Bozak Cma 10 2dl Manualidades
Before I start on the repair, here are some notes on the Bozak. Firstly, I’m working off the same schematics as everyone else since I’ve only come across one version, but I’ll include them for the sake of completeness.All PCBs affix to the motherboard using 0.15″ spaced pins. I haven’t been able to locate a replacement for the original stamped sheet metal units with two mounting points. For my replacement cards I used a generic Molex KK254 style right angle pin header, which fit slightly tighter than the original units, being a square extrusion rather than stamped metal. I can’t comment on how the original connectors will hold up with larger pins, but I assembled and disassembled this unit a huge number of times throughout the job and no problems. It feels much more solid. This unit has a motherboard labeled MB-4, which didn’t have mounting points for the bracket affixed to the output amps – a shame as they are top heavy and I’d prefer not to rely on foam for stability.
There were a few different foam compounds in this unit which had either turned rock solid or disintegrated over the motherboard.Removal of the balance controls is an obvious change to make. The original mixer used a B50K pot with a 10K slugging/law resistor, which (25K 10K) more or less gives you a pot centre position voltage divider equivalent of 6K8 and 25K, with the 25K to ground.
This means you wind up with a balance network loss of almost 2.2dB.Removing the pots does not require the installation of equivalent fixed resistors, in fact I’d advise against it. Start to finish, the mixer has headroom no human will come close to hitting. I have driven 30VPk-Pk out of it with no issue. The increase of 2.2dB subsequently improves the noise floor and the removal of the pot also drops crosstalk between channels and increases the input impedance.If you don’t want the pots, just remove them and do not replace them with anything.This unit arrived with two different era of phono preamplifier cards, though all had the same PCB as identified by serial number. Two of the cards came with nice Beyschlag resistors as detailed in the original schematics. The newer units came across as built down to a much lower pricepoint, with generic looking carbon resistors and 10uF electrolytics replacing tantalum caps in positions C7 and C27.Since water damage affected the original uncoated film capacitors in the response network (C8/C28, C9/C29) I replaced these with matched polystyrene capacitors.All capacitors were changed, with the exception of a couple.
The full list of capacitors and the replacements I used is here:2N3822 J-FETs in the summing and equaliser amplifiers had severe tin whiskers – though after cleaning I decided to keep them installed. I have a decent stash of original motorola units so I matched then taped four of them inside the mixer for a future repair if required.The Fset capacitors on the front panel equaliser PCB (C1,C11 C2,C12 C3/C13) were the only caps to make it through the process unscathed.The output amplifier is a solid Push-Pull output amplifier. The trimpot adjusts the bias of the input stage, used to make sure the amp clips symmetrically. Gain is set by R7/R27, 220R is used for the nominal 28dB in the schematics. To adjust the gain of the output amplifier change these resistors and recalibrate the bias trimpot. (Simulated) resistor changes are:(Note this table references my Pathos Mixer schematic, so the resistor is lised as R407, not R7/R27)(I also don’t recommend you use every value listed as changing the bias of the amp dramatically can affect the sound. I calculated them down to 0dB out of curiosity.
In my Pathos mixers I used 750R)Interestingly, this unit arrived with different values. The two output cards are arranged by channel, with the front facing amplifier on the PCB taking care of the headphones and the rear amp handling the main outputs on the back.Transformer is a 36VCT unit.
Urei 1620
The power supply collapses in simulation at roughly 280mA. It has a soft start, with roughly 7 seconds or so passing before the supply hits 40VDC. This PCB contains a 4P relay for Output and Headphone muting which is still easily available at cost, though I simply cleaned and actuated the relay a few times.The schematics floating around on the web split the motherboard other 2 files, so I stitched them together, you should be able to open and download a full sized version.The original front panel is Brushed aluminium, the remainder of the chassis being sheet steel – tough to machine with my setup. This steered me towards an isolator solution that took advantage of existing mounting holes.The knobs are Buckeye Shapeform DSN Series, still manufactured by the original company, though to my knowledge aren’t available for consumer purchase via any usual avenues. Minimum orders are by weight. A close equivalent are the EHC Knobs Designer series, which are available with a little hunting.
An item that has been used previously. The item may have some signs of cosmetic wear, but is fully operational and functions as intended. This item may be a floor model or store return that has been used. See the seller’s listing for full details and description of any imperfections.Seller Notes:“ Used Bozak, Needs Service.
Bozak Cma 10 2dl Manualidades 2018
Has a drop out issue or something like that. I dont personally know the in and outs of these mixers. Expect to have to tune it up. We also have a very worn original silver faceplate that came with it.Sold As Is ”Brand:BozakMPN:CMA102D.