3 outputs to one input

[SFM-Ptgal]

How can I join together the 3 balanced stereo outputs of a cart machine onto a a single unbalanced line input? I was told to use electronic boxes from RDL and others. The problem is that I can't afford such devices from a home user point of view.
Can I use resistances? How to join them to 9 wires? What values?

TIA

Pedro

 

[K6JHU]

You might try using three diodes (assuming the levels are about the same). The output is half wave recified but that is not an issue unless you are looking for superhi fidelity.

 

[raydofan]

You might try using three diodes (assuming the levels are about the same). The output is half wave recified but that is not an issue unless you are looking for superhi fidelity.

I don't think that is going to have good results with audio.

Try a resistor pad.

 

[ironbear]

You might try using three diodes (assuming the levels are about the same). The output is half wave recified but that is not an issue unless you are looking for superhi fidelity.

I don't think that is going to have good results with audio.

Try a resistor pad.

Diodes are fine for isolating and combining DC voltages. Never in an application mixing delicate audio signals (half the AC waveform will be missing and your audio will be hosed).

Cart machine outputs were often highly tolerant of improvised connections. More than a few vintage machines, including triple-decks (is this what you're talking about?) used opto-attenuators on the output circuits. These were used to disconnect the output when not in play mode, muting noise.

In a pinch these can actually be mixed by wiring the outputs directly together (or if you want to be cool, use 600 to 1500 ohm resistors). To get an unbalanced signal, many machines will let you strap each - signal to ground. Use only the + hots and ground to feed your unbalanced input, eh?

 

[OlderRadioGuy]

Audio level may also be a concern; for a home application, I'm speculating that the unbalanced input might be hi-Z, low level. If so, sum the three + outputs (as mentioned before) through 4700 to 10,000 ohm resistors (using the cart machine ground in lieu of the - output), and experiment with a lower resistance, say 1000 ohm, to ground at the unbalanced load to reduce the audio level to one suitable for the unbalanced input. We don't know the source impedance of the cart machine output - IF it is 600 ohms, and only if you're really fussy, the three outputs could also be terminated directly in a 600 ohm resistor.

 

[Chuck]

Audio level may also be a concern; for a home application, I'm speculating that the unbalanced input might be hi-Z, low level. If so, sum the three + outputs (as mentioned before) through 4700 to 10,000 ohm resistors (using the cart machine ground in lieu of the - output), and experiment with a lower resistance, say 1000 ohm, to ground at the unbalanced load to reduce the audio level to one suitable for the unbalanced input. We don't know the source impedance of the cart machine output - IF it is 600 ohms, and only if you're really fussy, the three outputs could also be terminated directly in a 600 ohm resistor.

A resistive combining network should work fine. If home brewing one, you might try Behringer's little micro mixer. I think you can buy it on line for about $20-25 USD. http://www.behringer.com/MX400/index.cfm?lang=eng
It would be a quick easy solution for a home studio.

 

[greg.hahn]

1 K resistors will work just fine.

Connect a 1K resistor to each + output, then connect them all together to go to the input.

If your cart machine has transformer balanced outputs, ground the minus side.

If it has active balanced outputs, leave the minus side floating, and connect the shield at both ends.

 

[CW]

1 K resistors will work just fine.

Connect a 1K resistor to each + output, then connect them all together to go to the input.

If your cart machine has transformer balanced outputs, ground the minus side.

If it has active balanced outputs, leave the minus side floating, and connect the shield at both ends.

Correct answer!
If they are active (opamp) outputs, they can expect to drive 600ohm to 20K loads with little change in level....by using only the + output (or the - output would work here.....they are both the same except the - output is 180 degrees inverted through an opamp stage), you get about a max level of -6dbm (you get +4 with both + and - connected properly)...consumer level is -10dbm...thus with a 1K or higher resistor inline with each machine, you will have a little voltage divider (the output of each opamp on the active outputs is mathematically ZERO...but usually more like 30ohms or so impedance) so you should be RIGHT on the money..
As for transformer outputs, they expect 600ohm loads...if you tie these via 1K resistors, you will see a loss but now you will have the full +4dbm/dbu output into the resistor combiner since you have to use both + and - as hot and ground in this case only! Coupled to the other 600ohm loads, you will see about a 3-6db drop in level....you MAY get close that way to a -10 but you may have to readjust levels to get it to sound ok...make sure ALL three machines are connected via the resistive mixer before adjusting.


What mode cart machines are they? If you need help in determing if they are transformer or active, we can find out for you.

 

[sparks794]

If you have the book on them you might take a look and see what the manufacturer suggested