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component confusion
well after my susscessful amp9 and my not as successful attempt at the amp32, I've tried to console myself by starting on a amp4, getting 0.3mm solder and a smaller tip have profoundly improved made my soldering.
My question now is about R55 and R58 which are on the PCB but no mention of them in the BOM or the AI, what values are they?
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R55 shows in the amp4 schematic as a 49.9k resistor and R58 as a 10k. Both of these appear in my schematic and in the BOM file.
Do you have a different BOM/schematic than mine?
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hmmm I was hoping that they were going to be the two identical resistors that were marked as "??" in the BOM in bag one or two
so yes unless your BOM has question marks in it they will be different
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It's been a while since I built my Amp4 but I seem to remember the actual value of R55 wasn't crucial and was actually supplied as a 50k or 51k. I think I still have the bags around somewhere and the Amp is currently in use, so if you really want to know I could pull the top and look.
As for the R58, you should have had a bag with several (4?)10k resistors.
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The circuit diagram for the Amp4 is certainly wrong in places. For instance, it doesn't include the voltage monitor (have I missed it?), and some of the transistors (LED drivers) have the wrong names. It needs labels for the pin numbers on the connectors, and more clear indications of connections between points that aren't explicitly shown. I can't be more specific as I don't have the circuit diagrams to hand and the site seems to be so broken since its re-vamp that I can't find them on-line any more - grrr!
I don't think the build instructions tell you when to put the large reservoir capacitors in. Pretty difficult to forget though!
I found the format of the long BOM very confusing; it should have lines between the different items as it's not obvious which description belongs to which. The component bagging system is well thought out, but somehow I still managed to install two chip capacitors in the wrong place.
Additionally, I'm not happy about the positioning of the fixing holes in the PCB - the ones at the corner are scarily close to the edges, with the one near the LED connector too close to components to allow shakeproof washers to be fitted. The ones either side of the power amplifier chip have too little clearance too, with one of them being stuck between two capacitors without a hope of getting a screw head or a fixing nut in. Luckily the board seems to be firmly mounted enough, with good contact of chip to case, without using these holes.
That's all the moaning over - after a stressful time building the amp (despite having access to a rework station), I'm glad that it works and there are an awful lot of good things about it, so many thanks!
Knight of the Solder Iron
Gosh what a struggle! I know what you've been through because I've been through it many many times... I shall have another go at Jan to have him straighten the files out some more, thanks on behalf of the community for you clear criticism.
If nobody would ever complain nothing would be improved either!
------X-max. can be several meters on any driver, too bad it can be done only once...------
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okay I have been quiet because i was pretty depressed, because after rooting the amp32, I put together an amp4, and it wouldn't start either, it kept blowing fuse after fuse (3A), I didn't touch either for a week then this weekend I kept resoldering joints and cleaning the amp4, I actually found a cap that was only soldered to the board on one side and I was so careful about watching for flowing solder joints too [:I] anyway I ran out of glass fuses and soldered on a 1.5A PTC, and kick me but it started working! and it sounds great. So I don't know if it was the unsoldered cap (C112) or that the inrush current was too high
or something else that fixed itself that I don't know about,
So I'm very happy, but in hindsight it was probably a little too difficult for my capabilities, especially soldering the small chip, I wouldn't have been suprised in the least if I had killed it with oversoldering and solderwicking. And I certainly don't have the skill to trouble shoot to fix major or minor problems.
So one question about the pots, I measure the output on the speakers fall from 40mV or so to 4mV over 10 seconds or so and no matter how much twiddling on either pot I do doesn't seem to make any difference to that, the amp sounds good but maybe it's not optimal? I notice the chip gets reasonably hot (~45 deg C) without heatsink, much warmer than the amp9.
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With two 10000uF capacitors, the inrush current of the Amp4 is pretty high. I am incorporating an old Dell laptop power supply (20V 3.5A) and if I just connect it straight to the board it doesn't work because it has a current-operated trip which only resets when the mains is removed. I'm bypassing the current sensing at the moment but better would be just to put a longer time constant on it.
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