The Wasp goes hsssssss?

Greetings all,

Newbie here--just bought my first couple modules, one of which was Doepfer's A-124 Wasp filter. My question is... is this thing supposed to hiss?

I finally put a spectrum analyzer on it, and I'm getting a single 23.7 kHz, -27.2 dB transient from the thing. Even with no sound going through it. In fact, as soon as I turn on my rack, the -20 dB light on my mixer recognizes sound on that track.

Whether the filter is set up as HP or LP, fully open or fully closed, I still get that spike. Oddly enough, when the filter is closed, the spike rises to -19.8 dB.

Is this part of the "character" of this filter? Other than the hiss, it seems like a worthwhile module.

I checked the rest of my modular setup, and a similar transient spike is present then too, but at a more acceptable -59.5 dB.

Any suggestions? Or did I just get a bum Wasp?

The WASP circuit relies on the non linearity behavior of a cmos ic described here

https://www.fairchildsemi.com/application-notes/AN/AN-88.pdf

It sounds to me like you are running a switching power supply that isn't filtering out it's PWM signal completely that the WASP is reacting with. The WASP is probably fine.

Interesting...

Power is provided by a Happy Ending Kit uZeus, but now that I think about it, the audio cables running between the Wasp and the mixer are draped over the top of an Emu sound module before plunging into the dark recesses of my equipment rack, where is is probably in close contact with the rear plane of several other components--notably, where the power supplies would be.

I run balanced patch cables exclusively in my rack, but of course the patch cables connected to the modular are 2-conductor, unbalanced. Since these wires run very close to several transformers on their way to the mixer, that could be the problem. I'll try rerouting the wires and see what happens.

Thanks for the tip!!

Got home tonight and discovered that the patch cable on the input side of my modular was laying across the power supply of the unit below it in the rack--and I had hope. However, no matter how I moved the cables around, the Wasp continued its -20 dB hiss.

I finally removed all the cables, both input and output, and put a probe on the output jack. Sure enough, the hiss is still there, so that tells me that the source of the problem is the uZeus. My other module (A-136 Dis) exhibits the similar behavior at a much lower audio level, so based on the tech sheet you provided, I feel like the Wasp is just more susceptible to these kinds of things.

So for now, I think I will just EQ out the hiss until I'm ready to upgrade to a cleaner power supply. I'll have to listen to it if I'm monitoring from the rack, but at least it will be inaudible when the audio reaches my DAW.

Thanks for all your help!