I have just been using the continuity tester. When the heat sink is ungrounded, there is no continuity in any of the mosfet leads. Only when the ground wire is attached.
The drains are connected to V+ and V-, which usually have a bleed-off resistor (2.2K in F4 Manual) to ground. Thus there will be connectivity from V+ and V- to ground. Can you measure the resistance using a multimeter with a low resistance range?
Pls look at this connection. The green power line from the 3-prong power socket ties to chassis and to one lead of the thermistor.The other lead of the thermistor ties to star ground which is made up of 2 green wires from the right and left psu pcbs. Is this correct per schematic? A thin pink wire connects from this *ground on the EU connector to ground on the pcb affixed to the heat sink. Is this correct per schematic? When the heat sink is bolted to the chassis it is connected to power ground. Chassis power ground and psu *ground are separated by thermistor CL10. Is 10 mean 10 Ohms?
That is probably OK. Since there are diodes in the PS, you should also measure the resistance with the multimeter leads reversed. If you measure the resistance from V+ and V- to ground with the output board disconnected you will probably see about the same resistance.
No bleeder installed. Using an old Peter Daniels PS board that happily powered a previous F4 build for years. Would it help to install one?
Hah, I was just trying to diagnose your circuit problems. I wouldn't worry about the resistances you have reported.
Thanks for ZM's schematic! Didn't know it existed.
Will definitely make changes to the board based on it.
I think the fets are well isolated. There is no continuity on any of the source pins and they all measure around the same 8k R to ground.
Generg: I will definitely try 220 mF C1 and C2. May also jumper D3 and D4 and add back R1 and R2 and be able to use the regular "In" pad.
Ihquam: Didn't mean to sound snarky. Good to hear.
Got some work to do....
Will definitely make changes to the board based on it.
I think the fets are well isolated. There is no continuity on any of the source pins and they all measure around the same 8k R to ground.
Generg: I will definitely try 220 mF C1 and C2. May also jumper D3 and D4 and add back R1 and R2 and be able to use the regular "In" pad.
Ihquam: Didn't mean to sound snarky. Good to hear.
Got some work to do....
Has anyone compared the F4 crippled according the ZM's schematic in post #2994 http://www.diyaudio.com/forums/pass-labs/97540-f4-power-amplifier-300.html#post2086609 vs. the F4 crippled in the fashion of the BA2 output stage? The primary difference I see in simulations is in the deep subsonic region.
Friends of F4..,,.
Do you think it is possible to influence the source follower outputstage to produce more or less k2 by changing the source resistors or the values of transconductance of the lower or upper IRF similar to F6.
Or is this not possible because the IRFs produce no gain in this constellation.....?
Do you think it is possible to influence the source follower outputstage to produce more or less k2 by changing the source resistors or the values of transconductance of the lower or upper IRF similar to F6.
Or is this not possible because the IRFs produce no gain in this constellation.....?
You may be able to influence the harmonic structure with different values of source resistor and bias points, but with a feedbackless source follower configuration you are more likely to get the biggest change with different FET types, IRF 2SJ/K FAQ.
RonD2,
Just had a close look at the photo of the board mounted on the heatsink in post #3753, are there any insulation washers underneath the two middle PCB mounting bolts furthest away from the FET's, it looks like the output track could be shorted to the heatsink.
Just did a quick check and this was the problem! Thanks to you (and kasey197) for finding this.
Actually thanks to everybody here. I really appreciate the help.
Generg: Of course I shouldn't jumper the diodes. My panicked brain has found many new ways to demonstrate my electrical naiveté! I have kept the original setup as pictured.
I will post more in a bit.