Transformer at input of SOZ to convert unbalanced->balanced?

[psarin]

another newbie question -

can i convert unbalanced output of my preamp to balanced by inserting a 1:1 audio transformer at the input of the SOZ amplifier? i'm having trouble simulating this, so i was wondering if any of you experienced folks had an opinion?

also, an unrelated question: is it ok to convert a regulated +/- 40VDC power supply to a -20-0-+20VDC power supply using a couple of caps and resistors? (see figure below)

thanks

 

[Henrik]

Hi psarin

An inputtransformer is not a good solution here, you should look for something else. I used a linedriver (opamp) from burrbrown until I had finished my balanced zenlinestage.

This is the powersupply for for my SOZ.
It works rearley great!
This supply gives you +19, 0, -19 volt.
The 46 v is directly from the diode bridge.

The regulation is from Ciuffolis Powerfollower99.

http://www.geocities.com/ResearchTriangle/8231/my/index.html

 

[Nelson Pass]

Jensen Transformer in Hollywood makes a
wonderful line level balanced transformer for
this.

 

[Stefano]

Jensen

...And wich is?

 

[hifimaker]

Is there a sonic improvement to externally converting an unbalanced source to a balanced source using methods, like the ones mentioned here?

I'm wondering if a balanced pre-amp or amp benefit from "balancing" an unbalanced upstream signal in this manner, ather than using existing unbalanced inputs?

-David

 

[Stefano]

jensen

I've found that jensen JT-11P-1 may have the caracteristics we are looking for, i wonder if is this that Nelson was thinking of, i suppose that this is the one used by jeff rowland d.g.

 

[Nelson Pass]

Responding to the last two posts, I believe the answer is yes
in both cases.

 

[tomchaoda]

unbalanced to balanced conversion

Another way of unbalanced to balanced conversion is to utilize BB DRV134 chip. I know someone in Taiwan made a small kit available. The circuit looks simple enough!

Thomas

This is the image of that conversion:

 

[tomchaoda]

unbalanced to balanced kit

and the real kit looks like this:

 

[Steve Eddy]

Re: jensen

I've found that jensen JT-11P-1 may have the caracteristics we are looking for, i wonder if is this that Nelson was thinking of, i suppose that this is the one used by jeff rowland d.g.

The 11P-1's secondary unlike its primary isn't quite balanced due to the winding techniques used. You can wire it up for symmetrical output as per AS-060 though if you want to ideally balance it, you'd beed a little capacitance across one of the voltage divider resistors. I don't recall offhand how much capacitance would be required but you can EMail Jensen and they can tell you.

Another option would be to use an output transformer to balance the output of the source component. The JT-11-DMCF or DMPC would be a good choice. However if the source's output is capacitively coupled, you need to make sure it's got several hundred uF of capacitance in order to avoid low frequency resonance (which would result in some response peaking) due to the much lower primary inductance compared to input transformers.

se

 

[fdegrove]

Hi,

Another option would be to use an output transformer to balance the output of the source component. The JT-11-DMCF or DMPC would be a good choice. However if the source's output is capacitively coupled, you need to make sure it's got several hundred uF of capacitance in order to avoid low frequency resonance (which would result in some response peaking) due to the much lower primary inductance compared to input transformers

You mean this OPT can't have any D.C. on it's primary?

Cheers,

 

[Steve Eddy]

You mean this OPT can't have any D.C. on it's primary?

Well, no transformer really likes DC on its primary or secondary. But the point I was trying to get across is if your source is capacitively coupled and you wish or need to keep it that way, you're going to need a bit more than the more typical 2-10 uF.

se

 

[gushogh]

A totally newbie question:

When you all talk about balanced / unbalanced what do you mean?

Is it just if there is a DC offset? E.g. if you have a supply voltage of +- 20V and a sine signal that is a oscillating around e.g. +1 volt and not 0 volt. (or a supply voltage on e.g. +19, 0 -21)

So balanced = is when something remove any DC offset .. right ?

Thanks gh

 

[fdegrove]

Hi,

Well, no transformer really likes DC on its primary or secondary.

That depends on how the xformer is wound.
I assume the Jensens weren't made for that but there is an elegant way around this.

You can shift the coupling cap to the ground leg and even if you need to increase its value to, say 47µF it's pretty much out of harms' way.

This is a technique called parallel feed, AKA parafeed ( or parrot feed as some mockingly call it) and is sometimes used in SE amps where you don't want to pay for that gapped SE xformer but still want to block DC and use a standard PP OPT for that SE output stage.

The idea stems from your good old WE engineers as so many other so called innovations we see lately.

People may find it useful to go from an unbalanced preamp output to a balanced connection for a balanced amp using balanced I/Cs.

Cheers,

 

[fdegrove]

Hi,

When you all talk about balanced / unbalanced what do you mean?

Errr...too late in the morning to 'splain all that....

So balanced = is when something remove any DC offset .. right ?

No, no...Not at all. We're talking baluns here.

Don't know of a site that explains it correctly using semis but surely someone else may.

Cheers,

 

[00940]

http://www.balanced.com/faq/balanced.html here's a good FAQ on this.

Fdegrove : it's awfully late indeed

 

[fdegrove]

Hi,

Fdegrove : it's awfully late indeed

That makes two of us unless you're up very early on a Sunday morning....

Preparing the coffee...

Cheers,

 

[Steve Eddy]

That depends on how the xformer is wound.

Hmmm. I know you can air gap the core to help in this regard, but how do you wind a transformer such that DC doesn't degrade its performance?

I assume the Jensens weren't made for that but there is an elegant way around this.

I know they're not air gapped.

You can shift the coupling cap to the ground leg and even if you need to increase its value to, say 47µF it's pretty much out of harms' way.

This is a technique called parallel feed, AKA parafeed ( or parrot feed as some mockingly call it) and is sometimes used in SE amps where you don't want to pay for that gapped SE xformer but still want to block DC and use a standard PP OPT for that SE output stage.

The idea stems from your good old WE engineers as so many other so called innovations we see lately.

Yes. Though not all source outputs are single ended and could be adapted to parafeed operation.

In any case, my point was simply that if you ARE going to have a coupling cap, it needs to be a bigger one than usual.

se

 

[fdegrove]

Hi,

Hmmm. I know you can air gap the core to help in this regard, but how do you wind a transformer such that DC doesn't degrade its performance?

It's the air gap I had in mind...

In any case, my point was simply that if you ARE going to have a coupling cap, it needs to be a bigger one than usual.

Usually, yes...
There's life outside of the Jensen catalogue though....

Cheers,

 

[Steve Eddy]

Usually, yes...
There's life outside of the Jensen catalogue though....

Sure.

So what would you recommend in a 1:1 line level output transformer with a high enough primary inductance that you could get away with a couple uF of coupling capacitance?

se