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Author Topic: Please help with impedance connecting laptop to mixer  (Read 5198 times)

Igor Krupin

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Please help with impedance connecting laptop to mixer
« on: February 08, 2016, 01:30:06 PM »

I'm using sabre-dac-uae23 dac from hifimediy (http://hifimediy.com/sabre-dac-uae23)

the output specs are as follows:
=======================
Open 2.2Vrms
4.7Kohm 2.1Vrms
1.8Kohm 1.9Vrms
510ohm 1.5Vrms
330ohm 1.3Vrms
30ohm 1Vrms

I'm connecting the sound card to mixer via 1/8 trs to dual 1/4 ts cable. It's an unbalanced connection (very short cable, I don't mind).

The mixer i'm using is Behringer UB2222FX-PRO

It has several stereo input channels rated at 10k unbalanced and 20k balanced.

See line 9/10, 11/12, 13/14 and 15/16 in this close up

THE PROBLEM:
=============

I only need to move the fader up very little from infinity for the sound to get loud. So i just nudge it up and the level is good. I would like the fader to be moved up to zero or a bit below for the sound to get loud enough.

All my other microphones and everything else is good. I think the system is properly "zeroed".

THE SOLUTION (that I need help with)
=============================

I'm thinking impedance is to blame here. I've tried to read several impedance articles and I just could not care for the theory, I need practical solutions. Once I have a practical solution I may be interested in the theory behind it.

What I want to get is this:

s2s-series

Will this solve my problem? What should i put for primary and secondary transformer impedance? I'm thinking 600 ohms to 10k ohms? Or should be it be 15k ohms to 150ohms? I'm not sure if primary means input and secondary output.

Please advise, thank you!
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Keith Broughton

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Re: Please help with impedance connecting laptop to mixer
« Reply #1 on: February 08, 2016, 01:50:50 PM »

Do you have the -10/+4 switch in the up position? Set to +4
Also, turn down the audio on the laptop...if that is what the source is.
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Igor Krupin

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Re: Please help with impedance connecting laptop to mixer
« Reply #3 on: February 08, 2016, 02:10:21 PM »

Do you have the -10/+4 switch in the up position? Set to +4
Also, turn down the audio on the laptop...if that is what the source is.

I did play with the switch, it's set to +4 and helped a little. Turning down the volume on laptop I could but I've read in many a place that when u turn down a volume on a pc it's a software trick (as opposed to having a hardware potentiometer) which causes dynamic range compression to increase.

Which got me thinking, I could just buy a volume control knob and apply it to the output from the laptop ... that would be an inexpensive solution.
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Igor Krupin

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Re: Please help with impedance connecting laptop to mixer
« Reply #4 on: February 08, 2016, 02:33:14 PM »

http://peavey.com/products/index.cfm/item/875/117099/USB-PUSBPlayback

Hey thanks good to know for next time i need to do the same setup. This looks like it would make things easy.
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Corey Scogin

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Re: Please help with impedance connecting laptop to mixer
« Reply #5 on: February 08, 2016, 02:36:45 PM »

I've read in many a place that when u turn down a volume on a pc it's a software trick (as opposed to having a hardware potentiometer) which causes dynamic range compression to increase

Which got me thinking, I could just buy a volume control knob and apply it to the output from the laptop ... that would be an inexpensive solution.

I wouldn't worry about turning down the laptop some. The digital dynamic range will be lessened but most likely unnoticeable until you get down very low.

A fixed inline pad may work instead of a variable one. I'm thinking -10dB should do it.

It's likely part of the volume issue is that the music is already compressed in such a way as to be "loud". Microphones and other live sources are much more dynamic which will sound quieter given the same peak level.

That D/A unit seems to be a bit hot for your purpose as "nominal" voltage at +4 dBu is around 1.2Vrms. Maybe its intention was more to drive headphones rather than a line level input.
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Igor Krupin

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Re: Please help with impedance connecting laptop to mixer
« Reply #6 on: February 08, 2016, 03:06:50 PM »

I wouldn't worry about turning down the laptop some. The digital dynamic range will be lessened but most likely unnoticeable until you get down very low.

A fixed inline pad may work instead of a variable one. I'm thinking -10dB should do it.

It's likely part of the volume issue is that the music is already compressed in such a way as to be "loud". Microphones and other live sources are much more dynamic which will sound quieter given the same peak level.

That D/A unit seems to be a bit hot for your purpose as "nominal" voltage at +4 dBu is around 1.2Vrms. Maybe its intention was more to drive headphones rather than a line level input.

Hey thanks I did not know about attenuator cables until now! I will order one and give it a try. I found a couple of 3.5mm ones (-6db and -11db).
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Russell Ault

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Re: Please help with impedance connecting laptop to mixer
« Reply #7 on: February 09, 2016, 12:36:48 AM »

THE PROBLEM:
=============

I only need to move the fader up very little from infinity for the sound to get loud. So i just nudge it up and the level is good. I would like the fader to be moved up to zero or a bit below for the sound to get loud enough.

All my other microphones and everything else is good. I think the system is properly "zeroed".

I usually try to avoid discussions about gain structure, but since no one else has mentioned it, I will:

First, I'm assuming that, even at its current very-loud volume, your USB audio adapter isn't clipping its input channel on your console (i.e. the "CLIP" light on the channel never turns on, even when it's really smokin' loud). If this is not the case, then you definitely need a pad cable/adapter/etc., and you can ignore everything else I'm about to say.

If my assumption is correct, though, you can solve your problem with the equipment you already have: you can change the point in your sound system where most of the gain is being added. Right now, I'm guessing, your speaker amps are turned up about as loud as they'll go, and your microphone gain knobs are pretty near their quietest. What I'd suggest trying is to turn all the volume knobs on all of your speaker amps (mains and monitors) down as low as they will go, put the fader for your USB adapter channel to the -10 line (that's the 10 below the 0, since Behringer doesn't put the little minus sign on this particular console), and then turn your speaker amp gain knobs back up, but only to the point where the sound coming out of your speakers is roughly as loud as you want it to be and not all the way up. After you've done this, you'll have to turn up the gain on your microphone inputs to compensate for your speaker amps adding less gain (which, as long as this doesn't result in the "CLIP" lights turning on on your microphone input channels, shouldn't cause you any problems).

People who have more knowledge and experience than me will hopefully go more into the theory of gain structure and system headroom (and some will probably disagree with my suggestion, and that's expected: put six sound guys in a room and ask them a question, and you'll get at least twelve correct answers...) but this should solve your problem, and for free!

-Russ
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Garry Wilson

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Re: Please help with impedance connecting laptop to mixer
« Reply #8 on: February 09, 2016, 10:18:07 AM »

I'm using sabre-dac-uae23 dac from hifimediy (http://hifimediy.com/sabre-dac-uae23)

the output specs are as follows:
=======================
Open 2.2Vrms
4.7Kohm 2.1Vrms
1.8Kohm 1.9Vrms
510ohm 1.5Vrms
330ohm 1.3Vrms
30ohm 1Vrms

I'm connecting the sound card to mixer via 1/8 trs to dual 1/4 ts cable. It's an unbalanced connection (very short cable, I don't mind).

The mixer i'm using is Behringer UB2222FX-PRO

It has several stereo input channels rated at 10k unbalanced and 20k balanced.

See line 9/10, 11/12, 13/14 and 15/16 in this close up

THE PROBLEM:
=============

I only need to move the fader up very little from infinity for the sound to get loud. So i just nudge it up and the level is good. I would like the fader to be moved up to zero or a bit below for the sound to get loud enough.

All my other microphones and everything else is good. I think the system is properly "zeroed".

THE SOLUTION (that I need help with)
=============================

I'm thinking impedance is to blame here. I've tried to read several impedance articles and I just could not care for the theory, I need practical solutions. Once I have a practical solution I may be interested in the theory behind it.

What I want to get is this:

s2s-series

Will this solve my problem? What should i put for primary and secondary transformer impedance? I'm thinking 600 ohms to 10k ohms? Or should be it be 15k ohms to 150ohms? I'm not sure if primary means input and secondary output.

Please advise, thank you!



This is what I use to get out of my laptop/ipod/ipad. I don't know if your sound card has a stereo mini out. I did notice that the adapter you are curruntly using id USB to stereo-mini.

http://www.amazon.com/Rapco-Horizon-LTIGLBLOX-Laptop-Interface/dp/B003MLBEYK

these work great, I bought 4, two with ground lifts, two without.

Garry W.
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Garry W.
CTS, SBE-CEV, A+
www.986sound.com

Igor Krupin

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Re: Please help with impedance connecting laptop to mixer
« Reply #9 on: February 09, 2016, 12:26:18 PM »

First, I'm assuming that, even at its current very-loud volume, your USB audio adapter isn't clipping its input channel on your console (i.e. the "CLIP" light on the channel never turns on, even when it's really smokin' loud). If this is not the case, then you definitely need a pad cable/adapter/etc., and you can ignore everything else I'm about to say.

True, it never gets anywhere close to "clip" light. On the mixer above the main mix faders I have leds that glow from green to red. Red is to indicate clipping. I hardly see any of the leds come on, maybe a row of greens now and then.

Large front view of the mixer

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ProSoundWeb Community

Re: Please help with impedance connecting laptop to mixer
« Reply #9 on: February 09, 2016, 12:26:18 PM »


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