Rocket Distortion Contortions

[aron]

>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.

OK, go to the members section and check out the simplified schematic. Note that I now tap the output from the junction of the collector of Q3 and the 10K.
Make sure that the last C4 is good and lot leaky (referencing the cleaned up schematic).

OK, I reread, you can put a big cap 100uF etc... from the V+ to ground to help with the humming.

[Brushthrower]

OK, changed I rewired the entire circuit and changed a couple of the caps I was a little uncertain of: C1, C4 and C8 (also spend a frustrating three hours with absolutely no sound, trying desperately to fix it and then realised my output chord was toast! Grrr.)

Basically I'm back where I started. The sound is much the same. I traced the sound running throughout the circuit and is good. Did a new voltage check with these results:

Q1
C=8.49
B=4.21
E=4.35

Q2
C=1.38
B=0.70
E=0.07

Q3
C=3.97
B=1.38
E=0.76

I've had it for today so I'll check out the simplified schematic tomorrow.

Just curious: What is the purpose of R14? It was listed as "optional" on the parts list.

[aron]

it looks like a pulldown resistor to reduce popping.

[Brushthrower]

Thanks. Please excuse my ignorance, but can I just put the 100uf between where the ground lead of the dc jack attaches to ground?

[aron]

Yes, you can put it from V+ to ground. But I think your problem might be a simple miswire somewhere.....

[Brushthrower]

Alright, I think I'm at an impass here. I suspect one of my components is at fault and I think I'm just going to have to rebuild from scratch with new all parts. Perhaps it's the 3DPT. Anyways, thanks for all the help. I'll let you know how it turns out.

[Brushthrower]

Hey Aron, I noticed that your schematic of the rocket has a 10K volume pot while the GGG version uses a 100K pot. Which did you use? Do you think this will make a significant difference? Just a thought.

[aron]

No, no significant difference. Can you post a picture of your board/wiring?

[Brushthrower]

Sure:

http://i135.photobucket.com/albums/q150/brushthrower/rocketwiring.jpg

http://i135.photobucket.com/albums/q150/brushthrower/rocketwiring01.jpg

[petemoore]

  Instead of reading all the way back through...
  Are those tantalum capacitors ? [polarized?].
  It would seem the AC portions of the signal path could put both + and - voltage across the staging caps at least.
 

[aron]

That 3PDT switch looks miswired to me at first glance. I will have a closer look tonight.

[aron]

Look at the beginner project wiring:

http://www.diystompboxes.com/smfforum/index.php?topic=970.0

[Brushthrower]

Thanks guys,

The caps are bipolar to the best of my knowledge. Nothing to indicate otherwise (ie one longer lead, etc.) The wiring diagram I based mine on is from the GGG site:

http://www.generalguitargadgets.com/diagrams/rocket_lo.gif

[Brushthrower]

I've rechecked my wiring to the GGG layout and it seems accurate. Checked out the beginner's wiring project and the two are definitely different. I sketched a little layout on my lunch break at work (I had to work in a adaptor jack):

http://i135.photobucket.com/albums/q150/brushthrower/rocketwiringlayout0001-1.jpg

Does this look accurate?

Thanks!

[aron]

OK, the switch is correct. What transistors did you end up with? Use your meter to confirm that the bias resistors are the correct values. If you audio probe, the the collector of Q3 should be loud.

[Brushthrower]

Sorry, Aron, just to clarify: The GGG switch is correct (or my revised on)? Damn, I thought we had nailed it!

I'm using 2N5088 transistors. Resistor values are correct. Q3 collector is very LOUD! So much so that I can hear it with the volume on my amp turned off.

[aron]

I had a reply... it seems to be gone.

Test the junction of R7 and R9. It should have plenty of volume and be loud and distorted. Let me know. Use the audio probe for this. It should not be clean sounding.

Aron

[Brushthrower]

Hi, sorry for the delay...was out of town for the weekend.

The sound at the R7/R9 junction is loud and fairly distorted but not nearly as much as the Q3 collector.

One anomaly I've just noticed is that when turning the volume knob of my guitar anywhere lower than maximum I either get a shrill screeching or sometimes pick up radio frequencies! This doesn't happen with any other pedal.

[PerroGrande]

That odd behavior brought on by the guitar's volume control sounds suspiciously to me like a wiring or solder bridge problem.

I built a circuit for a friend once that had some amazing problems that could be altered by messing with the guitar's volume control.  After a lot of troubleshooting, I discovered a trace that hadn't been completed removed during the PCB fabrication problem.  It was allowing some inappropriate positive feedback plus some DC shift at the input jack (the feedback was before the initial coupling capacitor).

So...

1) Check for bridges again...  and again... and again...
2) Check wiring again...
3) Plug a standard cable into the input (to turn the effect on), but do NOT plug in your guitar.  Use your voltmeter to see if there is a DC voltage between the tip and sleeve on the input jack.  There shouldn't be...  If there is, this is indicative of some sort of wiring problem -- typically a bridge of some sort on the circuit board.

[Brushthrower]

Thanks for that. Hmm...when I set the voltmeter to 200m it reads 0.1-0.2 across the tip and the sleeve. I've completely rewired with this remaining consistant so I think my next move will be to resolder all the components.