Might be between heat sink fins... A little hard to see. Suppose I just have to disassemble the amp and mess with the heatsink regardless. Sigh....
cal3713,
How about implementing a "clamp" to hold the MOSFET tightly to the heatsink? Something like the one in the picture. In the example the screws come from the underside and you can see the nuts on top of the clamp. In your case you can tap the screw-holes in the heat-sink and then thread the screws into the sink from the top.
How about implementing a "clamp" to hold the MOSFET tightly to the heatsink? Something like the one in the picture. In the example the screws come from the underside and you can see the nuts on top of the clamp. In your case you can tap the screw-holes in the heat-sink and then thread the screws into the sink from the top.
Attachments
Good news is that the tap was between fins, and I could actually get the drill in there without pulling the heat sink. Was relatively painless to extend the hole through the sink. Currently getting ready to go through the setup procedure.
Thanks for the tips. Fingers crossed that I can actually make it through this time.
Thanks for the tips. Fingers crossed that I can actually make it through this time.
Strike that, just stripped out the head of the screw I was using to go though the sink. Guess I have to walk to the hardware store before setup.
New screw is locked in. Cooking for an hour with lid on while monitoring IQ & offset. Will reset IQ if necessary and then work on input buffer. Fingers crossed.
While you‘re at it, watch for aluminium chippings within the amplifier enclosure.
I recommend going through it with a small brush and a vacuum cleaner with narrow nozzle mounted. 🙂
Regards, Claas
Edit: OK, was too late 😀
Don‘t disturb a running amp ...
I recommend going through it with a small brush and a vacuum cleaner with narrow nozzle mounted. 🙂
Regards, Claas
Edit: OK, was too late 😀
Don‘t disturb a running amp ...
Fortunately a dull drill bit, a pre-existing hole, and plenty of wd40 lubricant meant that all the al chips just stuck right to the bit. Just cleaned it off each time I pulled it out of the tap...
IQ set. Offset set. R6 set. R7 set. Music on crappy speakers. Time to move to the big system. Ready to get on my knees and beg for no more surprises.
After all that, I once again got the motor boating behavior when moving from crappy to expensive speakers.
After further investigation, I discovered that one amp's input jack is not making full contact with my interconnect's center RCA pin. Apparently the center pin on my shitty 1/8th inch phone jack to RCA cable is bigger than usual and completes the contact. My fancy silver cable and a standard MIT both failed and gave the motor boating behavior.
Gonna try switching input jacks from the F4 side to the SS side and will order some nicer ones to put in in the future.
Wow, can't believe I was done over a week ago, just had an unknown part failure.
After further investigation, I discovered that one amp's input jack is not making full contact with my interconnect's center RCA pin. Apparently the center pin on my shitty 1/8th inch phone jack to RCA cable is bigger than usual and completes the contact. My fancy silver cable and a standard MIT both failed and gave the motor boating behavior.
Gonna try switching input jacks from the F4 side to the SS side and will order some nicer ones to put in in the future.
Wow, can't believe I was done over a week ago, just had an unknown part failure.
Is it normal for the amp to motor boat if there's no input and it's not shorted?
Switching RCA's inputs didn't fix the issue. Attaching the mit cable to the phone->rca cable worked just fine. When it's attached to my pre-amp, then motor boating.
I'm confused. At least it appears I can trouble shoot the issue.
Switching RCA's inputs didn't fix the issue. Attaching the mit cable to the phone->rca cable worked just fine. When it's attached to my pre-amp, then motor boating.
I'm confused. At least it appears I can trouble shoot the issue.
Ok, I've identified the actual issue. For my problem channel, the second there's no input voltage and the input isn't shorted, it motor-boats. The other channel goes quietly into the night when I pull the source.
Currently DMMing around the two channels to try and identify the difference, but any input is welcome...
Sorry for bombing the thread with my live tweets.
Currently DMMing around the two channels to try and identify the difference, but any input is welcome...
Sorry for bombing the thread with my live tweets.
@Cal3713 -
When you say it works with the crappy speakers and then "motorboats" when you go to more expensive speakers. Are you saying that the ONLY thing you're changing is the speakers? In follow up posts you're talking about interconnects etc. which to me could imply that you're also changing other things even back to the source. It may help us to help you if you tell us exactly what's changing. It seems there may be more to it than just swapping the speakers.
If you're changing anything else other than the speakers... is it possible to literally JUST go from the crappy speakers to the good ones with nothing else changing?
Good luck!
FWIW - from my perspective... please keep posting. It's rewarding to see someone persevere and be cool enough to post both the successes and frustrations. We ALL learn.
When you say it works with the crappy speakers and then "motorboats" when you go to more expensive speakers. Are you saying that the ONLY thing you're changing is the speakers? In follow up posts you're talking about interconnects etc. which to me could imply that you're also changing other things even back to the source. It may help us to help you if you tell us exactly what's changing. It seems there may be more to it than just swapping the speakers.
If you're changing anything else other than the speakers... is it possible to literally JUST go from the crappy speakers to the good ones with nothing else changing?
Good luck!
FWIW - from my perspective... please keep posting. It's rewarding to see someone persevere and be cool enough to post both the successes and frustrations. We ALL learn.
silly question - did you set both buffers , both for Iq and DC offset , and just then closed small jumpers ?
also , be sure that jumpers are having proper contact .... I'm always squeezing that small contacts in jumper , to better bite pins
what is THF 51 gate voltage at programmed current ...... or even better - just measure DC voltage from THF gate to IRFP gate
also , be sure that jumpers are having proper contact .... I'm always squeezing that small contacts in jumper , to better bite pins
what is THF 51 gate voltage at programmed current ...... or even better - just measure DC voltage from THF gate to IRFP gate
Once I got into full trouble shooting mode, I just took the amp, the crappy speaker, my phone (the source for crappy speaker), and the cable for connecting phone to amp all over to the main stereo.
I then put an RCA female-female plug on the preamp end of my interconnect and drove the amp using my phone, connected via phone-to-amp cable. Everything works perfectly, until I pull the 1/8th inch plug out of the phone, then horrible motorboating noises.
If I do the exact same thing on the other channel (in it's own monoblock chassis), I get music but no motor-boating once the source is disconnected.
Clearly I have some problem in the first channel. Somehow it's oscillating to create that motor-boat sound whenever there's a) no input signal, or b) the input ground & signal are not shorted.
And thanks for the encouragement, I appreciate it... and can use it.
I set IQ and offset (after 2 full hours of cooking), turned off the amp, removed 0R1 resistor on V-... then turned the amp back on, reset offset, let it cook for 10 minutes, reset offset, then set R6, R7, turned the amp off, and put in the jumper.
Unfortunately I'm done for the day, but I will try to get more time later this week to squeeze the jumper and measure DC voltage from SIT gate (small pin) to MOSFET gate (rightmost pin when board is installed on heatsink).
[just putting pin locations in to remind myself later]
Thanks for all the help folks.
Actually, not a silly question. I woke up a couple hours early and was laying in bed thinking about my amp issues... I remembered when my previous board blew, I pulled this one and immediately started setup. Had stored it with the jumper attached. I remembered a minute or two into the process and didn't see/small any smoke, so I just pulled it and assumed things were ok. So dumb...
Got an hour before work. Gave the jumper a squeeze and reinstalled, no change in behavior. Silent with short on input, oscillations as soon as it gets pulled.
DC voltage between THF and IRFP gates ~ 3.6V. UPDATE. Now at 3.45V after 15 minutes.
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