[pfradale]

I picked up a (used) Sony SCD-1 from a local shop half a year ago and loved the improvement in sound; when I bought the Sony the shop owner suggested I get a balanced to unbalanced converter rather than using the Sony's unbalanced output; my pre-amp does not have balanced inputs.  I had him build one, which he did using a power transformer, XLR input and RCA output for each channel. The construction seems robust and the components used are fine.  I just put it into the system and found the following:

1) high frequencies are more pronounced
2) soundstage increased but at the cost of image--the system lost much of its presence
3) bass response is dramatically decreased
4) volume at any given setting is half what it would be using the Sony's unbalanced output.

Should this have been the case?  He had said that the sound would "open up", which I suppose it has, but at a cost of other important qualities. I'd like to understand better what is supposed to happen and why/how so I can evaluate this implementation. I am an electronics novice; I've built a Foreplay pre-amp in the past, built my own speakers and XOs, but that's about it.  Ignorance seems to have cost me, this time, and I'd like to learn more to avoid similar missteps. Thanks, folks.

Paul

[ctviggen]

Balanced means that there's a ground, a (+) line and a (-) line, which carries a signal of opposite polarity as compared to the (+) signal.  This way, noise on both lines can be removed.  This has more detail:

http://www.monstercable.com/RobertHarley/ch11_p07.asp

So, it depends on what your environment is like.  If you have a lot of noise (such as a lot of cables running together), then balanced ICs will help remove at least some of the noise.

I'm not sure what the converter is doing -- I assume it's powered?  If not it could have a transformer.  Anyway, the output issue is because the converter isn't putting out the correct signal level.  Other than that, I don't know what the converter's doing and why you lost so much.

I do know that in my own system, I prefer balanced and don't use unbalanced if I can help it.  I like balanced because I think the connectors are easier to use.  I also use balance because of the possibility of noise reduction, though I'm not sure if that really happens in my particular system.

[pfradale]

No, it's not powered; it has two transformers, one per channel.  I could understand a loss across the entire frequency spectrum, but the skew in frequency response threw me.  A startling amount of bass was lost, even when I upped the volume, using a dB meter to keep sound levels constant.

Too bad, really, since it is very nicely built, and I'd hoped for increased air in the upper octaves without loss of bass.

[JoshK]

Sounds like he got one of the phases backwards and you are getting cancellation.  Our ears hear lack of bass as improved detail and transparency in the mids to upper highs.  Bass frequencies are most affected by reversal of phase.  

I'd ask him to recheck his work for polarity.  BTW, I am reasonably certain that I read that the SCD1's XLR outputs were not "real" balanced outputs but just jumpered off the single ended output stage.  In which case I am not sure what he expects to acheive with this tweak.

[randytsuch]

You said he used a power transformer to build this converter?

I would not have used a power transformer, there are audio signal transformers that are made by companies like Lundahl, S&B, Jensen etc that are made for this type of application.

All transformers are not the same.

I also agree with Josh that you could have a phase problem in one channel.  You could check that by reversing polarity on one of your speakers, if one channel is out of phase, this would at least put them in the same phase.

Losing volume may be because the transformer is stepping you signal down, where it should be a 1:1 transformer.

Randy

[art]

With any decent coupling transformer........and we are not sure that is what he used........you have to terminate them properly, or you will get peaks in the top end respsonse.

Pat

[pfradale]

Thanks, everyone, for your input so far.  If I could trouble you for a bit more, I opened the case and got the following:

The transformers have a diagram on the top:

6   600 (ohm)   7
5   150 (ohm)   8
4                     9
         CT
3                    10
2   150 (ohm)   11
1   600 (ohm)   12

1/2 D8 30-15,000 CPS
Level + 16DBM
WV 175V
MFD. BY ADC

The connections are as follows (and are the same for each transformer):

#7 (yellow) --> RCA center pin
#12 (white) --> RCA outer ring
#12 (black) --> #10
#10, 9, 5, 4, 3 jumped (all connected to each other)
#4 (red) --> XLR #1
#6 (white) --> XLR #2
#1 (yellow) --> XLR #3

[randytsuch]

It might help to take a close up picture of the diagram on top of the transformer.

Randy

[JoshK]

Actually, do you have your Sony manual?  Can you tell us the wiring pinout for the XLRs on your sony?  They don't always follow convention, pro audio and consumer audio tend to follow different rules with XLR.