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  #1  
Old 07-26-2007, 11:42 AM
thermionic thermionic is offline
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Bozak CMA 10-2DL - Full Restoration Photos!

Hi,

Over the years, I’ve seen a few posts here relating to what’s involved with restoring a Bozak and how involved the process can be. In light of this, I thought I’d show a few pictures to give a glimpse into the process.

Understand that there are many time-consuming process that I haven’t documented here, for the sake of making you all fall asleep! But they have to be done! (An example would be cleaning up the old carbon resistors with solvent, prior to fitting them back on the pots – boring, but you have to do it!)

First step is to remove all the PCBs and replace the electrolytic capacitors - this is needed for several reasons. I won’t go into the sound quality issues (although modern caps do have an uber-low ESR and impedance compared to the caps of old), but one really important thing to appreciate is that, if the caps are 30 years old (your average Neve or API console from 30 years ago will be on its 5th set of caps by now…) and they start to pass DC, you risk damaging your pots – not funny if you’re fitting brand-new pots!

Do not attempt a re-cap without a temp-controlled rework station – the tracks are very fragile and they *will* lift off the board.
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Last edited by thermionic : 10-21-2007 at 06:48 PM.
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  #2  
Old 07-26-2007, 11:46 AM
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DSA.audio DSA.audio is offline
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too cool......

Thanks for providiing the "tour", I know I'll be watching it

warm regards,
David
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  #3  
Old 07-26-2007, 11:50 AM
thermionic thermionic is offline
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On this mixer, the plating on the connectors was oxidised, so the next step is to drill out the rivets, remove the old ones and fit new gold-plated sockets (I’ll spare you photos of the drilling process).
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  #4  
Old 07-26-2007, 11:52 AM
thermionic thermionic is offline
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Now we’ve got the easy stuff out the way…it’s time to start thinking about replacing the pots. In the case of this poor mixer, a previous owner had decided to soak the entire mixer in solvent, without re-lubricating the pots!!! All pots were trashed (aside from the AB Tone pots) and there was a “tide mark” all over the PCB…Not good!

Once you liberate the front panel and main PCB from the pots, this is the scene that greets you:
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  #5  
Old 07-26-2007, 11:53 AM
thermionic thermionic is offline
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Parts of the old loom were not in the best of condition…
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  #6  
Old 07-26-2007, 11:55 AM
thermionic thermionic is offline
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One of the most time-consuming activities is to remove the original resistors without ruining them! I could just reach for my metal-film resistor tray, but that would incur the wrath of the Originality Police… You can’t do this with a rework station – it’s a real PITA. The rework gun picks up the main solder and you have to use wick to remove the rest, whilst wiggling the resistors ever-so-gently so as not to stress them…you’ll invent new expletives doing this!
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Last edited by thermionic : 10-09-2007 at 05:08 PM.
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  #7  
Old 07-26-2007, 11:56 AM
thermionic thermionic is offline
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Having spent several hours swearing removing the resistors, it’s time to attach them to the new Balance pots and prepare the pots for attachment to the new Level pots.
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Last edited by thermionic : 10-09-2007 at 05:08 PM.
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  #8  
Old 07-26-2007, 11:58 AM
thermionic thermionic is offline
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Next, we attach the Ground bar to the new Level pots and get them into shape for installation. Judging from the kinks in the original bar, I suspect the originals were made by measuring a length of wire, soldering it, and bending it to suit the panel… I can understand this, for reasons of production, but I chose to use the front panel as a “jig” to keep the pots in-place, as well as using thicker gauge wire (it won’t make an audible difference, but having the lowest impedance to Ground makes sense and I’m sure the client won’t complain).
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  #9  
Old 07-26-2007, 11:59 AM
thermionic thermionic is offline
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Next step is to combine both pot types into an assembly, ready to be reunited with the front panel and PCB
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  #10  
Old 07-26-2007, 12:00 PM
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Reunification! Note that the only way to attach the Balance pot slugging resistors (not fitted to all Bozaks) neatly is vertically, which meant the pots had to be mounted at 90-degrees to prevent clashing with the Tone pot board.
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  #11  
Old 07-26-2007, 12:01 PM
thermionic thermionic is offline
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We’ll skip a few stages, such as aligning the Balance and Tone pots with the FFT analyser (a highly frustrating and time-consuming process! Once the pot is centred, you only have to nudge it slightly when attaching knob to upset the whole caboodle!)
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  #12  
Old 07-26-2007, 12:03 PM
thermionic thermionic is offline
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Prior to refitting the knobs, a lengthy soak in soapy water, combined with a vigorous brush with alcohol and bleach is required to remove 30 years of dirt:
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  #13  
Old 07-26-2007, 12:04 PM
thermionic thermionic is offline
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Et Voila! A working mixer! First thing to do is ramp the Bozak back up on a Variac to prevent stressing the PSU when powering up new caps for the first time. Next, check all outputs and inputs for DC. Next, listen!! If everything sounds ok, we move over to the analyser bench to centre the pots, check crosstalk, signal-to-noise – and crucially – channel matching… Whilst I think ALPS aren’t as good as P+G, I was absolutely blown away to see that all channels match within 0.2dB at any gain! I’m still amazed by it! As long as the Tone and Bal pots are centred properly, tracking never deviates by more than 0.2dB! Better than ALPS product specification! Dynamic Range is approaching 120dB above 150 Hz – not bad for a 30-year old mixer with carbon resistors! CD is only 96dB!
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Last edited by thermionic : 10-21-2007 at 06:54 PM.
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  #14  
Old 07-26-2007, 12:05 PM
thermionic thermionic is offline
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When a full restoration job is carried out, you tend to accumulate a lot of old parts… The client can have these back to dispose of responsibly – don’t put them in the local water reservoir! The bag weighs a few pounds!
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  #15  
Old 07-26-2007, 12:06 PM
thermionic thermionic is offline
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This job took a lot longer than expected, so much that a bit of a queue developed in the waiting room…
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  #16  
Old 07-26-2007, 12:07 PM
thermionic thermionic is offline
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Don’t hesitate to ask if you have any questions. I know this is a long post, but this is highly abridged! You would have a hundred page book if you documented every step! I’ll see if I can post a few plots from the analyser to back on the ‘specs – seriously good for a 30-yr old mixer!

PLEASE RESPECT ALL COPYRIGHTS ON THE PHOTOS – LINK TO HERE BY ALL MEANS, BUT DO NOT PUBLISH THEM ELSEWHERE AS I CAN ASSURE YOU THEY ARE COPYRIGHTED


Justin
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  #17  
Old 07-26-2007, 02:10 PM
clubman5 clubman5 is offline
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Justin, excellent work, and words of wisdom and experience, BRAVO! I tip my hat to you.

You like those Black Gate caps? I found something I like too! Elnas line of Silmic and Tonerex capacitors, smooth, and warm sounding, and the Tonerex series offer that slightly recessed sounding midrange I adore. IMHO, these caps go well in vintage gear, AND, they are inexpensive, not silly overpriced like many caps on the market today.

Great stuff, outstanding work from a true professional.

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  #18  
Old 07-26-2007, 02:35 PM
thermionic thermionic is offline
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Thanks for the positive comments, Scott!

The client requested Black Gate. I prefer not to steer people in any particular direction, cap-wise to be honest. I have certain brands I prefer, such as ELNA or Panasonic FC, but on the whole, I prefer the client to make an informed decision.

I do think the BGs sound excellent, but at the same time, if it were my own mixer, I'd probably be just as happy with ELNA or Panasonic. I tend to use these for my own listening and I'm quite happy. I will say that I don't think all modern caps are the same though, and I was recently surprised to see the difference swapping to an FC from a cheapo cap made.

The client knows that he can't go wrong with BG, so I guess he went for a safe option. He pays for the caps, so I'm not complaining

Justin
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  #19  
Old 07-26-2007, 02:49 PM
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Quote:
Originally Posted by thermionic
Thanks for the positive comments, Scott!

The client requested Black Gate. I prefer not to steer people in any particular direction, cap-wise to be honest. I have certain brands I prefer, such as ELNA or Panasonic FC, but on the whole, I prefer the client to make an informed decision.

I do think the BGs sound excellent, but at the same time, if it were my own mixer, I'd probably be just as happy with ELNA or Panasonic. I tend to use these for my own listening and I'm quite happy. I will say that I don't think all modern caps are the same though, and I was recently surprised to see the difference swapping to an FC from a cheapo cap made.

The client knows that he can't go wrong with BG, so I guess he went for a safe option. He pays for the caps, so I'm not complaining

Justin

Clients are ALWAYS right
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  #20  
Old 07-26-2007, 02:50 PM
clubman5 clubman5 is offline
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Black Gates are great, but too exactly what you put in is what you get out sounding for my taste. I like a bit of that coloration called warmth and creaminess. And BG,s are pricey.

I just state that for the money, and a particular flavor of sound, I found the Elna Silmics and Tonerex to be very like the way things used to sound. elna states that the newly developed silk fiber impregnated paper they use in the Silmics is how they achieve the tone. Big sounding bottom, smooth warmish midrange, and smooooooth top end without edginess.

I'm just happy they are making components that have certain unique tonal properties so that we can voice our gear to our individual tastes.

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  #21  
Old 07-28-2007, 10:39 AM
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I made it with original parts

do you believe the silver and gold jack sound different?

peace







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  #22  
Old 07-29-2007, 08:59 PM
djmariog djmariog is offline
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Here is a photo of one of the last Bozaks chasis that was sent to me.

I just used this chasis for a wave customer on a fully upgraded dl mixer to a dlc mixer. I will post some pictures of before and after.
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  #23  
Old 09-19-2007, 10:29 PM
djmariog djmariog is offline
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Bozak upgrade dl to dlc with true booth out

Photos of a upgrade by me of a Bozak dl to a dlc.
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Old 09-19-2007, 10:32 PM
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Quote:
Originally Posted by djmariog
Photos of a upgrade by me of a Bozak dl to a dlc.

more photos
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Old 09-19-2007, 10:34 PM
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Quote:
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more photos

photos cont.
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