• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Cary SLP-90 preamp power supply

Ok gents here is the deal. This is a dual mono mono preamp which i have posted the manual and schematic to if you scroll a bit. I don't why Cary continues to do these outrageous power supply schemes but it uses a 560uf directly off a 6ca4 in each channel with a 22k divider and then goes into another 560uf..What I did was put in a 35uf film cap in place of each 560uf in one channel and it seemed to be dead quiet as other channel..What I can fit in is a 100uf film cap and then I can fit a 45uf film cap for the second cap..I figured a little added insurance wouldn't hurt but have any of you guys done any upgrades on these preamps? I figured a 100uf film for the first cap would be adequate especially since the 35uf film worked ok. Any thoughts? It also has a 100k bleeder across the first cap.
 

Attachments

  • SLP-90.pdf
    137.9 KB · Views: 351
Last edited:
Electrolytics would be cheaper and just as good for the first one, and virtually indistinguishable for the second one. Changing something cheap for something expensive which does the job no better is not an upgrade, but a sidegrade. The real upgrade for this preamp is to replace the circuit with something better, or omit the line stage altogether.
 
No,they are not as a good for the first one and film caps aren't expensive if you

[buy them right.The 35uf you can get for 7 to 8 dollars surplus and it makes a huge difference on the charging cap as that sets the conduction angle. Check the pansonics at mouser and you will see how inexpensive they have gotten.
 
..and it makes a huge difference on the charging cap as that sets the conduction angle.


Are you talking about loss angle? i.e. Film caps come closer to a perfect capacitor, theoretical current leading by 90 degrees, since the loss angle is equal to ESR / Xc, the larger the loss angle the larger the ESR and the more heat gets built up in the cap due to these losses in the dielectric. in this regard film caps are better.

As stated conduction angle is set by DC load and the amount of capacitance and not the dielectric.
 
In a sherwood integrated amp the 35uf poly off the GZ34 made a big difference

in transient energy and I had lower distortion numbers on measurement.In a preamp,maybe not so much but in the sherwood amp is big enough that I continue the practice to this day. Try it yourself and take measurements of half and full power distortion.I still use lytics but I use them downstream..Anyway Conrad Johnon uses all film caps in their power supply of their film caps and amps so they must see some benefit. I don't know of anyone that would say a lytic would out perform a film cap but I can tell you that it cleaned up this cary SLp90 as it was very sluggish.
Here is a pilot 232 I rebuilt and sold and I posted the waveforms even at 10khz and I wish I would have posted the previous waveforms but I didn't but I did do a sweep as well.
http://www.usaudiomart.com/details/...uild-and-upgrade-by-mike-samra/images/827097/
 
Last edited:
Are you talking about loss angle? i.e. Film caps come closer to a perfect capacitor, theoretical current leading by 90 degrees, since the loss angle is equal to ESR / Xc, the larger the loss angle the larger the ESR and the more heat gets built up in the cap due to these losses in the dielectric. in this regard film caps are better.

As stated conduction angle is set by DC load and the amount of capacitance and not the dielectric.

You are correct.I was speaking in relative terms of its effect but it does run cooler and I have found especially in amps that the first cap is critical unless you are usinga choke IP.
 
Exactly

[Not only AJ,I stuck in the 35uf poly and the 100uf poly on each side and the muddiness is gone..I did put the 100k bleeder back in the first 35uf cap but maybe I don't need it..Anyway you are absolutely right..People get ridiculous with excessive capacitance and not only that,it can change the impedance of the power supply if you get excessive..I saw this happen on a pair of Dyna Mk6s.
When I discharged the 560uf caps with a dead short across the cap,I had to do this 4 times over the course of 4 minutes to get all the charge out of it..That tells you right there that the dielectric absorption is out of sight because if a dead short can't empty the cap,you know there is tons of wasted energy that the load will never see.These caps were as slow as a beach snail.
 
Modern panasonics which are closer to a film cap performance

that I have found..It makes more of a difference in a tube rectified circuit but believe me I can hear the difference on the MArtin LOgans or the big Ribbons..In the case of the Sherwood,the bass is just quicker and has more snap with the poly than it does with the lytic in the first cap..If there is no difference in these caps,why would they make polys because they are physically huge by comparison if a lytic will give you the same performance..What would be the point? When I do a mac mc30,I use a 100% film cap supply and I add a choke in place of the 150 ohm resistor..

Tubes Asylum