Transformer saturation idea

[raulgrell]

A recent discussion on this forum has shed light on the fact that transformers saturate more with low frequency signals than with high frequency signals. In another unrelated discussion, someone mentioned that a way to make the transformer saturate sooner is to let some DC into it.

What if a signal were to be split, one of the halves passed through a frequency to voltage converter such that a higher frequency signal would add more DC to the transformer. If indeed the saturation of the output transformer makes a strong, pleasing effect on the sound, then this "system" would help achieve a balanced saturation throughout the frequency range. Unfortunately I'm not experienced enough to produce this system... Someone here might!

While transformer have (in my opinion) a pleasing effect on the sound, I am not sure (judging by what people have told me) if it is caused by its saturation. This would be an interesting way to prove/disprove it.

What do you think?

[frank]

Me, I'm still waiting for folks to start dickering around with small output transformers in those circuits.  I think the results might be interesting and a step up from what is already a great start.

As far as output transformers and etc go, I don't know. I'm not holding my breath that emulating (or using an xformer in a 9v circuit) is going to make much of a dramatic difference if at all. One thing I do know is it is much easier just to build a tube amp than it is to attempt to accurately emulate it in SS, esp at 9v.
I will say that the ROG approach works well and sounds good on its own merit. And a lot of what a lot of people consider "tubey" comes down to EQ.

IMO, output transformer distortion is way overrated. Case in point, I'm working on an amp right now. Last night I subbed the smallish output transformer for a bigger one with a higher wattage rating. The sound instantly improved- better bass response, more headroom, a more interesting sounding midrange- etc. The smaller transformer was adding some distortion, but compared to the bigger one it made the overall tone of the amp sound like mush. These are both run-of-the-mill Hammond transformers, nothing special or expensive.

There's a reason that amp builders prefer bigger iron in an output transformer. It's not because they want more distortion- it's usually because they want less. They usually want more headroom and better bass response among other things. IMO, amps are kind of like pedals in that distortion is easy- headroom and EQ are the hard parts. There was nothing 'special' about the OT saturation I was hearing. It was just more distortion from another source and it smeared the frequency response of the amp, not in a good way.

IMO, the "effect of an overdriven output transformer" is a red herring. Yes, there may be all kinds of complex interactions but at the end of the day what does it really add to the mix of everything else going on in an amp? Not much - I-M-O. It may make for an interesting academic discussion to some, but practically speaking I don't think it's ever going to come to much in a pedal circuit.

Am I entering a private zone (I have insomnia too).
Maybee I should go bacK to my solder mask methods.

Saturation is a result of putting too big a voltage x time integral into the primary.

The voltage where a transformer saturates increases linearly with frequency. So to saturate at 1khz, you have to apply ten times the AC voltage that you do at 100hz because each half-cycle is 1/10 th as much time. So saturation is definitely a bass-response phenomena.

If you are feeding a large bass signal in and also a smaller treble signal, the bass signal can push the core to near saturation so the treble peaks push it in, but this happens near the end of a half-wave. If you feed DC voltage to a transformer, time becomes infinite, and the core will saturate - except for any magnetic field path which is air gap. This is why flat lamination cores have smaller inductance but more ability to tolerate DC than toroids - toroids don't have a functioning air gap. It's why matching the DC currents in your tube amp by using matched tubes or biasing individually is a good idea.

It's probably not practical for you to saturate the core at frequencies above 100Hz or so. Too much voltage needed. And you can never get saturation clipping evenly at a range of frequencies - I spent a lot of time trying to figure out how to do that a ways back.

The leakage inductance bump can be reduced by good transformer design, but it's hard to eliminate it with feedback because the leakage inductance is effectively in series with the OT primary and to an extent "hides" the transformer from the output tubes. The original article on the McIntosh transformer/amplifier made a big deal of this.

Using saturation for an audio effect is more difficult and subtle that people think. I hear people talking about the sound of an amp depending on OT saturation. It gives me an inner chuckle.

raulgrell

Chapter 5.3 of the big red book might have hint.

Read about source R and distortion with the different alloys.

What the people describe is almost always something that saturation cannot do. Saturation can be heard OK, but it's not what gets described in any case I've ever heard.

I meant that we hear more of saturation on the forum than we hear it in the speaker.  lol
As said before imagine a small 2,5in. spkr on a hard table.

raulgrell

Chapter 5.3 of the big red book might have hint.

Read about source R and distortion with the different alloys.

the big red book?

You will have to experiment with tiny transformers and power semis.
And read alot.

[raulgrell]

Yeah, those are the discussions I referred to in my original post. I have no time to dedicate myself to this. I'm in exam season, so I really have to focus in school...

It was just a pitch for those who may be interested...

[Mark Hammer]

Now I know that RG Keen had mentioned in past discussions about the properties of the preferred inductors for wahs that the desirable ones would acquire certain easy-saturation properties via becoming magnetized over time.  And I seem to recall that people had experimented with increasing the saturation via placement of magnets right on the inductors.  Is it possible to affect the saturation of small interstage transformers via magnet placement?  That is a totally naive question.  I am a babe in the woods when it comes to transformers.

[raulgrell]

I dunno... I'll ask my physics teacher...

[frank]

Mark, I don't know in what topic/folder of the forum to work anymore on that subject.  I think I will do a "just for kicks" plug-and play experiment with my ROG Prof. Tweed since it is already "ugly style" constructed.  When I will do so, I'll try the magnet trick.  I've tried to make the equivalent circuit of a real transfo in spice but it is a real nightmare. OT is not an easy subject. frequency responce of OT might be more useful then saturation in these ROGs.  Do we put that in the "What to do with ROG effects" folder ?
Salutations.

[frank]

I dunno... I'll ask my physics teacher...

Ouf!  I tough that you were leaving us.  Come back when your exams will be finished!

[DougH]

Yeah, those are the discussions I referred to in my original post. I have no time to dedicate myself to this. I'm in exam season, so I really have to focus in school...

It was just a pitch for those who may be interested...

By all means, don't stop investigating this based on my comments. I was just relating my personal experience and the hunch I've developed from it. I don't like to spend a lot of time on things I feel are a dead end or don't pay off, especially if I'm pretty content with applying other things I've learned that have paid off for me. Life is too short. But I may not be looking at the complete picture, or there may be an angle you are looking at that I haven't considered. Whatever you do, if you find out anything, report  back.

[frank]

Doug, I think I have an amplifier that his OT is saturating.  If it is so, it is a very "constricted" and bad distortion.  Now transformer design is a multifactorial thing and winding you own transfo for stompbox applications would be a sing of total dedication.  Then you'll have to have one of those to go with your mini transfo.

http://www.musictreasures.com/music/categories.asp?dir=Miniature-Instruments&curPage=2

[Mark Hammer]

Mark, I don't know in what topic/folder of the forum to work anymore on that subject.  I think I will do a "just for kicks" plug-and play experiment with my ROG Prof. Tweed since it is already "ugly style" constructed.  When I will do so, I'll try the magnet trick.  I've tried to make the equivalent circuit of a real transfo in spice but it is a real nightmare. OT is not an easy subject. frequency responce of OT might be more useful then saturation in these ROGs.  Do we put that in the "What to do with ROG effects" folder ?
Salutations.

Nah.  Leave it here so that people can use "transformer saturation" as a search term.  There are too many threads with "ROG" in them to make this content easy to find, and it won't be long before the thread you refer to is 3 or 4 pages back from the one people see when they log on, and totally off the radar.

[frank]

OUKI  Mark, see ya and, hell, I have the compassion for that snow nonsense!

[raulgrell]

What properties would the optimal audio output transformer have to display? I have to write a nice chunky 4000 word essay on a topic of my choice, maybe this could be interesting...

[frank]

What properties would the optimal audio output transformer have to display? I have to write a nice chunky 4000 word essay on a topic of my choice, maybe this could be interesting...

Raul,
Did you talk to you physics teacher?
Optimal depends on the application ! :
If you want optimum at large, look at Hi-Fi transfos topics.

I think if you cover the following subjects, and understand them well, you will have an understanding of what will be optimal for what you wanna do.

General description of the devices
What is impedance
Impedance matching
Uses for DC isolation
Magnetic materials used for the core and their properties vs the application
Alloys used, the metallic grains, orientation of the grains in magnetic fields, magnetisation
Frequencies ranges
Tube trans. vs semis trans.
Geometries of cores and windings
Electromagnetics basics
Magnetic flux theory
Inductance (self and mutual)
Resistance
Reactance
Leakage inductance
Winding capacitance
Magnetizing current of the primary
Eddy currents in the core (AC)
Hysteresis (B-H curves) (AC) (DC in time)
Core losses
Power effiency ratios (Primary vs secondary Power)
Reaction to different excitation shapes
Construction of the core
Toroids vs E-I shape core
Shielding
Insulated magnet wire
Isolation of layers of wire
Interleaving of primary and secondary coils
Temperature ratings (losses in the core)
Current (and voltage) ratings
Voltage vs current phase at different points of the coil
Tapping the coils
Transo for class A and B amplifiers
Fequency responce theory (dB vs fr.)
Complex numbers
Laplace transforms for working in the fr, domain
The effect of geometries in coils and cores on output wave
Capacitance of the windings
Magnetic flux in core and core gaps
Testing procedures
Old techniques for selection
The problems of non-linearity (Ex: saturation)
Modern simulation techniques (spice simulations, finite difference analysis of flux in the core)
Noise problems and and orientation of the transfo in the circuit
Input, interstage and output differences in the design of the transfo, draw some similitudes and differances.

Correlations between all these factors: you can put a lot of text there !!

This is what I think are the points on what you can dig.

You can fill 4000 words with that.
And draw a conclusion on what you have found to be optimum (and the relativity of it).
Hope it will help you.
And give me some news.
Frank