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Old 30th July 2014, 07:32 AM   #14091
fas42 is offline fas42  Australia
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Originally Posted by dvv View Post
Frank, the Otala/Lohstroh amp proved that you do not need fast output transitors to have a fast amp. Rated at 25W/8 Ohms, it hit 100 V/uS. Is that fast enough for you?
Really sharp slew rate is needed for FB to work properly, in amplifiers that essentially depend upon it. For those that have minimal global FB, far less of a problem, but then their outputs working properly are very dependent on the load being 'nice' to them. So, it's not Black and White - I prefer the amp to be able to take on all comers in terms of the load, and have the speed internally fast enough to react to all transient current demands. And that's not even considering how well behaved the power supply is while this is going on ...
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Old 30th July 2014, 07:43 AM   #14092
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Originally Posted by jcx View Post
are you serious? - or is this article totally wrong http://www.electrocompaniet.com/file...Vintage_EC.pdf
Hmmm ... treble distortion goes through the roof, and miniscule power supply. At a guess, my DIY gainclone had voltage rails at least 100x as stiff as that design ...
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Old 30th July 2014, 09:41 AM   #14093
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Originally Posted by gpapag View Post
The repeating large peaks (0.55Hz) are the 'once per revolution' artifact.
Donít assume that it is all due to the TT.
Most of it (if not all) is due to record eccentricity. How can you verify this?
If you have one test record only, shift itís position 90, 180 and 270 degrees in respect to the platter and repeat the test. Most probably you will notice a change in the amplitude of the 0.55Hz peak if there is also platter eccentricity (phase cancellation btn possible platter eccentricity and record eccentricity). If you will not notice a change in the amplitude, it is all due to record eccentricity.
Changing to different test records, amplitude will change (differences in records eccentricity).

We also see a second pattern in Janís diagram. It is a slower rotational velocity variation around 0.1Hz which may be due to belt and/or suspension stretching (I doubt the latter) .

The spikes and double peaks seen on the main waveform diagram are of some concern.
How did you produce this diagram Jan?

George
Bingo.
Bingo.
Bingo.
Adjust+

Actually the major portion is from the record hole which is larger than the spindle diameter leading to an eccentric record position, and by finicking the LP position I can bring it almost to zero.

Jan
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Old 30th July 2014, 09:54 AM   #14094
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I was not referencing your graph Jan, actually just looked at it now, what TT are you using as its very a rare LP which fits my tables loose even thou LP ECCENTRICITY can still be an issue..

Do you clamp after adjusting ...?
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Old 30th July 2014, 09:57 AM   #14095
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Its a basic Mitchell TechnoDec. I am using a clamp but that doesn't prevent the record being placed eccentric before clamping.
The test record hole is clearly larger than the spindle diameter, but I haven't checked out which of the two is out of tolerance. The test record comes with Adjust+.

Jan
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Old 30th July 2014, 10:08 AM   #14096
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I meant clamping after adjusting and Yep adjust+ comes with a test record and is a pretty powerful tool .....

Last edited by a.wayne; 30th July 2014 at 10:11 AM.
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Old 30th July 2014, 10:48 AM   #14097
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Originally Posted by jan.didden View Post
Thank you Jan.
In case you have finely adjusted the azimuth of your cartridge acc to this SW, were you able to notice audible difference compared to your previous Ď0 degreesí setting?

George
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Old 30th July 2014, 11:02 AM   #14098
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My RB-150 arm does not have the option to change azimuth; measuring it, it is at -0.5 degrees.

The res frequency of this arm and Ortofon Salsa seems OK though.

Jan
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Old 30th July 2014, 12:01 PM   #14099
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(I canít find a Rega RB-150 arm). You can always shim under the headshell if you are mazo enough.
If you experiment with shimming, record the accompanying change of cartridge/arm resonance peak.

George
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Old 30th July 2014, 12:13 PM   #14100
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Originally Posted by gpapag View Post
(I canít find a Rega RB-150 arm). You can always shim under the headshell if you are mazo enough.
If you experiment with shimming, record the accompanying change of cartridge/arm resonance peak.

George
Sorry its an RB-250. Yes its relatively easy to fix it but I just haven't taken the time for it.
Too busy with next Linear Audio Volume :-)

Jan
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