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2021.9.4 Circuit design for GIXIE Audio

We will design the circuit of the circuit block designed in the block diagram last time.
The block diagram shown last time is shown below.

There are three circuit blocks that have design elements here. Audio Amplifier, Power Regulator, and VU meter driver.
First, the circuit diagram of the designed amplifier is shown below.

Audio Amplifer

This is an amplifier Circuit below.

I used an amplifier IC (PAM8304) that does not require detailed design.

Ｄ Class Amplifer IC ＰＡＭ８３０４ＡＳＲ

■Summary
・Power Voltage：2.8~6V
・Output：
3W typ(5V・4Ω)
1.75W typ(5V・8Ω)
・Gain：300000/Rin
(30倍 about Rin 10kΩ)
・Loss Current at No signal：5mA typ(VDD=5V)
・Power efficiency：93% typ(RL=8Ω、THD=10%)
・Package：0.65mm、MSOP8

＊＊Quoted from HP of Akitsuki denshi＊＊

For the circuit, I used the reference circuit described in the data sheet here. The resistance value and the capacitor were decided sensuously.

The SD (shutdown) terminal is pulled up because it will stop unless it is pulled up.

　

VU meter circuit

Next is the circuit of the VU meter.

The VU meter is, so to speak, a DC ammeter. Instead of inputting the audio signal directly, it is amplified by an operational amplifier, rectified by a diode (converted from AC to DC), and the current is adjusted by a resistor and sent to the VU meter.

For the OPAMP, I used NJM4580, which can be used for general purposes.

　

Power Regulator Circuit

Next is the power supply circuit.
Since the power supply voltage of the amplifier ICPAM8304 is 6V at maximum, a circuit that can flow a constant voltage of 5V is required.

The circuit is a general circuit of a 3-terminal regulator. C4 and C5 are anti-oscillation capacitors. C6 is for ripple removal. It is also an RC low-pass filter for R5 and C9.

　

Regulator IC 　５Ｖ１．５Ａ　ＴＯ－２５２　ＮＪＭ７８０５ＳＤＬ１

■ Main specifications
-Output method: Series
-Output positive / negative: Positive power supply
-Input voltage: ~ 35V
-Output voltage: 5V
-Maximum output current: 1.5 A
-Dropout voltage: 2.2V
-Allowable loss: 1190mW
-Ripple removal ratio (PSRR): 78dB
-Package: TO-252

** Quoted from Akizuki Denshi **

Finally, the entire schematic is shown.

Next time, we will design the board for this circuit.

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Aug.29.2021 Desinging of GIXIE Case Audio

This is a new project.

Previously, Mystery I disassembled the wooden box .

In the previous blog, I disassembled this case and searched for its true identity. As a result, it was a watch, but I made it before, and I gave up because it would be too expensive to have six Gixie tubes.

Therefore, since there is this fashionable case, I wondered if it could be applied to something at least.

Especially in this case, there are 6 round holes with a diameter of 34 mm.

The speaker and VU meter were perfect size for GIXIE Case.

Therefore, I would like to make an audio amplifier speaker with 4 speakers and 2 VU meters.

Select of Speaker Unit

This time, the size is small, so I didn’t ask for sound quality so much, so I decided to give priority to design.

I chose the same speaker with a diameter of 34mm.

Amazon Small size Aluminium Cone Full Range Speaker Unit 1.5inch(34mm)3Ω/MAX8W

Price；￥590

Sold as a unit
1.5 inch full range speaker
15mm voice coil
Aluminum cone
Neodymium magnet specifications (magnetic shield specifications)

I’m a little worried that the impedance is only 3Ω, but I think it’s generally okay.

VU meter

I was worried that VU meters would be available these days, but when I searched for Amazon, I found cheap ones overseas.

The price is 1990 yen of two sets. Its so very Chiepfull.

Amazon VU Panel Level mater 6V〜12V 500μA High Resolution include the Back Light 2sets

Price；￥1990

Material: Plastic, electronic parts
Header DC resistance: 630 ohms
Backlight filament voltage: DC / AC 6V ~ 12V
Filament backlit 500μ AVU meter
It is widely used in audio recorder equipment

　

Block Diagram

The block diagram is shown below.

Since the impedance of a single speaker is low, it is difficult to connect speakers in parallel from a single amplifier. Therefore, you have to attach an amplifier to each.

Place two variable resistors in front of the amplifier and use this as a volume.

From the audio input, branch off from the amplifier and connect the VU meter driver in parallel.

Also, make it possible to input an arbitrary voltage with the DC jack, insert the regulator circuit, and supply it to each circuit.

Block Diagram

Next , designing Circuit of this Block Diagram.