Active/Passive DI's with Active or Passive DI's - Jim Williams love to hear from you

[True North]

I have noticed that I am not having a lot of luck with active pickups in my studio. I am not crazy about the tones and I am getting a lot of EMI noise. I think active pickups sound great through a good bass rig but through a DI I am not having much luck.

I was wondering if the fact that I was using active DI's with the active pick ups was aggravating the problem.

ALSO

I read this fascinating explanation from Jim Williams on his bass rig. Jim could you expand a little on this explanation below. How do you attach the copper foil to what ever you are lining. Does it naturally adhere ? Could you also expand upon the electrical tape in between the magentic poles thing. What magnetic poles are you specifically talking about. Any chance we could get a picture of your under the pick guard, I would love to see it, cheers!!

Originally Posted by Jim Williams

My bass has passive pickups. The P-bass pickup is one Seymour Duncan custom wound for me back in 1979. The pickup coils are wound to 1 k ohms instead of the standard 6 k ohms, DC resistance. They have a resonant peak at 32k hz, very airy and hi-fi. The J bass pickup is another custom job wound by Bill Bartolini. It's resonant peak is at 15k hz. The electronics are seperate from the passive pickups. I've never found a decent active pickup design as they all use poor quality semiconductors I would never use for audio.

So, that J-bass pickup is internally shielded, the plastic covers over the p bass pickup are lined with copper foil. That works very well. I only place a piece of electric tape across the magnet poles to avoid buzzes if the fingers touch them. The rest of the cavity and under the pickguard are all lined with copper foil shielding tape. It is imprtant to line the cavity around and under the pickup or your body will inject EMI buzz into the bottom of the coils.

As to the passive sound, easily done with this rig. Just run it into a 12 db/octave low pass filter set to 4 k hz. Run a high pass filter at 50 hz. Maybe 80 hz if you want that old Dual Showman sound. Internally, one could also place a small cap across the pickup to band limit it in a way that passive controls and cables do.

This is subtractive synthesis. Taking away what you don't want. Easy to do. The opposite is impossible to do. You will never extract 32 k hf harmonics out of a passive bass that has already decided for you how much string tone you will hear.

This is why I follow the Jimi Hendrix philosophy of recording:

"I want to see and hear everything".

Jim Williams
Audio Upgrades

[True North]

BUMPAGE - would love to hear from someone

[Jim Williams]

I can't tell you what to do to fix what I can't hear. If you have level problems, that will be heard as noise or clipping. AC powered "DI's or line amps are the way to go. I've not found the needed bass energy out of any "DI" that runs on phantom power. An active bass can be run right into any outboard if the level is high enough. Maybe try a passive Jensen DI with an active bass, I run mine into a custom mic preamp with a line input stage. It's a very fast FET circuit that is direct coupled, no capacitors in the audio path. Many of the active pickups have a plastic quality, use passive pickups to avoid that.

Jim Williams
Audio Upgrades