good evening,
making a home-brew whole house audio system, consisting of 4 zones each with a single speaker, each zone served by a dedicated mono amp. so far so simple.
i want to have a volume control for each room, and i would prefer to control the input signal before it gets to the amp, so that the amp's auto-detect feature will allow them to power down when i'm not listening to anything.
would microphone cable be the best option for sending my source signals? obviously looking for the best noise rejection.
thanks!
[EDIT]
thanks for the replies! i should have provided more information.
this is just in a small residential application, so i have two 30' runs (counting distance from the source, to the location for the volume pot, and back to the amp) and one 70' run.
making a home-brew whole house audio system, consisting of 4 zones each with a single speaker, each zone served by a dedicated mono amp. so far so simple.
i want to have a volume control for each room, and i would prefer to control the input signal before it gets to the amp, so that the amp's auto-detect feature will allow them to power down when i'm not listening to anything.
would microphone cable be the best option for sending my source signals? obviously looking for the best noise rejection.
thanks!
[EDIT]
thanks for the replies! i should have provided more information.
this is just in a small residential application, so i have two 30' runs (counting distance from the source, to the location for the volume pot, and back to the amp) and one 70' run.
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If the signal is balanced, and you have no option other than to send the line level each room before going back to the amps, and you have a way to passively attenuate the signal without degrading the cmrr of the balanced signal.... maybe. How far are we talking for line level runs? You didn’t state this explicitly but I’m assuming the amps are all together in some central locations long with the source? A motorized pot with the analog section at the amp and the dc control in each room might be better.
First option is unbalanced with the red wire signal into the control and the black wire the return to the amplifier the shield being used as common. That might work for short runs. But is not really a good idea.
Second is to transformer balance the send and receive. Look at Triad TY-146P transformers at $8.00 or so each. Then the control pot should be sort of balanced. This is done by making the wiper the input and the fixed terminals the output. You do have to put a fixed 600 ohm resistor in series with the input. That should work for a few hundred feet. Of course use a cable designed for permanent installation with a foil shield that gives 100% coverage. Braided shields are meant for portable or flexible cables. Larger diameter cables also turn out to have more effective shielding. But for what you are doing 22 gauge wires should be fine.
The best way is to use an LED photocell combo. This then only sends DC down the control cable. You should be able to find all the parts for less than $10 per channel. The basic idea is that you source a voltage to the control, this then is in series with a current limiting resistor to give you a maximum current of 10 mA. To feed the LED. The photocell is in series with the signal. As the photocell can be several meg ohms when there is no current you may not even need an additional load resistor. Typical pot values are around a megohm. Plenty of circuit examples on the web.
Just remember you can't put it on the web if it is not true!
Second is to transformer balance the send and receive. Look at Triad TY-146P transformers at $8.00 or so each. Then the control pot should be sort of balanced. This is done by making the wiper the input and the fixed terminals the output. You do have to put a fixed 600 ohm resistor in series with the input. That should work for a few hundred feet. Of course use a cable designed for permanent installation with a foil shield that gives 100% coverage. Braided shields are meant for portable or flexible cables. Larger diameter cables also turn out to have more effective shielding. But for what you are doing 22 gauge wires should be fine.
The best way is to use an LED photocell combo. This then only sends DC down the control cable. You should be able to find all the parts for less than $10 per channel. The basic idea is that you source a voltage to the control, this then is in series with a current limiting resistor to give you a maximum current of 10 mA. To feed the LED. The photocell is in series with the signal. As the photocell can be several meg ohms when there is no current you may not even need an additional load resistor. Typical pot values are around a megohm. Plenty of circuit examples on the web.
Just remember you can't put it on the web if it is not true!
i'm trying to confirm if microphone cable is the best option for exactly what you're describing. Monoprice 8.0mm Professional Microphone Bulk Cable - 500FT - Monoprice.com
as a controls and commercial audio guy, i was originally looking at using 18/2 STP, but got generally advised that foil shielding was inferior to braided copper shielding for this kind of application. which was news to me.
how would adding impedance affect the shielding performance of a cable?
i'll have to look up how audio isolating transformers work
my plan is to use a cheap-ish board amplifier to drive an 8r speaker, somewhere in the neighborhood of 75-100w. i was going to use a regular mono volume pot, somewhere between 10k to 50k once i had decided on my amplifier.
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i think a motor pot will end up being the best option. i didn't know they were available in modular options for $20-30 range. that will be cost equivalent to buying the dedicated cable for the volume control, and mean less wiring.
now i just need to find one that doesn't rely on a stupid IR remote, and can take hardwired buttons for the controls.
thanks for the suggestion!
how would adding impedance affect the shielding performance of a cable?
i'll have to look up how audio isolating transformers work
He didn’t say “shield”, he said “noise”. Mic cable get most of their noise immunity by being balanced lines that reject common mode noise. The shield blocks what it can and what gets through it affects both polarities equally and is nulled. Transformers have very high noise immunity because the impedance on both ends of the coil are equal and cancel very well.
The alps models I’ve played with just have + and - terminals for dc. I think you’d just need a DPDT switch with an (on) off (on) behavior. Wire the dc to the throw terminals (opposite polarity n one end compared to the other) and the common terminals to the motor coil.
If you use a low impedance signal source, from a pre amp say, then screened leads are not needed.
Convert the signal from the 'control room' to a higher impedance with a microphone type transformer, like this one; Z1677E | Through Hole Audio Transformer 300Ω 2mW | RS Components
Sending a 75R impedance ,probably less, signal is almost totally immune from noise, except if run alongside power cables.
This system worked on a run of over 800yards for our village fete so a few yards in a home should be no issue.
If you want a DC powered volume control on the amplifier end, you can send DC down the cable if you use a suitable coupling capacitor. The same as we do for 100volt line loudspeakers and 48volt phantom power in microphones.
Convert the signal from the 'control room' to a higher impedance with a microphone type transformer, like this one; Z1677E | Through Hole Audio Transformer 300Ω 2mW | RS Components
Sending a 75R impedance ,probably less, signal is almost totally immune from noise, except if run alongside power cables.
This system worked on a run of over 800yards for our village fete so a few yards in a home should be no issue.
If you want a DC powered volume control on the amplifier end, you can send DC down the cable if you use a suitable coupling capacitor. The same as we do for 100volt line loudspeakers and 48volt phantom power in microphones.
ah, so mic cable relies on being a balanced source for effective rejection.
thank you for clarification, this is finally within my limited understanding
Braided cable shields are inferior to foil. In the most critical applications they use both. Braid for depth and foil for 100% coverage. In cable tv systems they do both twice for four layers.
One trick for distributed RF is to use just braided cable strung out where you want the signal to service. There is enough leakage through the braid to provide the coverage. The cable is of course terminated with a resistor.
thanks for the suggestion, i'm looking into a PGA2311 solution now, since i can send control signals to the IC without concern about the noise from the motor pot bleeding into the signal.
as always, i nearly immediately fall into a rabbit hole as soon as i start trying to figure something out
thanks for the suggestion, i'm looking into a PGA2311 solution now, since i can send control signals to the IC without concern about the noise from the motor pot bleeding into the signal.
as always, i nearly immediately fall into a rabbit hole as soon as i start trying to figure something out
I did some stuff with the PGA line recently. I didn’t like the sound unless run differentially. Even then, now you’re talking about a micro controller and SPI communication that has its own cable length to deal with. Why do you think motor noise will contaminate the audio signal? These aren’t servos or steppers and you don’t need PWM to control them. You just apply the power and they start to rotate; apply it in reverse and they rotate back.
honestly, just from reviews from a few motorized pot kits from ebay
you, of course, have a good point. if the motor is only powered to change the volume, who cares if it's a bit noisy.
I would simplify setup to use low impedance out buffers , which combined to line level signals means almost any reasonable shielded wire will be enough.
So no need for elaborate motorized faders, remote LDR setups, etc.
Just one Op Amp output driving "send" signal, same for "return from pot" one, at most you may need to send +15/30V to feed buffer, no big deal.
That IF it´s needed, I think a signal driving a 5k or 10k remote volume pot, both send and receive and with no active electronics, can be protected enough by any reasonable shielded microphone wire.
So no need for elaborate motorized faders, remote LDR setups, etc.
Just one Op Amp output driving "send" signal, same for "return from pot" one, at most you may need to send +15/30V to feed buffer, no big deal.
That IF it´s needed, I think a signal driving a 5k or 10k remote volume pot, both send and receive and with no active electronics, can be protected enough by any reasonable shielded microphone wire.
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