NAP-140 Clone Amp Kit on Ebay - Page 14 - diyAudio
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Old 10th April 2008, 07:23 AM   #131
cdswift is offline cdswift  United Kingdom
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Default Re: Seller message

Quote:
Originally posted by ratchet
I ordered the kit a couple of days ago and got a reply from the seller saying that:

"Please take care about the pin out of Q1 & Q2. It is not matched with silk screen of PCB. Please see the photos in my listing. You should mount the Q5 on the power transistor or heatsink. Take care about the polarity of the transistor. Ignore the silk screen printing and follow the circuit diagram."

Also I was wondering if it would be worth the trouble to match the transistors for fhe and vbe (basic DMM way). Any ideas on that?
Other posters (including myself) have noted a small DC offset voltage at the output (mine is 70mv). I found a reference here: http://bbs.hifidiy.net/viewthread.ph...&extra=&page=8
that recommends selecting an hfe for TR1 that is greater than TR2 to address this.
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Old 10th April 2008, 08:53 AM   #132
hoka is offline hoka  Netherlands
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How do you read that stuff?

and what is the deal about the circled 620 Ohm resistor?

How do you measure hfe?

Questions, Questions, Questions,
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Old 10th April 2008, 02:13 PM   #133
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The bit he read is the yellow and green build guide from avondale audio for the NCC200. No Chinese required.

You can measure the hfe with almost any multimeter.
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Old 10th April 2008, 07:08 PM   #134
ratchet is offline ratchet  Netherlands
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Default hifidyi.net thread

Interesting!

The 1st..3rd image in post #215, would that be a soft-start psu, the little green pcb in front of the amps?
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Old 10th April 2008, 07:18 PM   #135
ratchet is offline ratchet  Netherlands
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Default hifidyi.net thread

On closer inspection it looks more like an overload protection circuit.
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Old 16th April 2008, 10:05 AM   #136
hoka is offline hoka  Netherlands
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The silkscreen for Q5 is wrong indeed, for a 2n5551 it should be mounted reversely! for a tip41c follow the "cbe" markings.

also my kit was supplied with just 1/4 w resistors for R26 and R27 you need to replace those too I guess for 1W types.
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Old 16th April 2008, 10:38 AM   #137
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1/4W resistors are OK for R26/R27, they dissipating only max. ~10mW.
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Old 16th April 2008, 10:00 PM   #138
hoka is offline hoka  Netherlands
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Blew it up again! after replacing most of the components, no luck on the second try. This time I fried R 35. at least that is where the smoke came from.

I'm about ready to give up on these boards
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Old 16th April 2008, 11:01 PM   #139
ttan98 is offline ttan98  Australia
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Quote:
Originally posted by hoka
Blew it up again! after replacing most of the components, no luck on the second try. This time I fried R 35. at least that is where the smoke came from.

I'm about ready to give up on these boards

A few suggestions:

1. use 1-2amp fuses on the +/- 35Vdc power supply.
2. use a variable transformer at the main and slowly increase the voltage, eg apply say 1/3-1/2 of the main voltage and measure relevant/key bias voltages on resistors and transistors. that way you can quickly detect incorrect orientations of transistors or incorrect values of resistors.

cheers.
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Old 22nd April 2008, 10:07 PM   #140
ratchet is offline ratchet  Netherlands
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Quote:
Originally posted by hoka
Blew it up again! after replacing most of the components, no luck on the second try. This time I fried R 35. at least that is where the smoke came from.

I'm about ready to give up on these boards

Hoka, did you also reverse Q5 as cdswift suggested? I checked on my boards (blue version) and the silkscreen is indeed wrong.
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