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ZON bass preamp
Posted: 08 Dec 2022, 16:54
by Yun_Suki
I don't remember which one...
But...however, I have made a copy that works fine.
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The progress of the reverse engineering will be updated again after a while...
Re: ZON bass preamp
Posted: 11 Dec 2022, 02:33
by darmstat
Is there a schematic?
Re: ZON bass preamp
Posted: 20 Dec 2022, 00:16
by george giblet
The preamp is the one with the Magnetic + Piezo pickups (ZP-3).
Any chance to get the cap values and pot values?
I've traced 99.9% of the schematic but there are very few caps values and no pot values.
Re: ZON bass preamp
Posted: 20 Dec 2022, 11:30
by Yun_Suki
This is the value of the component as well as the model number.
Re: ZON bass preamp
Posted: 20 Dec 2022, 11:35
by Yun_Suki
george giblet wrote: ↑20 Dec 2022, 00:16
The preamp is the one with the Magnetic + Piezo pickups (ZP-3).
Any chance to get the cap values and pot values?
I've traced 99.9% of the schematic but there are very few caps values and no pot values.
Hi，All potentiometers and trim potentiometers are 100KΩ
Re: ZON bass preamp [schematic]
Posted: 20 Dec 2022, 23:26
by george giblet
Thanks a lot for all that detailed information.
Awesome, stuff!
The schematic appears below. I've tried to match the part designators on the your PCB.
I've also added the EQ curves.
It is interesting how much the Mid switch frequency affects the bass control even though
the mid control is set flat.
The treble controls are not symmetric, there is more cut than boost.
The 100k's on the first stage of the magnetic preamp and the 470k/220k's on the
second stage are going to be adding a lot of noise. I suspect replacing
the second stage with a non-inverting amplifier like U3b would lower the noise.
The circuit and parts values are very similar to the National Semiconductors
applications notes and datasheets! (11k, 3k6, 100k pot)
Re: ZON bass preamp
Posted: 21 Dec 2022, 00:54
by george giblet
FYI, here's a pic of a 4-string (Zon Legacy Elite 4). You can see how the Piezo is wired.
Re: ZON bass preamp
Posted: 21 Dec 2022, 09:05
by Yun_Suki
george giblet wrote: ↑20 Dec 2022, 23:26
Thanks a lot for all that detailed information.
Awesome, stuff!
The schematic appears below. I've tried to match the part designators on the your PCB.
I've also added the EQ curves.
It is interesting how much the Mid switch frequency affects the bass control even though
the mid control is set flat.
The treble controls are not symmetric, there is more cut than boost.
The 100k's on the first stage of the magnetic preamp and the 470k/220k's on the
second stage are going to be adding a lot of noise. I suspect replacing
the second stage with a non-inverting amplifier like U3b would lower the noise.
The circuit and parts values are very similar to the National Semiconductors
applications notes and datasheets! (11k, 3k6, 100k pot)
zon ZP-3 V1.0.png
Wow, very detailed! Thank you for your contribution to the forum! (a Big Hug~)
Re: ZON bass preamp
Posted: 21 Dec 2022, 10:46
by george giblet
No problem. Thank you for all your efforts.
Re: ZON bass preamp
Posted: 21 Dec 2022, 10:50
by george giblet
I've managed to trace the ZP-2 as well.
Unfortunately this tracing doesn't have the accuracy of the ZP-3 schematic.
As far as I know, the ZP-x preamps are the polyfusion preamps and the ZB-x preamps
are the Bartolini preamps.
Re: ZON bass preamp
Posted: 21 Dec 2022, 11:23
by Yun_Suki
george giblet wrote: ↑21 Dec 2022, 10:50
I've managed to trace the ZP-2 as well.
Unfortunately this tracing doesn't have the accuracy of the ZP-3 schematic.
As far as I know, the ZP-x preamps are the polyfusion preamps and the ZB-x preamps
are the Bartolini preamps.
zon ZP-2 V1.0.png
pcb front - ZP-2 1997.jpg
pcb back - ZP-2 1997.jpg
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I've also got this board from a friend before.
But unfortunately, I lost it before I could collect the component values of the capacitor...
These are the photos that my friend provided me：
Re: ZON bass preamp
Posted: 22 Dec 2022, 03:15
by george giblet
Thanks for the new pics. They were very useful.
Since the one of the pots is removed I could confirmed the circuit around C5 and R7.
I also made a better guess of the circuit around U1a - still not confident it is correct.
Added better guesses for the tone control caps.
I updated the ZP-2 schematic in the previous post to version 1.1
Re: ZON bass preamp
Posted: 22 Dec 2022, 23:08
by george giblet
OK I've updated the ZP-2 schematic to V1.2
- fixed one error on U1a
- added more notes
- added trace info for older Rev A PCB
ZP-2 Rev A PCB (1995):
