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Old 10th November 2002, 01:49 AM   #1
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Default Converting single ended amp to balanced

I'm considering converting my McCormack DNA1 dlxe single-ended amp to a balanced configuration. SMC audio does convertions on the McCormacks using jensen transformers and I was wondering:

1) does running the audio signal through an extra set of trannies degrade the sound quality?

2) How feasible is it to do a diy conversion on an amp like this?

Thanks!
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Old 10th November 2002, 02:01 AM   #2
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Hello Sir,

I assume that You wish to modify the amplifier to accept balanced input. Am I wrong?

If such is the case, I don't see any technical valid reasons for doing that unless You use very long cables.
Transformes do in general exhibit rather high distorrtion at low frequencies.
I belive it's a better idea to implement a solid state balanced input stage.



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Old 10th November 2002, 02:06 AM   #3
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Hi Morello,

I've got a balanced preamp that I'd like to use with the single ended amp...

Do you have any suggestions on where I could find info on a solid state/passive single ended-to-balanced input stage?

TIA!
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Old 10th November 2002, 02:16 AM   #4
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Quote:
Originally posted by boyelroy
Hi Morello,

I've got a balanced preamp that I'd like to use with the single ended amp...

Do you have any suggestions on where I could find info on a solid state/passive single ended-to-balanced input stage?

TIA!
Hello Mr,

A lot of power amplifiers with balanced inputs uses a simple differential amplifier at the input comprising one operational amplifier per channel. There is a good book written by Ron Mancini. You can download the book (464 pages in PDF) from Texas Instruments website. It's free

Tell me if You want me to design a input stage.


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Old 10th November 2002, 02:21 AM   #5
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Go digging in the forum. There is quite a long thread on just this subject... i came away with the impression that the Jensen trafo is probably a good solution.

And with the number of interstage trafos the tube guys are using they can't be all that bad...

dave
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Old 10th November 2002, 02:26 AM   #6
haldor is offline haldor  United States
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If the preamp and amp are in close proximity (cable length is less than 8 meters) and both units are powered from the same electrical outlet then all you need is an XLR to RCA cable with Pin 2 of the XLR connected to the center post of the RCA plug and Pin 1 of the XLR connected to the shield of the RCA plug.

You can buy this cable at just about any Music store that sells PA gear.

Note: The output of the Preamp may be hotter than normal so expect that you will need to turn down the input attenuator on the amp. Standard PRO audio output levels are normally +4 dB, while consumer gear is -10 dB.

Here is a good reference on the subject.

http://www.rane.com/note110.html

P.S. Rane has a number of excellent application notes about system grounding, making wye cables, etc. Lots of useful, accurate info.

Phil
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Old 10th November 2002, 03:06 AM   #7
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Quote:
Originally posted by planet10
Go digging in the forum. There is quite a long thread on just this subject... i came away with the impression that the Jensen trafo is probably a good solution.

And with the number of interstage trafos the tube guys are using they can't be all that bad...

dave
Interstage transformers reminds me of tube-gear frpm the 30's

Tube amps with interstage transformers often exhibits copious amounts of distortion


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Old 10th November 2002, 03:19 AM   #8
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Quote:
Originally posted by Morello
Tube amps with interstage transformers often exhibits copious amounts of distortion
And there are guys here who will tell you that it is the only way to go to get the best sound

Implementation counts for a lot...

dave
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Old 10th November 2002, 04:09 AM   #9
haldor is offline haldor  United States
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Hi guys,

I don't understand the point of this. The benefit of balanced interconnects is that they reduce hum in long cable runs. Why recommend adding transformers or an extra active stage to the amps input when all guy wants to do is hook his preamp that has balanced outputs to his amp which has unbalanced inputs?

A balanced signal consists of a normal unbalanced signal (identical to the usual unbalanced signal only possibly a little hotter in level) plus an inverted copy of the signal. A balanced input only amplifies the difference between the + and - signals which means that by using twisted cables you can greatly reduce susceptible to common mode induced noise. I doubt if this is a problem in this particular case.

If you are connecting two pieces of equipment that are right next to each other there is no reason to not just use the + signal and signal ground out of the balanced output and connect them directly to the unbalanced input of the amp.

Surely you are not suggesting that adding unnecessary components to the signal chain are going to make it sound better? Why don't you also recommend he install an ADC on his preamp output and run SPDIF to a DAC on his amp. Because it would be expensive, complicated and not do anything to improve the sound quality, that's why. The same arguments apply to adding a transformer or active balanced input stage to the amp in this particular case.

Phil
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Old 10th November 2002, 04:28 AM   #10
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Quote:
Originally posted by haldor
If you are connecting two pieces of equipment that are right next to each other there is no reason to not just use the + signal and signal ground out of the balanced output and connect them directly to the unbalanced input of the amp.
No question about that...

dave
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