Mitsos API 312 / 990 Build Thread

[benlindell]

I found an easy method for taking of the channel frames.

I used a small flathead screwdriver to lift the tabs up a bit then used pliers or big wire cutters to lift them back completely. Then I grabbed the side tabs with the pliers and wiggled a bit to free the sides from the epoxy, then I grabbed down by one of the newly exposed corners and did the same, I went through 7 of them in about 10 minutes.

 

[grantlack]

Quick question so I can finish up some wiring... Pin 5 (center pin) of the daughter board molex is just a ground reference for the wire shielding (doesn't actually connect to the daughter board), correct?

 

[benlindell]

Quick question so I can finish up some wiring... Pin 5 (center pin) of the daughter board molex is just a ground reference for the wire shielding (doesn't actually connect to the daughter board), correct?

Correct.

 

[baadc0de]

Thar she blows

Front panel courtesy of grand master audio, power supply by ppa.

one of the last 4 channels (or opamps) has a fault somewhere as a regulator shuts off with them in circuit, so I'm running only the first four for now. Opamps are:

1-2 germanium by ppa
3-4 "enhanced" 2520 version by ppa
5-6 gar1731
7-8 gar2520

 

[mrclunk]

Nice work sir!
Be interested to hear the difference between op-amps and are those Omeg rev log pots?

 

[baadc0de]

Nice work sir!
Be interested to hear the difference between op-amps and are those Omeg rev log pots?

Thanks. Yes, those are indeed Omeg rev-logs. The black tri-level things below them are T-pad attenuators from hairball audio. I spent a fortune on them so I could have a post-transfromer output trim. It works nicely, though the output pad switch would be sufficient

How should one go about multiple opamp sound tests.. maybe I should playback something through the input of the same channel set at same gain, switching opamps? What little I did for now, it seems there is little absolute night-day difference between them. Maybe the iron is contributing more or they are just so much alike, or it's just my inadequate monitoring/shot ears. Don't know.

 

[mitsos]

Nice work bud! That's avery nice looking face plate.  I like the layout very much. Is that a par metal case?

RE: differences, I think you may be able to hear slight differences between opamps, but they will be subtle, unless you change to a totally different opamp(like a 990) which takes a different input trafo, but then you're talking 2 changes to the circuit.

You can also try a servo in one channel, to get rid of the output cap, things like that.

What are your thoughts on the Ge opamp?

cheers!

 

[baadc0de]

The case is from modushop and the front panel from grandmasteraudio, he also did the layout.

Yes, I don't hear much difference between opamps, but they're there if for some source there actually is a big difference or if someone with golden ears can say which one he prefers. The ge is no exception, I don't hear a very different frequency response, any bass shifts or specific distortion products with it that aren't there with the other opamps. Still, someone might find the differences worthwhile.

 

[mac]

Hey guys, is there a datasheet for the altran outputs from the group buy?
I got some extra quads C-4391 altrans which I want to try on some JLM Baby animals.

Mac

 

[mitsos]

I was looking for this the other day... 

here you go:

 

[mac]

Thanks Mitsos - SUPER fasst!!!! ;D

Mac

 

[r2d2]

so cooool "view" baadcode
the pots are
1 for input level
1 for output level?

peace

Thar she blows
Front panel courtesy of grand master audio, power supply by ppa.

one of the last 4 channels (or opamps) has a fault somewhere as a regulator shuts off with them in circuit, so I'm running only the first four for now. Opamps are:

1-2 germanium by ppa
3-4 "enhanced" 2520 version by ppa
5-6 gar1731
7-8 gar2520

 

[baadc0de]

yep, first is the input gain (as normal) the other a t-attenuator from hairball, usually used at the input of 1176. It works as an output trim, yes

 

[grantlack]

soooo close, just one last part to acquire.  and with that...

does anyone else in the US still need pots?  i got a quote from omeg but i'd like to get the price down if possible.  i'm just going with 10k's on the M1's for the record, can't find a small enough diameter shorting rotary to easily do my 8/1u cram.  everybody's options seem to be non-shorting  .  i'm also thinking the lug route is a better plan than pcb pin since the mounted depth ends up a bit shallow compared to the switches.  email me rather than posting if you do so we can keep this thread clean.

 

[r2d2]

coooooool
the trs input on the front is a "DI" input?

peace

yep, first is the input gain (as normal) the other a t-attenuator from hairball, usually used at the input of 1176. It works as an output trim, yes

 

[baadc0de]

coooooool
the trs input on the front is a "DI" input?

peace

yep, first is the input gain (as normal) the other a t-attenuator from hairball, usually used at the input of 1176. It works as an output trim, yes

Yes, it's a DI done as per suggestions made by mitsos - a switching jack is used, so that the passive input section is disengaged when a guitar cable is inserted into the jack and the opamp's input is taken from the jack instead. It works really well I feel there are more changes in the tone from opamp to opamp with DI instruments.

 

[mitsos]

Just to give credit where it's due, the switching jack DI was Nielsk's idea.  It's not a "new" idea I guess, but it is simple and I think it's quite neat. And your comment that tone changes with each opamp makes total sense of course.

Hope you're enjoying your 8 pack baadcode!

 

[baadc0de]

Oh yes! I just recorded some keeper tracks with them and APP-E opamps. Love it! Thanks for the excellent project

Though if I had to do 8 more, I would skip the daughterboard thing. Also, I'm kind of bummed I didn't take 2 more to make 990 preamps with. But no biggie, I have a JLM kit now for that purpose.

 

[mrcase]

hi all!

I´m a bit unclear about the aux output. what is it designed for? whats the different specs for it?
can I use it as a secondary output,  like going into a compressor and still be able to record the clean signal from the main output at the same time?
And is it possible to use the aux output as a second output (using eds 2503 output transformer) and get the input for the vu meter from there aswell?
or is there another point where I could grab the signal for the vu?

thank you so much for your help!

 

[benlindell]

hi all!

I´m a bit unclear about the aux output. what is it designed for? whats the different specs for it?
can I use it as a secondary output,  like going into a compressor and still be able to record the clean signal from the main output at the same time?
And is it possible to use the aux output as a second output (using eds 2503 output transformer) and get the input for the vu meter from there aswell?
or is there another point where I could grab the signal for the vu?

thank you so much for your help!

I think it was intended on being used for VU metering.