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NAP 140C Clone

Introduction

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.

Schematic
Useful links
Bill of materials

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.

Setting quiescent current

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:


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