Omega Boost debug

[spaceace76]

Hello,

I just finished putting the ROG Omega Boost together, and it's not working. I built it almost exactly as you see on the rog page, but I get no sound.

I noticed that my meter says there is continuity between ground and the hot side of the out jack, same with the hot side of my input jack, which worries me a bit.

The voltages I'm reading are:
Q1:
D: 9.43v
S: 9.42v
G: 9.34v

Q2:
D: 9.52v
G: 9.45v
S: 9.44v

I haven't hit it with my audio tester yet but I will when I get a chance. Any help is greatly appreciated.

[B Tremblay]

What was the change you made while building?

It looks like something isn't correctly grounded, judging by the voltages you measured.

[spaceace76]

the only change i made was to move one or two components so they fit on the board i used. the connections weren't changed though.

it looks like i forgot to plug cables into the input/output to measure the voltages, so here they are again with cables in (biased at ~4.5v):

Q1:
D: 2.17v
S: 0.99v
G: i only get a reading here when a guitar is plugged in, and its never more than .5mv

Q2:
D: 9.47v
G: 4.53v
S: 2.49v

[B Tremblay]

Does adjusting the trimpot change the drain voltage?

[spaceace76]

By drain voltage you mean the "d" pinouts on the transistors right? If so, yes on Q1, no change on Q2.

When checking with my audio tester, the signal was fine until testing at the output. The connection to master lug 2 was fine, but after the negative side of the 4.7uf cap it has no sound. I'll try swapping it out to see if that helps. Would a non-polarized cap be okay here? I think this is the only 4.7 polarized I have...

I'm glad I had about 5 other projects to occupy myself today! I think this would have made me crazy otherwise .

Thanks for your help B Tremblay, nice to get advice from the guy who came up with the circuit!

[B Tremblay]

OK, adjust the trimpot to have about 4.75v at the drain of Q1.

Was the Master control turned down while you were audio probing?  Is the output jack wired correctly?

[spaceace76]

I rechecked the output jack, ran a new ground wire, relocated the connection to a different point in the ground, ran the ground to the input jack's ground, all of them did nothing.

I think I'll mess with the output cap and see what I get. What happens when the output cap is installed the wrong way? Maybe I put it in wrong (despite the obvious label) or it's labeled wrong?

[B Tremblay]

Did you adjust the trimpot?

[spaceace76]

Yup. Sounded good when using the audio tester, but still nothing from the output jack.

I dunno if i mentioned this before, but the output jack shows continuity between ground and the output. I took the jack off and tested it and it came up normal. The output and ground wires themselves showed continuity, so either I wired it wrong or something else isn't quite right.

I put a blob of solder over the 1Meg, negative 4.7uF, and output connections, is that okay? Mine looks just like it does on your page, but with one long solder connection spanning those three pads.

[spaceace76]

 
Just remembered that I didn't have a 3n3 cap on hand so I used a .0022 instead. Would that be the problem?

[frokost]

No, you have already identified the problem: The output is grounded. Somewhere there is a short between the output and ground. Are you sure the 1M is actually 1M?

EDIT: And make sure that the volume pot is in the middle when you debug. I've made a fool out of myself several times thinking "why is there no sound, the volume is at it's fullest!" when it's actually turned all the way down .

[spaceace76]

Oooooookay well I feel a bit silly now.

I ran the wire for ground a little too long. The wire continued past the 1 meg up to the cap. 

I cut it and the circuit immediately started working. Thanks for the help! Sounds awesome!

Edit: which pin do I read to set the bias? d on q1?

[B Tremblay]

which pin do I read to set the bias? d on q1?

I'm glad you found and corrected the error.  Yes, the drain pin of Q1 is where you measure the voltage while adjusting the trimpot.