twang-a-matic

[Vince_b]

I tried both

Solution A:
1. Swop the polarity of the 9V Battery clip.
2. Swop the NPNs c to e and e to c, base in the same place. (Maybe use a 2N3904, but yours are also OK, try them, should work)
3. Swing R7 pot from old -ve rail  to the new -ve rail.
4  Swing both earth shield (rings) to the negative rail.
5. I would put. say a 180K resistor in series with C1 so as not to load the guitar pickups much. Try a couple of highish values but not so much that you get too much attenuation, but not too low so that guitar tone gets dull.

and

Solution B:
1. Remove NPN transistors altogether and replace with PNP (2N3906 - OK), but the emitter must be where the old NPN collector was and the collector must be where the old NPN emitter was for both Q1,Q2. Base kept in the same place.
2. Leave the rest of he circuit unchanged.
3. again, I would put. say a 180K resistor in series with C1 so as not to load the guitar pickups much. Try a couple of highish values but not so much that you get too much attenuation, but not too low so that guitar tone gets dull.

Solution A is quite noisy and the output level is really high. I put a 360k resistor in series with C1 to tame it a little bit. It sounded like a fuzz but with a strange crackling noise. With a lot of imagination it can sound like a distorted sitar. But the interesting thing about it is that when the "twang" pot is set on maximum, the volume level is very responsive to the attack on the strings. You can easily play either very low or very loud or anything in between.

Solution B is also very noisy but the output level is much lower than the bypassed signal and the sound is not distorted. It only changes the tone (more mids and highs).

The bottom line is that even with those mods this circuit is far from being great.

[Anthem]

Hi Vince

Now that you've gone to all that effort I hope we can tweak it into correct operation.

Another aspect of the circuit that is very odd is the 18ohm//2uF (R4//C2) parallel circuit, which seems to serve no purpose really as the 18 ohm is so low in comparison to the other values that it might as well be a short-circuit in parallel to the 2uF cap. This circuit serves to reduce the gain of the circuit below the frequency when the impedance of the 2uF cap equals 18. This f=1/(2xPixCxR) =4.423kHz. Which means the circuit amplifies the sound even more after this frequency which is absurd since below this the amplification is way too much already. Again I think a typo may have occurred here. Using likely values for R4  and related freqencies  ar e

R4 = 1K ; f=79.6Hz           -   linearly  low (Low E is about 82Hz) but in terms of feedback the gain below this R2/R4 is about 10 and increases after this f
R4 = 180 ; f=442Hz          -    the good old A4 frequency (1st string, 5th fret), could be, but gain would be 55 below this f and even more after it.
R4 = 18K ; f=4.42Hz         -   gain below this f very low (0,55) and increasing after it till the transistor gain limits it.

Also if you leave the circuit as it is (apologies) and then doing what slacker suggests and make R3=220K but also making R4 =1K  then the biasing would be OK too for Q1 but I fail to see it getting past Q2 unless R5 is swung from the neg rail to the +9V to turn it on.

Try it but I'll giive it a shot on LTSpice later and see if we can get a "rinkety tink tinkety" banjo timbre up and running ! This circuit is simple but to get results from simplicity can be quite hard to acheive.

[vendettav]

so far no clips??? 

[slacker]

Believe me you don't want to hear it. I breadboarded it with the R3 and R4 changes in Anthems last post and it works,  sounds like a dirty, misbiased treble booster with short sustain, I suppose it sort of sounds like a banjo if you really use your imagination. It also worked just changing R3 to 220k but was even rougher sounding, making the input cap bigger gets you a bit more sustain but it's still very gated.

[vendettav]

dude! get me the clips   

[Vince_b]

After some tweaking I achieved some pretty decent banjo tones. I did Anthem's solution A but without adding a resistor in series with C1 and I also changed R4 for 1k like he suggested.
It definitely works better with single coil and it also help if you play around the 12th fret and also turn the treble pot on your guitar near the maximum.

so far no clips??? 

I would like to post a clip but I don't have a mic to record.