There has been a bit of interest generated by a cheap copy of the NAP 140C amp becoming available on eBay. Initially the version supplied was closer to the NCC 220 from Avondale Audio but the recent ones are closer to the original NAP 140.
Information kindly supplied by Mike Redman from the eBay seller’s instructions and email.
Label on PCB |
Value |
Label on PCB |
Value |
R1 |
100K |
C1 |
10μF |
R2, R10, R20 |
22K |
C2 |
330pF |
R3, R32, R33 |
4.7K |
C3, C4 |
10μF |
R4, R37, R38 |
100Ω 1/4W |
C5, C6 |
100μF |
R6, R7, R8 |
1K |
C7, C12 |
39pF |
R9 |
27K |
C8 |
220pF |
R13, R14 |
680Ω |
C9, C10 |
470pF |
R15 |
27Ω |
C40 |
0.22μF |
R16 |
2.7K |
||
R17 |
1.2K |
D1, D4, D5, D6, D7 |
1N4148 |
R18 |
68Ω |
D2, D3 |
1N4005 |
R21 |
620Ω |
||
R22 |
390Ω |
Q1, Q2, Q3, Q7 |
2N5551 |
R23 |
560Ω |
Q4 |
2SB647 |
R26, R27 |
100Ω 1W |
Q5 |
TIP41C or 2N5551 |
R29, R30, R42 |
0.22Ω 3W-5W |
Q6 |
2SD667 |
R31 |
1.8K |
Q8 |
2N5401 |
R35, R36 |
47Ω |
Q9 |
TIP41C |
R41 |
8.2Ω 2W |
Q10 |
TIP42C |
TR1 |
2K2 |
Q11, Q12 |
2SC2837 |
Recommended working condition: +/-40VDC (30–0–30VAC 200W power transformer for stereo operation) and 20mA quiescent current.
You can replace Q5 by TIP41C (included with the kit). Mount the TIP41C as close as the output transistor. Then the thermal stability of the amplifier is better.
I have found out that the setting the quiescent current in the output transistors should be done as follows:
BEFORE APPLYING VOLTAGE TO THE PCB. Adjust the trim pot wiper to half the total value 1K1 (ohms). Then apply power and adjust the trim pot TR1 until a voltage drop of 2.2mV is measured across R29 the 0.22R resistor connected to the emitter of the top half of the output transistor pairs. Positive rail side. The quiescent current can be set as follows:
Voltage across emitter resistor (R29) |
Quiescent current |
2.2mV |
10mA (Min) |
4.4mV |
20mA (Typical) |
6.6mV |
30mA (****Max) |
The amount of quiescent current chosen depends of course on the size and thermal efficiency of the heat sinks chosen.
****Warning...Thermal run away and destruction of the output transistors will of course result if the heat sinks are too small to run with the amount of quiescent choose. Perhaps you can check these figure out and see how hot the amp gets and if it remains stable. Please don't take these figures as being suitable for the amp without testing them yourself.
Note:
