Can anyone verify this onboard preamp?

[scottyd]

Thank you, thats good to know. Which one would be best suited for a fairly strong bass pickup signal? Sorry for all the silly questions but heres what Im trying to get done., I have been building bass guitars for a few years. Ive recently started building my own pickups as well. Getting into the vodoo of pickup buiding I found out that the only difference between active pickups and passive pickups are these fairly simple ciruits. SOOO Ive been trying to build the circuits myself and its been a learning process, especially since Im somewhat new to electronics other than wiring pots and such. So keeping that in mind any help you guys have would be very much appreciated.

[Nigel Goodwin]

Originally posted by teemuk
[B]

Actually in the concerned application it would. Magnetic guitar pickups benefit from very large input impedances - even more so do piezoelectric pickups. Rather replace that 1 Meg resistor with 10 megaohm one.

It was 3.3 meg anyway, and I seriously doubt there would be any audible or measurable improvement in either removing it or replacing it with 10 meg!. Except it's going to pickup more noise and hum!.

[teemuk]

I stand corrected, and actually it was 3 Megaohms. However, with magnetic pickups there can be easily even 6 dB of difference in resonance peak levels between having an input impedance of 3.3Meg and 10Meg. This depends on the pickup of course. If the pickup is already damped by the resistance of tone controls and volume potentiometer then this doesn't make much difference but then again, we were discussing about connecting straight to pickup and thus retaining its natural resonance. For piezoelectric pickups the 10Meg is practically the minimum input impedance one can use.

[Nigel Goodwin]

Originally posted by teemuk
For piezoelectric pickups the 10Meg is practically the minimum input impedance one can use.

But we weren't talking piezoelectric pickups, we were talking proper guitar pickups, and even 1Meg is plenty high enough not to load a guitar pickup.

I agree that a piezo pickup (essentially a crystal microphone) would possibly benefit from 10Meg?, although you would need to check the manufacturers recommendations - and you couldn't remove the resistor in that case.

[teemuk]

Originally posted by Nigel Goodwin
But we weren't talking piezoelectric pickups, we were talking proper guitar pickups, and even 1Meg is plenty high enough not to load a guitar pickup.

Guess we just have to agree to disagree on this. I know that approximately 1Meg is a quite typical value for amplifier input impedance and high enough not to load the circuitry of a typical guitar too detrimentally. Still, I don't have to agree that this is the best arrangement.

In practice, a lot of the pickup output is already damped by the passive circuitry inside the guitar. (This is the reason for "treble bleeders" and such mods). In cases when amp is directly connected to pickup Tillman suggest removing the input resistor completely; this will create a very high input impedance. Is it better? That is a matter of taste. What I'm saying is that a low input impedance will damp the resonance peak and this is what 1Meg or even 3Meg will do in comparison to higher input impedances.

If one wants to damp resonance peaks then fine, who am I to argue, but suggesting to leave that 3Meg resistor in will do this so at least give the guy a chance to try both configurations instead of telling him that leaving it out would not give any benefits. You should know that most of the people starting these "newbie threads" will blindly believe everything that is told to them.

Edit: And you are right, this does not work with piezoelectric pickups since they are highly capacitive by nature. Piezos commonly have a very high output impedance so a high input impedance amp stage to follow them is a must. Of course, if manufacturer wants to recommend a certain value for Zin it is worth checking out.

[DrFrankenstein]

Originally posted by teemuk


Guess we just have to agree to disagree on this. I know that approximately 1Meg is a quite typical value for amplifier input impedance and high enough not to load the circuitry of a typical guitar too detrimentally. Still, I don't have to agree that this is the best arrangement.

In practice, a lot of the pickup output is already damped by the passive circuitry inside the guitar. (This is the reason for "treble bleeders" and such mods). In cases when amp is directly connected to pickup Tillman suggest removing the input resistor completely; this will create a very high input impedance. Is it better? That is a matter of taste. What I'm saying is that a low input impedance will damp the resonance peak and this is what 1Meg or even 3Meg will do in comparison to higher input impedances.

If one wants to damp resonance peaks then fine, who am I to argue, but suggesting to leave that 3Meg resistor in will do this so at least give the guy a chance to try both configurations instead of telling him that leaving it out would not give any benefits. You should know that most of the people starting these "newbie threads" will blindly believe everything that is told to them.

Edit: And you are right, this does not work with piezoelectric pickups since they are highly capacitive by nature. Piezos commonly have a very high output impedance so a high input impedance amp stage to follow them is a must. Of course, if manufacturer wants to recommend a certain value for Zin it is worth checking out.

I'm with teemuk here, ditch the input buffer cap and raise the input impedance so you're not hacking off your signal peaks. Once you drive the tone circuit with a preamp, you're really going to experience a sonic loss. Noise shouldn't be a problem if you drive the circuit with a well designed pre and your pickups aren't prone to noise...god forbid you're using nothing but single coils. I've got all my rigs so finely tuned that I have absolutely no noise, no noise gates and enough gain to burn a hole in the ozone.
Even with single coils there's nothing...granted I don't have the TV or monitor on...maybe I should have went with an LCD, I heard they don't cause pickup hum.

Every application I've ditched the input buffer cap on and increased the input impedance has dramatically increased the circuits performance and sound quality. I've seen this 3 tone circuit at least a half dozen times and everyone has one mod or another for it.

Personally, I say leave the tone shaping to your amps preamp or a pedal...though I don't care for pedals much as it is. You should have a good enough sound from your guitar that you don't want to mess with perfection. A built in preamp is always nice but I'll pass on the EQ controls. I say go with a transistor or even op amp driven preamp with a lot of clean gain once you have the pickups you're looking for.
I've gone this route and in my opinion, the EQ controls on a guitar don't do as much as you'd like. They'll seriously alter your tone but mostly you'll just want the slightest of tweaks from them. You might as well use trim caps that you can just set and never touch if you're really heart set on adding an EQ to your guitar.

The best route to go is a single tone control with an active midrange boost and cut, that's the only control I ever really used when I had my active guitar EQ. Boost the midrange for jazz, sometimes blues, sometimes metal or use it to scoop out all the mids for that rhythm metal tone, that old school glass blues tone and so forth. This is what Clapton uses but I think his only boosts midrange. You'll definitely want something that both boosts or scoops out the midrange.
Just my 2 cents but far more useable than the 3 band EQ. You start cranking the bass and treble with any serious amount of gain and it sounds like crap. Hence the reason I said trim caps that you can slightly tweak if you're still heart set on the 3 band. I'd only build one if a customer requested and I still know that the midrange boost/cut would make them happier 90% of the time.

That discrete FET preamp kinda sucks by the way...or at least with the way it's configuration is on that site I've built a few different versions on it and the only thing it did worth mentioning was eliminate noise. As far as dB gain though, it's useless unless you mod it for a lot more gain.
The one other good thing I can say is, it didn't seem to alter your guitars natural sonics.

[Brion55]

I've built this one several times. It gives you the option to change the center freq of the "mid" eq which can be very useful.

[Minion]

Originally posted by turbolx5oh
Check this web site out: http://www.till.com/articles/GuitarPreamp/

That is also not a proper Preamp, It has less than Unity Gain output so will not work verry well as a Preamp but it does add a bit of bite to your guitar sound.....

I suggest maybe going over to Diystompboxes.com and look for a good pedal curcuit with a tone controll and use that as a Preamp....

[Nigel Goodwin]

Originally posted by Minion


That is also not a proper Preamp, It has less than Unity Gain output so will not work verry well as a Preamp but it does add a bit of bite to your guitar sound.....

Don't know how you came to that conclusion?,as drawn it has a gain of about three times!.

[Minion]

No, it has a Gain of 3db not 3x, which isn"t much at all but in Practice it usually doesn"t add any Noticeable gain I have built this circuit many times and sometimes it actually reduces the output signal depending on the Fet.....

This fet booster works quite well and can add quite a lot of Gain with a Tube like overdrive sound at higher Gains and uses a Slightly more complex but more stable Biasing based on a Mosfet biasing arrangement.....


Cheers