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Thread: Bozak CMA 10-2 stereo mixer

  1. #1
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    Bozak CMA 10-2 stereo mixer

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    Was pretty excited to come across this mixer at an auction recently, especially given the good condition this old box was in. Since there doesn’t seem to be much information on the internet regarding these units (although there is a fair bit on the more famous DJ mixer, the Bozak CMA 10-2DL) I figured I would post some info and photos of the unit I have.

    Bozak CMA 10-2 stereo mixer. 10 channels of transformer isolated mic pres. Each of the 10 channels can either be mono or stereo (mono is pin 3 hot, stereo is left channel pin 3 and right channel pin 2). Each channel has only an XLR input, gain control, mono/stereo switch and a pan switch (for hard left, hard right or center). From here the signal goes straight to 2 x unbalanced stereo tape outs (pre EQ and pre master gain) on ¼” connections (looking at photos on the internet, these also were sometimes RCA connections). There are also 2 x XLR (unbalanced) master outputs which are post the high/low shelving EQ and post L and R master gain control.

    Reading up on some history of Bozak mixers, the first models were the CMA 6-1 and CMA 10-1 which were mono 6 and 10 channel ‘orchestral’ mixers developed in the 50’s. The CMA10-2 came after these but before the famous DJ mixer, the CMA 10-2DL which first came about in the early 70’s. Based on this, I would have a guess that this mixer was made sometime in the late 60’s.

    Unfortunately, the mixer didn’t come with any documentation in the way of manuals or brochures. Interesting to know if anyone else has come across these mixers?
    Attached Thumbnails Attached Thumbnails bozak1-jpg   bozak2-jpg   bozak3-jpg   bozak4-jpg   bozak5-jpg  


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  3. #2
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    I meant to reply much sooner, Chilljam. That is one cool mixer!!!

    I tried to find docs on it but came up dry. Sorry.

    But...super cool!!

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    Thanks Sweetbeats.

    Tracked a song with my band last night on it. The rotary knobs on each channel appear to work like a volume fader rather than controlling the preamp gain. From what I can tell the preamp gain is fixed, which is fine for most microphones but using a high sensitivity condenser like a Rode NT1 (as I found out when recording medium-loud vocals) would distort on moderately loud sources and turning the rotary knob to minimal doesn't change the level of distortion. There is a -10dB pad switch for each channel just above the mic input connector which helps control this but I have to use an external pad for some loud sources to control the level of distortion - though I wouldn't say it's an unpleasant distortion but important to be able to tame it when needed.

    Overall the pre's sound real good, definitely has a sort of hi-fi 60's sound (reminded me of something like Bob Dylan's Blonde on Blonde). Glyn John's mic setup on the drum kit (stereo SDC overheads and an EV RE320 on the kick) and instantly a great, natural sound. DI bass guitar had a very smooth and round bottom end.

    The plan is to use the Bozak for tracking AND mixing, if all goes well, would probably sell the mixer I was using previously in this setup, the Yamaha RM804.

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    Simply...

    Fascinating.

    Wish there was some way to see schematics...super cool find. Hope you post an example or two at some point of a project done through the Bozak.

    Thanks for putting this thread up.

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    Reached out to some folks about your Bozak. A couple comments from some in-the-know good people:

    “Great Sound Reinforcement mixer from the early 70s. WARNING: PIN THREE HOT, pin two may not be connected on unbalanced line inputs.

    I don't think it can hold a candle to the audio performance of a modern Mackie or Yamaha mixer, but it's a tank.”


    “These date to around 1967. The one that I was familiar with was kind of bare bones in terms of features, but really well built.

    it was all-discrete, and had a separate monitor output (not foldback monitor, but for the user). No aux sends, no eq on channels. Kind of a solid-state 1567a.”

    Check your PMs.

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    Yes, from what I've read the CMA/Bozak partnership started around mid-60's and they first manufactured mono mixers (CMA 6-1 and 10-1) before developing the stereo version I have.

    I like the comparison to the Altec 1567a, it's from the same era in terms of simple and minimal circuitry design. There is just a mic pre with 10dB pad, one pan selector and a summing amp into the stereo tape outs. There's a separate master output which goes through a high and low shelving EQ and a master gain control as well but that's it.

    Only just tracked the first song of a ten or eleven song album last week and will only start mixing after tracking is completed for all songs, but I'll endeavor to put up a sample to demonstrate the sound of the Bozak when I have something ready.

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    I have one of these. It came with a bunch of vintage gear I bought. I have never hooked it up. The cards in mine, including the mic cards, are different than yours. The mixer arrangement slots are from left to right looking at the face...
    # 1-7 Microphone preamps
    # 8 Phono preamp
    # 9-10 Line level jumpers
    # 11 & 13 Summing Amps
    # 12 & 14 Tone Amps
    # 15 Monitor output card
    # 16 & 17 Master main output cards
    # 18 Audio delay turn on relay
    # 19 (not shown) Power supply chassis mount
    7 CMA-481 microphone transformers
    1 Small tin can phono jumper
    2 Line jumpers
    2 Balance jumpers.
    I just was thinking about the Bozak yesterday and yours is the first post I've seen on one in the years I've had mine. Was thinking it was about time I should use it or sell it. I knew it was pin 3 hot but my understanding was it is only mono inputs. I've only opened it up and took a few pics but was told it is just mono ins so I'm curious about your info on stereo input. If you have any new info I'd sure be interested in any. Thanksbozak-jpgbozak-cma-jpg

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    Super cool, glad to see someone with a very similar unit.
    Initially I thought the mono/stereo switch being for toggling between mono and stereo channels... but found out that this is not actually the case.
    I've had a tech friend do some great work on my unit to make it more useful for multi-track recording, putting in buffered direct outs on every channel and also fabricating some line cards so I can use the original mic cards when tracking and then swap out for line cards when I want to mix down to two track. After looking at the circuitry, the tech noted that the mono/stereo switch is used to implement a panning law so that if the signal is pushed to one side only, it is as loud as if it were coming through both channels - remembering that each channel can only be panned hard left, hard right or both left and right (centre). So you’re right, the mic channels are balanced but mono only.
    Sound-wise, the Bozak trumps my other mixing console (Yamaha RM804) so it’s my go-to mixer now for both tracking and mixdown. I’ll post some clips once I finish mixing some songs I recorded over the last few months.

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    As I said, I have not looked closely at the cards but will in the next few days. Did you find any tantalum caps in yours and if so are they indeed the old wet type?

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