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Old 23rd February 2012, 11:23 AM   #2701
DF96 is offline DF96  England
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Quote:
Originally Posted by dvv
when I tune to a local FM station, I get some wonderful LF transients which I barely hear, but I can see the bass membrane pushing air like crazy.
Does the tuner have AFC? Most older (i.e. non-synthesised) tuners have this to prevent drifting off frequency. Snag is that AFC is a feedback loop, which if poorly designed can have subsonic response peaks - and may even boost low audio frequencies.
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Old 23rd February 2012, 12:52 PM   #2702
dvv is offline dvv  Serbia
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Originally Posted by DF96 View Post
Does the tuner have AFC? Most older (i.e. non-synthesised) tuners have this to prevent drifting off frequency. Snag is that AFC is a feedback loop, which if poorly designed can have subsonic response peaks - and may even boost low audio frequencies.
No, it doesn't. It's a reVox B760 digital tuner.
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Old 23rd February 2012, 01:31 PM   #2703
a.wayne is offline a.wayne  United States
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Originally Posted by bcarso View Post
This came up because FT is writing some material for installers and asked me about power amps. He is now rattling cages at Harman to get the powercube testing reinstated, so this may lead to some actual improvements in testing methodology there.
Good news , I guess most would fear such a test , well anything that would make most amplifiers sweat ...
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Old 23rd February 2012, 01:41 PM   #2704
DF96 is offline DF96  England
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I'm surprised that a Revox puts out subsonics. Could it be long distance multipath? Aircraft reflections?
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Old 23rd February 2012, 03:59 PM   #2705
dvv is offline dvv  Serbia
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I'm surprised that a Revox puts out subsonics. Could it be long distance multipath? Aircraft reflections?
Neither, I think. This happens with one station only, others are just fine.
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Old 23rd February 2012, 04:02 PM   #2706
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Probably it was unstable high-end boutique mic pre.
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Old 23rd February 2012, 04:02 PM   #2707
bcarso is offline bcarso  United States
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Good news , I guess most would fear such a test , well anything that would make most amplifiers sweat ...
I had the need of a very cheap multichannel amp a couple years ago and bought a discontinued Best Buy in-house brand off the floor at my local store. It was a hoot to lift the hood and see the size of the mains transformer and the teeny bulk caps. I also cringed as I saw who made it for them, Inkel, a Korean firm that is notorious for various good reasons. Suffice it to say this amp would likely produce some pathological powercube graphs, particularly if one attempted to drive all channels at once.

What puzzles me is who might be left in the vast Harman empire who knows how to design non-switching amps. The company has been IMO on a downward spiral of truly ghastly proportions, with the occasional glimmer of hope here and there, since a CEO with no audio experience whatsoever took over, moved corporate HQ to Connecticut and replaced all of his direct reports. The company has since shed a plethora of talented people. Whatever issues one may have had with Sidney Harman, people used to say we could do a lot worse. They are being vindicated in that judgment! So it goes. Of course we have Bose and Monster et al. to compare to, which makes the situation seem less bad I suppose.
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Old 23rd February 2012, 05:30 PM   #2708
a.wayne is offline a.wayne  United States
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Harmon had an PhD in social psychology , i have always felt , if i had to do it all over again , this was the way to go in business and politics .. IYO what was the best era for Harmon products .....?
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Old 23rd February 2012, 05:45 PM   #2709
dvv is offline dvv  Serbia
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Harmon had an PhD in social psychology , i have always felt , if i had to do it all over again , this was the way to go in business and politics .. IYO what was the best era for Harmon products .....?
To the best of my knowledge, Dr Sidney Harman has graduated electronics in the days of DC electronics, just as the late Bernard Kardon did. According to his own words, Dr Harman couldn't be bothered to get into AC electronics, so he took up leading the company, while Bernard Kardon took over the engineering side.

In 1958, they invented the world's first stereo receiver. After that, they simply pursued the wide bandwidth philosophy of Bernard Kardon, actually employing Prof Dr Matti Otala for around 7 or 8 years. It is said that the one and only Citation XX amp, said to be able to deliver 500 Amps of current in short peaks, was actually made under Otala's strong influence.

Harman/Kardon Citation XX on thevintageknob.org

As for myself, I admit to having swallowed their philosophy hook, sink and fishing rod. If its open loop response is below 60 kHz, I failed to do the job. If it NEEDS more than 30 dB of global NFB, I botched it.

On the other hand, we do live in the digital era, and it is possible, even if improbable, that some ultrasonic spurious signals could just get into the power amp, so an input filter placed at 300...400 kHz is well advised. After all, once you open the window wide, you open it both to the sunshine and to the dust and airborne dirt.

Last edited by dvv; 23rd February 2012 at 05:48 PM.
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Old 23rd February 2012, 05:48 PM   #2710
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Hi,

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Originally Posted by a.wayne View Post
IYO what was the best era for Harmon products .....?
The original Citation Tube based range. It was downhill from there, ever accelerating like a vertical drop rollercoaster.

Ciao T

PS, I had a look at the HK680, Dejan holds in such great esteem, it's not a bad design, but I take the Tube HK Citation I/II any day.

Last edited by ThorstenL; 23rd February 2012 at 05:53 PM.
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