Balanced line

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#101
Re: steve

AMPMAN said:
The point is while your drawings are fine for experienced people ,interpreting them can be perplexing to some. what is needed is a diagram showing how we can use our existing cd players with their rca plugs which are grounded. lets imagine a coil in a phono player, we take the leads straight to the inputs of a balanced preamp, its obvious that the current oscillating backwards and forwards will turn on the pos and then the neg inputs.The ground wire is then the shield,what is harder to grasp is when you ground one wire how can it turn on a transistor. the diagram I referred to shows how, I for one would like to see how its done in the p1.7 to recap most everybody has unbalanced equipment we want to be shown how to connect it to balanced in the simplest way possible, surely this not to much to ask.
Click to expand...

You want simple? Ok, here's the simple (and arguably the best) solution:

Step 1. Forget about converting your unbalanced outputs to balanced outputs.

Step 2. Forget about using your balanced inputs.

Step 3. Build this:

<center>
<img src="http://www.q-audio.com/images/simple2.jpg">
</center>

The JT-11P-1 will give you about 100dB of common-mode noise rejection. The JT-11P-1HPC about 95dB.

Don't want to build this? Skip to Step 4.

Step 4. Buy this:

<center>
<img src="http://www.jensentransformers.com/graphics/photos/L/ci2rr_e.gif">
</center>

There ya go. Simple. 🙂

se
 
#103
Ampman,

It's been already done. Just skip caps if you don't like them.
 

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#104
There ya go. Simple.

Perfect Steve. Clarity and convergence for a thread that seemed to be wandering. The circuit is good one for getting rid of common mode noise in a single ended interface with is to who point of balance interfaces to begin with. The transformers could be mounted at or inside the preamp circuit This would be the interface marked out with respect to the transformer schematic.
The Jensen transformers are very good units. Keep the transformer out preamp in cable. The transformer could have a short captive cable with a male RCA to connect to the preamp side.

There on many paths up the mountain and view from the top and satisfaction of the journey are what matters in the end. An arduous climb but a worthy destination on this one.

Thanks Steve.
 
#105
I'd like to convert my 3-way active XO to balanced inputs and outputs. It seems like the best solution would be to add the Jensen transformers, but, that would cost over $600 for the XO alone, not to mention the power amps the XO is connected to.... I'd like to avoid that.

Outputs:
Using the circuit Peter just posted would create two paths with the same phase and equal impedance, right?

D. Self seems to recommend Fig. 5B for home hi-fi. As I understand it, Fig. 5B from Doug Self's article would require 2 opamps and 4 resistors be placed in the signal path, just before the RCA jack. Impedance is set by Rs. I believe this produces an inverted signal to be compared with the in-phase signal at the input on the amp, which seems to be a very different solution. How do these two methods compare?

Inputs:
If I use Figure 9 from D. Self as the input, will it cause any problems when connected to the balanced outs from an Aleph P 1.7 or Borbely balanced line stage?

Finally, are there any special recommendations for a differential op-amp to be used in these circuits? What values for R and Rs in D. Self's Fig. 5B?

Sorry for all the questions.... I'm new to this and don't want to kill myself or my gear.

Thanks.

brad
 
#108
AMPMAN,

You're right, figure 15 does show how to go from an unbalanced out to a balanced in, but this isn't what I'm trying to do. I'd like to change-out my PCB-mounted phono plugs for chassis-mounted XLRs - both input and output.

Thanks.
 
#109
Re: steve

AMPMAN said:
I'm with einstien he said things should be as simple as possible but no simpler,doug selfs diagram achieves this precisley and economically why don't you post it on this site for all to see.😕
Click to expand...

What, you mean this?

<center>
<img src="http://www.q-audio.com/images/xlrphono2.jpg">
</center>

This doesn't do anything with regard to common-mode noise rejection because the source impedances are left unbalanced. The whole point of using balanced interfaces is to reject common-mode noise. The cable adaptor solution can help reduce noise caused by interchassis currents (i.e. ground loops) but you're right back to square one with regard to common-mode noise rejection.

se
 
#110
Re: dc

AMPMAN said:
you don't have to just go to doug selfs website there you will find fig15, which shows you to go from rca to balanced without opamps or any transformers clearly, which is all we wanted to know in the first place.:xeye:
Click to expand...

Again, the cable adaptor in Fig. 15 does not balance the output impedances and does not provide any real benefit in terms of common-mode noise rejection.

se
 
#111
dc said:
AMPMAN,

You're right, figure 15 does show how to go from an unbalanced out to a balanced in, but this isn't what I'm trying to do. I'd like to change-out my PCB-mounted phono plugs for chassis-mounted XLRs - both input and output.
Click to expand...

So all you want to do is be able to use XLR connectors instead of RCA connectors and don't care whether your ouputs or inputs are balanced?

What is your ultimate goal here? To just use XLR connectors or improve common-mode noise rejection?

se
 
#112
Steve,

I'd like to reduce common-mode noise rejection and capacitive crosstalk. According to D. Self's site re the cable in Fig. 15 "The rejection of capacitive crosstalk therefore depends on the unbalanced output impedance, and will be no better than for an unbalanced input, as at 1); the main benefit of this connection is ground noise rejection, which solves the most common system problem."

I said I'd like to replace the phono connectors with XLR jacks in my last post not because I've taken a fancy to the way XLR jacks look, but because I think the benefits provided by using balanced connections are, at least theoretically (having no personal experience with them), very appealing.
 
#113
dc said:
I'd like to reduce common-mode noise rejection and capacitive crosstalk.
Click to expand...

I think you mean you'd like to INCREASE common-mode noise rejection. 🙂

As for capacitive crosstalk, what sort of crosstalk are you referring to? If you mean interchannel crosstalk, I wouldn't lose any sleep over it.

Try this:

Play a piece of music and sit in your normal listening position. Mute the right channel and plug your left ear. What you're hearing is interchannel crosstalk. 🙂

But whether you're talking about interchannel crosstalk or capacitively-coupled interference on the line, then a transformer input still gives you excellent common-mode rejection even if it's being fed from an unbalanced source.

That's because first, the transformer's input floats and doesn't have any fixed ground reference point and second, because the transformer's common-mode input impedance is exceedingly high.

So again, with something like the JT-11P-1, you'll get about 100dB of common-mode noise rejection (whether its capacitively or inductively coupled into the line) even if you feed it from an unbalanced source. Feeding it from a balanced source only improves by about 7dB.

According to D. Self's site re the cable in Fig. 15 "The rejection of capacitive crosstalk therefore depends on the unbalanced output impedance, and will be no better than for an unbalanced input, as at 1); the main benefit of this connection is ground noise rejection, which solves the most common system problem."
Click to expand...

See above.

I said I'd like to replace the phono connectors with XLR jacks in my last post not because I've taken a fancy to the way XLR jacks look, but because I think the benefits provided by using balanced connections are, at least theoretically (having no personal experience with them), very appealing.
Click to expand...

Thanks. Now I know where you're coming from.

It's been my personal experience that using a good quality input transformer fed from an unbalanced source gives the best result. You get true galvanic ground isolation, better common-mode noise rejection than even fully balanced active interfaces, and last, but not least, reduced overall circuit complexity.

se
 
#115
Thanks, Steve, for being gentle with the overzealous newbie (me).

So, in sum, you're suggesting that the best possible solution would be to use unbalanced outs on the pre-amp to JT -11P-1 input transformers on the active XO network, then unbalanced out (phono jacks) of the XO to more JT-11-P1 input transformers on the amps?

I believe the Aleph P 1.7 offers both unbalanced and balanced outputs. In such a case, would you still recommend using the unbalanced outs?
 
#117
dc said:
Thanks, Steve, for being gentle with the overzealous newbie (me).
Click to expand...

Wait'll after the blood initiation before you thank me. 🙂

So, in sum, you're suggesting that the best possible solution would be to use unbalanced outs on the pre-amp to JT -11P-1 input transformers on the active XO network, then unbalanced out (phono jacks) of the XO to more JT-11-P1 input transformers on the amps?
Click to expand...

Well, "the best possible solution" as it relates to what has given me the best personal, subjective result.

I believe the Aleph P 1.7 offers both unbalanced and balanced outputs. In such a case, would you still recommend using the unbalanced outs?
Click to expand...

The beauty part is, beause you can feed the input of the transformer from a balanced output just as easily as an unbalanced output, it would require very little effort on your part to give it a try both ways and decide which result you like best.

Just because you're a "newbie" doesn't mean you can't decide for yourself what you prefer. And never forget that what you prefer is the only thing that really counts at the end of the day.

se
 
#118
Re: It's been my personal experience that using a good quality input

Fred Dieckmann said:
I'll be damned.... I actually completely agree with all of that too. Have our biorhythms synchronized or something?:bigeyes:
Click to expand...

By the way, where's your accompanying photo? The names you've used have never been very interesting, but I've always looked forward to see what photo you'd pop up with next.

se
 
#119
By the way, where's your accompanying photo? The names you've used have never been very interesting, but I've always looked forward to see what photo you'd pop up with next.
Click to expand...
Steve, take it easy.
Maybe I know what you are talking about ..., but I do not know why you are talking about... Let's go back to the interesting diyAudio dispute. Only for the technical dispute, PLEASE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
#120
El Cheapo Soloution....

Steve Eddy said:


You want simple? Ok, here's the simple (and arguably the best) solution:

<center>
<img src="http://www.q-audio.com/images/simple2.jpg">
</center>



Step 4. Buy this:

<center>
<img src="http://www.jensentransformers.com/graphics/photos/L/ci2rr_e.gif">
</center>

There ya go. Simple. 🙂

se
Click to expand...

Jason, I have made a similar-ish box to the 'Iso-max' shown above, except captive in/out leads, and three position DPDT switches.
Car audio suppliers typically sell such transformer audio isolation boxes quite cheap - mine cost AUS$12.00 and it works quite fine enough.
The switches are wired as reversing switches, enabling polarity reversal, with a center off position enabling muting.
With this box I can connect any 'on test' piece of gear on my bench to my reference source equipment without regard to which AC power point these items are plugged into.(NO hum loops)
It also converts my single ended source equipment to balanced for driving balanced input pro-gear.
Although this box contains the cheapest, sh*ttiest 1:1 transfomers that I could find, the audio resultant is quite fine without going to the expense of Jensen or other high priced stuff.
It is worth the experiment to verify if you like transformer sound before you invest in MUCH more expensive ones.

Eric.

You may need to play with loading networks on the secondary, to avoid peaking response due to parasitics causing HF resonance.
 
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