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Old 25th July 2012, 12:18 PM   #11
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Hi Jaap,

The original circuit appeared 8 years ago (tomorrow!):

New DHT heater

But I don't recommend building like that today. The transistors there cannot be obtained, and the performance is not so good. The new kits also have:

- much better noise rejection;
- temperature compensation;
- frequency compensation;
- +/- 20% adjustment of current, with 25-Turn trimmer
- takes only a few minutes to assemble;
- DIY price

You are correct, the bandwidth must be controlled, to get the best sound.

There's no need to have a compromised solution.... dc supplies need to be carefully designed to avoid sounding worse than ac.
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Old 25th July 2012, 01:42 PM   #12
popilin is offline popilin  Argentina
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Quote:
Originally Posted by Rod Coleman View Post
Hi Jaap,

The original circuit appeared 8 years ago (tomorrow!):

New DHT heater

But I don't recommend building like that today. The transistors there cannot be obtained, and the performance is not so good. The new kits also have:

- much better noise rejection;
- temperature compensation;
- frequency compensation;
- +/- 20% adjustment of current, with 25-Turn trimmer
- takes only a few minutes to assemble;
- DIY price

You are correct, the bandwidth must be controlled, to get the best sound.

There's no need to have a compromised solution.... dc supplies need to be carefully designed to avoid sounding worse than ac.
I have no doubt that this is a better solution.
The point is that the OP has only 5 VAC in the transformer.
Maybe I misunderstood because of my Tarzan-English.
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Old 25th July 2012, 06:18 PM   #13
disco is offline disco  Netherlands
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Was that the question? OK.
No, that's not possible with a common diode bridge and capacitor (nor with a voltage doubler circuit) because the ripple is too large. You need 8 to 9 volts AC minimum, more if there are serious line sags.
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Old 25th July 2012, 10:52 PM   #14
popilin is offline popilin  Argentina
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The circuit proposed in post # 7, you can work with 5V AC, using a 5V zener instead of a 7805.

It was designed to power a 5R4GY, in an experiment of thermionic emission, which required a high stability voltage.
The early prototype was checked for a week, with a deviation in the order of 1 mV.
Using a thermally compensated voltage reference, the results can be even better.
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Old 26th July 2012, 06:52 AM   #15
disco is offline disco  Netherlands
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Ah, active circuit round a low drop linear regulator, that's something else
How much line sag can it tolerate?
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Old 26th July 2012, 07:55 PM   #16
popilin is offline popilin  Argentina
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Using Schottky rectifiers, I estimate 5%.
Can be improved with a voltage doubler circuit.
If your line is crap
1. A good UPS can help.
2. Stay away from the line of the LHC.
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