Author Topic: Non functional hum canceling coil and bridge pickup on Series 1 (Read 288 times)

mgauction · « **on:** November 11, 2005, 05:18:38 PM »

This is my first post. Nice to meet you!

Hum canceling coil and bridge pickup are both non functional on Series 1. Where do you recommend I look for this switching problem in order to get it working properly? Thank you in advance for any help!

(Message edited by mgauction on November 11, 2005)

mica · « **Reply #1 on:** November 11, 2005, 06:33:37 PM »

Hi! We'll try to help you troubleshoot the problem. Are you experiencing lots of hum? How did you determine the pickup and the humcanceller weren't working? Are you using the 5-pin or the 1/4 output?

You can reverse the neck and bridge pickup connections on the preamp card to determine if the problem is the pickup or the electronics.

mgauction · « **Reply #2 on:** November 16, 2005, 07:56:20 PM »

Hello Mica! I had my tech reverse the pickup connections and the other pickup was inoperable. So we assume the pickups are OK. What can we check next, the preamp or pickup selector switch? Can you furnish a scematic of an early 1974 Series 1?

Also, we used the 1/4 output, not the 5-pin. And yes I am experiencing some hum, not a lot.

(Message edited by mgauction on November 16, 2005)

David Houck · « **Reply #3 on:** November 17, 2005, 06:03:42 AM »

I believe it is the case that the 1/4 output is stereo; so if you are using a regular mono 1/4 cable, then you will only get one pickup.

mica · « **Reply #4 on:** November 17, 2005, 12:24:37 PM »

Plug stereo headphones in the 1/4 jack and see if you don't hear one pickup in each ear then. If you do, then the bass is functioning as manufactured. You can rewire the 1/4 jack for mono or install a mono/stereo switch if you like. If you rewire in mono, you will loose the headphone capability. I can post directions for either procedure for you.

If you can't hear both pickups, a humcancelling procedure isn't easy to do. Once you do hear both pickups, you'll likely be able to reduce the hum to null.

mgauction · « **Reply #5 on:** November 28, 2005, 10:07:49 AM »

Mica - My tech went through the hum cancelling procedure and found that the adjustment of the two center trimpots did nothing. It appears to be more of a sixty cycle hum than a high frequency noise. Anything else we can do?

mica · « **Reply #6 on:** November 28, 2005, 12:09:08 PM »

This sounds like the humcancelling pickup has failed, is not connected, or the humcancelling section of the circuit has failed. It will be the source of the 60Hz hum since the pickups are single coil, and without a functioning humcanceller, there isn't any humcancelling.

Check to see that the humcancelling pickup is plugged in the center connector on the preamp board. Even if it looks like it is, just disconnect and reconnect to make sure, then repeat the humcancelling procedure I referred to in my November 17th post and see if there is any difference in the hum as you adjust the trimmers. Make sure you are listening to one pickup at a time and adjusting the trimpot for that pickup.

mgauction · « **Reply #7 on:** November 29, 2005, 11:57:45 AM »

Hi Mica - My tech checked and found no reading whatsoever on the hum cancelling coil.

mica · « **Reply #8 on:** November 29, 2005, 04:15:26 PM »

Then it sounds that at a minimum the humcanceller needs replacing. Only one channel of the preamp card has been tested so far (unless you did the earphone test?).

You may or may not attempt to remove the humcanceller yourself. Usually, they are glued in place and a sharp blow with a mallet will crack the bond. If if doesn't, then you'll have to be more aggressive in removal.

You can screw a wood screw in the center and use pliers to coax the pickup out or in the very worst case you can route it away.

Since your bass is a 1974, it will be best to send us a tracing of the cavity for the HX pickup, since there was no standard at the time. To order, call us at 707 523 2611 and ask for Valentino.