Helpful yes, thank you. I'll want to try your suggestions on some test metal before attempting it on another chassis.
Good news is that Plan B worked just fine. By pure luck, the two center-line holes from the botched attempt were the only ones I successfully drilled and tapped, and they are in the right position when the HS is flipped around. It was a little tricky to install the through bolts, but not much of a setback in the end. Not as pretty as ModuShop would have done it, but it has more personality, right?
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Interesting. I don't reacall how the heatsink frames were configured for my ACAs (I could look, but that would involve using a screwdriver ...). I just finished installing one side, and found it relatively easy to remove the frame temporarily.
I really do like those Japanese screwdrivers! Source?
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Oh, interesting, your picture frame mounts to the base plate differently from the one on the monoblocks. Yours is much easier to access.
ANEX low profile screwdrivers
ANEX low profile screwdrivers
All wired up! But no place to go just yet.I remembered vaguely that the insulating strips in some of the F5M kits were not insulating, and I just confirmed that my strips conduct. So unless Amazon can ship me some Polyamid tape tomorrow, no sound test this weekend -- bummer!
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It is 100% your call / decision, but... you have brand new anodized heatsinks.
So... if you'd like... you could... install the insulators and run a quick resistance check to decide if you want/need to get new insulators or not ... short or long term.
If you need certainty... definitely wait for new ones. If you know how to check, and you don't mind a few minutes work with a small chance that you may want/need to change them anyway... you can give the ones in the kit a try.
So... if you'd like... you could... install the insulators and run a quick resistance check to decide if you want/need to get new insulators or not ... short or long term.
If you need certainty... definitely wait for new ones. If you know how to check, and you don't mind a few minutes work with a small chance that you may want/need to change them anyway... you can give the ones in the kit a try.
I measured from the metal case of the FET, which is slightly exposed on the front, to the bare chassis. Yes, this was prior to wiring up PSU. I subsequently loosened both of the devices and insulated them with plastic cards to confirm that there was no other conductive path.
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They're connected to the cable shields for the audio inputs (twisted, shielded quad conductor).
Amazon came through with the polyimide tape, and I isolated all four power mosfets without having to disassemble too much.
On to biasing. Left channel behaving as expected, however on the right channel, the voltage drops across R6 and R7 never exceed 80mV with the pots fully clockwise. Anyone have thoughts on how to troubleshoot?
On to biasing. Left channel behaving as expected, however on the right channel, the voltage drops across R6 and R7 never exceed 80mV with the pots fully clockwise. Anyone have thoughts on how to troubleshoot?
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First, post pictures of the board and of the whole amplifier for the big picture.
For measurements, measure the PS voltages on the board to make sure that they are correct.
With a voltmeter at each mosfet G and S pins, turn the corresponding pot. Does the voltage change when the pot is turned? What is the maximum voltage?
For measurements, measure the PS voltages on the board to make sure that they are correct.
With a voltmeter at each mosfet G and S pins, turn the corresponding pot. Does the voltage change when the pot is turned? What is the maximum voltage?
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@Ben Mah here are the measurements you suggested making.
V+ 25.7v
V- -25.6v
Q3G 25.7 to 21.8v (CCW to CW)
Q3S 25.8 to 25.6v
Q4G -25.8 to -22.4
Q4S -25.7 to -25.6
While I'm still curious to hear what you make of them, unfortunately I created two bigger problems for myself. First, I blew out the (previously working) left channel while attempting to gather a comparitive data set; and then I shorted something while attempting to measure the voltage behavior across R5 on the right channel. So I'm going to have to pull both boards and test every component. I'm bummed.
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Yeah, this was the best I could find with next-day delivery -- good enough until the parts from DIY Audio get here.
I wouldn't be cranking on the pots willy nilly, that's sure to burn something up. Those pots are like faucets controlling the current through the power fets. You open one a little bit, then the other one a little bit, and keep repeating. It's a balancing act where you are equalizing how much "work" each device is doing. You go back and forth adjusting the two pots slowly and carefully, small bites at a time, watching the current through the source resistors (R6,R7) with your voltmeter to keep things more or less equalized as we hone in to that final setting of desired Iq and low DC offset at the output. So at minimum you have two voltmeters, one watching the source resistor voltage (use ohm's law to calculate current) and the other watching the DC offset voltage (always aiming for zero). These are your "eyes" so that you can keep track of what's going on as you adjust this thing. I would want to see Keratherm pads and some nice fat washers on those ouputs. We want as much thermal transfer as possible to the 'sinks.
When I'm measuring on a live circuit I will typically use small clip leads on the component leads before power up to prevent slippage, blown parts, followed by sadness and disappointment...
When I'm measuring on a live circuit I will typically use small clip leads on the component leads before power up to prevent slippage, blown parts, followed by sadness and disappointment...
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