John Curl's Blowtorch preamplifier part II - Page 641 - diyAudio
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Old 28th October 2010, 08:24 PM   #6401
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Old 28th October 2010, 09:13 PM   #6402
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Of course, these ceramic caps, being ....

the McMartin 'ma20' amplifiers have the 'Z5U' Dielectric.



as they work and sound, as well as they do,

i've been apprehensive to change anything.

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Old 28th October 2010, 09:17 PM   #6403
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So long as you are happy, Tomtt. And I will stick to my 2 buck chuck wine, because it works for me.
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Old 29th October 2010, 01:45 AM   #6404
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So long as you are happy, Tomtt. And I will stick to my 2 buck chuck wine, because it works for me.
That's fine John, how about a blind shootout SY tells Belle Helene from 2 Buck Chuck and you tell the difference between Dale RN55C and naked Vishays. No peeking.
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Old 29th October 2010, 02:16 AM   #6405
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Sound differences seem to need a different test than taste, BECAUSE the music is always changing, and taste stays the same.
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Old 29th October 2010, 02:27 AM   #6406
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Old 29th October 2010, 07:37 AM   #6407
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I had a double blind date with a belle Hélène once, but she turned out a bucking Chuck.
Hard to differentiate if not wire-wound.
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Old 29th October 2010, 08:40 AM   #6408
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Sonic reasons are not allowed to be discussed here. I will say that the BF would probably be OK, and operating voltage with only 50K max on the gate is certainly a different condition from 5G, or about 100,000 times different. ;-) Therefore, some care is still prudent, but not so much as in the microphone case.
Still, I would like to thank Ed Simon for the tip on the Dale resistors. My present employer found a cost effective Dale resistor that is completely non-magnetic, that works just great. In our reality, these questions are as serious as what topology to use.
John, I don't want to discuss sonic reasons here, I only want to mention that music - here the music as amplified signal - is really the dynamic condition

I will try out the BF but I my feeling tells me that the SK170 is the JFet for my circuit ...

What Dales you have in mind and what about the Caddock 132?


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Joao, it is still important to CASCODE the input part, if you have more than 10V on the BF862. The 2SK170 is a very good part for audio inputs, and I use them for just about everything that I make, including phono stages, line stages and power amp inputs. Their capacitance is not low, but their transconductance is good enough and their noise is reasonably consistent. They also have a complement. Usually, I operate the 2SK170 from 10-15V in order to get the lowest and most linear range of the non-linear input capacitance, but this would be BAD for a BF862. Anything above about 7.5V gets scary, as does above 18V for the 2SK170.
Currently I don't use the cascode even with the SK170 but I have to experiment with it as well and compare the circuits.

Can I contact you by PM for some questions out of topic?
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Old 29th October 2010, 03:47 PM   #6409
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Joao, I think that I understand what you want, but I cannot answer your questions here, because of the 'extra commentary' that almost always comes from people who do not think that questions like these are 'important'. Of course, you can PM me on specific issues. In truth, I have never found any 'dynamic' differences in fets. Resistors perhaps.
However, it is still almost impossible for me to say something about them here, except FACTS. For the record I have used Caddock power resistors and I like them. We have found a particular version of the Dale resistor to be pretty good, but I don't know its exact number. All that I was told is that it is non-magnetic. This is usually a very good thing, but not always necessary. For example, the end caps on the Roderstein Resista resistors have a slight magnetic attraction, probably nickel plating on the end caps, and it doesn't make much difference, in fact, they are a very good resistor at any price. Unfortunately, they don't make them anymore, and that is why we are switching to Dale for our less critical resistors.
Getting back to jfets, it is important to take care about voltage and leakage issues, especially at very high impedances, because then. a carbon resistor just might show its 'excess' noise due to the voltage drop generated across it by the current needed to supply the 'leaking' jfet.
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Old 29th October 2010, 05:21 PM   #6410
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In several places on this forum people have said that the parallel regulators are superior to the series regulators for high quality audio reproduction power supplies.
Is that so and if yes, then why (everyone's opinion is welcome) ?

Last edited by fireworks; 29th October 2010 at 05:24 PM.
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