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Tear down of Massdrop THX AAA 789 Headphone Amp
- Thread starter amirm
- Start date
solderdude
Grand Contributor
Chances are that upon 'start-up' one of the caps might shortly peak due to a capacitance difference.
When that happens a lot the lesser one may be damaged.
Not so with 25V rated ones but maybe 16V ones could be damaged in this way ?
That makes a lot of sense. Thank you for the insight. The rubycon caps that seem to fail are almost immediately downstream of the missing caps. Actually they might be in series, but I’m not sure.
I would be curious on the design schematic recommendations but not from random soldering of random caps on it and not even have the proper gear to measure the results
$1 in caps
5 minutes of soldering
3 hours of finding your soundcard and cables so you can perform a measurement
2 days of wondering why it got worse
MAB
Major Contributor
I think we are just curious about different things.
I am curious about the circuit, including the other omitted components, but no curiosity on capacitors without a circuit. I don't have the schematic, but it appears the caps are not the only thing omitted from these traces, and a few measurements says you will be adding caps to a 500Ohm resistor to tied to ground, I hope you appreciate the pointlessness if this is true (I don't have the schematic, but I measure!). The good news would then be you will have no chance of upsetting the existing circuit. But this is ASR, and we tend to do circuits, not components. I hope that distinction is clear since you seem very intent on the capacitors.
For instance, a member reverse engineered a module on a popular high-performance amplifier that had a systematic reliability problem:
Topping PA5 fix - D01 Module Replacement for everyone
Ive been working on the PA5 for a while now after mine died suddently, like many others https://www.audiosciencereview.com/forum/index.php?threads/poll-for-topping-pa5-owners-only-please.33293/ Most of the PA5 units develop a crackling, hissing or just go a little silent or completely dead on...
www.audiosciencereview.com
. Reverse engineering the circuit with a proper fix, and some appropriate measurements is interesting.You speculate on this circuit. Some of the terms you use are not familiar to me, perhaps there is a language barrier, or an engineering one. My version of finding out is just much different than yours.
oleg87
Senior Member
Again - I don't understand what problem you are hoping to solve.
In my line of work pretty much every PCB we design has un-stuffed parts that don't have a value or specific component specified on the schematic, because it costs nothing to copy+paste a few symbols on a schematic if you want some kind of flexibility for design tweaks/plausible use cases or your intuition tells you its not needed but you just want to err on the paranoid side because rev'ing a board takes money and time.
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Killingbeans
Major Contributor
Sure, if you can verify a change in performance with measurements.
But if the "ugrade" gets "verified" by ear, I honestly couldn't care less.
I appreciate you measuring and the circuit analysis you did. At the very least I now know I won't burn my house down, thanks.I think we are just curious about different things.
I am curious about the circuit, including the other omitted components, but no curiosity on capacitors without a circuit. I don't have the schematic, but it appears the caps are not the only thing omitted from these traces, and a few measurements says you will be adding caps to a 500Ohm resistor to tied to ground, I hope you appreciate the pointlessness if this is true (I don't have the schematic, but I measure!). The good news would then be you will have no chance of upsetting the existing circuit. But this is ASR, and we tend to do circuits, not components. I hope that distinction is clear since you seem very intent on the capacitors.
For instance, a member reverse engineered a module on a popular high-performance amplifier that had a systematic reliability problem:
People putting fans on this amp, taking it out of chassis, cold room, only turning it on for limited times, doing a voodoo dance, etc. to try to keep their amp running; this is not interestingTopping PA5 fix - D01 Module Replacement for everyone
Ive been working on the PA5 for a while now after mine died suddently, like many others https://www.audiosciencereview.com/forum/index.php?threads/poll-for-topping-pa5-owners-only-please.33293/ Most of the PA5 units develop a crackling, hissing or just go a little silent or completely dead on...
You speculate on this circuit. Some of the terms you use are not familiar to me, perhaps there is a language barrier, or an engineering one. My version of finding out is just much different than yours.
Going down the rabbit hole, to fit the diameter and pitch and height clearance of the through hole's the caps must be either 16V at 6800uF or 25V at 3300 uF. The caps further down the line on my Massdrop 789 that have not bulged are only rated for 16 volts as well.
Confirmed this morning the capacitors are indeed connected in parallel to the caps further down. I think these caps were originally intended to further smooth the two 12 V rails. All we’re doing here is adding more smoothing. The choice is now 16V or 25V caps.
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