RevoxB225

August 2008

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In this article I will try to describe my first encounter with the legendary Revox B225 player.The roots of this machine are in the first ever Philips CD player - first generation of CDM mechanism called later " the ZERO", many people including myself consider itto be one of the finest mechanisms ever. Something that definitely is NOT MADE ANYMORE TODAY. It is something you won't find on the supermarket shelve.

The Revox B225 has also the first generation Philips electronics - the chips are from the SAA 70xx series - starting from saa7000, 7010, 7020, 7030, etc. Each chipplays a different role, all aspects of digital signal processing are done separately - RAM, error correction, interpolation, digital filtering, oversampling, etc etc. You candownload the datasheet and read more about it.

What sets the Revox B225 apart from the crowd of tens of other similar machines based on the same electronics is the first ever use of display. The first players fromGrundig, Philips, Marantz, Loewe, B&O, and other German companies had only the LED display indicating track number up to 16.Just like these two:

B&O Beogram CD5500 and Loewe CD9000

Revox went further and provided the fully functional and informative LCD display. That is the weakest point of all Revox players - the display often breaks, leaks thecristal liquid, looses digits, etc. In the Revox B225, B226 and B126 - the LCD was NOT back-lit. So you could not see it in the dark room, even if there is a lightbulbbuilt in above the display.The luxury version - Revox B226S has a backlit - which is a real disaster. Probably 90 % of them are dead by now. And they can't be repaired, and can't be substituted.Some spare light emitting foils exist, but costing close to 100 Euro if you are lucky.

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RevoxB225 http://www.lampizator.eu/lampizator/REFERENCES/Revox B225/Revo...

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DAC Chip of the Revox B225

Anyway, back to Revox B225 - what is the key information is that te DAC is a 14 bit type, old grantfather of all DACs - the Philips TDA1540. On paper it is an enfantterrible, but many people swear they like the sound of this DAC.I would not even consider listening to the "mere 14 bit" machine if I had not tried before the Philips CD104. Electrically - Philips CD104 and Revox B225 are the samemachine, indistinguishable from one another. Funny thing is that on ebay the Revox costs easily 10 times the asking price of the Philips CD104.If you ask me, if someone wanted the CDM0 and TDA1540 sound, but BETTER build than Philips - the Loewe CD9000 is a much better built thing than the RevoxB225.

Enough boring you with description, lets look inside the Revox B225. Having done some works on 5 players from Revox - The B226, B226S, B126 and E426 - Iecpected to see a well built machine but nothing prepared me for THIS.

This is the drawer, which like some other drawers from Sony, Meridian 227, and Marantz CD73 - contains actually the whole mechanism in it. It is not a mere tray whichtakes the disc, but the whole ton of metal mechanism of Philips CDM Zero comes out of the player. Very impressive. It looks good, feels good and plays good. God if Icould have a SPDIF transport like that !!! But no - the Revox does not have SP/DIF yet. This format was not invented because noone needed external DACS back thenbefore 1985. The Philips TDA 1540 was the DAC chip to have and nobody proposed to build external boxes. I am sure it is possible to extract raw data from theSAA7000 chip and with a little help from additional SAA7220 we could produce SP/DIF but I havent tried it.

The big issue with this tray arrangement is THE MOVING MASS. To move this weight we need HUGE and torky motor and indeed, we find in the revox a giganticmechanism for moving the tray. There are no belts so it lives longer than the other belt based transports. All is mechanically coupled like in a tank.Overall, the combination of CDM zero, the huge tray, the moving mechanism and the LCD display makes this a very strong contender to the most interestingmechanism title.

What else is to be found inside Revox B225 player?

Well, lots of stuff. In fact this is the only player I have seen except the insanely overengineered Accuphases which is completely FILLED with electronics in its entire 3-6VOLUME not only on flat 2-d board. The Revox approach is to put multiple boards vertically and occupy the whole space available.Each board is a one sided traditional hand made PCB with a defined roles like DAC, Digital, Servo and Power Supply.


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On the photo above we see two most interesting boards - the Digital - (upper) and DAC/Output - (lower).

From right to left on the lower board we see: the SAA7030 digital filter with oversampling (sort of equivalent of the later SAA7220p/B), then two mono DAC chipsTDA1540, 7 decoupling caps around each dac just like in the TDA1541 (220 nF in this player).Then we see two double opamps per channel, so each signal goes through 4 opamp modules. Last device is a output muting relay and a pair of output sockets.

Of course Revox would not be a Revox if things were simple. Nothing is simple.Normal RCA cables don't fit here - the top cover prevents usage of any Gucci cables. Only very slim Mickey Mouse cables fit in these tight holes. I suggest to DRILLTHEM to some 13 mm diameter immediately.Another thing - detachable AC cord is non standard so forget about substitutes.Last but not least - ONLY oryginal Revox remote will work. Prepare yourself for a 80 Euro price plus shipping.


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Reverse side of the Revox B225 DAC PCB.

What I dont like about Revox engineering is the fact that the voltage regulators are VERY FAR away from the consumers. The trace from the regulator to the actualconsumer, say a DAC chip - can run for a meter of various wires, traces, connectors etc.Anyway, Revox B225 is a very welll regulated product ! Just look:


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These are 6 regulators of voltage (high end low noise low drop type from LM3xx series) sitting on common heatsink on the power supply card. Two chips on theextreme left are unknown, maybe diodes ?


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This is the empty space after removing two cards. You can admire the solid steel shaft for suspending the moving drawer.


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This is the transformer (EI type) and the back side of the mechanism assembly. The second steel shaft is visible.EVERYTHING IN THIS PLAYER is MADE OF METAL.

Tuning the Revox B225 CD player.

What could be improved in this player ? Well, lots of things.What I suggest is this program minimum:1. Clean, dust and WD40 the mechanism.2. Enlarge the RCA openings to accomodate normal cables3. Replace the AC input socket with Furutech or Shurter normal 3 pin type. Add a proper power cord.4. Check the green light bulbs in the drawer compartment - probably dead by now.5. Replace or add a bypass to the critical electrolytic caps that supply the DACs and the SAA digital set of chips. Use Os-cons or Tantalums. Plenty of space there.6. Increase the size of 7 decoupling caps by another 220nF or so, MKP type. Solder under the original ones keeping them in place.7. Replace the first pair of opamps with sockets, put good opamps in place of these OLD OLD ones. I used OPA2604 from Burr Brown.8. Remove the SAA7030 chip and create the NOS mode of operation.9. Take the signal from FIRST opamp half and take it to the RCA (first - float the RCA from the old circuits.) use a capacitor of choice to remove DC from the signal. Iused 2,2 uF MKT from Roedestein.

This makes a FANTASTIC PLAYER. Nothing is brutally changed from original Revox sound, it is just SO MUCH BETTER - it is not one league, it is two leagues higherquality. Everything you might have liked about the old Revox, you will like much more.Now I don't have doubts why people go crazy about the Philips TDA1540 DAC chip. It is phenomenal.


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This is the DAC and his first opamp. Signal stealing point is marked with a black arrow at the top. One channel only.

This is the other DAC and his first opamp. Signal stealing point is marked with a black arrow at the bottom.


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The signal stealing caps installed.

Three chips are removed - two old opamps and the oversampling chip.


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The non oversampling NOS bridge wires installed in the empty holes of SAA7030 chip.

For pin numbers see the NOS article.


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These are three power supply bypass caps - 100 uF tantalums: for plus 5V, minus 5V and minus 17V. Three caps PER CHANNEL.


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This is the SAA7000 digital demodulator chip with three power bypass tantalums and a 1K resistor that pulls the pin 16 to plus5V from Pin 18th to set the 14 bit modeof operation.


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Some other bypass tantalums - plus and minus supply of the first opamp, two caps per channel.


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This is the snipit bridge from first opamp to the RCA outputs. Note the two traces cut to float the RCA's.

I drilled the hole to pull the wires through to the other side of the PCB and connected the wires to the Roedestein capacitors.

SOUND OF NOS REVOX B225

After all mods I loved the sound. It is lively, solid, with meat, musical, open, effortless, and with nice presentation of details. Bass is very good and trebles are okay.Even without LAMPIZATOR - this is first class player. Very similar sound to TDA1541A. I could not tell them apart blindly.

Now lets do the right thing - Lets lampize the Revox properly with 6N2P tubes !!!!

..........................to be continued .....................\\\

See other revox articles:

Revox B226SRevox B226Revox B126

BACK TO LAMPIZATOR PAGE


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RevoxB225

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