Balanced buffer circuit questions...

Hi,
1. i am searching for a simple buffer, based on a 5534 or similar. I need to distribute an balanced Input signal to 3 balanced Outputs. It should be balanced in and balanced out. It should "sound" "neutral" as possible. Input Gain = Output gain of each Buffer....

2. If you can also show me in this circuit how I can make the gain different (poti) would be perfect... I mean: set the gain down individual via a Resistor citcuit or Poti at theses buffers....

3. btw. How many buffers can I "drive" from 1 input without any influences?
Is it possible to split 1 Signal into 10 with same gain and same "sound"?

I hope you can understand me, cause my English is terrible.....

Regards
leslie

2. If you can also show me in this circuit how I can make the gain different (poti) would be perfect... I mean: set the gain down individual via a Resistor citcuit or Poti at theses buffers....

Click to expand...

Do you need to set the gain of each output independently? What's the gain range? Only positive (say 0 to +15 dB) or negative as well (say -inf to +6 dB)?

There are several ways to solve your problem, give me a few hours and I'll draw some.

Samuel

First of all Thanks for your help.

1. For my Idea I need it "only" negative. There are Line Level Inputs +4dbu and it should go out at 4 dbu 3 times. It would be perfect if i can level it down from +4dbu to -inf. And if you can give me an idea to make the gain range from + 4dbu to more it would be nice also. But this would be than a line amp, or not?

And yes i need to set the gain of each output independently...

Here we go:

[removed]

Some notes:
* With a 5534, you can add up to 10 outputs. If you need more, use higher values for the pots, i.e. 20k for 20 outputs. For every output you need to add the output section - I hope this is clear.

* As shown, the output section has a gain of +10 dB; if you remove the 3k0 resistor, it will drop to 0 dB.

* You may want to pairwise match the resistors and caps of the input section to 1% for good CMRR.

* If you are using 5534 opamps, use a 10 pF cap for the internal compensation - except you lower the output gain. 22 pF would be adequate in this case.

As I noted in my earlier post, there are more complicated ways to do this, but this one will work very well and is about as simple as it get's.

Samuel

Thanks Samuel. A very cool simple Design.
2 questions:

1. Is it possible to explain me your "Impedance balanced" output? Never seen this before. How does it work?
2. Are these electrolytics Bi-Polar, or what does the "double +" means? I don´t think so, or?

What Du you think of something like this:

http://www.gyraf.dk/schematics/Neu_482.gif

It´s transformer based and a little bit more complicated.

Can I add a Poti between the Input section and every output section to level down the gain?

Can I also "transform" the discrete Output section of this design to a 5534/5532 based?

What Do you think.

Thanks.

Lelsie

1. i am searching for a simple buffer, based on a 5534 or similar. I need to distribute an balanced Input signal to 3 balanced Outputs. It should be balanced in and balanced out.

Click to expand...

May I be so bold to suggest the Beh. MX882 ? :roll:

It should "sound" "neutral" as possible.

Click to expand...

Some opamp-swapping might be required, which may be unattractive since I guess it's using SMD-components.

One of the two of the earlier model I have (MX662) had '4558 opamps...

At least for a starting point this box might be interesting, it has all the required I/O already in place.

Bye,

Peter

[quote author="clintrubber"]May I be so bold to suggest the Beh. MX882 ? :roll:
[/quote]

You are! :grin:

No, its a good Idea, but i want to integrate it in a bigger circuit. So I want to learn how it works and build it .... But thanks for your Idea....

Is it possible to explain me your "Impedance balanced" output? Never seen this before. How does it work?

Click to expand...

"Balanced" and "signal symmetry" are not the same; for balanced transmission, the impedance to ground on the "hot" and "cold" must match. Whether there is opposite voltage on them does not matter. Signal symmetry improves crosstalk onto other audio-lines as the electric fields of hot and cold cancel - but this is normally a non-issue. But it is possible to have +6 dB more output with signal-symmetrical outputs. In fact, a transformer-balanced output with unbalanced driver (as in the Neu-482) will loose it's signal symmetry at high frequencies due to the capacity between the windings. Check the white papers on www.jensen-transformers.com for more info.

Are these electrolytics Bi-Polar

Click to expand...

Yes. You can use non-polar types as well, but bi-polar is suposed to last longer.

Can I add a Poti between the Input section and every output section to level down the gain?

Click to expand...

You have to be careful as this is a single-ended design so that you don't have DC on the pot. And you may skip the 1k pot which trims the input gain.

Can I also "transform" the discrete Output section of this design to a 5534/5532 based?

Click to expand...

Yes, but as above, this is a single-ended design, and a 5534 will preferably used on dual rails.

Do you want/need input- and output-transformers? I'll draw something for you...

Can you tell me your application?

Samuel

[quote author="Samuel Groner"]"Balanced" and "signal symmetry" are not the same; for balanced transmission, the impedance to ground on the "hot" and "cold" must match. Whether there is opposite voltage on them does not matter. Signal symmetry improves crosstalk onto other audio-lines as the electric fields of hot and cold cancel - but this is normally a non-issue. But it is possible to have +6 dB more output with signal-symmetrical outputs. In fact, a transformer-balanced output with unbalanced driver (as in the Neu-482) will loose it's signal symmetry at high frequencies due to the capacity between the windings. Check the white papers on www.jensen-transformers.com for more info.[/quote]

ok, but the best way is to make the outputs symmetrically against zero voltage (ground), or not? So I use transformer, because then the 0 Volt potential has no DC connection with ground.

If I use electrically symmetrie at the In and Outputs then they are ground symmetrically but not groundfree! Because they have no galvanic seperation. Am I right?

[quote author="Samuel Groner"]
You have to be careful as this is a single-ended design so that you don't have DC on the pot. And you may skip the 1k pot which trims the input gain.[/quote]

So you mean because the PSU is unbalanced I have possibly DC between these both stages? Can I put some Capicators near the Pot to remove DC?

[quote author="Samuel Groner"]
Yes, but as above, this is a single-ended design, and a 5534 will preferably used on dual rails.[/quote]

The Input stage of this Neumann V482 also uses a 5534...
So it must work!....:grin:

[quote author="Samuel Groner"]Do you want/need input- and output-transformers? I'll draw something for you...[/quote]

Yes normally all my audio stuff has a Transformer based in and output. Perhaps a simple 1:1 only to make a galvanic seperation...

[quote author="Samuel Groner"]Can you tell me your application?[/quote]
I want to build a high quality Monitor section for my Studio. With different Inputs/ Volume/ Talkback/ Outputs/ Routing etc....

Thanks for Your help samuel. Thats very cool...

Leslie

The Input stage of this Neumann V482 also uses a 5534...
So it must work!

Click to expand...

Is this a 5534? OK...

You can add caps to make it work with a single-ended PSU, but it is simpler with +/- rails. And we don't like too many 'lytics in our signal path, do we?

I'll post a schemo when I get home.

Samuel

[quote author="Samuel Groner"]Is this a 5534? OK...[/quote]

Yes the TDA1034 is the old NE5534....

[quote author="Samuel Groner"]You can add caps to make it work with a single-ended PSU, but it is simpler with +/- rails. And we don't like too many 'lytics in our signal path, do we?[/quote]

You are right, but when it sounds good, it is good. And the old Neumann broadcast stuff sounds very good, because it doesn´t "sound"....:grin:

I like to separate my studio in a effect section with some Neve and API stuff and a neutral section, so I can choose what i need. And my Monitor section should not sound. It should only route my audio signals without any influences....:grin:

[quote author="Samuel Groner"]I'll post a schemo when I get home.

Samuel[/quote]

Thanks a lot Samuel. Its very nice that you help a newbie like me. I build a lot but now I want to understand a bit more whats going on and not only solder some Parts. I hope someday I can give it back to you....

Leslie

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If you want transformers to be sonically transparent, go for the best. That's why I suggested some Jensens. As shown, the two gain stages provide +6 dB each, which results together with the 12 dB loss from the input transformer into unity gain max.

You could change the first gain stage to +12 dB and make the second one a voltage follower, which would improve noise (maybe two or three dBs). As shown, the output-opamp will have higher slew-rate, which is a nice thing to have as well.

If you want best performance into difficult loads (long cables), you can add a simple discrete class A buffer (two transistors and a few other parts) and a load isolator (JT-OLI-3) for every output. I would suspect that this is overkill for your app, your control room does not have 100 m long cables, does it?

Samuel

Thank you very much Samuel. Its a great and simple circuit!
And no, I don´t have 100 m Cables...:grin:

But, i if you could explain me a simple Class A Buffer and show me the position in this circuit and explain me why, i would be happy. I am learning, so every Input is wellcome.....

Thanks Samuel.

Lelsie....

But, i if you could explain me a simple Class A Buffer and show me the position in this circuit and explain me why, i would be happy.

Click to expand...

I recommend you get a copy of "Audio IC Op-Amp Applications" by Jung; there are two class A output stages in there and many other useful circuits. Drop me a PM with your e-mail if you want me to scan these pages.

Samuel