John Curl's Blowtorch preamplifier part II - Page 1511 - diyAudio
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Old 18th August 2011, 01:18 AM   #15101
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Default Perseid meteor shower sound

Diversion. Listen to this:

Perseid Meteor Shower Sounds: Space Surveillance Radar Captures Celestial Audio (LISTEN)

Don't know how to pick up sound with a radar, but still cool.

vac

Last edited by vacuphile; 18th August 2011 at 01:22 AM.
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Old 18th August 2011, 04:30 AM   #15102
Pano is offline Pano  United States
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Same way you do with a radio, I guess. Thanks for the link.
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Old 18th August 2011, 11:06 AM   #15103
Jakob2 is offline Jakob2  Germany
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@ Thorsten_L.,

even if it is known that each switch position is connected to a different DUT, it is still a double blind test if the switching person and the listener do not know what DUT it is.
It might need more trial to reach the same level of significance, but that is normally a minor problem.

@ SY,

in fact the comparison of coupling caps was the very first controlled test we did aroun ´84.
Two capacitiors with different dielectrica from different manufacturers 4.7µF/5% each, output impedance <100Ohms, input impedance 47k.
Single blind test, 5 trials, positive identification of the better capacitor was needed for a correct answer. (better as chosen during the preceding sighted listening test).
I got 5/5 (actual p=0.031), the subjective evaluation led to the impression that the difference was´ huge´ yet hard to detect in a blind test at first. After we got used to the procedure the difference was still ´huge´ even under test conditions.
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Old 18th August 2011, 11:44 AM   #15104
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Hi,

Quote:
Originally Posted by Jakob2 View Post
even if it is known that each switch position is connected to a different DUT, it is still a double blind test if the switching person and the listener do not know what DUT it is.
It might need more trial to reach the same level of significance, but that is normally a minor problem.
In our case the question we are asking is "which is better" (differences are taken as existing), so for our use the protocol is more suited.

Quote:
Originally Posted by Jakob2 View Post
I got 5/5 (actual p=0.031), the subjective evaluation led to the impression that the difference was´ huge´ yet hard to detect in a blind test at first. After we got used to the procedure the difference was still ´huge´ even under test conditions.
Yes, this issue (unknown procedure, test-stress) together with expectation bias (pacebo/nocebo effect) combine to make getting "null results" quite easy, especially in the kind of challenges ABX proponents are want(on) to issue.

To me for example it is crucial that s much information is extracted with as few trials as possible, this reduces the needed attention span and stress (and cost). Equally it is VERY important to me that listeners are familiar with the system, the music and the process, yet that the identity of the change being evaluated is kept secret, so where there is no expectation there is no expectation bias and stress and unfamiliarity is minimised.

Of course, unlike some, I am not in the business of reliably producing null results in blind testing regardless if real differences are present or not. My game is in answering the question if a cheaper part can perform subjectively as well as an expensive one and which of those available are most suitable to my requirements, so my methods of course differ from those employed by the ABX Mafia.

Ciao T
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Old 18th August 2011, 11:58 AM   #15105
rsdio is offline rsdio  United States
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Quote:
Originally Posted by john curl View Post
Everyone, and anyone who wants to know about the BLOWTORCH principles, limitations and costs, just look at the first 100 pages of the previous Blowtorch thread.
Ok, I just started skimming that thread, and message #34 says
Quote:
Originally Posted by SY View Post
Just chatted with JC. Yes, the case is indeed milled from a solid billet of aluminum. Pantograph lettering. $3000 manufacturer's cost for the case alone. All FET, no feedback, servoed. First stage is 4 quadrant comp diff, second is folded cascode using MOSFETs run at high current. Servo with roughly 1 sec time constant.
This has me baffled - the definition of 'servo' involves feedback. So, how can the Blowtorch be "no feedback" if it includes a servo?
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Old 18th August 2011, 12:58 PM   #15106
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Perhaps the real meaning behind 'no feedback' was actually 'no feedback to speak of within the audio band' ?
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Old 18th August 2011, 12:59 PM   #15107
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Quote:
Originally Posted by rsdio View Post
Ok, I just started skimming that thread, and message #34 says

This has me baffled - the definition of 'servo' involves feedback. So, how can the Blowtorch be "no feedback" if it includes a servo?
The servo only corrects the DC errors, the ac gain is unaffected by this. So John is correct in what he says about his design. the servo is to keep the output node at 0 volts.
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Old 18th August 2011, 01:02 PM   #15108
SY is offline SY  United States
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Yes- "no feedback" in the audiophile sense (I'm sure there are also followers in there, which in a technical sense is absolutely feedback, but there's no explicit out-to-in loop).
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Old 18th August 2011, 01:03 PM   #15109
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Jakob, who is "we"? And where would I find details on the test setup? Danke schoen!
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Old 18th August 2011, 01:11 PM   #15110
DF96 is offline DF96  England
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So the servo has a brickwall filter? In a no-signal-cap, DC servo design the LF point is set by the (capacitors in the) servo rather than the (capacitors in the) main amp circuit. Unless done very carefully, this could be worse. Getting a servo right is much harder than getting a CR rolloff right.

Yes, a servo means feedback at DC and subsonic at least, tailing off into the audio band. A 1 sec servo time constant means (other things being equal) an LF point of 0.16Hz so feedback is 40dB down at 16Hz. Very small, but not negligible?
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