stereo out effects - best practice in a world of mono cables?

[samhay]

I'm building a mono-in, stereo-out tremolo. It seems I have 3 options as far as the output jack(s) go:
- 2 x mono jacks
- 1 x mono + 1 x stereo (2 jacks)
- 1 x stereo (1 jack)

Do people have a preference as to which method to use?

2 x mono is clearly the most straight forward to implement.

I guess that it is best practice to wire the stereo jack Left-to-tip, Right-to-ring as in headphones?
In this sort of pedal the Left and Right channels are arbitrary, but there is nothing wrong with being consistent.

In the case of 1 x mono + 1 x stereo, is there convention regarding whether Left or Right channel goes to the mono jack? I'm leaning towards Right so that if a mono jack is used in the stereo jack, you still get both Left and Right channels out.

Finally. I am not aware of any clever way to prevent a mono jack from shorting the Right (ring) channel to ground in a stereo jack. My design can inherently handle this, but again is there best practice to protect against this (other than insuring the circuit won't melt if it happens)?

Seems like a lot of questions. Thanks.

[Groovenut]

IMO, the end use for this would generally be with a dual amp setup. From an end user POV, I would think two mono output jacks would be prefered as there is no need for special cabling or a Y adapter. If you have the real estate for two jacks that would be my choice.

My two cents....

[Steve Newton]

Unless you really have to save space then just go with a mono jack on each output.

If you feed it into commercial stereo FX they will be 2 x mono ins, it will interface with anything without any need for a special cable.

[Granny Gremlin]

As above... but to address the other points:

- in a L + R jack setup, L=mono (standard)
- yes re: the stereo jack wiring (L=tip)
- mono + stereo jack is a very nice option to give as it covers the usual  (as everyone else has posted) as well as giving you the option to clean up your cabling and use a stereo (TRS) cable, but also the most complicated.  This is not common and there is therefore no standard, per se, but basing our thinking on the logic behind L = the mono /main out, the stereo jack should be L if both jacks are being used (and stereo if a single TRS cable is used). ... might be a tad easier to wire it the other way though.  It shouldn't matter too much as long as clearly labelled.

[samhay]

^My two cents....
Thanks. That's what I'm looking for.

^Unless you really have to save space then just go with a mono jack on each output.
It will be the difference between using 1590B and 1590BB, but this is not a deal breaker.

^As above... but to address the other points:
Thanks for the comments.


I was starting to wonder if the 3rd option might not be a bad idea: 1 x stereo out.
A problem with this is that it makes the switching more complicated if the bypass signal is fed to both channels - a 3PDT is required to prevent tip and ring shorting when not bypassed. If the ring is not bypassed then this will also short signal to ground if a mono jack is used. This problem goes away if the bypassed signal only goes to the left channel and/or with a mono/stereo switch that bypasses the ring connection, but then you lose a channel in bypass.

[anotherjim]

Where do you find a true stereo cable? Most are figure-8 twin mono. A balanced twin+screen cable is not really suitable for stereo as the signal cores are not screened off from each other. I would use 2 separate mono feeds.
Since the old days of 5pin DIN hi-fi interconnects, I can't think of any current audio interconnects that run stereo in a single sheath cable apart from SCART A/V (and that has separately screened audio feeds in it). Headphones do of course, but they don't have to be screened at all and crosstalk isn't going to be noticeable.

[samhay]

Interesting point.

First 'stereo' TRS cable I found:
http://www.amazon.co.uk/PCL3-Professional-quality-stereo-RED/dp/B002U8ZT6U/ref=sr_1_2?ie=UTF8&qid=1300121753&sr=8-2

'... Features LYNX double-screened single-core 7.0OD oxygen free copper twin-core+shield microphone cable with exellent RF rejection and very low capacitance...'

[Granny Gremlin]

In my (limited - it's not often I have to do this) experience this has been negligable.  But if you're worried you can use a composite cable (litterally 2 mono cables attached at the outer jacket level in parallel, often used for hifi interconnects which are also HiZ unbalanced and interchangeable - this would require the use of those extra large barrel TRS jacks - the ones for speaker cable - and not be too pretty).  Or you could use mulkticore mic/line cable (e.g. snake cable) and just not use the second conductor of each twisted pair.... better yet, use the twisted pair for signal and the shield around each pair as a shield only (connected to sleeve at one end of the cable only), like this stuff:

[anotherjim]

Well, true that crosstalk in stereo is rarely tragic. Hi-fi reviewers might lose sleep over it, but there's stereo and there's 2 channel.

Where its critical could be a clean send from an effect such as distortion or delay where you want the clean for recording so you can use modelling software if the wet signal you liked during tracking turns out not to be so likeable in the mix. If there's delay on one side and the other (no delay) is going to a high gain distortion or whatever downstream, the delay signal pick-up will not be trivial.

You can get true stereo single cable, but it's a special and you may not have a spare if it fails. Mono cables are easy to carry as spares because they're more useful.

[Transmogrifox]

If it means anything in the light of a "standard", my old DOD "Ice Box" chorus uses separate 1/4" outputs for Left and Right...although I think the output "Left" jack is the battery connect stereo jack, so you MUST use left as mono (or at least have something plugged into it) to make the effect power on.  I suppose that "feature" would be up to you.

Left is the default mono, so when using the chorus in mono the left channel is used.

[MrStab]

one way to do it is to make jack A the Mono and TRS output, and jack B the 2nd-channel-on-mono-cable-only output. So B's Tip is connected to A's Ring via. the switching lug, but plugging anything into B will disconnect that. Ofc, if the user uses a mono cable for A with nothing connected to B, then B-Tip will be grounded via. A-ring (now A-sleeve).

so basically, you'd have: "L/STEREO" and "R" on this hypothetical enclosure.

that took a lot of thinking for my picobrain ages ago, but it turned out some company already has such a system as standard on all their stereo effects. can't remember which, but convergent evolution suggests it might not be such a bad idea.

if the bypass is buffered to avoid passive signal splitting (though you may have implied otherwise with the 3PDT mention, Sam), maybe you could cheat with some active circuitry, if only to prevent one worst-case input scenario.

switching ties my brain in knots but hopefully i've not spaghettified this one too much.

[PRR]

> First 'stereo' TRS cable I found:

I do not know WHAT all that puffery says.

But "microphone cable" often means two hot wires under one shield (balanced mike).

Agree that (unless source impedance is very high) cross-talk is a non-issue for most uses.

I used to run very-fine (binaral) stereo over hundreds of feet of mike cable.

In the proposed use, both amp/speakers are in the same room, so X-talk as small as -10 dB won't spoil the sound.

[samhay]

When on, the output impedance of each channel will ~ 2k. I don't think crosstalk will be a big problem, but sometimes we have to build things to find out.

> if the bypass is buffered to avoid passive signal splitting (though you may have implied otherwise with the 3PDT mention, Sam), maybe you could cheat with some active circuitry, if only to prevent one worst-case input scenario.

Not planning on using buffered bypass, but as this will go late/last in the signal chain there will be some buffering beforehand.

> I do not know WHAT all that puffery says.

I'm glad I'm not the only one.

[Granny Gremlin]

so basically, you'd have: "L/STEREO" and "R" on this hypothetical enclosure.

(Yep.)