John Curl's Blowtorch preamplifier

[jacco vermeulen]

really naked ?

Seems pretty clear what the Spy from PMI thinks of such components and Cryo-treatments, maybe Mr Ironside Hansen is willing to share his thoughts too ?

(my favorite McGoohan part is the one in Ice Station Zebra, maybe the nuclear sub is to blame, my phallic obsession is bigger than yours)

 

[jan.didden]

Seems pretty clear what the Spy from PMI thinks of such components and Cryo-treatments, maybe Mr Ironside Hansen is willing to share his thoughts too ?

(my favorite McGoohan part is the one in Ice Station Zebra, maybe the nuclear sub is to blame, my phallic obsession is bigger than yours)

Jacco,

Have you ever thought about taking up writing novels?

Jan Didden

 

[jacco vermeulen]

A cool McGoohan quote : "The problem with Scotland is that it is filled with Scots".
Same-same for Holland.

 

[AndrewT]

A cool McGoohan quote : "The problem with Scotland is that it is filled with Scots".
Same-same for Holland.

I'm sulking.

 

[Edmond Stuart]

A cool McGoohan quote : "The problem with Scotland is that it is filled with Scots".
Same-same for Holland.

The problem with Holland is that it is filled with Jaccos.

edit: I still remember your ridiculous imputations.

 

[jacco vermeulen]

Mr Stuart,

touche.
At the time i expressed my apology to Franklin for the hasty insinuation, you can have it too.

Edit : the quote is from the William Wallace movie, ~1300AC, just in case you thought it was contemporary.

 

[syn08]

I wonder which opamps today would be good candidates. Personally AD825 has caused no problems but AD797 has always been a bit more sensitive against oscillations. Of fast opamps I have only tested AD817, AD825 and AD797 but OPA134 has worked good according to others.

Later on I will test LME49710.

I got the best results with AD8610, OPA211 and ADA4899-1 (for outputs up to 10V). If you can live with 10V outputs, ADA4899-1 is, to me, clearly the winner. Indeed, AD797 is a bit difficult to stabilize and requires some tweaking.

The National opamps are good in this application, but nothing to write home about.

 

[peranders]

Just to be sure, you talk about super regulators?

 

[syn08]

Just to be sure, you talk about super regulators?

Yes, this one http://waltjung.org/PDFs/Improved_PN_Regs.pdf

 

[Blues]

Jacco,

Have you ever thought about taking up writing novels?

Jan Didden

Let's leave that to Grey...😀

 

[scott wurcer]

Scott,

In a sense, that 797 is too smart for its own good. How many application designers realise/understand that capacitive error correction?

Jan Didden

In the beginning I never knew why anyone would want 1nV at gain of one. The part was designed for ATE and other instrument use, the rest was for fun. The rbb on the input devices was reduced below a critical threshold for the ft on this process, the "10 turns of wire on a resistor" input snubbers work best but marketing forbid this on the data sheet.


BTW I got the brush-off at the AES conference from DR. L, I guess I wasn't an insider. Also someone tracked me down to say that the distortion neutralization "had to be just feedback in disguse". Where have I heard that before?

 

[syn08]

the distortion neutralization "had to be just feedback in disguse". Where have I heard that before?

I don't know, but prof. Hawksford may have a clue 😀

 

[chascode]

These resistors look like 'naked' Vishay resistors and they are supposed to sound very good, but they are very expensive and delicate. They sound even better after being cryoed.
Many here have little or no idea what we do to get good sound.

We routinely use heat treat annealing and quenching, as well as cryo treatments, to stabilize the metallurgical properties of all kinds of metals: steel alloys; silicon iron, nickel-alloy and vanadium permendur magnetic materials; copper and silver-plated copper wire, among others. I always temperature cycle my toroidal current transformer designs from -55C to +120C to relieve the mechanical stress on the core due to the winding process. This eliminates any magnetostriction that might adversely effect the hysteresis loop of the material. I need to reduce the phase angle errors down to 2 minutes of a degree. A small tank of liquid nitrogen is not all that expensive, but the magnetic core material we use is very expensive.

My dad used to machine the titanium connecting rods for off-shore power boat racing big-block Chevy engines, and those rods and the metal head gaskets were cryo treated for longer life at high temperature, high rpm operation.

I'm not a metallurgist, but there is a vast body of information stemming from WWII where cryo treatment was first used and documented to achieve selected properties. It is not a far stretch to believe that cryo treatment can alter the properties in some desirable manner for the materials used in high-end audio.

Best Regards, Chuck Hansen

 

[scott wurcer]

What's the spec for voltage coefficient of resistance? That's where a lot of the fancy stuff falls down.

One needs to be careful to separate the TC related changes from the true voltage coefficient. The third order true voltage coefficient figures heavily into the behavior of your typical light bulb stabilized wein bridge oscillator (a little known fact).

 

[Edmond Stuart]

Wien bridge

One needs to be careful to separate the TC related changes from the true voltage coefficient. The third order true voltage coefficient figures heavily into the behavior of your typical light bulb stabilized wein bridge oscillator (a little known fact).

Old geezers do know that bulb trick.
http://upload.wikimedia.org/wikipedia/commons/8/8e/Wien_bridge_classic_osc.png

 

[lineup]

Comment: AD797 comp cap C2

It's Walt's super regulator from the AA article except I added the distortion neutralizing capacitor to the 797. I pointed out to Walt that this cap cancels the output impedance of the amplifier but it never got into the article. 1e-6 Ohm from DC to 100kHz.

Yes, it's the capacitor from output to current mirror input, see figure 31 (capacitor Cn) and figure 44, table 6 (capacitor C2).
.

See my attachment.
It is my discrete AD797 Clone from 2006.
( http://www.diyaudio.com/forums/showthread.php?threadid=92094 )

Supply is +/- 15 VDC.
Image shows 10Vrms output = 14.14 Volt peak!

into 2200 Ohms at +20 dB gain. (x10, set by 24k/2.4k)

I do not remember I did try some different values (47pF) for C2 in my simulations. The distortion is so vanishing low, that eventual improvement by tweaking compensation caps are hard to measure.
At least with my Simulation software ( EWB MultiSim9 )

Compared to typical IC op amp designs, some of the latest presentations here are a breath of fresh air.
They are push pull, class A, low feedback designs.
/snip/
However, the design principles of the Boxter, or Blowtorch are more sophisticated,
and require much more attention to detail, which makes for world class performance,
which I hope the Blowtorch thread is all about.

> .... the Blowtorch thread is all about.

True, john curl 🙂
This thread is (or should be) about a TopClass discrete pre amplifier.

In any popular (frequent posts) topic there will be other people 'advertising' or pointing to their own belongings: so called 'audio achievements'. This is most often the result from our human way to let our selves be dominated by Our Own Egos, without some little effort for self control.
Me self is no exception from this.
Hope I can be egoistic with some style and grace
as now being an older gentleman ( born 1951, like Hugh Dean ).

However, can be of some interest to compare Blowtorch to other hifi amps. Now, I do not think this top class 'Blowtorch' design has much to fear. At least from preamps based on Any Operational Amplifier Chip.
( .. and we have also another forum for .... Chip Amps 😉 )


Hope you do not mind, john curl, that I posted my AD797 Clone attachment.
At least it is a discrete amplifier schematic, using virtual transistors, BC550C etc..

Regards 🙂 lineup, Sweden May 2008

 

[scott wurcer]

One is a Quan-Tech resistor analyzer that I can use to check the "excess noise" generation of a resistor.

We use Quan-Tech's (the old ones with all the meters) to monitor our thin film, it's pretty rare to read more than 6-10nv at 10Hz on a 1k resistor that's 25 micon square and a few hundred atoms thick.

I know what you mean, the guy that designed our sources retired years ago but luckily he made sure we had the formula.

 

[scott wurcer]

Seems pretty clear what the Spy from PMI thinks of such components and Cryo-treatments, maybe Mr Ironside Hansen is willing to share his thoughts too ?

In the spirit of full disclosure; In 1988 we sent a Japanese company 12 dacs where 6 had been cryoed. They separated them back into two groups with 100% accuracy.

 

[jan.didden]

[snip]BTW I got the brush-off at the AES conference from DR. L, I guess I wasn't an insider. Also someone tracked me down to say that the distortion neutralization "had to be just feedback in disguse". Where have I heard that before?

Depressing. I just got a comment on my error correction article from someone 'proving' that it cannot possibly work, conveniently ignoring a working prototype. His comment was actually addressed in the article which he obviously missed. I wonder whether anyone still READS these days, or just jumps to conclusions on the face of a single concept diagram.
Maybe it's part of keeping fit, you know, jumping to conclusions, flying off the handle, that kind of stuff 😉 .

Sorry for the off-topic rant....

Jan Didden

 

[MikeBettinger]

Mike, which came first, the marketing or the discovery? (Of the naked Vishay resistor)

My offhand comments were not centered on whether or not the resistors worked but on the slant presented by the datasheet; "for the high-end when nothing but the best will do" paraphrased of course.

As has been pointed out, these have been available for years. I actually considered them two years ago when I built my preamp. I built two sets of boards and based all of the signal path resistor footprints on the Vishay S-102's. I built one set with the Vishays and Caddocks and the other with the metal film resistors I have used for years.

After reading about the naked Vishays on one of the threads here I looked into them with the thought that I should use nothing but the best, but then talked my self back into reality and bought the S-102s.

Bottom line, The magnitude of the difference between the two was such that I could live happily with either. This was the basis for my comment about other aspects of a design being more important to the end result.