Neovibe built, speed and depth pot trouble

[Alex C]

Hello there, I just finished my Neovibe, and to my amazement, it fired up first time!  I have come to expect the worst when testing my builds, but this time it worked!
...but not perfectly.  Here are some of my problems:
1) A loud hum is present regardless of settings.  This is not present when the effect is bypassed (I used true bypass).  I used an 18vac wall wart adaptor from Mouser, and I suspect that this may be the problem.
2) The speed pot is effective only in the extreme end of its rotation, where it is fastest.  I would say the first 4/5 of rotation does nothing.  I searched and found a posting by Tychobrahe1979, who says:

1. Wire the speed control according to the schematic not the parts layout. Otherwise your speed control will be more like an on/off.

I just searched more and someone said to switch pads C and E.  I'm off to try that right now.
3) The depth pot has a similar problem, not affecting anything until about halfway. There has been no mention of this having mislabeled wiring.

Both pots have been triple and quadruple-checked for correct wiring (according to parts layout), all parts are as specified in the parts list, and I have experimented with the idle bias trimpot extensively, and I can't figure out what's wrong.  I have looked at the lamp while adjusting the speed and depth settings, but the pulsing and intensity of the light just matches what I was hearing.  
I guess my next step is to test the voltages that are included in the schematic, and other basic debugging steps.  I was wondering if these are common problems or if anyone has had this problem before.  

Alex

[Jim Jones]

Hi Alex,

Can't help you with the Depth pot, but the Speed pot is drawn incorrectly on the layout diagram - the schematic is correct.

Jim

[Alex C]

Well hello again, I have fiddled with lots of things, and here's what I came up with:

1) The horrible hum is coming from the wall wart.  I wired up two 9v batteries in series just to test, and the sound is clear and pure.  Excellent! Someone had mentioned an 18V adaptor that Dunlop makes, I'll check that out.

2) The speed pot has been corrected.  It works fine now.  I'm planning on doing the mod suggested by others to increase the maximum speed (changing R42 and R43(both 4.7k) to 2.4k.  Others have reported good results with this.  

3) I "fixed" the depth pot- after all my double and triple-checking I was still wrong.  

I also plan to replace R35 and R36 with a trimpot.

So I have answered my own questions (but thanks for your help Jim) and I could have done all of this without posting, just searching.  Sorry.  Maybe someone can read this in the future and correct/avoid their own problems.  

Alex

[Yazoo]

I'd be grateful if you could spell out the pin wiring for the speed pot. I'm not sure which pin is 3 and which pin is 1 in the schematic.

Thanks in advance.

[smallbearelec]

At the time that R. G. Keen designed the Neo, a 100K dual reverse-audio taper pot was not available to DIYers. If you would like one (which will put the slow speed at the counter-clockwise end where you would expect it), please see my stock list. And, congrtaulations on your build!

Regards
Steve Daniels
smallbearelec.com

[Yazoo]

I've just replaced my speed pot with a reverse-audio taper pot from Small Bear, and it did the trick. I now get control over the whole range of the pot, instead of just the top quarter/fifth when a non-reverse pot was fitted.

[RedHouse]

Someone needs to correct that dang PDF once and for all.

The grief over that wiring error (speed pot) just seems to go on, and on, and on....

ad nausium, ad infinitum

[R.G.]

It does indeed go on and on and on and on...

I dug out my original docos on that. Had to go to a three-year old backup to find them... 

I've corrected the schemo, and I'll try to get Mr. Sleep to replace his copy of the article. I can replace mine on GEO, but I suspect that many people get it through General Guitar Gadgets.

Interestingly, I think that even if Jerry and I replace them, it won't stop the problems. My stuff gets cold-copied into disks and web sites all over the net and resurfaces in the old way all the time. The old ones never die. But we can make it better for the folks that read GEO and the fora here.

[RedHouse]

Always the gent, thanks RG.

BTW can you link us to your updated doc?
(I searched geofex and did not find it)

[Aharon]

I could not find it either.
Aharon

[Aharon]

The 2n2222 seems to have a max limit collector current of 1A,why isn't it more popular for the Univibe?
Aharon
http://www.fairchildsemi.com/ds/2N/2N3904.pdf
http://www.fairchildsemi.com/ds/PN/PN2222A.pdf

[DEZREJECT]

can you post pics of your board? id like to see the light section.. some mp3s wouldnt be too bad... you guys just wait til i get building pedals again... i sold most mine... u guys will drown in pantera covers with crazy effects lol and howd the build go..? anything that was troubling besides what you posted here?  the best feeling in the world is to turn it on and hear it work... id like to build a neovibe... maybe with a foot controler and such like the original.. but i have enough light controlled audio circuit hell to worry about with the super duper all in one wah im working on... so it throws me off a lil but it seems liek an amazing lil pedal... besides jimi liked it right?


whats your opinion between the neovibe and say a rotovibe style pedal? can yo uget that swooshing leslie around the room sound just as good wth ur pedal?

[R.G.]

I'll get the revision posted as soon as I can.

The 2222 has a max current of 1A, but its gain peaks at about 100. Mostly it's a lower gain device. It's probably good as the second stage of a darlington.

I can hear the gears turning in you low-gain silicon hunters... yes, good device to check out.

[RedHouse]

So while I'm waiting, I took the PDF from GGG and modified page 6 and 7, I corrected the pot wiring and also cleaned up the PCB traces while I was there.

RG, Is there any way I could send it to you for review (appoval/disapproval)?

[R.G.]

Sure you can. Send me PM.

[RedHouse]

PM'd ya ...awaiting a response

[Aharon]

BUMP

[R.G.]

I have an update to my artwork I'll try to get posted tonight.

Bump.

[Aharon]

Great RG.I wasn't trying to rush you I just wanted to keep the thread alive for updates.
Thanks
Aharon

[Aharon]

BUMP