Studiomaster 12 into 2
I kept an eye of one of these since I started to build my homestudio. The only reason that spoke against such an old-fashioned mixing console is the space that it needs on the desk. Now, or better in the near future, the Study-room studio will change it's location and get "more space". What a seldom and nice situation ... "get more space" means ... get a little bit more gear :o) And as I saw the offer for this wonderful studiomaster 12 into 2 console it was not a big decision. But keep in mind ... a mixer restoration needs patience ! In this case nearly everything exists 12 times ... and that only is done with a lot of patience :o)
Like almost I started with a brief visual inspection of the ingredients ... really nice design with a lot of space inside. Perfect for restoration. Then a first test with "power supply only" ...
to check the voltages. Wonderful and quiet linear regulated power supply ! Love it ... no humming noise from the transformer ... only voltages in the valid ranges.
Then I reconnect everything and check each single function of the whole device. This should be done carefully ... keep a notice for every failure that appears otherwise you will do this more than
once :o)
Here the inspection results:
- Hum at all outputs
- Crackling noise from channel 7
- 3 PFL momentary switches doesn't work
- 2 Fadercaps missing
- No illumination on the meters
- loosen Tolex on the front
- some wear and tear on the wooden sidepanels
- dusty and dirty frontpanel and fader- and potcaps
- crackling pot's that are partly hard to rotate
But beside this ... all channels, all sliders and the meter's work. The frontpanel is in good condition, no deep scratches, only dust and dirt :o)
Restoration
1) Demounting and cleaning
- Demount the wooden sidepanels
- Demount Fader-and Potcaps
- Loosen and demount the Pots.
- Clean the potcaps and the mechanical parts
- Clean and polish the faceplate
2) Tolex and Wood
- Glue the Front-Tolex
- Overwork the wooden sidepanels
3) Recap the whole thing:
Hum on all channels points to dry electrolytic capacitors. This bahaviour reduces the capacity and the caps can't do what they should do ... filter the resulting hum from the dc supply lanes.
Recapping is neccessary to restore the original function again.
- starting with the Power Supply
- Summing Amp
- Echo1, Echo2 and Foldback Channels
- all 12 Input Channels ... puh :o)
Prepare OP-Change ... (add sockets)
- Add sockets on the the Summing Amp
- and on Channel 1 first (for a test)
- change the coupling caps on channel 2 to MKP series
Crackling noise from Channel 7:
I break it down to the 4 input-transistors on Channel 7. One of those must be the root cause, because as I treated the board with a Coolant-Spray this were the components that respond at most. Without a schematic I can't say exactly what this network do, but I think it is a form of input differential amp. After I changed all 4 transistors the Channel is quiet again like all of his neighbours.
Some PFL momentary switches that don't work:
This was funny ... only cold junctions nothing else. After resoldering the bus connections everything works like expected.
Crackling Pots that partly are hard to rotate:
Ok, that's more or less normal. After cleaning with contact-spray the crackling was gone, don't forget to rotate after cleaning and if it still crackles repeat the cleaning process. To ease up the mechanical rotation I treated the pot-axes with a little bit of fader-grease. Very nice product ... it's not like new after treatment but much better than before.
The meter-illumination
This was surprising. Each of the meters had 2 little bulbs inside ... unfortunately nothing like a sofitte that could be easily change. No, these ones are soldered in and really small ! I can't
detect any information about voltage and power. And ... they are connected in series. But that's not all ... the bulbs of the second meter are connected also in series. Result after opening the
meters and measuring these little bulbs ... only one is defective. But this one stops the whole thing :o) I bypassed the defective one with a roughly calculated resistor and ... tataaaaa ... 3 of
them starts softly glowing. Wonderful !!! I think I replace it with 4 new ones 6V/0,24W or 6V/0,78W.
Re-Assembling all components ... and be happy about the result. But take a look at your own !
Maybe, after a while of usage, I will test some different OP-Amps in Channel- and Summing stages. But it is still a wonderful sounding and looking console, isnt it ?
