Is it possible to reach digital zero with API 312?

Hi,

I have finished my API 312 with ED2622 and Fabio's opamps. Voltages i'm running for opamp is 16V. I'm just curious about the signal level. The maximum gain setting is set, I'm shouting as I can and Logic shows something around -10. For conversion I'm using Rosetta800. The mic is tube mic with 200Ohm output. Is it everything ok?

Are the 2622 primaries in parallel? You should have plenty of gain with a 312 circuit.

I connected the jumper on 1 pin with 2 pin and 3 pin with 4 pin. jsteiger, is it right connected?

Hi,


  Apogee Rosetta 800 can be set at 3 different operating levels, -10dBV     (dig ref -13dBfs), +4dBu    (dig ref -16dBfs), or +4dBu    (dig ref -20dBfs). These are selectable by internal jumpers.


  I would be very surprised if a correctly operating 312 would fail to run to full scale deflection, even at the low sensitivity setting (+4dBu (dig ref -20dBfs). However, it might be wise to check how your unit is set-up. I would recommend the middle setting( dig ref -16dBfs) if I were you.



   Kindest regards,


     ANdyP

Thanks AndyP, I'll check it out!

The sound I get is good, rich and open. Just the level can be higher. After record end I always add more 9-10dB internal gain.

bongolijus said:

I connected the jumper on 1 pin with 2 pin and 3 pin with 4 pin. jsteiger, is it right connected?

Click to expand...

Yes, that is right.

the api 2520 + transformer output, as normally wired, will be able to produce an output level close to or exceeding +28dBu

full scale on AD converters are generally +24dBu or lower - and this is often adjustable either with a gain pot or jumpers... 

I've not run into an AD converter with a full scale HIGHER than +24dBu

Hm, can be something wrong with the opamp? When I move the gain switch from 1st position to last, the gain level rises just a few dB.

It might help to know what boards you are using (pictures might be better). Have you double-checked the gain adjustment circuit? Pot(or switch) and feedback R should be about the same value, and R in series with pot should be 1/100 of that, for 40dB max opamp gain.  If you're using a switch, triple-check the resistors against whatever calculator you used to get the values, and make sure it's properly connected.

Double check your input trafo is inserted correctly. If it's backwards, you won't have much gain at all. You could also have a fried winding on your input trafo so check continuity/DCR on the primaries and secondary, you should be able to check this even in circuit. I once had a similar situation to yours and it ended up being a fried secondary on the trafo. Symptoms were very little gain change, and oscillation at max gain.

It could also be a problem with the opamp, of course. That should be fun to figure out.  I suppose you don't have any known working ones, otherwise you would have already tried to swap them around?

A scope would help trace the problem.

If nothing else, take some macro shots and post them, maybe someone will spot the problem.

measure the gain if possible.  lots of simple ways to do that.

And what's the source ?
drum , very different than voice
or did i miss it and you run full mixes through them ?

Mitsos, you were right, dead input trafos..FAK. I have built two of these, when I ran the second one it was fine, I have the tons of gain.

What can cause that? overheating? Can do that bad voltages? The powersupply I tested and it gave me proper voltages at the first fire up..

Really good preamp.. Very like the tonality of these..

Thanks for your help guys!