keep it centered... so mostly air between them.
(However, in an ordinary audio interconnect, or a phono interconnect, most of this really doesn't matter.)
(Also, just for the record, many "exotic dielectrics", like "organic cotton", actually aren't very good at all for various reasons, and so should be avoided.)

Jun 6, 2023 13:24:35 GMT -5 405x5 said:

Jun 6, 2023 12:07:55 GMT -5 AudioHTIT said:

.......................

“non-standard cable“……??
Forgive me, but considering what’s out there, what is meant by this?

[AudioHTIT]

Jun 6, 2023 13:19:21 GMT -5 KeithL said:

If you're really determined to get into the finer details here there are a lot of them... not all obvious...

For example it's going to matter whether your two signal leads are parallel or are a twisted pair.
For another thing most phono cartridges have a recommended capacitance... the sum total of the cable and the input of the phono preamp.
However that recommended capacitance is not zero... and some cartridges actually specify a somewhat higher capacitance than others.
It's also worth mentioning that cable capacitance tends to matter quite a bit for Moving Magnet cartridges...
However, because Moving Coil cartridges operate with a much lower load resistance, they don't tend to care much about cable capacitance...
And, as to how well shielded a cable is, you're looking for things like "shield percent coverage" for braid shield... and whether a foil shield is included or not...
And, to be quite blunt, many turntables are grounded poorly, or not even wired properly at all.
And the grounding on both the turntable and your preamp will affect your results.

And, likewise, what you do with that separate ground lead will also sometimes make a major difference.
(Many turntables have a separate ground lead... some keep it separate, some tie it to the ground of one of the RCA connectors, and some don't have one at all.)

It's also worth pointing out that, in many cases, how you run your cables matters more than the cables themselves.
For example, especially with low level signals, you DO NOT want to run signal cables parallel to and near AC power cables.
You want to keep them as far apart as possible and, if they need to cross, try to make them cross at right angles.

I suppose it's also worth mentioning that you really want a continuous ground...
(So none of that odd stuff, where the shield is only connected at one end, and the drain only at the other, and there is no actual ground path between the ends.)

Personally, if I was making a cable, and it had a twisted pair of conductors, I would treat the twisted pair as a single wire, with both ends of both connected to the center pin...
Then connect the shield to the shield on both connectors.
(This gives you the equivalent of a single conductor and shield.)

I've seen lots of justifications for doing it one way or the other...
But I've never seen a clear consensus that any one of them is actually better in any significant way...

It's also worth mentioning that it doesn't always work out as you expect...
And both turntables and cartridges are sometimes not grounded in the standard way...
(I talked to one person recently who was getting hum... which entirely went away when he disconnected the separate ground lead.)

Thanks for your detailed response (I would expect no less 🙂)

I’m aware that most cartridges like a specific capacitance (in fact I still have a little resistance and capacitance loading box given to me by Nelson Pass many years ago), but I’ve been unable to find the recommended value for my cartridge — a MoFi MasterTracker MM Cartridge (part of the Fender / MoFi turntable). According to the Belden 8451 spec sheet, the cable is reasonable in capacitance between conductors (34 pF/ft), but doubles conductor to shield, they spec and show it being twisted pair, but I don’t see that when I strip the cable.

The way I built my turntable shelf the phono preamp can sit very close to the turntable, if I wanted I could probably make a 6” cable work, but I’m targeting 12-18”, and the audio path does not parallel or cross AC. The signal path is: MoFi Cartridge / Tonearm —> 12-18" Phono Cable (w/ground) —> XPS-1 —> 5-6' Line Cable —> RMC-1 Analog 1. With the generic cables I’ve been using, and a ground wire (TT ground lug to XSP-1 lug), I have not had a hum problem.

As far as that “odd stuff, where the shield is only connected at one end”, if you look at my drawings (and we consider with RCA cables the ring to be ground), then there is always a solid continuous connection, it’s only the shield that isn’t terminated at one end — as you sometimes see with balanced cables that have a separate drain and shield (8451 has a drain and foil shield). So I’m not clear that any of my options don’t meet your criteria, but I gather you recommend option 2 . While that would certainly have the least resistance (which does seem desirable for low level signals), I still don’t know where that falls in the high / low capacitance rating (which is just saying I’d still like to know which has the least capacitance, even though I hope it won’t matter). Also for clarity, I’d be soldering the drain wire to the ring for my ‘shield’. I’ll also be making both the phono and line cables. Thanks again for your comments and advice.

Edit: I missed your response on center conductor surface area and capacitance, (not knowing) that’s why I considered both the single and bonded signal leads. For another option, I could slightly increase the distance between the signal and the shield, by pulling out one of the signal wires (essentially making the cable ‘standard’)

Here’s Belden’s ‘photo’ and description of 8451

1 Pair 22 AWG stranded (7x30) TC conductors, polypropylene insulation, paper wrap, twisted pair, overall Beldfoil® shield (100% coverage), 22 AWG stranded TC drain wire, PVC jacket.

[AudioHTIT]

Jun 6, 2023 12:53:14 GMT -5 ttocs said:

I also use Rane as my reference for how to correctly make cables!

So if you look at 20A in the Rane information it shows RCA connectors at each end, the Signal wire, and the Shield is connected from end to end. Whether you use one or both internal wires available is up to the cable maker. It will result in lower resistance for the Signal wires, which I'm not sure what ramifications there might be but I've done this for many of my cables. What I really don't know is what this does to the overall capacitance, but I can measure that!

Using a regular multimeter for "Capacitance" is more for measuring capacitors. To measure Capacitance, as well as Inductance and Resistance, very accurately I use this: Hantek 1832C LCR Meter which I got from that rain forest place on the triple dub.

So that looks cool, my multimeter also has capacitance measuring, which seemed to confirm the cap values when I recapped my guitar amp. But the real question is what do I connect to the meter, the signal and shield on one end? Twist the shield and signal together on one end and measure the other end, then cut the reading in half? Measure the signal on opposite ends? And what would you do if you had connectors on? 😮 They certainly would alter the reading (and they don’t fit in the little holes 🤷‍♂️)

[ttocs]

Many questions, many more answers - only know some of them. (Spoken like the wise Master in Kung Fu.)

This should be self explanatory enough. Capacitance shown on the display, and the adjoining image shows the wire configuration measured.

The cable is a 22AWG twisted pair inside of a foil+bare-wire shield, and is about 15" long.

Black & Red wires tied together at each end. The R&B pair and Shield are connected to the meter. Highest Capacitance.




Black & Red wires separated at both ends. Only the Red wire and Shield are connected to meter, Black wire floating at both ends. Medium Capacitance.




Black and Red wires connected to meter at one end, both separated at the other. Shield floating at both ends.

[AudioHTIT]

Jun 6, 2023 17:11:21 GMT -5 ttocs said:

Many questions, many more answers - only know some of them. (Spoken like the wise Master in Kung Fu.)

This should be self explanatory enough. Capacitance shown on the display, and the adjoining image shows the wire configuration measured.

The cable is a 22AWG twisted pair inside of a foil+bare-wire shield, and is about 15" long.

Black & Red wires tied together at each end. The R&B pair and Shield are connected to the meter. Highest Capacitance.




Black & Red wires separated at both ends. Only the Red wire and Shield are connected to meter, Black wire floating at both ends. Medium Capacitance.




Black and Red wires connected to meter at one end, both separated at the other. Shield floating at both ends.

OOOH! OOOH! Mr Cotter, Mr Cotter, you've done the exact tests! Thank you Scott! Do you still have the lab setup? (or is Igor taking a nap in there?) What if you tied the black and drain wires together at one or both ends and measured between that and the red wire? This seems to show wiring scheme #1 might have the lowest capacitance.

[ttocs]

Jun 6, 2023 17:22:23 GMT -5 AudioHTIT said:

OOOH! OOOH! Mr Cotter, Mr Cotter, you've done the exact tests! Thank you Scott! Do you still have the lab setup? (or is Igor taking a nap in there?) What if you tied the black and drain wires together at one or both ends and measured between that and the red wire? This seems to show wiring scheme #1 might have the lowest capacitance.

You know, your suggestion probably would've woken me up in the middle of some night as the one I missed doing!

EyeGor, Wake up!!

[ttocs]

Black & Shield tied together at each end, Red wire floating at each end. This one surprised me!

[AudioHTIT]

Very interesting, I'm still thinking #1 for lowest capacitance ... thank you so much! Give EyeGore, the night off!

Jun 6, 2023 17:43:49 GMT -5 ttocs said:

Black & Shield tied together at each end, Red wire floating at each end. This one surprised me!

[marcl]

Jun 6, 2023 17:43:49 GMT -5 ttocs said:

Black & Shield tied together at each end, Red wire floating at each end. This one surprised me!

Didn't Ethan Winer determine as part of his null test that the most expensive cables had the highest capacitance?

[ttocs]

Jun 6, 2023 17:55:54 GMT -5 AudioHTIT said:

Very interesting, I'm still thinking #1 for lowest capacitance ... thank you so much! Give EyeGore, the night off!

I actually didn't test according to your #1 diagram. But I did just now and got 96pF. So it would seem that if the Shield is involved, whether connected at one end or both, has a medium amount of Capacitance.

The lowest Capacitance is connecting the Red wire to Center Conductor, Black wire to Ground, and leave the Shield floating. (My test #3.)

[ttocs]

Jun 6, 2023 18:09:36 GMT -5 marcl said:

Didn't Ethan Winer determine as part of his null test that the most expensive cables had the highest capacitance?

Yes, he did. And that is what I found 12 years ago when I tested about 6 different speaker cables ranging in price from a few dollars to $1800. As the price rose, so did Capacitance, and my stats hated the high dollar cables. The treble disappeared but the bass remained. Bass didn't increase, treble decreased.

Ok, that last statement is a bit misleading. The zip cord use for speaker wire had no bass and lots of treble. But once in the realm of sufficient bass it didn't increase more with each more expensive cable. So, at each end of the scale are the extreme examples of treble or bass, and in the lowest part of the median area is where I found Xanadu.

[Boomzilla]

Want to be tricky? Use a cable, but don't connect the shield or the ground. Put a big insulating tube around the wire, and then shield & ground the outside of the insulating tube.

[ttocs]

Well, not quite like Boom explained, but somewhat close, I think.

Two lengths of the same cable rolled up side by side in tin foil, using just one of the center wires of each cable, all others floating. As soon as I involve the outer shielding, tin foil, Capacitance goes up.

[AudioHTIT]

Jun 6, 2023 18:37:06 GMT -5 Boomzilla said:

Want to be tricky? Use a cable, but don't connect the shield or the ground. Put a big insulating tube around the wire, and then shield & ground the outside of the insulating tube.

Boom, I like the suggestion, and might try a spin on it. Since ttocs measurements show including the shield with the ring increases capacitance, then instead of letting it float I connect the drain wire (shield) to an external (but related) ground — like this:



I need to setup a way to measure noise / hum before testing, maybe the digital out into the Mac.