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OPT Not Always the Case

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In Reply to: RE: DIY 300b SET 10 Watt AMP posted by Eli Duttman on October 06, 2007 at 15:03:18

Though I 100% agree that the quality of the output transformer is paramount (in SET design), do not get sucked into the belief that only good transformers come from western known manufactuers.

In a recent post of mine, I tested the $800 Plitron output transformer 3.5K for SET design against a rare chinese Zuoshi brand OPT. To my surprise the Plitron was NOT EVEN CLOSE to the quality sound of the Zuoshi. I'll give some credit to the Plitron that the sound may be suitable for many, to my ears, the sound was very analytical - removed all the sonic character of the 300B.

The Zuoshi was exotic alone. Weighing over 6.5kg each, it came potted in a (mu-metal? like square case) with OIL filled inside. 3.3Kohm primary. I won't mention prices on the Zuoshi but let's say that i'm sick of hearing people say China made stuff is rotten. The fact is the more you pay doesn't mean anything on the sound quality you like!

Why the poor performance or sound of the Plitron? I have 2 reason:

1) Toroidal design itself is not ideal for single ended. The idea of making a cut into the toroidal so it mimmicks an air gap of a conventional EI output transformer is not sonically good. After several decades, EI OPT have been the norm and why toroidal outputs are rarely used? Perhaps in practice it doesn't sound good, though many will find the odd high end makes do very well in marketing. "Mr. Vanderveen"

or

2) The quality of Plitron's output transformer is questionable. Just like certain Chinese made iron is questionable regardless of price.

Follow Ups:

RE: OPT Not Always the Case - dave slagle 05:24:13 10/07/07 (3)
if the cut in a toroid is not "sonically good" how do you explain the use of C-cores which from the cores perspective is the same thing.

dave
- Saturation Point - Super_BQ 12:18:40 10/07/07 (2)
  Does a C-core output transformer give more inductance than an EI core for the given size? In SET design, the output wattage is not high enough to make C-core effective for good sound; that is the operating range is less than a watt which isn't working in the C Core's optimum range. (hence why the thin sound). Of course if you do run the amp at over half it's power rating (ie. disco / PA system where high SPLs are required), then I could see the point with C Cores. Also those with SET amplifiers tend to use high efficiency speakers so anything more than 5 watts is just fudge.
  
  Now if we're talking about C cores in PP applications, then that's a horse of a different colour and off the topic what the original poster asked.
  
  As the usual disclaimer, just my opinioin and many will disagree!
  - RE: Saturation Point - dave slagle 13:05:07 10/07/07 (1)
    Does a C-core output transformer give more inductance than an EI core for the given size?
    
    if the parameters are kept the same then the operation should be the same. (for non-oriented materials, if grain oriented steel is used then i would expect better results from the C-core)
    
    In SET design, the output wattage is not high enough to make C-core effective for good sound; that is the operating range is less than a watt which isn't working in the C Core's optimum range.
    
    what exactly is the C-cores "optimum range"
    
    Now if we're talking about C cores in PP applications, then that's a horse of a different colour and off the topic what the original poster asked.
    
    i fail to see why the type of operation matters.
    
    dave
    - RE: Saturation Point - Super_BQ 20:07:11 10/07/07 (0)
      I will go back to my original post that, if C-Core was so good in SET designed amplifiers, then why don't we see more of it being used? I also don't believe the extra cost to build a C-Core (or Toroidal SET OPT) is the primary reason for their lack of popularity. Do a search online (AA, DiyHiFI, etc.) and you'll find the merits of why EI is still commonly used (even in the most high-end exotic amps). Perhaps we need an explanation of the 'thin' sound from?
      
      For some good reading:
      
      http://www.turneraudio.com.au/output-trans-theory.html

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