Author Topic: EEVblog #378 - Dumpster Diving Teardown Repair  (Read 24037 times)

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Offline Pentium100

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #50 on: November 01, 2012, 11:27:05 pm »
If you're using only "legacy" analog sources, then perhaps. There's the option of using a "hybrid digital" amplifier that gives the great efficiency of a digital amplifier without having to (in the traditional sense) convert the signal to digital.
When I am choosing an amplifier, the efficiency does not really matter to me. I do not need a very powerful amp (2x100W is enough, at least for the speakers I have) and I am not using it 24/7 at full power, so I'd rather have higher sound/build quality, more tape loops or a cheaper amp. My sources are mostly analog too, I have a PC and a CD player connected to the amp, but the analog connection has enough quality for me (I could always use an external DAC if I really wanted to).

I have a little class D amp (2x5W or so) about the size of a Socket A CPU. It sounds OK, unless some peak drives it to distortion, then there is a lot of distortion. Also the amp causes quite a lot of noise on the radio.
 

Offline mzacharias

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #51 on: November 02, 2012, 12:00:22 pm »


They designed and tested at 110VAC then they negotiated a 630V MKT type in large quantity and in several values for their whole production range. The large voltage margin will cover X spec inability they rest assured, is my scenario. Did the final boards, and went to production. Then all the 230-240VAC countries importers started receiving units to repair. They simply did not test at 240VAC. Was late, no X2 or 1000V PP cap at that size and value. My wild scenario, but if those units are not committing  suicide like Lemmings in America too, it maybe holds some water. 8)
[/quote]

Worked on dozens of Yamaha's with this type of power supply. Never seen that cap go bad in the American version - only ever heard of it from the 240V models.
 

Offline nitro2k01

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #52 on: November 02, 2012, 06:48:13 pm »
mzacharias, what if they had put two of those in series? Double tolerance. Bigger drop, but that's ok since the voltage is double. Only problem is how to mount them.
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Offline tom66

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #53 on: November 02, 2012, 07:42:30 pm »
Or use 1kV ones, I have seen them readily available. Or a resistor and second tap off trafo (best solution IMO.)
 

Offline JoannaK

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #54 on: November 02, 2012, 08:18:38 pm »


Troubleshooting waveforms.

Thanks.. New things learned today, thanks to you, Dave and the whomever (sorry, didnt check the name etc) at Yamahe doing those videos.

 

Offline Salas

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #55 on: November 04, 2012, 02:55:56 pm »
Worked on dozens of Yamaha's with this type of power supply. Never seen that cap go bad in the American version - only ever heard of it from the 240V models.

Thanks for the info. They should have developed that PSU in a 110V lab building confidence all along for the component choices as well then. 240V mains slowly degrading that MKT inside takes long enough to have escaped their international models probably shorter pre production testing it seems. 
 

Offline T4P

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #56 on: November 06, 2012, 12:00:25 pm »
Plenty of new amps use class-AB (my brother bought one just a year ago -- a Denon 7.1 system), it's just it's becoming less common because you can reach the same performance with class-D nowadays. The only benefit is either wanting a nice room heater, or for audiophiles who like "the sound" of class-AB.
They absolutely hate the sound of AB, they want Class-A!

When I am choosing an amplifier, the efficiency does not really matter to me. I do not need a very powerful amp (2x100W is enough, at least for the speakers I have) and I am not using it 24/7 at full power, so I'd rather have higher sound/build quality, more tape loops or a cheaper amp. My sources are mostly analog too, I have a PC and a CD player connected to the amp, but the analog connection has enough quality for me (I could always use an external DAC if I really wanted to).

I have a little class D amp (2x5W or so) about the size of a Socket A CPU. It sounds OK, unless some peak drives it to distortion, then there is a lot of distortion. Also the amp causes quite a lot of noise on the radio.
Socket A? Must be quite old Class D tech also, many folks bang on about inefficiency so we give them good Class-D now!

Worked on dozens of Yamaha's with this type of power supply. Never seen that cap go bad in the American version - only ever heard of it from the 240V models.

Thanks for the info. They should have developed that PSU in a 110V lab building confidence all along for the component choices as well then. 240V mains slowly degrading that MKT inside takes long enough to have escaped their international models probably shorter pre production testing it seems.
How do you ever know? Japan's power supply is 110V @ 60Hz! It's a definitely thing that they will have a variable AC source but i guess it takes a long time for the MKTs to slowly eat itself out
 

Offline SeanB

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #57 on: November 06, 2012, 03:27:12 pm »
Japan has110VAC 60Hz and 220v 50Hz, and there are areas where the two are intermingled. Why do you think they leapt so fast onto autoswitching voltage power supplies, while the rest of the world was using a switch on the back of the equipment.
 

Offline Pentium100

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #58 on: November 06, 2012, 08:41:33 pm »
Socket A? Must be quite old Class D tech also, many folks bang on about inefficiency so we give them good Class-D now
Well, the most space on the board is taken up by a 2200uF/25V capacitor. The amp is based on a chip (the chip is under a heatsink, so I do not remember which one) and is available from China on ebay.

It does not seem to have any output filters, so while it sounds OK, I don't turn it on wen I am listening to FM radio.

As for the efficiency - to me efficiency matters the most on battery powered devices (unless the device is big and can have a big battery), it also matters a bit on high power devices that I keep on 24/7, but for something like an amp I'd rather have higher quality (or a tube amp, even if the sound was the same, tubes are cool).
 

Online NiHaoMike

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #59 on: November 07, 2012, 02:27:19 am »

That explains how the Delta Sigma modulators in a digital amplifier work. As noted, a higher carrier frequency gives better quality (most amps run at a few hundred kHz with some going into the low MHz), but having more orders in the modulator also helps (at the expense of being harder to design).

BTW, if you're starting from digital, the process to convert it to analog likely goes through Delta Sigma in any case. Therefore, digital input amplifiers make a lot of sense with digital sources.
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Offline Pentium100

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #60 on: November 07, 2012, 07:29:00 pm »
BTW, if you're starting from digital, the process to convert it to analog likely goes through Delta Sigma in any case. Therefore, digital input amplifiers make a lot of sense with digital sources.
Well, I guess if you have only digital sources you might as well use a modulator that can provide a lot of current to drive the speakers. On the other hand, as I recall, there are also multi bit DACs (essentially a network of very precise resistors), but I do not remember what their pros and cons are compared to single bit DACs.

Still, for me analog-only amplifier is better, since I have a lot of analog sources (and for my digital sources, if I want, I can get an external DAC independent of my amp).
 

Offline tom66

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Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #61 on: November 08, 2012, 10:36:22 pm »
Japan has110VAC 60Hz and 220v 50Hz, and there are areas where the two are intermingled. Why do you think they leapt so fast onto autoswitching voltage power supplies, while the rest of the world was using a switch on the back of the equipment.

Japan is 100V all around, it is just the frequency which is different. 50 Hz in the east, 60 Hz in the west. For old transformer supplies, I think you could get away with using a 50 Hz transformer, it would work acceptably at 60 Hz (but not the other way around...)
 


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