J99 clipping?

[pilahaka]

I've had my J99s and A12s for a while now. Really nice

The only potential problem I've observed is that the either the input or output stage on the J99 is clipping on sources I would not expect it to. It seems like the input stage to me.

The J99s clip with sources that my A12s and the Great River preamp do not. I can plug an SM7 into it crank the preamp up to 11 (no, seriously) and it will clip when I sing into it. I don't even have to sing that loud.

The converter is not the culprit because it's reading about -6db coming in. And what gets recorded is at the same level, well under 0db, but the distortion (the bad kind) is clearly audible. If I turn down the gain it seems to be less of a problem, but that might be because the level becomes too low to hear the distortion.

Is the J99 functioning as expected, or could there be a problem in the construction. Is this what is referred to as "headroom?"

Thanks.

[tpryan]

You have more than one and they both behave the same? What op-amps are you using? What voltage did you set the local regulators to? Can you use your DAW to generate a test signal? What does the waveform look like?

[pilahaka]

I'm using the John Hardy 990Cs. I do have two J99s and I think they're behaving the same way, but I haven't tested it definitively. I set the regulators to 24v.

I can generate a sine wave with my DAW and record it.

That's a little more scientific. I'll post the results.

[pilahaka]

In looking at it more scientifically I think it's functioning like it should, but you tell me, 'cause I'm pretty green.

Ok, so I ran a sine wave into the J99 then into my converter to record it. I have the Fireface800 set to output at -10dbV. With the J99 gain set at 6, if the meters on the output read anything over about -24db then the tops of the sine wave starts getting clipped off. I have my converter input sensitivity turned down so that the converter doesn't clip. If I turn down the gain a notch the clipping stops.

It seems like a pretty hot signal, but I readily admit that the difference between dbV and dbU escapes me, so perhaps I'm doing this wrong. Anyway, does that seem like a good test.

Perhaps I just have the gain turned up too loud when I'm using my SM7 and the A12 doesn't clip because it has a little less gain available.

Thanks for your help. Sorry to be a pain.

[tpryan]

OK, with the Fireface set to -10dBV, the manual says that 0dBFS = +2dBV. That means your -24dB output is -22dBV at the output. At click 6, the J99 delivers either 40dB or 46dB of gain, depending on how you have the input transformer jumpered. Using the lower number, 40dB of gain added to your -22dBV input yields +18dBV of output. +18dBV is a little more than +20dBu. The Fireface manual says that 0dbFS (clipping) at the "low gain" setting is +19dBu. So I think you're clipping your converters. Try using a 20dB in-line pad between the preamp and the Fireface and see if the distortion disappears.