The through hole version was posted by Nordic and not by me. Instead of using trim pots I suggest to use a volume pot with a switch - you will be able to turn off the preamp if you need it. Also there is no room on the board for trim pots. You would need to design a new board. In my opinion the preamp will work very well without any changes with any Fender-type bass guitar. You may only consider decreasing high frequencies boost (two components have to be changed).
Mark
Mark
@funkytek:
You can get a 250k (or other value) audio taper pot with a DPDT pull switch from Small Bear electronics (smallbearelec.com). That's what I used and it works great! (see the photo a page or so back) I used the pot as the treble control of the tone stack. The bass is set. I thought it might be handy to go "stock" on a few occasions but I find myself switching back and forth far more often than I expected. It's great to have such versatility.
Ken
You can get a 250k (or other value) audio taper pot with a DPDT pull switch from Small Bear electronics (smallbearelec.com). That's what I used and it works great! (see the photo a page or so back) I used the pot as the treble control of the tone stack. The bass is set. I thought it might be handy to go "stock" on a few occasions but I find myself switching back and forth far more often than I expected. It's great to have such versatility.
Ken
I do like the idea of a bypass switch. I won't have access to the bass until next week (I leave it at our rehearsal space). I am wondering if I have room for 2 stacked pots and a micro toggle. Then I could have one pot set be volume and balance. The second would be bass and treble. I don't need a midrange control at the bass. I can do that with my fingers. The toggle would be the bypass.
If that will all fit, with the board and battery, then I will be a happy camper.
If that will all fit, with the board and battery, then I will be a happy camper.
Jfet preamp guitar amp demo
LOOk at this, i think you can get a nice result:
Good luck
http://www.youtube.com/watch?v=KVB0ukhl-rY
LOOk at this, i think you can get a nice result:
Good luck
http://www.youtube.com/watch?v=KVB0ukhl-rY
Mr. Hugsley:
I've read with much interest your preamp schematics. I have elementary needs. I need only to buffer my dual-humbucker bass to avoid resistive and capacitive loading. Mr. Tillman suggests that one could use his J201 preamp after the volume and tone controls (all intact...just inline with the output jack). Wouldn't having the 500K volume control on each individual pickup still load them, so that highs would be diminished? Would it not be better for me to use a preamp on each pickup? Therein lies my dilemna. I want to combine (or mix) the pickups, preferrably with individual volume controls. However, the Tillman circuit is not suited for this. Should I use your circuit with the low noise 2N5087 transistor to provide a low Z output and then maybe use a 10K resistor from each preamp leading to a 10K volume control, then combine the wipers to the output jack? I do not care about onboard bass and treble controls at this point. I'd rather disconnect the tone pot altogether. Thanks so much. Your posts are very enlightening and very much appreciated.
I've read with much interest your preamp schematics. I have elementary needs. I need only to buffer my dual-humbucker bass to avoid resistive and capacitive loading. Mr. Tillman suggests that one could use his J201 preamp after the volume and tone controls (all intact...just inline with the output jack). Wouldn't having the 500K volume control on each individual pickup still load them, so that highs would be diminished? Would it not be better for me to use a preamp on each pickup? Therein lies my dilemna. I want to combine (or mix) the pickups, preferrably with individual volume controls. However, the Tillman circuit is not suited for this. Should I use your circuit with the low noise 2N5087 transistor to provide a low Z output and then maybe use a 10K resistor from each preamp leading to a 10K volume control, then combine the wipers to the output jack? I do not care about onboard bass and treble controls at this point. I'd rather disconnect the tone pot altogether. Thanks so much. Your posts are very enlightening and very much appreciated.
I've tried the Tillman preamp on bass, but I didn't like it too much. In my opinion a opamp preamp works better. Alternatively, I am working on a discrete preamp for my bass.
The loading of 500k pots is minimal so you shouldn't worry about that, in a passive bass the cable provides a roll-off point much lower than the pots will!
A very simple non-inverting opamp stage works fine, even better if you use a nice opamp, I like OPA2134 myself. In my precision bass I used one of those, one half is the preamp, the other half of the dual opamp provides a precision bias voltage.
The loading of 500k pots is minimal so you shouldn't worry about that, in a passive bass the cable provides a roll-off point much lower than the pots will!
A very simple non-inverting opamp stage works fine, even better if you use a nice opamp, I like OPA2134 myself. In my precision bass I used one of those, one half is the preamp, the other half of the dual opamp provides a precision bias voltage.
Thanks, Jarno. I was checking out a schematic using a Burr-Brown OP134A. I have to brush up on the latest opamps. Like the high-Z input, very low-Z out, which lends itself to a mixing of the two pickups easier. I also like the adjustment of the feedback resistor for gain. Makes it easier to tailor the level for single coil or humbuckers. I am not sure of the overload voltage for the Jfet input of that opamp, but I'm sure a voltage divider would take care of that. There's plenty of 'make-up' gain in that opamp. I am confused as to what kind of discreet preamp you're thinking about, since you like the opamp so well. My opinion is that a discreet FET (J201) is more suitable with a guitar than a bass. I don't necessarily want a 'thick tube' sound. If I don't overload the input, I'll settle for the tight, clean output and let my amp take care of the rest.
input range of an op amp is usually to within 0.7V of the rails. the input level at which the op amp clips depends on the gain. so for an op amp with a gain of 5, and rails of +/- 9V, the input level to clip the op amp would be about +/-1.8V (about 1.3Vrms). for a buffer (gain of 1), your input range before clipping would be +/-8.3V (5.86Vrms). so within the normal levels you will get out of pickups (and even "hot" pickups) you really don't need to worry about overloading the inputs of an op amp, even a jfet input one. just don't drive the inputs differentially, as many op amps CAN get overloaded inputs from too high a differential input voltage (the limits on most are between +/- 0.7 to +/- 1.5V) standard op amp circuits (unity gain buffer, noninverting gain amp, inverting gain amp) all have differential voltages very close to zero, so you don't have to worry about it. op amps are very different than single ended transistor preamps, and can handle a lot higher signal levels without overloading the inputs, while single ended transistor preamp limitations are the forward and reverse bias limits of the input element (gate on a JFET, base on a BJT. these limits can be relaxed (to a point) with emitter or source degeneration resistors, but the op amp is definitely a better choice.
Pickup buffers
Hello SharynMac58,
The funny thing about guitar pickups is that they don't exist in a vacuum. The series resistance, parasitic capacitance and series inductance of a pick-up play a major role in determining the overall "tone" of your guitar. However, the volume/tone control pot resistance (although minimally with 500k Ohm pots), the guitar-amp input impedance (again, minimally at 1.0 MegOhm input resistance) and the guitar cable capacitance (usually around 33pF/ft) effect the tone as well.
You're correct about the resistance loading cutting down on your "high" frequencies but, with the inherent series resistance of a hum-bucking pickup being around 9kOhm to 18kOhm, the pot and guitar amp loading effects will be minimal. However, it's the resonant effect of the guitar pickup inductance and guitar chord capacitance that can't (and shouldn't) be ignored. This resonance can actually enhance the tone of your pickup if crafted correctly.
You can experiment with a quality, low-noise, hi-Z input, low power-drain opamp to buffer you pickups as suggested by others, but you should try out different values of loading capacitance (say, between 100pF and 470pF) in parrallel with a 1.0MegOhm resistor shunted across the inputs of your opamps. I believe you'll find that, in this way, you will have very good control of your humbucker tonal characteristics.
Please remember that these are only suggestions, your "ultimate" tone is what sounds best to you and finding that tone may take many iterations of experimentation. That's the fun part!
JP Hugsley
Hello SharynMac58,
The funny thing about guitar pickups is that they don't exist in a vacuum. The series resistance, parasitic capacitance and series inductance of a pick-up play a major role in determining the overall "tone" of your guitar. However, the volume/tone control pot resistance (although minimally with 500k Ohm pots), the guitar-amp input impedance (again, minimally at 1.0 MegOhm input resistance) and the guitar cable capacitance (usually around 33pF/ft) effect the tone as well.
You're correct about the resistance loading cutting down on your "high" frequencies but, with the inherent series resistance of a hum-bucking pickup being around 9kOhm to 18kOhm, the pot and guitar amp loading effects will be minimal. However, it's the resonant effect of the guitar pickup inductance and guitar chord capacitance that can't (and shouldn't) be ignored. This resonance can actually enhance the tone of your pickup if crafted correctly.
You can experiment with a quality, low-noise, hi-Z input, low power-drain opamp to buffer you pickups as suggested by others, but you should try out different values of loading capacitance (say, between 100pF and 470pF) in parrallel with a 1.0MegOhm resistor shunted across the inputs of your opamps. I believe you'll find that, in this way, you will have very good control of your humbucker tonal characteristics.
Please remember that these are only suggestions, your "ultimate" tone is what sounds best to you and finding that tone may take many iterations of experimentation. That's the fun part!
JP Hugsley
It is hard to get these JFET in my country . Is it possible for BS170 or 2SK117?
next time i get a chance to build an onboard preamp, i have a couple of ideas i'm going to try, one of them being a variable cap to load the pickup with...
And a resistor, that works too. I have both a resistor and a cap in my precision bass, with a DPDT center off switch.
Center is standard P-bass, down is the resistor a woollier sound with less treble, up is the cap which adds high end snap to the standard P-bass sound, I use it if I have to slap or for a more modern sound.
Center is standard P-bass, down is the resistor a woollier sound with less treble, up is the cap which adds high end snap to the standard P-bass sound, I use it if I have to slap or for a more modern sound.
New JFET Guitar Preamp Project
Hello Opor,
The BS170 is an Enhancement mode mosfet so the JFET circuit designs and methods described in this post will not apply without major bias changes. The 2SK117, however, is a JFET and may work very well as a project/experimental device.
It seems that the main issue you may have with the 2SK117 would be in a battery-powered, portable application. If you qualify and bias the 2SK117 as described in this post, you will end up with a relatively high DC bias current (depending on the device, possibly as high as 5.0mA) and suffer from low battery-life as compared to a J201 (possibly 1/10 the battery-life of a J201). If that doesn’t matter for your application, then the 2SK117 looks like a very good device for audio.
Please let me know how it works out for you.
JP Hugsley
Hello Opor,
The BS170 is an Enhancement mode mosfet so the JFET circuit designs and methods described in this post will not apply without major bias changes. The 2SK117, however, is a JFET and may work very well as a project/experimental device.
It seems that the main issue you may have with the 2SK117 would be in a battery-powered, portable application. If you qualify and bias the 2SK117 as described in this post, you will end up with a relatively high DC bias current (depending on the device, possibly as high as 5.0mA) and suffer from low battery-life as compared to a J201 (possibly 1/10 the battery-life of a J201). If that doesn’t matter for your application, then the 2SK117 looks like a very good device for audio.
Please let me know how it works out for you.
JP Hugsley
Hi. I'm reading all that incredible thread and i'm trying to understand some theory about preamps/buffers/eq... I have a guitar with an undersaddle piezo pickup. If i connect it direct to my guitar amp it's sound well and loud. I want to add a basic baxandall eq to the guitar. Can i use this pre and the emitter follower with the EQ in middle or will be a notiseable loss in volume and gain?
Is a preamp/eq/follower what i need or i'm going in the wrong direction?
I hope you understand my question because my english is too bad.
Thanks a lot.
Is a preamp/eq/follower what i need or i'm going in the wrong direction?
I hope you understand my question because my english is too bad.
Thanks a lot.
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