Sorry but I still don't understand the big problem with JFETs. The circuits I initially posted look much simpler and work with a regular 9V battery.
What advantages do opamps really give me?
Not to be annoying but I like the appeal of discrete transistors and also it is a circuit I already built so I know I can make it work.
Also I don't care for the higher frequencies (regarding loading losses) as long as the bass and mids are all still there.
What advantages do opamps really give me?
Not to be annoying but I like the appeal of discrete transistors and also it is a circuit I already built so I know I can make it work.
Also I don't care for the higher frequencies (regarding loading losses) as long as the bass and mids are all still there.
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The interactions are complex and depend on the output impedance of the four voltage sources to be mixed and the content and phase relationships of the signals to be mixed. By 'output impedance' we mean how close to a perfect voltage source the four voltage sources are. If the impedance is low then the output of each FET stage is unaffected by loading. If it is relatively 'high' then the output of each FET is changed by the loading,
The loading each FET sees is changed by the output of all others changing in response to the signal. That change feeds back through the passive mixing network and can 'modulates' or change the output of each voltage source in complex ways.
The opamp mixer removes that interaction because each FET drives a point that sees no voltage change in response to all the signals. There is no interaction.
The opamp is technically the better solution but passive mixing is often used.
I will use it in combination with Graphtech ghost saddles in my fretless bass.
I think I will take my chances with the FETs then. Output impedance of the buffer design was extremely low in my tests. Even a 3uF cap in parallel just barely produced an audible difference in the high frequency noise floor.
Would there be any benefit to lowering the input impedance of the master buffer circuit since it already receives a buffered signal?
No benefit. There is no noise penalty to the high impedance because the input impedance is shunted by the low output impedance of the stage driving it.
What does the master buffer circuit's schematic look like?
In general, for low thermal noise, any resistors in series with the signal path have to be small and any resistors in parallel with the signal path have to be large. How small or large, respectively, depends on the requirements and the impedance level.
In general, for low thermal noise, any resistors in series with the signal path have to be small and any resistors in parallel with the signal path have to be large. How small or large, respectively, depends on the requirements and the impedance level.
Just curious why don´t you use the Factory recommended setup:
https://cdn.shopify.com/s/files/1/2...quickswitch_fixed_2020_08_20.pdf?v=1597946137
Their Acoustiphonic board does exactly what you want to do:
https://cdn.shopify.com/s/files/1/2...quickswitch_fixed_2020_08_20.pdf?v=1597946137
Their Acoustiphonic board does exactly what you want to do:
What kind of resistance should the intermediate trim pots have then?
I will probably use the third layout on the first page for the master buffer.
If the input buffers were ideal buffers, the lower the potmeter resistance, the less noise you would get from them. However, as the buffers are not ideal, you also don't want them to load the input buffers too heavily, as that would reduce the buffer output signal level and signal handling and aggravate distortion.
I guess something of the order of 10 kohm would be a reasonable compromise, with 4.7 kohm mixing resistors. It is only a guess, though.
I guess something of the order of 10 kohm would be a reasonable compromise, with 4.7 kohm mixing resistors. It is only a guess, though.
Ok, so just the usual range of pots you find in active basses.
Is there any connection between the optimal value of the trimpots and the "input resistor" that sets the impedance of the master buffer?
Is there any connection between the optimal value of the trimpots and the "input resistor" that sets the impedance of the master buffer?
I'll take your word for it, as I haven't a clue what is normally found in active basses.
It would be nice if the value of that input resistor were much greater than one quarter of the potmeter resistance plus the mixing resistance, which is met when you use 1 Mohm.
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I will use a pretty unsual wiring scheme (still working out the details) that isn't really compatible with standard piezo buffer designs.
For example, +9V will be fed into the instrument throgh an TRS cable and the blending with the magnetics is done passively, including phase reverse and series/parallel switches. Even if the 9V supply dies or there is no TRS cable avaiable, the bass will remain fully functional and you always get the vintage passive jazz bass mojo instead of modern trebly 'high definition' harshness.
I even explored completely passive piezo designs using transformers or permanent series wiring with magnetic pickups but sadly this doesn't seem to be feasible.
Lastly, I simply want to practice my soldering skills because I plan on making some more complex preamp replicas and effect pedals after this project.
That brings me to another question: Are there push pull pots designed for standard vero/perf board hole spacing?
Most pots employ this spacing for the regular solder lugs at the top and even the DPDT poles align horizontally but the middle poles are not aligned vertically.
My plan is to have the whole wiring inside the bass be done on two veroboards, one on each side of the pots. One board will have the buffer circuits, trimpots and caps for easily accessible finetuning and then on the other side, I will have the pots sitting at an right angle, directly mounted inside one long 'master board'.
I figure point to point will be unpractical given how complex the wiring will be.
Simple answer is you can't.
To make an individual discrete buffer inverting requires an additional stage or a total reconfiguration of the single FET but it then would not be a buffer.
Far better if you want phase inversion would be to use a single inverting stage at the output to invert everything. An opamp is the logical solution for that.
To make an individual discrete buffer inverting requires an additional stage or a total reconfiguration of the single FET but it then would not be a buffer.
Far better if you want phase inversion would be to use a single inverting stage at the output to invert everything. An opamp is the logical solution for that.