new power supply circuit board
Revox B77
1.177.313 new development
Here comes the brand new power supply board for all Revox B77 tape recorders.
The new printed circuit board has been developed from an audiophile point of view. For this purpose we have provided the AC input voltages of the power supply board with additional interference suppression capacitors. The rectifiers have 4 additional parallel capacitors, the conductor tracks are particularly wide and 70 µm thick here too! Other filters with LC elements, blocking and support capacitors.
The biggest challenge is certainly the installation of the new circuit board. You have to disassemble the machine quite a bit and the connections coming from the transformer have to be soldered.
the technique
two separate controllers
Twice LM317
Here, too, we do without exotic voltage regulators. We prefer to use the well-known LM 317 regulators. The regulators are mounted on a real heat sink. The heat sink is aligned in such a way that the air can flow past the thermals as freely as possible and dissipate as much heat as possible unhindered!
Also the rectifiers are placed so that the air
can flow past particularly well. The rectifiers are also very large, oversized and no longer covered by the too small and too hot cooling plate!
dissipation
The total power loss has remained the same. Only the power loss is divided between two voltage regulators. More important, however, is the separate supply of the audio boards with 21 V and the speed control, the capstan control or sound motor control is also now supplied with separate 21 V from the second transformer winding.
Filter
2 LC links
Together with the charging capacitors, the coils not only form an LC low-pass filter with a cut-off frequency from approx. 300 Hz. The coils also effectively limit the charging current peaks, so that interference peaks and transients are also effectively suppressed and avoided. All this calms the operating voltages and reduces the residual ripple.
Ten capacitors
We use 10 additional capacitors to smooth the rectification and the AC input voltages. There is no simple copying here, others can do that - not us at revox-online! After all, the power supply is the basis and should already be well designed and use all of today's possibilities and knowledge!
capstan control
completely separated from the audio voltage.
Not only did we build the voltage regulator twice, but the voltage itself now comes from the transformer winding that supplies the logic and no longer from the transformer winding that is responsible for the audio section! Does that bring anything?
It would be a shame if we hadn't used this option!
power strips
for through-hole contacts
You don't have a lot of choice there!
Since we also want to offer our printed circuit boards individually, we have to be compatible with the existing printed circuit boards and peripherals. Hardly any longer obtainable plug and socket strips are used with a spacing of 5.00 mm and not with 5.08 mm. The difference may still go for smaller plugs with 3 or 4 contacts, but no longer with 15 contacts as with the drive control!
Since we also want to offer our printed circuit boards individually, we have to be compatible with the existing printed circuit boards and peripherals. Hardly any longer obtainable plug and socket strips are used with a spacing of 5.00 mm and not with 5.08 mm. The difference may still go for smaller plugs with 3 or 4 contacts, but no longer with 15 contacts as with the drive control!
5,00 mm * 15
We use 5.08mm female and male headers.
The socket strips are split into smaller groups just like the plug strips of the drive control. This is where the difference from
0.08 mm no longer matters. Everything fits like a glove, including the original drive controls!
socket strips
for through-hole contacts! We at revox-online have these socket strips in stock. So you don't have to desolder old sockets from the old circuit boards and solder them back in here! You will receive a fully assembled, functioning and tested circuit board!
the layout
The conductor tracks
The conductor tracks are particularly wide and round. The conductor tracks for the motors are all additionally laid on both sides. We cannot change the positions of the plugs, sockets and fuses, the positions are specified by the tape machine and are tough specifications that we also have to follow. Worse is the availability of the special socket strips with 5.00 mm spacing and the socket strip with the through-hole contacts for
the sound engine control.
shielding
There is shielding only around the low voltage.
The cables around the motors are not shielded, as with the new deck control. The attachment of the circuit board is of course also specified and cannot be changed.
Two tin bridges are responsible for adapting to the MK I or MK II versions of the Revox B77. Thus, the power supply fits all Revox B77.
the installation
Housing
Remove device
First of all, the four rear housing screws must be loosened and the tape machine carefully pulled forwards out of the housing.
But beware! Never place the device on its front side!
Slowly lever the device out of the housing - it works!
ATTENTION! Pull out the mains plug before opening!
115 Vac / 230 Vac can be deadly!
Ventricular fibrillation caused by electric shock can be fatal even after 3 months! Always consult a doctor after an electric shock!
Drive Control
To remove the drive controller from the Revox B77, the screws on the drive controller's cooling plate must be loosened and all the connectors on the drive controller removed. J5 on the power supply board, the front 15-pin connector can also be unplugged.
Now pull the circuit board away to the outer edge.
sound motor control
to remove the sound motor control, a screw must also be loosened from the heat sink. First pull off the three flat plugs of the Varispeed connection. The screw does not have to be unscrewed completely.
Now pull the printed circuit board to the right towards the connection panel.
upper front panel
The upper front panel of the Revox B77 is attached with 5 screws, these must be loosened. In addition, the pressure roller, which is attached with a screw, must be removed and the tape head cover removed.
Now you can carefully remove the front panel and set it aside.
Remove transformer unit
Soldering experience is required!
unplug
Before loosening the four screws of the transformer, you should remove all pluggable connections from the power supply board (11 flat plugs to the motors, 2 flat plugs coming from the speedometer and the connectors J1, J4 and J5). Even if the allocation and the color coding are described in our instructions, you can quickly take a few photos with your cell phone, never hurts!
padding
You should create a work surface behind the device with books, crates or boxes approximately up to the height of the transformer. After unscrewing the transformer, you can place the transformer on the work surface, unscrew the power supply board and desolder the wires. It's not exactly level here. The transformer unit should not pull on the cable when it is lying on the work surface.
Danger! Do not drop the unit so that the transformer pulls on the cable!
Unscrew the transformer
After the upper front panel has been removed, you can easily access the four fastening screws of the transformer.
Unscrew the transformer
The transformer should be removed and reinstalled as a complete unit with connection panel and power supply board. Now you can easily get to the power supply board and do all the necessary work easily and conveniently.
And while you're at it, you should also replace the mains suppression capacitor behind the connector panel.
Screw off
After the printed circuit board has been unscrewed, you can unsolder the soldered strands coming from the transformer. The same applies here: taking a few photos with your smartphone makes it easier to assemble later. The positions of the strands on the new circuit board have not changed. This is also described in the instructions!
manageable effort
The effort is relatively high. However, everything is doable. With the procedure described here, it goes quickly by hand. We will always supply the interference suppression capacitor via the mains voltage. We consider the replacement of the interference suppressor to be important!
Anyone who enjoys tinkering and can solder a little will be fine with it. The big advantage of the new power supply is the complete separation of the voltages for the audio area and the control!
new
Power supply board 1.177.318
Power supply board 1.177.318
for all Revox B77 can be found in our shop
Thomas Schröder
Schottjer Straße 30
26529 Upgant-Schott
Germany
Schottjer Straße 30
26529 Upgant-Schott
Germany
49 4934 - 80 44 39
info@revox-online.de