DH Pitch Shifter from GGG debugging

[Samuel]

Got everything built - no signal through the effect. GOing through with the audio probe, the signal dies at the first half of the opamp. I suspect the weird bipolar PS is the problem. JD Offers a layout for non bipolar operation and that's what I've used. Here's the schem:

http://www.generalguitargadgets.com/v2/diagrams/dh_pitch_shifter_sc.gif

I'm getting the following voltages at the 4558 tell me if these look realistic.

1: 8.58
2: 4.89
3: 4.89
4: 4.89
5: 1.10
6: 4.89
7: 4.89
8: 4.89
I'm suspicious of pin 5, cause its supposed to get V-. I've double checked the board layout - should I just go for the dual battery bipolar power option?

[Samuel]

I'm using this with a wall wart BTW. I'm pretty fuzzy on bipolar power. Pretty frustrated with this build. Has anyone out there successfully built this thing before?

[jsleep]

I know of at least two people who have built it, Dean and I.

Put your black meter probe on ground (not neg ps) and take the readings again.  The ground is the trace between the two pads where the power is attached.  You should get some meaningful readings on the IC pins if you measure this way.  From the readings you listed, I'm guessing you hooked the black probe to the neg power for reference.

With the ground reference, pins 3 & 5 should be zero volts, pin 4 should be around -3v, etc.

What I get with this ps is basically plus/minus 3volts as the bipolar power.  This seriously cuts into your headroom specs, I hope that I have mine built right.  It does seem to work rights, so I think this is correct.

Let us know the readings with ground ref.

JD

[Samuel]

OK, I'm getting the following:

1: 0
2: 0
3: 0
4: -3.8
5: 0
6: 0
7: 0
8: 3.6

OK So I guess the proper power *is* there. So why is the signal croaking at R1? I've remelted the solder joints, and I even tried holding a 100K resistor onto the first pad of R1, but leaving it off the second. The signal gets through the resistor, it's just somehow being killed off on the pad leading to pin 2 of the opamp.

BTW is it normal to get a continuity beep between pins 2 and 4 of OA when its in the circuit? And if not, how in the world is *that* happening?

Thanks for the help, JD

[M.D.]

could the oa be bad?

Mike :twisted:

[Samuel]

Nope. Swapped it out for another 4558 and a TL072. No dice.

[Samuel]

bump for JD

[jsleep]

Hi Samuel,

I don't know what to tell you without being able to look at the board, etc.  Possibly a short circuit somewhere around that IC, hairline crack in a trace or something like that.  You have it narrowed down, keep looking and maybe you can find it.  It's worth it if you can get it to work, I really like the effect.

JD

[Samuel]

OK I appreciate you taking a look at that stuff. Didn't mean to be a pest, if I was. Sigh. I'll keep checking it out!

[jsleep]

No, you are not a pest.  I can feel your pain, I've been there many times. If I have something I just can't get working, I build it again from scratch and so far it always works on the second build.  I keep the first one hoping that someday I'll figure it out just for my own satisfaction.

JD

[Samuel]

Yeah it's just a bizarre thing. I've been having alot of success building recently, and to not be able to get a signal into and out of a stinking opamp takes you down a notch! I think your suggestion is a good one. I might also just breadboard it on account of the fairly reasonable parts count and see what happens.

Thanks again!

[ExpAnonColin]

Where did you get the chip?

How does this thing sound as a clean pitch shifter?

-Colin

[Samuel]

Chips are available from SmallBear. As to your second question....um, wish I knew!

[smoguzbenjamin]

JD should be able to answer that question

[Samuel]

[Dean Hazelwanter]

Hi Samuel...

Don't give up, I think we can help you nail this down.

If this was me, this is how I'd approach it.

If you have the opamp socketed, remove the opamp from the socket. If the signal doesn't die anymore at the R1 R2 junction, the opamps are bad. If the signal still dies at the R1 R2 junction, it could be a number of things. You mentioned you 'tried holding a 100K resistor onto the first pad of R1, but leaving it off the second.' If you then touch this unconnected end of the flying resistor to the 2nd pad, does the signal die again? If not, R1 is the problem; if yes, disconnect the 'output end' of R3 and R4, to rule out something connected to the output of the opamp stage dragging the signal down.

Try these things and get back to us!

BTW, I do get continuity (on diode test mode with about 0.65v displayed) in 1 direction only when measuring between pins 2 and 4.

HTH!