Adding DC jack to GGG Big Muff Pi --> drop in sound?!?

[Danny G]

Anyone add a DC jack to the GGG Big Muff Pi?

I've built several BMP's in the past using the GGG layout and they've all sounded great.  

Recently I built another one using parts I've never used before--tropical fish caps for the 0.1 uf's and a big poly film cap for the 3900pf tone cap, as well as a DC jack.  I fired it up and noticed it sounded "neutered"--lacked gain, kinda muddy--compared to the one I'm currently using.  I haven't had time to really de-bug it yet so I haven't really worried about it.

I just built one for a friend (using metal film 0.1 uf's and a ceramic tone cap) and in testing-firing it sounded great.  Then I put it in the box with a DC jack, and wouldn't you know it, it sounds like the one I've been having problems with!!!

Does adding a DC jack affect the voltage of the GGG BMP this much or something?  It's one of the few pedals that DON'T have a DC jack on the layout, so I'm wodering if it wasn't designed for it or something.

Any ideas?

[ninoman123]

DC Jack shouldnt change the tone. Is the voltage on the supply 9v? Sometimes if the pedal isnt getting enough juice it can sound muddy, but then again some people like that sound. Did you try it with a battery too? If it sounds muddy with the battery the problem is in the circuit, not the power supply.

[Danny G]

I tried it with a battery and a 9v power supply.  Different batteries in each unit, similar sound w/DC jack.

I'll check the voltages with my DMM when I get a chance.

Any other ideas?

[ninoman123]

Make sure your wall wart is filtered well.  I use one of the Boss wall warts for my adaptor and it works well.  If you buy a cheap Radio Shack one, they usually arent filtered well enough for audio use and it could change the sound, but it usually just causes hum.  So make sure you have a nice wall wart supply.  You could also try a larger cap for the 100uf to ground.  Thats the power supply filter, increasing it might help your sound out a little.  You could also try changing the input/output caps to a lower value.  Try .068 or so. Lowering it will filter out more bass, see if those suggestions help at all.

[Danny G]

The drop in sound has nothing to do with using a power supply or a battery, it has to do with the added jack itself.

I've built 4 of these without the jack and all have sounded great.

I then built two with a jack and they both sound identically neutered.

Therefore, the jack is somehow interfering with the overall signal.  anyone else experience this phenomenon?

[Ed G.]

Only way I could see that happen is if the switch in the dc jack somehow had some resistance. This should be easy to check with a multimeter.

[ninoman123]

Well the jack connects to a power supply I assume? Meaning it could have something to do with the power supply. You could solder the wall wart to a 9 volt clip instead of a jack, And clip the two 9 volt clips together. I personally have never experienced this. Im just trying to give you some stuff you could try to trouble shoot it. So I really dont think its the jack because that shouldnt change your sound.

[Danny G]

Here are some tranny voltages from the original I built and the two affected BMP's.  Lemme know if anything stands out as odd:

Fully functional BMP:

C,  B,  E

Q1:  3.70   0.65   0.01
Q2:  3.65   0.60   0.04
Q3:  3.18   0.54   0.00
Q4:  3.55   1.42   0.82


BMP w/DC jack 1:

Q1:   3.78   0.62   0.02
Q2:   3.79   0.62   0.02
Q3:   3.64   0.62   0.02
Q4:   4.04   1.59   0.98


BMP w/DC jack 2:

Q1:   3.74   0.63   0.03
Q2:   3.79   0.63   0.02
Q3:   3.80   0.63   0.02
Q4:   4.37   1.71   1.11


Anything look strange to you guys?  Seems the C of Q3 and Q4 of the affected BMPs seem a little higher.  If this is resulting in a neutered sound (WAY less gain), what can I do about it?

Gah!

[Danny G]

bump