NAP-140 Clone Amp Kit on Ebay - Page 13 - diyAudio
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Old 5th April 2008, 02:08 PM   #121
john65b is offline john65b  United States
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Hey, off topic, can a 2SC5200 be substituted for the MJL21194?

I have a few of the "real ones" and wondered if possible...

2SC5200 vs MJL21194
15A vs 16A
230V vs 250V
150W vs 200W
30mhz vs 25mhz

Crazy/dumb idea?

Sorry for the lame question
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Old 5th April 2008, 02:47 PM   #122
hoka is offline hoka  Netherlands
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I had a heatsink attached but I do not know which way to turn the trim pot to attain minimum bias. as it said in the instructions I put it halfway at 1k1 both ways.

apart from the ones that are visually damaged, what components should I replace?
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Old 5th April 2008, 03:05 PM   #123
Did it Himself
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2SC5200 should work fine.

Have you a schematic supplied with the kit Hoka? Maybe we can work out which way the pot should be set for minimum bias, and also any likelihood of the setting being very critical and causing your problem.
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Old 5th April 2008, 04:49 PM   #124
hoka is offline hoka  Netherlands
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Here is the schematics:

Click the image to open in full size.

can't get the orientation right
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Old 5th April 2008, 05:19 PM   #125
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If you can set the pot such that you have about 800 ohms measured across R17 that will give you the minimum bias current.
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Old 5th April 2008, 07:51 PM   #126
Dave S is online now Dave S  United Kingdom
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John65b,

The AKSA does exactly what the designer intended - gives a "rose tinted" sound. The NAP140 clone sounds very Naim-like to me.

I prefer the pukka NCC200s and my Leach low TIM to both.

I have not tried a P101. I gave up with MOSFETs some time ago (although my GB150s suit my kitchen system very well).

BTW one of the worst amps I ever built was an Aleph 3 clone - what a waste of energy!

Dave.
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Old 6th April 2008, 03:37 PM   #127
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This thread has been interesting so far. I was considering buying the Citation 12 kit from the same seller on ebay. Whats the general opinion on that design?
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Old 7th April 2008, 08:17 AM   #128
cdswift is offline cdswift  United Kingdom
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Default Blown up NAP140 clone

I got my amps working this weekend - yet to be assembled with a decent psu into a case so cannot yet comment on how they sound. However, some observations:-

If Q5 goes open circuit, the drive to the output transistors will be huge and turn them on maximum - this would definately blow them up and a few peripheral components to - like the pre-drivers. The current limiting transistors Q7 & Q8 should stop this except for the fact that C3 and C4 will appear as a short when the surge starts and thsi will ensure that Q7 & Q8 are off instantaeously. As the C3/C4 capacitors charge up, Q& & Q8 will turn on and then limit the output drive - but this is almost certainly too late to prevent damage.

Therefore Q5 is very important - I would strongly recommend using the TIP41 and mounting it on the heatsink to compensate for thermal runaway. Also, from memory this weekend, the legend on the PCB is also incorrect for Q5 - I checked the PCB tracks before deciding where to connect 3 flying leads from the PCB to the offboard TIP41.

The multi-turn blue bias pot increases bias current when turned clockwise and decreases it when turned anti-clockwise.

I have found that you need to me even more careful than historically with these new silver solders. One of my power transistors appeared to be soldered good, but when I put a meter on the leg above board and checked connectivity below board there was an open circuit. I would suggest very careful inspection with a magnifying glass and a good light. I stress - any open circuits around the bias transistor and its associated components will blow the amp up.

Hope this helps

Chris
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Old 7th April 2008, 08:34 AM   #129
poynton is offline poynton  United Kingdom
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Default Re: Blown up NAP140 clone

Quote:
Originally posted by cdswift


I have found that you need to me even more careful than historically with these new silver solders. One of my power transistors appeared to be soldered good, but when I put a meter on the leg above board and checked connectivity below board there was an open circuit.

As good a reason as any for NOT using silver solder.
I still have 2 full rolls of 60/40 lead solder.

Andy
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Old 9th April 2008, 05:53 PM   #130
ratchet is offline ratchet  Netherlands
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Default Seller message

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?
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