Can I turn these into preamps?
« on: October 16, 2006, 06:23:39 AM »


drpat

Can I turn these into preamps? New
« Reply #1 on: October 16, 2006, 07:30:16 AM »
...
« Last Edit: September 17, 2010, 06:01:11 PM by drpat »
I use the LA2a on very hot signals like lead vocal.

kato

Can I turn these into preamps?
« Reply #2 on: October 16, 2006, 11:47:01 AM »
As long as you're comfortable desoldering the 2520 opamp from the board, then yes.

Then all you need is an input transformer ($50 - $80 depending on if you go Cinemag or Jensen.) Another dozen or so parts are needed (less than $20.) Get a PCB - or save the money and do it on perfboard. Pretty easy for this few components.

See the schematic and decide if you think you can do it. It's as simple a preamp project as you'll find - but the parts are expensive so it may not be the ideal first preamp (if you think you might screw something up.) Be careful when desoldering and resoldering the opamp - too much time in contact with the iron can do damage.

Of course, you'll also need to build a power supply, knobs, enclosure, etc.
Check the meta: API Meta <-- there's an amazing amount of info and lots of people willing to answer beginner questions.

Welcome!

Kato

rascalseven

Can I turn these into preamps?
« Reply #3 on: October 16, 2006, 01:57:24 PM »
Yeah, you'll have no trouble making a couple of great 312-type preamps with those cards.  Be aware, however, that those cards have the 2623 output transformer instead of the 2503 used on the 312.  According to api transformer info the 2623 can do 1:1 or 1:2 outputs, which makes me think they're trifilar wound, instead of the quadfilar winding of the 2503.  So you will not be able to provide simultaneous 1:2 AND 1:1 outputs with those.  

Practically this is a non-issue, however, as most people only use a single 1:2 output, which these will easily supply.  I'd be shocked if there was much noticable difference in the tone.  

Regarding the desoldering of the opamps, DO be careful not to keep the iron on the leads more than 5 seconds or so.  If that's not enough to desolder (using a good quality desoldering braid), then let it completely cool before putting the iron on them again.  Better to be very safe than sorry, as those opamps are basically like gold.  API will sell you replacements if you send them a bad one, but they're like $75 each still, so better to be very careful with any that you have rather than incur more expense.

Even better, see if you can buy or borrow a desoldering gun (with a built in vacuum pump) with a large barrel tip (those 2520 pins are much bigger than typical DIP-style opamp pins).  That would be the best for this type of job.  I finally broke down and bought one at Fry's for around $120-ish.  I've never regretted that purchase.

Also, regarding input iron, I suggest Cinemag 75101 inputs on those.  Compared to the 115k-types often used on those the sound is much richer, silkier, and fuller, without being mushy or dull at all.  Just my 2-cents.

That's a good find.  Good luck with your bidding!

JC
"If you dig the gig, do it. -But listen to the signal, not the person talking."  -Keef

Can I turn these into preamps?
« Reply #4 on: November 04, 2006, 09:34:12 PM »
Okay I've been doing a little reading and decided to buy a couple of boards.  I tried to contact the guy at this site for two of them but never got an email back.  Is there another place I can get the boards?

3nity

Can I turn these into preamps?
« Reply #5 on: November 04, 2006, 09:42:42 PM »
that's fabio!!! he's maybe somekind of bussy if you're in the USA go to this site: http://www.braudio.com you can buy it from them!!!
Life is a path, death the destination.

Can I turn these into preamps?
« Reply #6 on: November 04, 2006, 11:06:50 PM »
thanks!

jensenmann

Can I turn these into preamps?
« Reply #7 on: November 05, 2006, 05:54:47 AM »
Fabio just married and is pretty busy in honeymoon :wink:
He will surely reply as soon as he´s back in town
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

matta

Can I turn these into preamps?
« Reply #8 on: November 05, 2006, 07:46:11 AM »
Quote
Fabio just married and is pretty busy in honeymoon


Better not tell Fabio's wife! Since he has been married for years and has 2 children!!! I'm SURE she would want to know about this one... I'm not the one going to break the news! Hah hah!!!

I think you meant Rafa who has recently gotten married and is prob still on Honeymoon, they are both from Brasil though :green:

Cheers

Matt
Matt Allison
www.matt-allison.com

Quote
We are not going to start thinking of ways to get an octopus to commit a crime, cause that just has failure written all over it – Earl J Hickey

jensenmann

Can I turn these into preamps?
« Reply #9 on: November 05, 2006, 11:27:22 AM »
:shock:  Oooops :oops:

I didn´t want to be indescrete, though
 :wink:


 :green:
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort


Can I turn these into preamps?
« Reply #10 on: November 05, 2006, 07:45:18 PM »
Great I've ordered 2 PCB's, most of the parts from the API 312 Parts list.  Well the semiconducters, resisters, and capacitors at least.  

I am curious as to whether there are switches I can buy that have buttons you can push with l.e.d.'s  that light up indicating on/off.  I think that will look cool. :D

Also the output transformer I bought doesn't have the same color code as the ones on the PCB's I bought.  I think that will be a problem for me.  I don't know anything about testing that kind of thing.

Can I turn these into preamps?
« Reply #11 on: November 25, 2006, 04:14:14 AM »
:?:

Will these work for potentiometers?  I could not find 22k rev log pots.


http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=22532&Row=515614&Site=US

raysolinski

Can I turn these into preamps?
« Reply #12 on: November 25, 2006, 06:49:21 AM »
The 22k rev log's are impossible to find in the US. WHat you need to do is match the resistor in the feedback loop with the pot value and it will preserve the gain structure..any pot will work (linear, log, reverse log) but the law  of the pot  curve changes the way the gain is applied..linear is straight so the first 3/4 turn of the knob won't do much...log is slightly better as the gain changes alittle more evenly  over more of the turn and rev log gives more of the feel you are probably used to..I have 6 of these guys , all with  different pots, and they all work fine...

Ray
"orange whip?..orange whip?...3 orange whips please"

Can I turn these into preamps?
« Reply #13 on: November 25, 2006, 07:59:06 AM »
Excuse my ignorance but your saying  a 25K rev log like this one from digikey (#KB2531S28-ND) will work  buit i have to change a resister where on the board?  


You said feedback loop but I have no idea where I should be looking.  And how do i make sure it matches?  Matches in resistance maybe?


 

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