To myself it sounds gooood! My monitors with Fostex fe207e's are not the last word in bass I'm sure, but what I am hearing sounds super. Seems like there is much more definition in certain ranges than before. I would definitely recommend trying this mod to anyone willing to drill an extra socket in their Seduction, and the extra holes for nylon standoffs. Check out the pictures I posted previously in this thread to see where I placed components. I wanted to keep the new socket centered on the top plate which required drilling out where the stock chassis ground was. So if anyone does decide to try this out please do not overlook drilling a new spot and installing chassis ground. Also, please keep in mind I have the anticipation upgrade installed which has a C4S load to going to each plate. If you do not have anticipation installed you may have to design a bit different - I'm not sure.
The following is more information (than you require probably) for anyone interested in proceeding. It allows an Anticipation upgraded Seduction to be modified to use a choke input filter feeding into a single C4S which in turn feeds a gaseous voltage regulating tube plus Anticipation C4S board, while keeping the same PT1 transformer that comes as stock. While the PT1 specs say 20ma max - that is most likely based upon a capacitor input filter. A choke input filter passes current at a more steady rate than the rapid swings of a cap input filter and produces less strain/heat on a transformer.
To recap the choke input power supply:
PT1> Bridge rectifier> L > C1 > R > C2 > C4S > 0C3 (VR Tube) > 4xC4S
Bridge Rectifier - I used 1A Schottky SiC (silicon carbide) that come in a TO-220 package. I liked the fact that they have low/no switching losses due to their operation. I soldered them into a bridge using a 5 terminal strip placed in the hole where the previous 1st section of power supply was located. Remember the center lug of the strip is grounded to the chassis! Also, the metal back/tab on these are
NOT isolated from the internals, so they cannot touch anything including chassis and are at dangerous voltage. The negative side of the bridge
output should be grounded. Both sides of the rectifier input attatch to both sides of the PT1 250V secondary. The center tap is not used and must not be grounded. I repurposed the stock center tap wire to connect the 0C3 to the input of the anticipation C4S board.
http://en.wikipedia.org/wiki/Bridge_rectifierL - For filter choke I used a Hammond 157G (30H, 595ohm, 40ma). You could get away with a lower value choke so long as you stay above the critical inductance value. L = (supply voltage)/(load voltage in milliamps). That is the minimum below which voltage will spike for a given current going through. Bigger is better for ripple reduction I'm sure, so this seemed like the one to get for me.
http://ken-gilbert.com/power-supply-design-henry-pasternackC1 & C2 - I kept the 220uf Panasonics mounted to the stock terminal strip. Be sure to cut the old high voltage output STP wires leading out (but keep the ground wire inside connecting to the ground plane.) You could go much smaller if you wanted and still get a good noise reduction.
R - Replace the 1k resistor mounted between C1 & C2 with a higher watt value. This R can act as both filter component and voltage dropper. You can select a value which gives a filter output voltage 30V more than the VR Tube you wish to use or greater. C4S needs a certain amount of voltage drop or greater, plus a VR tube needs this extra headroom to fire up and function. I went with 2kohm. If you use a different choke than this build remember that its resistance will be different and the filter's output value will be different. Using Duncan amps PSU designer I came up with these resistance vs. output values:
500 ohm - 194V
1 kohm - 182V
1.5 kohm - 170V
2 kohm - 157V
2.5 kohm - 145V
3 kohm - 132V
C4S - I repurposed a dual C4S board that came out of paramounts during soft-start upgrade. I
highly recommend getting a C4S manual from the fine folks at Bottlehead to understand how to properly use and obtain component values. Be aware that the new boards look different but the circuit layout is the same. If you have a newer board it will use HLMP-6000 LED's which are different than in the old manual. Because of this the table for determining R1 should be disregarded and instead use the formula R1 = 0.855/current(in amps). If you screw this up like I did and order the manual table1 value you can solder a second resistor of appropriate value across R1 to get in line with the formula. It can be lower wattage because it won't be passing much current. With the amount of current that will be going through I chose to use the MJE5731A for Q2 because it can handle a higher wattage and easily accepts a clip on heatsink. From forum posts of PJ's it appears the appropriate amount of bias current should be ~10% of the current being passed. Mine is set at 2ma assuming input voltage is 157V. The current passed in my build is set to 25ma. Note that VR tubes require 5ma minimum to pass through to stay alight when setting C4S current.
VR Tube - I used an 0C3 but looks like an 0D3 would work well too. Just make sure the filter output voltage is high enough according to whatever tube's specs. Bypass across cathode/anode with a cap < or = to 0.1uf. Above this value there be dragons. I used one of the 0.1uf orange drops that came as coupling caps in the stock kit. Read up on VR tubes! Fun!
http://tubedata.milbert.com/sheets/141/g/GL874.pdfThe top of the VR tube should have both an input coming from the filter output and output wire going to the 4xC4S board input. If you decide to mount a choke on nylon mounts be sure to attach a wire going to ground to its chassis like done on the PT1. Also, I
triple checked that the TO-220 rectifier diodes were not touching chassis - or anything else, and that no legs were soldered to the center grounded terminal lug. This build could be done without adding a C4S to feed, but more careful selection of R will be required. Refer to the VR tube manual to get that info.
I hope some find this information useful! I learned a lot during the design and execution of this build and it took awhile of searching through disparate sources to fully grok what I had got myself into. It sounds great though, I haven't been able to stop listening to vinyl for days!
