Tri-Vibe Help Needed, Please

[RickS]

Just built a Tri-vibe from Slacker's Veroboard layout.  First of all--credit where credit's due--ROG for the concept and design, and to Slacker for the Vero layout.  Thanks, guys, for sharing your knowledge and efforts.

I haven't installed the board and off-board components in a box yet, just wired it up on a chair and plugged it in to test--basically a "breadboard" setup, running on 9V battery putting out 9.64 volts.  Mostly, it works, but with a few bugs, and I could use some ideas if anybody can help:

1.) Getting a pretty strong "thump" that increases in rate with the rate pot, but goes away at lower levels of rate.  Assume it's LFO related, but I would not describe it as a "tick", nor the whoosh-whoosh somebody described earlier.   Would putting it into the (metal) box shield it and eliminate the thump?

2.) Both pots seem to have a lot of "wasted range" at both ends of the wiper travel.  I did use an A taper pot for the Rate pot, and reversed leads as described in ROG's build notes.  The 820K resistor stays the same, bridging #1 and 3 lugs on the pot, but does the jumper from lug 2 stay on lug 1, or go to lug 3 when the leads are reversed?  Could this be some (all!!) of my problem?  [ I do plan to eventually replace the Rate pot with the right one--a 500K C-taper, but from the build notes in ROG's article, I was expecting only reverse operation, and maybe some "bunching" up of the effect at one or the other end of the wiper travel--not a noise problem]

3.) I had to substitute 2 of the diodes, because I mis-ordered.  I used 2 1N914 diodes I had on hand to sub for the 1N4149's specified.  They seem to be indistinguishable, in fact, on line, the Fairchild data sheet is the same for both diodes, and I could find no mention of any significant difference.  But--obviously the guys at ROG know what they're doing, I only occasionally think I know what I'm doing. . . (and am often wrong)  Any chance this is my problem?

4.)  I ran out of caps and had to use a disc cap for one of the 4n7 caps.  I don't recall seeing any disc caps in anybody's build photos, and according to an article I read somewhere, disc caps can be microphonic.  Although I thumped the cap several times with a finger, it did not make any noise, or alter the thump-thump-thump which is what I would expect a microphonic component to do (like tubes in my amp when they get microphonic).  But again, any chance this is the problem?   Why don't builders use disk caps in stompbox or other audio circuits?

5.)  Is there anything about going from the two TL-062's to the single TL-064 that I should check that might be part of the problem?   (Other IC's used include NJM13600D and TL072, all from Small Bear)

I have not measured any voltages in the circuit, but can, if this would help someone point me in the right direction.

Thanks in advance for any help anyone can give me.  This is really exciting looking forward to my new, quiet Tri-Vibe.

[Scruffie]

Saw your recent post and searched your posts to find this...

1) LFO Click... The Metal Box may help yes, also short wires to pots (breadboards are noisey things) and make sure your electrolytics are the right value, installed the correct way. I think some people complained of this, Proper power filtering might help too (An Electrolytic of 100uF+ Value to ground from 9V plus a very small ceramic cap across 9V & Gnd in the pF range)

2) Seems to be a common issue with the pedal, don't know what you can do about it really, your parallel resistor should be across lugs 1 & 3, wire as normal otherwise, try upping the value from 820k to 1M though.

3) Same thing, no issue there.

4) Some people claim different caps make a difference, others don't, i'm in the against party for the most part and using a film cap isn't going to cure your problem, using a different value however... (Not sure which cap you refer to in the circuit, don't have the schematic to hand) Caps can vary greatly due to poor tollerances at 10% that 4.7n could be 470pF off in either direction, probably not going to be the source of your problems though.

5) Not that I know of... I suppose having it all on one chip might create cross talk or something... maybe a different Quad Opamp might help, might not, TL074 is meant to be lower noise but in these circumstances... doubt it'd change much.

Voltages always Help.

Sorry for the short and sweet answers, watching a film  also, not the most knowledgable person, i'm sure someone more knowledgable can come along to help out but I hope that helped a bit. 

[RickS]

Thanks for the response.  My build was based on Slacker's Veroboard layout, and although it did work, it was noisy, and not nearly as well as the various clips on the forum.  I looked and looked, but could not find what I'd done wrong.  I've abandoned the Vero layout, and decided to try ROG's posted perfboard layout, because it's the basic, source schematic and layout.  Appreciate the help.

Rick