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Old 17th March 2013, 10:46 AM   #9491
RCruz is offline RCruz  Switzerland
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I am starting to really like the buffer with the ccs in it's tail. Bass gains in definition and there is an overall increase in speed and attack... This requires much care in setting the correct riaa curve because it can "show" any flaws that where hidden by the buffer with large Rs arrangement.... I believe this resistor acts as a local feedback that tends to mask things a bit.

I wonder if we could have even more gains by fixing the drain operation voltage with an active boostrad over the common source.....
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Old 17th March 2013, 10:55 AM   #9492
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RCruz,
Would you skecth what you have tried.
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Old 17th March 2013, 11:13 AM   #9493
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Hi buzz, just followed the last schematic for the folded where there is a ccs under the output CS.

I edited my last post with a schematic from AR
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Old 17th March 2013, 11:23 AM   #9494
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Ok. That is what i have. Thanks. I like your idea and Allen has a bit of a reputation with that particular preamp. I listened again yesterday with brothers ortofon bronze. It is simply wonderful. I am sure there are others that are as good, but at this point it would seem we are just talking flavor rather than quality.
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Old 17th March 2013, 11:35 AM   #9495
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What output cap are you using ?

My latest build uses a plain MKP from auricap and it just sounds incredibly good as is....
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Old 17th March 2013, 11:56 AM   #9496
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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.
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Old 17th March 2013, 12:00 PM   #9497
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RC here is a bunch of circa 10mA 170s and an 8mA one (magenta). Says -0.59V Vgs(off) for 1uA Id when the ~10mA ones are -0.65V averagely. Anything else you wanna know?
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Old 17th March 2013, 12:03 PM   #9498
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You are right... this design can be finetuned by choosing the comoponents.... In my previous buildI used clarity cap MR and i was a really big improvement.... With this last one I guess it will even be more noticeable.

After one night burning, the Benz is now singing better than ever....
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Old 17th March 2013, 12:11 PM   #9499
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Quote:
Originally Posted by Salas View Post
RC here is a bunch of circa 10mA 170s and an 8mA one (magenta). Says -0.59V Vgs(off) for 1uA Id when the ~10mA ones are -0.65V averagely. Anything else you wanna know?
Perfect.. this info corroborates my last fet measurements.

Must update the simplistic calculator
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Old 17th March 2013, 12:18 PM   #9500
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Quote:
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.
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....
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