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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old 17th June 2018, 02:53 PM   #4781
huggygood is offline huggygood  France
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mine have basically EI and C core.
I tried with a toroid and I was not convinced
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Old 17th June 2018, 08:18 PM   #4782
john_ellis is offline john_ellis  United Kingdom
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A bit off-topic but I much prefer EI cores to toroids. As mentioned earlier in this thread twin bobbin construction really minimises inter-winding capacitance. HOwever, I suspect many toriods are designed to run near flat out, taking advantage of the high mag field they can work at, but which might mean they might "clip" magnetic saturation with slight over voltage, etc.

In a prototype 100W amp I specified a low mag (70% normal) toroidal design to evaluate, and it runs cool and seems to be fine. Not detected problems from hitting saturation (excess hum) or noise, yet but still under development.

General statements like this however really shows the need for investigation.

Maybe diy-audio followers can measure the performance of the transformers and report?
- a different thread I think.
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Old 17th June 2018, 08:56 PM   #4783
huggygood is offline huggygood  France
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for me,the best price/quality/efficience
TTSA0200 - Transformer AUDIO TSA200VA - voltage to 50V - Shop Toroidy.pl
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Old 18th June 2018, 11:22 AM   #4784
nigel pearson is offline nigel pearson  United Kingdom
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JLH noticed very fast transistors did not suit the design. I think this is easy to understand. Medium speed transistors keep the design more stable without adding capacitors.
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Old 18th June 2018, 11:29 AM   #4785
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by nigel pearson View Post
JLH noticed very fast transistors did not suit the design. I think this is easy to understand. Medium speed transistors keep the design more stable without adding capacitors.
A good example was the 1980's Maplin 225WRMS amp with 2n3055/mj2955.s.
I recently bought one in with missing transistors.
So I bought in new 2n3055 and the amplifier started oscillating.
I had to increase VAS capacitor to stop the oscillation.
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Old 18th June 2018, 11:37 AM   #4786
anti is offline anti  Slovakia
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Old 18th June 2018, 11:46 AM   #4787
nigel pearson is offline nigel pearson  United Kingdom
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When I used BC337/327 and Indian 2N3055 ( E? ). I needed 27 pF on the VAS NPN to remove a tenancy to oscillation. It was very mild about 500 kHz, I think it was about a 2 dB mini mountain between about 500K and 3 MHz.

Something to play on your JLH. He built his to replace a 1947 design of equal fidelity. A Williamson. DTN was 19 who designed that for MO GEC.

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Old 18th June 2018, 03:26 PM   #4788
johnego is offline johnego  Indonesia
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Quote:
Originally Posted by huggygood View Post
yes but with a increased output capacitor,the mid and high are impacted .
for me,6800uf to 10000uf are the best compromise for the jlh

Best compromise depends on the quality of the cap. The better the caps the more capacitance you can add without sacrificing mid and high too much. Theoretically, I guess even 3300uF will give sufficient bass roll-off point.


When I want only a single cap on board, I will usually use Philips axial 2200uF. But for serious implementations I use paralleled caps out of board.
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Old 18th June 2018, 04:03 PM   #4789
nigel pearson is offline nigel pearson  United Kingdom
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Each speaker determines the needs. 3300uF should be OK. I use 4700 uF to my 15 inch. 1000 uF to my 12 inch and I think 4u7 to my tweeter.
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