Mythbusting S/PDIF, TV Coax interchangeability, limits

Discussion in 'The Projects Forum' started by Yesm8, Apr 22, 2016.

  1. Yesm8

    Thread Starter New Member

    Apr 20, 2016
    Hello my endearing copper obsessed savages,

    I seek to find a final answer in my quest to the ultimate budget garden speaker setup.
    I was first planning for a project box with mono amp boards to power 6 seperate speakers.
    That would leave my volume controls in the house though instead of where I need them (at the speakers).
    The same being the case if I shell out the cash for a second hand PA amplifier.
    So I switch my focus and plans.
    I want to hook up these small and insanely cheap amplifiers (in mono, using only 1 of the stereo outputs with a mono source).

    The only thing I need to bring from the house is a source.
    I'm thinking digital S/PDIF coax given the apparent losses with regular analog RCA, TOSLINK (optical), the pragmatic impossibility of sending 6 small DACs audio through USB and the same "handshake" and range impossiblity with bluetooth.
    It is actually surprisingly remarkable we don't have a decent, widely used and accepted wifi or single end, direction, near field RF solution, standard for sending wireless audio to multiple speakers.
    All we really have is DIY, expensive limited proprietary "brand" concepts like SONOS and logitech squeezebox and crappy short-range, finicky bluetooth connections which also are pretty proprietary.
    We really need to see a standardised format like HDMI for wireless audio over RF.

    That said... I really would like to avoid having to buy this hilariously priced 6 way S/PDIF coax splitter/amplifier: (well basically I wouldn't)
    I'm thinking after reading many threads about the near infinite range and splittability of coax cable. Do I even need such an amplified splitter?
    Can't I just use a CATV splitter, COAX cable with RCA plugs?
    To ultimately go to 6 different cheapo DACs mounted with the amp and a solar powered battery (all providing the needed 5v of both amp and dac)?

    The main questions however... Will this 6 way passive splitting of the digital audio render the signal too weak or jittered, noisy? Do I need to wire resistors between the DAC and the coax cale for it to see 75 Ohm impedence? Do I need to "amplify" the signal as the existence of such a product would indicate? Given the (10-20m) lengths I want to run the coax cables... Is this possible? Is making my own 6 way digital S/PDIF amplifier realisttically feasible and where/how could I do this? As every thread I read on this seemed to be able to run the digital S/PDIF, coax through nearly every thing imaginable, y splitters, RCA analog cables, CATV splitters... One guy even claiming he ran a signal through clothes hangers to prove a point at one instance...

    Long story short. Does this have a chance as the threads on it gave me the illusion it does. Does anybody have a way in which it COULD work... Is making my own amplifier feasible, worth it? Or does anybody have an alternative solution to multi-zone, affordable audio?
  2. wayneh


    Sep 9, 2010
    I have a home intercom with a half dozen zones. It uses simple two-conductor wiring from the central amplifier with volume controls on both ends.
  3. Yesm8

    Thread Starter New Member

    Apr 20, 2016
    It is of course possible to use a volume control at the speaker. But the components I am able to get are so cheap it seems worth it to me to do it like this for audio quality purposes. Perhaps the 6 mono amp solution with volume controls built into the speakers is the most sensible solution. With home intercom do you just mean some way to talk to the man at the door or a sound system for music? And are they wired to a self-made amp or some PA amplifier? Are multiple speakers wired to a single output (I guess not since you say half a dozen zones).
    I heard about negative effects of volume control at speaker level and wiring multiple speakers to a single amp output. I'm doing it for the hopefully enjoyable sound I'll get so I'd rather not compromise too much.

    My main question remains whether someone has any real idea what the limits of RCA, coax cable lengths and splitting before losing function are. Because if somebody can somehow confirm that this should work or shouldn't work... I can get on with a solution that DOES work (for a reasonable price and with reasonable quality, which seems quite the challenge).
    The problem is a complete lack of consumer grade solutions in this respect it seems to me.
    No doubt audio engineers, DJs, party gear professionals have balanced and unbalanced splitters, mixers, etc in abundance. It's for small projects like this a lack of "cost-effective", down to earth, efficient products seems to be lacking.
  4. Yesm8

    Thread Starter New Member

    Apr 20, 2016
    Should I just conclude that it can't be done?
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    The time from post #2 to #3 was 17 minutes. I think you can conclude that we're not in as big a hurry as you are.

    Given the repeated use of the word "cheapo" to describe your components, and the fact that this is an outdoor listening environment with enormous masking background sounds, I don't understand why you want to preserve digital audio signals to the speakers. You absolutely positively will not hear it. I'm not picking on you or your idea, just pointing out that yards and cars are *horrible* listening environments. Since the amps are only 5 W, you could run power and analog audio out to them on CAT-3 or CAT-5 cable with everything hard-paralleled on a terminal block. No active or passive electronics in the distribution system, no need for solar power, etc. Once you're committed to running a cable to each speaker, make the cable do all of the work.

    And, to clear up a misconception -

    "the near infinite range and splittability of coax cable."

    does not exist. For true signal integrity, coax cable needs source and destination termination in its characteristic impedance, and acts as a distributed lowpass filter. Over a short distance, most of the stories about weird hooks probably work. But digital audio is a high-bandwidth signal, cable TV splitters *do* attenuate the signal based on how many taps there are, and it just seems like a whole lotta work for mono audio delivery.

    If you are concerned about noise pickup with an analog audio signal, then simple shielded cable with enough DC power superimposed to run an amp is a simple project lotsa people around here know about.

    nsaspook likes this.
  6. wayneh


    Sep 9, 2010
    It does both.
    It's a commercially available home system, with the main amp in the wall in the kitchen. I don't know how the speakers are wired internally, whether they are applied in parallel to a single amp output or whether there are multiple amps. Each speaker channel (and there are actually 10) is selectable with a 3-way toggle switch. You can select whether to listen to the remote speaker/microphone, "off", or to send the intercom signal to that speaker. The intercom signal will be a mix of any music playing and the sounds being monitored by the system. So you might have low music and also be able to hear if the baby starts crying upstairs.
    I can't comment on the quality implications. The system works well, and I believe the speaker itself is the weakest link in terms of sound quality. FWIW, the speaker channels expect to see a higher than normal speaker impedance. I think it was 65Ω. An 8Ω speaker works, but I added an impedance matching transformer to protect the amp.
  7. Yesm8

    Thread Starter New Member

    Apr 20, 2016
    I know that none of these products fit exactly what I'm looking for or even the designed purpose (as simple, affordable 6 or more way mono/stereo RCA or S/PDIF distribution amplifiers don't seem to exist on the market).
    But which of these products would give me the most success in trying to distribute audio over 6 channels?

    Analog RCA to drive one channel of the small stereo amps distributed through this 8ch video amplifier?

    Basically doing the same with this 8 way video & audio splitter. (makes the most sense with the RCA red/white in and outputs actually being made for the purpose of audio distribution)

    Or distributing a coax S/PDIF signal over 6 channels through this CATV coax amplifier?

    I want this to be as "value for money" as possible and I am pretty allergic to redundant in or outputs.
    Ideally the passive splitting of the coax would work but that is highly unlikely as I'm aware.
    The positive reports of this type of stuff working made me hope for the best, question the feasibility in this forum.
    In terms of my satisfaction with audio quality I think the active CATV splitter distributing an S/PDIF signal to cheap DACs
    built into the garden speaker cases if possible would give the best audio quality but I'd like input from you guys as to whether that would actually work.
    So my best option would probably be to either use the 6 channel RCA video distribution amplifier for 6 mono audio signals (if that works, would like some input if possible) or use the 8 channel stereo+video RCA distribution amps to send the mono signal ignoring 2 of the 3 outputs per channel which dissatisfies me in terms of power usage, efficiency and overall outcome of the project.
  8. Yesm8

    Thread Starter New Member

    Apr 20, 2016
    In response to analogkid.

    I am interested in your suggestion of using CAT 5 cables for both power and the audio signal.
    I'd still need to split the mono audio signal 6 times though or are you confident that wiring them all to a single output of a DAC in the house would provide enough audio fidelity, current etc? (probably not)
    How would you suggest I provide the necessary 5v 2A to each of the speakers?
    I'm quite ignorant of the electrical side of things so I'm not sure what sort/type of adapter I'd need to buy or build.
    I'm not sure what you mean by "hard-paralleled on a terminal block".
    Do you have experience with using CAT 5 to run audio signals or can you link me to a project/thread where they do this?
    This would give similar audio quality to running a dedicated RCA analog?

    Thank you both for the input.
  9. Sensacell

    Well-Known Member

    Jun 19, 2012
    CAT-5 cable is a great solution for any remote signal / power application.

    Since CAT-5 is 8 conductor cable, you can use 6 wires for DC power, parallel 3 of the 4 pairs for lower resistance.
    Run the audio over the 4th pair as BALANCED AUDIO, use an audio transformer at the receiving end to avoid any ground loop issues and to convert the signal back to UNBALANCED- then feed this into your amp. you can easily run 30-40 watts remotely this way.

    I would use 24 Volts with a DC-DC converter to get you back to 5V at the amp end, this way voltage drop in the cable is automatically compensated.

    It's simple, cheap and will sound great, the balanced and isolated audio transformer concept keeps you noise free.