John Curl's Blowtorch preamplifier

[tvi]

The BSS8402DW is available from Mouser & Digikey for less than a buck each.

And the PHC2300 is available at Digikey

These are dual complimentary (N+P ch) SMT devices, don't know how well matched they are internally though and they aren't a powerful as the Hitachi devices.

Regards
James

 

[john curl]

Think power dissipation.

 

[Terry Demol]

Hysteresis, B = f(H), and you seen that Bsat = 0.25T.

Have you measured the strength of magnetic fields in and outside
an enclosure?

 

[Justcallmedad]

What about the Toshiba SJ313/SK2013 pair? did you test it ?

 

[PMA]

Have you measured the strength of magnetic fields in and outside
an enclosure?

Oh sure, for my professional purposes it is necessary. I have a H probe developed. I have never done it for audio system enclosures.

 

[Terry Demol]

Oh sure, for my professional purposes it is necessary. I have a H probe developed. I have never done it for audio system enclosures.

So what were typical field strengths?

 

[PMA]

So what were typical field strengths?

Are you examining me? Why are you interested?

Thy typical intensity where my instruments work is like 12.73 kA/m. That makes B = 16mT in the air. For relative permeability of 200 you get B = 3.2T (Tesla)

 

[EUVL]

Richard,

> What about the Toshiba SJ313/SK2013 pair? did you test it ?

I have and can confirm they are excellent parts, especially when a well matched pair is used in a bridge configuration.


Patrick

 

[Justcallmedad]

Hi Patrick,

I have and can confirm , especially when a well matched pair is used in a bridge configuration.
Patrick

Yes I know, they are excellent parts, I tested them in a folded cascoded configuration (second stage for an RIAA preamp) but I never tried with the IRF510/9510, essentially due to the IRF P parts problem (never could find the Fairchild/Harris ones), and as they are cheaper and easier to find than the Toshiba for future projects... Maybe the Fairchild FQP7N10/FQP8P10 could be O.K.

 

[EUVL]

Richard,

I have yet to find an IR part which is so even order terms dominant that they cancel to near perfect linearity in a bridge configuration.



But maybe the IRF Fans at the Pass Forum might shred some light on their experience.


Patrick

 

[lumanauw]

The BSS8402DW is available from Mouser & Digikey for less than a buck each.

And the PHC2300 is available at Digikey

PHC2300 is an interesting part. 300VDC (but no transconductance data?), could be used for many purpose in power amp. Maybe we can built input differential, VAS and predriver using only this device? Mr. Pass?

 

[Terry Demol]

Are you examining me?

Of course not - but I can see that I am winding you up

Why are you interested?

You stated 0.25 Tesla saturation level for work hardened or welded
304 SS. So obviously I am interested how that relates to a real
world condition - IOW are we likely to see fields causing this level
of flux in a typical audio environment.

The typical intensity where my instruments work is like 12.73 kA/m. That makes B = 16mT in the air. For relative permeability of 200 you get B = 3.2T (Tesla)

The 3.2 Tesla hinges on the relative permeability of 200.

Non magnetic SS has a relative permeability of 1 in annealed
condition. Work hardening (bending, cold rolling etc) will increase
this value but it's difficult to get accurate figures - still from what I
can find, 200 looks much too high.

http://www.assda.asn.au/asp/index.asp?pgid=18535

If you can find more accurate data on this I'd be interested.

T

 

[PMA]

This makes no sense, as I spoke about H intensity during tests of HV high-power circuit breakers at this facility:

http://www.zku.cz/index_a.html

However, for B = 16mT and Bsat = 0.25T I would get saturation for relative permeability of 15.625

I belive that this debate is useless for audio.

 

[PMA]

To conclude, even if the stainless had rel. permeability = 1, it has much higher resistivity than Cu and Al. For this reason the skin depth would be higher. So it would make no sense to use it for shielding.

Shielding, fortunately, corresponds to laws of physics. Contrary to audio curcuits listening evaluation. But, as seen here, people are able to come with conjuration even for shielding, when used for audio purposes.

 

[Vogue]

PMA,

Another conclusion could be to use aluminium bolts and screws to assemble the chassis, as aluminium is a better conductor than iron/steel, and does not cause corrosion i connection with the aluminium sheets.

Vogue

 

[AndrewT]

........use aluminium bolts and screws to assemble the chassis, as aluminium is a better conductor than iron/steel, and does not cause corrosion in connection with the aluminium sheets.

no.
The main conductor of heat between the two chassis components is the clamped interface. Little heat whether the fixing is made of aluminium or less conductive material passes up through the long length and small cross sectional area of the bolt or set screw.
Using a high tensile aluminium alloy for the bolt or set screw virtually guarantees that the alloying constituents of the fixing will be different from the alloy chassis. Changed the alloying components alters the resistance to corrosion. Adopting aluminium alloy fixings does not eliminate the possibility of corrosion, but is very likely to reduce the severity of that corrosion. But, coatings on the steel fixings can achieve similar corrosion reduction potential.

 

[Vogue]

no.
The main conductor of heat between the two chassis components is the clamped interface. Little heat whether the fixing is made of aluminium or less conductive material passes up through the long length and small cross sectional area of the bolt or set screw.
Using a high tensile aluminium alloy for the bolt or set screw virtually guarantees that the alloying constituents of the fixing will be different from the alloy chassis. Changed the alloying components alters the resistance to corrosion. Adopting aluminium alloy fixings does not eliminate the possibility of corrosion, but is very likely to reduce the severity of that corrosion. But, coatings on the steel fixings can achieve similar corrosion reduction potential.

Point taken - but steel is not a good conductor compared to aluminium. But what is the likelihood of corrosion between alu and alu of a different alloy compared to the proberbility of corrosion with aluminium and another metal?.

Vogue

 

[AndrewT]

Adopting aluminium alloy fixings.............. is very likely to reduce the severity of that corrosion........

 

[Terry Demol]

This makes no sense, as I spoke about H intensity during tests of HV high-power circuit breakers at this facility:

http://www.zku.cz/index_a.html

Well exactly, how many HV high-power circuit breakers are in the
vicinity of home or studio audio gear?

However, for B = 16mT and Bsat = 0.25T I would get saturation for relative permeability of 15.625

http://socrates.berkeley.edu/~fajans/pub/pdffiles/SatNonMagSSRSI.PDF

In all cases the relative permeability of 304 was below 1.8.
So in normal usage conditions ie; home or studio electronics the
enclosure will be nowhere near saturation.

I belive that this debate is useless for audio.

Functionally, an enclosure machined from billet aluminium is great.

It is also a very effective way to spend lots of money.

Using some form of sheet metal is a necessary option for many.
Why not look at the merits of various types.


cheers

T

 

[PMA]

The Blowtorch case is similar in construction to my outer instrument case (AL thickness). That is the only reason why I came with analysis of interference fields. We touched EMI protection High End here, so we spoke about magnetic material saturation, skin depth etc.