Converting WOPL inputs to XLR...

jbeckva

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#2
Sir Joe, what would it take to XLR a WOPL input?
A heck of a lot I suspect.. XLR inputs will generally feed into both inverting/non-inverting op amp inputs so imagine the rev E board schematic-wise and see how it would have to change to accommodate. Be one heck of a change!

Just an example here I drug up from the intertoobs.. But Joe's going to be the reply of authority here.. :)

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Gepetto

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#3
An XLR-RCA converter located very near the inputs Lee. Sell on Amazon for about $8 apiece

The largest challenge is space Lee. Those XLR input jacks take up a ton of backwall real estate. Recall that when the did it for Aerosmith (the amp lot that you purchased), they used phone jacks which suck for differential input purposes (and in general, I hate them on the Crown amps that I have).
 

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I realize the space problem. I was thinking of XLR'S on the monster monos..
Will have lots of room there..
 

laatsch55

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A heck of a lot I suspect.. XLR inputs will generally feed into both inverting/non-inverting op amp inputs so imagine the rev E board schematic-wise and see how it would have to change to accommodate. Be one heck of a change!

Just an example here I drug up from the intertoobs.. But Joe's going to be the reply of authority here.. :)

View attachment 34728
Jeez....all that??
 

laatsch55

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#7
If they are a balanced source.....I won't be converting unbalanced sources to balanced...
 

grapplesaw

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#8
Lee I am using Rane Balance buddy set up part BB44 and BB88
There is no problem using signal from balanced to unbalanced or the reverse with these units. They are transformer only setup. Also act as a dc signal block as the transformer will not pass dc current.

https://www.rane.com/bb44x.html

Here is a ic you could use in reverse setup inside the amp

https://www.diyrecordingequipment.com/pages/balanced-input-output-assembly-guide

Here is a good article on it as well. Elliot also has a kit for sale


http://sound.whsites.net/articles/balanced-2.htm
 

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mlucitt

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#10
According to Bill Whitlock, unbalanced cables result from one wire being grounded and the other wire carrying signal (normal for audio cables between the pre-amp and the amp). Balanced cables result from both wires (and everything connected to them) having the same impedance. This is hard to do.
Balanced cables originated in the telephone 600 Ohm lines that had to run long distances. They did this with an array of matching impedance equipment on both ends to reduce the signal loss.

My conclusion is that with short audio cable runs, we don't have much signal loss. We also want our pre-amp and amp power-line grounds connected together at the power outlet ground to reduce the risk of electric shock. Keeping the power-line grounds connected to a good electrical service ground can also reduce 60 Hz hum, if done correctly.

Microphones use balanced cables because their output is 5-50 millivolts and even a little signal loss is intolerable at those low levels. Many microphones "cheat" by not using a transformer to get a + and - differential output signal to drive a balanced XLR cable, the only downside is that with only one signal line, the output is cut by half.

Our pre-amps (and other input devices) typically output .3 to 2.0 volts (line level) and there is not much loss at that signal level. The exception is the turntable, the common moving magnet phono cartridge only outputs 3-6 millivolts (and a moving coil cartridge only puts out 1-1.5 millivolts). So, one would think that balanced cables would be ideally used for phonographs. Not so because the phono cartridge has no ground reference, it is floating. Floating sources connected to single-ended input (one signal wire and a common ground) with unbalanced cables act like they are connected by balanced cables. This is due to the impedance being the same in both wires because they are floating at the source. Therefore, the industry standard for phonographs is coaxial cables terminated with RCA plugs.

Because Phase Linear amplifiers are single ended input devices, the unbalanced, coaxial, shielded interconnect of six feet or less is the best way to connect the pre-amp to the amp. As Rod Elliot said, "In general, a home hi-fi needs balanced interconnects like a fish needs a bicycle, but someone, somewhere, decided that balanced connections 'sound better', but not because of noise reduction. Balanced connections are not used because they sound better or even different from any other. They are used where mains earth (ground) noise causes (or may cause) interference to the signal."
 
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#13
Here's a thought. If you want to run an amp bridged for mono output, the +/- signal of the XLR covers the bases. Radio Shack used to sell an XLR to 1/4" adaptor that used a miniature transformer. I have no idea what the frequency response was. Also, i think it was for microphones and line levels would probably overload the xfmr.
 
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mlucitt

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#15
Some of the road warrior "band amps" were converted from RCA to 1/4" because the 1/4" plugs and jack connectors were more common (used on all guitars and speaker cabinets) and Speakon connectors were not around then. Older Crown amps used 1/4" jacks, too. Some people like them better than RCA jacks.
 

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#20
Sorry, I had not gotten to that thread yet. Definitely a pro audio pre. They do not make them much nicer than that...

Rather than converting or modifying a PL amp, I would use a box like this and keep my amp stock:
https://www.parts-express.com/art-cleanboxpro-stereo-balanced-unbalanced-converter--245-868
Although the Clenboxpro may solve the problem $69 probably doesn't get you audio grade components throughout. The advantage of XLR's is a balanced output that is less immune to noise. If noise is not an issue then one of the pins can be tied to ground resulting in a single ended output. Typically pin 1 is ground and pin 3 is the inverting (-) input. Pin 2 is the non inverting (+) input. An interconnect with a jumper wire from pin 1-3 would provide single ended output without phase inversion. It would be important to verify the preamp output has a series resistor on pins 1 & 2 so that the preamp output is not damaged by shorting the pins together. The owners manual probably addresses this.
 
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