Navigating the Oceans of Schematica

Goal

Look at a large schematic diagram and get a sense of the overall structure and signal flow of the circuit.

1. Interpreting schematic intent

  • Every schematic has components part of its power supply

    • single supply? ± split supply? multiple power rails?

What is the entire circuit’s reason for existence?

  • What connectors are / would be on the outside of the box?

  • How would these connections show up on the schematic?

Symetrix 610 “Magic Delete Button”

symetrix 610 front back

Consider Symetrix 610 “Magic Delete Button”, what types of connections does this box have? Focus on the purposes instead of the physical connector hardware.

Click to reveal after thinking first

  • Conservation of energy related (power supply input!)

  • Signals going into the box.

    • Information supplied outside and communicated to the inside.

    • Energy going into the box.

  • Signals going out of the box.

    • Energy delivered to outside devices.

  • What else?

2. The Phantom-powered Menace

Pull-up resistors can be a source of trouble!





phantom powered pullup

3. Identifying amplifiers

3.1. Three types of 1-transistor amplifiers

Before we do detailed circuit analysis for a bunch of single-transistor amplifier types, it is useful to see the results that you get 90% of the time.

Overview of tables in Tourbook: Bipolar transistor amplifiers

aoe fig2 7 transistorman
Figure 1. Transistor man from (Horowitz & Hill, 2016)

Handout for today day06_handout-orig.pdf is pages from

  • Sony_XDR-F1HD_audio-amp_bw.pdf

  • HF1-1.pdf

  • yamaha_pm1000-channel.pdf

3.2. Single-transistor amplifiers

Amplifiers are for some sort of signal, and naturally have

  • input(s)

  • output(s)

  • power, bias, housekeeping, etc.

We will 99% work with amplifiers with a single input and a single output.

Tourbook Table: Bipolar single-transistor amplifier types

First, find the overall signal input and output!

Trace the input signal to the first transistor and/or trace the output signal backwards to the last transistor.

From the handout, identify the amplifier types for:

TA7642

  • T1

  • T2, T3

  • T4

  • T7

  • T10

Sony XDR F1HD

  • Q102

  • Q103

  • Q202

  • Q203

HF1 amateur radio transceiver

  • Q121

  • Q3

  • Q72, 73, 74

  • Q112

  • Q113

  • Q51

  • Q52

Yamaha PM1000

  • Q5

  • Q10

  • Q11

  • Q6

  • Q7

  • Q8, Q9

3.3. There are always exceptions

The mute circuit of the Sony XDR F1HD, an FM radio receiver, is rather interesting!

https://www.circuitlab.com/circuit/j3n98tj5m2zp/sony-xdr-f1hd-mute_math/

It intentionally uses a BJT in reverse-active mode, which is unusual.

RT6N140C transistor datasheet → this is worth looking at!

Wherein the transistor datasheet shows that it is designed for operating in both active modes. This is needed since both the collector and emitter voltages of the transistor are at 0 V DC and the audio signal therefore swings above and below zero.

Youtube: Sony XDR F1HD audio mute circuit

4. References

Horowitz, P., & Hill, W. (2016). The Art of Electronics (3rd ed.). Cambridge University Press. https://artofelectronics.net