In my experience overspecifying the core size too much is not good because stray capacitances get higher.
Moreover the best core section is the square one (or a close one), especially when using E+I types, because this gives lower leakage inductance in comparison to a core with the same section area but different shape.
If you use silverwire i agree but almost any transformer for a 300B with copperwire should cost no more then $200-300 each (including amorphous core). I make transformers for over 20 years so i know it's possible.....
I do not agree. The core alone doesn't turn a bad transformer into a high quality transformer. Most of the quality comes from the windings, geometry and optimization and you can have high quality EI as well. The common grade is M6 with 0.3-0.35 mm lamination but you can also find rather easily M4 0.2mm thickness and this is more then enough for OPT's used with speakers.
Higher quality with 0.1 mm lamination also exists as well as nickel cores with the same thickness....
A square core section (or a close one) still gives advantages with C cores. The further you move away from a square section the worse is for leakage inductance. C cores are only less affected by this but the issue is not eliminated.
I just say that the (HiB) c-core deliver the best options. For example if you have a very good EI transformer and you replace the core for a c-core it will be even a better transformer, and that is a fact.
btw, a good c-core is made of M0 material (that is what is use)
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It is a fact but what is its relevance?
Compare an old Tango U-808 and a XE-20S and you will see that the REAL measurements and listening tell a different story from you find in the datasheet.
In this case (headphone amp) best cores for low signal level are nickel first and amorphous second. You can easily find nickel in EI laminations and it is surely better the C HiB core.
Pieter Treurniet's reply:
First of all you have to distinguish what "low level", "mid level" and "high level" is.
My suggestion:
low level: moving coil cartridge and microphone signals;
medium level: all kinds of line level signals, i.e. output signals of source equipment;
high level: signals from driver and output tubes anodes (interstage and output transformers).
For low level signals I prefer nanocrystalline toroidal cores; because of the very thin lamination these have the lowest core losses (better than 0.1 mm permalloy (80% nickel) and very high permeability (on par with the best permalloy).
For medium level applications I would prefer a good quality permalloy (80% nickel), amorphous or even better the socalled Finemet cores. Finemet c-cores are nanocrystalline and combine the qualities of nickel (high permeability) with amorphous (low losses - low eddy currents).
For high level duty finemet or amorphous for interstage transformers, and for output transformers finemet, amorphous or HiB silicon steel c-cores. Forget EI.
In the case of SE interstage and output transformers much of the initial permeability of the various materials goes down because of the airgap; nonetheless my customers hear the better quality of the low loss materials which is what finally counts.
Just my personal opinion, based on working with these materials over the last 15 years or so.
Pieter
Tribute Audio Transformers
Well that's a good direction for a spud amp using a 6c45pi or high gm triode connected pentode, but this is a small nickle parafeed OPT and not a high power amp. Its a great way to go if you want a high quality headphone amp for sensitive phones but its not going to power the planars with authority.
I haven't found any transformer winder willing to quote a custom secondary single feed nickel core for power DHT's there's just too much permeability.
For singlefeed power DHT's like the 300B I think the C HiB core is going to be the best option?
Can you be more detailed on this? I do not understant the connection between single feed (single secondary?) and permeability.
I think amorphous is better for an headphone amp. At low level (i.e. most of the time) it performs better.
Bas, now you are mr Treurniet personal assistant, can you ask Pieter if these high perm. materials are really available (for example a 300b transformer) and if so will it cost 1-2 times as much or 10 times or more?
Hi Regal,Ale, I could ship you one NOS VT-225 if you want to trace it and share the model and send her back. It would be interesting to compare to a Sovtek 300B
As you know, I'm more than happy to trace and develop a SPICE model. I suppose you're in the US? Would be great if someone UK based makes same offer as shipping costs will be lower...
Anyone?
Cheers,
Ale
I completely agree with what Bas/Pieter is saying, we want a high perm (amorphous), low loss "series" Feed ~60 mA C-core with 5k primary and 4 x 8 ohm secondary's.
To me this is a very exciting to have somewhat of a "spec" for the DHT headphone amplifiers. A quality transformer for headphones has been a long time coming.
But we need to somehow keep costs and the commercial side of a this out of this thread . I'm pretty sure we don't want to be discussing pricing here.
I am reaching out to the mods to give direction on the best way to proceed , possibly Bas open a thread under group buy? Or we can just email for pricing separately (but it would be nice to somehow get a volume price break.)
Two weeks ago I had a pair but I sold it to MerlinElMago. If you can wait until June I have another pair in Italy.
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You can also believe that donkeys fly, it doesn't make any difference to me. You spend your money....
Two weeks ago I had a pair but I sold it to MerlinElMago. If you can wait until June I have another pair in Italy.
Moglia I see vega65 offered 307a, also I have a couple of 307a at your disposal.