Bad Stone, no LFO

[edash]

Hello all! I've been pulling my hair out over this one for a bit...

I made the http://topopiccione.atspace.com/PJ05EHBadStone.html bad stone and I'm getting a signal through, but no phasing at all. It becomes rather distorted sometimes. There is no noticable difference in sound whether battery is connected or not.

I've been through the circuit, realised there was a short between the 1/2 rail and the ground, fixed that, and found the transistor I was using was incorrectly positioned. I've now replaced it with a BC548, as with the layout on the site.

I've used TL072s for the opamps, and an LM324 for the quad, along with a 4049 (couldn't get a 4009)

If anyone has any thoughts, they would be most welcome. I found a similar topic, which seemed to have the same symptoms if it's any help. http://www.elixant.com/~stompbox/smfforum/index.php?topic=40457.0

Here are the chip readings, many thanks.

IC A:
1. 1.27
2. 2.81
3. 2.72
4. 0
5. 1.35
6. 2.74
7. 4.22
8. 6.28

ICB:
1. 2.84
2. 2.75
3. 2.74
4. 0.00
5. 1.06
6. 1.24
7. 1.28
8. 6.28

ICC:
1. 5.14
2. 4.67
3. 5.14
4. 0.00
5. 2.74
6. 3.34
7. 1.57
8. 6.27

ICD:
1. 2.81
2. 2.73
3. 2.72
4. 0.00
5. 2.65
6. 2.65
7. 2.65
8. 6.26

ICE:
1. 4.59
2. 2.73
3. 4.58
4. 2.73
5. 4.58
6. 2.72
7. 4.58
8. 2.73
9. 4.58
10. 5.12
11. 4.58
12. 2.73
13. 4.58
14. 4.58
15. 2.71
16. 4.56

ICF:
1. 0.55
2. 1.35
3. 0.82
4. 6.41
5. 0.88
6. 0.79
7. 0.80
8. 0.80
9. 0.83
10. 0.82
11. 0.00
12. 2.39
13. 0.78
14. 5.28

Battery: 7.73
Vbias: 6.38 (Green)
1/2: 1.34 (Orange)

Q1:
E: 4.70
B: 4.77
C: 5.26

Notice the lack of movement on ICF, no sign of the LFO - at any speed. Or setting, I have both manual and auto wired up as per schematic. All wiring appears correct, and I have checked component values.

- Ed

[bluesdevil]

Putting a 100uf cap between 1/2 voltage rail and the full +9 volt power rail (after the 100 ohm resistor)got mine to finally work:
http://www.elixant.com/~stompbox/smfforum/index.php?topic=42189.0

[edash]

I've just tried adding a cap like that... there seems no difference

Thanks for you suggestions.

[gez]

Try a fresh battery for starters!  Better still, use a 9V PSU.  It could simply be that the LFO is latching due to the low supply (though I haven't checked thru the schematic/your voltages thoroughly so it might be something else).  If you want to stand any chance getting this to work, sort out the power first.

Check values for that string of resistors to ground that form the divider to bias everything (R3, R4 etc) and use the chip specified for the LFO (IC F). 

[edash]

I've checked through the bias resistors again... Can anyone quote me any values for a working badstone... To see if it is my bias voltage that's way off.

Tried it on fresh battery, also no change.

This is extremely confusing. Any values from a working badstone would be very welcome. Many Thanks.

[Sir H C]

Your battery voltage is scary low.  See how the 1/2 is really 1/4.  That is the problem that bluesdevil's bad stone had.  Required the cap to get over the start-up issue.  What size capacitor do you have at the 1/2 point? 

[edash]

I added a 100uf cap between the 1/2 and the full voltage rails, I used an axial electrolytic - putting the + on the full and the - on the 1/2.

[A.S.P.]

worx now?

[edash]

No change that I can see :/

Am I correct in thinking, that even if the LFO wasn't working, and I put it on the manual phase mode, that I would get manual phase working?

At the moment, I'm getting no effect on either auto or manual modes, could this suggest a different problem?

[Zero the hero]

Hi edash, yes the phasing should work in the manual mode.
The vbias is very low, check R3, R4, R38, R39 and C3.
Try using a sound probe to see where the signal's lost.

[lovric]

could it be that R50 is too big? measure it, it could be 110-120R, because of lousy tolerance... maybe it'll bring down a new battery too. your batt was 7.73V and pin 8 on all 4558s is 6.28V...
R3, R4, R38 or R39 may be smaller than schem says and steal the voltage?