I need a line level splitter and don't want to spend $50+ on a transformer - diyAudio
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Old 8th February 2011, 05:21 PM   #1
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Default I need a line level splitter and don't want to spend $50+ on a transformer

I am interested in building an op-amp or discrete (transistor) splitter. I am using one balanced output from my mixer to feed two different amps (both have balanced inputs). The application is live sound vocal monitor system, we have enough amps and have found need to individually control the monitor speakers volume to balance with the musicians stage volume (guitar, bass, drums). The drummer sings lead most often and needs a very loud monitor while the guitarist and I try to keep our stage volume down and therefore need less powerful monitors.
My worry is simply using a "Y" cable seems to reduce the fidelity so I am looking for a circuit that I can build to accomplish my goals (one balanced input approx. line level to two balanced outputs). The most common way pros deal with this is a $50 to $60 splitter transformer, but I am on a strict budget and must try to find a less expensive alternative. Plus this is what I do for fun. Can anyone here suggest a suitable circuit?
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Last edited by bassmeknik; 8th February 2011 at 05:24 PM.
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Old 8th February 2011, 05:31 PM   #2
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This device will be mounted inside of the amp rack and a power supply could be 9 volt batteries or 110 volt power (prefer 110 volt).
I am capable of building a suitable power supply. Also I am interested in a low distortion (high fidelity) design not the cheapy op amps many forum users pan... I know there are good op amps just not very familiar with them, I have been building transistor and tube audio equipment for 40 years for personal use, but I haven't played with op amps much.
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Old 8th February 2011, 05:37 PM   #3
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A Y cable should be fine. You say it "seems" to reduce the fidelity, if it's a good quality lead correctly wired then it should be OK.
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Old 8th February 2011, 05:40 PM   #4
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A similar application might be when playing at a larger than normal venue and need to add more pa main amps to enlarge the system capabilities (adding more amps to the mixer main output)
The most common use is to split the signals of each instrument and vocal mic to send feeds to (A) the monitor mixing console and (B) the main front of house mixer (or) to a recording device set up at the performance to make a live recording. However, this app. uses mic levels not line level I will need to be able to handle line levels without clipping.
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Old 8th February 2011, 05:41 PM   #5
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Quote:
Originally Posted by bassmeknik View Post
I am interested in building an op-amp or discrete (transistor) splitter. I am using one balanced output from my mixer to feed two different amps (both have balanced inputs). The application is live sound vocal monitor system, we have enough amps and have found need to individually control the monitor speakers volume to balance with the musicians stage volume (guitar, bass, drums). The drummer sings lead most often and needs a very loud monitor while the guitarist and I try to keep our stage volume down and therefore need less powerful monitors.
My worry is simply using a "Y" cable seems to reduce the fidelity so I am looking for a circuit that I can build to accomplish my goals (one balanced input approx. line level to two balanced outputs). The most common way pros deal with this is a $50 to $60 splitter transformer, but I am on a strict budget and must try to find a less expensive alternative. Plus this is what I do for fun. Can anyone here suggest a suitable circuit?
I think that simple Y-splitter would be a good place to start. I don't think that it will reduce "fidelity", although since you didn't say exactly what you mean by "fidelity" I can't be sure what you have in mind. I assume that this is live music, not audiophile audio or a recording studio we are talking about here? Usually the issue is noise and immunity from interference, and I believe that's the primary reason for using balanced lines, not because they offer superior fidelity (e.g. versus unbalanced cables). Since cable runs are typically longer for pro audio, there is lots of opportunity for interference to find its way in to the signal.

Let's assume that you can adjust the gain for each monitor at its amp. In that case, as long as the total impedance of both the loads in parallel does not drop below what the equipment that is sourcing it can handle, I think you should be fine with the Y.

-Charlie
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Old 8th February 2011, 05:48 PM   #6
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Yes interference is a concern not so much "fidelity" though I am a "clean freak" when it comes to my audio signals... how many amps can I expect to daisy chain together in parallel before impeadence mismatch or input/output loading between the mixer and amps might become an issue?
The cable runs are short the amps all live in the same rack and the mixer is onstage also never more than 4 feet away.
We are a small classic rock cover trio.
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Last edited by bassmeknik; 8th February 2011 at 05:51 PM.
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Old 8th February 2011, 07:17 PM   #7
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I have a similar but different need...
I recently purchased a new vocal processor that includes a harmonizer that creates useful background harmonies, However the guitarist uses a lot of effects and the processor needs a relatively clean (instrument) signal to work properly.
Now I am sure most with guitar experience will understand his uneasiness with my need to split his signal EARLY in the signal chain before the effects render it useless for the harmonizer. Most guitarists (frequently erroneously) don't want any additional color added to their sound or do they want any signal loss (pesky guitarists).
SO, I need to take a guitar level (near mic level) signal and create a second output for the harmonizer whilst maintaining the beloved guitar signal chain as unmolested as possible....
This is all unbalanced high impedance signal and a parallel or Y type connection won't satisfy the guitarist as it causes noticeable signal loss. Is there a way to match the input and output gains so as to satisfy the guitarist that his signal (level) hasn't been degraded significantly?
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Old 9th February 2011, 07:51 AM   #8
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With Chris Squire's bass he was so paranoid about going through anything active when it wasn't absolutely essential we built a relay switching box, which guaranteed no semiconductors unless an effect was switched on.

A decent active DI box has an input impedance if many Megohms, and often a buffered output; and is a useful thing to possess, anyway.

Your average professional mixer output has an output impedance of a few tens of ohms, and a current drive capacity of giving full level at spec into six hundred ohms (hangover from telephone periods, when matched six hundred ohm drive/load was the norm. But means you can hang a pair of phones on the output for line checking, too.) Normally an amp's input impedance will be at least ten kilohms; which means that a single mixer output can drive sixteen amplifier inputs without reaching its specified limits; in studios we generally hang all the tape machines (same input specification) off one stereo bus; that can often be ten or twelve.

Now, I'll admit a cheaper mixer might fudge the figures a little bit, but normally its peak output would be +20 dBm, or thereabouts, while the amp gives full output at 0 dBm, so you've a lot of spare headroom, so, to be conservative, perhaps don't hang more than ten or so amplifiers onto a single mixer output without buffering…

Unless you want a project to start with, in which case a stereo balanced buffered output matrix could be a worthwhile unit.
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