I should have mentioned I'm not installing balanced XLR inputs for now, only RCA. My understanding is that since I will be using an XLR to RCA adapter ( unbalanced ), I'll just connect 1 wire from the post to the amp board's input, and the shield from the post to the board's ground. If I ever install XLR balanced inputs, I'll connect the balanced pair of wires to the amp board's input and the sheild to the board's ground. ( not sure about directionality though and if the ground should be left floating on the amp side )
XLR should be grounded on both sides. The negative and positive signals are both sharing that ground reference. I don't think you want to leave one side floating. I could be wrong though, but when I connect balanced, I connect 3 conductors at both ends, no floating conductors.....unless you have 4 conductors I suppose....then you have an extra 🙂
The cable you posted has two conductors and a shield. For an unbalanced (single ended) signal + ground connection, I would use the two wires for signal and ground, connected at both ends, and use the shield as a shield. I think somebody already pointed out that the ground reference of both the source output and of the amplifier input and the chassis ground on either side can very well be two different things, with a DC resistance and possibly also a frequency dependent impedance between them.
If only one of the two sides has a chassis connection to (house wiring) safety ground, I would connect the shield at both ends to the device chassis. If both sides have chassis connection to safety ground, I would leave the shield connection on the source side optional, and test whether making a shield connection there introduces hum.
Regarding cable directionality, I think the marking on the cable is just to help you distinguish the end with shield connection from the end without shield connection, should you decide to fabricate your cable in such an asymmetric way.
It's perfectly fine.
No. You may need to provide a bit more detail re: what input configuration works for you, but the F5m is (as designed) SE only. If you want balanced in the future, then you'll need to make modifications. Me, I'd leave it alone.
It's just wire. You can strip out the conductors and use it for... well... anything you'd use wire for. It's (IMO) better for SE than balanced, but I've used it for balanced. It's just... wire. The existing twisted pairs, the fact that it's abundant, and it's essentially free to me are my motivating factors.
It depends on the adapter. Can you send a link, please. Either way, your RCA input wiring should stay the same on the F5m, IMO.
You can install XLR jacks, but unless you modify the amplifier, you will not install balanced inputs. I hope that's clear. The way you're describing (if I understand you correctly) will not work properly. If you want to take (just for convenience) an XLR output from a pre-amp carrying a balanced signal and plug it into your F5m and get music, the easiest way to do it (IMO) is just to use the adapters you have.
The connection of Pin 1 of an XLR jack is often discussed. I agree that it should be connected on both sides if it's carrying a balanced signal.... now... connected to what potential...? If you're talking about connecting the conductor commonly used as a shield for use as a GND vs. shield ... that's another discussion also.
The negative and positive signals 'reference' each other for differential. GND is just a construct. You can always reference "GND", and that's what it's commonly used for, but it's not entirely relevant to the differential signal. Current flow is another matter.
The 4th would typically be a shield. +, -, GND, shield, if we're talking about "microphone cables". Again... lots of discussion and lots of debate. There are standards, and there are some potentially valid reasons for deviation from the standards. 100s of pages of discussion in the forum and standards available for reference.
@roboDNA -
When we repurpose purpose-built cables for other applications, it can get fuzzy.
Summary of what I think I understand.
You have a pre-amp or source that is balanced and will output a differential / balanced signal from the XLR outputs. It does not have RCA outputs or you don't have a proper RCA cable, or you just like XLR cables. So, you will use an XLR to RCA adapter between the pre-amp / source and the F5m. The adapters typically short the negative signal (Pin 3) to GND (Pin 1).
If so...
You only need two wires / conductors inside the amp, but you have three in the cable you want to use.... so...
For RCA inputs on the F5m - What I would do with your cable is:
Red wire - connect it the (+) pad (near the word input) on the amp board and the center pin of the RCA input
White wire - connect it to (G) pad (near the word input) on the amp board and the lug / tab on the RCA input.
Shield - Unconnected (others may have a strong opinion differing and good reasons... so ... YMMV).
Again... that's what I'd do if I only had that cable to use. I would not show that as an example in the guide you're creating. I'd use a simple two conductor arrangement for the guide, but ... that's me.
There are tons of pictures of builds in this thread to emulate. When in doubt... I'd just do what 6L6 did.
Sorry for a long post... and mine is only one of many opinions. Mine is also definitely not an 'expert' opinion.
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@ItsAllInMyHead thanks for the detailed info. My mixer has unbalanced output as well so I'll use a 1/4" TS cable for each channel, and add a 1/4"TS->RCA adapter at the end. ( keep it simple ) I see what you mean about the amp being SE. I guess the F5m would need a differential amplifier instead of the SE for balanced and there would be 2 inputs on the amp board for each channel instead of 1. I was originally planning on having my mixer about 20' from the amp so figured balanced would be better but I don't think it would have been a huge improvement over unbalanced anyways. I can also move the mixer closer to the F5m if I am concerned. I don't plan on doing a balanced mod since I'm very happy with the SE amp.
I'm still not 100% sure on how shielding between the 2 devices would work but I'll just get 1/4"TS->RCA adapters and worry about it if I get a hum. I can see why there are so many opinions on earth ground shielding to avoid 2 devices to fight over earth ground. It makes sense to me to leave shield disconnected on 1 end if both devices are earth grounded, and connected if 1 device is not earth grounded. ( bit of a rabbit hole )
I think I'm all set now and can finish the wiring.
I'm still not 100% sure on how shielding between the 2 devices would work but I'll just get 1/4"TS->RCA adapters and worry about it if I get a hum. I can see why there are so many opinions on earth ground shielding to avoid 2 devices to fight over earth ground. It makes sense to me to leave shield disconnected on 1 end if both devices are earth grounded, and connected if 1 device is not earth grounded. ( bit of a rabbit hole )
I think I'm all set now and can finish the wiring.
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keep it simple:
having just XLR out (source side) and just SE input (down-side/amp)
make cable having XLR on one side and RCA on other side
XLR pin 1 goes to RCA GND (shield of cable usually)
XLR pin 2 goes to RCA Hot (hot of cable)
do it any differently, you'll end with hum
exception - source end stage needing balanced loading for best performance, but these are more than rare; I remember one from Papa's, but forgot which one; BOSOZ maybe?
having just XLR out (source side) and just SE input (down-side/amp)
make cable having XLR on one side and RCA on other side
XLR pin 1 goes to RCA GND (shield of cable usually)
XLR pin 2 goes to RCA Hot (hot of cable)
do it any differently, you'll end with hum
exception - source end stage needing balanced loading for best performance, but these are more than rare; I remember one from Papa's, but forgot which one; BOSOZ maybe?
@Zen Mod Just so I understand correctly; My mixer has 1/4"TS unbalanced outputs as well and I plan on using those instead of the balanced XLR outputs it also provides. I have 1/4"TS cables so was planning on getting 1/4"TS->RCA adapters. I hope I understand correctly that this will not introduce hum and is the simplest approach. ( no need to make my own cables with XLR->RCA ends )
from my explnation - just replace XLR with TRS
be sure to use 3pole jack (TRS) and leave neg phase pin unconnected (2pole - TS would unnecessary short negative phase output)
practically - SE signal is GND and positive of Balanced
Balanced is SE signal with added Neg phase
That's all you need for basic understanding, more or less in Layman terms
see here: https://deercreekaudio.com/tech-blog/f/trs-interconnect-cable-considerations
be sure to use 3pole jack (TRS) and leave neg phase pin unconnected (2pole - TS would unnecessary short negative phase output)
practically - SE signal is GND and positive of Balanced
Balanced is SE signal with added Neg phase
That's all you need for basic understanding, more or less in Layman terms
see here: https://deercreekaudio.com/tech-blog/f/trs-interconnect-cable-considerations
I'm curious to find out how the F5m design can be modified to allow balanced input. I'll start with SE but I don't think I can have my mac, mixer, synths and turntable all within a short distance from the amp. The turntable comes with a set length cable too ( 1.3meters ). I'll need to run RCA or 1/4"TS just over 15feet from my mixer as it is now and there is also some power running along the same runs. Single Ended will be good but if a mod is possible, I'll eventually be looking at this again.
I'm running 20' single ended from my JC-2 to the ACA using twisted pair in a floating shield grounded at the pre, along side several power cords and a 6' RGB LED strip. No hum or nasties of any kind. I don't think at such lengths balanced mode is necessary, but YMMV.
You could buy and install input transformers (balanced in, single ended out) while you wait for F5m design modifications. When that happy day arrives, remove the transformers, perform the modifications, and have a great day. Manufacturers to consider: CineMag Inc, Jensen Transformers, Edcor Electronics.
If you make the amp a proper balanced amp (two amp boards tied at the feedback), you will lower the distortion but will also have a higher 3rd harmonic distortion as compared to the 2nd harmonic. Not necessarily a bad thing but this amp was designed around the output devices creating a nice 2nd harmonic distortion. So the sonic will change.
If you stick to the suggestions above, then you will be better off.
If you stick to the suggestions above, then you will be better off.
Thanks for all the info. I'll stick to SE and leave it up to someone else with more expertise to make a mod. I don't want to change the sound either since it's my first build. If for some reason I get hum, I can also re-organize my equipment to be closer, or I can just run cable across the floor hidden with some duct tape for a shorter length 😉 Could be a reason for me to build a second amp too like Aleph Jzm suggested by @birdbox
Is another option to use a passive Direct Inject box from my mixer to the amp? This way I would only need to run 2 balanced XLR cables to the DI Box sitting next to the F5m.
If it's your first build I definitely agree that you should build it as designed to increase your chance of success.
Just make sure you buy a chassis that you can use to swap out boards. There will be plenty of opportunities in the future to try new designs, including balanced designs.
Just make sure you buy a chassis that you can use to swap out boards. There will be plenty of opportunities in the future to try new designs, including balanced designs.
Something like these DI Boxes. They look like transformers and I would connect it in reverse:
https://www.sweetwater.com/insync/di-boxes/
I'll revisit this once I have my amp built successfully and sounding good over SE cables. 🙂
https://www.sweetwater.com/insync/di-boxes/
I'll revisit this once I have my amp built successfully and sounding good over SE cables. 🙂
@roboDNA - Don't try to fit all the strands. Trim them.
You could also peel back a few strands and wrap them around the axis of the remaining wires to create a bit of a "stop" near the insulation.
Numerous techniques. Those are just two that I sometimes use.
Not all 16AWG wire has the same effective or actual OD. I don't worry about it too much.
Edited b/c 6L6 and I posted at roughly the same time.
You could also peel back a few strands and wrap them around the axis of the remaining wires to create a bit of a "stop" near the insulation.
Numerous techniques. Those are just two that I sometimes use.
Not all 16AWG wire has the same effective or actual OD. I don't worry about it too much.
Edited b/c 6L6 and I posted at roughly the same time.