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Post by pablogilberto on Oct 11, 2021 6:47:40 GMT -5
Gello
I'm interested in learning more about active guitar wiring circuitry like the on-board preamp usually found in bass guitars.
I have basic understanding of electronics.
I have few questions.
#1 Do you know references like books / videos / tutorials that I can read about this subject?
#2 Is there a page/site where I can get schematics and try to build and experiment.
#3 Any tips are welcome
Thank you!
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Post by newey on Oct 11, 2021 8:01:47 GMT -5
#1 Do you know references like books / videos / tutorials that I can read about this subject? Not specifically for that. I'm sure there are general resources on amplification, which presumably would include preamps, but I'm not aware of anything specific to onboard guitar preamps. Many pedals have a preamp powered by a 9V battery which would be pretty similar to one inside the guitar, and there are many websites where pedals are discussed and schematics provided. Yes, right here. Our own JohnH has written at length about making a buffer circuit from JFETs here A buffer circuit is essentially a preamp with zero gain, and one can fairly easily add differing amounts of gain to such circuits, and JohnH links to some of those. One of those is the "Fetzer Valve" circuit, linked to therein. Of course, there is no free lunch here; adding more gain introduces distortion at some point, and one ends up with something more like an overdrive or distortion circuit. See above. Another simple one is the classic Electro-Harmonix LPB-1 (for "Linear Power Booster"). There are schematics for this around the web. While it is an external preamp, it can (and has) been built into guitars, using some type of switching to switch it in/out, and using a stereo jack to disconnect the battery when no cable is inserted (just as with most pedals). |
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Post by JohnH on Oct 11, 2021 15:38:28 GMT -5
Newey linked to where I was playing with inbuilt buffers using jfets. Page 1 of that thread has most of the info.
jfets are ideal for a very simple circuit driven from a guitar since you can get high input impedance, reasonably low output impedance, low noise and very low current draw. You'll see two basic configurations, either as a x1 buffer (source follower), or with gain (common source). Both can give you an output that will drive long guitar cords without changing tone, and if so designed, drive a line input on a mixer if you want, instead of just a hi-Z amp input.
I found that the best jfet that I tried for use in these guitar circuits with 9V supply was a 2n5457, though others can work ok particularly for the x1 circuits. But they are inconsistent within a batch, so best to pick the resistor values to suit the individual part, to get best response ie about 5V dc at the source in the x1 circuit, or at the drain in the gain circuit.
I think discreet jfets are getting rarer though.
For the gain circuits (by which I mean it in the pure sense that it increases volume, rather than necessarily adding distortion), it's best not to go for too high a gain, maybe x2 or x3 so it stays as a clean boost. These circuits can also make a great distortion/drive though too, for which it probably needs a couple of stages and is best put in a stompbox for ease of operation and also to avoid feedback of high gain signals into the sensitive guitar input wiring.
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Post by Jaga on Oct 12, 2021 17:53:03 GMT -5
I'm researching the same thing currently. Actually I would like to develop some solution for Jaguar basses. Hence, I'm interested only in 2-band preamp designs  I found the following interesting articles:
Baxandall tone control, the site has a lot of very useful information (previous project is based on this circuit)
BTW, I really like when Bass/Treble pots have center detent feature.
Hope this helps.
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