Mitsos API 312 / 990 Build Thread

[mitsos]

after a failed attempt at a direct M1 clone (cut traces, jumping offboard to a home made pcb then back again,as well as a DIY 990) just to much to troubleshoot.

I thought that would be complicated. It could have been made simpler if I had thought about it a bit more during the design phase, but it wasn't part of the plan, so it got overlooked. 

I'm (vary far) away from my desk atm, but I have a dual channel I'm finishing up that I can check when I get home next week.  I think I was running it at 20-21V just to keep it safe. You shouldn't really have problems if you have a regulated PSU, but I would keep it under the absolute max ratings for the 604.

also what type of molex connectors are you guys using for the bias input and servo in/out jumper? the "normal size" that most guys on the board use dont seem to fit along with the DIY990s. do they fit with John Hardys  990's ?

I am using breakaway vertical headers, albeit with JH990s, I think I have a DIY 990 that I can check for fit. I believe mine are something like this mouser item:
517-6211TG 

for the +18V  i was planning on taping off the +24V leg of the psu and add  another stage to the psu. is this how it should be done?  can anyone recommend some starting component values to acheive near 18v?  any help is appreciated.

I tapped off the rectifiers, just run another cap, LM317, etc and get another output. This way you can use heavier duty rectifiers if needed and not be dependant on the amp limit of the +24V 317.

and mitsos thanks for the 2 pcbs.
8) 8) 8) 8) 8) 8) 8) 8)

no prob, glad you're getting this thing finished.

 

[dmp]

I used these boards as is to make a 990 and haven't had any problem running at +24v / -24v.
I'd have to check what OpAmp I used but I think it was a 604. I thought I posted all the details but it doesn't seem to be in this thread. Was there another build thread?

 

[mrclunk]

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.

If i'm using the aux xform output just for a VU meter do i really need to add a buffer circuit? I thought if its a separate winding it won't interact with the main output windings? (and won't increase THD on the output)

 

[mitsos]

sorry was out of town for a week... well, I've never actually used it for a VU, but I certainly planned to, and will likely do it at some point.  I would just try it, and see if it has any detrimental effects. You can always add a little buffer circuit on perf board (maybe mount it directly to the back of the VU), though I doubt many companies did this "back in the day."

 

[mrclunk]

Thats cool, i ended up making some buffer pcb's anyway. Not tried them yet but the rest of the amps done, will take some pics at the weekend.
thanks.

 

[BarneyBrougham]

Hey everyone.

I built 4 channels of the API boards. Works great. Very very happy with them but i have run into a big problem. Self inflicted unfortunately.

So...i have an original Univibe pedal from the 60s, for guitar...fixed it to Australian power. worked perfect in australia. brought it to europe...problem with the grounding it seems. But it works...tried to fix the grounding issue.

anyway...i plugged it directly into a DI on one of the API channels....it worked for maybe 5 minutes until i started to hear a low clicking sound in the headphones, the pres were getting warmer then blew a 47ohm resistor in my PSU. the 48v rail, and the LM317 on the same rail.

my PSU is fixed now...plugged it in...no phantom power on my APIs...then one channel worked...then the effected channel caused the PSU to start smoking again...same resistor, same rail...blew the LM317 again too.

So im trying to find out is there damage to the pcb or the DOA....what could this powered pedal plugged into my DI do? blow something on the DOA? the PCB? a resistor or cap....to much voltage into it does what?

ive searched for shorts everywhere and cant find any...unless something is blown, but where to look? nothing else is burnt like in the PSU. All the voltages on the PSU are correct, and stay correct when turned on...ive left it on (not plugged into the pres) for over an hour, measuring constantly.

im kind of a little scared to turn it back on again to fix it. i feel a bit blind not knowing where to look....because i need it for some sessions in july and dont want to destroy it further.

my PSU is the JLM powerstation....and before this incident all 4 channels were working flawlessly. pads, phasing, 48v, DI, Aux out...everything. had it turned on for 7 days, 12 hours a day tracking drums. no issues at all.

anyway....any advise would be amazing!!

thanks!!

 

[Harpo]

... brought it to ... blew a 47ohm resistor in my PSU. the 48v rail, and the LM317 on the same rail.
...then the effected channel caused the PSU to start smoking again...same resistor, same rail...blew the LM317 again too.

...ive searched for shorts everywhere and cant find any...

Might be a mechanical fault, caused by transport.
Make sure, the pcb fixing bolt/washer/nut/standoff isn't shorting the +48V rail to case ground.
For your next resistor/regulator/zener supply fix, instead of replacing with a LM317 again, better use a LM317-HV or TL-783, so the voltage differential between regulator in/out doesn't exceed parts max.rating when there is a short on output.

 

[mitsos]

Hi Barney,

I would first check what Harpo said. The 47R in the PSU would only blow if there were excessive current caused by a short, most likely to any fixing bolts between the two switches on the main board.  Might be an easy fix of using nylon hardware.

With phantom disconnected at the PSU end, do the preamps work 100%? (besides phantom of course!).

good luck!

 

[BarneyBrougham]

OK IM BACK!! all 4 channels working!!

Thanks again for the great advise guys.

there was a short somewhere on the 48v rail on the pcb...not sure where it was, i couldnt find it.

so i just cleaned up everything and did lots and lots of measuring to test everything was ok.

i also added some isolation to the standoffs, screws etc.

CHEERS!!!

the only thing that isnt working....the led lights on my switcheds arent working...what could that be?
Damian

 

[mitsos]

good job fixing that.

Were the LEDs working before? If so, I would check that the DC and ground connection of the LED circuit, make sure that's OK first. The circuit itself is separate from everything else, just LEDs and their current limit resistors, so it should be rather simple to find the issue.

good luck!

 

[BarneyBrougham]

yep they were working before.

but...i did just check each channel individually, and the last one in the end stopped working.

ill put all 4 channels together in the morning again, and then see how the others are too.

hey what a great project!! was my 1st project...jumped right in the deep end..

i also just finished 2 neumann U87s...another great project.

any recommendations for different pres or other cool stuff i could build? 4 neve channels could be also awesome haha. open to all ideas )

cheers,
Damian

 

[BarneyBrougham]

one more thing....should my DOA's be getting warm, hot when its turned on?

they get warm almost immediately and continue to rise in temp....i keep turning it off just to be sure nothing happens.....is this normal?

 

[mitsos]

one more thing....should my DOA's be getting warm, hot when its turned on?

they get warm almost immediately and continue to rise in temp....i keep turning it off just to be sure nothing happens.....is this normal?

What DOAs are you using, what voltage are you running them at, and what are they going into?  They will all warm up a bit in normal use.  2520's, melcors not so much, unless you run them into a heavy load or near their voltage supply limit (+/-20VDC).  990s get a bit warmer, especially at +/-24VDC, but the ones I have (john hardy) don't get HOT, just warmer than my 2520s.

Did you figure out the LED issue? If 3/4 channels work, then that would mean you PSU is OK, so first check the LED power and ground connections on the faulty PCB, and that all LED current limit resistors are properly installed.

 

[BarneyBrougham]

DOAs are 2520 from classic API....the voltage going in is 15.2v across each of the 4 channels, its just the 2 big black guys on each DOA that get hot.

Red pcbs..analog design i think they say..yours right? )

As for the LED...no idea...i was checking some soldering when doing all my testing searching for problems, so maybe i did something...actually i did do something as it worked before....all the switches work, just no lights...i dont know which resistors/solder points are for the LEDs ??

PSU is all good now...had to do a little surgery...but its fine now.

 

[mitsos]

DOAs are 2520 from classic API....the voltage going in is 15.2v across each of the 4 channels, its just the 2 big black guys on each DOA that get hot.

Red pcbs..analog design i think they say..yours right? )

As for the LED...no idea...i was checking some soldering when doing all my testing searching for problems, so maybe i did something...actually i did do something as it worked before....all the switches work, just no lights...i dont know which resistors/solder points are for the LEDs ??

PSU is all good now...had to do a little surgery...but its fine now.

well, I don't think they should get SOO hot, but I don't have any atm to test.  Were they getting hot when you were using them before?

back to the LEDs, the LED pins are the front-most pins on the switches.  The LED resistors are vertically mounted near the switches. 

 

[Soeren_DK]

Anybody remember what we paid for the boards, lights and the Altran 3982 traniees? I have a pair up for sale in the black market but I can't find the old thread where the prices were.
http://www.groupdiy.com/index.php?topic=49533.0

Cheers
Soren

 

[mitsos]

The old BM threads expired by now.  I know the PCBs 12, and IIRC the trafos were 25 and switches  between $1.50 - 2.

cheers!

 

[laddie.music]

Do you know if these mitsos boards are compatible with lead free solder?,  just wondering as I read on a hakko post a while ago that some boards are not in fact lead free compatible...

 

[mrclunk]

Hi,
I've just put together a two channel box of the Mistos 312's but i've the an issue on both channels.
I'm only getting about 7dB of gain...

I'm boggled as to whats wrong and the fact that its exactly the same prob on both channels makes me think ive missed a link or component somewhere..
Checked the my gain pot and fb network, thats ok.
The PSU checks out and the im getting the correct gain after the input xform. Its got to be something to do with the opamp or surrounding circuit.
The ML2520 opamps where kits but i doubt i messed up both of them in the same way...
Any ideas??

 

[mitsos]

oh man, guess I've been offline a lot lately!

Laddie, sorry for the delay. I don't remember if these boards were ROHS or not, don't have any where I'm at. If they don't have the symbol then I'd say they are not.  But I've also never heard of any problems switching between leaded and leadfree, the only potential issues I've heard of is with mass production (wave soldering) where the entire PCB has to be able to survive higher temps for a much longer time. This is a non issue with hand soldering, though.  Hope that helps ease your mind!


mrclunk... That's a nice enclosure, I want one!  Can you provide some more info on the issue or more detailed pics (I know you probably don't want to remove the PCBs from the case, but it would really help to see what's going on)? 7dB's at the output transformer secondary? That's definitely weird, because just the input trafo  should give you up to 20dB (actual gain depends on the input trafo).  If you are not using a DI, you need to jumper the DI +/- pads, and there is a (1K) series resistor before the opamp also that needs to be there (or a jumper).  If you are building a straight 312, you should leave the "BIAS", "DC SERVO" and "IC OUTPUT" sections empty. They are each marked off with white lines.

Anyway, a (closeup, detailed) picture is worth 1000 words, top and bottom pics are worth at least 2000!