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Tuesday, December 22, 2015

Output Transformer Design

Output transformer design (输出变压器设计和调音) is an art. There is no right or wrong when you have reached a certain level of competencies in the design world. 

Below is an example of how we tune our Level 3 Nanocrystalline Output Transformer for 300B PSE use. Take a look at these 2 output transformers. Both are designed for primary 1.5K, air gapped to 160mA. 

You can see that with different winding methods, the results are quite different. Which one is better, which one is worse? Take a guess!

300B PSE output transformer 1:
  • 20 Hz (-0.25dB) – 1kHz (0dB) – 20kHz (-0.43dB) at 8 Ohm at 1W
  • Full spectrum: 10Hz (-0.6dB) – 1kHz (0dB) – 68kHz (-3dB)
  • Primary DCR: 49.5Ω (50Ω) (B-P,9℃)
  • Primary inductance: 12H (11.9H) (DC bias at 180mA,20Hz,5Vrms)
FFT results
300B PSE output transformer 2:
  • 20Hz (-0.49dB) – 1 kHz (0dB) – 20kHz (-0.1dB) at 8 Oh, 1 W
  • Full spectrum: 10Hz (-1.2dB) – 1 kHz (0dB) – 100 kHz (-1dB)
  • Primary DCR: 22.7(22.3)Ω(B-P,12℃)
  • Primary inductance: 6.6H(6.5H)(DC bias at 180mA,20Hz,5Vrms) 
FFT results

There is no winner here actually. Both are excellent. What matters are how it is used, and what it is used for - the application matters. I have highlighted in BOLD, the main differences. At a glance, output transformer 2 seems to be better, right? Well, there is more than meets the eye. 

In layman terms, output transformer 1 is better for more difficult loads and will be better in controlling the speakers. Output transformer 2 has lower distortion and has wider bandwidth but is not as good as one on difficult loads.


For general loudspeakers, output transformer 1 will be a better choice. It has higher primary inductance and therefore will present a better load at low frequency for better low frequency response and control. For those with very efficient speakers like Lowthers, Fostex and horns, output transformer 2 will yield better results and lower distortions. These types of speakers do not need that much primary inductance and will benefit from the lower distortion and higher extensions. 

Still, it is not a rigid rule. It's up to each individual's taste. If one wants more control, body and tonality, they can still go for output transformer 1. Output transformer 2 will sound livelier and airy but will not be as thick and authoritative compared to output transformer 1.

For those that asks us to design for them, we will choose the design for them if they do not specify clearly.

Wish our readers and customers a very merry Christmas and a wonderful New Year!

J&K Audio Design
12/23/2015

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Level 3: depends on type, size and complexity. Email us for details.

Iso-trans: link 1, link 2

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* Finished amplifiers, DACs, audio gadgets, upgrades and repairs - this is not our core business and we do it out of passion. We do not have fixed models, fixed price and we customize for each individuals. The sky is limit of creativity.

* Our product lines are always improving and increasing. If you do not see what you want, contact us!

* Please email for volume discounts, distributor and OEM pricing.

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