Univibe Build

[Spencerleehorton]

Right some form of success today!!
I thought I’d check the R47 resistor to Q13 was a 4.7k rather than a 47k and it was 47k, replaced with 4.7k and now I get much more effect and unit sounds so much better.
Still not there yet as there is hum and when on vibrato mode it does seem louder than on chorus, I can live with that but the hum has to go?
No hum when I plug straight into the amp so leads are fine.
Hum there when in bypass and gets worse when effect on?

 

[Spencerleehorton]

Ah ok, well that shines a light on the power side of things, I’m using a 15v regulator at the moment so I’ll experiment with higher voltage, I’ve got some 18v regulators and some 24v

 

[Spencerleehorton]

I also don’t have the bias offset so I’ll look into that.
I also have some mumetal which I can use to make the light shield and see if that improves anything?

 

[Spencerleehorton]

Little video of where I’m at!!

 

[Spencerleehorton]

I suspect my noise problem is the transformer being too close to the pcb and parts, i will remove from inside and see how it sounds with the mains txf outside the enclosure.
or it could be that the mains txf isnt touching the case or its just too old and noisy?

 

[dai h.]

This (build info document) is from Bob Burt (Classic Amplification)'s site:

https://web.archive.org/web/20100923164409/http://classicamplification.net/Forumvibe/ForumVibe2.pdf

(hey a Roland Cube amp! Had one. Sounded pretty good hooked up to a friend's broken Mitchell (defunct Boogie copies maker) that had an EVM12L--its speaker that is)

 

[Spencerleehorton]

yeah i already had that link in this thread.

i also found this which has some great little bits in it

http://www.lynx.net/~jc/pedalsUnivibe.html

 

[CJ]

I had the fulltone dejavibe,it sounded great for about three years the something began to change. I think it must have been the cells,

 

[Spencerleehorton]

Well the hum is still there even when the univibe is not powered but fx is on?

So must be a wiring fault or a part failed?
I’ve moved txf as far away as I can in enclosure now.

Will test all voltages now, my B+ is 24v to LFO and 15v to transistors.
Will document all transistor voltages.

 

[InterstellarObscure]

i also found this which has some great little bits in it

Speaking of different Univibe bits, if it’s not too far off topic—have you ever come across a Univibe voltage control modification?

 

[Spencerleehorton]

No I haven’t? Is this something you know about?

 

[Spencerleehorton]

well the hum is still there and im pretty sure its my power setup which is at fault.
ive got a 3 way wall plug wired to the DPDT power switch, then from there to the mains transformer.
if the gnd on the 3 way plug is attached to the case the hum goes but when i then plug into the wall the hum comes back!!
the 24v transformer is fairly old so could be at fault, i do have another transformer which i can try and see if the problem remains once ive changed the transformer?

 

[volker]

Speaking of different Univibe bits, if it’s not too far off topic—have you ever come across a Univibe voltage control modification?

Make the dual-pot a dual-optocoupler and control the LED current.

 

[Spencerleehorton]

just want to stay on point with original univibe, parts and setup for a close as possible to Jimi sound.

 

[Spencerleehorton]

here is my first pcb with labels.
ive done the bias bulb mod and works fine.
Just need to check all components tomorrow.
Im using a dual 100k pot for speed so i can take out those 300k resistors (anything that is * is not staying in)


this is the new pcb which I will test as soon as the other parts arrive.

 

[Spencerleehorton]

shouldnt really need to put this but im having strange hum problems?, using a roland cube amp and pluggin this univibe in to test it, when i plug in the power lead into the same 4 way as the amp is plugged into i get loads of hum?
this is even without the univibe turn on?
ive changed transformers thinking it could be this old transformer? but it does exactly the same on another transformer so it cant be that?
ive even disconnected the secondary frm the univibe to see if its something the univibe side but it still hums?
its going to be something silly i just know it!!!????

 

[Spencerleehorton]

on the Vibe A pcb, when i test voltages with MM on gnd and red tip touches the 15v rail the hum goes away?

 

[peterc]

Sounds like a missing ground? Have you tried a mains transformer with a centre tapped secondary ? Then connect the CT to earth.
Good luck

 

[Spencerleehorton]

yeah sounds like a missing gnd to me as well, or transformer interference within the audio signal, ive managed to get it much quieter now but its still there?
i suppose i could do the two 100R resistor trick to put in a GND, will see if that makes any difference.
building up the Shin Ei version now so will test this and see if this hums as well!!!

 

[Spencerleehorton]

On vibe A I changed the 15v regulator and it took the high pitched buzz off, now left with just a little bit of what sounds like mains hum.
Will try some 100R resistors on secondary to get artificial centre tap and see if that takes the other hum away.