John Curl's Blowtorch preamplifier

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scott wurcer

scott wurcer

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Joined 2004
From Bateman....

100 nF 50 volt C0G ceramic, With no DC bias this multilayer capacitor measured just 0.00004%. Second harmonic was -131.7 dB

Excuse me if I don't get excited by .1 ppm distortion. (ceramic at that)

John, people extrapolate that experiment to mean that if you put in a tone burst the tone burst comes out some time later. By implying that a capacitor "remembers" anything more than the history of DC voltage applied nonsense is encouraged. You could take a perfect 1000uF and parallel it with the series comination of a 1k and 10uf, charge it up and short it, you get the same result.
 
john curl

john curl

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Joined 2003
It seems to me that if you put an asymmetrical pulse through a cap, there is still action in the cap after the pulse has gone away. Also, where does the energy come from to charge the cap after it has been discharged? Third, there are no RESISTORS built into the cap, that is just a convenient model. The real forces are molecular dipoles that 'dance' with the music.
By the way, I really need today a really good .1 uF 25V bypass ceramic cap of a size compatible with an AD797 type circuit. Got any suggestions? Those polystyrene .1 uf caps that I like to use are just too big! Help!
 
syn08

syn08

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synaesthesia.ca
PMA said:
To me, any higher order distortion (4th and higher) above -130dB should be avoided. In case that caps bring such distortion, it is best to avoid.
Click to expand...

My understanding was for PS decoupling purposes, not for signal.

For this purpose, I have used these devices without any problems. If -130dB distortion on the power supply lines where everything is attenuated by the 60-70dB PSRR is important/audible then you guys are indeed out of this world. But then, what do I know? :D :D :D
 
S

Sigurd Ruschkow

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Joined 2004
John -
maybe you could try a PPS SMD cap instead of a 100nF ceramic that you wanted. I have used RIFA's PPS SMD caps in some projects. They are in the right size.



SIgurd

john curl said:
By the way, I really need today a really good .1 uF 25V bypass ceramic cap of a size compatible with an AD797 type circuit. Got any suggestions? Those polystyrene .1 uf caps that I like to use are just too big! Help!
Click to expand...
 
Wavebourn

Wavebourn

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fredex said:
Training yourself to hear minute details can be rewarding if that is what you are into. But it can make one restless and this works against experiencing a deeper enjoyment of the music.
Click to expand...

You are right. It was hard for me yesterday to concentrate on a play and enjoy. I always was thinking like "Crappy stage monitors are too loud!", "Why they don't throw out that lapel microphones at all? When one of them dropped her lapel microphone on a stage her voice started to sound better!", and so on...
 
syn08

syn08

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john curl said:
Thanks for the input. Expensive aren't they? Oh well, that is the price for low nonlinear distortion ceramic caps. I am surprised that they make them at all, and I bet they still have plenty of DA.
Click to expand...

0.1uF C0G's are very unusual and I can barely think of an application where they would be really required and unreplaceable. 1nF C0G and similar values are, as they should, in the penny range.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=BC1025CT-ND
 
john curl

john curl

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Joined 2003
OK, let us clarify a few things, and why I even asked questions about caps.
First, there are 3 separate areas where we need caps: Coupling, EQ, and power supply bypass.
Coupling is the most easy to remove. EQ is difficult to use anything but good caps. Bypassing is a mixed bag where you want good RF bypass, YET non-linearity in the cap can be detected with many discrete hi end circuits, such as the Blowtorch and Vendetta Research circuits.
About 25 years ago, and before, I happily used tantalum bypass caps with values of 47uf to 150uf. I still have 100's of them available to me.
Doing an A-B test with my early Vendetta SCP-1 about 25 years ago, I clearly heard a difference between the 150uf tantalum caps and 8uf polypropylene caps in the power supply bypass.
What a drag! I had to redesign both the case and the power supply buffers to get it to sound its best. I would not have done it on a whim.
Now, IF anyone can make a perfectly good audio preamp that sounds as good as anything out there with ceramic or tantalum bypass caps, well good for them. It might be that IC's with their superior power supply rejection, will tolerate nonlinear caps in the power supply bypass. I hope so.
Now why .1uf? This is the STANDARD bypass demanded by IC manufacturers. Look at the data sheets, fellow engineers. Not 1000pf, not 10nf, but .1uf. Can I use smaller caps safely? Help, Scott Wurcer. Clue me in. Is the .1uf cog cap, your cap of choice instead? Darn, they are even more expensive than your IC in the same catalog. Still, they are fairly linear, aren't they?
 
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