API 312 Thread!

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
janvanvolt said:
Hi, i mailed you my documentation.
(and thanks for the Hi-Z info. Can't await to get the missing transformator and power it up :)

I've just replayed some days ago, but I want write it's possible to make simple mods to 312 reliquia to eliminate the cap C3 in the feedback network to avoid its distortion, when there is my APP2055 or APP99F into this pre:

- desolder c3.
- in the c3's place solder a wire
- change to 100k the RS5 value
- put to ground RS6


 
 
Just to make sure:
Can someone confirm that the colours of the EA 2503 leads are the same as the cinemag output thansformer?
In other words I can just put the coloured leads in the corresponding holes of my 3nity PCB?

I can still smell the burned resistor on my rev A 1176 after wiring the output transformer the wrong way.
 
Hank Dussen said:
Just to make sure:
Can someone confirm that the colours of the EA 2503 leads are the same as the cinemag output thansformer?
In other words I can just put the coloured leads in the corresponding holes of my 3nity PCB?

I can still smell the burned resistor on my rev A 1176 after wiring the output transformer the wrong way.
I believe so, but
check here : www.cinemag.biz
and here: www.classicapi.com

Both sites have datasheets with wire colors.
 
Hi to all,

I'm gathering parts for a dual API 312, using Bob's PCBs, Classic Api transformers and Gar2520 DOAs. I've also started building a JLM power supply (I've used a couple before and I'm happy with them !) which leads me to my question: what voltage should I feed the preamps (what mains transformer should I use).
On Bicyclerecordings' schematic I read +/- 24V but the DOAs seem rated for +/- 16 to 20V.
I am certainly missing something simple here so... All inputs are welcome, thanks, Piotr.
 
The 8 channel unit I built uses 990 op amps and the schematic and BOMs reflect that. Folks substituting parts may need to make a few changes themselves. 2520s are normally run at +/- 16 or 17 volts.
 
Quick question regarding C4 and C5 on Bob's board. I am guessing that there are 3 holes to accommodate larger lead spacings? I have some 5mm Wimas that I want to use.
 
That's true. Just make sure you get the voltage side of the cap in the right pad. I think the extra ones all go to audio ground, though I'm not totally sure and don't have the board in front of me.
 
Hi !

thanks for your answer about the Opamps and supply voltages Bob. Would you recommend John Hardy's 990Cs Opamps for your board in the API 312 version ? Thanks ! Piotr.
 
They're good amps and would certainly work great there. Sonically, I haven't done any strict comparisons, but the difference a 990 and a 2520 wouldn't be overwhelming or anything.
 
Im building the access 312, almost everything works except when i turn phantom on i keep blowing r3 i bypassed it for a moment and got fireworks on c5. I'm thinking i have too much current running through there. Im running through PPA's psu2 with a parallel [email protected] xformer. Any one with some additional ideas?

Picture%206.jpg


 
bluesbaz said:
Im building the access 312, almost everything works except when i turn phantom on i keep blowing r3 i bypassed it for a moment and got fireworks on c5. I'm thinking i have too much current running through there. Im running through PPA's psu2 with a parallel [email protected] xformer. Any one with some additional ideas?

Is C5 installed correctly? Either it's in backwards or something's the matter with it if it's passing DC.
 
Well I'm not sure exactly what the DCR of a backwards electrolytic is, but from what i know it's basically a short and 48V across 470 ohms give you about 5 watts! Maybe some electrolytics have a higher reverse DCR than others?
 
yeah I had something similar phantom drawing too much current blows up resistor.  It was a short.  In mine the switch casing was touching a bolt grounding it to the case.  Another time I had an internal short in a lm317 so now I check the ICs meticulously.
 
Mitsos: What is the pitch in your 312 pcb molex connectors? Is there easy way to determine pitch from pcb layout (in general)?
 
Hi, they are the normal KK type. I think 0.1" (2.54mm).

About pitch, you say in general, you mean for this board, or for any board? I'm not sure if the image I posted is 1:1 scale. I will check. If so, then just print and measure. Or I could check my files and post pitch here (I assume for the electrolytic caps, right?).

EDIT:
cap pitch is mostly 5mm. All the wimas, the lytic in the gain adj circuit, the output lytic (might be 5.5mm, I'm measuring with a ruler atm), and the feedback cap.
The exception to the rule are the power filtering caps which are 3.5 or 4mm. It will for sure fit 100-150uF 35V PAnasonic NHG, FC, or FM caps. You could use smaller caps as well (47uF is probably fine) and 100 is a nice average.

Hope that answers your question!
 

Latest posts

Back
Top