Hi,
I wasn't able to find out why an OPT should not be too big. Is there maybe no reason as long as ridiculous dimensions are not close yet?
Thank you!
I wasn't able to find out why an OPT should not be too big. Is there maybe no reason as long as ridiculous dimensions are not close yet?
Thank you!
As I (vaguely) understand it, a bigger transformer for lower bass will give less treble. All other things being equal.
Mainly price, weight and size.
A bigger core, which we can translate to higher core surface area, gives advantage to better overall parameters.
-Less turns are required. This reduces leakage inductance by a square factor, also ohmic losses go down, permits different interleaving that will reduce overall capacitance if done right.
-Bigger core increases mean turn length, which increases leakage inductance, capacitance and ohmic losses in a linear way.
Example - 4 times the surface area results in only 2 times MLT increase. Which translates to 4 times lesser turns needed, 16 times leakage inductance reduction, 2 times ohmic losses reduction (cancels with MLT), 2 times lesser capacitance (cancels with MLT).
So a bigger core is always better, but price jumps enormously with exotic core materials, like amorphous or nanocrystalline. My nanocrystalline 300B SE transformers which Ale Moglia uses have a small 9cm2 nanocrystalline core, but 4000 primary turns. Some sectioning tricks and hybrid air dielectric materials are used to keep parasitics down as possible.
A bigger core, which we can translate to higher core surface area, gives advantage to better overall parameters.
-Less turns are required. This reduces leakage inductance by a square factor, also ohmic losses go down, permits different interleaving that will reduce overall capacitance if done right.
-Bigger core increases mean turn length, which increases leakage inductance, capacitance and ohmic losses in a linear way.
Example - 4 times the surface area results in only 2 times MLT increase. Which translates to 4 times lesser turns needed, 16 times leakage inductance reduction, 2 times ohmic losses reduction (cancels with MLT), 2 times lesser capacitance (cancels with MLT).
So a bigger core is always better, but price jumps enormously with exotic core materials, like amorphous or nanocrystalline. My nanocrystalline 300B SE transformers which Ale Moglia uses have a small 9cm2 nanocrystalline core, but 4000 primary turns. Some sectioning tricks and hybrid air dielectric materials are used to keep parasitics down as possible.
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Primary inductance determines the LF limit of an OPT when the transformer is driven by a source with a series resistance, like a tube's plate resistance. Get a transformer with the required winding impedances and sized to handle the required power, maybe a tad more. Going bigger gets you nothing but added expense, weight and parasitics.
In pro audio up to line level, big cores (around 50-100% bigger) more often than not don't sound as good as small ones. Main reason is slight saturation from smaller cores sounding a bit more euphonic, beside other advantages already mentioned here.
Big cores come handy for push pull which is rarely used for so small levels, and in occasions when one wants certain sound they give in cap coupled designs (better bass, "wider sound", etc).
Big Ni or Ni/Fe cores with winding for push pull cost around 50-100% more than smaller transformers for cap coupled circuits. I'm not sure why i haven't seen bigger Fe cores than needed, probably because of advantages Ni offers in bigger cores.
Big cores come handy for push pull which is rarely used for so small levels, and in occasions when one wants certain sound they give in cap coupled designs (better bass, "wider sound", etc).
Big Ni or Ni/Fe cores with winding for push pull cost around 50-100% more than smaller transformers for cap coupled circuits. I'm not sure why i haven't seen bigger Fe cores than needed, probably because of advantages Ni offers in bigger cores.
I doubt there is any measurable difference for the likes of a common PP output transformer. OP what is the amp circuit and operation you are considering (eg. class A PP) ?
It is the balance of leakage inductances and capacitances that determine the high frequency response, not the magnitude of just capacitances.
A higher power amp with a large OPT will operate fine at very low signal level - magnetising current level differences are not a concern if the amp uses feedback.
It is the balance of leakage inductances and capacitances that determine the high frequency response, not the magnitude of just capacitances.
A higher power amp with a large OPT will operate fine at very low signal level - magnetising current level differences are not a concern if the amp uses feedback.
Transformer winding and transformer design in general is about compromise.... bigger core, less turns to put on and better LF response but costs more and weighs more. Same goes for other parameters, designing and winding a tfmr is analogous to juggling, you're happy juggling away with three oranges, then someone throws you a running chainsaw.
Andy.
Andy.
There are "Moving Companies" in most countries.
Small Cranes are available for rent.
Mono Blocks are suggested, especially if the moving company is not Bonded and Insured.
Small Cranes are available for rent.
Mono Blocks are suggested, especially if the moving company is not Bonded and Insured.
Ironic because in musical instrument amps they tend to use smaller cheaper transformers.
And have seen a lot of excuses for using such small cheap transformer.
Funny to be on the other side of the story.
Usually High frequency bandwith not a concern.
Bigger the better for most, but operating a lot of speakers was more impressive.
Like high current 2 ohm taps.
I tried to get Hammond to do a custom high current transformer with 2 ohm tap.
They dont want to do it because it lowers the high frequency bandwidth. And
are more proud of sound quality reputation.
And have seen a lot of excuses for using such small cheap transformer.
Funny to be on the other side of the story.
Usually High frequency bandwith not a concern.
Bigger the better for most, but operating a lot of speakers was more impressive.
Like high current 2 ohm taps.
I tried to get Hammond to do a custom high current transformer with 2 ohm tap.
They dont want to do it because it lowers the high frequency bandwidth. And
are more proud of sound quality reputation.
I have some early Electra-Print output transformers that Jack Elliano designed.
(Two 3k single ended, and two 5k single ended).
They had 4 identical secondary windings.
You could wire the 4 secondaries to get 1 Ohm, 4 Ohm, 9 Ohm, and 16 Ohm.
Good for 60mA DC primary current.
Very Nice!
(Two 3k single ended, and two 5k single ended).
They had 4 identical secondary windings.
You could wire the 4 secondaries to get 1 Ohm, 4 Ohm, 9 Ohm, and 16 Ohm.
Good for 60mA DC primary current.
Very Nice!
Because the amp is a part of the instrument. Cleaner / flatter does not mean better. The non linear character is the main part of the amp design, and I don't think it's different when we talk about domestic audio tube amps. Adequate amount of low frequency distortion from output transformer is not a bad thing, I guess.
Guitar amps only REQUIRE 80 Hz response. And turning up its bottom octave usually results in undesirable sound anyway. Running an electric guitar through a flat amplifier and speaker results in too much low end. Bass amps are usually cleaner, have feedback and bigger transformers. 40 Hz response is desirable there, but not always done either (for weight reasons). The SPEAKERS usually don’t make it down flat to 40 - useable to 40 yes, but not flat. Requires too big a box. Usually muso’s go high end super high power solid state with the 5 and 6 string rigs that go deeper. They may resort to using DSP to get the low end EQ out of a speaker small enough for the road crew to move (also requires lots of watts).
