Impact of OT materials/construction on performance

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Leonc, Feb 1, 2012.

  1. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Anyone with experience care to share their "research" or anecdotal findings on the impact of OT size and construction on an amp's performance?

    E.g., given two transformers with the same primary and secondary impedance, what factors would make one sound bigger or smaller or cleaner or dirtier than the other? Would it be the size of the core? The gauge of the windings? The composition of these parts? All of the above? Etc.....

    The reason I ask is that I'm considering building a Martin 112/Dearmond R15 type amp which is very close to a 5E3, circuit-wise. Yet anecdotal info indicates that these amps use an OT that's physically notably larger than those you typically see in 5E3s. Is it correct that all other things held equal, an OT with 6.6K primary would result in a bit more clean headroom than one with an 8K primary?

    Or perhaps this biz with the OTs is less of a factor than I'm giving it credit for and it's just the other circuit design differences that account for the different performance... Actually, I'm sure that all the differences between the 5E3 and these Martin/Dearmond amps contribute...just trying to see what more knowledgeable/experienced amp builders/designers thoughts are on the relative effects and importance of OT size/construction...

    :huh
     
    Last edited: Feb 1, 2012
  2. diagrammatiks

    diagrammatiks Member

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    well the primary load difference will definitely effect the amp.

    but that has nothing to do with the quality of the OT which is another question entirely.
     
  3. phsyconoodler

    phsyconoodler Member

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    All of what you said rings true.It does indeed make a difference.The Deluxe Reverb uses a 6.6k primary OT and it does help a bit with headroom with a pair of 6v6's.It also distributes load better so you can add an extension speaker with no ill effects.
    A 6.6k load doesn't care if it's seeing a 4,8 or 16 ohm load whereas an 8k likes to be closer to the load line.
    I find in my builds the sweetest sound comes from using a 6.6k load with a pair of 6L6's especially.
    there are lots of other factors too,like whats in-between the windings,paper or plastic,how it's wound,either uniformly or scatter-wound,the type and thickness of the wire,etc.etc...
     
  4. neteraser

    neteraser Member

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    Don't ask. Wind your own at least once in a life. You will understand many things about amplifiers.
     
  5. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    neteraser...I'm sure you're right and that would be a cool project someday...

    In the meantime, how do number of windings correlate to impedance? I would assume that more windings usually = more wire = higher impedance...true?
     
  6. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Let me put that question another way. Suppose you have two OTs, each with 6.6K primary and 8 ohm secondary and each constructed with paper and uniformly wound. One is notably larger than the other, perhaps due to different core size. What, if any, differences might you expect in the performance of the amp with each of the two OTs?
     
  7. neteraser

    neteraser Member

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    I don't know. I doubt it's a good idea to just talk about things like "a bigger iron". Bigger iron = different design. I'd have to find a point of compromise once again. If you don't, both transformers with smaller and bigger iron won't have a sound. Then, there's no point in comparing them since they don't satisfy to begin with!
    :) LOL
    Sorry, I'm just a beginner. It's possible to design two transformers with very similar ideas but a different iron size. But I yet have to do that.
     
  8. phsyconoodler

    phsyconoodler Member

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    Try it and see.No one is going to be able to quantify that for you without having all those specifications and a scope to find out what the actual differences really are.
    A transformer winder like Heyboer of Mercury Magnetics can tell you what you want to know.
    you need to do some homework on transformers.This has been talked about many times in the past.Sometimes it takes trial and error to come up with nice tone,it's not always "use this tranny and it will be the holy grail".
    There are lots of variables which you touched upon in your original message.
    One persons silk scarf is another's sows ear.
    It's like popping a big ass OT on a Deluxe Reverb.Sure it's fatter sounding and may have more poop but it loses some of the subtle harmonics and chime.
    It's always a trade-off one way or other.Good here,not so good there.
    e.g. I built a Tweed Deluxe using reclaimed iron that was huge compared to the stock iron.It sounded huge and broke up much later that the stock one's did.But it had less subtle undertones and the driven sound was stiffer and less complex.It kicked ass for country but was lacking a bit for blues.
    It really depends on what you want to hear and how and what you play.
     
  9. neteraser

    neteraser Member

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    Yeah... and also I have to say... you have to see which size of iron to use while you design an amp. It easy like this "oh, here I need, say, EI96, it'd fit really well!" So there should be literaly no such thing like "bigger" or "smaller" iron. Sorry, just switching to a bigger iron may be a stupid idea. There should always be a deeper concept to a sound. A spirit, a soul... I dunno! And you don't know what effort is needed to hand-wind a transformer... If you say did a mistake and you finally see you really needed EI90 there, I'd simply give up and start a different build.
     
    Last edited: Feb 1, 2012
  10. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    psychonoodler - Yes, I do get it--there's a great deal of subjectivity involved. But in your post, you're alluding to some of the things I am trying to get at. E.g., it's implied in your post that the larger transformer--while speced to work in a 5E3 circuit--increased the volume at which the amp broke up and its overdriven sound was stiffer and less complex than with the smaller OT...if that kind of result it generalizable, then that's exactly the kind of info that I was looking for.

    But I do totally get your point about a lot of what's right or wrong sounding being in the ear of the beholder. I'm sure that experimentation is a good idea...but given my desire to limit the cost in dollars and time, the more info I can gather going into my experiment, the better. Thanks, as always, for your input, it's greatly appreciated.
     
  11. donnyjaguar

    donnyjaguar Member

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    In my experience the weight of the transformer is a good indication of how well it'll work. Larger cores have greater magnetic permeability and hence better performance at lower frequencies.
     
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  12. phsyconoodler

    phsyconoodler Member

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    Trouble is when you limit time and cost the results are usually unremarkable.
    Spend some more time researching and a few more dollars and get a remarkable result.
     
  13. donnyjaguar

    donnyjaguar Member

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    I've also found in my hi-fi builds that larger transformers have less "sparkle" at the treble frequencies. Probably not a big issue but I'm told by a 12 string player the extreme treble end is missing from most amp's.
     
  14. guitarcapo

    guitarcapo Senior Member

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    There's also the durability issue of a larger OT. I've heard the analogy of an output transformer being
    like a car transmission. Turns ratios being like gear ratios.....the object being transferring power etc....
    Not to belabor that, but I can imagine an overly built transformer being sluggish due to inertia at a certain point.
     
  15. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Yeah. If I look at the amps I tend to enjoy the most...thy tend to have smaller OTs, actually (e.g., Vibrolux Reverbs, brown Deluxe, Magnatone 213). It seems that I like the way these amps open up when you push them. I'm sure the "smallish" OTs have something to do with it. There are plenty of exceptions...I've loved the Ampeg VT-40s I've owned and some of the bigger Fenders and JTM45 type amps as well as a few Dumbles I've gotten to play through. But these amps are all too loud.

    I think what I may wind up doing is buying one of Dave Allen's large-core, Deluxe type OTs (believe Heyboer makes them) and probably and also buy something closer to 5E3 type OT, but with multiple taps, then just try them both and see what works best for my tastes...
     
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  16. diagrammatiks

    diagrammatiks Member

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    what.
     
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  17. Tone_Terrific

    Tone_Terrific Member

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    But the sparkle may be distortion, like an exciter maybe (?), not as accurate but perceived as better.
     
  18. guitarcapo

    guitarcapo Senior Member

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    Not giving up the high end . Sluggish like a heavy transmission like a truck transmission on a sports car sort of idea.
    It's an analogy. Sorry if it's confusing.
     
  19. barfoden

    barfoden Member

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    Yes It would be great to know the primary impedance of that large OT in the DeArmond R15 amp..
    I have seen a picture of it and it is much larger than a fender deluxe OT..

    Someone mentioned that the 8K impedance lends itself well to a pair of 6v6gt tubes with ~ 350V in cathode bias..If you go fixed bias the 6.6K is a little more suitable and will give you more power,,
    The old 6v6gt datasheet only shows a pair of tube in grid bias with 285V on the plate and screens with a 8K primary impedance and an output of 14 watt..
    Somebody posted on a thread that he actually got a little less clean power out of a 5e3 (360V/320V screen) when he used a 6.6k OT instead of the 8K OT.
     
  20. mark norwine

    mark norwine Member

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    easy to calculate, if you have one....
     

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