John Curl's Blowtorch preamplifier

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john curl said:
Please understand everyone, the best quality costs big money. I have a .3 uf Teflon cap in my new phono stage that costs me $40. Do you think that I would not replace it with something cheaper, IF I thought it would sound just as good?
IF you don't give a darn about what works and what does not, please just defer from taking cheap shots at the rest of us.

No, I think you wouldn't replace it. And that's not because of the "sound" but because you need to keep the mythology and legends alive. That's the way you (and others) chosed to survive in the audio industry.

Granted, I'm pretty sure this kind of approach is, after 40 years, already an automatism that does not involve any cognitive process. Therefore, you are not a snake oil merchant. You are simply wrong. And please, don't mention again large ceramics. Those are never NP0.
 
I 'believe' that Teflon is a better material than Mylar or even polypropylene. Whether it is better than polystyrene is still up for debate. Let us hope that polystyrene is really enough. I am not sure, as I have lived with both. Anyone else have some REAL input, and not just this reactionary nonsense?
 
Hi John,
OH baloney, Anatech. I got my first large value ceramic caps when I worked in the Ampex research department. They were MORE expensive than mylar, but they were small.
Well, gee John. I must be amazingly adept at this stuff, because I had figured out that for myself on my own bench. Mind you, this was in the 80's because that's when I began to get some test gear together. I also read manufacturer's data sheets and experimented by myself. I had already figured out the the data sheets of that period and earlier were sometimes inaccurate. Now, knowing that I'm not brilliant, I just like to test things for myself when time permits. What is your excuse?

I say again. If you use parts without knowing their properties, that is your error and no one else's. Components for audio back then didn't really exist as the audio market was tiny and the market got by with normal industrial devices for the most part. So data aimed at audio designers did not really exist.

Do you know how I clued into the better capacitors? I read data sheets for electronic measurement systems. If you look back at some data sheets of that period, look for something called an "integration capacitor" for the A/D of a meter for example. Low and behold, they are concerned with many things that you are. The recommended part was (and is) ..... the same ones you like now. Low DA plastic based, like Teflon is today. All you had to do was look at an industrial use that required accuracy at high impedances. Sample and hold capacitors are also subject to the same criteria. The information was there John.

Now, how many of the "high end" designers specified tantalum capacitors? John, did you ever use them? I found that normal electrolytic caps sounded better. The THD measurement is usually tiny, but it is lower. So next time you want to patronize some of our members here, don't. Sit back and consider how you learned. You were about as clueless as all of us starting out, and you learned. In the course of learning, you made errors as well. So stop making like you appeared on this earth fully formed and taught.

Anyway, for most applications the NPO ceramic is fine. I would probably use a Teflon if I had it, or I would use (and do) the polystyrene and mica capacitors. However, an NPO ceramic capacitor is probably not going to cause audible problems there. NPO caps usually have a black stripe on them if there is any marking to be seen.

Is there anything that you disagree with here? If you aren't sure, those application notes and a data sheets on voltmeter chips, A/D converters and sample and hold systems are still out there. Have a read. While you are at it, look at the copy write dates on them.

You know, I never did say that all ceramics were okay. I never did disagree with you on your choices of capacitor types either. I didn't even attack you. All I did was to point out how silly it is to create something without knowing the properties of the parts where it matters, and then blame the parts and manufacturers.

-Chris 🙄
 
Hi Andy,
I was originally going to use mica here. But the data from Bob Pease's 1982 article on DA (attached below) shows mica to be inferior to NP0 ceramic with respect to DA.
Well, I have stated that I use Mica, although I prefer Polystyrene capacitors. I have used Polypropylene. I may have tried a Teflon type at some point, but it may not have seemed better than the Polystyrene I was using.

Your application is actually very critical as you well know. It's the high voltage swing coupled with the high impedance of that circuit that will really allow the non-linearities show up. There are other studies that show that DA in capacitors is often non-linear, so no surprises there. Again, test and measurement applications have been there and done that.

Have you ever tried the Xicon NP0's?
Actually, no. I haven't bothered because I prefer Polystyrene, and Polypropylene is not available in the 100 pF range that I know of. I'll have to look at Mica capacitors more closely, because I know they can be variable in quality depending on the supplier.

The Mouser catalog shows that the cheapo Xicons meet this requirement.
I have only bought from Mouser once. Getting Mouser to ship to Canada is downright painful, which is too bad because they do stock some cool stuff.

Is that what you expected me to say?

-Chris

Edit: I guess one of my points is that NPO ceramic caps can not be dismissed out of hand. I am distrustful of them myself, but I have been learning that I was wrong to believe all ceramics were bad.
 
anatech said:
Actually, no. I haven't bothered because I prefer Polystyrene, and Polypropylene is not available in the 100 pF range that I know of. I'll have to look at Mica capacitors more closely, because I know they can be variable in quality depending on the supplier

I was considering polystyrene as well for this application. Unfortunately, the ones that are readily available to me are 50V only. I have seen 630V parts available from "audiophile" suppliers, but I hate to buy stuff from such places.

I have only bought from Mouser once. Getting Mouser to ship to Canada is downright painful, which is too bad because they do stock some cool stuff.

Ah, that's too bad. I didn't realize they were so hard to deal with for shipping to Canada.

Is that what you expected me to say?

Well, I had no preconceived idea of what you might say. You have more practical experience in this area than I do, which is why I asked. My professional experience with components is for military applications, which are a different kettle of fish in many ways. For instance, polystyrene and polypropylene are never used in military apps because of the temperature range. And those apps don't care about capacitor distortion for instance.

I just found out that I can get 1 kV NP0 Vishay/Sprague ceramics from Mouser, so I think I'll try these rather than risking the cheapo Xicons. All of these are cheaper than micas for the same capacitance and voltage, which is nice. Thanks for the feedback.
 
I don't think there are many choices for a miller cap (say 10-50pf range) that are reliable, affordable and offer good sound quality other than silver mica.

NPO's ok - but whats their performance like with say a 200Hz 40Vpk-pk wave with some 10KHz of 3 or 4 volt s super-imposaed on top of that?

Polystyrene at these low levels seem very difficult to get - I tried at DK and Mouser and spent hours looking around in Akihibara with no luck.

Teflon - same story - seems the y only really start to become availalble once you get into 100's of pF.

BTW, I'm alkso using silver mica on the input filter as well - 100pF.

I guess my amp must really have a dose the 'sound of sprinkling iron' 😀
 
"Since late last year, Mouser is my prime shopping portal for parts."

I agree - they have been great for me here in Japan and their catalog is good. Nice source for MF resistors I found

As for RS
:dead:
arrogant bunch of jerks. They don't have stock in Japan of what I want so I called UK and asked if the y would ship to me: No they told me. So I asked them if there was some other way - cow on the other side said - no - we can't help you and put the phone down on me. Last time I buy from them. 2nd or 3rd bad expereince. Absolute *********. I hope DK screws them in Europe.

DK - expensive, but great service and great catalog and always got stock.

Newark - half the stuff in thier catalog is not in stock (my expereince anyway). Are the y linked upo with RS. It figures
 
Hi John,
You know, I have treated you with more respect than that.
OK, Chris. Get me an NPO .3uf cap and I will try it.
This is a silly comment, and you well know it. This is not a normally available value that I ever recall seeing.

I will say this though. If you were to order this part, and it was supplied, the price tag would be insanely high. Just for that you might start using them. Actually, that comment wasn't fair for me to say. I did want to make a point that we don't have to get personal about any of this.

What my intentions supporting the use of ceramic NPO caps was is to say they are not nearly as bad as some of the press they have received. I used to look at them as being "junk" like the rest of the ceramic family, but I have been learning that the NPO types are in fact better than some preferred types. Certainly not as bad as I once thought. Of course, my comments must apply to the normally available values. Let's keep our comments useful to everyone else who cares to read them.

Now, ceramic capacitors are very good for RF bypass applications where the circuit is low impedance or has very little voltage swing. An example of this would be to bypass a DC power buss. Better than most other types of capacitors, the right part for the right job.

-Chris
 
Here's what Cyril Bateman has to say about NP0:

By Cyril Bateman
"For almost all circuit needs the conventional COG ceramic provides the most nearly perfect capacitor, having better
characteristics than mica or any film except perhaps for PTFE. It has a temperature coefficient of ± 30 ppm, negligible voltage
coefficient, capacitance stable over time, negligible capacitance variation to high frequencies, minimal dielectric absorption and
‘Q’ approaching 1000 at 1 MHz."
 
Hi Andy,
I was considering polystyrene as well for this application.
My normal first choice, but mine are 630 V. I bought mine at hamfests and some from audio suppliers. Newark has some also at 630 V. I'm sure there are other suppliers out there that may stock these.

Well, I had no preconceived idea of what you might say.
Please allow me to apologize to you then. I was feeling annoyed with John's manner of addressing us and was being cautious. I thought you might be setting me up. I'll do my best to accept questions at face value from here on in.

Hi SY,
The problem with polystyrene is temperature sensitivity.
Absolutely!
That is how I decide whether I'm using a Polystyrene or Mica in any particular position.

Hi Bratislav,
Actually, early Krell designs (yup, those enjoying 'class A' whatever and still sought after by many audiophiles) have tantalums in them.
...and they are by no means alone there. Most late 70's and early 80's US built equipment had some tantalums in there. It's interesting to note that the wet tantalum capacitors are totally different to the solid Tantalum types. If you see a wet tantalum capacitor in your equipment, it's probably good. They are also better than electrolytic caps and about $30 USD to replace each. Leave them be, just test them to confirm they are still good.

Hi syn08,
Not anymore! They now have the same policies and shipping costs as Digikey and Newark. No Customs hasless, etc...
Cool! Thank you for that. The first time was so unpleasant, I wrote them off.

Hi Peter,
When I need a cap that small, I usually twist the wires: sounds better than mica
Yes, I've done that before. Very handy when you don't have a small value. You do have to watch that they are not so long that they pick up noise. Also, the wire may relax over time. Bummer. I even wound some tight with the drill, but the wire relaxed over about a year. Then I mashed it with a hammer. That fixed it. No, really! I hit the "capacitor" with a soft hammer enough to compress the insulation a little. The flattened "capacitor" was then trimmed down to it's proper value again. This time it stayed. :devilr: That was in a ramp generator I no longer own, but I bet that still works fine. I won't warranty any voltage rating on it though!

-Chris
 
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