I'm sorry, when I said "shorted" I was incorrectly describing it- it's as you say, turned so that the path of resistance through the pot from the wiper is at maximum, e.g. the wiper is turned to the side of the pot that itself is tied back to the wiper via a jumper (the wiper and the other end of the pot go into the board). And yes, I was half wondering if trying 2R7 resistors in R3 and R4 would do the trick. I suppose I could use alligator clips to clip on an 8R power resistor in parallel to see if that has an effect first.
For whatever reason I could not reproduce the original 26R reading between line in - and TP-gnd (even though it's in my notes!). I re-read it now as 0R2.
I took a bunch of other readings between TP-gnd and other ground points. TP-g is about 12R to all the mounting holes of the amp boards (hence to heat sink and star ground), which makes sense to me as there is a 10R thermistor between "PS negative" (where Tp-g connects) and star ground. The chassis itself is effectively (fractions of an Ohm) at earth ground / star ground potential; I think the worst I measured is 0R5 between one of the un-anodized mounting holes on the heat sink and the star ground.
Now, I used a bunch of brass washers between the amp board mounting bolts and mounting holes because I thought the amp board ground plane and the mounting holes were meant to be connected and continuous with chassis ground. Granted I really don't know what I'm doing and I'm still learning, but I think I need to better isolate "circuit ground" (PS negative and the entirety of the amp board) from earth / chassis ground. Intriguingly, on the other channel, which is even more of a mess if you can believe it (the power resistors R3 and R4 heat up north of 120 degrees), I measured a volt of potential difference between that channel's TP-g and star ground (!), so that may be more of an extreme example or consequence of shorting circuit ground to earth ground potential. Yikes! Good thing I'm not pretending to be a professional!
You need it in series. Parallel always lowers resistance (but raises capacitance).
Finished my F3 and fired up the left channel with a variac. I couldn’t get the voltages to get to the right points, realized my variac was set on 90 volts not 115. duh. Then I struggled over 2 days and still couldn’t get the voltages right. Today I moved my three voltmeters to the right channel to see what it would do and hooked up my last volt meter on the left channel. I then realized the new meter was reading 15 volts and not 21 volts like the day before. Wow I had a bad meter. Once I understood that I got both channels set in five minutes! Rechecked over the next couple of hours. Installed the F3 in my system. I am absolutely amazed. It is the best amp I have heard yet on these speakers. And I have a F4,F5,BA3,and F6. May not be the best amp for every speaker but on my easy to drive speakers it is glorious nothing but 3d soundstage, speakers completely disappear. Thanks to CSample for the great boards and the DIY community for all your help over the years. And a special thanks to Mr. Pass. Over the moon in missouri.
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Hi everyone, I'm still having challenges getting my bias points set properly, though I did find and fix a shorted capacitor on my LH board which now at least makes the two boards behave the same as described below. Also all testing is now being done with circuit ground isolated from earth ground, shorted inputs, and the indicator LED in place.
I have a question about this circuit. If one or more of the capacitors on the output capacitor board were shorted (by the same bad soldering technique potentially), would that lead to an inability to get TP1 much above 16.6V? I can get TP5 to just about 8V and TP4 to about 3.5V but only when TP3 is at 1.4V instead of 1.1V, or what I interpret to mean about 20% more current flowing across the LU1014D than spec.
If I wanted to test this, what could I put in place of the output cap board? I have on hand a couple pairs of 6800uF 25V capacitors, and a pair each of the 1000uF and 220uF caps used elsewhere in the F3.
I have a question about this circuit. If one or more of the capacitors on the output capacitor board were shorted (by the same bad soldering technique potentially), would that lead to an inability to get TP1 much above 16.6V? I can get TP5 to just about 8V and TP4 to about 3.5V but only when TP3 is at 1.4V instead of 1.1V, or what I interpret to mean about 20% more current flowing across the LU1014D than spec.
If I wanted to test this, what could I put in place of the output cap board? I have on hand a couple pairs of 6800uF 25V capacitors, and a pair each of the 1000uF and 220uF caps used elsewhere in the F3.
Thank you ZM. So if you had to make a choice, would you rather have 3V5 at TP4 if it meant 1V4 at TP3 (and 21 at TP1), or is the 1V1 at TP3 really that critical? I'm thinking the 21V and the 3.5V across the LU1014D are really the most critical.
I can hit all of the other numbers and TP5 more or less if I set the R5 pot to about 1V4 at TP3. For the curious, I had to replace the two 2R power resistors in parallel with the R5 pot with 2R7 values to hit this, and I'm estimating I need a 3R2 in place of that pot for final settings.
I can hit all of the other numbers and TP5 more or less if I set the R5 pot to about 1V4 at TP3. For the curious, I had to replace the two 2R power resistors in parallel with the R5 pot with 2R7 values to hit this, and I'm estimating I need a 3R2 in place of that pot for final settings.
With R3 & R4 at 2R7 and R5 at 3R2 and a 1.4V drop the bias current would only be 1.47A vs. the desired 1.65A. If I understand correctly the bias current is controlled by R6,R7&R8, maybe it would be worth checking the values of these resistors. Regarding the potential short in the cap bank is there any DC present at the negative output terminal (ie. DC getting through the cap bank)?
Is it possible I just have a lower transconductance LU1014D? As I understand it, the current across it should go up with drain voltage, so targeting 3V5ish would make sense even if the voltage drop and hence current across it is lower than the schematic.
As for measuring R6,7,8, I'll try that, but I don't want to lift any legs as it's been a pain to clean out the holes on the resistors I've already swapped.