Mitsos API 312 / 990 Build Thread

[mikefatom]

The Aux output is simply the third secondary winding of the output transformer.
You can use it as another balanced output.  However, it will have 6dB less than the 'main' output.
You can also use it to feed a VU meter.

In any case, you should always buffer the signal going to your VU meter circuit.

 

[mitsos]

Yes, in fact the Aux output is the fourth winding of the output trafo.  Most 312 clone PCBs just have pads for that winding that co nowhere, so I figured I'd set the little guy free!  You can use it for whatever you want, as Mike says, it will be 6dB less than the other output (main out is 2 windings in series, so 1:2, Aux output is 1:1). My plan was the use it either for a backup recording, VU, or direct out in the baby "console" I want to build for myself. 

Keep in mind this is only if you are building this with a quadfilar output trafo (2503, CMOQ, Altran quad from group buy).

HTH!

 

[okgb]

you can also use it as a monitor out for
no latency in the headphones
I used a pair to feed v.u.'s directly with no
problem except i had to put a kill switch cause
the sound of needles hammering the meter was too much
to take

 

[mrcase]

Alright! cool! I gonna use it as direct outs!
And it shouldn´t be a problem to also tap the vu input from there at the same time, no?
I gonna use fivefish 5 LED vu meter.

thanks a lot!

 

[mitsos]

Hard to say, never used it. I would guess it won't be a problem, but you might want to drop Owel a line to confirm.

 

[mrcase]

I´ll try it as soon as the meters are here!

cheers!

 

[daggertX]

anyone have a picture on how to connect the daughterboard?  are they just the unlabeled  2 solder pads?

 

[mitsos]

Do you mean connecting the audio or power?

The power (+V and G for LEDs) is passed through vertical headers (if you mount the PCBs on top of one another) or with wires (if you mount them next to each other). Those are the two unmarked pads within a box at the front edge of the PCB.

The audio is connected through 4 numbered pads (1,2,3,4) and they correspond to the numbers on the 5 pin molex (middle one, marked "G" is for the shield if you use shielded cables for this).  I normally use a quad mic cable (canare is great, but I think Mogami Neglex would be easier to wire because the wires are 4 different colors, vs Canare's blue and white pairs). 

I hope that helps!

 

[mrcase]

Hey all!

Is everybody using Plastic phone connectors like this one?: http://ultralite.eu/Neutrik.html?neu_nr=G&wa_id=590&art_id=NMJ4HCS
or would it be ok to use a metal one for the DI input like: http://www.banzaimusic.com/Switchcraft-SC-12A.html (which I already have)
I´ve read  its better to use plastic ones because of insulation, what do you guys say?
also I´m planning to have all the DI inputs on one side of the panel so I will have cables running through the case.
do you think I will run into problems there?

thanks + cheers
martin

 

[mitsos]

It depends how you run your grounds, but you generally want the jack to be isolated from the case. I know they make sleeves to isolate those metal jacks, so if yours are like that, then go ahead and use it. It must be switched (that particular switchcraft one is not switched, but if google translator is correct, the neutrik one is) so that it breaks the mic-in part of the circuit when you insert a guitar cable.

As far as having them far away from their respective channels, it may or may not be a problem, since your case will be shielding everything, but I would test it first. If you find it to be problematic, you could use a shielded mic cable and run the shield to ground. That's what I normally do, not because I've had problems but just because it keeps the cables neater.  BTW, I normally run the ground to the channel's ground (there are a few ground pads near the DI input pads) and then have each channel going to PSU ground and then to the case.

cheers!

 

[mrcase]

cool thanks mitsos for the quick response as always
which connectors do you use?

best,
martin

 

[nielsk]

One thing to keep in mind with the DI, do not plug a un-terminated cable in & leave it. These do not like it! Plug in the instrument 1st...

 

[martthie_08]

finally got the faceplate on my unit, have been using it "naked" for the last couple of weeks (sounds great).

More pics and infos at http://homepage.mac.com/marten.thielges/racking/apiX8.html
thanks for this nice project!

cheers, Marten

 

[mitsos]

Good job! Nice to see them all packed together like that! but wait a second, that doesn't look like an SSL4000 or a green pre!  

Thanks for sharing, looks really nice!

 

[mrcase]

Hey!

I´ve finished my 4x mitsos api312  build some time ago. all works fine but I still got one issue.
my gain pots are noisy if I change the gain. they produce noise as soon as I touch them. I checked the ground connection on them and its fine, OR should they be isolated from the frontpanel? I am using the bourns potentiometers and knobs from classicapi...
please help! Otherwise I love those pres! 

 

[mitsos]

Well, I'm sorry to hear about that. The good news is, it's not normal so hopefully you can fix it 

If the noise is when you touch the pots (or simply bring your hand near them) then it sounds like a shielding issue. Check for continuity  between your faceplate and the rest of case (might as well check the rest of the panels as well, while you're at it), you might need to scrape some paint from the edges of the side panels where the faceplate screws on to the case.

If the noise is when you turn the gain then it could be DC in the gain circuit, and I'd look at the 330uF cap near the pot. I don't think 4 caps would have gone bad, but maybe they are in backwards or something?

hope that helps!

 

[mrcase]

thanks mitsos!
so the pots should have a connection to the rest of the case, right!? I also thought maybe its an issue with the aluminium knobs but i guess not...
gonna check the continuity again, though it was fine the last time I checked. I dont think its dc since I hear some noise as soon as I touch the knob.

 

[mitsos]

Is it a buzzy high pitched sound? Like an antenna getting interference?  I haven't used the bourns metal shaft knobs, but I've never had this issue with other metal shafts, and many people use the bourns pots with knobs from classic api without isolation, so you should be ok there.  Check the continuity first, if that doesn't solve it, then try adding the two 1000pF caps (if you already haven't) in front of the input trafo jumpers.

 

[mrcase]

hey!

back again and quite clueless...
I´ve checked continuity between the case, pots, etc. everything is well connected. one funny thing - as soon as I put my had to the knob AND the frontpanel I have no noise. so it seems like I need to be grounded to the frontpanel!!????
here is an mp3 of the noise I produce by touching the knob: http://thebandaloop.com/pot_noise_api.mp3

thanks as always
martin

 

[mitsos]

It still sounds to me like you've got some problem with grounding/shielding.  Most times the problem is continuity between case and front panel, but now I have to ask, is your case properly tied to ground?  The way I normally ground these is IEC -> star/case -> PSU -> then to individual channels that are daisy-chained at this point.  FWIW, I run each DI ground to the preamp PCB it's connected to, but that shouldn't have anything to do with your problem.  You said you checked continuity, so you have continuity from panel to panel of the case, all the way to the IEC?