Converting balanced audio to unbalanced audio

[Neal]

While this might be somewhat off topic I have a Car Stereo project where I'm intergrating a factory OEM stereo through a "incar PC" then onto replacement speakers and amps. (Been reading the PC based audio threads on here)

The idea is to have flac and 24/96 music playing via a high end sound card into a 2.1 / 4.1 setup built for sound quality goals.

My question is around the factory stereo which will provide CD Changer FM/ NAV / TV / Telephone via it's factory tuner which is located in the boot.

I wish to take the 4 channels from the tuner which are balanced audio and convert them to unbalanced RCA to feed into the sound card. I understand that there are two ways of doing this, One is via isolating transformers and the other is via electronics conversion. Since I have 4 channels to convert can anyone suggest any products or ways I can do this in a cost effective manner ?

[JamesB]

My first though was this (http://www.twistedpearaudio.com/linestages/ballsie.aspx), but it's out of stock. I haven't tried this one, but have had good experience with their kits...

[Michael Wong]

What make/model car stereo is it ?

First time I've seen balanced audio mentioned in car audio.

[Antipodes]

The thing with balanced outputs is that they are not all the same. Sometimes the +ve signal is 'referred' to the -ve signal and the earth is loosely tied. In that case referring the +ve to the earth gives poor results comparing to referring the +ve to the -ve. Sometimes the +ve signal is referred to the earth, and the -ve signal is also referred to the earth. In that case referring the +ve to earth will give a good result.

You could find out how the balanced signal is designed, or you could experiment with different solutions...

Or you could simply employ the all-purpose solution, which is to tie the -ve to earth and refer the +ve to that. By that I mean connect the -ve leg of the output and the earth of the output to the earth of the input; and connect the +ve of the out put to the +ve of the input. Going from balanced to single-ended is really simple if you do that, and there is no need for a transformer. A transformer is really only relevant if you want to go the other way - single-ended to balanced - and best avoided (I really dislike the sound of every transformer I have ever heard).

For a technical discussion with pictures I highly recommend you reading the following
http://www.rane.com/note110.html

[Antipodes]

If you encounter interference issues you might also benefit from reading the following...
http://www.rane.com/note165.html

[Zero]

Are there benefits from converting a power amplifiers input to balanced?
I have a pair of rmb1080 rotel power amps, and whilst they have balanced inputs, it looks done as a cheap afterthought by rotel using an IC on a small board.

Using the balanced input is actually poorer sound quality than unbalanced because of this and I would be keen to modify them if possible to utilise the balanced outs from my ead ovation preamp.

[Michael Wong]

True balanced circuitry is expensive.

9/10 the simplicity and shorter signal paths of single ended circuits outweigh the potential benefits of balanced circuitry.

[Clevo]

True balanced circuitry is expensive.

9/10 the simplicity and shorter signal paths of single ended circuits outweigh the potential benefits of balanced circuitry.

My experience is that balanced circuitry is only used, in conjunction with low impedance. to reduce interference pickup on long cable runs. I fail to see any real need for it in the home environment with short runs and a relatively benign environment. As Michael says to do it properly after market is expensive.

Brian

[Owen Young]

Zero,
It looks like you have a non-balanced Rotel amp which has a balanced-unbalanced converter cct at the front, in order to accept a balanced input. So, the signal is going thru some addit circuitry... poss some degradation in sound.

If you have balanced source (eg. balanced output DAC + balanced preamp cct) then balanced amp might be sensible. But if you have to run the signal thru (one or more) 'converters', then.... not so good. If unbalanced source, you may get better results if you use the unbalanced outs from your DAC or pre.

The way I see it, balanced vs unbalanced/single-ended, is like PP vs SE.
Balanced (like PP) has the potential of cancelling out 'common mode' noise/interference, which is a big reason why it is used in pro/studio, long run situations - the AC signal 'floats' symmetrically +/- above 'Ground' & should remain thus from source to amp outputs.

And yes, it tends to be more costly as you might imagine the entire amp cct is 'mirrored' + & -ve... therein lies another debate, as to whether one can have truly symmetrical behaviour with different types of PNP & NPN transistors, valve phase splitters, etc... but that's another debate.

Just my 'amateur' views ;)

Edit: I see that your DAC is unbalanced output & the Rotel pre also?


Are there benefits from converting a power amplifiers input to balanced?
I have a pair of rmb1080 rotel power amps, and whilst they have balanced inputs, it looks done as a cheap afterthought by rotel using an IC on a small board.

Using the balanced input is actually poorer sound quality than unbalanced because of this and I would be keen to modify them if possible to utilise the balanced outs from my ead ovation preamp.

[Neal]

I'm learning more ! thanks for the replies.

The Car Audio tuner in question is a 2002 Becker Bm53 which is part of multi component system for BMW NAV and Audio

It looks like the balanced audio runs one twisted pair connection for each of the audio paths (e.g. left front , right front , left rear , right rear) It doesn't seem to run third / ground like those xlr fittings.


Thanks for the advice on transformers and balanaced audio converter circuit

The info on the internet is limited on the Tuner output stage and I haven't been find a circuit diagram. I'll try grounding the VE+ / Ve- to see if I can gain a clear audio out.

I guess if I can't do this then there could be the possiblity of working out the output stage on the tuner and adding RCA outputs before the balanaced audio output stage.

My plans for the audio side is as follows

Replace the 2 way door speakers with Percison Power Components speakers 5 1/4 inch
Replace the rear shelf mid bass with Percison Power Componets speakers 6.5 inch
Find a replacement for the rear side 2.5 inch mid/tweeters (maybe just use the tweeter from above)
Re-use my soundstream 4x100w and 1x600w amps (Unfortunately they don't support balanced audio but have high level speaker and unbalanced audio like the high end models do)
Re-use my old trusty Boston Acoustics C110 10inch sub (It's compact and has fast clean bass)
Add terratec sound card and route the factory tuner and PC sounds and connect to the amps.

[Zero]

Thanks Owen, and apologies to anyone if I have hijacked the thread.

Owen, I have been slack and hadn't updated my sig - but Ive done so now.
I still have the Assemblage 2.7 dac that you have been helping me with and the rotel rc1070 preamp, and yes both are unbalanced.
I got really frustrated with the repairs on the Assemblage dac, so I put it on the back burner until I can face it again without getting depressed.

I have had an Enlightened Audio Design Ovation for a while now while the Assemblage has been out of action.
It has balanced outs, and uses two BBpcm1702 dacs in unbalanced mode and four BBpcm1702 dacs in balanced mode, which is why I'm keen on using the balanced outs.

In practise however with the rotel amps the sound quality has been worse with balanced and it took me forever to figure out why.
I believe it is the crappy conversion circuit in the rotels that is the culprit which really annoyed me lol.

So it sounds like its more expensive than its worth to modify the inputs on the rotels to be truely balanced?

[RexJ]

Most commercial amps have a differential circuit. Track down the cct diagram and you'll find something that looks like 2 transistor/FETs back to back with their ground legs tied together perhaps through a ccs. The input ends up on one device, the input on the other is tied to ground. To convert this circuit to balanced input, lift this from ground etc. Some amps have a shorting bridge on the XLR input, some a switch.

[Owen Young]

Ah sorry Zero, I misread your post.
Prob best to go with what sounds best...unbal outs from your Ovation pre.
Using something like say a Jensen Transfomer (adaptor) will be signif $$ & only achieve for you a change from unbal to bal ICs & introduce the vagaries of another device in cct (the TX).

Unless someone (like Chris Marquet) can advise you that your amps can be professionally & easily converted to balanced operation. However, may be worth an enquiry, see this current thread. (http://www.audioenz.co.nz/forums/showthread.php/12918-Is-Chris-Marquet-still-working?p=156696#post156696)

[Zero]

Yea thanks Owen.

I plan on seeing him some time soon anyway.
He knows the rotel range really well.
I'll ask him his opinion.

[Antipodes]

The whole concept of balanced circuitry involves additional circuitry in the signal path.

A system that is so-called 'balanced throughout' will split and recombine the signal again several times along the journey, in order to cancel noise at suitable places along the way. Some pro audio DACs split and recombine 3 or more times within the one component. Therefore you end up with transformers or invertor stages to split the signal and transformers or differential input stages to combine the signal again. This means additional circuitry in the signal path. It is therefore a trade-off between additional circuitry and the benefits of signal to noise ratio.

For any particular piece of gear, whether balanced sounds better than single-ended will depend on the implementation - as with all technology, but especially this one.

Assuming the EAD is 'balanced throughout', it will combine the signal and then split it just before the output connector. Therefore you don't lose the benefits of any balanced circuitry used further upstream when you use the unbalanced outputs. What you do lose is the larger voltage swing, the benefits of cancellation of cable noise in the connection to the amp, and the ability to drive the balanced inputs of the amp (if that is beneficial). Amongst those 3, the input of the amp is the most important, and cancellation of cable noise (assuming they are reasonable lengths) is the least important.

Just because the input of the Rotel uses an IC to combine the balanced signal doesn't make it a bad thing. It depends on how well it is done. Even those (relatively rare) power amplifiers that have balanced outputs combine the input signal to cancel noise before splitting it again for amplification.

[Gary.M]

You're singing my song sir!



True balanced circuitry is expensive.

9/10 the simplicity and shorter signal paths of single ended circuits outweigh the potential benefits of balanced circuitry.