John Curl's Blowtorch preamplifier part II

[john curl]

Quote from Feb. 2012 issue of 'Stereophile' p.125 'The Vendetta SCP-2D is the quietest audio component I've ever had. ... It's also the most reliable component I've ever had in my system. ... my SCP-2 has been turned on for 22 years, and has run flawlessly the whole time.'

That about sums it up!

 

[SY]

That about sums it up!

Indeed it does. Taken at face value, this anecdote and your experience suggest that for a well-designed circuit for audio, the board material's dielectric properties aren't very important.

 

[Wavebourn]

Indeed it does. Taken at face value, this anecdote and your experience suggest that for a well-designed circuit for audio, the board material's dielectric properties aren't very important.

That's right. And when active components are used properly influence of passive components is non-significant.

But what would John do with his well-designed circuit without that forces that pushed it from napkin drawing to listening rooms and magazine reviews?

 

[auplater]

Gold directly over copper... recipe for life cycle disaster...

use some Pd or Ni or such...

the small amounts in 23+C Au are there for brightness, hardness, make-break cycle improvements, and minimal leveling... don't do much for the diffusion problem

John L.

 

[john curl]

The gold was put there merely as protection against tarnishing. It does NOT make contacts, as every contact is soldered with SN-62 rosin core solder. It was a common quality surface when the price of gold was much lower (about 5 times lower). It is true that IF the gold layer is too thin, then pinholes will allow the copper to be exposed. Some later board batches were disappointing in this regard. We do not use gold for this purpose anymore or for the last 20 years. We now use Teflon with a quality conformal coating. This is what the Blowtorch used.

 

[simon7000]

Indeed it does. Taken at face value, this anecdote and your experience suggest that for a well-designed circuit for audio, the board material's dielectric properties aren't very important.

Or the heat from the circuit drops the relative humidity inside the reasonably tight case to keep the circuit board dry.

Ever have to use a crisper to store your saltines and other stuff?

 

[Wavebourn]

Vacuum tubes in condenser microphones play similar role keeping capsule dry.

 

[john curl]

Right you are, Simon. Especially when 95% of the surface is coated with gold, the box has no vents, and the class A circuit runs 24 hr/day (for 22 years in one example).

 

[SY]

Let me guess- neither John nor Ed has ever tried drying nylon. Takes 80°C and either vacuum pumping or recirculation after dehumidifying. But that's fine, it's good to see that circuit board dielectric properties don't cause a preamp to sound bad.

Mikes are a different story, leakage at high Z is the major issue. But I can't think of any mike designer who would use a leaky material like nylon.

 

[john curl]

Oh well, in any case, the Blowtorch used Teflon. And my newer circuits either use either FR-4 or Teflon, depending on the product.

 

[auplater]

surface finish

The term is both misleading and inaccurate.

It would be better to know what the plating specifications were. When I specified and purchased plated parts, it did indeed cost more to have a matte finish, but if I recall, it was a result of quantity. Matte finish was not the typical plating specification, so it was a special process. If I also recall accurately, matte required a thicker coat for solderability shelf life due to the lack of a barrier for oxygen.

There are other options, like having another metal within the plating of course.

Then again, only the vendor can really tell us why the cost difference.

Given the fact that auplater and SY are here, maybe they can weigh in? My experience is based on specifying, purchasing, testing, and using in production the different plating schemes..they could speak on the chemistry aspect..

jn

Yes, that is indeed correct. The subsurface "shining through" must be some lay term for the lack of true understanding of what's going on.

The final finish on any plated object is determined by several factors... substrate micro-finish, subsequent leveling of nickel or copper plating from organic modified baths, thickness of the coating applied, and method of measurement.

Matte finishes have much higher micro-surface roughness, large grain size, and lower corrosion resistance per unit thickness, so unless one was wire bonding semis, brite finishes were(are) the norm. Not using a diffusion barrier at anything below 2.5u gold plating is problematic and poor engineering (except in special rf applications, then use Pd or other non ferromagnetic barrier)

 

[Wavebourn]

Mikes are a different story, leakage at high Z is the major issue. But I can't think of any mike designer who would use a leaky material like nylon.

"M7 capsule-article by AG

M7 capsule

The M7 capsule first showed up in 1933 and was skinned with a 10µm PVC. The material back then had to be – and still is today at MTG as well as STM – casted on water. ( The thickness of the material fluctuates between 10 and 12µm. After the war Neumann Berlin obtained their M7 capsules from Gefell, later on only the membranes . In 1955 Neumann Berlin hired a chemist responsible for the production of membrane films . In 1956 the first M7 capsules with PET polyestermembrane showed up. Those new capsules had a much better longterm stability as well as (because of the thinner membrane of about now only 6µm) the remarkable side effect of better low frequency response. In more than 50 % of all M49 microphones that were fitted with a M7, you can still find the M7 PET capsule, not only (like often times falsely assumed) the M7 PVC capsule. Since 1958/59 the M7 was abandoned and replaced by the K47 capsule. The failure rate in the production process of the M7 capsule was simply too high since you only had about 10 minutes to correctly position and finetune the membrane until the glue started to stiffen . The cogset of the K47 made it easier to finetune the membrane (it now got screwed on instread of glued Because of that the failure rate of the capsules got reduced drastically and so about 80 or even 90 % of the capsules could now be used after production. Back then the PET 6µm membrane film was obtained by the companies that also produced the capacitors."

 

[john curl]

You might be right. I did NOT invent the term: 'shining through' for this, but I have examples here of both technologies in an RCA connector, one direct over copper, and the other with a nickel interface (2.5 to 1 price difference) and the reflectivity is virtually the same with normal light. I also have dull finishes, extra bright finishes, and everything in between in RCA connectors. Go figure!

 

[john curl]

Of course, I use Teflon standoffs for my condenser mikes.

 

[simon7000]

Let me guess- neither John nor Ed has ever tried drying nylon. Takes 80°C and either vacuum pumping or recirculation after dehumidifying. But that's fine, it's good to see that circuit board dielectric properties don't cause a preamp to sound bad.

Actually I have, much more polycarbonate than nylon. Before you cold form plastics you need to get the moisture content low enough so that you don't get bubbles.

Time and temperatures are the secret polycarbonate can dry in as little as 24 hours nylon takes 72. Never tried a vacuum.

 

[SY]

Nylon and PC are completely different, though both are thermoplastics. Nylon sucks in considerably more moisture and holds it much more strongly. Much leakier, electrically. PC is a pretty good dielectric, nylon not so much.

 

[simon7000]

Thanks SY I would never have know that without your help.

You do know the tale about the telegram Trotsky sent to Stalin on Christmas eve? It read " I was wrong you were right."

 

[john curl]

I don't have any nylon caps, but then I don't have any FR-4 caps either.

 

[SY]

You do know the tale about the telegram Trotsky sent to Stalin on Christmas eve?

I prefer the letter that Sir Archibald Clark Kerr wrote to Lord Reginald Pembroke.

 

[SY]

I don't have any nylon caps, but then I don't have any FR-4 caps either.

There's a reason for that. Thermosets do not make good flexible films. And polypropylene (an excellent film-former) is much cheaper, but makes a lousy circuit board.

You won't find polystyrene circuit boards, either.