Amp/Preamp Asylum

Looking for a new Amp or Preamp? If you're after tubes, post over here.

Return to Amp/Preamp Asylum


Message Sort: Post Order or Asylum Reverse Threaded

Converting dual mono amplifier from single ended input to balanced input - Possible?

104.200.151.29

Posted on May 16, 2016 at 14:06:18
Tims
Audiophile

Posts: 20
Joined: March 1, 2002
Beginner's question!
Is it possible to convert a dual mono stereo amplifier that has single ended input (i.e. RCA connectors) to one that accepts a balanced input (using XLR cable/connectors).

My understanding is that since each stereo channel has it's own transformer etc that it should be possible and I get the benefits of a balanced system but am I missing something here?
Any discussions or links that can enlighten me appreciated.

 

Hide full thread outline!
    ...
They do make RCA to XLR adaptors, posted on May 16, 2016 at 14:14:49
Try it and listen. All that really matters is what you hear.

 

No, posted on May 16, 2016 at 15:40:38
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
You can get cable adapters to allow a balanced device to be plugged into it
but it wont be changed to a balanced circuit. You have a single ended amp not a balanced one. Totally different circuit design.

ET
ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

RE: Converting dual mono amplifier from single ended input to balanced input - Possible?, posted on May 16, 2016 at 21:02:37
PAR
Balanced transmission of an audio signal from one component to another requires both to have a special circuit using either transformers or active devices (see link).

Adaptors are made which allow the connection of a single ended output to the XLR connector of a balanced input or vice versa. However it is just a way of linking the two together. The result is still single ended and will have none of the possible advantages of a balanced connection. I say possible as you can see that balanced circuitry requires additional components compared to a single ended one which may or may not be a good thing in any practical implementation.

 

RE: Converting dual mono amplifier from single ended input to balanced input - Possible?, posted on May 16, 2016 at 22:31:55
Schurkey
Audiophile

Posts: 121
Location: The Seasonally Frozen Wastelands
Joined: May 14, 2015
Sure. Audio by VanAlstine sells a device that would provide the inverted signal that drives the second channel in a common-ground stereo amplifier.

The first time I saw it, it was a "kit" for home assembly. Not any more. http://www.avahifi.com/index.php?option=com_content&view=article&id=115&Itemid=171

The up-side is that you get (theoretically) four times the power output from your amplifier. (More realistically, about three times the power.) The downside is that it's about ten times more likely to be driven into thermal failure.

Be sure your amplifier is TRULY common-ground. Lots of amplifiers claim to be common-ground, but actually have a resistor between each negative binding post and chassis ground, so 2x the resistor value between the two negative binding posts. This plays hell with Polk SDA speakers, I don't know about the AVA inverter. It would be worth your trouble to ask them.

Of course, IF (big IF) you have a preamp with a balanced output, you've already got the inverted signal, so no need for the AVA box.

 

RE: Converting dual mono amplifier from single ended input to balanced input - Possible?, posted on May 17, 2016 at 01:14:28
PAR
I don't think that the Van Alstine device will do what the OP wants. He is looking to convert the input to his amplifier to accept a balanced signal. Quoting the AVA web page on it: " The AVA stereo phase inverter bridge can be used to generate a balanced output signal (e.g., for interfacing to balanced inputs commonly found on pro-audio equipment" . That is it turns a single ended OUTPUT into a balanced one to feed to a balanced input. As I read his post it is the input on his amp that he is asking about.

 

If the transformer to which you refer is an input transformer, yes, but if not, its still possible:-, posted on May 17, 2016 at 09:19:56
Ralph
Manufacturer

Posts: 4769
Location: Minnesota
Joined: April 24, 2002
-Even if the amp has just a single ended input and no input transformer, it is still possible to have it process both phases of the balanced input (although technically it will be differential and not balanced).

If pin 2 of the XLR is driving the same input as the RCA connection, then pin 3 could be used to drive the cathode of the input tube, via a coupling capacitor. This cap would be of the same type and ratings as a cap that might be used as a cathode bypass capacitor for that stage.

This works quite well, even if the cathode is the same point to which the negative feedback is applied (if the amp has negative feedback).

The hardest part of this technique is finding a spot to install the XLR connector and then installing it. The hookup itself is really simple, as all that is needed is the electrolytic cap for the pin 3 connection. If the amp already has a cathode bypass cap installed, then you are all set- simply move its connection from ground to pin 3. If you do that, please note that a jumper pin from pin 3 to ground should be used if you are using the RCA input.

This approach does not change the character of the amplifier at all but it does allow it to process both phases of the input signal.

 

balanced (impedance) Differential signal, posted on May 23, 2016 at 07:50:53
BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002
Balanced lowers EMI noise picked up on long cable runs - independent of whether there is signal on both, one or None of the connections. Differential signalling allows twice (+6 dB) signal levels to be transmitted without increasing circuit power supply voltages or gain. Balance circuit can be set up using transformers or not.


"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

RE: Converting dual mono amplifier from single ended input to balanced input - Possible?, posted on May 24, 2016 at 03:17:57
SgreenP@MSN.com
Audiophile

Posts: 3536
Joined: April 23, 2007
Tims...you're spinning your wheels with little chance of going forward.

 

Page processed in 0.036 seconds.