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. 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:
Nicely done!! You should (sorry, you Must!) brand modded Walkmans with your logo, as Great Northern Sound did for Wadia CD/SACD players. I will be the first in line to get DD Walkman repaired and modded this way
By the way, the converter itself is only 1x1 cm large. Here is the link: http://www.ebay.com/itm/-/272565317808
I don't understand a single thing from that pcb diagram but I can clearly understand the passion you put in this. Well done, kudos to you
Thanks to Mike Fremer we know that we are privileged to live in the Golden Age (2nd Coming?) of Vinyl. Once @mihokm finalizes his mods we should add Walkmans to this list!!! The reason I suggested slapping Mihokm logo onto modded DDs is pure and selfish : this will increase resale value of the Walkman. @mihokm, just let me know if you want to do this, I found a very cheap company which makes tiny metal stickers of your own design. I use it when selling my revived Discmans, does not work $$ in my case but nurtures my Ego a little bit
Thank you so much Jorge I think it is important to make this mod available for everyone. I'm too busy to work on so many walkmans, I will better work on new things. I mean doing research, improvements, modifications - and then I will publish it for free. Like this one. But I'm doind many repairs, anyway. I think it is good idea to have metal stickers. And may be one day I will finish my primary job (IT specialist) and I will start to earn money by doing walkman repairs.
' waiting until all parts for new center gears are tested and finished', is this the fix for the wm-d3 split gear proble ? I am new here and have been looking for a d3 but became wary of buying one because of that gear problem. when do you think they will be available and how much might they cost ?. it is great you have taken on these problems with the old but great designs. much appreciated out here.
Honestly I hope you keep your current job in IT and keep all walkman's activities as a side occupation or a simple hobby. I know a guy in a nearby town who is a certified Revox technician, he has a long queue of works (average waiting time 6 months) but he still keep his old part-time job: from Monday to Wednesday it is "real" job, from Thursday to Monday it's R2R. He could live off its work as Revox technician (he wrote several books and often attends fairs and events) but he prefer to keep a foot in the real world with a proper job. He knows the analogue craze might be a fad and in 10 years he might have a lot fewer machines to repair; staying out of the job market for 10 years is way too long, it would be very hard to jump back.
Yes I second this never do what you love as a job, it can get frustrating better to keep it separate it’s more fun that way.
Yes, it is good to have different job and hobby, otherwise the hobby would become boring. I even do repairs for almost free, I do not want to make money by this activity. I'm sure I would stop loving this if I did it with intention to earn money. May one day...
@mihokm, Yes!! What I said was wishful thinking, Not an advice! I am blessed with a job that I like but having a hobby is totally different. My second, newly acquired hobby of fine-scale modeling (efforts posted at square-2.com) is just for fun and the fact that months and months of spare time result in a piece with no financial value is my way of staying sane You are able to do something more useful, good for us
Please give test voltages for pinouts for diagnosis. Thank you! I found them in the service manual for WM-DD3. Thank you again.
This is pretty fascinating and am tempted to give it a go for my DDIII. @mihokm , that link to the converter is no longer valid, I wonder would you be willing to post further details on it??
I think it may be like this one; eBay item number: 274522077007 Or search for 0.9 - 5V to 5V DC-DC Step-Up Voltage Boost Converter
Thanks Matt, that looks like a likely candidate. So that would be the little component you can seen tucked inside the larger board in Marian's photo. I may be reading the circuit diagram wrong, but there seems to be more components used in the images than appear on the diagram? Anyone else tackled this?
I think the DC-DC board is just this little PCB I've shown in the photo. It looks to be stuck to another PCB which I assume is original to the Walkman.
