[Flatpicker]

During a test on a friend's studio, I've notice some limitation on headroom of my API stuffed with Melcor opamp...

Take a scope and function generator, input a sinewave, crank it up and see what +/- voltage it clips at. Do the same with a 2520 if you have one and see if there's any difference.

[andre tchmil]

ahum, ahum   :?

[soundguy]

hey fabio-

for guitars and drums, I have to use a pad on just about every mic pre I have, certainly so in regards to the API gear here.  This of course will depend on a)the level of the source you are recording and b)the output of the microphone you are recording it with, two big variables, but having to pad these things is certainly not unusual for me, if anything, its the norm.

dave

[rafafredd]

That would be a good reason to go for a lower ratio transformer, like 1:6 or 1:5...

[Bauman]

Thanks Dave, so looks like I really need a pad on my api board....

Rafael, I'm using a OEP on this, it's 1:6.45 ..  :sad:
Now I'll upgrade with a 1:10 cinemag, then seems the pad will be necessary...

Any more comments??

cheers!
Fabio

[fallout]

Andre, from what i understand, with modern transformers you wont need the 1000pf cap on the primary. What you put on the secondary depends on what input transformer you use.  The datasheets for the transformers should give you a general idea.

-Jay

[andre tchmil]

thanks fallenout, but I was also wondering if 1000PF is the same as 1.0 NF

[fallout]

yes, 1000pf = 1nf

-Jay

[Bauman]

Yet about input transformer for API, I dunno if you guys notice this:

http://www.apiaudio.com/apihomeSet2.html

The API 212L mic preamp is a design that will fit into the API Legacy series consoles, as a discrete API 2520 op-amp and the Richenbach RE-115K-EPC input transformer, with an API output transformer.

cheers!
Fabio

[smilinfu]

I am using a couple different lundahl input transformers on mine (1:10),  I could notice no immediate difference with the 1,000pf caps on the transformer primary.  Although there may have been something wrong with the test, as it seams there should be at least some difference.

I was wondering if the 120pf cap supposed to be electrolytic?  I am still having a hard time getting decent high end from my attempt, and the feedback loop seams like a likely culprit.

[sismofyt]

You can't get a 120pF electrolythic cap, the don't make 'em much smaller than 1yF. It has to be ceramic or polypropylene/polystyrene/polywhatever.. for high frequency work it's allways best to avoid electrolythic caps as they're not very effective at high freq.

Edited to ad that the intended use is often stated in catalogues like Farnells. Which is free (at least where I live) so it's a handy thing to have :wink:

[smilinfu]

Thats what I thought.  I am just running out of ideas as to where the highs are going and do not want to take the whole thing apart to start over agian  :sad: . I may try some other types of caps, to see if that does anything.

[fallout]

The 120pf cap is not an electrolyric type... A poly cap will work just fine!  :cool:

-Jay

[Bauman]

If someone need it, here's the pinout and dimension info for Cinemag CM75101-APC:

http://www.thediypill.phx.com.br/forumfiles/cm75101_data.pdf


Fabio

[JustinS]

Hi guys,

check out this website...

http://www.oldschoolaudio.com/products.html

OSA make 3 different versions of a 312'ish pre, all well and good... the major difference between the dif versions seems to just be the input transformer they use, the first is a custom, the second they don't mention & the third is a Lundahl 1538XL.

The 1538 is a 1:5 see:

 http://www.lundahl.se/catframe.html

So how do they do it??  They quote the same gain range for all 3 pre's, and the trad input tranny for 312's is a 1:10 / 1:8, so are they just lying about the gain range, or are they getting more gain from somewhere else.... maybe using the output tranny at 1:2 or higher or something?? What is the go??

Justin.

[dasbin]

Now here's an interesting thing.


OSA is using the Cinemag CM75101-APC as input, right? The Seventh Circle A12 kit uses the Cinemag CMMI-10PCA for input. I wonder what the difference in sound is.

[andre tchmil]

Thought I posted this recently, but can't find it anymore, so here we go again.
2 questions.
I'm using the Lundahl LL1636 trafo on the input: what to do with the R4 and C5 as on the original 312 layout. ? And if I need to use them, what type should  C5 be.

For the C6 , I'm using a 120Pf Styroflex polarized cap. what direction should the poles follow ? (still a newbie) :grin:


On the OSA page I saw a 312 clone with an output gain pot.
What is the value and where to connect this?

thank you

[andre tchmil]

ahum :grin:

[PRR]

> I'm using the Lundahl LL1636 trafo on the input: what to do with the R4 and C5 as on the original 312 layout?

This depends on the transformer. Use the R-C network recommended by the transformer maker.

> I'm using a 120Pf Styroflex polarized cap. what direction should the poles follow?

picoFarad caps are almost never polarized. Polarity matters only for electrolytics, which are only used about 1 microFarad and up.

And if "Styro..." means polystyrene, then it isn't polarity sensitive.

If it has a band on one end, that is the Outside Foil. It will work either way, but maybe less stray capacitance if the outside foil goes to the less sensitive side of the cap. If one leg is grounded, outside foil should go to ground. If one side goes to an opamp output, outside should usually go there. But considering the typical size of a 120pF cap, it probably does not matter.

[chrissugar]

The Lundahl 1636 do not need the RC network. This transformer has the self resonant point above 250kHz. This is a very good transformer. I use the 1636 in 12 preamps and they are amazing.

chrissugar

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