Preamplifier 2012 (1)

Part 1: introduction and line-in/tone/volume board

Labs Project

Based on a Labs project | April 2012 | Find it here

Besides presenting a truly high end audio control preamplifier for home construction, this article series also aims to show how low-impedance design and multiple-amplifier techniques can be used to significantly reduce the noise levels in analogue circuitry. The result of the design effort is a top-notch preamp that’s brilliant not just sonically but also in terms of cost/performance ratio.

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Materials

110650-PCB.pdf

Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

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PCB

Download Gerber file: 110650-1-V12

Download Gerber file: gerber files of all six boards with outline files

Extra info / Update

Specifications
Test conditions: supply voltage ±17.6 V; all measurements symmetrical; tone control defeat disabled.
Test equipment: Audio Precision Two Cascade Plus 2722 Dual Domain (@Elektor Labs)
THD+N (200 mV in, 1 V out) 0.0015% (1 kHz, B = 22 Hz – 22 kHz)
0.0028% (20 kHz, B = 22 Hz – 80 kHz)
THD+N (2 V in, 1 V out) 0.0003% (1 kHz, B = 22 Hz – 22 kHz)
0.0009% (20 kHz, B = 22 Hz – 80 kHz)
S/N (200 mV in) 96 dB (B = 22 Hz – 22 kHz)
98.7 dBA
Bandwidth 0.2 Hz – 300 kHz
Max. output voltage (200 mV in) 1.3 V
Balance +3.6 dB to –6.3 dB
Tone control ±8 dB (100 Hz)
±8.5 dB (10 kHz)
Crosstalk R to L –98 dB (1 kHz)
–74 dB (20 kHz)
L to R –102 dB (1 kHz)
–80 dB (20 kHz)

Component list

Resistors
(1% tolerance; metal film; 0.25W)
R1,R2,R39,R40 = 100Ohm
R3-R6,R41-R44,R78,R79 = 100kOhm
R7-R12,R16,R17,R21-R24,R33,R34,
R45-R50,R54,R55,R59-R62,R71,R72 = 1kOhm
R13,R51 = 470Ohm
R14,R15,R52,R53 = 430Ohm
R18,R35,R36,R56,R73,R74 = 22kOhm
R19,R20,R57,R58 = 20Ohm
R25-R28,R63-R66 = 3.3kOhm
R29-R32,R67-R70 = 10Ohm
R37,R38,R75,R76 = 47Ohm
R77 = 120Ohm
P1,P2,P3,P4 = 1kOhm, 10%, 1W, stereo potentiometer, linear law, e.g. Vishay Spectrol cermet type 14920F0GJSX13102KA. Alternatively, Vishay Spectrol conductive plastic type 148DXG56S102SP (RS Components p/n 484-9146).
Capacitors
C1,C2,C10-C14,C26,C27,C35-C39 = 100pF 630V, 1%, polystyrene, axial
C3,C4,C28,C29 = 47µF 35V, 20%, bipolar, diam. 8mm, lead spacing 3.5mm, e.g. Multicomp p/n NP35V476M8X11.5
C5,C6,C30,C31 = 470pF 630V, 1%, polystyrene, axial
C7,C32 = 1µF 250V, 5%, polypropylene, lead spacing 15mm
C8,C9,C33,C34 = 100nF 250V, 5%, polypropylene, lead spacing 10mm
C15,C16,C40,C41 = 220µF 35V, 20%, bipolar, diam. 13mm, lead spacing 5mm, e.g. Multicomp p/n NP35V227M13X20
C17-C25,C42-C50 = 100nF 100V, 10%, lead spacing 7.5mm
C51 = 470nF 100V, 10%, lead spacing 7.5mm
C52,C53 = 100µF 25V, 20%, diam. 6.3mm, lead spacing 2.5mm
Semiconductors
IC1,IC3,IC5-IC10,IC12,IC14-IC18 = NE5532, e.g. ON Semiconductor type NE5532ANG
IC2,IC4,IC11,IC13 = LM4562, e.g. National Semiconductor type LM4562NA/NOPB
Miscellaneous
K1-K4 = 4-pin straight pinheader, pitch 0.1’’ (2.54mm), with mating sockets
K5,K6,K7 = 2-pin pinheader, pitch 0.1’’ (2.54mm), with mating sockets
JP1 = 2-pin pinheader, pitch 0.1’’ (2.54mm), with jumper
K8 = 3-way PCB screw terminal block, pitch 5mm
RE1,RE2 = relay, 12V/960Ohm, 230VAC/3A, DPDT, TE Connectivity/Axicom type V23105-A5003-A201
PCB # 110650-1
Note: all parts available from Farnell (but not exclusively), except PCB 110650-1.

Discussion (0 comments)

Malcolm Mr Bloor 8 years ago

Fitted mine in a aluminium case 330x240x75 (approx). Still not fitted the level board, which I built for completeness, as I will have to sneak it in under the other boards (bit tight for room). As I record (transcribe) the odd vinyl record, I fitted the jumpers used to disable the first input channel when using the mm/mc board. I then use what was an input as an output from the mm/mc board to feed my computers A/D convertor. The installation is a little crude, but the results are sweet. Thanks DS.

0 Comment(s)

C Gunn 5 years ago

Have completed and have been testing with a Q-watt amp . Sound is impressive
The treble does not change when adjusting the pot
Measured the AC voltage on both outputs no change . Placed it on the scope and have seen no change in amplitide when adjusting the treble as compared to the bass.
Any comments on this would be appreciated

Have Denon Bluetooth to XLR input , DAC to RCA and Turntable to MM input . All working

Complete the enclosure in black walnut with a stainless steel front plate . The connection finished off with carbon fiber . Did the design with solidworks software and had the wood and metal cut out with a CNC machine

0 Comment(s)