tnsilver
Stereo Puppy
A year ago I encountered a unique DIY project. This talented electronics major from the University of Bar-Ilan in Tel-Aviv had built his very own CNC machine. I was amazed. I told him that if I fail to google up somebody who DIY'ed a ballistic missile in their own back yard - his is the coolest project I've ever seen.
I was struggling, at that time, with a 9090DB unit I picked up in a tag sale. I was stuck with a faulty F2624 driver amp board. It's rails lifted, it had too many DIY jumpers, missing solder rings, bad rails under the Molex assemblies, shot trimmers and it was giving me hell.
I've asked Anatoli, the owner of the CNC machine, to carve me up a new F2624 board and that made him laugh. As it turned out, he could actually do it, but he said there's a much better way. Being an Electronics major and a university technical assistant, Anatoli had both the knowledge to re-design the board plus the access to the university labs and testing gear. He also had the right designing software. Almost a year later we ended up with this:
The new F2624 Driver amp board
First thing Anatoli asked for was the schematics. You all know how ridiculous and erroneous those are. It seems the 9090DB service manual was made to fool technicians. It's a circus of a document. As a result, Anatoli had to reverse engineer the F2624 board I sent him and over time, he came up with his own schematics.
We started to look for modern replacement parts. The board's 70's components all have modern replacements. Those are light years advanced than their 70's counterparts but some components, like the VD1212 red dotted rectifiers and the Temperature compensating STV-H3 diodes are no longer available. We also had to locate some suitable heat sinks and Molex connectors. We then had some boards printed. It took the better part of this year (2013), and finally... It was done. I got the first working board last week.
Fresh F2624 PCB's
I put my tag sale 9090DB on the workbench, plugged it to a DBT and installed the new board. Anatoli had tested the newly fabricated board in his lab to his very own satisfaction but all that time, he did not have access to a working 9090DB unit. This board had yet to prove it's worthiness.
I was terrified of the PITA bias procedure, This very gig caused me to blow my outputs more than once in the past, by overshooting the trimmers setup. I was very careful this time. We've discussed this procedure in length and paid a lot of attention to this issue. To my surprise, it was rather easy this time. I waited the 4 specified minutes for the unit to heat up and started adjusting the bias towards the 30mA mark. Very stable, very consistent, very easy - the bias current went up to ~30mA and started to drop to the 29.1mA after exactly 4 minutes, where it stayed fixed. I was enthusiastic.
My $25 tag sale purchased unit had some mods done on it , including the replacement of the OEM filter caps to a pair of Nichicon KG 15,000uF/80V 100mm long Super Through's and I could not be any more happier with the result. It was still on DBT but I've never heard a DB sing like this before. Crystal clear, punchy lows with the land mark richness of the famous 9090DB warmth plus endless power reserves. I was freaking high!
Initial F2624 Driver Amp Board Testing
This week the unit was put on mains. I just can't get enough of it. Both phono inputs work flawlessly, the AUX entry is spec-less and even the overhauled Dolbey board plays it's test tune with both meters reacting evenly and when no source is playing, the unit is dead silent (even at near max volume).
Another shot of the new F2624 board
So, why am I so proud of this board? Well, first of all, it's one hell of a vintage resurrection project. Second, Anatoli and me defined some objectives prior to getting started, such as the complete ban of low quality cheap Chinese components. It's all high end electronics here now. Nichicon EC's and MUSE bi-polars, Murata MLCC's, KOA Speer resistors, ON Semi-conductors, Zetex transistors and other quality components. Then, we wanted to correct all that is wrong with the OEM board.
You all know how the rails lift when you over heat them by accident when leaving the tip of the soldering iron on them for too long, and how those flimsy soldering pads tear and detach from the board. There is no one here who ever serviced one of those boards and could not stop second guessing the lousy silk screen. You just can't trust it.
With the OEM silk screen, diodes directionality is marked wrong, some caps polarity is either missing or wrong and those transistors ECB markings are so missing on the back of the board, it's crying out loud. Most of us, who serviced that board, probably had to resort to some kind of an improvisation to adjust newly ordered replacement caps lead spacing to the holes on the board. I haven't mentioned yet the need to serial solder two 1N4148 diodes in mid air to replace the VD1212 diodes or the annoyance in having to sort out the Zetex ZTX694B pin out to match the 2SC1400 differential pair transistors. In short - the OEM board rebuild is a pain! All of this hardship - is now eliminated! However, our most important goal, our prime directive, was to not alter the legendary 9090DB vintage sound!
F2624 Front (Component Side)
List of features in the new F2624 driver amp board
F2624 back (Conductor Side)
Anatoli and me are planning on placing the new F2624 board back in production. We can manufacture them at an impressing rate. We did not, however, plan any marketing strategies yet so please don't ask for quotes and discounts yet (although I'm gonna push for an 'Exclusively Sansui' membership discount. :yes.
Any comments are welcome. Feel free to ask anything (no answers are guarantied) and most importantly... Get jealous guys. The more the better. We've earned it :wave:
In the mean time... here are some more pics...
F2624 Both Sides
F2624 Old Vs. New
Cheers
Tom
I was struggling, at that time, with a 9090DB unit I picked up in a tag sale. I was stuck with a faulty F2624 driver amp board. It's rails lifted, it had too many DIY jumpers, missing solder rings, bad rails under the Molex assemblies, shot trimmers and it was giving me hell.
I've asked Anatoli, the owner of the CNC machine, to carve me up a new F2624 board and that made him laugh. As it turned out, he could actually do it, but he said there's a much better way. Being an Electronics major and a university technical assistant, Anatoli had both the knowledge to re-design the board plus the access to the university labs and testing gear. He also had the right designing software. Almost a year later we ended up with this:
The new F2624 Driver amp board
First thing Anatoli asked for was the schematics. You all know how ridiculous and erroneous those are. It seems the 9090DB service manual was made to fool technicians. It's a circus of a document. As a result, Anatoli had to reverse engineer the F2624 board I sent him and over time, he came up with his own schematics.
We started to look for modern replacement parts. The board's 70's components all have modern replacements. Those are light years advanced than their 70's counterparts but some components, like the VD1212 red dotted rectifiers and the Temperature compensating STV-H3 diodes are no longer available. We also had to locate some suitable heat sinks and Molex connectors. We then had some boards printed. It took the better part of this year (2013), and finally... It was done. I got the first working board last week.
Fresh F2624 PCB's
I put my tag sale 9090DB on the workbench, plugged it to a DBT and installed the new board. Anatoli had tested the newly fabricated board in his lab to his very own satisfaction but all that time, he did not have access to a working 9090DB unit. This board had yet to prove it's worthiness.
I was terrified of the PITA bias procedure, This very gig caused me to blow my outputs more than once in the past, by overshooting the trimmers setup. I was very careful this time. We've discussed this procedure in length and paid a lot of attention to this issue. To my surprise, it was rather easy this time. I waited the 4 specified minutes for the unit to heat up and started adjusting the bias towards the 30mA mark. Very stable, very consistent, very easy - the bias current went up to ~30mA and started to drop to the 29.1mA after exactly 4 minutes, where it stayed fixed. I was enthusiastic.
My $25 tag sale purchased unit had some mods done on it , including the replacement of the OEM filter caps to a pair of Nichicon KG 15,000uF/80V 100mm long Super Through's and I could not be any more happier with the result. It was still on DBT but I've never heard a DB sing like this before. Crystal clear, punchy lows with the land mark richness of the famous 9090DB warmth plus endless power reserves. I was freaking high!
Initial F2624 Driver Amp Board Testing
This week the unit was put on mains. I just can't get enough of it. Both phono inputs work flawlessly, the AUX entry is spec-less and even the overhauled Dolbey board plays it's test tune with both meters reacting evenly and when no source is playing, the unit is dead silent (even at near max volume).
Another shot of the new F2624 board
So, why am I so proud of this board? Well, first of all, it's one hell of a vintage resurrection project. Second, Anatoli and me defined some objectives prior to getting started, such as the complete ban of low quality cheap Chinese components. It's all high end electronics here now. Nichicon EC's and MUSE bi-polars, Murata MLCC's, KOA Speer resistors, ON Semi-conductors, Zetex transistors and other quality components. Then, we wanted to correct all that is wrong with the OEM board.
You all know how the rails lift when you over heat them by accident when leaving the tip of the soldering iron on them for too long, and how those flimsy soldering pads tear and detach from the board. There is no one here who ever serviced one of those boards and could not stop second guessing the lousy silk screen. You just can't trust it.
With the OEM silk screen, diodes directionality is marked wrong, some caps polarity is either missing or wrong and those transistors ECB markings are so missing on the back of the board, it's crying out loud. Most of us, who serviced that board, probably had to resort to some kind of an improvisation to adjust newly ordered replacement caps lead spacing to the holes on the board. I haven't mentioned yet the need to serial solder two 1N4148 diodes in mid air to replace the VD1212 diodes or the annoyance in having to sort out the Zetex ZTX694B pin out to match the 2SC1400 differential pair transistors. In short - the OEM board rebuild is a pain! All of this hardship - is now eliminated! However, our most important goal, our prime directive, was to not alter the legendary 9090DB vintage sound!
F2624 Front (Component Side)
List of features in the new F2624 driver amp board
- Double layered PCB. All wiring is done on board, no need for air wiring components
- Dual footprint for ceramic caps will fit both 2.5mm and 5mm lead spacing
- Dual footprint for EC's will fit 2 sizes as well (8 - 10mm diameter with 3.5 - 5mm LS and 16-18mm diameter with 5-7.5mm lead space)
- Trimmer footprint will fit the original trimmers (5mm between wiper pin and the two other pins) and will also fit modern substitutes with 2.5mm spacing between wiper pin and the other two pins.
- All parts are placed on top of the board as well as R901/902. Placement under the board is obviously still possible if anyone insists on doing so
- D05/06 (VD1212) footprint now allows the use of 2 1N4148 plain Jane rectifier diodes in series directly on the board. No need for air soldering.
- Fits the original connectors, no need for any changes to other parts - just plug directly instead of the original board.
- All parts other than the Zetex differential pair transistors are pin compatible with the stock parts. The heat sinks are of slightly larger size than the OEM counterparts.
- The thermal diodes (STV-H3 replacement devices) had been selected after testing the temperature coefficient in a temperature chamber at the Bar-Ilan university lab and after selecting the best matching modern equivalent components for the originals.
- Detailed silk screen on both sides of the board. The top side contains part numbers, EBC marking for transistors, polarity marking for capacitor and diode directionality. The back side contains polarity marking for capacitors, pin numbers on all headers and EBC markings for BJT's.
- All parts (other than the thermal diodes) are readily available for purchase with concurrent mass suppliers (DK, Mouser etc...).
- Use of BZX55 low noise zener diode as replacement for the OEM Zeners
- Audio polar capacitors replaced with audiophile level Nichicon MUSE bi-polar electrolytic capacitors and it's possible to use film caps too - if you choose to.
F2624 back (Conductor Side)
Anatoli and me are planning on placing the new F2624 board back in production. We can manufacture them at an impressing rate. We did not, however, plan any marketing strategies yet so please don't ask for quotes and discounts yet (although I'm gonna push for an 'Exclusively Sansui' membership discount. :yes.
Any comments are welcome. Feel free to ask anything (no answers are guarantied) and most importantly... Get jealous guys. The more the better. We've earned it :wave:
In the mean time... here are some more pics...
F2624 Both Sides
F2624 Old Vs. New
Cheers
Tom
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