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Old 6th December 2018, 03:37 PM   #1091
vdi_nenna is offline vdi_nenna  United States
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Why would you quote that entire posting?
Just point to the post number or take a snippet of the post. Just a waste of space.
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Old 6th December 2018, 03:41 PM   #1092
Skylar88 is offline Skylar88  South Africa
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Quote:
Originally Posted by vdi_nenna View Post
Why would you quote that entire posting?
Just point to the post number or take a snippet of the post. Just a waste of space.
+1
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Old 7th December 2018, 02:17 AM   #1093
Pano is offline Pano  United States
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OT rude posts removed.
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Old 7th December 2018, 10:15 AM   #1094
frenchy is offline frenchy  France
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Hello
now powered up the M2 ishikawa for offset and problem adjustment.

test conditions:
*RCA plug in short circuit.
*16 ohms load resistance on speaker outputs
*on the 230v is tested with a 60w bulb in series.

Observation at power-up:
*Only the card powered, the 60w bulb lights up for 5s and then goes out.
*with the motherboard equipped with ishikawa connected to the PSU board the lamp remains off and then lights up gradually.
*same symptom for channel A and channel B

So I suspect a short circuit
That is my problem.

when do you think?
Did I understand correctly the fact of short-circuiting the RCA input socket?

Thank
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Old 8th December 2018, 02:38 AM   #1095
Mark Johnson is offline Mark Johnson  United States
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The diyAudio First Watt M2x
M2x takes about 2 minutes after switch-on, to gradually increase its bias current. Eventually bias current grows large enough that a correctly built M2x draws about 120 watts to 140 watts from the AC mains. This is probably enough to light up a dim bulb tester.
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Old 8th December 2018, 02:57 PM   #1096
xrk971 is offline xrk971  United States
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Some measurements of the Melbourne:

The Melbourne Class A Headphone Amp and Pre-amp

I was shocked how good it sounded driving my headphones. Both 250R and 50R - sounded clean and powerful. No audible hum. This is with +/15.5v rails provided by Mark Johnson design and Prasi layout BJT cap Mx and linear 15v trafo.

Click the image to open in full size.

2Vpp into 240R load:
Click the image to open in full size.

This was as close as I could get to providing a 600ohm load to emulate the Edcor (519R). 2Vpp into 519R:
The diyAudio First Watt M2x-melbourne-th-2vpp-519r-45ma-fft-03-png

4Vpp into 519R:
The diyAudio First Watt M2x-melbourne-th-4vpp-519r-45ma-fft-04-png

I think this is a very nice harmonic distortion profile and should be a good input stage for the M2X.
Attached Images
File Type: png MELBOURNE-TH-2Vpp-519R-45mA-FFT-03.png (75.3 KB, 280 views)
File Type: png MELBOURNE-TH-4Vpp-519R-45mA-FFT-04.png (76.7 KB, 207 views)
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Last edited by xrk971; 8th December 2018 at 03:01 PM.
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Old 9th December 2018, 06:27 PM   #1097
dBel84 is offline dBel84  United States
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I am coming to the end of my tether....


rebuilt the right channel again and tested it on the bench for some time - came up to normal bias point, adjusted the offset easily and stable for about 2 hours before I turned it off.

Tested it in my test system - came right up, offset started at 140mV in both channels, settled to around 1mV fairly quickly. Bias good and overall seemed to be behaving, no hum or hiss at all from speakers. ( I did build little mumetal enclosures for the edcors.

absoutely lovely music playing and kept watching it carefully for the first 90 min - no change in behavior at all with heatsinks settling down at 52deg C and the little tabs on the fets sitting about 10 deg higher.

Left it playing for about 3 hours, checking on it every 30 min odd. Final check - same channel dead

odd thing is that the 3A fast blow fuse does not go, just the negative rail of the SMPS current limiting as it is shorted to ground through the 2SJ201

This will be the third set of these precious mosfets to have been sacrificed without me understanding the circumstance of the failure.

- given the general start up and initial stabilization, the amp is working

something catastrophic is happening after some time and I have no means to measure it

perhaps sticking a gopro on the multimeters and seeing what happens when it does this again - assuming I can find anymore fets

..dB
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Old 9th December 2018, 06:45 PM   #1098
Mark Johnson is offline Mark Johnson  United States
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It would be comparatively inexpensive to perform the experiment of temporarily replacing the rare Toshiba FETs with ordinary IRFP240/IRFP9240 industrial FETs, and seeing whether or not those blow out too. You could also connect some 5000W unidirectional TVS diodes across the rails, or across each rail individually, just to deal with random spikes and ick noise put out by the SMPSs. (possibility??)

Last edited by Mark Johnson; 9th December 2018 at 06:55 PM. Reason: change example to 5 kilowatts
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Old 9th December 2018, 06:57 PM   #1099
MEPER is offline MEPER  Denmark
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If each channel has its own SMPS then try to "switch" to see if error follows SMPS?
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Old 9th December 2018, 08:10 PM   #1100
dBel84 is offline dBel84  United States
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{headhung in shame} {tail between legs} - if only we had the appropriate emoji's to appropriately express my embarrassment and shame

KERATHERM!!

I know ZM in particular preaches this loudest of all - the store was out of stock and I ordered what I thought would be a suitable alternative option from wakefield.

I kept studying the schematic trying to figure out how the drain might short to ground without the mosfet actually shorting out between its pins. I thought I would try an experiment and remove the daughter board - not that I thought that was to blame but just wanting to remove all variables. them I inserted a thin plastic sleeve between the fet and the heatsink after unbolting it - no more short !!

this would explain why I managed to fix everything with replacing the fets as I was replacing the heatpad too - these must not be up to snuff and although I am not seeing visible holes in the pads, they are shorting the output devices to the heatsink and thus ground.

If only I had not run out of keratherm before starting this project/or ordering more when i did and before they ran out of stock - will soon have more on the way.

thanks all for thinking about this and feel free to laugh along as i beat my head while chanting and walking in a circle.

..dB
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