qs about ots for gurus...R.G?

[swt]

hey guys. I know there's some taboo about this, but this one is something intriguing me. We all Know the preference of core saturation in ot in tube amps, That is, it's a kind of distortion we can never get in other way. But as we also know it's caused ( mainly in vintage amps), because of underrated ots. So it's always been a touchy subject to me, when designing an amp, in safety terms, to put it that way. So the question is: if i'm about to wind my own tranny...wouldn't be better to use a bigger core, bigger wires, etc to get the power to handle the specific watts, but use less turns in order to saturate the core??.
Thanks a lot for any reply!!.
( excuse my english!)

[Eric H]

hey guys. I know there's some taboo about this, but this one is something intriguing me. We all Know the preference of core saturation in ot in tube amps, That is, it's a kind of distortion we can never get in other way. But as we also know it's caused ( mainly in vintage amps), because of underrated ots. So it's always been a touchy subject to me, when designing an amp, in safety terms, to put it that way. So the question is: if i'm about to wind my own tranny...wouldn't be better to use a bigger core, bigger wires, etc to get the power to handle the specific watts, but use less turns in order to saturate the core??.

Thanks a lot for any reply!!.
( excuse my english!)

I believe this is one of those over-hyped areas of concern to a lot of beginning builders.
Some of the old amps had under-size OT's, perhaps, but many of the best have adequate transformers -- most old Marshall. Fender Tweed twins, tweed deluxe's, BF Super-Reverb's usually are running on their original 40-50 year old OT' s--hardly under-rated .
Most of the best modern makers use very adequate (even over-rated) iron: Dumble, Matchless, Soldano, Trainwreck,, etc. They do use very well-made OT's.
I think there are better, and safer ways (particularly if you are winding your own) to get the tone you seek.
My opinion.

-Eric

[The Tone God]

We all Know the preference of core saturation in ot in tube amps, That is, it's a kind of distortion we can never get in other way. But as we also know it's caused ( mainly in vintage amps), because of underrated ots. So it's always been a touchy subject to me, when designing an amp, in safety terms, to put it that way.

There actually is not a preference for core saturation per se. If you ever heard large amounts of core saturation you wouldn't like it. In terms of safety as long as the windings are properly rated and the heat levels stay within safe levels then having an undersized core will not pose much of a safety hazard. It'll sound like crap though but YMMV.

Transformers are, and have been for a long time, under rated for safety reasons. When you read about Fender putting 18w tranformers in 22w deluxes it sounds like a big deal but thats only roughly 20% beyond rating which is not that big of a deal so the amount of saturation is little if any. Its kind of sticky and may even be against code to use under rated OTs these days but Fender took advantage of it in the those days.

IMHO the tone is not in the undersized core. Time would better spent focusing on other aspects of the amp to get good tone. As mentioned many amp builders use proper or oversized transformers without loss of old school tone.

So the question is: if i'm about to wind my own tranny...wouldn't be better to use a bigger core, bigger wires, etc to get the power to handle the specific watts, but use less turns in order to saturate the core??.

The wattage that a transformer can put out is not really determend by the windings but the size of the core. If you throw 50 watts into a core rated for 20 watts your only going to get 20 watts and alot of noise.

Don't screw with the number of turns. The number of turn determine the impedence matching abilty of the transformer. This is one of the main functions of the OT.

Andrew

[Paul Perry (Frostwave)]

I'm not an amp designer, builder, or user. But, if you want to make a transformer that is easy to saturate, I believe that what you need is, in effect, less iron, to make the core easier to saturate. One way to do this, is to put an air gap in the core. There used to be a device called a "saturable core reactor", which was used in power control, using this principle (plus control windings)..
Note if you dick around with the number of turns on a given transformer, you will change the load, and bad shit might happen. Not for the fainthearted, but of course at FX levels, go for it!!

[Doug H]

Just to throw another wrench in the works:

Someone over at  ampage has mentioned several times that hammond OTs are underrated by about 50% (according to hammond rep). The hammonds are really intended more for hi-fi's than guitar amps, so they have an extended hi-freq response that some amp builders find harsh. He found that by running them at twice their rated power (perfectly safe according to hammond rep, supposedly) they rolled off the highs and were more suitable for guitars. I don't know, maybe that's supposed to be part of "the sound" too.

I agree with the others on here, I don't think there is anything particularly special about OT saturation, it's just another source of distortion. I believe a lot of this hoo-ha over transformers comes from the idea that the transformer distortion contributes to "the sound" of a dimed plexi, which does not have a particularly high-gain preamp.  I would guess Marshall tried to address this with their master volume stuff, unsuccessfully perhaps, but attempting to get "the sound" out of the preamp at any volume. In any case, most modern high-gain amps seem to work on the same principle, whereas their "signature sound" can be achieved somewhat at different volume levels due to the preamp design and etc.

FWIW, I don't believe you have to be stressing the OT just to get "the sound".  There are other ways of achieving that, depending on preamp/poweramp design, whether it is intended to distort or it's an unintentional side-effect that just so happens to be a "happy accident" (which is where a lot of vintage mojo and mythology comes from, IMO), etc, etc.... And if the OT high-freq response is too strong, a conjunctive filter can do wonders for that IMO. I don't know why some seem to find strapping an RC ckt across the OT primary so distasteful, but whatever...

Doug

[RedHouse]

IMHO, I believe that though the transformer may contribute to the tone, it's a passive contribution, a taking away of sound quality attributes rather than adding to.

I am of the opinion that the tubes, capacitors, and resistors in the signal path have much more of a contribution to the good qualities of the sound in a tube amp than the transformer does.

Hey just for fun, go over to www.18watt.com and take the two transformer listening tests, you can hear 9 different transformers in the same amp for comparison, you may be surprised which one(s) you choose!.

[Doug H]

Hey just for fun, go over to www.18watt.com and take the two transformer listening tests, you can hear 9 different transformers in the same amp for comparison, you may be surprised which one(s) you choose!.

I listened to that a while ago and, maybe it's these computer speakers, but I was completely baffled. To my ears, there wasn't a significant (or even noticeable) difference between any of them except for one and it ended up being a different amp or something.

Doug

[Eric H]

I am of the opinion that the tubes, capacitors, and resistors in the signal path have much more of a contribution to the good qualities of the sound in a tube amp than the transformer does.

.

and the largest contributor will be the speaker  ;-)

-Eric

[The Tone God]

Someone over at  ampage has mentioned several times that hammond OTs are underrated by about 50% (according to hammond rep). The hammonds are really intended more for hi-fi's than guitar amps, so they have an extended hi-freq response that some amp builders find harsh. He found that by running them at twice their rated power (perfectly safe according to hammond rep, supposedly) they rolled off the highs and were more suitable for guitars. I don't know, maybe that's supposed to be part of "the sound" too.

You ain't kidding. Hammond transformers are HIGHLY underrated. Hammond transformers are made in Canada and CSA code requirements are quite strong. My expereince has been this with regards to transformers. Asian transformer are slighly overrated, US transformers are generally on spec sometimes alittle underrated, Canadian transformers very conservatively rated.

I like hammond PTs. Built like tanks. I don't like their OTs for guitar amps. IMHO I find them to hi-fi for guitar and too lo-fi for most stereos. In other amps their good. Hammonds construction has improved since the old days and it shows in their sound changing over the years. Better winding, cores, laminations, etc. have contributed to this.

Just a few thoughts.

Andrew

[R.G.]

There's no taboo. It's just not too commonly needed.

The facts is:
- With common grades of linear transformer iron, transformer saturation distortion is almost pure third harmonic, no higher orders. Third harmonic with no higher harmonics can sound nice, so there is some basis in fact for a preference for saturation. There are some "square loop" materials that give other results, but that's very unusual, and I know of not one instance of them in audio cores.

- saturation is done by putting too big a volt-second input on a transformer primary. You cannot saturate a transformer from the secondary side. saturation happens when the combined volt-seconds on the primary pushed the core magnetic field off the linear region, and the coupling from primary to secondary is compromised because the magnetic field can no longer link them. The secondary shows a soft rounding down of the wave peaks.

- since saturation is a low-frequency effect (more seconds in the volt seconds), it is primarily a low-end issue. In moderation, it gives some reedy character to bass notes. In excess, it gives bass "mud".

- OTs have a strong tone shaping possibility. They have enough parasitic effects to cause distinct audio changes. Hifi transformers have been popular in many cases because they are designed to be linear far outside normal guitar ranges and this lets the audio through relatively un-affected. The worst transformers (IMHO) were the CBS era Fender MBA-specials. The suits at CBS did cost cutting, including cheaper transformers. This meant marginal core stacks and no interleaving. That gave bad saturation and both high and low frequency losses. Transformers can be tone shapers. Hifi transformers are designed NOT to to that, and which sounds good to your ear depends on your ear.

- power rating is a thermal issue. Lots of iron and copper makes for high power. I can guess power rating on 60Hz power tranformers by hefting the tranformer. Hifi audio transformers tend to be about three times the weight for the same power rating as a power transformer. Guitar OTs you almost can't tell, because there's more of an open playground, as witness the CBS era Fenders.

Now to your specific question: big iron, big copper and few turns will not give you core saturation. It will give you a transformer with no low end because there is not enough primary inductance. For saturation, you want small size.

[swt]

This has been really helpful, and instructive. Thanks a lot guys!!. The reason i'm asking, is because i wind my own trannies, but i've been using e155 cores for 50w pp. And most bradns uses E112 Or E 125. So i was just checking if i'm on the right track. Thanks again!. Any other suggestions?