Transformer balanced output?

[gtrmac]

I built an FET preamp based on New York Dave's Guitar Booster and I want to add a transformer balanced output.

Any suggestions for this are welcome. I looked over the notes on the Jensen website but I would like to avoid adding Opamps or IC's so that I can stick with a single voltage power supply. I want to use a wall wart to power it and it would be simplest to use a single voltage supply.

I have a buffer stage which can be used to go to the transformer if needed.

Thanks for all suggestions.

 

[pstamler]

What kind of loads will you be driving? If it's a standard 10k load (most soundcards, multitrack recorders, etc.), then a 1:1 Jensen transformer designed for 10k loads will work fine; use a coupling cap, of course, between the circuit and the transformer.

If you need to drive 600-ohm loads then you're talking a whole nother ball of fish. These days 600-ohm loads mostly show up as the inputs of vintage compressors (LA2, 1176, etc.) and their clones.

Peace,
Paul

 

[gtrmac]

Thanks for the info. I don't see a 10k:10k transformer on the Jensen website though so I guess I'll look elsewhere.

 

[babyhead]

http://www.jensen-transformers.com/ln_in.html

They also have a good applications page...

http://www.jensen-transformers.com/apps_sc.html

Enjoy.

 

[Samuel Groner]

You don't need a line in, you need a 1:1 line out transformer. Forget about impedance (a 600:600 works well as a 10k:10k for your application). There's about a dozend different types on the Jensen site--the JT-11-BMCF is a common choice for highest quality, but likely overkill regarding level and distortion for your application.

I would like to avoid adding opamps so that I can stick with a single voltage power supply.

What makes you think that you need dual rails with opamps? About any audio opamp is easily used with single supplies by adding a few passive components to the standard circuitry.

Samuel

 

[Svart]

edcor?

 

[gtrmac]

[quote author="Samuel Groner"]You don't need a line in, you need a 1:1 line out transformer. Forget about impedance (a 600:600 works well as a 10k:10k for your application). There's about a dozend different types on the Jensen site--the JT-11-BMCF is a common choice for highest quality, but likely overkill regarding level and distortion for your application.

I would like to avoid adding opamps so that I can stick with a single voltage power supply.

What makes you think that you need dual rails with opamps? About any audio opamp is easily used with single supplies by adding a few passive components to the standard circuitry.

Samuel[/quote]

Thanks for the information. I am currently using an SSM2142 to balance the output and this requires +/-15volts, sorry for the confusion there. I'd like to use an external wall-wart to power the unit and it seems simpler to get them with one output voltage.

 

[capnspoony]

Hi ..

Ive posted a similar post to this one and I don't have any advice on the topic but .. I was hoping someone could walk me through the steps of determining what kind of transformer works for what.

how do you choose 600:600 or 10:10K?

how do you know to use 1:1 line or 2:1 like in the pultec for output trafos?

I'm trying to figure out what would be good for this eq

http://www.ethanwiner.com/spect-3.jpg

any light on this situation would be great

thanks :thumb:

 

[bobkatz]

[quote author="capnspoony"]Hi ..

Ive posted a similar post to this one and I don't have any advice on the topic but .. I was hoping someone could walk me through the steps of determining what kind of transformer works for what.

how do you choose 600:600 or 10:10K?


[/quote]

It's really the turns ratio that counts, but a transformer that's designed to be a 10K:10K probably is not going to be ideal. The 600:600 transformer will reflect the source impedance of your circuit and deliver a low output impedance, depending on the buildout resistor in your circuit. You should drive a square wave through the system and see how it comes out, and perhaps load the transformer if you get overshoots.

Use a 1:1 transformer for lowest output impedance, don't use a 1:2 unless you absolutely need some "free gain".

 

[capnspoony]

what does 600:600 exactly mean .. I have seen 150:600 and other combinations ..

does a 600:600 mean 1:1?

I know that I want to minimize my output impedence and have a higher input impedence is that correct?

what would i choose for this circuit?
http://www.ethanwiner.com/spect-3.jpg

 

[CJ]

A 600:600 is 1:1.

A 10K:10K is 1:1.

The 10K:10K should have more henries, to get that 10K at 1 K-CPS.

2pi F L , 2pi F is a constant for our purposes, so the L will control the reactance>impedance.

A 10K:10K will chew up less signal if coming from a higher impedance source.

 

[capnspoony]

can anyone tell me what i should use to balance

http://www.ethanwiner.com/spect-3.jpg

thanks!

 

[Svart]

10k:10k from the opamps or 10k:600.

try edcor transformers. very cheap, very good. Perfect for this. not a "color" transformer though, too clean for most people.

 

[capnspoony]

hi guys .. thanks for the reply ..

how do you choose the 10k 10k ?

what would you choose if you wanted to add more low end to the circuit?

money isn't a problem

im just starting out in electronics .. just graduated with a standard physics degree but never got a chance to get into electronics and im addicted already

 

[PRR]

> what does 600:600 exactly mean

It will have low loss with 600 ohm load, but its input impedance will drop below 600 ohms below the bottom of the audio band.

A 10K:10K will have low loss for 10K load, high loss for 600 ohm load, but its input impedance below the audio band will be dropping from 10K ohms, so should be higher than the 600 ohm winding.

> what would i choose for this circuit? http://www.ethanwiner.com/spect-3.jpg

The output chip is a TL074. The' TL07x series can NOT drive 600 ohms well, strain to drive 2K acceptably, should probably be loaded with 5K or more.

If you used a 600:600, and assuming that the transformer designer figured the "bottom of the audio band" was 20Hz, then the transformer looks like 600 ohms at 20Hz, 1.2K at 40Hz, 2.4K at 80Hz, 5K at 160Hz. Even though you load the secondary with 10K or 22K loads (modern studio loads), the TL07x will strain in the bass.

So you must use a 10K:10K.

Interestingly, he shows a NE5534 as a high impedance input. The 5534's low noise and high drive are wasted here. If you swap it with one section of the TL074, so the 5534 faces the transformer, you could drive 600 ohm windings and loads fine.

 

[capnspoony]

prr thank you for your help!

I'm starting to get the idea of these trafos

I'm a bit confused by

< then the transformer looks like 600 ohms at 20Hz, 1.2K at 40Hz, 2.4K at 80Hz, 5K at 160Hz. Even though you load the secondary with 10K or 22K loads (modern studio loads), the TL07x will strain in the bass. >

so I can use a 10K:10k for the output and swap the 5534 chip with a 600:600 for the input stage?

thanks again .. sorry for being so newbie

 

[gtrmac]

EDCOR looks like the way to go. I will order a couple of the 10k/10k trannies and try it out.

Can I just wire them into the output with the primary single ended and the secondary balanced and will I only need a coupling cap to block DC?

I'm confused by the Jensen diagrams with the active circuitry. Is all that stuff necessary? What's the advantage of those circuits?

 

[Sleeper]

PRR wrote

The output chip is a TL074. The' TL07x series can NOT drive 600 ohms well, strain to drive 2K acceptably, should probably be loaded with 5K or more.

all the electronics is necessary to OPTIMALLY drive the transformer.
Optimally means low noise, low distortion, flat across the signal range.
PRR wrote

If you used a 600:600, and assuming that the transformer designer figured the "bottom of the audio band" was 20Hz, then the transformer looks like 600 ohms at 20Hz, 1.2K at 40Hz, 2.4K at 80Hz, 5K at 160Hz. Even though you load the secondary with 10K or 22K loads (modern studio loads), the TL07x will strain in the bass

PRR- this is the best explanation I've read about how this works, I've been looking at transformer datasheets and hooking stuff up wrong just to see what happens, using my ears, etc. but you just nailed it. Now I completely get it.
Thanks
Kelly

 

[maxime]

hello,
admirable answer!
as a newbie I understood something ...
I have a question to ask, still. I wish to use 1/1 S.E.T. output transformers I got from a spare sony mxp2000 console master strip (designed in the eighties). this strip has 6 of them.
these transformers follow some hybrid drive stages, and are terminated by a 100 Resistor and 3900pF cap, will those be ok for the outputs AND inputs of a 1176?
would a 20 hz square wave test with the rated impedances be sufficient to determine this?
thank you
maxime