Audio Note Interstage Mono Block 300D User manual

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Manual Version 2.1 - January 2010

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Table of Contents
Section1: Introduction............................................................................................................................................................3
Circuit Description..............................................................................................................................................................3
Section 2: Mechanical Section...............................................................................................................................................5
Tang Strip Installation ........................................................................................................................................................5
150R Mill Resistor Installation............................................................................................................................................6
Heat Sink Installation .........................................................................................................................................................7
Ceramic Hardware post installation....................................................................................................................................8
8 Pin valve base installation –rectifier location..................................................................................................................9
Installation of the three Power Supply Caps ......................................................................................................................9
Installing the Mains transformer.......................................................................................................................................10
Installing the Interstage Transformer................................................................................................................................11
Installing the Choke..........................................................................................................................................................11
Installing the Output Transformer.....................................................................................................................................11
Twisting the Wires............................................................................................................................................................12
Section 3: IEC Section and Chassis Ground.......................................................................................................................13
Chassis Ground Connections ..........................................................................................................................................13
IEC Wiring........................................................................................................................................................................14
Section 4: Power Supply Wiring ..........................................................................................................................................17
Section 5: Filament Supply Section.....................................................................................................................................25
LM1084 regulator install...................................................................................................................................................26
Section 6: Installing the Front Insert Plate...........................................................................................................................28
Section 7: Mains secondary to Filament Section Wiring......................................................................................................30
Section 8: Installing the Front Insert Plate...........................................................................................................................32
Front Insert Panel Wiring .................................................................................................................................................34
300B Filament Wiring.......................................................................................................................................................38
Interstage Transformer Wiring .........................................................................................................................................38
Front Insert Plate Wiring Chart check list.........................................................................................................................39
6SH7.............................................................................................................................................................................39
TAG Strip......................................................................................................................................................................39
300B TOP.....................................................................................................................................................................40
300B BOTTOM.............................................................................................................................................................40
Section 9: Final Connections...............................................................................................................................................41
Section 10: Finishing Off and Testing..................................................................................................................................42
Power Supply Checks......................................................................................................................................................47
Audio Checks...................................................................................................................................................................49
Final Stage.......................................................................................................................................................................50
Appendix..............................................................................................................................................................................51
Resistor Color Code Reference .......................................................................................................................................52
AC Wiring Guide (T-199 Mains Transformer)...................................................................................................................53
Full Schematic..................................................................................................................................................................54
Wiring Reference 1 ..........................................................................................................................................................55
Wiring Reference 2 ..........................................................................................................................................................56

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Section1: Introduction
Thank you for choosing to purchase the new version Interstage Mono Blocks from AudioNoteKits Ltd.
Circuit Description
The model is the 300B Parallel version which provides approx 20W of single ended power with zero feedback –The
design is unique in that is uses a 1:1 interstage transformer between the driver stage and the output stage –see below for
a brief circuit description:
These amps are fronted by a 6SH7, connected as a triode, which may seem a little unusual, but apart from the 6SH7 and
the similar, but in a smaller package 6AU6 both being good sounding valves, and the fact that they are available at
reasonable prices there are good technical reasons for using it. The idea with these amps is to use an interstage
transformer, and only ONE amplifying stage before the output valves. This makes for an incredibly direct route, and the
amps sound better for it. Really, listening to such an amp is a revelation, there is only one gain stage, and there are no
coupling capacitors. The underlying coloration which coupling caps of all sorts produce is absent, and there is a far
greater sense of immediacy and dynamics. If you can imagine, the effect of the bifilar interstage is to knit together the
anode circuit of the driver valve and the grid circuit of output valve, what happens in one happens in the other.

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I explained in the interstage transformer article about the virtues of transformer coupling to the output valves, and here the
bifilar interstage transformer is used to full advantage. The extremely high impedance AC load to the 6SH7 means that
you get more or less the full gain of the valve, and the loadline is horizontal, which means because the 6SH7 is so linear
the distortion produced by the driver stage is very low, and predominantly even order. It’s an innate characteristic that a
good triode has a constant mu over a wide range of operating conditions, therefore, as has been known for a long time, if
a triode is run in constant current mode (either by active load, or by transformer or choke loading) then the valve is as
linear as it can be. The secondary side of the transformer provides a low impedance path to ground for grid current.
A triode-coupled 6SH7 has a mu of 40 odd and an anode impedance below 10K, also it’s nicely linear, both as a triode
and as a pentode. The high gain, and low impedance means that the input sensitivity of the amp with only one stage, and
with a pair of 300Bs is still reasonable, if we were to look at using a 6J5 say, the gain is less than half and you start
needing serious volts to drive the thing, also the 6J5’s anode impedance is significantly higher and that would limit
bandwidth due to loading by the transformer and by the 300Bs. There is some kind of phobia, caused by a lack of
understanding about triode connecting pentodes, it’s really a case of choosing the right valve, and then using it in the right
way to get good sound.
There are some of the old telephone triodes out there, such as the 417A and 437A, but these are pretty scarce, and by all
means if you are up to it you can experiment and modify and try replacing the 6SH7 but if you melt your Western 300Bs
don’t call Brian!
Andy Grove - Audio Note design engineer

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Section 2: Mechanical Section
The first part of this manual will be the mechanical installation that is required –once that is completed we will proceed
with the wiring part!
First of all we use Metric Hardware in the kit –M3 and M4 metric –an M4 screw is similar to a #8 in the imperial system
and an M3 is between a #4 & #6 –so the M4 is the bigger of the two –we will also be using flat and pan head screws –
the flat or countersunk screws are very hand when we need a flat surface for a transformer to sit on the screw for
example! Ok lets get started!
Tang Strip Installation
Let’s start by installing the two “Tang Strips” – these are used to support the front insert plate that we will be installing later
on.

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Install the tang strip as shown with the
PEMS (little threaded standoffs) facing
up to the sky.
Now use the black or stainless M3
10mm screws and m3 nuts to secure
the tang strips to the chassis.
You can position the front insert plate
in the chassis just to see how it fits but
we will not be securing it in place now
–we will be building on the front insert
plate and installing the completed
section into the mono block later on!
150R Mill Resistor Installation
Our next step is to install the 150 ohm Mills Power Resistor –this resistor is installed against the chassis –use the 2 x M3
countersunk 10mm screws and M3 nuts to secure into position

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Heat Sink Installation
Our next task is to install the heat sink against the chassis which will be used by
the Filament Section of the Monoblock. Basically the 300B tubes receive a 5V
DC filament voltage via a regulator that needs to be heat sunk in order for it to
operate properly.
We will be installing two bars against the chassis.
Here the first bar is placed against the chassis.
Note this is the bar with just two holes in it .
The second bar that is placed on top.
Use the M4 countersunk screws
provided and thread them through the
front of the chassis.
Place the second heat sink with the 4
holes on top with the countersunk heat
sink holes facing up!
Tighten with the M4 nuts.
Now take the M3 25mm screw and the
M3 spacer and install such that the
spacer secures the screw into position
(see next illustrations also).

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The idea is that the filament board will
eventually sit up on the screw and
align with the heatsink!
Ok good work so far!
Ceramic Hardware post installation
Now we will install the ceramic posts
for the power supply hardwiring –they
use M3 countersunk screws which go
through the top of the chassis and
secure the ceramic posts on the
underside of the chassis.
The first picture simply shows the
posts laying next to the holes they will
be inserted into.
Here you can see the hardwire posts now installed in the chassis.

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8 Pin valve base installation –rectifier location
Now we will install the 8 pin valve base into the rear hole –the only trick is that the notch in valve base faces towards the
front of the chassis.
Installation of the three Power Supply Caps
250uf 500v
250uf 500v
100+100uf
Install the three caps into position.
The 35mm clamps are a bit tight but you should be able to
secure the caps into position as shown.
Use the M4 screws to secure into position.
Here below you can see the caps from underside of chassis.

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Installing the Mains transformer
We are going to install the T-199 Mains transformer now into position.
I suggest you lay the transformer upside down beside the chassis in the format
shown.
The Mains transformer has a primary side (0 110 120 etc.) and a secondary
(400 300 0 300 400 etc).
The Primary is the side with less wires - these wires are connected to the IEC
or AC inlet socket –so let’s position the transformer so that it the primaries are
situated at the back of the chassis.
The primaries for the Mains
transformer can be threaded through
the grommet hole quite easily but the
secondaries will need a little help –we
suggest you give the secondary wires
a light spray with the WD40 so that
they can slide through the grommet
hole a little easier.
Continue feeding the wires through while
the mains transformer lies on its side as
shown.
Now install the rubber strips into position over the holes so that the transformer
can sit on top of these and isolate from the chassis and secure the mains
transformer in place.
Once all the wires are fed through you can use a cloth to wipe off any excess
WD40 spray.
Here you can see the completed
Mains transformer installation.
Primary Side

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Installing the Interstage Transformer
Lets install the Interstage transformer –this is the transformer shown below with the 4 colored wires on it. Use M4 screws
and washers to install. The choke, which is similar in size, just has two black wires.
Installing the Choke
Install the CHOKE in the same
manner.
Installing the Output Transformer
The Red/Black pair go through the
hole nearest the front of the chassis.
The output wires (group of three) want
to be closest to the capacitors.

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Twisting the Wires
The underneath view of the chassis with all the transformers now installed!
The next step is to twist the same colored wires together on the Mains
Transformer for the upcoming wiring jobs!

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Section 3: IEC Section and Chassis Ground
The first picture shows the IEC socket
installed in the back of the unit with the
2 x M3 10mm csk screws, along with
the mains switch, which simply pushes
through the hole. Install these as
shown.
The second picture shows the Chassis
Ground screw which is one of the
Mains transformer screws.
Chassis Ground Connections
Our first task is to take the green wire
from the Mains Primary and we are
going to connect it to the chassis
ground point.
Extend the wire past the chassis
ground point –then strip it and TIN the
wire (tinning is the process of adding
solder to a bare stranded wire so that
it can be easily connected to another
solder point).
Add the Ground Lug to the tinned wire and then solder the ground lug onto the
wire.
Since you have unhooked the nut on the chassis ground point we are going to
add two more prepared cables from the IEC bag to this chassis ground point...
Add in the wire with the GND lug and
crimp on it as well as the green wire
with just the GND lug on it.

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Now you can install the green wire
with GND lug and crimp on to the GND
post of the IEC socket which is the one
on the bottom of the IEC.
The third wire will be used later for the
power supply ground.
Gently tighten the nut –we may be
moving the wires a little so no need to
tighten too much!
IEC Wiring
In this section we will be hooking up the IEC section –the following example is for 120V operation –refer to the
appendix for wiring for all the world voltages.

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We have provided a number of pre-made cables & parts for this section to make it nice and clean
1. 2 CRIMPS
2. Heatshrink
3. IEC GND >> CHASSIS GND cable (already used)
4. Blue/Brown Twisted CRIMPED cable
For 120 V operation take the twisted white and twisted black pairs of wires.
Let’s start with the white pair – we will be cutting this wire, stripping the ends off,
twisting the two ends together, tinning, adding a crimp to the end and soldering
the wire on to the crimp, then installing the heat shrink!
It is a good idea to read a few pages before beginning so you understand the
process.
This is what we will end up when we have completed the white wires.
Let’s start by trimming the white wires
–leave some extra length in case you
mess up and need to start again –I
would leave about 5 inches of twisted
white wire at least.
Here we have cut the wires, twisted
together and then TINNED them (i.e.
added solder to the exposed wire).
You may want to trim the tinned wire
to the desired length and then place
the crimp over the tinned bare wire –if
it does not fit then try smoothing out
the tinned wire with soldering iron.
Then add some solder in the hole
showing –use a fine tipped soldering
iron –make sure the solder “Takes”
such that the solder is shiny and the
wire has accepted the solder!

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Then add the prepared heat shrink on
the end.
If you do not have a heat gun you can
run your soldering iron over the heat
shrink quickly and it will shrink –clean
off any excess solder off your
soldering iron if you use this method.
Once that is complete you can insert
the crimp on to the bottom of the
rocker switch. Make sure you wait for
the crimp to have cooled down a little
after putting on the heat shrink.
The second picture here also shows
black wires now installed onto the
rocker switch. You can do this now.
Now take the prepared twisted cable
and install on the IEC as per the
picture to the left.
This completes the IEC section –well
done!

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Section 4: Power Supply Wiring
In this section, we are going to start wiring the power supply. You should follow the following diagram as you progress
through the section. It may be a good idea to use a highlight pen on the diagram as you progress.
Rectifier Wiring –8 pin tube valve base
We are now going to wire up some of the Mains secondaries to the Rectifier
Valve base at the back of the chassis.
In order for the tube to work at all we have to provide a filament voltage to the
tube –in the case of the 5AR4 the filament voltage is 5V AC.
If you look on your transformer wiring chart you will see that the yellow
secondaries are the 5V AC –so we will connect these to pins 2 & 8 of the 8 pin
rectifier base.
You will see a notch on the 8 pin valve base and the notch is between pins 1 & 8
. after the notch counting clock wise starting from one from the side of the base
as shown in the picture opposite we can see where pins 2 & 8 are.
1
4
5
6
7
2
3
8

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Take the yellow twisted wire and cut to
an appropriate length like in the
photographs –leave a little extra –
now cut the wires, strip the insulation
off the end and I suggest tinning the
wire and then trimming again –then
position the wire into the correct valve
base pin –then apply solder –you will
see that the tinned wire will take the
solder easily –I suggest you use the
bottom holes of the valve base.
The rectifier tube also takes the high voltage AC which in this case is 400v AC
on each wire (in opposite phase) and we apply to pin 4 & 6.
Here you can see the red wires hooked up to pins 4 & 6.
That completes the AC wiring for the Rectifier tube.
Power Supply Chassis Ground
Take the third wire that you previously connected to chassis ground –we are
going to connect it to the bottom of the LEFT hand ceramic power supply post.
Strip the wire and it is a good idea to tin the wire before inserting it into the first
position by just pushing a little with your soldering iron you will find that the
tinned wire will quickly adhere to the post.
Now take the Blue/White wire from the Mains secondary and this will go into
position 2 on the LEFT hand side ceramic post.
If you check out the Mains transformer chart you will see that the BLUE/White
wire is the center tap for the 6.3V AC 1A that we will be using for the 6SH7 tube
filament later on –We will be raising the filament supply for this tube by 40V –
see overall technical description of the amplifier.

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Installation of the 100R resistor into
the first position –this resistor is
between power supply ground and
chassis ground.
Now add the .001uf capacitor across
this resistor and leave the leg on the
right side so that we can bend it up
and have it connect to position 2.
Now add the 47K resistor in position 2 and leave the extra as we will bending on
the LEFT side this time –see next part.
You can install the 330k resistor now into position and connect the LEFT side
between the 47K & the 330K resistors.
Now on the top position on the ceramic hardwire post we want to add the pair of
15K resistors and they are connected to each other on the LEFT hand side –
see graphic.

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Now let’s wire in the CHOKE.
The choke has two wires –both black and either can be used as input or output
–a choke is basically one long piece of wire wrapped around a core in order to
slow down any AC movement –they are used in power supplies smooth out the
DC that is created by the rectifier tube. Start by taking the CHOKE Wires –we
will be connecting one end to the ceramic posts in position 3 - RIGHT Side (the
other end will connect to the 150R power resistor later on that is connected to
the chassis). Check out the schematic of the power supply and you will see
these connections.
Trim the choke wire (leave a little extra) and tin it and then position into the
ceramic post 3-LEFT –at the same time cut a length of RED wire and also TIN
and insert into positions 3 LEFT and 9 Left –with both wires installed in 3 LEFT
you can then add solder and make a single solder connection at 3 LEFT.
The graphic opposite shows a map
of the wiring for the Power supply up
to this point.
Refer to the appendix of the
complete wiring progression from
this point forward.
15K
15K
330K
47K
100R
+
+
+
+
Interstage
CHASSIS GND
S-GND
2
1
3
4
5
6
7
8
100+100
250uf
250uf
Mains
Transformer
secondary
150R
.001