neovibe quasi working build

[vince76]

it's night and I just finished working to my neovibe (thanks r.g. keen for your great article).
It has some minor problems but the sound is just the wonderful one I was looking for.
I would be glad if someone who already built this effect could give me some help...
I can hear a phasing noise probably due to the transformer A.C. ??
The volume control mutes the effect when it is at max and when it is at min and works as a volume control in the middle part. what I did wrong?
At last I don't know if the switch works well (can someone tell me how to test it?)

Thank you in advance,
Vincenzo.

[R.G.]

I can hear a phasing noise probably due to the transformer A.C. ??

Is the noise a phased hissing sound? Or a hum?

The volume control mutes the effect when it is at max and when it is at min and works as a volume control in the middle part. what I did wrong?

The two wires that go to the outside connections of the pot are reversed; change them round.

At last I don't know if the switch works well (can someone tell me how to test it?)

In one position there should be a phasing sound, in the other a pitch shift/vibrato.

[vince76]

wow... thanks  R.G. I'm very happy you answered to me.

I was not precise in definition... I think it's definitely hum coming from transformer. I tried to twist the AC wires.. nothing. I will put the trasformer in another box

I checked the wiring on the volume pot... they seem to follow the schem. I will try to reverse and post

The phasing sound is very good to my ears... in the opposite position I think it's not working (I hear a very very very light chorus effect, but it can be my imagination, think I wouldn't be able to say this if I did'n know there was that switch )


thank you again

[vince76]

Here again
I checked wirings and seems to be ok
I took some voltage measurement
in the attached image
in yellow the readings from the spec in the Keen's article
in red mine voltages are they a little high?  why I have an unstable reading?

to R.G.: what I wanted to say with:"The volume control mutes the effect when it is at max and when it is at min and works as a volume control in the middle part. what I did wrong?"
is:
the volume mutes the effect both at min and at max position...
Excuse for my english

Thank you for the help


P.S. I attach the image with correct voltages only, as desumed from the article, maybe it is useful to someone

[vince76]

anyone?

[vince76]

Hope someone's answer
I take a 12V and a 9V battery, wired in series and put DC directly in the Neovibe. In this way have no hum or noise.
The question is:
after cahnging two trasformers, put them in a box away from the effect box, what should I try to eliminate the hum?? I still want to use a trans to power the effect.

About the volume pot:
the volume mutes the effect both at min and at max position...
the wiring seems to be ok

Waiting hopefully,

Vincenzo

[vince76]

the phasing hum has gone with a laptop 19V adapter (isn't a switching power supply?)
still have the volume issue: there is a point when I turn up the volume where the sound become distort at first. Above that the effect mutes.
I take voltages around the transistors

Q1
E 1.18
C 2.29
B 0.95

Q2
E 1.71
C 4.94
B 2.3

Q3
E 4.31
C 12.25
B 4.94

Q4
E 4.94
C 16.7
B 4.75

Q5
E 4.33
C 12.44
B 4.89

Q6
E 4.89
C 16.95
B 4.77

Q7
E 4.34
C 12.53
B 4.91

Q8
E 4.97
C 16.94
B 4.82

Q9
E 4.38
C 12.44
B 4.96

Q10
E 6.19
C 16.87
B 6.02

Q11
E OSCILLATING
C 17.78
B 3.32

Q12
E OSCILLATING
C 17.78
B OSCILLATING

Q-LAMP
E 3.57
C 15.29
B 4.11

Q-RREG
E 16.78
C 17.78
B 0

I replaced 7815 believing it was strange to read 16.78V at the output... seems to have correctly soldered it. I checked schem and some pics from other post.

where am I wrong?

vincenzo

[R.G.]

What type number of transistors did you use?

Did you look up the pinout on a datasheet for that type?

[yeeshkul]

Q8
E 4.97
C 16.94
B 4.82

emmiter above the base ... i wouldn't exclude the same trouble i had - a cheap DMM with some low internal impedance.

[vince76]

thank you very much R.G.!
I used bc547c instead 2n3904. First time I put them reversed believing equivalent=same pinout. but they are CBE (flat side facing you) instead EBC.
when put them in the wrong side the effect didn't work at all.
today I will check color band of resistors on the board again hoping a wrong resistor!!???.
Reading posts on this forum I learned that emitter above the base is a bad thing because the transistor won't work, but I've read other Neovibe debugging pages where a working effect has some transistor with emitter above the base.... I can't understand when it is BAD.

yeeshkul:
Q8 is not the only one... I've
Q1,    Q4,    Q6,    Q8,    Q10.
Since I'm always happy when I can learn something... when E>B is BAD? are there cases in witch it's ok?

edit:
I think I found the answer on misbiasing here:
http://www.diystompboxes.com/smfforum/index.php?topic=56998.20
R.G. explains on measurement error

yeeshkul:
I read your posts before but I can't understand this:
"i wouldn't exclude the same trouble i had - a cheap DMM with some low internal impedance"

thank you guys.

[vince76]

though: may be the minimum or maximum resistance value of LDR off of spec create my volume issue?
I measured them when I put in and realized they were ok , but now I can't remember...

v.

[yeeshkul]

When you have a multimeter with a low internal impedance (Zi), this imedance adds itself in parallel to the impedance of the measured circuit(Zc). The result is a parallel combination od Zi and Zc. A total impedance (Zt) of the parallely connected impedances is (as always) smaller than the smaller of Zi, Zc values. Thus the DMM returns a false value because it considers a false impedance Zt = Zi || Zc instead of  Zc itself.
Cheap DMMs have about Zi~1Meg  while the better ones have Zi~10Meg.

In case of Neo, the measured voltages can get strange because of the impedance involved. I t happened to me and a few other people:). That's why you have emitter voltages above the base.

[R.G.]

I used bc547c instead 2n3904. First time I put them reversed believing equivalent=same pinout. but they are CBE (flat side facing you) instead EBC.
when put them in the wrong side the effect didn't work at all.

The reason I ask is that you have to get the right pins in the right holes by the function of the pin. The Neovibe is laid out for transistors which have the pinout EBC when the flat is facing you  and the pins are down. The BC547 is CBE, so it's backwards. Another reason I asked is that some transistors in that same package are ECB, and that trips up a lot of people.

Reading posts on this forum I learned that emitter above the base is a bad thing because the transistor won't work, but I've read other Neovibe debugging pages where a working effect has some transistor with emitter above the base.... I can't understand when it is BAD.

It's bad whenever it's real. The ones where something worked with the emitter higher than the base (on an NPN; PNPs are the opposites in terms of voltage polarity) are the ones where the measurements were incorrect because the meter could not read them correctly. If the voltages had been read by a perfect voltmeter that could measure very high impedances, they would have read correctly as yeeshkul points out.

There is a trick that can help here. If you measure with your black lead on the emitter and red lead on the base of each transistor, it should read the correct voltage. It's when it is from base to ground that it fools you in most  cases.

However, I'm beginning to think that you may have an oscillation problem. When the signal distorts and then quits entirely as you manipulate the volume control, there are two major possibilities - miswired volume control, and then oscillation when the volume control is turned up. The first one is usually easy to find. If you've checked the locations of every wire against the drawings, then that says probably not miswiring, although this is easy to miss for me at least. Oscillation in a Neovibe is rare (I've never seen a real one that I remember) which is why I didn't suggest it earlier. It's also the devil to root out unless it's some silly simple thing like a wrong component value or a part in the wrong place.

So there's a different set of questions to be answered.
1. Did you use perfboard, make your own PCB, or buy a PCB from someone else? (because it may be a PCB or board wiring problem)
2. Components C3, C4, and C26 are important for ensuring that this does not oscillate. Check those again and ensure that they are correct value, correctly installed, and so forth, especially C4.

[vince76]

Hey R.G.
you are always right!
It was a cap and it was the board I etched!
I understand it reading another post, another your post...
the cap was shorted because two traces were touching and this caused a pop in the bypass switch.
so I reached indirectly the solution. the volume is working now. the cap was C16.

Thank you all for the help the effect is simply wonderful.

vincenzo

[R.G.]

Hey, cool! You found it! Good work.