The Pass P1.7 schematic notes "80V unreg" so that is a good starting point.
Multiply by 1.414 to get the rectified voltage. Diode loss will drop this slightly.
60V x 1.414 = 84.84V
55V x 1.414 = 77.77V
So 60V is the best fit. I'm running a 120VA transformer but it is massive overkill.
Raw DC = a bridge rectifier and filter capacitor at the minimum. Some also like CRC or CLC DC supplies.
To find the dc voltage of a given transformer multiply the known AC secondary voltage by 1.4 and subtract two from the total for the drop caused by the bridge. That gives you the raw dc available up to the current ability of the transformer.
In this case 60 x 1.4 = 84 - 2 volts for drop in bridge = 82 volts.
Note that with this board the smoothing capacitor is already there.
Mark
To find the dc voltage of a given transformer multiply the known AC secondary voltage by 1.4 and subtract two from the total for the drop caused by the bridge. That gives you the raw dc available up to the current ability of the transformer.
In this case 60 x 1.4 = 84 - 2 volts for drop in bridge = 82 volts.
Note that with this board the smoothing capacitor is already there.
Mark
my only issue was that Plitron apparently thinks the nominal voltage is meant for under full load, so if the Xformer is oversized like mine (120VA) it puts out quite a few more volts, thus the surprise heat on the reg fet for me.
Sonny, it's normal practice to rate transformers at full load current. There is also a nominal primary voltage used. All these tolerances can stack up and result in a lot higher output voltage than the nominal. For example my line voltage is normally 120volts and say I buy a 60v 30va transformer with 18% regulation and 115v nominal primary voltage. My unloaded secondary voltage would be 60 x 120/115 x 1.18 =73.87v X 1.4=103.4VDC peak which is bad news for someone planning on using 100volt capacitors. One of the advantages of a larger transformer is that the regulation is typically better.
My advice would be to build in a large heatsink for the regulator to deal with the heat. Even with 100volts going in, each board only draws 60ma giving 2.4watts of power for the heatsink to deal with. Not a lot if you have the space to install a larger sink.
It's great to hear that all you guys are getting your FETs and building the preamps. Anyone close to a listening test on a finished preamp?
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If i'm correct the fets need to be matched in the p1.7 . Bought some matched irf9610 and irf610. Only later to realize that the types were matched .(not irf9610 with irf610) Now i have 4 matched irf9610 and 4 matched irf610. Dumb. .....
On the package there is some information about the matching.
Irf610: Vgs 3,24V Ia 1,60mA
Irf9610: Vgs 3,36V Ia 1,43mA
Would these still be a good match for the p1.7?
On the package there is some information about the matching.
Irf610: Vgs 3,24V Ia 1,60mA
Irf9610: Vgs 3,36V Ia 1,43mA
Would these still be a good match for the p1.7?
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It is not the ideal setting for this application but my guess is that they will still be close enough to work fine at the higher currents. You are way better off with the matched FETs then to go with random unmatched parts. The most critical parts to be matched are the 610 gain stage pairs. The current source parts are not as critical.
I matched FETs for the recent group buy using the boards that Koja made. I do have 1 set left that are supposed to be sold but haven't been paid for yet. I could also sell you 2 matched pairs that you could use for the gain stage. These would be matched within 1mv at 20ma current and a temperature of 30C. Send me a private message if you want to discuss this further.