API 312 Thread!

[babyhead]

I have been following this thread for a long time and I am just about to fire up my version of the 312. However, Im not getting voltage to the - of either opamp. I think that D1 is screened backwards. Did I miss this in any of the 20(!) previous pages? This is getting so close, I can almost hear it!

-BH

 

[louder]

alo baby
do you have +/- volts at the psu?.if not,there must be something wrong at the psu;if okay in the psu,then it is at the main board.
did you measure with or without opamp?.
best regards
pedro

 

[babyhead]

Im testing resistance from the negative rail to the opamps. Just a meter, no PSU. I'm pretty sure that D1 is backwards almost just by holding it up to the glow of my monitor. Now is not the time to work it out, though. Soon!

-BH

 

[pmroz]

.

babyhead, i have a pre working here. D1 is screened correctly on the pre board. Also, D1 is for '+V'. D2 is for '-V'
So D1 shouldn't affect -V, D2 should.
You can check the components and paths with this link:
http://www.thediypill.phx.com.br/forumfiles/R312parts_rev3.pdf
This way you don't have to hold it up to the light to see the traces.

From the link, you can see D1 joins '+' supply header to '+' pin on opamp. Anode/cathode for pos voltage.
D2, however, is wired cathode/anode from 'minusV' pin of header to minus pin of opamp, allowing only negV to pass.
Looking from top, you can see they appear to be oriented the same, but the one is passing posV, the other negV.

Im testing resistance from the negative rail to the opamps. Just a meter, no PSU

Haven't done this method. Not sure if neg 'resistance' will show up past the reversed 1n4007 without voltage present. Why not hook up PSU and check volts?

 

[Greg]

I also have a pair of these up and working, so I'd say the PCB layout is correct.

BTW- These preamps kick ass !!!

 

[Rob Flinn]

I`ve been playing with the pair I made over the last few days & I like the sound of these mic amps very much.

 

[pmroz]

.

crap, that last post was 100 for me... and i was saving it to say
:grin: :grin: :grin: (first-ever emoticons) and
:sam: :guinness: :sam: :guinness: :sam: :guinness: :sam: :guinness: Beverages for everyone!
FABIO, for the great project and boards, and patience.
RAFAFREDD, for all the info and even more patience.
Peter C (all the Peters), Kev, Dan Alexander, all the Melcor/A.P.I heads who came before this project.
JLM, for PS help, GREG, PRR, NYDave, soundguy, Gyraf, CJ, Gus, Marik, Jaako, Fum, Alk, Simon (UK****), Rob Flinn, Bcarso, TK, etc etc etc!
Everyone who had to read my dumb questions!
Chae and Ethan, and any other Prodigy staff! Great forum!
Oh, i see one is guinness, in that case
:guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :guinness:

Thanks to all of you (+ internet 'library'), i went from 'what's a cap?' in November to working preamp in March. Including building opamps.
And the first one sounds NICE! It kills me.
Can't explain how great it was even just to turn the pots on PS V+/V- , and watch Vs rise or fall...

3 more pres to test today, still need to get them in a box and shielded.
But like the French girl says "once you taste a small amount of success, you will find it suits you".

Tried some sources not mentioned previously, with very nice results (except some rf from no case). Pre used was CMMI-8PCA/BC opamp/Profile4804. Most were MD421/pre/DAW:
Solo trumpet, Trombone, Conga (esp nice for quinto, but great for all), Sax (alto/tenor/bari) from quiet mellow to 'Clarence Carter' NY (NJ) overdrive sound, great. MD421 and KSM32 both sound nice.)
Horn section should sound nice with more pres. I'm thinking of recorded 'Chicago' sound... that hi-vol breakup... of course you need the players for that.
Harp!! (harmonica) blues-style with EV664. Hi-gain on this pre kills it! (in a very good way). Thought i'd need to mic a toob amp for this, not any more.
BTW used amveco 62085 toroid (22+22, 50va), 78S12 for REG_SW, and TQ2-12V for relays (thanks JLM and whoever mentioned 78S05?). Regs are cool to touch with no connection, barely warm with 1ch/ all switches on. Will post 4ch power tests later in week.
Also i'll trade the 1731/BCs and in/out trafos (Altec 1:4 in, Melcor 400-17 out) when they're done, and post some A/B soundclips.

More questions:

Re: shielding... CJ suggested covering the opamps with some case. At this point my plan is make boxes out of galv. sheet metal or sheet plastic, lined with copper foil, connected to GND on opamp. Anybody have a slicker way? A source for cases like on the originals? Jewelry box etc?

Curious when soundguy said he uses these for DI guitar, which input on Fabio's board did he mean? DI or HiZ? Input before or after in trafo? I'd like to put whichever on front panel.

Fabio or anyone else have further impressions from tracking? A/B results from different configs?
Thanks again, everyone... what you all said is true, the moment the sound came out, i became a DIY junkie.

 

[Bauman]

YEA YEA YEA! I'm kinda freaking out with this also...
I have so many people to thank for all the support also. This is a unbelievable group of people!!

No sessions here yet, trying some small changes on the opamps yet.

Re: shielding... CJ suggested covering the opamps with some case. At this point my plan is make boxes out of galv. sheet metal or sheet plastic, lined with copper foil, connected to GND on opamp.

I found this very important. Do a test. Hit hi gain and try to get your hands close to the opamp... You don't need to touch, just to get close. :wink: Maybe with the top cover grounded it will be ok, but I think it worth to have this individual extra shiled...

Curious when soundguy said he uses these for DI guitar, which input on Fabio's board did he mean? DI or HiZ? Input before or after in trafo? I'd like to put whichever on front panel.

Just a short note: every channel goes with a little retangular boards that is for the DI plug.
It's based on Bo Hansen DI circuit, and the wires out of it goes to point A,B and C next to the relay near the opamp. It doesn't uses the input transformer in the path, it goes direct to the opamp. Man, it sounds so good! Even just the input plug and a opamp makes a great DI!

Fabio or anyone else have further impressions from tracking? A/B results from different configs?

No tracking yet but next weekend, drum session.

HEADS UP:
I did 8 different 25.20BC with different resistors and caps and transistors to test against api.25.20.


First impressions:
- R3 and R4 doesn't work with 82k as in the schematics. Use 20k!
- I think R2 needs to be 360R or 390R... will confirm but the best block I have tested
(#4, the one with the best stability and very near to API25.20) was the only one that had R2=360R. Those resistors are near the edge of the board, not hard to change...
- on 25.20BC, the background noise is a little bit higher that in the API25.20. Will try to mess with output biasing for the BD139/140 to see if it gets better. The best block (#4)
was done with 2N3053 and 2N4036 and was identical to my ears to the original 2.5.2.0.
when it comes to noises w/o input signal .

Even with this little issues, I found out the sound to be very good. We are very excited to hit REC!!

More latter this week!! Back to fine tunning.

cheers Paul!
cheers ya all!!
Fabio

 

[Kev]

:green: :thumb:

it's all good

very sorry that I haven't been able to join you guys as often as in the past.
The year that has just gone has been so very unusual (many of you only know half the story) and on the back of a couple of very tough years.

I'm just glad I managed to give it all a big enough push to get the ball rolling and things have been strong enough to continue to roll.

Both P1 and P2 have had many people put there own twist to it and even now in a thread close by ... James Lee is asking for input to his new PCB ideas
http://www.groupdiy.com/index.php?topic=6419

Fabio,
I've been expecting a comment from you ... ref your Letter Box ... I'm now getting concerned that something has not arrived ??

 

[Bauman]

Fabio,
I've been expecting a comment from you ... ref your Letter Box ... I'm now getting concerned that something has not arrived ??

KEV!!

YEA I GOT IT!! THANKS A LOT!!
Joe told me I can drop them on the micpres were now I have the 992 installed. Plug and play...
Gonna hit the studio with those little things by the end of week.

btw, this week I´ll be finally forwarding some stuff to AUS :twisted: to my new friend Alex C. He will then forward THE pack to ya. Or do you prefer to receive and forward to him? :green:

Also Pete P., expect something soon there!! Better late than never dudes!!

it´s all good Kev!
:guinness:
Fabio

 

[fallout]

Fabio, what are you using on the 25..2,0BC for C2/C3? are you using 47pf or 10pf? I think i saw you mention somehwere that c2 should be 10pf like the Melcor.. Does this apply to c3 as well? Or should c3= 47pf and c2=10pf.. Thanks!

-Jay

 

[Bauman]

Jay,

Right now I´m using C5=10pF and all the other caps like the schemo :wink: . Try R2=390R also...

:guinness:
Fabio

 

[Kev]

[quote author="Bauman"][... to my new friend Alex C. He will then forward THE pack to ya. Or do you prefer to receive and forward to him? [/quote]

should I know Alex ?

As you know Fabio, I'm here to serve. Whatever you feel comfortable with is fine by me.
I'm never far away and here for the very long haul.

As for your new toys ... I actually don't know if I paid orthem ... or if Joe gave ...
... at our last divy-up , I think Joe gave me an excellent discount so you can view it both ways if you like.

Big thanks to Joe.
and more cool DIY stuff to come.
:thumb:

 

[fallout]

[quote author="Bauman"]
- on 25.20BC, the background noise is a little bit higher that in the API25.20. Will try to mess with output biasing for the BD139/140 to see if it gets better. The best block (#4)
was done with 2N3053 and 2N4036 and was identical to my ears to the original 2.5.2.0.
when it comes to noises w/o input signal .
[/quote]

Do you recomend the 2n3053/4036's over the bd's? Do any additional changes have to be made to use the 2n's? Thanks!

-Jay

 

[Bauman]

Do you recomend the 2n3053/4036's over the bd's? Do any additional changes have to be made to use the 2n's? Thanks!

It´s not clear to me yet. I just know that the best block I have uses R2=360R and uses 2N´s at output

New tests this week when I get the blocks back to studio...

:guinness:
Fabio

 

[pmroz]

.
Jay, i think it was C5=10pf on Fabio's boards. probably you already sorted.

Kev, i remember 'Kev's Green Pre' site from years ago. It seems that you're partially to blame for this great internet DIY thing going on...
so here's to you. which do you like? :guinness: :sam: :guinness: :sam:

Fabio, pres here were noisy because no RL. I left it off to A/B trafos, then forgot to put it in for Cinemag. stoopid.
With CMI-8PCCA and RL=100K almost all noise is gone. BTW the hand trick makes a BIG difference without RL abracadabra...
With RL, hand-trick removes very slight residual noise that remains.

No 360R so tried R2=450R for 25*0BC, with BD135/136 out pair. Seems to clear some distortion from -3db and 0db positions on stepped-gain. Had assumed distortion was just pre overload. with 450R, -3db is now usable with same SM58 mic (no pad). Thought it might be due to 450R reducing overall pre-gain, but input levels in DAW are equal for 100R and 450R on 2 matched BCs/ matched pres. If 450R helped quieter settings, my ears couldn't tell.
With R2=450R, pres unboxed on desk, separate PS in case, noise was low enough to keep last Tuesday's vocal tracks.

first o-scope i ordered arrived DOA, try to be more empirical with next tests. For now i'm swapping and listening on 2 pres. Also Nuendo can see a bit.

a good meta might be: scope & test equipment technique, test methodologies, even add gain structure... .?

 

[Kev]

[quote author="pmroz"] ... Kev, i remember 'Kev's Green Pre' site from years ago. It seems that you're partially to blame for this great internet DIY thing going on...[/quote]

thanks
the page still does exist in the original location
but now also has a new home
http://www.diyfactory.com/projects/green/green.htm
and
don't forget this is Pete C's project !!


[quote author="pmroz"] ... a good meta might be: scope & test equipment technique, test methodologies, even add gain structure... .?[/quote]

Yes Mark B. and I have talked about this a few times.
A web page is coming
but
so is Christmas

Mark's other pages now have a new home too :
http://www.diyfactory.com/data/mbsignaltracing.htm
http://www.diyfactory.com/data/mbresistors.htm
http://www.diyfactory.com/data/transformer_connections.gif

 

[pmroz]

.

Thanks for links Kev....

i need to visit DIY Factory more often...

and beers for Peter C and Mark !
:guinness: :sam: :guinness: :sam:

 

[BackHand]

I and a couple of other guys are just about to build us some API preamps. One question that have come up is if there is a possibility to make the preamps with Variable Impidance :razz: ? We all have the latest revision of the boards.

Is it possible to have a Variable Impidance pot or such on the API 312?
and if, how do we make it work :grin: ?

 

[Bauman]

bh,

If using Cinemag CM75101 as input transformer, you can wire a toggle switch to its primary to have a 150/600 impedance selector...

:guinness:
Fabio