Audio Note Interstage Mono Block 300D Instruction 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 characteristi c 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.

5 6 7

+ 39 hidden pages

Audio Note Interstage Mono Block 300D Instruction Manual

Specifications and Main Features

Frequently Asked Questions

User Manual