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post #1 of 14 Old 04-07-2011, 04:23 AM - Thread Starter
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Howdy,

Got a receiver (RCA pre outs), getting some amps with XLR inputs.

I see you can get RCA to XLR cables....what about the impedance issue?

Is an active convert needed? something like this?:

http://eavtech.com.au/branded_fr...rbbl4_ld.shtml

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post #2 of 14 Old 04-07-2011, 09:25 AM
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The way PROS do it is to use a balun. BAL/UNBALANCED transformer. I make my own using Jensen transformers. Just google Jensen transformers. The site will show you the models and wiring diagrams.

Many home style amps use differentially (electronic) balanced inputs. These are notorious for introducing hum/noise, especially when connected to a 2 conductor signal feed such as an RCA or 1/4 phone. The transformer eliminates that issue.
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post #3 of 14 Old 04-07-2011, 10:01 AM
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Stay with RCA to RCA. With the XLR inputs on the amp you will not gain anything due to not having XLR out to XLR in. This has been discussed before on the Polk and online-shashki Forum and is a waste of time and $$$$. I have the same thing with a Pio SC-37 RCA and Carver Grand Cinema amp with XLR in's. I finally ended up with RCA to RCA.

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post #4 of 14 Old 04-07-2011, 11:09 AM
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Quote:
Originally Posted by bsoko2 View Post

Stay with RCA to RCA. With the XLR inputs on the amp you will not gain anything due to not having XLR out to XLR in. This has been discussed before on the Polk and online-shashki Forum and is a waste of time and $$$$. I have the same thing with a Pio SC-37 RCA and Carver Grand Cinema amp with XLR in's. I finally ended up with RCA to RCA.

He can not stay with RCA to RCA if the amp he wants has only XLR.

There is a whole DIY community that uses pro amps having only XLR inputs connecting them to RCA outputs on common AVRs and Pre/Pros

A simple google search on "RCA to XLR cable" will get you everything you need. I have bought expensive brands and cheap ones. They all work the same way.

The one difference that could be an issue is the voltage sensitivity differences. RCA (unbalanced) is <= .775Vrms and XLR (balanced) is >= 1.228Vrms. Sometimes the max voltage out of the AVR does not match that of the AMP and another device is needed for increasing the signal (Ie. Samson S-convert). This problem happens for a small percentage so do not worry about it up front.

Gizmologist's post about "introducing HUM" is a good one. That does happen too but there is a way to eliminate that without spending big $$$ on Jensen products (I own those too). There is a way to run a ground wire on the RCA end to ground the amp and AVR.

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post #5 of 14 Old 04-07-2011, 01:25 PM - Thread Starter
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Thanks Penn - I'll got with some cables first and see what happens.

Cheers

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post #6 of 14 Old 04-07-2011, 07:20 PM
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If you do have signal strength issues you could also use an Art Cleanbox Pro if you have problems finding a Samson S-Convert. I thought the Samson S-Convert was discontinued.
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post #7 of 14 Old 04-07-2011, 09:58 PM
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The amp has NO 1/4" inputs? If it does, I could go RCA to 1/4"

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post #8 of 14 Old 04-07-2011, 10:19 PM
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Originally Posted by MichaelJHuman View Post
The amp has NO 1/4" inputs? If it does, I could go RCA to 1/4"
Most amp i've seen with 1/4 inch jack are still balanced (TRS). Like Penn wrote just try it RCA to XLR if you do not have issue life goes on and enjoy. Just keep the cable as short as possible. Mine are 6 feet long and not a single problem.

Warning to prevent risk of injuries, you should always be smarter than the equipment you are about to use.
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post #9 of 14 Old 04-07-2011, 11:17 PM
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post #10 of 14 Old 04-10-2011, 04:09 PM
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Quote:
Originally Posted by Secret Squirrel View Post

If you do have signal strength issues you could also use an Art Cleanbox Pro if you have problems finding a Samson S-Convert. I thought the Samson S-Convert was discontinued.

Has the Cleanbox been fixed? Last word on it I saw was that it had really crappy low frequeny response, even above point where it would be only a concern to subwoofer use.

Just because there is a knob doesn't mean you should turn it.
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post #11 of 14 Old 04-11-2011, 06:34 PM
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Originally Posted by whoaru99 View Post
Has the Cleanbox been fixed? Last word on it I saw was that it had really crappy low frequeny response, even above point where it would be only a concern to subwoofer use.
I thought the Cleanbox was the one that some complained about the low frequency issues. I have not heard of any issues with the Cleanbox Pro. They are two different devices so they may not have the same issues.
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post #12 of 14 Old 04-11-2011, 08:05 PM
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As every piece in the signal chain adds some level of noise and "coloration" to the overall signal, using full range passive devices like transformers is the pro's choice.

The Jensen transformers are somewhat pricey to some budgets but are well respected by those who make a steady living designing systems.

I also have several transformers from OPAMP Labs in Hollywood. These are 20-20 flat and rated at +18 db. Many broadcasters have these in studios and mobile rigs for buffering and isolation. Excellent response and in octal based plug ins (tube style) and with MuMetal shielding. VERY reasonably priced.
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post #13 of 14 Old 04-12-2011, 05:59 AM
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These are 20-20 flat and rated at +18 db.

We require measurements from 5Hz on up

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post #14 of 14 Old 04-12-2011, 06:08 AM
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Don't sweat it.

I've been using various combinations of RCA to XLR to TRS etc for years without a single problem, although I have very short runs.

The only RCA to Balanced issues I've had are when going to Phoenix connectors (euroblock). They are fragile, they hum, and they are inconvenient.

They might be good for installations, but suck for those of us who tweak or move things. I hate Phoenix connectors so much I'm getting rid of a perfectly good amp because of them. They are evil.
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