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Yamaha A-1000, A-700 PSU Modification - Complete Basic Solution

B

bartek_k

New Member
As a continuation of the thread: https://audiokarma.org/forums/index...ng-else-will-still-work.962306/#post-15203392 I've decided to develop a complete basic solution for power system modification in Yamaha A-1000 (A-700) and share it here.

This modification significantly improves the sound quality of the amplifier. The sound have higher resolution, it is cleaner, the separation of instruments and their sustain is improved. The dynamics and quality of high tones will improve. (I don't know Audiphile slang in English so they are just translated)

It works great with amplifiers with refreshed electrolytic capacitors.

The overall effect of improvement is always there, but the specific sound and tones characteristics are influenced by the capacitors used. Therefore, you should listen to several types of capacitors from different manufacturers and choose the best one for you.

I recommend using connectors like these:
image.jpg

to replace capacitors without soldering and solder them permanently only after choosing the ones you like.

In the Gerber zip file attachments there is a ready PCB design, which you can upload on the website of the PCB manufacturer, such as Chinese JLCPCB or others.

You are making modification at your own risk, so always measure the output voltages before installing in the amplifier and never change the + and - voltages.

Circuit additionally transfers about 2 x 5 Watt of power to the heat sink, so make sure you have a good connection with the heat sink. Components must be electrically insulated from the heat sink!


Schematic:

A-1000 psu mod - schematic.jpg


Wiring diagram:

A-1000 psu mod - wiring diagram fhd.jpg


Connect GND to central GND point on main board like is shown on diagram. I'm using Molex KK254 connectors or similar. The pcb board is designed for them.

What to remove from phono board:

A-1000 psu mod - remove.jpg


Mounting:

A-1000 psu mod - mounting.jpg


PCB Gerber file: http://hifi-retro.vxm.pl/images/A-1000_PSU_MOD/A-1000 PSU Mod - HiFi-Retro for DIY.zip

PART LIST:

Voltage regulators

LM317/LM337 - Classic 3-Terminal Adjustable Regulator. I suggest improved types LT317/LT337 which have 3 times lover noise and better other parameters. TO-220

Transistors

T1 - NPN 20 Watts in TO220 package. Sanken 2SC4883 or 2SC4382 are a good choice.

T2 - PNP 20 Watts in TO220 package. Sanken 2SA1668 or 2SA1859.

it is important to use genuine parts due to the constant power load of about 5W per transistor. Fake products can fail.

Diodes

D11,D21 - 27V Zener diode 0,5W. Can be BZX55 low noise zener diode

D31,32,41,42 - 1N4002 or similar diodes.

Resistors

R10,R20 - 10 Ohm 3 W - To protect transistors from burning because of high current peak when turning on and high output capacitance.

R11,R21 - 5,6 kOhm

R31,R41 - 240 Ohm

R32,R42 - 3,92 kOhm for Yamaha A-1000 (22V) or 3,16 kOhm for A-700 (18V)

Use 0,5 W, 1% tolerance metal film resistors with 50 PPM/C or better for best results

Capacitors

C12,C22 - 100nF - 5mm lead spacing

C11,C21 - 220-330 uF / minimum 35V - 3,5mm lead spacing, 8mm diameter max

C13,C23 - 470-1000 uF / min. 25V - 7,5mm lead spacing, 18mm diameter max. You can hear a different types in sounding, but not so much as Cadj and output capacitors.

C31,C41 - 100nF - 5mm lead spacing

C32,C42 - 10-22 uF / min. 25 V - 2,5mm lead spacing, 6mm diameter max. Cadj capacitors. Very important for sounding and overall performance.

C33,C43 - 10-22 uF / min 25V - 2,5mm lead spacing, 6mm diameter max. Output small capacitors close to the Ic's. Important for sounding

Cout+,Cout- - 1000 uF / min. 25V - 7,5mm radial or 10mm Snap In lead spacing, 22mm diameter max. Very important for final sounding and overal performance

I recommend using 50V capacitors because they usually sounds better.

You can also watch my modified Yamaha A-1000 on this video:

Enjoy!
 
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This is ultra amazing @bartek_k! thank you very much for preparing this for us! After i finish up with my chores i will get started on this.

LOG
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Nov. 26, 2021 6:23pm - PCB's ordered from JLCPCB
Nov. 26, 2021 7:58pm - all parts ordered from Digikey
 
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I had ordered 1/4 watt resistors by mistake, and had to wait until i had a larger order to get the 1/2 watt ones. I realized after that the red capacitors were too tall and would interfere with the TO-220 devices when it was time to screw them in...so i just soldered them farther away from the board and then bent them downwards. Here's my progress so far:

board.jpg
 
I see the progress. About the screws, you can use an Allen key threaded screw. The only disadvantage is that you need to cut the thread in the holes, but even with the cheapest screw tap it is very simple.

607439_1.jpg


Resistors R11,R21 must be minimum 0,5 W. You can reduce the zener diode current by putting higher value of those resistors like 10 kOhm which will give around 5 mA zener diode current. Others 0,5 W resistors can be replaced by 0,25 watt.

I see you chose elna rfs capacitors as output capacitors. In my experience, they don't sound good. But you will listen yourself and decide.
 
bartek_k said:
I see you chose elna rfs capacitors as output capacitors. In my experience, they don't sound good. But you will listen yourself and decide.
Click to expand...
Same experience here (Elna RFS / Silmic II).
Not very good power supply filters (input or output), and they take a long time to improve.
 
@bartek_k and @zaibatsu what capacitor would you suggest for that position? I am going to be making a Mouser order very soon for another project, and can add some replacements for these. But unforunately Mouser doesn't have the boutique capacitors that PartsConnexion has.
 
Ok I hooked it up (left the phono board unconnected), turned the unit on, played some music, and the music tugged at my heatstrings and was great! However, I don't know if its because of this mod, or just because i haven't listened to the A1000 in a long time. The first time i heard the A1000 i had an emotional reaction to the music as well. Then as i listened regularly there was no emotional reaction. This has been the first time i stopped using it for a couple of months and now the emotional reaction is back again!

I was supposed to be doing other things at home but ended up listening to songs for over 1 hour, it was so great to hear good music after such a long time.

Anyhow, this modification is staying in there! And it also will allow me to completely remove the phono board and make room for the DAC board, if i decide to go that route. Thank you @bartek_k for providing the files and instructions! If my A1000 is anything like the one from you youtube channel, that has stable voltages on your oscilloscope, then i'm really happy to have made a leap in audio clarity. Thanks once again, and i look forward to your future mods and projects!!
 
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It's great that everything works and you are satisfied. The supply voltage at the moment is stable like the view from the oscilloscope on my channel.

If you spend some time on choosing caps, you can still get a lot more. I really recommend replacing the Elna Silmic II with other capacitors. On the output you can translate the Nichicon FG you have on pre-filtration or check, for example, Panasonic FM, Illinois Cap. KXM, Nichicon KZ ... C13, C23 - pre-filter you can check Panasonic FM, Kemet ESY, Rubycon ZJL ... C32, C42 are a Cadj of LT317 / 337 chip. They are very important. Panasonic Fm works very well here, but also polymer ones like os-con or others can give great results in sounding.

It's all like tuning an instrument before a concert :-) Your Yamaha A-1000 has already had the capacitors replaced, so everything has to be adjusted (by correct selection of capacitors) for the best results and your hearing.

When you listen more time and get your opinion on how yamaha plays now, share with us :-) Maybe some photo?
 
I was previously listening to the A1000 with the new green board on top...insulated with a plastic bag underneath. Here as some pics of the final installation.

I had to use a mini-ratchet to get the screws into place...i used the same black self-tapping screws that are used for the regular transistors.
01.jpg

Here it is installed!
02.jpg
 
Nice, how it's sounds now? I see you didn't change elna's caps. If i can recommend something - change elna rfs to panasonic fm 1000uf/50V on this place and change 680uF marked on pic, because as I watch your old posts, you have also elna there (looks like). You can change it to Rubycon ZLJ 680uF/80V if you have enough bass. If not, rubycon has a really good quality in sound but not enough mass on bass freq. Elna silmic on 330uf near those can bring it back probably. I think you will hear how's the capacitors are important for overal sounding...

a-1000 680uf.jpg
 
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A very funny thing happened.

When I used a plastic bag to insulate the board, everything worked perfectly.
01 working.jpg

When I installed it, i might have did something bad...there were some wires underneath and not allowing the board to sit properly, so i pushed the board down hard to squish everything together and then added mica pads and screwed in the transistors. When i hit the power switch, after 3 seconds the relay didn't click, but i heard a loud hisssssssss and then smoke came up from underneath the board, LOL!
02 marked up.png

I will open it up in the coming days to see what happened. Happy New Years everyone!
 
avionic said:
Did you use insulating screw bushings on the TO-220 transistors as well as mica ?
Click to expand...

No i didn't use the bushings, only the mica. oops now i can see where the problem is. I wonder what part could have let out so much smoke from underneath? I was coming directly from the center...as if it was the relay? I'll find out soon enough and report back.
 
It appears that capacitor C11 was shooting out smoke from the top after about 5 seconds after power up. The smoke wasn't coming from under the board as i thought. Its a good thing that there's not too many parts on this new board for me to check. And i guess since transistor T1 was in contact with the heatsink, that is the first place i'll start with!

01 red smoking capacitor.png

02 schematic.png
 
It seems that the defect, although serious, can be easily repaired. Probably due to a short circuit with the heat sink, the transistor burned and gave full supply voltage to the capacitor, which fired due to exceeding the maximum voltage. There is a transistor, a capacitor and probably a zener diode to be replaced. Check r10 and r11 resistors. The LM317 should rather be fine, I used to have a similar adventure in my layout and the LT317 was fine after. And once again, I remind you that the transistors and lm's must be isolated from the heat sink and screws with the washer mentioned by @avionic
 
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