Solid state guitar and bass amp preamp circuits

[Gus]

edit

[stm]

Gus, hope you changed your mind to delay the post until you are ready to.  I'm always interested in this subject.  Lately I've been studying old/vintage Fender amps (those with three-knob tonestacks, four 10" speakers and glassy semi-clean tones with a hint of compression and sustain).  I'm not necessarily thinking about using FETs.

Regards from Chile!

[tca]

I'm always interested in this subject.

+1

[samhay]

I came by this thread during the weekend and meant to check back.
In part, it pointed to a handy list of Vox schematics that I hadn't seen before: http://www.voxamps.com/support/circuits/
I'll leave the rest up to Gus (or not).

[tca]

I found these ones a few days ago: http://www.award-session.com/award-session_manuals.html

[stm]

If I may tell a story of my own here...

I had my first electric guitar at the age of 15, around 30 years ago.  It was a very basic guitar with a single coil in the bridge and a tone and vol pot.  No guitar amp, just the mic input to a three-in-one Sansui "hi-fi" that had tuner, a cassette player and a turntable in a convenient tabletop unit.  Output power was 5W per channel in a pair of single-speaker closed baffles.

At the same time, I was starting in the world of electronics--my father was an EE, so I had access to a protoboard, components, datasheets, an oscilloscope, and a tutor.  (I have to reckon I was a lucky bastard in these respects).  In addition, I got a set of photocopies of an old National Semiconductor book that contained several application circuits for audio: two-knob and three-knob active Baxandall tone circuits, an analysis on the passive James tonestack, an octave-band equalizer, a very basic fuzz circuit (that started it all for me), a tremolo, and a six-stage phaser that I never built due to the impossibility of getting hold of the AM97C11 quad JFETs it called for.

I had lots of fun playing around building effects for my guitar, but they always sounded dull and bass heavy.  At that time there was no Internet or guitar amp or pedal schematics around, so everything was new to me.  Anyway, one of the first experiments I did was to measure the output voltage of the different strings, and I noticed that the higher notes produced much less output than the lower notes.  I equalized this with a some hi-pass and treble boost filters, and the tone of my guitar improved a great deal, but I always thought that I was correcting something wrong on my guitar and hi-fi equipment, instead of believing that this was the way things were done in the realm of electric guitars.  Also, I didn't know a thing about high input impedance to retain high end in a guitar; my knowledge at that time was that 47k ohms was a "fine" line-input impedance.

Why I am telling all this?  Because if I had had access to the Vox AC-30 Top Boost preamp circuit by then, then things would have made much, much sense to me.  I would have known for a fact that a very high input impedance (1M ohm) was needed, and that this 500pF/500kohm hi-pass filter to cut low frequencies from 600 Hz downwards was something "normal" to have in a guitar preamp.  Also, I would have understood that having a set of tone controls that would easily let you add 20 dB or more of high-frequency boost was nothing to be ashamed of.  When I knew the Vox preamp schematic many years ago, I could finally say that I'm not afraid of boosting highs and cutting lows as needed anymore.

Afterwards many more "revelations" came, but I don't want to monopolize the conversation here.  Please tell your revealing-moment stories too!

[Eddododo]

I'm a little confused as to what's going on here

[stm]

I found these ones a few days ago: http://www.award-session.com/award-session_manuals.html

There's some interesting information in there.  I liked the article on preventing new string detuning.  Haven't heard of that before.

[tca]

Why I am telling all this?

Oh, well, I got my first 300V electric shock (capacitor discharge) at the age of 10 if that counts for anything!

[pappasmurfsharem]

I found these ones a few days ago: http://www.award-session.com/award-session_manuals.html

There's some interesting information in there.  I liked the article on preventing new string detuning.  Haven't heard of that before.

I don't have any new strings ATM to test this, while it makes some sense I am skeptical, it seems like fresh strings stretch out a considerable amount, but if this really works... awesome.

[deadastronaut]

nice links guys....

[stm]

Why I am telling all this?

Oh, well, I got my first 300V electric shock (capacitor discharge) at the age of 10 if that counts for anything!

Considering that you survived to tell the story it is in order to say you learned a valuable lesson.
I once touched with a finger the two terminals of a neon lamp fed from 220 VAC.  Very painful!

[stm]

I found these ones a few days ago: http://www.award-session.com/award-session_manuals.html

There's some interesting information in there.  I liked the article on preventing new string detuning.  Haven't heard of that before.

I don't have any new strings ATM to test this, while it makes some sense I am skeptical, it seems like fresh strings stretch out a considerable amount, but if this really works... awesome.

I've heard also that when strings are wrapped on top of each other on the corresponding barrel they tend to detune when using the whammy bar.  I've also read that friction in the nut can be a source of loss of tuning when bending.  Myth or reality?  I don't know.

[deadastronaut]

I found these ones a few days ago: http://www.award-session.com/award-session_manuals.html

There's some interesting information in there.  I liked the article on preventing new string detuning.  Haven't heard of that before.

I don't have any new strings ATM to test this, while it makes some sense I am skeptical, it seems like fresh strings stretch out a considerable amount, but if this really works... awesome.

hmmm..i'm not having that either...

'' I frequently put new strings on my
guitars only an hour before playing at a gig and
suffer only very minor detuning. Usually none
after ten minutes of playing''.

great gig then ..  even with a decent floyd ,  you've got to bed them in....any guitar really...

ive never liked bright new strings for gigging anyway, i like em a little bedded in, and not so bright it makes you blink....

[Kipper4]

I was having problems with my strat when using the whammy bar.
Best solution for me so far was remove the strings from the string tree and apply a small amout of graphite to the nut.
Not ideal but it helped.
oh and not crossing the strings on the capstans helps too.
I always strech my new strings after first tune. works for me.

[bluebunny]

. . . and not so bright it makes you blink....

No, indeed.  You'd leave that to one of your famous LED light shows!   

[deadastronaut]

 

[bluebunny]

Ha ha.

Go on holiday!   

[Tony Forestiere]

I found these ones a few days ago: http://www.award-session.com/award-session_manuals.html

There's some interesting information in there.  I liked the article on preventing new string detuning.  Haven't heard of that before.

I don't have any new strings ATM to test this, while it makes some sense I am skeptical, it seems like fresh strings stretch out a considerable amount, but if this really works... awesome.

hmmm..i'm not having that either...

'' I frequently put new strings on my
guitars only an hour before playing at a gig and
suffer only very minor detuning. Usually none
after ten minutes of playing''.

great gig then ..  even with a decent floyd ,  you've got to bed them in....any guitar really...

ive never liked bright new strings for gigging anyway, i like em a little bedded in, and not so bright it makes you blink....

I'm having a bit of a hard time with this: http://www.award-session.com/pdfs/Why%20do%20many%20old%20guitars%20sound%20mellower%20than%20new%20ones.pdf

Old guitars DO often look cool and feel wonderful... but not always the best sounders
after all this time. Some are probably best used as music room decoration for collectors,
as their 'best before' date has long expired!

If true, then I will be the person who will gladly take all of your "Old" and "Expired" 50's and '60's Strat, Les Paul, Gretsch, Tele, and SG guitars off of your hands. You don't want to waste your time with instruments whose "time has passed". I will gladly dispose of them free of charge to you. PM me with your shipping address so I can figure out how much S and H you will be paying.  

*edit* Forgot the main reason I was following. What has Gus got up his sleeve? Sorry for the derail.

[deadastronaut]

What has Gus got up his sleeve?

+1 curious too...