SOHA v3.0 walkthrough

Wrote by Zang(digi01) 2006.9.1


Introduction
SOHA is A Simple Tube/Opamp Hybrid Amplifier projected by Alex Cavalli, Mark Lovell and Bill Pasculle(headwize.com members).Discuss thread at here.
For easy assembly I have design a double layer circuit board,shown below:

Click here to see full-size photo(100KB).

Building & comment
SOHA V3 builder's thread
Walkthrough by mb3k


SOHA v3.0 PCB design
The PCB is a flexible design based on this schematic.



The PDF file show layout details.Click here to download the pdf file.
As a diy workshop project is free.Click here to down the gerber file.
The board connection method.Click here to down the gif file.


BOM list (the blue assigned component s is MOD able)
R1 100k Log Pot
R2, R12 300R 1/8W
R3, R13 560R 1/8W
R4, R14 2k Trimpot
R5, R15 1M 1/8W
R6, R16 150R 1/8W
R9 2k2 1/8W
R10 1k3 1/8W
R11 11k 1/8W
R7, R17 1k 1/8W
R8, R18 360R 1/8W

VR1 12V Fixed Regulator 7812
VR2 -12V Fixed Regulator 7912
VR3 Adj. Negative Regulator LM337(Small heatsink needed)
D1, D2, D5, D6 1N4148 or similar
D3, D4 1N4002
BR1, BR2 100V 1A WOB packaged recitifer

C1, C13 1000u 10V
C2, C14 100n 100V
C3-C6 100u 100V
C7, C8, C11 47u 16V
C9, C10, C12 470u 35V

V1 12AU7/ECC82 or equivalent
U1, U2 OPA2134 or similar, dual or single

T1 30VCT 400mA Transformer
FUSE 0.3A
K1-1,K1-2 2P2T 220VAC1A switch

STEP BY STEP Assembly
T1, Power supply of U1,U2 =>Check +12VDC, -12VDC
U1,U2 parts
Plate supply of V1 =>Check +60VDC
CSS parts
Filament supply of V1 =>Check -12.6VDC
V1 parts
Check +40VDC Rch/Lch,adjust R4,R14 (You can't set the plate voltage correctly without the volume pot installed.)
Overall wiring
Test point is commented by Pieter(superdac)



CSS Tips



1N5297 ccs wiring
J113 ccs wiring (R8,R18 1.5K 1/8W)
LND150 Source Follower (use with BJT opamps output stage)

LND150 ccs wiring
Revised by rreynol : R7/R8 and R17/R18 are silkscreened in reverse to what they should be when using an LND150 on the v3.0 digi boards. R7/R17 should be 360 Ohms and R8/R18 should be 1KOhms. You can verify this by looking at the tracings and checking to make sure the G pin of the LND150 connects to a 1KOhm resistor and the S pin connects to a 360 Ohm resistor.


MOD Configuration
R6,R16
Quote mains_hum : The purpose of the resistors is purely to get roughly similar perceived loudness from low impedance ( 32Ω ), medium impedance ( 150Ω ), and high impedance ( 300Ω ) headphones for any particular volume pot setting.
The resistors are not mandatory. There are so many different headphones out there and so many individual music sources available to drive a SOHA (meaning different input voltage levels), there is no one simple answer to what works best hence we kept the ability to experiment.

VR1,VR2
For TO92L packaged regulator,VR1(78L12) should be Rotate 180 degrees.


SOHA V3.0 PCB is available.the below button is for 2PCBs order including shipping.

December 25, 2007 15:49 PM