Rocket Distortion Contortions

[Brushthrower]

Hi all,

I'm a brand-spanking-newbie and I've chosen Aron's Rocket as my first project. I used the General Guitar Gadgets schematic and PCB and have got it working (more or less). However, I've been running in circles trying to get it to function 100%.

http://www.diystompboxes.com/pedals/rocket.JPG
http://www.generalguitargadgets.com/diagrams/rocket_lo.gif

I've followed that design faithfully except for using a BC337-25 transistor for Q2 and Q3 as the 2N5089s that I bought proved problematic in those positions (hopefull I didn't fry them). Q1 is a 2N5089.

The problem I'm having is with the distortion sounding rather weak - kind of like a mild overdrive rather than a "screaming fuzz" - and a loud and constant humming when the pedal is plugged into an power adaptor, although not when it's on battery power.

One other thing I should mention is the enclosure I used has plastic sides where the audio jacks are attached. To ground the circuit to chassis I soldered a lead from the volume pot to the ground of the stereo audio jack.

Here's the transitor readings:

Q1
C=8.76
B=4.36
E=5.08

Q2
C=1.46
B=0.69
E=0.07

Q3
C=3.81
B=1.46
E=0.86

I also made the audio probe and traced the sound trough the circuit. One suspicious thing I noticed was that there was a significant drop in sound directly after C3. I changed the cap, but to no avail.

Any help or suggestions would be greatly appreciated!

[Cardboard Tube Samurai]

I found this to be a very underwhelming effect to be honest.

[sean k]

Sounds like your power supply, or adaptor, hasn't got enough capacitance to ground so your getting ripple through. Try 100uf from B+ to ground somewhere and it should tidy up the hum. I'm not sure what the gain is on those BC337's is... just checked, about a 100 so thats not much. Swao the 2N5088, which usually run about 450hfe, to Q3 and put the BC337 in its place, Q1, and that might give you a little more ommph. Another thing is the feedback resistor between the emitter of Q3 and the base of Q2. Changing that to a higher value puts less negative feedback on the base of Q2 so the input signal to it is larger, so the output is larger. Also a bypass cap on the 100 ohms on the emitter of Q2 will raise the gain a bit. The resistor after C3 could be halved as well to let more signal through and also bringing the output closer to the collector on Q3 will raise the output signal. I'd take out the 10k resistor and put in the two fixed ends of a trimer then take C6 off the middle wiper lug which would increase the output as you bring it closer to the collector. I'd also remove C4 or at least make it a .001 nano because a cap from signal to signal to B+ is just like one to ground and will remove signal, well, at least thats my understanding, and I'd try it out to see what happens. So all these things I'd do one at a time and watch for improvments.

All of these things would be done because the hfe on 337's isn't really enough to get this thing "screaming"

Goodluck! Love the moniker, Cardboard tube Samurai is a classic bunch of words.

[petemoore]

To ground the circuit to chassis I soldered a lead from the volume pot to the ground of the stereo audio jack.
  Everything marked Gnd. [and the sleeves of both jacks] should be common and ground.
  The first stage is an impedance booster [buffer] and should sound 1/1 volume before /after.
  The next stage is a feedback amplifier [Fuzz Face], and the voltage you've posted don't look bad particularly, if you have a 7.8v or so power supply, other than a battery that might do better with a recharge.
  With 9v supply, Q2 bias would look a little low.
  You'll have to judge, or adjust Q2C bias to 1/2v.
  I'm not sure what is going on, other than it should screaming, high output.

[Gus]

It is a mod of the 3 tran.

One it was made for 200 and up transistors the first the highest hfe as possable.  The 100 ohm and 10K "control" the gain of the first FF type fragment transistor.

Next don't worry about C4 it is there to take the edge off it is a lowpass.

The 3 tran is a buffer to a 10k to a FF type circuit I like this better than C to b caps.  Note the bias pot it is there for more than just bias it can be used to get different sounds.

The rocket used the distortion section from the 3 tran

[PerroGrande]

The Rocket is actually one of my favorite effects.  I use one in my pedal board and have received numerous compliments on its sound.  Mine is built with 2N5088's in all three positions, although the 2N5089 should work well.

The voltages on Q1 look a little squiffy to me.  I would expect the base to be a diode-drop (0.65v or so) higher than the emitter, even in a follower configuration.  Is this a typo, by chance (hopefully)?

[aron]

Yes, it should scream. It should be smoother than you expect from Si Transistors too.

[PerroGrande]

Yeah -- it should have substantial scream potential, all while staying fairly creamy.

When you say the 5089's proved "problematic in those locations", what exactly do you mean by that?  Mine is based on 5088's completely (including the SMT version that I built) -- the 5089 is *slightly* different, but not enough so to cause what you're experiencing.   The BC337-25 is lower Hfe (250 typically) than either the 5088 or 5089 -- I've not tried this circuit with transistors in this range, but anything over about 200 like Gus mentioned should be okay. 

[Brushthrower]

Thanks everyone for your responses.

To answer PerroGrande's question: When I had the 5089s in and followed the sound path with my audio probe I found level dropped at Q2 and was absent after Q3. I put in BC337-25s in Q2, Q3 and this resolved that problem. Perhaps it was a defect in the transistors or I damaged them while installing. I bought some new 5088s today (and some 5089s just for the sake of comparison) socketed these ones but it seems the increased hfe has not helped. The fuzz is still anemic at best.

Yeah, I was wondering about the voltages on Q1 myself. Not a typo, I'm afraid. I checked all three transistors with the new socketed 5088s in and found these results:

Q1
C=8.72
B=4.34
E=5.01

Q2
C=1.36
B=0.71
E=0.07

Q3
C=2.57
B=1.38
E=0.78

So, only slight changes all around and still those dodgy Q1 readings.

[aron]

Well, I just made another one tonight. Assuming no mistakes (yeah right), I will have more info tomorrow.

[aron]

Make sure that your transistors are oriented correctly as well.

[Brushthrower]

Haha. Thanks,  Aron. That was the first thing I checked!

[Gus]

In case you don't know this BC and 2N often pinout different    ECB vs EBC

[aron]

Mine works. I had one mistake but it's rocking right now. I will follow up with info. I haven't played this thing in so long.....
I used all 2N5089.

[maartendh]

Hello,

I used three BC547-C transistors, which worked out fine - one of my favorite distortions! The BC 337-25 you used has a gain which is somewhere between 160 and 400 times, so there might indeed be a chance that you picked one  which has too little gain. Probably the BC337-40 (ranging from 250 up to 630) will give you better results (or BC 547, 548, 549, 550, each of them with the suffix C). Your problem with the 5089 indicates however that there might be another problem...

Best of luck,
Maarten

[MikeH]

I can offer no help, but I just wanted to say that your avatar pic is seriously giving me the creeps.  Welcome!

[aron]

Check that the 47K resistor does go from the base of the transistor to the emitter of the last.

This thing has too much distortion with the 2N5089 I think. I need to try 2N2222 or similar.

Listen to how much distortion is here!!!!!
(Note that I made a mistake on mine, I put a wrong value resistor on the base of the 2nd transistor. In this sample, I shorted that resistor out).

http://www.diystompboxes.com/pedals/sounds/Rocket08.mp3

Did you try adjusting the 4.7K pot? I used a trimmer there.

[Brushthrower]

Again, thanks for all the responses.

Aron: the 47k is connected properly. And I have adjusted the 4.7k pot to good results in regards to the tone. After a bit of tinkering I succeeded in getting a solid signal running all the way through the circuit when listened to through my audio probe. However the output signal is now weaker than ever

Out of desperation I'm just going to redo all the wiring in hopes that it is just a bad connection somewhere. I'll post an update when I'm done.

[aron]

OK, lower gain Si in buffer and in Q2 position. 2N5089 in last transistor Q3.
Still has lots of distortion but the character has changed a lot. No changes to circuit other than rebiasing and tone control change.

http://diystompboxes.com/pedals/sounds/Rocket08b.mp3

This thing has tons of distortion - recorded through my 12" combo bassman with SM57.

[aron]

I don't have a good meter here, but when I take this pedal home I will post the voltages. I think you just have a wiring problem.