So a I just built my first bass. It is heavily inspired by the Rickenbacker 4003 bass. But it has a hotter than average Seymour Duncan Jazz Bass pickup and a Bartolini Rickenbacker neck replacement pickup. I have a blend and balance pot instead of a three way toggle. I know that I am gonna have to fix something because sometimes I get shrill screech and/or a total loss of sound for a second. But my main concern is that the passive channel has a LOT more hum than the active preamp I installed in the bass. I have a toggle switch to change between just using passive master tone and master volume controls to using the active tone preamp which is stacked. The active tone preamp can cut and boost high and low frequencies. When I have active on, it is almost completely silent. Switch to passive and the hum is very present. it’s like night and day. I also noticed that the passive tone pot also still influences the active tone but not visa versa. I don’t really mind that, but I do wonder if it indicates a problem. One more thing is that the passive tone pot also completely kills the signal like a volume pot when turned all the way down, which is strange. It didn’t do that before, but I had to rewire a few things to get rid of phase cancellation. I don’t know why the tone does that now. I am not as concerned with that quirk. I just want to fix the weird loss of signal at random times and I want to reduce the hum to nothing if possible. The passive tone definitely gets noisier when i turn it up. Active gets a little more hum when I boost the highs. But it is still not nearly as loud as passive. I hope someone can help me. Thanks.
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Passive tone pot is much noisier than active preamp.
- Thread starter Leroyatleroys
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- hum canceling wiring
I kind of winged it from three different ones. I mainly used a Bourns blend and balance pot schematic to wire the pickups. Then the preamp directions. Then the toggle for passive/active I worked in between connecting the preamp to the pickups. I will dig and post what I can find. It really is my first time tryin this ever. I kind of didn’t originally plan to add the preamp.
Usually squealing and instability is due to improper loading of high impedance inputs, or open feedback loops creating a very high gain situation.
So these are the schematics I used. I will note that the active/passive switch diagram has a box that says “pickup switch”, when in reality he meant “pickup”. But you basically link that in between where the preamp would connect to the pickup output. I regret not drawing a big schematic of my own, but the connections seem to work for the most part. Just a seeming grounding issue and occasional loss of signal for a second(also kind of depends on whether I move it a certain way.)
Attachments
I will also note that the way I have them wired reflects more of a Jazz Bass configuration than a Rickenbacker 4003 config.
The pots that came with the kit I used are 500k. Should I use 250k pots instead or should I change the way I grounded everything?
When does it squeal? Does it do it if the passive volume control is turned all the way down, or half way open? Instability can also be caused by not enough capacitance, or a total lack of a power supply bypass cap; 9 volt batteries have a fairly high internal resistance so in most instances this cap is necessary.
It doesn’t really squeal anymore. But the signal still occasionally cuts off. The squealing is kind of rare, but it is something to note. I find it odd that the active aspect is the part that generally works well. I could actually play gigs and record with the preamp on. But I really don’t like to rely only on active, even with a premium retail guitar. Though I just remembered that sometimes the active still gets brief noise.
It sounds like you may have some issues with the switches, the pickup selector and /or the bypass switch. The bypass switch contacts should be a type specifically for low level audio signals. Anything else will tend to cause issues due to oxide build up.
This migh
the blend pot seems to be working fine. I did have a phase issue but I fixed that by switching the active and ground on the neck pickup(Jazz Bass pickup.). But if the active/passive switch is not adequate, why does it seem to sound fine when on active? Will post more pics later.
Phase issue? You reversed the pickup wires? Is one of the leads connected to internal shielding on the pickup? If so, this is most likely the source of your hum. Why did you think it was out of phase?
