Tony,
I had a very similar looking waveform a couple of times with 2-wire AT853's... which are known to brickwall/overload at "loud" levels... where "loud" is a relative term. Going from a 9V to 12V battery box seemed to reduce it in my case. A friend had a similar situation with some chopped Nak 300's when they were fed with a low input voltage (in the 3V range). Given at least 6V, his Naks work better. Other people have seen similar results when Nak 300 batteries are getting weak.
I don't know enough about Nak700's, or the mod that's done, to comment if that's whats likely to happen. Obviously the -15db attenuator barrels seems like the logical next step. I would think if the capsules are starving for voltage, then attenuators won't help that. If the caps have enough output to overload the FETs then attenuators would do it.
Joe
Hi Joe,
I'm not sure about the low voltage. What would a wav form look like with a low voltage problem? Wouldn't both the top and bottom of each wav/channel be affected? I know those screenshots suck, but the top half of the wav is the part that was way wrong. The bottom half is what I expected to see based on where I set my levels. I'm leaning towards the asymmetrical overload that mshilarious described, or at least started to, he hasn't been back.
This mod is the same as the Nak 300 mod. Utilizing the barrels for an "active" type of setup. I'm using the AT 8533 power modules. 48V to 9V adapter. The 700's run on 6 volts. I've run these modded Naks with both sets of barrels. I did about 5-6 theater type shows with the -15db's>722. Even from the 5th row at the Beacon I had to have the gain on the 722 beyond 3/4's. It was the same at most other shows with those barrels. I switched to the regular barrels and found the levels to be more predictable and I never had this "overload" problem I experienced here.
I hope what happened was a combo of a loud DMB stack tape and no attenuation in the barrels. A switch back to the attenuator barrels should solve this problem for loud shows, so I've been told. I'm probably the only person with modded 700's that uses the regular/0 attenuation barrels in their mod. Everyone else uses the -15db barrels and they even go as far as stating that the regular barrels are useless for loud PA recording. I guess I was bound to get burned sooner or later.
This is the part I really don't get. I had the 722 set on low gain anticipating an overload problem. I don't understand where the overload happens. If the caps overload before the FET, does the attenuation in the barrel catch that and any setting on the pre is too late?
Always appreciate your input Joe.
Thanks, Tony