Author Topic: 1979 Series I noise (Read 1623 times)

FC Bass · « **on:** May 01, 2015, 07:53:53 AM »

Very happy with my Series I bass, but it is a bit noisy.
There?s the directional hum (when you come near an amp, I didn?t record that) and some high frequency noise (fi you can hear my wireless mouse on the recordings)

You can download the recorded the noise (.wav file) here: Click here, 23 mb download

Noise with all gain down: 00:04

Noise with pickup gain at 50%

Bridge pickup: 00:16
Neck pickup: 00:28
Both: 00:40

Cycling through humcancelling procedure from 0 to 100% and back, then looking for the quietest position (0% on bridge pickup)

Bridge pickup: 00:52
Neck pickup: 01:16

Spoiler noise for comparison: 01:56

I think there?s something wrong in the bridge pickup circuit, the pickup has been replaced somewhere in the past.
The humcancelling procedure doesn?t sound the same as on the neck pickup, the hum doesn?t pass through a null; it just gets quieter when turned to zero. (most counter clockwise position)

I can?t change the pickup connections on the preamp board for easy troubleshooting, because the new bridge pickup wire is soldered direct to the board (no connector)

On the ? input it looks there?s a cut black wire, pointed out by the green arrow.

Pics:

(click pictures for full size version)

FC Bass · « **Reply #1 on:** May 01, 2015, 08:39:16 AM »

Did some more detective work.

Looks like all the wires that should connect to the 1/4 output are there.

It looks like the bridge pickup is wired wrong:

pierreyves · « **Reply #2 on:** May 01, 2015, 10:34:22 AM »

Flip, for what are you waiting for ? HERE ?

FC Bass · « **Reply #3 on:** May 01, 2015, 10:49:35 AM »

Can you fix it for me? :-)

I changed the pickup wire and the hum cancelling procedure works the same now as on the neck pickup. (with the same results as you can hear on the neck pickup)

Counterclockwise there's high frequency stuff going on, clockwise there's the low pitched hum.

terryc · « **Reply #4 on:** May 01, 2015, 12:28:32 PM »

Would it not be a better choice to let Ron Wickersham work his magic on it, in the long term it would be worth it!

sonicus · « **Reply #5 on:** May 01, 2015, 12:50:41 PM »

Perhaps it might be prudent to insure the power source is clean as well and therefore a look at or replacement of the filter capacitors in the power supply . Just thinking ___ .

FC Bass · « **Reply #6 on:** May 01, 2015, 05:30:54 PM »

fwiw: Noise is the same through the 1/4 jack powered with batteries... (though it's wired stereo, so I can only check the neck pickup)

mica · « **Reply #7 on:** May 01, 2015, 08:20:49 PM »

Have you made any changes since you made the recording?

FC Bass · « **Reply #8 on:** May 01, 2015, 08:25:25 PM »

Only soldered the bridge pickup correctly (I think, reverse of the above picture)

mica · « **Reply #9 on:** May 01, 2015, 08:57:05 PM »

So there was no change after resoldering?

FC Bass · « **Reply #10 on:** May 02, 2015, 06:20:55 AM »

Sounds like it got a bit better, this is with both gains at approx. 50 % and all controls open/max Q.
Bridge pickup, both and neck pickup: 6 mb Wav download

(Message edited by fc_spoiler on May 02, 2015)

FC Bass · « **Reply #11 on:** May 02, 2015, 06:33:13 AM »

.... and the hum cancelling procedure now works as it should on the bridge pickup.
Though there is no real quiet position, there is a quieter position somewhere in the middle but the noise from the most counterclockwise and most clockwise position are overlapping. (same on both pickups as you can hear in the first recording of the procedure on the neck pickup)

FC Bass · « **Reply #12 on:** May 02, 2015, 10:08:58 AM »

The high frequency noise (the beeps) is coming from my laptop, if I turn the bass towards the laptop it gets louder.

JimmyJ · « **Reply #13 on:** May 02, 2015, 03:16:40 PM »

Hey Flip,

You've definitely solved the MAJOR problem of the bridge pickup being wired backwards. The way it was caused the noise reduction circuitry to act as a noise PRODUCTION circuit and simply add more noise as you turned up the trimpot.

Listening to your latest wav file, I think you are now within spec - for a '79 without Ron's latest mods.

We benefit from these big open-sounding single-coil pickups which hear not only the string moving in the magnetic field but also any broadcast hum or noise within feet, or the neighbor's copy machine, or the radio station down the block... Thats the nature of amplifying the output of a coil of wire.

Humbucking pickups usually try to fix this by putting a 2nd coil either next to or under the pickup coil and wiring the two out of phase to each other. But my understanding is, when the 2nd coil is within the pickup's magnetic field it will inevitably hear the string and do something unmusical to the tone.

Alembic's very clever solution was to move the hum canceling coil away from the pickup - and also for both pickups to share it. The downside is, since it's physically an inch or two away it hears noise and hum in a slightly different time and thus can't cancel it out 100%.

Having played Series basses since the mid-70's, I was well aware of the need to find the quiet spot. Though sometimes a nuisance (and man, even some studios were impossible) I found it worth dealing with because of the great tone.

Now Ron has found additional magical individual tweaks which can considerably lower the noise floor on these instruments. This has almost eliminated the issue for me but there are still some instances when I need find the quiet direction and keep the neck pointing that way.

Remember that if you crank up the Q you are adding a large boost to the high frequencies which will also include a lot of the inherent noise.

That's a fine looking bass with its original flat-pack circuit board and it sounds nice in your samples. Enjoy it and play the heck out of it immediately!

Jimmy J

(Message edited by jimmyj on May 02, 2015)

FC Bass · « **Reply #14 on:** May 03, 2015, 06:09:59 AM »

Thanx Jimmy!

I'm a bit spoiled with the ultra quiet activator equipped basses, tone of the Series can't be beat though. :-)
I think you're right about being within spec, if I turn away from the laptop I can get it almost 100% quiet :-)
(on the recordings the distance between laptop and bass is about 3 feet)

I also found this: http://club.alembic.com/Images/394/44491.html
I'm going to get a couple of resistors next week (for the mono 1/4 mod) so I might as well give this a try.

Mica: The 15Kohm resistor must be placed between the shield and signal cable of each pickup?
And is there a way to test the matching of the pickups myself?

Might also be an option to order a complete new pickup set (incl dhc would be best I think?) but I first need to recover financially from this purchase...