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Combining Audio with 10k

post #1 of 12
12/18/11 at 11:34am
Thread Starter 
I'm combining audio from multiple line outputs into a single line input.

I understand the need to use 10k resistors to isolate each source from shunting each other, so I am using this premade device instead of wiring my own:

STD-10K
http://www.rdlnet.com/product.php?page=349

This device claims to be able to combine/divide up to 4 devices properly with 10k resistors. However, using my multimeter, there is only 1200-ohm between each + terminal (or 600-ohm per terminal).

Does anyone else use these devices?
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post #2 of 12
12/18/11 at 12:02pm
Hi Josh,

It sounds to me like you simply received a mis-marked version. I think you received a 600 ohm version marked as a 10k version.
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post #3 of 12
12/18/11 at 12:03pm
Thread Starter 
You are probably right... but I have 2 like that, same way. They might have been from the same batch.
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post #4 of 12
12/18/11 at 1:07pm
Quote:
Originally Posted by joshf View Post

I'm combining audio from multiple line outputs into a single line input.

I understand the need to use 10k resistors to isolate each source from shunting each other, so I am using this premade device instead of wiring my own:

STD-10K
http://www.rdlnet.com/product.php?page=349

This device claims to be able to combine/divide up to 4 devices properly with 10k resistors. However, using my multimeter, there is only 1200-ohm between each + terminal (or 600-ohm per terminal).

Does anyone else use these devices?

DO NOT do this. If you need to combin two sources, get mixer. It will cost you under $100.
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post #5 of 12
12/18/11 at 1:16pm
Quote:
Originally Posted by ap1 View Post

DO NOT do this. If you need to combin two sources, get mixer. It will cost you under $100.

Why? There is no harm in resistor coupling of Line signals. What do you think happens inside a mixer? Same thing. If the mixer has buffer amps for each channel it will provide better isolation between sources, but there is no danger in doing what the OP wants to do.

For the OP, call RDL and ask them. They have good tech support.
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post #6 of 12
12/19/11 at 7:14am
Thread Starter 
Why shouldn't I do this? I have no need for individual volume controls, so a mixer is overkill. There has been lots of discussion here about using 10k resistors when using Y-Cables to combine signals.

That being said, these RDL 10k combiner devices are not actually what they seem to be. I called tech support and they said there is only about 1.2k between each device even though it is called STD-10K. They said the 10K in the product name is actualy referring to the impedance of devices you connect to it... not the resistance or isolation between those devices.

So, that being said... do I still need 10k resistors between each device that I combine, or will the STD-10K device properly/safely combine without additional resistors? One of this device's specifically intended purpose is to combine signals 3-in, 1-out.
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post #7 of 12
12/19/11 at 7:18am
Quote:


DO NOT do this. If you need to combin two sources, get mixer. It will cost you under $100.

It is a mixer.
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post #8 of 12
12/19/11 at 11:15am
Quote:
Originally Posted by joshf View Post

Why shouldn't I do this? I have no need for individual volume controls, so a mixer is overkill. There has been lots of discussion here about using 10k resistors when using Y-Cables to combine signals.

That being said, these RDL 10k combiner devices are not actually what they seem to be. I called tech support and they said there is only about 1.2k between each device even though it is called STD-10K. They said the 10K in the product name is actualy referring to the impedance of devices you connect to it... not the resistance or isolation between those devices.

So, that being said... do I still need 10k resistors between each device that I combine, or will the STD-10K device properly/safely combine without additional resistors? One of this device's specifically intended purpose is to combine signals 3-in, 1-out.

You should be fine. If the source device has an OPAMP driver stage, the impedance is usually 100 ohms or less. Some consumer devices have series resistors anyway.
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post #9 of 12
12/19/11 at 12:53pm
RDL products have an excellent industry rep and work quite well. You will find any number of their products in broadcast and industrial apps.

There is zero danger in using this device as a passive mixer.
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post #10 of 12
12/19/11 at 1:10pm
Quote:
Originally Posted by Gizmologist View Post

RDL products have an excellent industry rep and work quite well. You will find any number of their products in broadcast and industrial apps.

There is zero danger in using this device as a passive mixer.

For the price of RDL unit, one can get active mixer like this http://www.behringer.com/EN/Products/MON800.aspx
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post #11 of 12
12/19/11 at 6:53pm
The RDL is the simplest ready-made device that fits the needs of the OP. Building it himself will cost even less and be quite simple. 4 -10k resistors all connect at one end as the mix out and each line in to a dedicated Iso resistor. That is the way it was done for many moons. A separate buffer amp for each channel is NOT always necessary, Shure had a very successful and industry dominating of mixers for about 30 years using (M68) using ONLY Iso resistors and a 20k pot controlling each input on a 4 mic mixer. There are hundreds of thousands of these still in use today.
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post #12 of 12
12/19/11 at 8:21pm
+1
Quote:
Originally Posted by Gizmologist View Post

. . . A separate buffer amp for each channel is NOT always necessary . . .

. . . as there will typically be a buffer-amp at the output of each device being mixed anyway. The only components for a mixer that would be missing are the summing-junction resistors, which the RDL unit provides.
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