3 - N5X schematic
barry (Administrator) 12-30-2013 at 01:36 AM.
Post: #1
[Image: n5xsch1.jpg]

CLICK HERE to open a window showing the N5X's full-size schematic. This diagram shows all of the component values added and with numbered lugs for all off-board components. All components are numbered on the schematic (R1, C3, D4, etc), so that you can relate this schematic to your Kit contents listing and the turret board layouts.

Do I need to be able to read a schematic?
This is a very common question for new amp builders who may feel intimidated by a diagram covered in rather mysterious electronic symbols. The short answer is 'no'; the rest of the build guide shows exactly where everything goes and how it's all connected.

[Image: n5xsch3.jpg]

But it is a good idea to become familiar with schematics. They are the definitive guide to how any circuit works. From a schematic, you can follow the signal path, check the connections of components, and so on. An experienced amp builder or amp tech can even look at a schematic and work out everything from there, with no other documentation.

As always, if you break a complex structure up into smaller parts, it's a lot easier to understand. If this is your first build, you will find that the following description will help you understand the whole schematic of the N5X amplifier as a group of smaller circuits, each with their own job.
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barry (Administrator) 12-30-2013 at 02:04 AM.
Post: #2
Block diagram
The main schematic looks very busy, and is crammed with information. It's a lot easier to understand if you think of the circuit as a number of modules. This diagram shows them colour coded.

Along the top, there's your guitar signal path from left to right:
* green box = guitar input, first amplification stage and Gain control
* yellow box = second amplification stage and TMB tone controls
* red box = Master volume and power stage

[Image: n5xblk1.jpg]

Along the bottom, there's the power supply, with the mains entering at bottom right:
* grey box = mains-side circuit
* orange box = heater supply for the valves
* blue box = power supply with VVR
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barry (Administrator) 12-30-2013 at 02:07 AM.
Post: #3
First amplification stage
The guitar input socket is shown at the top left, and it feeds into the light green shaded section. This is the first stage of the amplifier and it uses one half of the ECC83 preamp valve (V1a) to amplify the low-level guitar signal.

The resistors and capacitors around V1a set the way that it works - how much current flows at idle and what EQ is applied to the signal passed along to the next stage. There's also one half of the Boost switch (S1a) here - it controls which is any capacitors are used to add an extra boost to part of the guitar signal.

The final part of this section of the circuit includes the Gain pot, which controls how much of this boosted signal is fed into the second stage.

[Image: n5xblk2.jpg]
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barry (Administrator) 12-30-2013 at 02:09 AM.
Post: #4
Second amplification stage
The guitar signal - still fairly clean so far - is fed into the second part of the amp (shaded in light yellow in the block diagram). This uses the other half of the ECC83 preamp valve, V1b. Many of the components are similar to the first stage, and there's the other half of the Boost switch, here, too. If the Gain control is set high, the incoming signal will overdrive this second amplification stage to create some preamp distortion.

[Image: n5xblk3.jpg]

The output of this stage then runs through a network of resistors, capacitors and pots that allow you to control the treble, middle and bass frequencies of the signal that will be passed along to the power valve. This is a 'lossy' tone stack, meaning that in order to adjust the TMB frequencies, it must throw away part of the amplified signal. With the Bypass switch (S2) enabled, however, you can choose to have the full output of this stage passed along to the power valve.
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barry (Administrator) 12-30-2013 at 02:14 AM.
Post: #5
Power stage
The reddish shaded section shows the power stage, which includes the Master volume control, the power valve and the output transformer. The Master volume is the simplest part - a pot that lets you dial in how much signal the power valve receives. Low settings for cleaner tones, and at higher settings you can overdrive this valve to get maximum distortion.

[Image: n5xblk4.jpg]

The N5X includes a 'noval' socket for EL84 valves (like the SE-5a), but also has an octal power valve socket, V3. So you can plug in a 6V6/6L6/EL34/etc instead of the EL84. These bigger valves have different overdrive characteristics and tones, and you can experiment to find your own tone.

The power valve works with high voltages and low currents, and the output transformer transforms this into a low-voltage, high-current signal that's suitable for driving the speaker (which you connect to any of the jack sockets at the top right of the diagram).

And that's all there is to the signal path of the amplifier! An amplifier with a simple signal path like this remains very dynamic - responding well to changes in your picking style and/or pedals - and allows you to dial in a surprising amount of distortion.
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barry (Administrator) 12-30-2013 at 02:16 AM.
Post: #6
Mains circuit
The signal path runs from left to right at the top of the diagram, but the power supply runs right to left at the bottom of the diagram. So the first stage is the mains circuit, with the IEC mains adapter at the bottom right.

[Image: n5xblk5.jpg]

The light grey section shows the part of the amp that operates directly from the mains supply. It includes the fuse, On/Off switch and a neon indicator. Just as important is the connection of the Earth wire from the IEC lead to the amp's metal chassis. Via these components, the mains is fed to the mains side of the power transformer, which has a range of inputs to suit your local mains voltage: 100V, 120V, 220V, 230V and 240V.
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barry (Administrator) 12-30-2013 at 02:21 AM.
Post: #7
Valve heater supply
The mains transformer has two outputs, known as secondary windings. One of these supplies the valves with a low voltage to (literally) warm them up. This is the heater supply - shown in light orange in this diagram.

[Image: n5xblk6.jpg]

The heater is the part of the valve's internal electrodes that glows dull-orange when an amplifier is switched on. Once it has warmed up, a valve can start to conduct the guitar signal, but not before. This is why there's always a small delay between switching an amplifier on and being able to hear any sound.
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barry (Administrator) 12-30-2013 at 02:31 AM.
Post: #8
High-voltage supply
The power transformer also provides a high-voltage AC output in addition to the heater supply. This high-voltage winding is shown in the light blue section of the block diagram.

It feeds into some diodes which work together to turn the AC voltage into the DC voltage required by the valves. The large power supply capacitors and resistors filter out mains hum and pass the DC voltage on to each of the amplification stages (shown by the red triangles).

[Image: n5xblk7.jpg]

In the N5X, there's a Variable Voltage Regulator (VVR) circuit - shown here as the darker blue block. You can use the VVR pot to dial down the voltage supplied to the power stage. There's just one good reason to do this: it lets you have power-valve distortion at any room volume, from 0W and 5W.
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barry (Administrator) 01-20-2014 at 05:02 AM.
Post: #9
Direct links to reference diagrams
This guide is written in several sections, ranging from a basic description of the N5X to very detailed instructions on how to build each and every part of the amplifier. I recommend following it step-by-step and paying attention to the tips and suggestions.

However, if you're an experienced amp builder, you may just want to dive into the build and do it your own way. To make that easier - and for easy reference for all builders - this, the last entry on each page, lists the important reference diagrams:

* Schematic
* Power supply board
* Main board
* Finished layout
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barry (Administrator) 01-20-2014 at 06:23 AM.
Post: #10
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