Looking for a schematic please, DOD 1642 XLR II mixer

[Analog_Fan]

so the footprint matched?

 

[stagekraft]

New parts arrived this morning...
Quick comparison;



Should be simple enough to swap levers, I'll check it out this evening....

JohnR

 

[stagekraft]

Carefully unbend the ten little tabs on each pot.
Gently lift the phenolic element off the housing.
Swap the wiper levers, and re-assemble...


And there's the new pot with the old lever, took less than two minutes...


That's why we call it DIY...

 

[JohnRoberts]

I can't tell which is the new or old, but I notice a design difference between the wipers. I will ASSume they both use 3 fingers for contacting the resistive element, but the finger(s) connecting to the wiper output terminal looks different. Multiple wiper fingers generally deliver less wiper bounce as we don't see more than one finger disconnected at the exact same instant. Of course we don't listen with our eyes, or shouldn't. I don't expect this to be a huge deal in your application.

JR

PS: [TMI] I encountered a scratchy wiper noise in one console EQ pot. We had two approved vendors for these specialized pots (Alps and Noble?). Alps tooled up a fully custom 4 finger wiper, while the other vendor cut corners and tried to use a standard 3 finger wiper. This particular EQ circuit was very sensitive to wiper bounce as it momentarily opened up the op amp NF path. Little things can make an audible difference. [/TMI]

 

[stagekraft]

I did get a reply from someone at AlphaTaiwan, that they need a minimum order of 1000 pieces to make them for me,
I asked them if they had knowledge of what their stocking distributors had, and was told nobody carried the part I was looking for...

 

[JohnRoberts]

Back in the 70s when I bought directly from alps for my kit business the minimums were around 1k, I did buy one value 5k at a time (my parametric kit used 8x100k pots each).

JR

 

[stagekraft]

Alright....

After being sidetracked on another project for a couple weeks, I finally got back to this one...

I have modified and replaced all the sliders, so that's taken care of.

And I did figure out the solder-pad jumpers on the aux sends.
sends 3/4 can be independently configured as pre-EQ or post fader, pretty typical.
sends 1/2 can be independently configured as pre-EQ or post-EQ or post fader

It's an interesting design, 6 send outputs, but only 4 send pots per channel, and a push switch that changes sends 3/4 to 5/6,
so with a little moxy you can obtain 6 aux mixes.

Now, while going through all the functions of all the input channels, I came across one channel that has some very low freq.
oscillation going on with the Low EQ, all looks good with the Low pot set flat, but as I start to boost the Lows, a very slow
oscillation starts (maybe 1Hz), and the more I boost it, the faster the oscillation gets (maybe up to 10 Hz).

I can't hear it going on, but can see it on my scope...

I have not traced it out completely, but appeares to be a typical Baxandall type 3-band EQ.
I have seen very high freq oscillation in other circuits in the past, but never low freq oscillation like this.

My first inkling is something with the opamp, but this is a dual opamp in a SIP package, and of course I have nothing compatible
in my parts collection.

So before I go searching out an opamp, I'll ask ya'll if anyone has experienced something like this??

 

[JohnRoberts]

motorboating, LF oscillation is generally associated with PS but this does not seem like that.

The fact that LF boost supports it and changes the frequency is a useful symptom.

Does that LF boost/cut circuit work properly otherwise?

Rather than suspect a faulty op amp I would look at the pot and perhaps a faulty electrolytic capacitor but this is mostly guessing.

JR

 

[stagekraft]

Hey All,

Well, I set this aside a few months ago, it was aggravating me too much, and was time to walk for a while.
Besides, it is non-essential personal gear, something I picked up cheap earlier this year with thoughts of using
it to replace the noisy little Behringer rack-mount mixer in the B-system.

Last time I was working on it, I set it up with the same signal into two adjacent channels, all controls set the same,
then walked through the circuit board on each channel with my scope probe, hoping to find something inconsistent.
Everything looked identical, except the motor-boat condition previously described.

I was laying in bed this morning, thinking about the repairs to my trailer, and an old stage monitor I was rebuilding,
A hundred different things... typical morning...

Suddenly, this mixer popped into my head, and something John Roberts had posted last time I was here.

"Does that LF boost/cut circuit work properly otherwise?"

Well no, it does not, nor do the mids or highs, signal is passing through, but no real boost or cut.

Then that fabled light-bulb went off in my head, an epiphany even...

I've got a parallel signal path across that EQ circuit...

After taking care of some other chores this morning, I went out to my shop and uncovered this mixer that has been
taking up half my testbench (and driving me nuts) for months, after probing around looking at it from this vantage point;

Dang, there it is, Self Induced misery....

Yep, I created this problem...

Remember I previously described the little solder-jumper-pads to change the pre-post configuration of the Sends?
Well, there it was, couldn't see it, even with the magnifying glass, but I could measure it, must have been just a
whisker of solder on one jumper pad that I had "opened", right next to the one I had "closed".
Pre and Post connected together...

Got the solder wick and completely wiped the solder from both, then re-soldered the one I wanted "closed".

Problem Solved...

Just goes to show, that it just goes to show you...


JohnR

 

[MidnightArrakis]

Hey All,

Well, I set this aside a few months ago, it was aggravating me too much, and was time to walk for a while.
Besides, it is non-essential personal gear, something I picked up cheap earlier this year with thoughts of using
it to replace the noisy little Behringer rack-mount mixer in the B-system.

Last time I was working on it, I set it up with the same signal into two adjacent channels, all controls set the same,
then walked through the circuit board on each channel with my scope probe, hoping to find something inconsistent.
Everything looked identical, except the motor-boat condition previously described.

I was laying in bed this morning, thinking about the repairs to my trailer, and an old stage monitor I was rebuilding,
A hundred different things... typical morning...

Suddenly, this mixer popped into my head, and something John Roberts had posted last time I was here.

"Does that LF boost/cut circuit work properly otherwise?"

Well no, it does not, nor do the mids or highs, signal is passing through, but no real boost or cut.

Then that fabled light-bulb went off in my head, an epiphany even...

I've got a parallel signal path across that EQ circuit...

After taking care of some other chores this morning, I went out to my shop and uncovered this mixer that has been
taking up half my testbench (and driving me nuts) for months, after probing around looking at it from this vantage point;

Dang, there it is, Self Induced misery....

Yep, I created this problem...

Remember I previously described the little solder-jumper-pads to change the pre-post configuration of the Sends?
Well, there it was, couldn't see it, even with the magnifying glass, but I could measure it, must have been just a
whisker of solder on one jumper pad that I had "opened", right next to the one I had "closed".
Pre and Post connected together...

Got the solder wick and completely wiped the solder from both, then re-soldered the one I wanted "closed".

Problem Solved...

Just goes to show, that it just goes to show you...


JohnR

I know that this is a MACKIE mixer, but it has the same "name/number" as your DOD mixer and somewhat figured that there may be some striking similarities. I did come across a schematic for the MACKIE 1642, but I had to subscribe to the website in order to download it and I wasn't in the mood to do that. Does this help you at all???

JBW

/

 

[Analog_Fan]

Well, I set this aside a few months ago, it was aggravating me too much, and was time to walk for a while.
Besides, it is non-essential personal gear, something I picked up cheap earlier this year with thoughts of using
it to replace the noisy little Behringer rack-mount mixer in the B-system.

a while ago, some asked me to "overhaul" a 12 channel Behringer mixer.

once i opened it, i saw all tracks on the pcb have/had 90º angles, every single one of them, maybe some Chinese dude in a sweatshop routing the board.
Coolaudio (Uli Behringers Hong Kong based silicon company) EQ ic's.
not worth spending the money or rip off and i reassembled the unit and it was given away.

one could assume that behringer is some sort off investors money company.

 

[Analog_Fan]

I know that this is a MACKIE mixer, but it has the same "name/number" as your DOD mixer and somewhat figured that there may be some striking similarities. I did come across a schematic for the MACKIE 1642, but I had to subscribe to the website in order to download it and I wasn't in the mood to do that. Does this help you at all???

JBW

/

use a trow away email addres.

 

[JohnRoberts]

I know that this is a MACKIE mixer, but it has the same "name/number" as your DOD mixer and somewhat figured that there may be some striking similarities. I did come across a schematic for the MACKIE 1642, but I had to subscribe to the website in order to download it and I wasn't in the mood to do that. Does this help you at all???

JBW

/

"1642" is a popular numbering convention for small mixers representing 16 input channels, 4 sub buses, and 2 (stereo) mix output. I probably did at least one 1642 during my career with mixer products.

JR

 

[Analog_Fan]

My first inkling is something with the opamp, but this is a dual opamp in a SIP package, and of course I have nothing compatible
in my parts collection.

So before I go searching out an opamp, I'll ask ya'll if anyone has experienced something like this??

you can design a PCB as "single inline package" and use a SMD opamps, have populated by Aisler in Germany or so.

Like the (Rohm) BA662A clone from Open music Labs, witch is also a SIL 9 package.
check out the pcb file, it's very smal.
http://www.openmusiclabs.com/projects/ba662-clone/index.html
The Mitsubischi M5218A is a dual opamp in SIL package used in the TR-909.