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JLH 10 Watt class A amplifier
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Old 17th July 2017, 04:37 PM   #3881
Sk8Ter is offline Sk8Ter  United States
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Default Sony V-fet

anyone build more closely to what Mr Nelson has done with a SIT?

He gets better bandwidth from what i can see.



Lawrence
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Old 17th July 2017, 04:47 PM   #3882
prasi is offline prasi  India
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Hello Nico/gabor,
Help needed. I plan get a somewhat universal transformer for this and any other future class A amp. What would be a suitable (somewhat luxurious, so that its truly universal trafo) transformer VA for 15VAC, 18 VAC, 20 VAC and 22VAC secondaries for this amp.? all secondaries on the same trafo, so that I can use whichever one that suits that particular class A amp I build.
I am not looking at calculations for minimum VA requirements, but something having 1.5x to 2x the minimum required that will take care of most class A amps requiring these AC secondaries.

I was going to get a 1000VA one , but in these difficult times, its slightly going out of my budget.
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Old 18th July 2017, 02:55 AM   #3883
gaborbela is offline gaborbela  Canada
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Quote:
Originally Posted by prasi View Post
Hello Nico/gabor,
Help needed. I plan get a somewhat universal transformer for this and any other future class A amp. What would be a suitable (somewhat luxurious, so that its truly universal trafo) transformer VA for 15VAC, 18 VAC, 20 VAC and 22VAC secondaries for this amp.? all secondaries on the same trafo, so that I can use whichever one that suits that particular class A amp I build.
I am not looking at calculations for minimum VA requirements, but something having 1.5x to 2x the minimum required that will take care of most class A amps requiring these AC secondaries.

I was going to get a 1000VA one , but in these difficult times, its slightly going out of my budget.
Hello prasi
Here is the designer calculation .
Originally he built it as 2 mono blocks, so I am not sure he made the calculation based on that!
Please read it, I hope someone else who already built the amp will share his experience.
For example some people for the 20W Hiraga Class A use a 2X18V 300VA transformer I used for mine 500VA. I do like to oversize the PS start from the transformer. For Pass Aleph30 some used 400VA I used 625VA and the transformer was warm after a few hours usage.
To under size the PS or the transformer one of the worst think we can do at Class A operation. The other hand if we need a 500VA but we use 1KVA it is a waste of money, ad extra weight and need extra room inside the amp enclosure.
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Old 18th July 2017, 03:12 AM   #3884
ashok is offline ashok
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Quote:
Originally Posted by prasi View Post
just got these monsters, 300mmx200mmx83 mm serrated fins.
That's from Pune , right ? Forgot the suppliers name.
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Old 18th July 2017, 04:41 AM   #3885
prasi is offline prasi  India
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That's from Pune , right ? Forgot the suppliers name.
Yes. Just Google akash heatsinks pune
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Old 18th July 2017, 01:11 PM   #3886
AndrewT is offline AndrewT  Scotland
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A classA amplifier uses a transformer rated somewhere from 6times to 10times the maximum ClassA output power.

If you have a 50W+50W stereo ClassA amplifier, then you need at least 600VA and could work economically with up 1000VA. Any more than that is wasting resources.
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Old 18th July 2017, 01:15 PM   #3887
AndrewT is offline AndrewT  Scotland
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If you buy a big toroid then it will have a big hole in the middle that can accommodate a lot of extra turns.

Buy a 1000VA 16Vac dual secondary.
It will have low regulation and a low Turns per volt.
Add on a bifillar winding that gives 2VAc.
Then add on another bifllar winding for 2Vac and finally a third 2Vac bifillar winding.

You now have the option for 16, 18, 20 & 22Vac dual secondaries.

2Vac could be as few as 4, or 5Turns But you would need thick wire (3.6mm diam). Might be easier to use thinner wire for a paralleled secondary (double 2.5mm diam).
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Last edited by AndrewT; 18th July 2017 at 01:18 PM.
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Old 18th July 2017, 02:09 PM   #3888
prasi is offline prasi  India
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Thank you Gabor and Andrew,
Very good info. Thanks a lot.
regards
Prasi
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Old Yesterday, 12:52 PM   #3889
gaborbela is offline gaborbela  Canada
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Hi
I would not go as low as 2x16V, would start at 2x18V and up, You got those nice pieces of heatsinks those can handle 18V and up especially if you do not use regulators. High power regulators create a lot of heat also.
When you ad some wires to your transformer make sure that does not crate any mechanical noises.
Originally the designer uses 2v18V 300VA per mono block. He uses regulated PS so he get 18VDC.

About the amplifier I didn't have any progress, Last week my lower back pinched (not the first time) the nerve so everything is on hold. I spent the whole week on pain killers and most time at the bed. Monday will see my family doctor, I hope she will send me to a specialist.
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Old Yesterday, 06:12 PM   #3890
prasi is offline prasi  India
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Hi Gabor,
I wish you a speedy recovery from the temporary affliction. get well soon!.
And thank you for your suggestions.
Regards
Prasi
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