ZOMBIE CHORUS NOT "CHORUSING"...

[Thomeeque]

I'm limited now in writing (in train ), so just quick check: with R5 still out (you won't need it back until this issue is fixed actually) try to pull BBD out - do you still hear clear sound?

T.

[maarten]

Problem is either with the 4046 or the 3007, seems to me. Maybe you can isolate the problem further by measuring again at pin 2 and pin 3 (= 4) of the 4046 and noting whether there is a difference when you flip the modeswitch; maybe this will give you a clue whether the 4046 is working well or not...
Maarten

[Thomeeque]

 We know that there is a signal passing from input to output even with R5 (dry path) removed. This means that either:

• (1) topology is not correct (error in layout or some shortage) or
• (2) wet path (BBD /MN3007/ + LPF /right half of the top TL062/ + clock signals) works correctly, but frequency is not altered by LFO (otherwise Adriano would hear vibrato) or
• (3) BBD /MN3007/ is burned in the way, which would pass signal from it's input to one or both of it's outputs directly, not thru the BBD delay-line.

Ad 1) topology can be simply checked by pulling MN3007 out (I hope that Adriano used socket for this IC) - if there will be still clear sound at the output then topology is definitely wrong (because there should be no other way for signal then thru R5 and BBD) - this should be IMO done first!

Scenario 2) can be checked by several ways - one was already proposed implementation of feedback from out to in - this should generated echoes tail. Another could be to set much lower clock (by significantly bigger cap between pins 6 and 7 of 4046, something like 22~100nF), signal should be strongly (and audibly!) delayed and degraded by low sample rate.

Ad 3) even when everything is possible I really doubt that this has happened (there's a lot of components between in and outs inside MN3007 and there's no simple shortage between in and out - DC levels differ). Grounding of any clock input should not injure MN3007 chip according to it's datasheet. It could injure 4046 (as the output was shorted), but even this is not very probable.

T.

[Renegadrian]

• (1) Checked the original layout and my shrinked one with hollis schem - layout is correct
  Also I got clean sound with and without the 3007 (I have it socketed of course!!!). Checked again the traces, no solder bridges.
• (2) put a 100nF cap between 4046 pins 6 and 7 - I barely hear a ambulance-ufo-mosquito sound that reacts to the rate pot, like it's changing the frequency or speed - that pot without that additional cap slows and speeds up the barely audible ticking
• (3) I have to get some more 3007 I think - no changes with another 4046 I just tried (all ICs have sockets).

thx for the suggestions, slightly getting mad!

[maarten]

Maybe a biasing problem with the MN3007? I recall there also was a version with 12K/10k (Hollis' original?) whereas you use 15K/10K. Maybe use a trimpot for finding the right Vbias for the BBD to work - just a wild guess...
Maarten

[Thomeeque]

(1) Checked the original layout and my shrinked one with hollis schem - layout is correct
Also I got clean sound with and without the 3007 (I have it socketed of course!!!). Checked again the traces, no solder bridges.

OK, if you hear clear signal at the output with both MN3007 (wet path) and R5 (dry path) pulled-out, there is definitely something wrong and needs to be fixed (there's no other path on schemo - wet and dry only ) - if the layout is correct (even to me it seems to be) and if there are no bridges, only other possibility is that top TL062 is defective and that signal is somehow leaking from left half (input buffer) to the LPF (right half) inside this chip. But according voltage readings this IC looks healthy - anyway try another one there.

(2) put a 100nF cap between 4046 pins 6 and 7 - I barely hear a ambulance-ufo-mosquito sound that reacts to the rate pot, like it's changing the frequency or speed - that pot without that additional cap slows and speeds up the barely audible ticking

What you hear barely is cross-noise from LFO (ticking) and from clock (with 100nF cap we have moved clock frequency to audible range) - since the pitch is altered by LFO, whole LFO+clock system seems to work correctly (it's still not 100% sure /there may be issues at higher frequencies or at final outputs/, but let's say with very high probability it works).

We can try to test BBD directly now. Have an audio probe. Put BBD back, as 4046 use that new one (not the one which had grounded outputs). Set max depth and middle rate. Turn it on, put some signal at the input. First check that BBD has this signal at it's input (pin 3). Now cross your fingers and check signal at it's outputs (pin 7 or 8 ) - what do you hear? Vibrato by any chance?

T.

[Renegadrian]

OK back again with some reports - I guess I had some sort of connection on R5, now I tried again to pull it away and guess what, NO SOUND. 3007 was in. So the problem should be before the output.
Audio probed, the 3007 I had in had input at pin 3 but no sound at pins 7-8. OK let's try the second one I have.
Now I have that crazy vibrato sound you wrote about. (I guess the other 3007 is gone?!)
So forget about the R5 passing thru (maybe a tiny bridge?!) - what do you suggest me as my next step!?
Thank sou so much again, I appreciate your posts and help! 

[Thomeeque]

OK back again with some reports - I guess I had some sort of connection on R5, now I tried again to pull it away and guess what, NO SOUND. 3007 was in. So the problem should be before the output.
Audio probed, the 3007 I had in had input at pin 3 but no sound at pins 7-8. OK let's try the second one I have.
Now I have that crazy vibrato sound you wrote about. (I guess the other 3007 is gone?!)
So forget about the R5 passing thru (maybe a tiny bridge?!) - what do you suggest me as my next step!?
Thank sou so much again, I appreciate your posts and help!  

OK, so mystery with unintentional 3rd signal path is over - good! Now it's much easier (well, work is almost done actually) - if you hear vibrato at the output, you can put R5 back (remove additional clock capacitor if you still have it there) and your chorus should be fully functional!

First 3007 is either defective or it just requires distinctively different bias voltage - you can try to follow maarten's hint (put trimpot over R12/R13 divider and try to dial bias which would make it work) - you can try this even with functional 3007 to get best out of it (dial point with less distortion - but it's a bit hard without oscilloscope). According MN3007 datasheet you should stay between 5 to 10 volts, don't go outside these limits.

Good luck, T.

[Renegadrian]

if you hear vibrato at the output, you can put R5 back (remove additional clock capacitor if you still have it there) and your chorus should be fully functional!

Guess what, now IT WORKS!!!  YEAHHHHH VICTORY!!!
Nice simple chorus - I thought it was more difficult and had more components, looking at the BoM it's not so many components after all (apart from the 4 ICs)
Thank you again for your suggestions!!! I really appreciated your help...

[Thomeeque]

if you hear vibrato at the output, you can put R5 back (remove additional clock capacitor if you still have it there) and your chorus should be fully functional!

Guess what, now IT WORKS!!!  YEAHHHHH VICTORY!!!
Nice simple chorus - I thought it was more difficult and had more components, looking at the BoM it's not so many components after all (apart from the 4 ICs)
Thank you again for your suggestions!!! I really appreciated your help...

Great - congratulations!

If you will put it into the box, try to keep all signal wires as far from LFO section as possible (and wires to speed pot as short as possible), otherwise you can get ticking even when effect will be bypassed.

My pleasure T.

[deadastronaut]

waheyy glad you guys got it going....ive been reading this with an interest.....but lack of knowedge lol...

so is that vero layout ok after all....?

i built the john hollis chorus pcb version...and had to do the anti ticking mods...and had to put a voltage regulator in it
it worked ok on a battery at 8v....but didnt work on a psu at 9...strange but it works now......simple cure too...

will you have to do an anti tickin mod on this version?.......
was there a dodgy connection on the vero?
also have you tried it on a psu yet?.........

cheers rob.

[Renegadrian]

Rob the shrinked layout I posted is definitely verified!
The mod against the ticking is about a second vref, as you can see there at the bottom, two 10k to feed the bottom IC.
Yeah I think some strange bridge or whatsoever and some problems with the 3007 I had in, this second one I have now is working 100%.
A.

[deadastronaut]

Rob the shrinked layout I posted is definitely verified!
The mod against the ticking is about a second vref, as you can see there at the bottom, two 10k to feed the bottom IC.
Yeah I think some strange bridge or whatsoever and some problems with the 3007 I had in, this second one I have now is working 100%.
A.

cool..glad its working 100%....

so its the vero on the right then...great..the one i made ended up a bit butchered because of the ticking mods
i hate having to upset the pcb when its all been done neat and tidy!..lol...it works lovely though
its a nice chorus...well smooth...and clean...i was well surprised how good it is...

cheers adrian. rob.