Sound Quality Vs. Measurements - Page 153 - diyAudio
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Old 28th January 2012, 09:04 PM   #1521
tvrgeek is offline tvrgeek  United States
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I just fount the interview with Lohstrom that Jan did. The schematic of the amp in that page looks nothing like the RA 840BX I have. The Rotel looks much closer to the "Basic" amplifier , Figure 3.1 in Cordell except without the Miller comp in the VAS and it has two compensation networks after the VAS. This is the amp Cordell uses as a starting point, where everything gets better. So, after I understand the Hafler, I should switch to understanding this one and "follow along" doing the calculations. It may be easier to understand. It too has features that don't make sense to me, besides a few drawing errors. Like .22 Ohms on each output emitter, but another .22 ohms on the input to the output network. This is the simplest of all my amps, yet the one that "passed". Wonder what that means?

I should get the service manuals for my 951's today and see if there is a family resemblance across 10 years. The 951's at lease have protection circuits in them. Just by parts count, must be pretty simple.
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Old 28th January 2012, 09:09 PM   #1522
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by CopperTop View Post
I'm sure you can measure a difference between capacitors - it would be surprising if there were no difference, and if there was a difference I think I could do that without a problem, thanks
Yet in post 1216 you claim the difference is unmeasurable as far as you know (I took exception to the "we"):

Quote:
Originally Posted by CopperTop View Post
So the difference between capacitors which is so small it is dismissed by many, and as far as we know unmeasurable
I somehow am unable to reconcile these to two statements, they cannot be equally true.

And I am not interested in what you should have said, but in what you claimed, in writing in public.

Quote:
Originally Posted by CopperTop View Post
but in this application and position in the circuit, what I should have said is, how measurable is the difference in 'warmth' of the sound?
Measurable in what sense?

For example a blind (not ABX) preference test could be used.

Quote:
Originally Posted by CopperTop View Post
It sounds as though it should shout out from the frequency response or other measurements. Sorry for my ignorance. How big is this measurable difference?
Which one?

In terms of measured distortion between a generic electrolytic exposed to around 2mA AC current (original DH-100 circuit) and my suggestion of around 2uA into a high quality film capacitor?

As a rough guess, a few orders of magnitude.

Between different film cap's, depends on many factors, anywhere between FA and 20dB.

Ciao T
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Old 28th January 2012, 09:09 PM   #1523
anatech is offline anatech  Canada
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Hi CopperTop,
Some capacitors do behave in ways that can destroy the accuracy of an amplified signal. As Thorsten has said, the type of capacitor used can make a huge difference in sound quality. Also remember that each capacitor type does have an application, something that the design does very well. Non C0G / NP0 ceramic capacitors would not be a good choice in a signal amplifier where voltage changes across their terminals, but are often the only choice at high frequencies seen in RF work.

How much effect a capacitor has in a circuit will depend. The worst case would be a high impedance point in a circuit that has a large changing voltage across that capacitor. Something like, say the voltage amplification stage perhaps? Some capacitors are very non-linear when passing a large varying current through them. A good example of this would be the output coupling capacitor used in unipolar amplifier designs (not bridged).

If a sonic difference is so great that it can be heard, for sure you can measure the parameter that is having this effect. You might have to work at discovering which characteristic is at fault, but it can be quantified.

-Chris
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Last edited by anatech; 28th January 2012 at 09:11 PM. Reason: inserted missing word
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Old 28th January 2012, 09:13 PM   #1524
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by tvrgeek View Post
I just fount the interview with Lohstrom that Jan did. The schematic of the amp in that page looks nothing like the RA 840BX I have.
My Service Manual says:

Rotel RA840BX4

That one is definitly an Ottalla/Lohstrom. I would have expected Rotel not to change the whole thing wholesale for a minor revision and that was the schematic I could readily find.

Ciao T
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Old 28th January 2012, 09:19 PM   #1525
tvrgeek is offline tvrgeek  United States
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Anatech,
3 out of 4 NAD's I have owned died. No failures of Denon, Hafler, B&K, Apt, Nak, Luxman, Teac, Jvc, Thorens, Kenwood, Onlyo,Sanyo Plus, and I can't remember what else. My NAD C30 CD is doing just fine. Fingers crossed as there are not many plain CD's left that fit on a 12 inch shelf. I did not see corrosion under the glue. No cats in the house though.

NAD's advertising was feeble compared to Curtis Mathis TV's though. "The best darn TV and worth the price". "Quality is Job One" Rule one in advertising, take your worst attribute and advertise it.
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Old 28th January 2012, 09:21 PM   #1526
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Thorsten, could you spell OTALA, rather than Ottalla? Thanks.
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Old 28th January 2012, 09:29 PM   #1527
tvrgeek is offline tvrgeek  United States
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Mine is just plain RA840 BX. I wonder if the schematic in Jan's article is the one you are thinking of?
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Old 28th January 2012, 09:32 PM   #1528
tvrgeek is offline tvrgeek  United States
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See if it uploaded this time
Attached Images
File Type: jpg 840bx.JPG (55.2 KB, 112 views)
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Old 28th January 2012, 09:36 PM   #1529
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by tvrgeek View Post
Mine is just plain RA840 BX. I wonder if the schematic in Jan's article is the one you are thinking of?
Yes, this is rather different.

Only distinguishing feature, Resistor loaded VAS to reduce open loop gain (the Hafler has it as well...).

Quite brutal.

Ciao T
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Old 28th January 2012, 09:43 PM   #1530
tvrgeek is offline tvrgeek  United States
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That is the R 632, Collector of VAS to ground?
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