API 312 Thread!

[rbaker]

I'm just about ready to order the rest of my parts for 2 312s from fabio (his 2520's and boards showed up yesterday)

I was given some older mci channel strips which I had originally intended to rackmount but it just didn't look like it was going to happen. The strips have jensen je-115k mic input transformers so I figured I'd use those.

I using greg's part list for the guide and he used jensen 110k's. I realize that they are not THAT much different (1:8 instead of 1:10 mine) Could someone explain how the increased ratio might affect the sound? more gain/more aggressive etc?

Also I was looking on the jensen site and each has a diagram of typical use for each transformer (which closely follows the fabios schematic) the resistor that connects two of the secondary leads on the 115k is 150k. on the 110k it is 100k, which is also what is specified on fabio's part list.

#1 if I use my 115k's should I change to that value (150k)?

#2 are there any other resistance values that I should change based on this transformer? if so how might I figure those values? (trying to learn something here rather than simply getting the answers)

In a completely unrelated question, greg's bom has switches that are $8 each. Is that required (ie: is there something I'm missing?) or are they just really nice switches?

 

[smallbutfine]

No answer right yet... :? Holiday is over, tomorrow is reunion day and i decided to finish minimalized 312's on fabio's board using the full trafo option, no input pad (maybe veroboarding an output pad later, as this seems more useful to me) and reducing the opamp supply caps to 100µ and the pp cap to very low 22µ for testing (maybe over the connectors place, setting the final cap in the board later). I do not have much need for pp as i mainly have dynamic, ribbon and valve mics and my pp condensers are not really decent anyway...so maybe i'm happy with this solution.
I will start with a frontpanel switch version with shielded cable, so i can fit relays later, when not happy with them as is.
All this might take the parts count to an absolute minimum, i guess...hmmm. Even in the psu as i need no relay voltage...
I will post results if i'm done.

Kind regards,
:thumb:
Martin

PS: For VU i think i will be connected to a secondary winding of the output transformer originally? Is this possible with the cinemag cmoq2s?

Another question that i found actually answered here http://www.groupdiy.com/index.php?topic=17628&postdays=0&postorder=asc&start=0 and that would be of interest for others was: Is a chip opamp xxx adequate in this application, with CMOQ-2s - generally YES (OPA604, AD797, NE5534).
So i will try this out and compare later to DOA...exciting.

 

[delaymix]

Hello,

I have finished constructing to 4 units Api 312 Fabio version.
Now I am fitting the feeding of the LM317 and my doubts are to that voltages worked better.

I have constructed opams 2520 and 1731. Whereupon values of voltage is obtained the best sound?

+- 15 ?
+- 18 ?
+- 24 ?

+- 24 v , it can be excessive? They are possible to be burned opams?

Thanks

 

[BR]

rbaker

you can check out my BOM which is based on a cinemab input but I do have cheaper switches that I used on my build that is on the my thread in The lab. I think they are a little over $3.
http://www.braudio.com/product_files/CAN312_BOM.xls

the power supply is here
http://www.braudio.com/product_files/CAN312PSU_BOM.xls


Hi delaymix,

adjust the supply to read + and - 20V at the sockets. I think that is the best voltage for the 2520, but I think it will work for the melcor too.

peace
Gil

 

[smallbutfine]

:thumb: Very appreciated!

 

[guavatone]

I just fried one of Fabio's potted DOA's. I am using 4 "original 312" circuits with 2 JH-990C and 2 of Fabio's. I am not sure what it was, but I hooked up a JLM PSU set up for+/-24V without load and it seemed fine.

Then I hooked the 4 312's up and the 2520 started to smoke. Power Caps sizzled VDC was all over the place. Then later when I took it out I saw a bulge in the blakc plastic. Well, I guess I'm putting in an order for more 2520s. Now I have just 2 990C's in the box and the Voltage is stable.

before the JLM I was using another PS and thought it was the problem since regs were getting hot. Either the 2520s and 990s don't play nice together but I don't see why. Most likely it's the 24DC Voltage.

Any ideas? Could it be a Current problem?

 

[hejsan]

I'm not sure, but I don't think the 2520 was made for +/-24 volts, right?

 

[JLM Audio]

Yes 2520 is +/-18v MAX unless you want it to smoke which would be bad for its health :sad:

 

[Walrus]

From the original data sheet dated 1972....

+-12VDC to +-20VDC.

 

[guavatone]

Always seems I need to find these things out the hard way. Well, at least I'll let other's benefit from my folly. I wanted to hear the difference between Fabio's 2.5.2.0 and 990c's. That smell doesn't seem to go away.

Now I have some JLM 5 rails coming if I want different Voltages in the same box.

 

[usekgb]

Things just don't work as well when you let the smoke out. :sad:

 

[delaymix]

Hello,

I have made the first tests of boards of Fabio, everything seems to be in order of apparent form. Although I have still not been able to listen high volume, opams 2520 seem to work correctly, but I am not very safe of some things... :?

I use the transforming input CM75101APC and in the output CMOQ-2L, and TQ2-5V for the switch.

I have adjust the PSU of Fabio without load with tensions of +20.60v. and -20.60v. up to here everything is correct.

When I use opam 2520 the positive tension remains with the intact value to +20.60v. but the negative tension falls until -7.70v.

When I use opam Melcor the 1731 positive tension remains equally intact to +20.60v. and the negative tension falls until -3.42v.

My doubt is if these falls in the negative tension are normal. He is correct this?... :?

Opams 2520 seems to work correctly, to simple ear the sound seems to be good, correct. There are no oscillations.

Opams Melcor 1731 sounds quite rough and profit not to eliminate the oscillations. I have put a condenser of 100pF between the bolt O and the entrance bolt (-), this would be in parallel with the C5 of 120pF of the board.

I do not know that I am making bad... Some idea to finish the project and that work correctly?

Thanks.

 

[3nity]

Guys, does anybody knows if i could use 2N2003 as substitute for that BC560??? that was the only one i could find locally. i use it on the greens led meter buffer. I believe here is not the same application???
Another question i'm using OEP in the input, do i have to lay it down and solder or do i have xtra wiring to do?? Relays now, i have the 9V aromat, did you know if i have to change some resistor values to get the 9v from the Fabio PSU??

i'm almost there, only a few resistors and i'm done.....thank you guys.

 

[BladeSG]

[quote author="3nity"] did you know if i have to change some resistor values to get the 9v from the Fabio PSU??

[/quote]

I think you put a LM7809 reg in there instead of the 7805, but I can't be 100% sure as I discarded the idea of using that PSU in favor of Joe's PowerStation.

 

[drpat]

It seems as if there's a layout error on the pp2520 board. Look at the placement of C5. According to the schematic, it shouldn't be touching R2, R3, C4, Q1 or Q4, and it is. But it's not touching Q2,Q3,C1 and R5 like it should be... Did I miss something in those long ass 25.20 threads?

 

[BladeSG]

[quote author="Bauman"]Hi Greg,

Also, I don't think a relay is involved with the PP, just the PAD, POL, LINE, and HIZ.

true. no extra bucks in PP relay needed
The thing is the capacitor will keep some charge for some time, I was not aware it was an issue since I used to turn off the phantom before I disconnect the mic, then the mic bleeds the PP out the cap... : :wink:

you can do this: do not use the PP LED where it was supposed to be but connect it in the PP
going to the input connector. raise the the led resistor to 5k1 at least. it will turn on when the power is on the way to the input connector and will drain the charge when the PP is turned off...


:guinness:
Fabio[/quote]

Just wanted to make sure I'm understanding....

Do you mean that the 470R gets replaced by a 5K1 resistor?

 

[hejsan]

Ok, I have read a lot in this thread about relay substitution. I however didn't quite get it,

Can I use a 48V relay like this: digikey partno: 255-1801-5-ND, (TQ2-48V)

If I do, could I just skip parts R10, REG_SW, C18, C19, R11 and LED_SW from the power supply and use the phantom directly?

Or would the phantom power produce some bumps in the audio when switching the relays?

Thanks,
hejsan

EDIT: digikey not mouser

 

[BR]

Yes, correct..

but that partnumber is for Digikey... :green:

I don't think you will have audio problems.

I'll try using those on my next pair. Please let me know how yours turns out.

Just a stupid question, did you check to see if the footprint will fit in Fabio's board?.

thanks
Gil

 

[hejsan]

Thanks for the confirmation!
[quote author="BR"]
Just a stupid question, did you check to see if the footprint will fit in Fabio's board?.[/quote]
It is in the same "2 Form C" category as the 5V relay in Greg's partlist.. whatever that means, so they share a construction diagram.

 

[hejsan]

[quote author="drpat"]It seems as if there's a layout error on the pp2520 board. Look at the placement of C5. According to the schematic, it shouldn't be touching R2, R3, C4, Q1 or Q4, and it is. But it's not touching Q2,Q3,C1 and R5 like it should be... Did I miss something in those long ass 25.20 threads?[/quote]
I bump that!