Alembic Guitars Club
Alembic products => Owning an Alembic => Troubleshooting => Topic started by: LMiwa on December 27, 2025, 09:48:09 AM
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I recently acquired a set of jazz bass activator pickups with a VVT module. I believe this is referred to as a JZ/AE-1 set. I have installed it in a bass and it’s working great!
I have attached two photos of the electronics. I think it is a few years old based on the fact that it has two volumes instead of volume and pan, and also because it has a RC4458(?) chip on the filter board.
Questions:
Is the small pot on the filter board for output level adjustment?
Is there a way to adjust the filter Q - resistor value changes, for example?
Are there any upgrades that should be performed?
Anything else I should be aware of?
Thanks in advance for your assistance.
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The trimpot is for output indeed, you could add a Q-switch: https://store.turbify.net/alembic/qforac.html
Not sure if I read it right, but based on the stamps I think the set is from 1988?
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That add-on Q switch looks like an RC resonance circuit. I’m not looking for on-the-fly resonance control. I’m more interested in being able to tailor the Q for my specific bass/strings. So knowing which resistor and capacitor control the Q might allow me to experiment with different values. And even better, if there was a listing of recommended R/C pairs that produced various Q values, that would be amazing!
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The Activator sets with a filter but without a Q switch have an always-on boost of 8 dB for a narrow frequency band around the cut-off frequency. Adding a Q switch actually gives you the option to not have that boost (leaving just the "natural" resonance of the LPF).
There are a couple of variations of the Q switch, like 2 or 3 positions and various levels of Q boost, but you'd need to confirm what is available for this particular set-up. I had a Spoiler with a 3 position Q switch for 0, 3 and 6 dB, and to my ears a 3 dB difference was fairly subtle, and a 6 dB difference pretty noticeable - but I felt both were an improvement over the original 8 dB, which I felt sounded a bit harsh.
Another update would be the Pan Preamp, which gives you a separate level for each pickup, making it easier to balance their outputs. I think it does replace the two volumes with a volume and a blend.
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Having had the variable Q on a Series II, I liked the ability to select the Q values, but then once I had it adjusted to where I wanted it (different for each pickup), I never changed the Q, though I did change the filter cutoff frequency. Having had a bass with Signature electronics, I found that I favoured the 3dB setting.
With the Activators, I'm finding the Q to be higher than I'd like. If it is just a matter of swapping resistors/capacitors, I'd be up for trying various values until I found my sweet spot and then having the new value permanently.
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Not entirely sure what you mean by "the filter amount"? But anyway, on a Signature with a 2 position Q switch the setttings are likely to have been 0 and 8 dB, on a 3 position I think they would normally be 0, 6 and 9 - unless you had customized electronics.
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Are there one or two components on the filter board that can be changed to reduce the Q?
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And one more thing…
When both pickup volumes are on full the bass is silent. But when both (not just one) volumes are off, there is a good bit of noise.
Are the volumes “pre-filter” and is the noise being picked up in the filter circuit?
Do I have some other fault in the wiring/circuit?
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Just a long-shot thought, something that happened to me once... verify the pickups are connected in-phase correctly. I don't have any experience with the two-volume harness, but with a set of TC-1 activators I accidentally mounted the modular connector to the the bridge pickup backward. This put that pickup out of phase. The result was similar to what you describe.
At one point, I was receiving a Cuban radio station. I kinda' miss that...
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I tried swapping one pickup and got the “out of phase” cancellation with both pickups on full, so I think they are correct.
I may have to look at the control cavity shielding next…