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Author Topic: Laptop Playback cable  (Read 1108 times)

Tim Weaver

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Re: Laptop Playback cable
« Reply #10 on: July 30, 2017, 01:37:18 pm »

The cheap route is a bsic cable.

http://www.zzounds.com/item--HOSHMXY?siid=177858&-cSx1QIVCA5pCh3RSAofEAQYBCABEgKs8PD_BwE=

If you use a mac or another apple device, this is likely all you'll need. Aplle has pretty decent audio outputs.

If you use something other than mac, I have noticed that the audio quality is sometimes questionable, but more often than not they have a ground buzz if the power supply is plugged in. On battery power they typically work fine, but plug it in and there's that old 60 cycle again.

If you work with a variety of devices, the USB DI is a wise investment.
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Jonathan Johnson

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Re: Laptop Playback cable
« Reply #11 on: August 01, 2017, 03:27:34 pm »

I like the Peavey USB-P that Mac mentioned. I have one myself. It uses a "class" driver that's built into every modern version of Windows and MacOS, so there's nothing to install. You just plug it in and it works (you might have to select it as the output device). Of course that might not work with mobile devices like tablets and phones -- in which case you're stuck with a 1/8" TRS output.

If 1/8" TRS is your output device, then the simplest way is to use a cable that splits it to 1/4" TS left and right channels and connect it to the line input of the mixer channel. It probably depends on the mixer (others will know more about this than I do and are welcome to correct me), but I think that the mic input goes through a preamp that the line input doesn't. So using the line input should give a "purer" signal. (Unless the mixer pads the line input and feeds it through the same preamp.) This is only recommended if the connecting cable is less than a couple meters long, as the unbalanced line may be subject to interference.

If you have to go a long distance, the better option is to use the 1/8" TRS to 1/4" TS cable into two DI channels (I recommend passive DI with transformer isolation/impedance matching and ground lift), and balanced XLR from the DI to the mic input of the mixer (with padding on the DI if necessary) or if your mixer has true balanced 1/4" line inputs, then balanced XLR from the DI to an XLR to 1/4" TRS adapter into the mixer's line input. Whatever you do, don't just plug both left and right outs into both input/thru jacks on a single-channel DI -- this can cause problems in some cases.
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Jean-Pierre Coetzee

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Re: Laptop Playback cable
« Reply #12 on: August 02, 2017, 10:58:36 am »

I like the Peavey USB-P that Mac mentioned. I have one myself. It uses a "class" driver that's built into every modern version of Windows and MacOS, so there's nothing to install. You just plug it in and it works (you might have to select it as the output device). Of course that might not work with mobile devices like tablets and phones -- in which case you're stuck with a 1/8" TRS output.

If 1/8" TRS is your output device, then the simplest way is to use a cable that splits it to 1/4" TS left and right channels and connect it to the line input of the mixer channel. It probably depends on the mixer (others will know more about this than I do and are welcome to correct me), but I think that the mic input goes through a preamp that the line input doesn't. So using the line input should give a "purer" signal. (Unless the mixer pads the line input and feeds it through the same preamp.) This is only recommended if the connecting cable is less than a couple meters long, as the unbalanced line may be subject to interference.

If you have to go a long distance, the better option is to use the 1/8" TRS to 1/4" TS cable into two DI channels (I recommend passive DI with transformer isolation/impedance matching and ground lift), and balanced XLR from the DI to the mic input of the mixer (with padding on the DI if necessary) or if your mixer has true balanced 1/4" line inputs, then balanced XLR from the DI to an XLR to 1/4" TRS adapter into the mixer's line input. Whatever you do, don't just plug both left and right outs into both input/thru jacks on a single-channel DI -- this can cause problems in some cases.

This, also don't use XLRs.

Apart from the mic input being through a HA it also has phantom power which the 1/4" inputs do not and phantom power kills electronics, most OP amps aren't  so happy receiving a 48V DC signal.
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Rob Spence

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Re: Laptop Playback cable
« Reply #13 on: August 02, 2017, 12:46:55 pm »

When I need to take inputs from an 1/8" I use a Radial SB-5.
Easy and not too expensive.

Good note above to the dangers of inadvertently putting phantom into someone's phone or laptop.


Sent from my iPad using Tapatalk HD
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Jonathan Johnson

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Re: Laptop Playback cable
« Reply #14 on: August 02, 2017, 12:57:29 pm »

This, also don't use XLRs.

Apart from the mic input being through a HA it also has phantom power which the 1/4" inputs do not and phantom power kills electronics, most OP amps aren't  so happy receiving a 48V DC signal.

At this risk of putting words in Mr. Coetzee's mouth, you shouldn't connect a laptop or other non-XLR device directly to the XLRs because they could be damaged by the phantom power. In the case of a DI box, you *can* connect the XLR output of the DI box to the XLR input of the mixer, even with phantom power, because that is what DI boxes are designed to do.

Just wanted to (hopefully) clarify that, because I think I misunderstood Mr. Coetzee's statement the first time I read it.
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Bill Koonce

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Re: Laptop Playback cable
« Reply #15 on: August 02, 2017, 10:33:58 pm »

IME most mic preamps do have the option to turn off phantom power. For those that don't, using a transformer for impedance matching will ensure that no DC passes to the other transformer windings, or on to the laptop.

Since most unbalanced connections are high impedance, the reason to use some sort of "black box" between hi-Z and XLR is for impedance matching, as well as a balun. You wouldn't need a box to feed a pair of hi-Z 1/4" TS or RCA input jacks, and most mixers I use do have one or two of these. For headphone outputs, the impedance may an unknown.

The main reason to convert to a balanced line with STP cabling is for long cable runs. If the laptop is 100' away from the mixer, then you need the STP cable for common mode rejection. Whether the STP cable is terminated with XLR or (1/4") TRS is immaterial. If the distance is 3', then using STP is not strictly necessary.
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Mac Kerr

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Re: Laptop Playback cable
« Reply #16 on: August 02, 2017, 10:41:21 pm »

This, also don't use XLRs.

Apart from the mic input being through a HA it also has phantom power which the 1/4" inputs do not and phantom power kills electronics, most OP amps aren't  so happy receiving a 48V DC signal.

The Peavey USB-P is transformer isolated. It won't be damaged by phantom power.

Mac
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Jonathan Johnson

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Re: Laptop Playback cable
« Reply #17 on: August 03, 2017, 06:10:15 pm »

IME most mic preamps do have the option to turn off phantom power. For those that don't, using a transformer for impedance matching will ensure that no DC passes to the other transformer windings, or on to the laptop.

Many mixers have only one switch for the phantom power on all XLR inputs. So if you need to power one thing with phantom power, you're delivering phantom to every device that's connected to an XLR input. Transformer isolation to the rescue. Or you turn off phantom at the mixer and use an inline phantom power adapter.

Quote
Since most unbalanced connections are high impedance, the reason to use some sort of "black box" between hi-Z and XLR is for impedance matching, as well as a balun. You wouldn't need a box to feed a pair of hi-Z 1/4" TS or RCA input jacks, and most mixers I use do have one or two of these. For headphone outputs, the impedance may an unknown.

The main reason to convert to a balanced line with STP cabling is for long cable runs. If the laptop is 100' away from the mixer, then you need the STP cable for common mode rejection. Whether the STP cable is terminated with XLR or (1/4") TRS is immaterial. If the distance is 3', then using STP is not strictly necessary.

Good advice.

(STP=Shielded Twisted Pair)
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Bill Koonce

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Re: Laptop Playback cable
« Reply #18 on: August 03, 2017, 07:49:41 pm »

For anyone with an "all or nothing" phantom switch on their mixer:

http://repforums.prosoundweb.com/index.php?topic=20612.0
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Jean-Pierre Coetzee

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Re: Laptop Playback cable
« Reply #19 on: August 06, 2017, 12:02:05 am »

At this risk of putting words in Mr. Coetzee's mouth, you shouldn't connect a laptop or other non-XLR device directly to the XLRs because they could be damaged by the phantom power. In the case of a DI box, you *can* connect the XLR output of the DI box to the XLR input of the mixer, even with phantom power, because that is what DI boxes are designed to do.

Just wanted to (hopefully) clarify that, because I think I misunderstood Mr. Coetzee's statement the first time I read it.

This is what I meant... Sorry for the confusion.
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