John Curl's Blowtorch preamplifier part II

[fas42]

Originally Posted by kgrlee

We have the technology to get around wonky contacts!

The source is fed via a "hand crafted by virgins from solid Unobtainium" wire wound pot specially selected by JC himself to BOTH Blowtorch and the evil 4558 device. They feed matched Parasound A21s or some other choice device of JC's.

Switching is done by trained monkey ... I mean highly qualified engineer switching the speaker cables.

Sorry, Richard, you've just shot yourself in the foot ... how are we going to get around the "wonky contacts" between cable and speaker, eh? ...

Frank

[john curl]

Our double blind tests were not necessarily ABX tests. There are other forms that work better, in my opinion. You have my opinion from 32 years ago, IN PRINT. That is all I have to say.

[kgrlee]

Originally Posted by john curl

Our double blind tests were not necessarily ABX tests. There are other forms that work better, in my opinion.

JC, would you like to describe YOUR double blind tests?

I've described an alternative to ABX which I call ABC. Is this a form that in your august opinion "works better"? If not, have you any suggestions to improve it.

You have my opinion from 32 years ago, IN PRINT.

JC, your letter to the editor is somewhat vague about the test itself. Anyone have a copy of the original article so we can put JC's learned opinion in the correct context?

Sorry, Richard, you've just shot yourself in the foot ... how are we going to get around the "wonky contacts" between cable and speaker, eh? ...

No problem with that Frank. We just weld the cable to the speaker terminals like JC recommends.

The problem is changing the cables over at the two matched Parasound A21 outputs. JC, what welding rods do you recommend for this?

We could use the A21s to do the welding by shorting the speaker terminals but it's probably less complicated to train our monkey to use a welding torch and angle grinder. I'm open to suggestions.

[1audio]

Originally Posted by simon7000

OK you've convinced me to add the two bias resistors. However note the actual output is direct coupled and runs at 3.3 volts

The rubidium standard is the Stanford PERF10 Rubidium Frequency Standard - PERF10 which can lock to a GPS source for long term stability. The rated life of the lamp is greater than the design life of the system.

The VCXO details are not given on the schematic. It uses peltier devices to cool it. There are a few tricks in mounting it to reduce vibration transmission. Jitter is in the reasonable picoseconds range.

Using this quality of reference adds 0.12% to the cost of the entire system. The master clock syncs over 200 slaves.

As to the nice references, I can't disagree with the techniques shown, as I am using them to recover the signals from the fiber with them. Jitter is below what my AP can measure.

Schematic attached.

Now the issue is what will it take to measure the jitter?

Last to first, SRS has a really good new phase noise feature in their audio analyzer. Its also way cheaper than most commercial solutions. The sales guy claimed it can measure AES as well as the HF clocks. The floor I saw was in the -165 dB range and possibly below -150 at 1 KHz.

The SRS Rubidium is very good. Long term is better than a good crystal, but short term a free running really good crystal oscillator (Like a Wenzel) is better. And they can be made at audio clock frequencies. Getting ppb from one is well within their capabilities. The really good ones are export controlled so more trouble that they are worth. but cheaper than the SRS clock. You could use both and set the time constants to get the best of everything. Adding a GPSDO would be the final step and not expensive in this situation.

How much pulling on the oscillator do you need for this? Are you syncing to something like video?

Peltier coolers on a crystal is unusual to say the least. The high accuracy low phase noise (essentially very high Q) crystals (SC cut) need to be something like 80C to get stability from them. There is a whole science of double oven controllers for that. They don't pull very far but its probably not needed.

[john curl]

As I recall, Moncrieff's test was what you might call a double blind ABA test, using a multi-position SILVER switch wired for ABABABABA ... Then A and B are found later, once the choice is made. Works for me!

[john curl]

Go for it, Ed Simon! It is refreshing to see an all-out effort made. This was the original principle that the Blowtorch was made. Cover EVERY BASE possible. Accept NO compromise that is made for cost saving or ease in construction. Heck, we only had enough parts to build 50 units, why not? There was no mass production involved where a small cost saving saves millions of dollars. The real EXPENSE of the CTC Blowtorch is in the LABOR of designing, building and testing it.

[john curl]

This morning I thought that I might bring up the TRADE-OFF'S in audio design, that are of course necessary, to meet different cost levels and ease in construction.
For the record, for Parasound, I have 3 models of power amp that I put my name or reputation to. However, Parasound makes many more power amps, some at a similar price to some of my designs, most at a lower price.
The question is: Why buy a more expensive design than the cheapest one that will essentially fit your needs? I am not looking for ad hype here, or listening differences, just hard, cold facts about what the tradeoffs are. (more later)

[kgrlee]

Originally Posted by john curl

The real EXPENSE of the CTC Blowtorch is in the LABOR of designing, building and testing it.

JC, can you tell us a bit more about the testing seeing as Hirata, Quan and Listening were not on the agenda?

[simon7000]

Originally Posted by 1audio

Last to first, SRS has a really good new phase noise feature in their audio analyzer. Its also way cheaper than most commercial solutions. The sales guy claimed it can measure AES as well as the HF clocks. The floor I saw was in the -165 dB range and possibly below -150 at 1 KHz.

The SRS Rubidium is very good. Long term is better than a good crystal, but short term a free running really good crystal oscillator (Like a Wenzel) is better. And they can be made at audio clock frequencies. Getting ppb from one is well within their capabilities. The really good ones are export controlled so more trouble that they are worth. but cheaper than the SRS clock. You could use both and set the time constants to get the best of everything. Adding a GPSDO would be the final step and not expensive in this situation.

How much pulling on the oscillator do you need for this? Are you syncing to something like video?

Peltier coolers on a crystal is unusual to say the least. The high accuracy low phase noise (essentially very high Q) crystals (SC cut) need to be something like 80C to get stability from them. There is a whole science of double oven controllers for that. They don't pull very far but its probably not needed.

Demian,

I plan on picking up the SR1 analyzer very soon.

I have attached a shot of the sweep noise from an eBay $60 rubidium oscillator.

The roadies today use an Apogee Big Ben word clock on their consoles because they notice an improvement.

So we are in agreement that a high quality crystal oscillator is adequate. As the screen shot shows the 200hz sweep noise from a rubidium source may be a problem if not used with a crystal oscillator.

Where we differ is that my system is not just playback. I also have A/Ds and record. Accurate time stamps are very useful in recording. So the full works with GPSDO is useful. I expect the video guys will take a clock from my system.

Now as to crystal temperature. You are right in that crystals have long been designed to work in an oven, so they cut them to work best at an elevated temperature. However if you look at the curves you will see they flatten out at lower temperatures. One issue is how accurately you can control temperature. So my playing around has shown lower jitter at freezing. Due to the properties of the frost formation the temperature is quite uniform and stable. (Moisture in the air is the actual regulation mechanism!)

[mullardel34]

Originally Posted by john curl

The question is: Why buy a more expensive design than the cheapest one that will essentially fit your needs? I am not looking for ad hype here, or listening differences, just hard, cold facts about what the tradeoffs are. (more later)

John,

The only reason that has ever prompted me to purchase a particular audio component over another less-expensive, ostensibly comparably-performing audio component is the perceived sound of the component in my home music reproduction system. "Better sound" is the only cold, hard fact for the selection of audio gear, IMHO....

In my case, I only purchased my Audio Research D-79B power-amplifier (ARCDB - D-79) to replace my D76A power-amplifier (ARCDB - D-76) because the D-79B significantly raised-the-ante on the sonic performance of the D76A. Yes, these are "oldies, but goodies", but they've held their own in comparison with everything that I've tested in my reference system over the years.