?balanced inputs/outputs

[Unmeshed]

Sorry if this has been covered previously.  I am a newbie who always wanted to build my own stuff.  I am considering the ForeplayIII partnered with a Cary CAD 120 amp and would like to take advantage of the balanced input if possible since I am told this would have a lower noise floor than the RCA jacks.  First of all, would this board agree that the balanced inputs would be quieter? Secondly, could the Foreplay III be built with balanced inputs/outputs?  Thanks!

[JC]

I can't speak to the amplifier, but only in general terms.  Balanced audio lines certainly have their uses, particularly for long runs and in electrically noisy environments.

If these conditions are not an issue, though, I really don't know that you will gain much, if anything, in terms of lowering the noise floor at nominal line levels.

To put it another way, in a typical home hifi installation, I would certainly put my money elsewhere first.

[Grainger49]

Just a few observations.  The FP III, like all standard Bottlehead equipment, doesn't have balanced inputs or outputs.  I can't speak for the custom work they do.

That said, there is one kind of noise that balanced interconnects rejects.  It is common mode noise picked up in the interconnects.  If that is a problem then balanced outputs/interconnects/inputs will definitely help.  It doesn't do a thing to help the noise floor.  It requires twice the electronics, and therefore expense, to execute balanced inputs or outputs.  Twice the electronics can raise the noise floor in a piece of equipment because you have twice the amplifying devices.

[Paul Joppa]

In our custom work, we use transformers when we need to interface balanced lines. For the Foreplay, I'd suggest the Altec 15095, 15K single-ended to 500 ohms balanced, as an output transformer. You can put together an external box for this, as is often done for moving-coil phono cartridge step-up transformers. An alternate, once Mike is back to taking orders, would be the Magnequest B7-15K. Both of these will reduce the Foreplay gain.

What a good balanced setup will do is exactly what Grainger says - reduce hum and buzz that is caused by currents in the ground line of unbalanced interconnects. There are some excellent white papers on the subject at the Jensen Transformers web site.

As for hiss and rumble noises, these are most often due to sub-optimal gains in individual components of the system. My white paper on that subject is on the Bottlehead Community page, titled Signals, Noise and Signal-to-noise Ratio. Here you will find some cases where a reduction in the Foreplay gain (e.g. with a transformer output) might be a benefit in terms of noise.

As you can tell by the referenced white papers, this is a fairly complex subject to treat accurately!

[Unmeshed]

Thanks for the input fellas (and the reading assignment-though I suspect it might be over my head).  For now I guess I'll stick to the unbalanced input/output option.  I found this website almost by accident and had my interest piqued when someone had favorably reviewed the Foreplay III to a BAT VK-5i.  I had considered that unit because of it's balanced circuits.
How about those "power-line conditioners" or AC generators would they eliminate  or prevent a "noisy electrical environment"?  What causes ground loop problems?  If I build my kit correctly can I still have these problems?

[JC]

"Noisy electrical environment" can also refer to a situation where there are many signals running around in close proximity to one another.  A radio or TV studio, for instance.  Balanced lines are inherently better at rejecting such "proximity" influences.

Power conditioning can indeed be useful, particularly if you have reason to believe that there is stuff other than power coming in on the lines.  I think that is a safer bet all the time, but finding it and quantifying it can be extremely difficult.

"Ground loops" generally refers to a situation where a piece of equipment has more than one ground reference connected to it and there is a significant difference in potential between them.  For instance, a piece of gear may have a safety ground through the third wire on its AC cord, and a signal ground through its interconnection to another piece of gear.  If the potential difference between them is other than "zero", one or another piece may see that difference as a tiny signal Voltage and process it as such.  In the case of audio gear, that most likely manifests itself as hum.  On a video monitor, it might show up as "hum bars" rolling vertically through the picture.

Unfortunately, the potential difference between various "grounds" may be caused simply by the length of the paths they take back to common points.  On the brighter side, though, it is usually easy to control this in a typical home hifi setup through simple steps like having all the AC cords plugged into a single power strip.  Every set-up is unique, certainly, but I haven't run into a grounding issue yet in a home environment that wasn't ultimately solvable.  Even with unbalanced signal wiring.  OTOH, as installations grow in physical size, it is perfectly possible to have ground loops even when balanced signal lines are used.  In those cases, the use of transformers is usually essential.

Yes, it is indeed a big subject.

[Grainger49]

Thanks for the input fellas  . . . 

How about those "power-line conditioners" or AC generators would they eliminate  or prevent a "noisy electrical environment"?  What causes ground loop problems?  If I build my kit correctly can I still have these problems?

I bought a power conditioner back about 18 years ago.  It lowered the noise level in my system.  What they do depends on the incoming power.  If the incoming power is clean the "conditioner" does very little.  If the incoming power is full of notches, spikes and harmonics then it decreases the noise level.  As JC points out there are other sources of noise that a conditioner doesn't address.

One of those other sources of noise is ground loop problems.  The FP III is a major rework of the FP 2.  Bottlehead learned what worked for the FP 2 and plowed all that back into the FP III.  Ground loops often happen when different sources have noise on the chassis and therefore on the outer shell/ground of the output interconnect.  The FP III switches both the source hots (R/L) and ground when it selects an input.  This eliminates the major source of ground loop hum.  The power amp chassis and input common is tied to the FP III chassis.  That is something that the output transformer described by Paul Joppa would lift (remove).

[Unmeshed]

Wow, thanks again for all the info.  I am pretty excited about this project now as I can see I have ALOT to learn.  I haven't even unpacked the amp yet and was going to wait until after the new year to begin building the kit.  I am sure I might need some help there as well.  Then maybe I'll build some speakers......