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

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psarin

Member
2001-11-09 6:35 am
Mars
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
 

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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
 

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Re: jensen

Stefano said:
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

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
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,;)
 
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

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
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

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
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,;)
 
fdegrove said:
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

diyAudio Senior Member
2002-08-21 1:20 am
Belgium
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,;)
 
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