John Curl's Blowtorch preamplifier part II

[john curl]

Steve, usually a material with a percentage of iron or nickel is magnetic. Of course, there are exceptions like stainless steel, but at what cost and tradeoff?

[john curl]

Let's call it 'near ferromagnetic'! '-)

[EUVL]

Even austenitic stainless steel like 316 is not totally non-magnetic.
It is only less magnetic compared to normal steel or martensiticstainless steel like 420.


Patrick

[magnoman]

Sorry for the dumb question but can someone briefly describe the problem with having ferromagnetic material (for example nickel plated aluminum) as part of the case.

Thanks
-Antonio

[SY]

Not at all a dumb question. I'll bet you get a lot of dumb answers, though.

There's actually some good reasons to use a ferromagnetic case, but that's a hard sell in this market segment.

[auplater]

no problem with "dumb" questions...as it would seem "dumb" statements are completely acceptable as well...

[vacuphile]

Originally Posted by john curl

Steve, usually a material with a percentage of iron or nickel is magnetic. Of course, there are exceptions like stainless steel, but at what cost and tradeoff?

Stainless steel without iron? Or possibly other alloys with iron or nickel can be non magnetic as well? Plse be consistent in your thinking.

[john curl]

I am not here to parse what 'magnetic' is.

[john curl]

Magnoman, we hi enders tend to avoid making our cases with steel or anything magnetic. We did not start that way, and 30-40 years ago, steel was the usual material that we made chassis from. However, we have shifted to aluminum for the most part, for reasons beyond this discussion. It does have to do with distortion generation, I will offer that.
However, aluminum must be rather thick in order to reduce the magnetic component of EMI, much thicker than steel. Therefore, to effectively use aluminum and avoid steel, we must use a relatively thick shell. All my best designs use aluminum when and where we can.
Aluminum also finishes well. When we use a thick case even with aluminum, of course it gets heavy, but if we made a steel case with the same dimensions, it would be much heavier. It is NOT weight that we are after, or we would use steel, instead.

[ThorstenL]

Hi,

Originally Posted by Bonsai

I doubt there is any advice I could take seriously from you.

Then don't.

Originally Posted by Bonsai

Fuses may well be non linear, but if they are located in the rails and causing measurable levels of distortion you have a serious problem with your design. Period.

Ahh, so on top of perfect designs, you also have perfect Op-Amp's that have infinite PSRR and are unaffected by supply voltage changes and perfect Poweramplifiers that also have infinite PSRR and are unaffected by supply voltage changes. It seems you are quite a designer then, even making your own perfect Op-Amp's, maybe you should sell the technology to TI/BB/NatSemi, they shure could use it.

Originally Posted by Bonsai

Secondly, this is a DIY site, so no need to plug your stuff here or keep referencing it. I am the second or third individual that has raised this issue.

If linking to stuff on a website that illustrates something is plugging a product that many here are guilty of "plugging" products. If you think what I am doing is out of order, why don't complain to the moderators about the posts it is easy?

Originally Posted by Bonsai

Finally, I absolutely would not spend $10k on your phonograph stage, rest assured. I just don't see the value in something that electronically falls way below the benchmark (remember, you told us low distortion is not that important, and as for RIAA curves, well anything goes, including a standard RIAA curve thats out by 2dB), and is then dressed up in coat and tails and masqueraded as high end.

First, I could not care less what you buy or not. Very few here have the kind of money to spare to buy AMR's products anyway...

Past that, I have no idea what phonostage you are talking about as having a RIAA EQ that is 2dB out from standard, but it is certainly not any I designed (be it published here in detail, or commercial ones), maybe a design of yours? If you want to criticise my work, make at least sure you got you facts right.

As to "falls below the benchmark", exactly what is the benchmark? And who sets it?

Independent measurements are published and can be accessed by anyone.

Finally, if you quote or paraphrase what I wrote, try getting it right.

I wrote that single number THD is meaningless and has no valid correlation with distortion audibility, a position strongly supported by research going back over 60 years and widely published including in the JAES. It has been long known that low THD is not a guarantee of low distortion audibility, neither is relatively high measured THD an indicator of highly audible or highly objectionable distortion. If you are so ignorant to not even know this, maybe you need some more education?

Originally Posted by Bonsai

Thanks for the compliments on my designs by the way. Pity I cannot return the favor.

Not a pity at all. A compliment from you is one I really can do without, if I actually got one I would be worried I am dong things very gravely wrong.

Ciao T