API 312 Thread!

[laitue5]

Great! I was "breaking my head" on this thing! Thanx!!!

 

[electrog]

so, i've finally begun assembling the parts to put together two 312 type pres using Fabio's boards and i have a question regarding the transformers. I've found a wealth of info about different options for the input, but much less so for output. as the profile's aren't available, any advice on my other choices? what specs should i be looking for? why? i've been reading up like crazy, but still feel a bit lost.....

david

 

[Bauman]

David,

Well, in the profile spot you can use Jensen JT-123-ALCF:
http://www.jensentransformers.com/datashts/123alcf3.pdf

or some Cinemag CMOQ-2S, but they are smaller...

I plan to roll my own output trafos for this to put an end on this issue,
looks easy, just waiting for the Litz wire...


:sam:
cheers!
Fabio

 

[electrog]

i'll simplify my question...

the cinemag CMOQ-2S specs seem to indicate that it is a 150ohmx4 transformer, while all other candidates are 75ohm - clearly it still works, as alot of people seem to be using it, but surely it must make some difference? any reason not to go this route, as the price certainly suits my pocketbook?

thanks,

david

 

[dasbin]

SCA uses the Cinemag as an output trafo in their kits... everyone is absolutely in love with SCA's sound. I've heard it compared to a 312 where a couple people said it sounded almost exactly the same.

I'm using CMOQ-2S in Fabio's boards here, they work perfectly... they are the same size as a real API output trafo. Sounds great for sure.

 

[electrog]

fabio & dasbin,

thanks for the input! (or output really :wink: )

david

 

[guitarmaker]

I've finished 6 API clones. Two have the Sowter in/out iron. Two have the Cinemag in/Profile out and two have the Cinemag in/Cinemag out. I easily prefer the all Cinemag pres. Sowter is my second favorite. The Sowter has a cool bite to the tone but I prefer the smooth tone of the Cinemag pres. All are cool, just different.

Steve

 

[Bauman]

Steve, which Cinemags are you using? How do you compare this one with the one with Profile out??

cheers!
Fabio

 

[guitarmaker]

For the input I used CMMI-8-PCA. Output was CMOQ-2S. I think these Cinemags give the best detail and depth. The Profile sounded flat in comparison.

Steve

 

[bubba_b]

So, after about 3 months of doing basically no DIY ( I know....I hang my head in shame...) I'm back on the bench. I just wrapped up my first API 312 and lo and behold...it's not working right! It powers up, all the switches and LEDS are doing what they're suppossed to do (at least they sound like they are), but I get no signal from the mic and it gets extremely noisy, like a guitar cable with your thumb on the end of it plugged into an amp, the more I turn up the gain. Flipping the -20db pad decreases hiss, but not hum, phantom works and the phase works, but no mic and lots of noise.

FYI: I'm using Fabio's board and PSU with an OEP input tranny and a Cinemag CMOQ-2S output. Any ideas? It's helped me alot in the past just being able to look at pics of your guys' finished stuff, but I can't find a finished API on here anywhere!

 

[Bauman]

Hey,

Are you using all relays? If you are not using the RL_LINE, you need to bypass it with a couple of jumpers or nothing will hit the input transformer.

:sam:
Fabio

 

[bubba_b]

I have all the relays in and I'm not using the LINE_IN. I have the MIC_IN and RL_HIZ hooked up. Are you saying I need to jumper the LINE_IN or take the RL_LINE relay out and bypass that? Also, the SW_LINE has nothing in it, either. Does that matter?

 

[bubba_b]

Ok, I took out the RL_LINE relay, jumpered 1-5, 2-6 and still no change. Lots of buzz, all voltages from the PS look good (+/-18V on CN1, approx. +45V on phantom). When I switch on the pad or phase rev, the buzz changes pitch, but still just as loud.....still no signal.

Oh, and when I power off, I get radio stations until the caps drain, then the radio fades away.

 

[Bauman]

OK, when you have RL_LINE on place you don´t need any jumper...

Next thing to check is: did you make the jumper over RL_PAD relay
(indicated by a cross on silkscreen) ?

Can you check with a test tone if any signal reach the input transformer?

:guinness:
Fabio

 

[bubba_b]

Ah....I did not have those jumpers in. I put 'em in and I now have signal and everything works, but there's still really bad hum and a loud "pop" when either the phase or pad are engaged.

The Hi-Z input works great, though. No problems there.

 

[dasbin]

[quote author="bubba_b"]there's still really bad hum[/quote]
Near your power transformer?
The card in my rack which is closest to the transformer has quite audible hum when the gain is turned up near maximum. I even shielded the power transformer with some thick grounded metal, and wrapped my output trafos in copper foil, but this didn't seem to help any. I think the opamp is quite sensitive to the electromagnetic field.

and a loud "pop" when either the phase or pad are engaged.

Mine have a pop, it is not "loud" by any measure though. Maybe increase the value of the cap in the feedback loop? Not sure about this one... I do think this value is too small anyway though as my pots are noisy.

The Hi-Z input works great, though. No problems there.

Can you try something? Plug in a guitar to the Hi-Z and see if the DI relay stays engaged all the time as you turn the volume knob on the guitar. Both my Hi-Z inputs have a problem where the relays go nuts switching in and out as the knob is turned or sits within a certain range.

 

[bubba_b]

Thanks dasbin, it was the transformer. Turned it slightly to just the right spot and it went away. I knew they could be noisy, but MAN! That was really bad. Thanks again....now to go play with my new toy.

 

[tony dB]

what kind of capacitors have you guys used?
I am following the v3 BOM but didn't see any specifications.
Any other things to ad to the BOM?

Cheers,

Tony

 

[louder]

alo tony
for the melcor,i used cog.
for the main board,used .1 ceramics.
as for electro`s,i mixed pana fc, and nichicon`s pw.
best regards
pedro

 

[tony dB]

Thanks Pedro!