John Curl's Blowtorch preamplifier part II

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I use this one, and it easily withstands any test we can imagine, including 100kHz sine and 20kHz square. Difficult test conditions make easy real life operation.

Pavel,

A very nice choice of capacitor! 400V/uS! Do you ever get a 200 watt 8 ohm output at 200,000 Hz to over stress it? :)

In some old tape players they used a metallized polyester capacitor 2.2 uf /250 VAC as I recall. They used to fail every two or three years of use. Taking them apart showed a nice burn out trace the entire length of the dielectric. Reduced the capacitance enough the motors would not run. So the solution was to use a 660 volt rated part. It was chassis mounted with fast-ons so the size difference was not an issue.

These look like they will not have the problem at all even on an AC line so a great part suggestion.
 
Thank you Ed, these are nice capacitors and they are MKP, metalized polypropylene ("The R46 Series is constructed of metalized polypropylene film
encapsulated with self-extinguishing resin in a box of material
meeting the requirements of UL 94 V–0").
It is good to have a look sometimes to other than "audio" brand of components. I started to use similar parts for the Zobel about >10 years ago, after a standard MKT capacitor exploded during similar test, at this position.
 
Thank you Ed, these are nice capacitors and they are MKP, metalized polypropylene ("The R46 Series is constructed of metalized polypropylene film
encapsulated with self-extinguishing resin in a box of material
meeting the requirements of UL 94 V–0").
It is good to have a look sometimes to other than "audio" brand of components. I started to use similar parts for the Zobel about >10 years ago, after a standard MKT capacitor exploded during similar test, at this position.

Pavel,

There is one thing we disagree on though. Otto Zobel worked at Bell labs and designed his network to be a constant input impedance using the image technique.

So I can see calling the series RC network across an HF driver a Zobel as it tries to flatten the impedance to allow simpler crossover design or even better match cable loss (Zobel's original goal!)

So even though this is a series RC network it is not intended to be constant impedance and probably shouldn't be called a zobel.

Snubber or HF load is probably a better term.

ES
 
OK, I have no problem with this, and we called it Boucherot long ago :D

Boucherot? the guy was a genius but I am not sure that this was his work either.

I think the humor is if you place the network across a tweeter it is a zobel, but when used at an amplifier output it is not. No wonder some folks get confused.

But when I use your find of a snubber I'll call it a "Pavel."
 

Thanks, I knew him from Ocean and other power electronics. But it is still the same network used for improving the impedance image, here though the intent is damping oscillations. So Boucherot cell would be correct for amplifier outputs and Zobel network on drivers. Jargon hides the issue that it is the same topography of an RC network.
 
Mooly, I think that is what happens, whether we know it or not. To take a drastic example, if you're used to an opan and airy sounding amp, less than that will not suit you. Lately, for technical reasons I had to replace my own speakers with my old but refreshed AR94 speakers. The sound was different of course, but fortunately most of it was along similar lines as with my speaker, so the change was not too big, but it was easily detectable, as were the differences, mostly at the extremes. Everything else was exactly the same, so I detected them according to what I am used to and expect to hear.
 
I think that Mooly is 'rambling' in the right direction and has raised an important issue. This is why it is important for us to listen to live music as often as possible. Far better to have a true reference to what you replay on your kit.

[Having said that I have always preferred location recordings of live events to studio recordings - except perhaps for some small simple music. Live performance recordings usually have a sense of 'occasion' and continuity which is (usually) often lacking in a studio recording.]

I have a small collection of old analog master tapes which sound totally totally different to the eventual vinyl pressed from them. It was always important to me to remember the shortcomings of the post-production changes when listening to and comparing the replay systems.

AS for our systems having signature sounds I am sure that Mooly is right and that we do make the comparisons he mentions. Live performance attendance will show us just how poor our total system is (and this includes our listening rooms - I cannot make my listening room take on the characteristics of say Wembley Arena on one hand and St John's Church in Smith Square on the other.). All we can - at present - hope for is something which brings the spirit of performance to us over as large a range of recordings as possible. I suspect that this is the reason why SET amp based systems are so successful for many when coupled with simple single driver speakers - despite their numerous faults in the eyes of lab. testers.

It is for these reasons that for me the ultimate test of a system (including its location) is "Can I live comfortably with this signature and performance ?", rather than having to know how it measures. It is a fact that the better specified systems have almost always fallen short - for me - of satisfactorily meeting this requirement. ;)
 
Speaking of 'open', 'airy' and other terms used to describe the 'sound' of an amp, try this, guys :D

Alan Alda Center for Communicating Science?

All right, and how would you describe a recording which appears to be unfettered by personal taste (0f the sound engineer) and the room it is played in, but rather conveys a feeling of free space, as opposed to the same material coming across as having been made in a small acoustically untreated room?
 
I think that Mooly is 'rambling' in the right direction and has raised an important issue. This is why it is important for us to listen to live music as often as possible.

I have a small list of calibration references, e.g. a small chapel in the east of the country for 'a capella'.
Acoustics of most live venues suck in a major way, imo. Call me an arrogant P.
 
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Mooly, I think that is what happens, whether we know it or not.

I bet stranger things have happened. Perhaps new amp designs should be tested using 100% unfamiliar music first. Or take say 10 tracks from a consistently recorded studio album and listen to 5 random tracks via amp #1 and the other 5 via amp #2. As the listener, you would not know which track was tagged to which amp. You would need to live with that combination for some time so that the each track became familiar. Then reverse the set up and see whether any preferences follow the amps or not. Method flawed but you get the idea.

Mooly,

Read the book "On Intelligence" by Jeff Hawkins. It nicely explains the current brain research and even postulates why learning new things changes with experience.

ES

Thanks Simon.
 
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