Using Transformers to Transform Audio

Hi guys,

I just read this article on TapeOp and got very excited: http://tapeop.com/tutorials/76/transformers/
Unfortunately I'm kind of a newbie and there is not enough technical informations for me in the article.

What I understand is that all I need is to solder two cables to a transformer right?
Is it doable with any transformer (input transformer, ouput transformer...)?

If anyone of you has done it before or gets the idea (technically speaking) I'd be thankful for any kind of information!

Thank you!
G.

In general it is important to drive a transformer from a low source impedance.
(Anyway not higher than the impedance of the winding of the transformer itself.)
Driving a tranformer from a high impedance will cause low frequency losses and extra distortion.
But I am sure that CJ could give you a better lecture about this! 

Thank you Ruud.

I actually plan on using this kind of stuff at a line level from my DAW.

Who is CJ by the way?  ;D

CJ is an other forum member, who knows a lot (if not: everything!) about transformers.

Great! I hope he's going to end up here sometime.

What I understand is that all I need is to solder two cables to a transformer right?
Is it doable with any transformer (input transformer, ouput transformer...)?

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Yes, it is doable with any transformer.  Ideally you want a 1:1 ratio transformer.  In order to learn better how it all works just grab any transformer you have lying around to start with.  Take a cable with your preferred connector on one end, and whack off  the other end and use alligator clips or just tie the leads together and go.  Your only concern is knowing which are the primary leads and which are the secondary leads.  Try it both ways.  You might like it stepping up or stepping down the signal.

I do find it ironic that so many people cite their like of transformers for removing the crispiness and harsh top.  It does make one want to scream "stop recording and mixing with too much top" LoL

Hint:  If you want more of that top dousing effect, strap a resistor on the output side of the transformer - across the line from lead to lead.  The lower the resistor value, usually the better for this purpose.

i wish i knew everything about transformers but the math is too heavy, worst math in all of EE,

we do take apart a few audio  transformers around here, there is a thick coat of black tar and polycrysteleine wax on the ceiling,

transformers have all kinds of non linear characteristics that engineers hate, but audio geeks like, such as frequency roll off, bass compression, roll off caused by many turns of wire that form capacitors, and compression caused by too much current(voltage) going thru the winding's, this is called saturation, when the core can not hold any more magnetic lines of force(flux)

saturation goes up as frequency goes down and also when the audio level goes up, different alloy metals will saturate in their own way, you can see this in what is called a BH loop,

there is also some phase shift going on at the extreme hi and lo freqs, due to leakage capacitance and inductance  at the high end and wire resistance at the low end,

doing some Neve work, here is a plot showing inductance vs level, at two different freqs, the ability of the core to attract flux is called permeabillity, this perm number change as the core gets saturated due to freq and level variations,

for some good books and other info, see the Transformer Meta>

http://www.groupdiy.com/index.php?topic=467

CJ said:

transformers have all kinds of non linear characteristics that engineers hate, but audio geeks like, such as frequency roll off, bass compression, roll off caused by many turns of wire that form capacitors, and compression caused by too much current(voltage) going thru the winding's, this is called saturation, when the core can not hold any more magnetic lines of force(flux)

saturation goes up as frequency goes down and also when the audio level goes up, different alloy metals will saturate in their own way, you can see this in what is called a BH loop,

there is also some phase shift going on at the extreme hi and lo freqs, due to leakage capacitance and inductance  at the high end and wire resistance at the low end,

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Fantastic explanation, CJ.  I'm very drawn to components that impart pleasing harmonic overtones and my personal experience has been that vintage iron (esp the really old stuff)  is more inclined toward this than newer equivalents.  I've never found why that might be though.  Would a richer sounding transformer be that way because of manufacturing technique/looser tolerances, materials, or just age/use?
And, speaking of use, do audio transformers such as we commonly see in recording gear go through any actual change over decades of use?
Thx.

Wow thank you very much to all of you!

I found the transformers cited in the article. I think I might start with them as the marking of the pins is  clearly identified and they are pretty cheap.


I learned about the 600Ω standard reading a great article on SoundOnSound yesterday: http://www.soundonsound.com/sos/jan03/articles/impedanceworkshop.asp#

- Do I wire Primary and Secondary both to 600ohms for line level use?
- By the way how do I know exactly which pin of an XLR connector goes to which pin of the transformer?
- I'm going to put this installation in a metal box, I guess a have to ground both connectors to the chassis right?

Thank you again! It's great to learn.

be careful with those pins, they are very fragile,

old transformers can experience magnetic aging  in the lams which means the perm drops as they get older, maybe the grains start to revert to a more random orientation, which will mean lower inductance,

I will CJ. Before touching anything I need to figure out the wiring between the transformer and XLR's.

they are pretty cheap.

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Nope, not anymore.  Unless you are paying 10 to 15$ ea then they are not cheap.  You could get those and many other transformers like that at those prices at one time, and not so long ago.  75-100$ is not cheap.  I also recall that shortly after that porn article in Tape Op you cited came out there was a big jump in the price of the HS-56/5X (it almost doubled overnight)  Seems like they were still obtainable at around 50$ - still not cheap but better than 100 ea.  Some ebayers were asking 200 per pair at one point. 

Also, those particular transformers are in the high fidelity end of things so you  have less shunting capacitance which results in the loss of high frequency response (top end smoothing)

Top end smoothing is exactly what I am after  ;D

I'm sure they're fashion and overpriced. That say, I don't think $100 is expensive for a amazing tool I'm going to use everyday. I can't see any other audio equipment in this price range I use that often.

The auction I'm targeting is $80 for a pair of HS66 (one of them being used and has a broken pin).

Golgoth said:

Top end smoothing is exactly what I am after  ;D

I'm sure they're fashion and overpriced. That say, I don't think $100 is expensive for a amazing  :'(tool I'm going to use everyday. I can't see any other audio equipment in this price range I use that often.

The auction I'm targeting is $80 for a pair of HS66 (one of them being used and has a broken pin).

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You won't get those HS66s on eBay for $80.  They're popular for Pultecs and you are much better off going for UTC A20s, which many would argue sound better, and they're also around your budget.
Also , lassoharp just told you that you're NOT not to get much top end smoothing with those (nor will you from the UTC for that matter).

I guess my english is not perfect, sorry if I don't get all the subtilities.
I'll check the A20, thanks. Is it a deal if I get the pair of 66s for $80 anyway?

Golgoth said:

I guess my english is not perfect, sorry if I don't get all the subtilities.
I'll check the A20, thanks. Is it a deal if I get the pair of 66s for $80 anyway?

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You won't get them for $80.  I know because I've been watching them all week for a certain project and have planned to bid more than $80.  And there's probably others willing to bid more than me.  To give you an idea, the last HS66 I had I sold on here for $75 (for one).  I like the A20 better and I've seen them go for $40 to $50 frequently on eBay.  As mentioned though, you may want something with more coloration.

Actually the big deal for me at the moment is not about which transformer to choose, I suggest we talk about this later. I first need to get some knowledge I don't have.  ;D

I am posting here to get technical informations because I don't know how to wire these things to XLR connectors. I don't know if it's going to work well at a line level and which impedance to choose. I don't know what to ground either.

All I know for now is:
- I can solder a low value resistor to the outputs to get a top dousing effect.
- Ideally a 1:1 transformer
- Maybe I need to stop recording and mixing with too much top

Just to clarify, I did not open this thread to be told what to buy and at what price. What is cheap or not. This is my business and I don't mean to be rude at all saying that by the way!

Golgoth said:

All I know for now is:
- I can solder a low value resistor to the outputs to get a top dousing effect.

Click to expand...

If you're going to yet your sound that way, why bother using the transformers at all?

Golgoth said:

Just to clarify, I did not open this thread to be told what to buy and at what price. What is cheap or not. This is my business and I don't mean to be rude at all saying that by the way!

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People are trying to help you.  If you're going to snap at them for offering honest help then best of luck to you.

Yes Bowie I know you're trying to help. I just feel like I'm misunderstood about what I am really asking for.

I don't know how to wire these things to XLR connectors. I don't know if it's going to work well at a line level and which impedance to choose. I don't know what to ground either.

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I had suggested using alligator clips for convenience.  That way you can audition numerous transformers before committing to soldering them together in a box with XLRs, etc, in case you find one that you really like better than the others.

For grounding, ground the shield directly to the case/box for the permanent build - pin 1 on the XLR to case.  I usually always go ahead and ground the incoming wire (source to box, then leave the outgoing wire (box to next piece of gear) unsoldered and wait to see if it needs to grounded, since it should already be grounding to case at the input of the following piece of gear.

Pin 2 and 3 on the XLR for each signal lead from the transformer primary and secondary.

As far as phase goes, it may not matter but you can always put a phase flip on one side if it does. 

You can get fancy too and use switches to select impedance taps for repeat coils like the UTCs or Triads.

Maybe I need to stop recording and mixing with too much top

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I didn't mean you personally.  Was just referring to the increasing crispiness of a lot of modern stuff (actually all the way back to the 70s when compared to lots of earlier stuff)