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Old 17th March 2013, 12:19 PM   #9501
Salas is online now Salas  Greece
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Originally Posted by buzzforb View Post
SIO.
My brother will not let me play the cap game with his RIAA, so I will have to do it with my version. When we changed from the original Obbligato to the SIO, I knew this was an excellent pre. THe reason being, the cap largely defined the sound. I cannot emphasize this enough. If you want to "hear" a cap, this is the design for it. I wish i had a lot of cap experience, because if i had a favorite, it would be found in both coupling cap positions. Rush has used a DCB1 as the output buffer, allowing for small but high qulaity interstage. This may be the ideal scenario, but i do like the simplicity of teh current setup. If someone told me the copper VCap would improve sound, I would have no qualms buying it.
What this preamp is? I say that its a 5 yrs slow investigation of how far simple classic concepts can take us for replaying vinyl. No super clever circuitry aids (the designer ain't particularly bright in handling complex electronics anyway, not an engineer), SE open loop, few junctions, an alike philosophy PSU to package it. There are loose ends of course in this minimal control approach that may allow some parts coloration come through. How do you solve this? With money, can be an automatic answer. And if you want it be best? With more money! Well, not always... With experience in building and tuning and decent parts you can make it sing great. Just takes some hands on and after a couple you get the knack.
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Old 17th March 2013, 12:29 PM   #9502
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He has integrated MingDa. As for RIAA caps, they have remained equal. The only thing that has changed is the output cap. I dont doubt you tha spending more money is not necessarily the best route. I personally do not buy into that thinking. I was just saying that the circuit is very much worth tailoring and I wish i had more experience with individual caps as I think you could pretty well define your sound with this thing. If RIAA cap is about value more than anything, I will take that approach and use good quality Siemens Ks in exact values. Reasonable price and very well regarded polystyrenes, mostly due to tight winding and superior quality control. Or so i have heard. I will focus my playing with the output cap.

As you know, I very much like your philosophy. Not trying to improve anything. Just tweaking to my ears, as these designs seem well suited for.
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Old 17th March 2013, 12:34 PM   #9503
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They are made for the joy of audio diy mainly. Not carved in stone. Your bro is not letting you touch it though. He must be fully content I guess.
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Old 17th March 2013, 12:35 PM   #9504
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Irritatingly so
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Old 17th March 2013, 12:36 PM   #9505
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P.S. Pay attention to the interstage capacitor also.
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Old 17th March 2013, 12:40 PM   #9506
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Beware.... I played a lot with cap types in the riaa filter circuit and in the beguinning I believed the differences I heard where due to cap type... I have built many and now I know the cap value is determinant... not cap dielectric or electrode material.

For instance, switching from 15.15nF to 15.6nF totally kills the magic... the same with the 47n that should not be replaced by 46,5 or 48n....
Your conclusion makes scientific sense.
But even though I am not a believer in much of the nonsense reported in sound quality comparisons, I must forewarn about reading too much into a purely "capacitance value" effect.

In a RIAA stage the capacitors are imposing a very significant impedance to passing the Audio Signal. This is quite different from coupling capacitors where the audio portion of the AC signal is insignificant.

Where a capacitor has significant impedance at the wanted audio signal frequencies then dielectric does have a significant effect on the way the signal is transferred across the capacitor.
Dielectric will have an audible effect even when cap values are very accurately matched. It may take extreme differences in dielectric parameters to show the audible effect for some of the caps in the RIAA, but do not discount the notion that some caps may show an effect for what might appear to be quite small differences in cap parameters.

But this can ONLY be validated if the differences in cap values are very rigorously eliminated for the whole range of operating temperatures inside the working RIAA stage.
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Last edited by AndrewT; 17th March 2013 at 12:45 PM.
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Old 17th March 2013, 12:40 PM   #9507
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I remember your suggestion about inter-stage value. What would that change bring? Both are in signal path, so both should be important. I understand function of output cap value and would assume the interstage serves a simliar purpose
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Old 17th March 2013, 12:44 PM   #9508
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Asking me or Andrew?
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Old 17th March 2013, 12:46 PM   #9509
AndrewT is offline AndrewT  Scotland
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Buzz,
does the capacitor have significant audio signal across it?
or
does the capacitor have insignificant audio signal across it?

Once you know that, you can make a decision on whether the capacitor type needs special consideration for optimum signal passing capability.
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Old 17th March 2013, 12:50 PM   #9510
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You.

@Andrew,
Caps have a sound. I dare not even speculate as to why this is, but they do. Both of the coupling caps do pass the signal, so i assume that they will ultimately put their "performance imprint" on the sound. Significant is a tough question. It is significant enough that the value is important for the passage of the signal across the full audio band. Dont know if that is correct thinking.
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Last edited by buzzforb; 17th March 2013 at 12:53 PM.
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