Uni Vibe Clone Noise problem

[davidhaus]

Hello,

i finished building my Uni Vibe Clone called "Forum Vibe FV5 REV5"

Project documentation files:


http://www.classicamplification.net/fv/files/fv5_vint2n_02.htm
http://www.classicamplification.net/fv/files/fv5_vint2n_03.htm
http://diy.musikding.de/downloads/forvibevint_en.pdf
http://diy.musikding.de/downloads/wire_04.jpg
http://basicaudio.net/univibe-ForumVibe-final.pdf

Problems:

1) There is noise. It disappears when i touch C1. How can i fix this? I can't touch it all the time obviously 
2) When i turn down the speed, the LFO LED is contantly light up instead of just lighting up slowly matched to the set speed.
When i turn up the speed it works though, it does light up machted to the speed then.
3) The effect in slow speeds isn't really noticable. I pretty much cant hear the throb anymore in very slow speeds.

Changes i did:

1) I removed/shorted R47, the one in front of the Trimpot. I did this because the light bulb wasnt bright enough to get the throb even when i turned the trimpot all the way down.
2) I am using a 18V DC power supply, therefore i removed the bridge rectifier. (the noise isnt coming from the power supply, i tested with 2x9V batteries in series - same issue)
3) One leg of the LFO LED broke, so i changed the LED. i measured both types. Original: 1,82V C=9pF   New: Uf = 1,85V C=4pF so pretty much the same.
4) C14 is supposed to be a 470pF Capacitor, in the kit i got one with roughly double of that value though.

List with Transistor values is attached

[davidhaus]

I soldered a 47pF Capacitor between C1 and Earth to simulate me touching the Capacitor.
It worked, the noise is gone

The other two problems still remain though.
My Transistor values differ a little bit from the recommended ones.
How can i bias them without having trimpots? Should i use parallel resistors to increase voltages?
I have no experience in doing that. What would you recommend me to do?
By the way, sorry for my poor english, its not my first language.
Cheers!

[ElectricDruid]

Did you use an LED instead of a bulb? I can't see an LED on any of the schematics.

If you did, that's probably the source of several of the problems. An LED will behave very differently from a lightbulb, and the circuit was designed for a bulb.

HTH,
Tom

[davidhaus]

For the actual effect i have a light bulb built in just like in the original schematics. But the kit i used has a few changes to the original like for example an additional LFO Led to show the speed. You can see it here:

http://diy.musikding.de/downloads/wire_04.jpg

[Icescreamer]

I soldered a 47pF Capacitor between C1 and Earth to simulate me touching the Capacitor.
It worked, the noise is gone

The other two problems still remain though.
My Transistor values differ a little bit from the recommended ones.
How can i bias them without having trimpots? Should i use parallel resistors to increase voltages?
I have no experience in doing that. What would you recommend me to do?
By the way, sorry for my poor english, its not my first language.
Cheers!

Sorry for reviving an old thread. But my problems are so much similar to to this post that it would be weird to start a new thread. Not in the last place because the solution is already mentioned in this post.

I also had a hissing noise in my forum vibe FV-5.
I also got rid of R47.
My voltage readings are very similar (a little low compared to others).
The noise persists when using batteries.
The noise issue is fixed when either touching C1 ( which is a film cap in my case, so I am not even touching it on a conductive surface)
And most important: The problem is fixed when attaching a 47pf cap from c1 - to ground.

However I'd like to learn something from this.

Why does this cap solve my noise isue. Is this a good solution, or does it just obscure another underlying problem?

Some explanations are appreciated.

Here is a link to the documentation.

https://www.classicamplification.net/fv/

Edit: Added a link to the documentation

[willienillie]

I just built this back in January.  I didn't experience any noise problems.  I did use a metal can transistor for Q1 like the originals, maybe that helped?  Probably not.

Unrelated to your noise issue, there is an error on the layout, R48 and R49 are reversed.  This error is carried over to the 100k trimmer version of the "bias offset" mod.  If you use JC's original mod with a 250k trimmer instead, though, it becomes irrelevant.