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dbx 286splitting output to go into e.q.

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dbx 286splitting output to go into e.q.

Postby David English » Thu Sep 17, 2020 12:45 am

Hi,
to those who know much more than I.
I am using a sennheiser 416 condenser mic into the 286 s as a channel strip, into a DBX 231s E.Q. then into my desk via line input on desk( zed 60 fx), but sometimes I need to use the two units to go into the camera preamp to record a demo video . just one vocal channel for Skype tuition.

To save unplugging this 1/4 inch cable from the e.q. output and then plugging into the XLR output with an xlr to xlr cable into the camera, all from channel 1, can I split the output from the single 286s output into left and right I/4 inch balanced inputs on the eq and use channel 1 out as normal into my desk and use channel 2 output of eq into my camera to save unplugging all this stuff. I have a balanced 1/4 inch splitter cable with balanced pugs on all 3 points

I called dbx harman but he wasn't sure when I asked if I could just plug into both outputs of channel 1 at same time, 1/4 and XLR as something in the book about 2 ohm load , but it did say you could use both channels at once.
I have no idea about loads, I would just have one lead in use at a time, but he said maybe having a lead hanging with no load on it may cause hum, as an incomplete circuit or something.

cheers and thanks to those who offer their time and help.
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Re: dbx 286splitting output to go into e.q.

Postby resistorman » Thu Sep 17, 2020 3:34 am

David English wrote:can I split the output from the single 286s output into left and right I/4 inch balanced inputs on the eq and use channel 1 out as normal into my desk and use channel 2 output of eq into my camera to save unplugging all this stuff. I have a balanced 1/4 inch splitter cable with balanced pugs on all 3 points

I think this would probably work fine. Why not try it? Also, there are 2 outs on the eq, you could try sending the XLR to the camera. Or how about using the aux send from the mixer?
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Re: dbx 286splitting output to go into e.q.

Postby David English » Thu Sep 17, 2020 11:13 am

thanks ,
I was mainly wondering the ohms loads, for the output of the 286s and the split signal ohms going into the 231 e.q.
when the signal is split will it be enough ohms to power the signal to both left and right
cheers
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Re: dbx 286splitting output to go into e.q.

Postby Hugh Robjohns » Thu Sep 17, 2020 11:50 am

David English wrote:...can I split the output from the single 286s output into left and right I/4 inch balanced inputs on the eq and use channel 1 out as normal into my desk and use channel 2 output of eq into my camera to save unplugging all this stuff.

Short answer: YES

Longer answer: The whole raison d'etre of the 'matched voltage' analogue interfacing system we have been using in pro-audio for five decades is specifically to allow passive signal splitting at line level between equipment.

However, this concept requires a low source (output) impedance (typically 100 Ohms or less) and a high destination (input) impedance (typically 10,000 Ohms -- 10K Ohms -- or higher). Usually, the destination impedance should be about 10x greater than the source impedance -- and your DBX units, not surprisingly meet these requirements.

So you can safely use a balanced parallel or splitter cable between the single output of the 286 preamp (200 Ohms output impedance) to send the signal into both channels of the 231 graphic EQ (40K Ohm input impedance). Because a passive split means the two inputs are in parallel, the destination impedance seen by the preamp will be half of an individual input, so 20K Ohms -- but that is still ten times greater than the source impedance, so all is well.

You can then connect the two separate outputs of the EQ to your camera and mixer, where they will be completely independent of each other.
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Re: dbx 286splitting output to go into e.q.

Postby David English » Thu Sep 17, 2020 3:29 pm

wow, Smart man, thanks a lot I had to read it about 6 times, so as long as I don't burn up any of my new gear, many many thanks
David
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Re: dbx 286splitting output to go into e.q.

Postby David English » Thu Sep 17, 2020 3:35 pm

thanks again Hugh, I missed the K in 40, as in 40,000, i thought I was reading 200 out chickens into 40 chickens but it was into 40,000 chickens.
that explains it in my head after I re read your post.
stupid me. cheers
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Re: dbx 286splitting output to go into e.q.

Postby David English » Thu Sep 17, 2020 3:39 pm

just one more question please, sorry to bother you, why are the ohms in greater than the ohms out, why does the signal strength vary and not flow through evenly to a standard, ??? cheers
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Re: dbx 286splitting output to go into e.q.

Postby Hugh Robjohns » Thu Sep 17, 2020 4:46 pm

David English wrote:...why are the ohms in greater than the ohms out, why does the signal strength vary and not flow through evenly to a standard, ??? cheers

If you want the full lowdown, there's an article here that might be helpful:

https://www.soundonsound.com/techniques/understanding-impedance

But the simple(ish) answer is that it's all to do with Ohms Law that you might have learned about at school.

A sound source and receiving equipment can be represented like this:

Image

The signal generator in the source creates an AC voltage. That forces current through the output impedance (effectively a resistance), down the cable, through the input impedance of the receiving equipment, (another resistance) and back to the generator.

Now that arrangement can be redrawn as a simple potential divider like this:

Image

Where Vin is our source signal generator, R1 is the output impedance, R2 is the input impedance, and V out is the signal received at the destination.

We want as much of that source voltage to arrive at the destination as possible, which means we need as much of it as possible to be developed across the input impedance (R2), and as little as possible across the output impedance (R1).

Ohms Law states that V=IR -- voltage is the product of resistance and current. Clearly, the same current flows through both R1 and R2, so if we want the maximum possible voltage to appear across R2, it has to be as large as possible, and R1 has to be as small as possible.

This arrangement is called 'voltage matching' because the voltage at the destination (almost) matches the voltage generated at the source.

However, there are practical limits as to how large and small those impedances can actually be in real-world electronics, so a typical ratio is about 10:1, as discussed earlier.

And if R2 is sufficiently large, it is possible to parallel several of them -- which is what happens when you passively split a signal to feed multiple destinations -- without dragging down the voltage that is developed across them too much. In practice, it's usually possible to split a signal to four destinations and only lose less than 0.5dB of signal voltage compared to the level when feeding a single destination.

To answer your other question, if R1 and R2 were equal -- in other words if the output impedance matched the input impedance, then you'd end up with half the source voltage developing across the output impedance, and the other half across the input impedance -- so the destination would get a signal that was half the size of that created by the source! Which wouldn't be very helpful in our situation....

Nevertheless, this arrangement was and sometimes still is used in specific situations. One of the benefits of this arrangement is that it maximises the transfer of power (as opposed to voltage), which can be important in some specific (non-pro-audio) circumstances. And it's also important for the transmission of signals along very long cables (long relative to the signal wavelength) to prevent reflections within the interface -- something which affects video and digital audio, for example.

So AES3 interfaces have a 110 Ohm source impedance, and a 110 Ohm destination impedance, too. S/PDIF and video connections both use 75 Ohms at both ends...

But for analogue pro-audio, we are only concerned with the transfer of signal voltages, and so we use low source output impedances and high destination input impedances.
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Re: dbx 286splitting output to go into e.q.

Postby David English » Thu Sep 17, 2020 11:04 pm

Good morning from Australia
thank you very much again, very informative and I appreciate you for taking your time to help me.
Cheers
David
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Re: dbx 286splitting output to go into e.q.

Postby David English » Thu Sep 17, 2020 11:28 pm

hi
it splits fine thanks
in the book it says in one line.
''more than one output can be used simultaneously, as long as the combined load is not greater than 2 ohms.''

does that mean instead of using a splitter I can plug into the channel one 1/4 inch output and the xlr output at the same time.
I wont because of confusion, and your previous advice,, but if you did, how do you know the ohms loading from the mic/desk and camera preamp/

I am a retired construction engineer and I used to enjoy listening to the electrical guys etc. on site
thanks again, I read your bio, I got more info from you than DBX technical, he just said it should work.

thanks a lot.
just a fun thing since you are in England?, many years ago I went to abbey road to do the tourist thing, I set up my camera to take selfies going across that pedestrian crossing, took a few photos then a council worker said I was on the wrong crossing, ha ha cheers
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Re: dbx 286splitting output to go into e.q.

Postby Hugh Robjohns » Thu Sep 17, 2020 11:40 pm

David English wrote:in the book it says in one line.
''more than one output can be used simultaneously, as long as the combined load is not greater than 2 ohms.''

Almost... what it actually says is:

DBX wrote:More than one output may be used simultaneously as long as the combined parallel load is greater than 2 kΩ.

The K is important -- it means thousands... so the minimum acceptable load is 2000 Ohms.

does that mean instead of using a splitter I can plug into the channel one 1/4 inch output and the xlr output at the same time.

Yes... provided both destinations have input impedances of greater than 4000 Ohms.

how do you know the ohms loading from the mic/desk and camera preamp

You'll need to check the specifications for the desk line input and camera input. A typical console line input will be 10,000 Ohms or more (10k Ohms). A mic input is typically 1,500 Ohms (1.5k Ohms)
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Re: dbx 286splitting output to go into e.q.

Postby David English » Fri Sep 18, 2020 5:34 am

AMAZING THANKS, GREAT BIO/RESUME ALSO. CHEERS
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