Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Seduction => Topic started by: balancedtriode on September 29, 2010, 07:16:50 AM
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i just finished my stereomour ... it sounds unbelivable.
just ordered the seduction phono stage and would like to upgrade the caps like i did in the stereomour
was wondering
what the values of the caps are so i can order caps b4 it arives
thanks in advance
-c
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Seduction stock caps - most important ones first:
Interstage 0.1uF/400v
Output 0.47uF/400v (can be larger; we use 1.0uF in Eros)
RIAA caps (n.b. these must be 5% or better precision)
0.033uF/400v
0.010uF/400v
0.0012uF/630v
High voltage power supply 220uF/200v or 250v - three of these
Low voltage power supply 10000uF/10v - one of these
Any voltage rating over 250v is OK as long as the cap can fit. Physically large caps and/or long leads make the circuit more prone to RF interference. Just sayin'.
There are three potentially significant resistors as well:
Input 47K - many experimenters say this is the most significant one.
RIAA input 66.5K 1%
RIAA turnover 9.64K 1%
If you don't use the C4S upgrade, then the 18K/1watt plate load resistors are important; they must be able to handle DC current quietly, so metal film or non-inductive wirewound are preferred. Stock is a good carbon film which we think works well. Avoid carbon composition or metal oxide!
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thanks paul one more question
how many of each cap are there
probably 2 right?
-c
edit:just notice u listed the number of caps
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Interstage and output are pairs. Each of the RIAA are also pairs.
As PJ points out the B+ power supply requires 3 caps, common to both channels.
The heater supply is a single capacitor.
PJ and Doc are very careful with choosing components.
And from what I understand the RIAA EQ caps are most important to be the designed value. I don't know if improving the make up of them matters. To get an accurate RIAA you want the caps to be as close to the specified value as possible.
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Unless you plan to use film cap (very large) in the power supply, I would stick with the stock caps. They are pretty good for electrolytic...John
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Just a note on power supply capacitor size. This is a very common misunderstanding. When the capacitor is "small" then the current through the rectifier is limited by the capacitor's impedance and a larger cap will draw more current. But once the capacitor is "large" then the peak current is limited by the transformer's resistance. The boundary between "small" and "large" occurs when the series resistance is on the order of the capacitive reactance at the power frequency (i.e. 60Hz). In the old days of vacuum tube rectifiers, this was important and still is, but solid-state rectifiers have a much greater peak current capability relative to their average current rating and such supplies are usually designed with very "large" capacitors.
For example, in the Seduction the power transformer resistance is 0.58 ohms (including the reflected primary) and there is another 1.2 ohms before the capacitor, for a total of 1.78 ohms. At 60Hz, a 1500uF capacitor would have that reactance, and the stock 10000uF is obviously "large", and a capacitor even very much larger will not draw much more peak current.
I just now modeled this in PSUD, and the stock supply draws 1.9826 amps peak. With a cap 10 times larger, it draws 2.016 amps - only 1.7 percent more. So if you can find room for a larger cap, it will work just fine, and will reduce the ripple on the heater supply. I'm not saying you can hear that, just that it's OK to try it and find out if you can hear it. :^)
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Can I jump in with a generic Seduction question. Is there any reason I why I can't replace the stock group plane with one of solid copper?
Thanks,
alan
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...Is there any reason I why I can't replace the stock [ground] plane with one of solid copper?...
None at all. Just remember, if the copper is thick it can be hard to solder to unless you have a high-wattage iron.
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Thanks Paul
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Hi Paul,
I'm currently building the Seduction and I have a pair of 2.2uF (450V) Auricaps in the parts bin, would these be acceptable drop-ins for the output or are they too large?
TIA
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I have had 2.2uF in my Seduction for some time. There has been no problems. I think a long time ago, before I put that large a capacitor in my Seduction PJ said it didn't matter.
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Hello,
Does anyone have a good source and/or recommendations for the RIAA caps? Parts Connexion doesn't have the lower values (.033uF and .0012uF) and even eBay doesn't have much. They do have Russian PIO but those are usually only rated at 200V. As well I assume that the vintage Mullard Mustard caps that I see on eBay are probably a bad idea due to their age - has anyone tried them?
Thanks
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You want 5% or better caps here, to maintain RIAA accuracy. They are hard to find!
One possibility is to change the whole circuit to use 0.010 and 0.030uF; you can make up an 0.030uF from three 0.010's in parallel, and that value is usually available in whatever flavor you like. Here's the directions in brief:
Change the 66.5K resistor to 73.2K 1%
Change the 9.64K resistor to 10.5K 1%
Change the 0.033uF capacitor to 0.030uF
Change the (0.010+0.0012uF) capacitor to 0.010uF
If there's a revision some day, this will be in it.
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Thanks Paul. I think that I will try that. I found something you wrote on the old forum about the Rel-Cap Polystyrene 0.01uF 2% - they are still available at Parts Connexion so I will order some. I will continue to search for a 0.03uF so that I don't have to use three is parallel but if I have to I will do it that way.