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Old 12th September 2012, 12:32 PM   #27571
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John,

Looks like the second stage of maybe the JC 80 Phono preamp stage with active RIAA bass boost. First stage if it follows your usual topology likely has passive RIAA HF filter at it's output. Was the input jfet 2sk146 or a pair of thermaly coupled 2sk147 - don't think you were using 2sk389 back then ?
Is there a door prize? A bottle of Patron anjeo ( I don't like the silver) ? A six pack of Bud? Would a double blind test reveal the difference between them or am I so burnt out I couldn't tell?

Last edited by ticknpop; 12th September 2012 at 12:39 PM.
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Old 12th September 2012, 01:42 PM   #27572
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Quote:
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If after listening for a while, you "learn" to spot something in the sound, why would it go away just because you're not allowed to use anything but your ears?
Because of a possible fault in the test and it's procedure. Such a possible fault may be a change in the way of listening, compared to normal listening, too short listening sessions, etc'.

This is why for such test to be valid, it must be able to give also positive results.
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Old 12th September 2012, 02:16 PM   #27573
coluke is offline coluke  Italy
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Quote:
Originally Posted by Joshua_G View Post
Because of a possible fault in the test and it's procedure. Such a possible fault may be a change in the way of listening, compared to normal listening, too short listening sessions, etc'.
Still wondering why if you can't hear sound differences in a blind test, then the test itself must be possibly faulty by definition.

L.
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Old 12th September 2012, 02:29 PM   #27574
zinsula is offline zinsula  Switzerland
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Of course. But, if for example, the switch box does overshadow the differences of two amps, you would have the differences without switchbox but not in the test itself.

That's one reason why it's important to insert, in this example, two amps in the setup which are known to show differences when tested blind.
If the test person can hear it, you may go forward and insert the amps of interest.
If not, either the setup or the test person (or, in other tests, the measurement gear etc.) is incapable of differentiating, despite in an earlier controlled test it was possible to do so.

Just one example.

You do that in many tests. Inserting a kind of baseline group, with known characteristics.
If the DUT's behave differently as previously known, you have to investigate further, and the test as it is is not valid anymore.
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Last edited by zinsula; 12th September 2012 at 02:33 PM.
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Old 12th September 2012, 02:50 PM   #27575
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I didn't realize that I could confuse anyone with this schematic. No wonder, that its big brother, the Para JC-2 was virtually ignored. (Shock and Awe, I guess) '-)
It comes from a NOT produced discrete phono stage, designed 18 years ago for Parasound. This happens to be the second stage, and it has part of the RIAA in the feedback loop.
The design is modeled closest from the AD825 IC video amp, but with a complementary mos fet output stage. Most parts would be Toshiba, jfet would be 2sk170, but BF862 would probably work OK.
It is here as an alternate example that has been offered to rival the truly complementary jfet input design of the Vendetta. It is not as 'good' if 'quality' or elegance is important, but it will measure and sound very good.
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Old 12th September 2012, 02:51 PM   #27576
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Coluke, 'A breath of fresh air' '-) You noticed!
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Old 12th September 2012, 02:54 PM   #27577
coluke is offline coluke  Italy
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I think that selecting
Quote:
Originally Posted by zinsula View Post
two amps (...) which are known to show differences when tested blind.
without blind testing them could be quite difficult...

As far as the switchbox influences and DBT procedures are concerned, I'd like you to have a look at a real example: http://www.nousaine.com/pdfs/Wired%20Wisdom.pdf, and tell what in your opinion is wrong with test methodology and results.

L.
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Old 12th September 2012, 03:10 PM   #27578
zinsula is offline zinsula  Switzerland
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You misunderstood.
- Switch box was an example which could influence the outcome due to the test setup. Could be somthing different too. Eg. Room, Speakers, whatever. Not really important, it was an example.

- The two amps formerly tested as being different, difference which had be detected in a earlier DBT test (by, perhaps, different testers in another test setup, but accepted to be different sonically by a scientific method)

I was merely explaining why it's important to have positive controls too.
If the test person is deaf, no difference is there between an IPhone speaker and PA speakers, when you evaluate it's test results.
You have to find out before carrying out your test, that your measurement setup is sensitive enough for a certain task.
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Old 12th September 2012, 03:20 PM   #27579
SY is offline SY  United States
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IOW, frequency response.
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Old 12th September 2012, 03:47 PM   #27580
zinsula is offline zinsula  Switzerland
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Quote:
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IOW, frequency response.
Fine if this (only this, i understand?) positive control works reliable enough for you.
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