SRPP
6SN7 Line Stage Pre Amp
Click
here for Picture
Click
here for Line schematic
Click
here for Power Supply schematic
Click
here selektor and delay circuit
SRPP
Basically SRPP is anode follower with constant
current source as the load instead of resistance such as anoda follower
in general.
Comparing to general anode follower SRPP
offers some advantages such as :
a) Constant current source will provide
high impedance to let the circuit achieve higher gain than it
could get with resistor
as the load.
b) Constant current source help the circuit
to reduce all noise and hum from power line.
c) Beside work as anode load the constan
current source also perform as cathode follower that provides
low output impedance
to drive low impedance load
The Line Circuit
After you saw the line circuit you may think
that it's so simple, that's right because simplicity reflects My Phylosophy
No. 1 of My Audio Phylosophy
The line circuits require 200VDC and consume
10 mA current. Why I adjust the bias current so high is becauce I want
to ensure that the circuits will work in pure Class A and linear as posible.
Beside that I also follow sylvania data book recomendation, mention that
for linear operation 6SN7 must work with 100 V and 10 mA bias current.
This idea reflect my Philosophy No.
2 and No.3.
Negative feedback is something you'll nerver
find in this design because I apply Zero
Feedback Design concept.
I provide two output terminal low impedance
output (Low Z output) and high impedance output (High Z output). Through
Low Z output the circuit will perform as pure SRPP and totally the music
signal will pass through 2 stage, the lower tube as anoda follower and
the upper tube as cathode follower.
Through high impedance output the circuit
will perform as anode follower with constant current load and totally the
music signal will pass through one stage only.
If you want best sound quality I suggest
you to pick up the signal from High Z output because in this configuration
the music signal only pass one stage. The fewer component on the signal
path the better sound quality it will be. Also don't forget to check the
power amplifier input impedance because High Z output also require
high input impedance from the power amplifier.
If your power amplifier has low input impedance
( bellow 15 kohm) I suggest you to use low impedance output. In other side
low impedance output perform tight bass sound.
I do not use any capacitor on the input
or in other word I apply DC coupling. I'm sure that using capacitor
on the input side as the coupling element will never better than direct
coupling no matter how expensive the capacitor that you use.
Setting the sound level can be done by the
use of 50kohm potentiometer.
Power Supply
Basically the power supply unit for this
pre amp consist of three part :
a) High voltage supply regulator,
that produce 200 VDC
b) Heater supply regulator, that produce
6.3VDC
C) Power supply for delay and selector
* High Voltage regulator
This part consist of 4 stage of regulation
:
- Pi stage by C21-C28 and R18
- Zener dan Source Follower by Z1 and Q6
- High voltage floating regulator by
LM317
- Servo Regulator by IC1 and IC2
The main transformer provide 200V, 15V and
10V for high voltage regulator, delay&selector and heater power supply.
Especially for high voltage regulator
I provide 200mA trasnformer range though acctually it only has to serve
for 40mA current consumsion. As seen on the regulator schematic I provide
1980 uF capacitor as the pre regulator after bridge dioda though actually
it only serves for 40 mA curent consumsion.
It reflect My Audio Phlosophy No 5
Over
Capacity .
After pre regulation there still 3 other
regulation stages, and those are Zener & Source Follower, LM317 Floating
regulator and finally Servo regulator.
* Heater Supply
I use the combination
between LM723 and 2N3055, I'm sure that you know them very well.
I don not denie that generally tube designers
prefer to use LM317 as heater regulator because of it is cheap price and
simpleapplication, but in case of stability, ripple rejectio ratio LM723
are much better than LM317. The application of high quality regulator for
heater is also important, because all noise appears on the filament could
induct into the cathode and then appears on the output.
Besides that I also apply soft start capability
on the heater supply to maintain heater filament lifetime.
* Selector and Delay power
supply
I don't provide special
design for this stage because it contributes nothing to overall sound quality.
Delay & Selector Input
When you turn on power
switch on the front panel of the casing you will not hear the music imediately
because of delay process. I provide this mechanism in order
the tube has enough time to get heated and stability before it can produce
optimal sound.
I prefer to use relay selector design instead
of mechanical selector under 2 considerations :
- The applications of relay selector design
will help to avoid crowded cable line inside the casing that
could generate hum, noise,
crosstalk and also make the inside casing does'nt look nice.
- The applcations of relay selector design
will help to make a proper distance between left and right
channel avoiding cross
talk.
Components
Finally component have
to be considered as one important think that determine final quality of
the design. Strong phylosophy will not work without high quality
components.
* PCB, I use overplate PCB to maximize the
thickness of cooper layer, in order to reduce cooper loses
from the PCB.
* Tube, I use Russian NOS 6SN7 tube with
gold plated socket
* I use Solen MKP capacitor for Low Z output
and Siemens Oil cap for High Z Output
* All resistance are 1% Metal Film
* And finally I use Tokyo KO ON Potentiometer
for level controlk
Listening Impression
When we did trial, we use such equipment
as :
CD Player
: TEAC
Pre Amp
: SRPP 6SN7
Power Amplfier : Thule (Solid State)
Speaker
: Tannoy Wesminster
Cable Power
: CARDAS
We were trying some Album such as Something
In Common ( Earl Klugh & Bob James), Michael Allen (Michael Allen),
Potrait of Cuba (Paquito Rivera), Dave Grussin Dedicated to Duke Ellington
(Dave Grussin) and what we can tell you are :
* Depht, This pre amp
perform very precise dept and show very good staging effect
* Detail, Every kind of instrument
sounded clearly
* Stereo image, This pre amp also
performed very clear horizontal position of every music instrument
* Ear Friendly, Although we had been
listening music using this pre amp for many hour we did not feel
ear fatique, the sound produce by
this pre amp was so Ear Friendly.
Beside that this pre amp also perform
hot vocal sound that make it very interesting on playing women
vocal such as Linda Ronstadt,
Marry Black etc.
