Changing the trim pot into a fader... Easy?

[Category 5]

Supposing I wanted to convert the 6db trim pot onto a full on fader. Is it as simple as changing the pot or a couple of resistors?

My reason for wanting to do this is so that I have the ability to drive the preamp into varying degrees of distortion if I desire. I do not want to be limited by the output of my mic (since there is no pad).

I am finding that most of my condensers are neading less that 4 or 5 steps on the main gain switch. Is it possible that at those lower gain settings I am not getting as much harmonic content as I would at higher gain settings? I mean, the distrotion is not linear is it?

Shane

[tpryan]

Not easy. The trim pot is in the feedback loop and it would take some cutting and jumpering to get it across the output. You wouldn't want to do that anyway, since then the output impedance would vary with output level. If you want to run the preamps hotter, the thing to do is pad the output with some line level attenuators. If you google "balanced pad" or "H pad" I'm sure you'll find some schematics.

Distortion does vary linearly with gain. More gain, more distortion, since there is less negative feedback being applied. Distortion also increases with frequency, since the open loop gain of the op-amp rolls off at 6dB/octave. Less feedback, more distortion.

[Category 5]

So am I right then in assuming that running an input with -10db pad enable, and with higher gain would yield more distortion that running without the pad but at a lower gaine setting (assuming equivalent output level for both scenarios)?.

...or would the distortion be the same for both scenarios.

My point is that some of the distortion is what is desirable about these designs, and running the main gain dial at 3 or 4 is pretty conservative from an overall gain standpoint. If the even order distortion isn;t occurring much until higher gain levels, then some form of input pad seems like a reasonable consideration.

Most of my mics are not equipped with a pad, so putting one between the mic and the pre seems logical assuming it woudl enable me to get the levels into the "sweet" distortion range. Keep in mind I am not talking about full on clipping, just mild saturation.

Shane

[screws]

A pad in front of the input is defeating the purpose. If you want the mic pre to slightly clip, you must pad the output, not the input. Try the "Atty"

[Category 5]

Thanks Steve!

I wasn't thinking straight. Of course you're right.

We'll get together at your studio soon...as soon as all these hurricanes finish. Somebody stop them please!

Shane