I am determining which output transformer to build for a Push-Pull 50 watt amplifier.
Not looking for a what is the best but instead a discussion of the pro's and con's of each option. Take this thread wherever you want as long as it's informative.
- What are the strengths and weaknesses of choosing a good C-Core? EI-core? - How significant is the inductance peak EI-cores have at 50% power? C-cores peak in inductance at 100% power correct?
- M3 or M6 strengths? I notice Hashimoto's C-cores (too expensive for me
) use M6 core for their outputs. If I go Onetics I can choose M3 or M6 cores. Would it be wiser to go for M6 and go to a higher level of winding quality such as level three? Or the added expense of M3 and level 2 quality?
- Do larger output transformers lose anything in quality of sound? I came across a well respected user on this forum claim that the larger output transformers sound like a wet blanket was over them. That smaller outputs such as 10w PP sounded much clearer.
Thanks
Not looking for a what is the best but instead a discussion of the pro's and con's of each option. Take this thread wherever you want as long as it's informative.
- What are the strengths and weaknesses of choosing a good C-Core? EI-core? - How significant is the inductance peak EI-cores have at 50% power? C-cores peak in inductance at 100% power correct?
- M3 or M6 strengths? I notice Hashimoto's C-cores (too expensive for me
) use M6 core for their outputs. If I go Onetics I can choose M3 or M6 cores. Would it be wiser to go for M6 and go to a higher level of winding quality such as level three? Or the added expense of M3 and level 2 quality?- Do larger output transformers lose anything in quality of sound? I came across a well respected user on this forum claim that the larger output transformers sound like a wet blanket was over them. That smaller outputs such as 10w PP sounded much clearer.
Thanks
If you can find C-cores Grain orient silicon steel will be best for an output at my opinionI am determining which output transformer to build for a Push-Pull 50 watt amplifier.
Not looking for a what is the best but instead a discussion of the pro's and con's of each option. Take this thread wherever you want as long as it's informative.
- What are the strengths and weaknesses of choosing a good C-Core? EI-core? - How significant is the inductance peak EI-cores have at 50% power? C-cores peak in inductance at 100% power correct?
- M3 or M6 strengths? I notice Hashimoto's C-cores (too expensive for me
- Do larger output transformers lose anything in quality of sound? I came across a well respected user on this forum claim that the larger output transformers sound like a wet blanket was over them. That smaller outputs such as 10w PP sounded much clearer.
Thanks
Hashimoto uses the same from Ncore..
http://www.tube-amps.net/Technical_Aspects.htm
C-cores yes, for several reasons:
- more efficient than EI, so smaller cores, or (better) less windings and therefore lower DC resistances (copper losses):
- easier to make accurate centertaps, important for PP transformers.
Don't forget to apply a small airgap also in PP transformers.
Ncore is more known as being class d amplifiers by Hypex.
You mean Nicore, who have several qualities in c-cores; HiB is very good and can be had in several lamination thicknesses.
- M3 or M6 strengths? I notice Hashimoto's C-cores (too expensive for me
1) C-core.
2) M6 by today's standard is a junk quality material. Price difference between M6 and higher quality / lower loss M3, HiB is just a few $$$ per kg, it doesn't make any sense to save unless you buy a truckload of cores for a cost-constrained project.
3) I have no adoration to Hashimoto. After disassembling broken Sansui AU-111 transformer (Hashimoto possibly is ex-Sansui transformer unit) I found product of very average quality by all means, nothing special or groundbreaking. It wound straight on cardboard paper coil, no even plastic bobbin.
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Well designed unit should have optimal geometry, neither undersized or oversized. For reference 60W PP C-core unit should weight about ~5.5 kg without cage, 50W slightly less.
Oversized transformer will have excess leakage inductance and stray capacitance, which will affect stability of the amplifier with deep GNFB, cause phase shift at higher frequencies, and as result, higher THD and intermodulation distortions at 10 - 20 KHz.
Pegasus123, Hashimoto C-cores are HiB 0.27 mm. These have 1.1 W/Kg iron loss @1.7T/50Hz.
M3 EI cores are 0.27 mm but higher loss at 1.3 W/Kg @1.7T/50Hz.
M6 EI cores are 0.3 mm with 1.6 W/kg @1.7T/50Hz.
EI cores are only used on smaller transformes. You can make very good transformers with M6 nonetheless.
Pieter T gave you good advice. I only diagree on the fact that you need a gap. A small gap (small in comparison to typical SE) would be only required if you cannot achieve a decent DC balance. The tiny natural gap will be enough to take care of imbalance equal or less than 4-5 mA.
Although Hashimoto originates from Sansui you can't compare that transformer with the top products they make today. Materials are miles better for sure. They still use cardboard instead of plastic bobbin but that can only affects the coil-to-core insulation which is high enough in 99% of cases.
If the winding quality were poor there would be no chance to get 60-70KHz @ -1 dB or better.
M3 EI cores are 0.27 mm but higher loss at 1.3 W/Kg @1.7T/50Hz.
M6 EI cores are 0.3 mm with 1.6 W/kg @1.7T/50Hz.
EI cores are only used on smaller transformes. You can make very good transformers with M6 nonetheless.
Pieter T gave you good advice. I only diagree on the fact that you need a gap. A small gap (small in comparison to typical SE) would be only required if you cannot achieve a decent DC balance. The tiny natural gap will be enough to take care of imbalance equal or less than 4-5 mA.
Although Hashimoto originates from Sansui you can't compare that transformer with the top products they make today. Materials are miles better for sure. They still use cardboard instead of plastic bobbin but that can only affects the coil-to-core insulation which is high enough in 99% of cases.
If the winding quality were poor there would be no chance to get 60-70KHz @ -1 dB or better.
Sowter uses (M6) grain oriented silicon iron core, and isn't for Junk, but sounds really good..
SOWTER U027 PUSH PULL OUTPUT TRANSFORMER KT88 Fixed Bias300B
Your sansui transformer is like my dynaco A-470 in construction, may have 4 primaries and 3 secondaries, Primary dosn't have perfect balance, but sounds good to me ( not the original schematic from Dynaco)
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So if I understand this correctly as long as the transformer is competently designed the wattage rating will not matter? So if I were to build a 50w amplifier with a OPT rated for 100w nothing will be lost fidelity-wise? Or a 10w amplifier with a competently designed 100w OPT?
seek out the postings of Tubelab, he tortures tube amps and opt's
for breakfast....
He's the reason I am asking. I found an old post of Tubelabs where he claimed bigger transformers sound like a wet blanket. Given that it was a 100 watt Hammond I am not sure if that comment could be applied to all transformers regardless of quality.
I would post the link to that comment but I have no idea where I found it on this forum.
I would post the link to that comment but I have no idea where I found it on this forum.
Bigger cores mean less turns, which could mean less capacitance, depends on how it is wound. Typically the bigger winding window will get fully used for a corresponding higher power rating, so that would bring capacitance up. I think I would not go over 2X for the OT over-wattage (for E-I). That will bring the peak (for E-I) permeability up to near the max (1/2) power usage then. For a C core or toroid, probably best to size according to rating.
maybe, but split bobbin will decrease amount of copper you can put there.
not many are using plit bobbins.
each winding turn at bottom will be little shorter, than turns at the top layers.. (+closer to core-magnetic properties of winding)
inductance/parasitic inductance/ differences, of bottom and top layers.
you will not get a symmetric result.
Sowter uses split bobbin for perfect balance on PP
Lenard audio has a good article for output transformers specially for PP
Valve Amps: Output transformers
He describe simple bobbin, split bobbin and pi winding, the third I think needs a lot of work but may results are very good and worth to try
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