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    quad cap quandry

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    Captain Coconut

    Posts : 213
    Join date : 2009-10-13
    Age : 64
    Location : Great White North

    quad cap quandry

    Post by Captain Coconut on Sat Jan 25, 2014 12:11 pm

    I find myself agonizing over capacitor values in the power supply of the ST-35. I have posted this same query on another site and got one response from a member who is also on this forum. It was advised to keep the 1st section lower than the 2nd. Dave's Lab (who inherited Audio Regenesis) uses values of 47-120-120uF, which is in keeping with a lower 1st stage. Diytube, in their version of this amp, uses 120-120-120uF. Dynaco uses 60-40-20uF in the original. (I'm leaving out the final stage since I'm using the Enhanced Fixed Bias and using a separate cap for this).

    I don't see any need of going over 120uF in any stage, but I wonder what would be optimal values. Currently I'm using an 80-40-30-20 quad cap where I've strapped the 30 and 40 together for the 1st stage, to give me a 70-80-20uF set-up. The driver stage (20uF) might be a little wimpy, so I might reconfigure it to 40-100-30, or 40-80-50, or 50-80-40. As you see, there are several combinations available. How would you configure the 80-40-30-20uF cap that I have? And what would you use if you were doing a scratch build?

    Thanks, CC

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: quad cap quandry

    Post by peterh on Sat Jan 25, 2014 12:33 pm

    Captain Coconut wrote:I find myself agonizing over capacitor values in the power supply of the ST-35. I have posted this same query on another site and got one response from a member who is also on this forum. It was advised to keep the 1st section lower than the 2nd. Dave's Lab (who inherited Audio Regenesis) uses values of 47-120-120uF, which is in keeping with a lower 1st stage. Diytube, in their version of this amp, uses 120-120-120uF. Dynaco uses 60-40-20uF in the original. (I'm leaving out the final stage since I'm using the Enhanced Fixed Bias and using a separate cap for this).

    I don't see any need of going over 120uF in any stage, but I wonder what would be optimal values. Currently I'm using an 80-40-30-20 quad cap where I've strapped the 30 and 40 together for the 1st stage, to give me a 70-80-20uF set-up. The driver stage (20uF) might be a little wimpy, so I might reconfigure it to 40-100-30, or 40-80-50, or 50-80-40. As you see, there are several combinations available. How would you configure the 80-40-30-20uF cap that I have? And what would you use if you were doing a scratch build?

    Thanks, CC

    It's a question of how much ripple you tolerate. How much is it today ? How much hum
    is in the output terminals ? And, how much of that hum is 120hz and how much is 60hz ?
    ( 120hz might be reduced by larger caps / adding a choke, 60hz is more likely picked up in the signal path).

    Optimal finally, from what view ? Cost efficient ? Power consumption ? sound quality ?

    DarthBubba

    Posts : 81
    Join date : 2012-05-05

    Re: quad cap quandry

    Post by DarthBubba on Sat Jan 25, 2014 5:29 pm

    Captain Coconut wrote:I find myself agonizing over capacitor values in the power supply of the ST-35. I have posted this same query on another site and got one response from a member who is also on this forum. It was advised to keep the 1st section lower than the 2nd.

    I'm not sure, but I believe that "rule" (no more than 40uF between the diode tube and the choke) was a function of not over-drawing the vacuum tube rectifiers used in amps prior to the ST-35/SCA-35.  The solid state diodes in the ST/SCA-35 probably would not be damaged by the momentary surge.  I use inrush limiters on mine, but I'm a "Belt-and-suspenders" kinda guy.

    Captain Coconut wrote:Dave's Lab (who inherited Audio Regenesis) uses values of 47-120-120uF, which is in keeping with a lower 1st stage. Diytube, in their version of this amp, uses 120-120-120uF. Dynaco uses 60-40-20uF in the original. (I'm leaving out the final stage since I'm using the Enhanced Fixed Bias and using a separate cap for this).

    I dunno; a high ripple current cap in the first cap location was my major concern.  Low-Z/low-ESR caps were used after the choke (yes, I use a choke).

    Captain Coconut wrote:I don't see any need of going over 120uF in any stage, but I wonder what would be optimal values. Currently I'm using an 80-40-30-20 quad cap where I've strapped the 30 and 40 together for the 1st stage, to give me a 70-80-20uF set-up. The driver stage (20uF) might be a little wimpy, so I might reconfigure it to 40-100-30, or 40-80-50, or 50-80-40. As you see, there are several combinations available. How would you configure the 80-40-30-20uF cap that I have? And what would you use if you were doing a scratch build?

    I'd go 40-80+30-20 or 40-80+20-30 to give the output tubes the biggest, quietest reservoir to draw from.  If I were scratch building a system I'd start with a chassis with more room underneath to stash chokes, big coupling caps, big power supply caps, and so forth out of sight.  Very Happy

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