Sony WM-DDIII output amplifier modification

mattb1970 · Feb 12, 2021

Jut re-read your message and had another look at the photo. the larger board looks to be proto board (Veroboard).
I agree, there looks to be 2 extra resistors or inductors (green colour) as well as an extra capacitor. I think the brown components towards the bottom are the 2.4M Ohm resistors.
Hopefully @mihokm can clarify.

C83 · Feb 12, 2021

mattb1970 said: ↑

Jut re-read your message and had another look at the photo. the larger board looks to be proto board (Veroboard).
I agree, there looks to be 2 extra resistors or inductors (green colour) as well as an extra capacitor. I think the brown components towards the bottom are the 2.4M Ohm resistors.
Hopefully @mihokm can clarify.
Click to expand...

Exactly, yes, the equivalent space on my own DDIII:

[GALLERY=media, 1615]IMG_0062-crop by C83 posted Feb 12, 2021 at 11:36 AM[/GALLERY]

edchocolate · Mar 14, 2021

mihokm said: ↑

While waiting until all parts for new center gears are tested and finished, I prepared design of headphone amplifier used in Sony DD models. This design can be used in any DD walkman, although DC2, D3 and DD100 are missing space necessary to put additional circuit. This time it is not mechanical but electronic design.

The aim was to use modern electronic components, that were not available at the time where DD models were produced, to improve audio quality. What this design is about?

1.
When you use high quality, high impedance headphones, walkman is not able to support sufficient power. The reason is that maximum peak-peak amplitude of signal on the output of TA7688F is 2.4V. It is given by TA7688F bias DC voltage, which is only 1.2V. Even if you use 3V battery, the output peak-peak amplitude without distortion will be only 2x1.2V

2. When you use modern, low impedance earphones (like 16 or 32 ohm), the low frequency signal will be attenuated. It's because 220uF capacitors are used on the output of TA7688F. You can calculate easily what is impedance at frequency of 20 or 30 Hz.

In the following design, I solved both weaknesses.
View attachment 5920
1. I used small modern step-up DC-DC converter to boost power voltage to 5V. TA7688F was designed to work with this voltage. It was very difficult to find suitable converter. I bought many different on eBay. Most interfere with audio circuitry. At the end, I was very lucky. The smallest one works fine. It works from voltage of 1V and it is able to support 500mA current.
On the output, I connected high quality 1500uF Fujitsu capacitor. It is good to manage current peaks.
I had to shift bias voltage of TA7688F from 1.2V to 2.5V. For that, I connected IC input to 5V via 2.4 MOhm resistor.

2. I replaced 220uF Rubycon electrolyte capacitors with parallel connection of two modern tantalum-polumer 220uF capacitors, giving capacity 440uF and unbeatable ESR of 20mOhm!

Here are some pictures of my work:
View attachment 5918
View attachment 5919
Click to expand...

Great thinking ... i like the tants a lot, neat. Im very encouraged by this posting. As they say, “if it aint broke... break it and fix it beta!”
yay!

Emiel · Sep 22, 2021

mihokm said: ↑

While waiting until all parts for new center gears are tested and finished, I prepared design of headphone amplifier used in Sony DD models. This design can be used in any DD walkman, although DC2, D3 and DD100 are missing space necessary to put additional circuit. This time it is not mechanical but electronic design.
Click to expand...

Did you finalize the board and testing, and can you show pictures of it? Thanks!

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Sony WM-DDIII output amplifier modification

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Sony WM-DDIII output amplifier modification

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