Discussions on Balenced Amplifers

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ok, this is a subject which i think is pretty interesting. i must say that there is an interest on this forum about balenced inputs and outputs.

now so far the best gainclone only balenced implementaion was just 2 amplifers giving a differential in - differential out.

the only single gainclone implementation i've seen was a AC-coupled difference amplifer. the problem is that this circut isn't balenced unless there is no signal or noise. otherwise the noise rejection will depend upon the voltage to the noninverting terminal, so more noise = less rejection of noise!

i made a simple volume control that is balenced, but it is obviously conditionally balenced -- it works on the principle that the source and destination is balenced.

now i was looking over the specs of the lm4780, mind you not the choice of many, but still the CMRR of the chip falls severly, so any noise rejection will be limited more to lower frequencies. fine this works for hum if hum is the problem.

so i wanted to start a hopefully meaningful discussion on how best to implement a balenced input amplifer
 
What do you say about that?
 

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mskeete said:
do a search on the google for superbal
you can find an example circuit here
http://www.dself.dsl.pipex.com/ampins/balanced/balanced.htm


This is one of the pages I read when making my bal. gainclone ;)

I can't understand what all the fuzz is about. min. 45dB CMRR, and 0,00078dB signal imbalance (10 ohm SE output Z from source). Who needs higher performance than this for audio?
 

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Mad_K said:



This is one of the pages I read when making my bal. gainclone ;)

I can't understand what all the fuzz is about. min. 45dB CMRR, and 0,00078dB signal imbalance (10 ohm SE output Z from source). Who needs higher performance than this for audio?


well, the circuit isn't balenced. while it is capable of canceling equal noise on both inputs, it is not capable of picking up the same noise on both inputs. if it were balenced, i would not be able to pick up all that hum on my crossover (which uses the circiut with less gain as an input buffer). i can pick up hum by moving the cables near a transformer.
 
Re: Ssm2142 / Ina134

Steve Eddy said:


Thanks. It's worked for me for quite a few years. Though it can be considerably more expensive than some of the others presented.

se

You're welcome. The initial cost is an issue, but there's all the advantages the Tx's have, and providing you don't toast them, will hold their value well for later resale.

dhaen said:
Transformers are best, but....
The best non-transformer, non valve solution:
http://www.analog.com/Analog_Root/productPage/productHome/0,2121,SSM2143,00.html

Well John, the 2142's had better have improves a lot since I last used them, because they sounded dire.
 
Re: Re: Ssm2142 / Ina134

Brett said:
You're welcome. The initial cost is an issue, but there's all the advantages the Tx's have, and providing you don't toast them, will hold their value well for later resale.

Perhaps in the pro audio market. With the exception of transformer-based attenuators and MC step-ups, transformers are almost unheard of in high-end home audio.

se
 
The only input transformers that are mentioned in these forums seem to be ones specially designed for music (pro-fi, or hi-fi) use, and are thus fairly expensive.

Has anyone thought of using cheaper alternatives like those made by Tamura or Hammond? The following transformers from Tamura look interesting, but what do you guys think of them? Can anyone suggest a good circuit using one of these transformers for making a bridged amplifier?

On page 3:
http://dkc3.digikey.com/pdf/C041/1160-1165.pdf
 

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Mad_K said:
yep, a basic difference amp... very informative datasheet also ;)

edit: was supposed to quote dhaen...

just out of curiosity, how is that IC balenced. i agree that it is a difference amplifer, but i don't agree that it has equal input impedances. as i understand it, the idea is to have equal impeances to pick up equal noise then use a difference amplifer to cancel it out.

no one has been able to show me that this circuit is balenced with any input signal. it is balenced without a signal though, so i guess during silence - when noise could be heard - the noise rejection increases.
 
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