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Old 7th August 2004, 08:57 PM   #1
nordine is offline nordine  Chile
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Join Date: Aug 2004
Location: antofagasta
Default help with this Vibrato Circuit

hi all,

well i'm a begginer in electronics, so i'd like to know some stuff that must be basic, but it's been bugging me a lot last days

there's this Vibrato Circuit i found:

Click the image to open in full size.


i had some doubts, but i assembled it anyways
...

it didn't work, not even a slight scratch or noise, or humming, nothing, its dead

now, this was my "doubt" before trying to build it:

is that OUT line correctly placed along the IN line???
i mean... for an audio circuit, where a signal is supposedly filtered and messed up and stuff... can the output signal be contiguous -in the circuit- to the In line??

in the website ( http://www.lh-electric.4t.com/projects/t_circ.htm )the author states that any general purpose PNP or NPN transistor should work

i used two 2N3904

are the transistors the problem?
is this circuit?

what is it??

thanks
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Old 8th August 2004, 06:37 AM   #2
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Join Date: Jul 2003
Location: Newcastle, Australia
Then second transistor is drawn upside down - the emitter should be connected to ground.

Circuit is actually tremolo, not vibrato. It should modulate the volume level of the signal going through it.

The connections are correct. The first transistor forms a low frequency oscillator with P1 being the "rate" control. This is fed to P2 ("depth" control). The second transistor in conjunction with the 100k and 39k forms a variable voltage divider.

Cheers
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Old 8th August 2004, 07:25 AM   #3
Nasse is offline Nasse  Finland
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Just a quess but I would try higher hfe transistor for the oscillator.

And when it starts to work, you´ll get ticking and thumping in your speakers (there are nicer treomolo circuits around...)
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Old 8th August 2004, 11:34 AM   #4
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I simulated it in spice and should work.. The first transistor is indeed the oscilator and it should not be loaded too much, so a 100K resistor in series with its output before the 47nF cap should ensure that....

The seconmd transistor is not drawn wrong.. it actually doesn't matter how it is connectec......it works both ways..

If the circuit doesn't work.. try to find out which parts doesn't work..disconnect the two transistors at the 500K pot... check if the first transistor is indeed oscilatting at around 8Hz (P1 in the middle) ... and check if sound if coming through if you connect input and output... then come back here again...

goodluck,
Thijs
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Old 8th August 2004, 12:15 PM   #5
nordine is offline nordine  Chile
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Join Date: Aug 2004
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Default whoa

can't believe it..

i've been asking people out w/ this all last week and no one replies or advices something clear enough to try it

then i come here and voilá... lots of replies, and lots of things to try and do

thank you guys for being kind, helpful and nice

should be back soon with what i got


see you,
and thanks!
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Old 8th August 2004, 01:29 PM   #6
nordine is offline nordine  Chile
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by the way ( before attempting any changes)...

now that i think about it, capacitors have voltage settings. i didn't mind this, but now... seeing a simulation worked and my circuit didn't, i'll list caps used and their specs, to know if they are the problem

C1: 47n - 473J, 100v
C2: 4.7u polar - 50v
C3: 1uF - 160v
C4: 0.68uF - (this one is special... the guy at the store didn't have .68, so he gave me 2 caps that put in paralell give .69) 2A224K and 474J


..about doing this schematic and not some other smoother effects.. ..i did choose this one because it seemed very simple ( and inexpensive.... well, and because i found all parts in the same store..... which is the best i can get here in Antofagasta)
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Old 8th August 2004, 08:08 PM   #7
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The capacitors voltage values are just fine.. go ahead and build it.. I'm gonna build one too tommorow, just for fun.. I play a little guitar and build several distortion effects allready, yet I would like a tremelo effect.. so why not.. I just decided to try your circuit....It really should work,


Thijs
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Old 8th August 2004, 08:18 PM   #8
nordine is offline nordine  Chile
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Join Date: Aug 2004
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yeah, i'll rebuild it from scratch... i must have fried a transistor or something in the process

i'm doing it for my CT-350 ( casio keyboard)... the jazz organ preset just cries for tremolo... despite the noises it'll probably do while i'm not doing anything w/ the keyb', that'll sure add some "vintage" cheesyness to the already cheesee casio
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Old 10th August 2004, 05:39 PM   #9
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Hi again,


So I build it.. slightly modified to run of a 9volt battery and PNP transistors only.. I didn't had any NPN anymore.... on my osciloscope it looks pretty good, but the sound is a bit too drastic ON/OFF ... not very liquid... and I had to use a Proco RAT distorion pedqal as a buffer.. using it dry resulted in a muffled sound with little treble... but it does work.. instantly.. ... and it does a good job for just a handful (actually less) on parts that can be found on my floor...

goodluck,
Thijs
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Old 14th August 2004, 05:25 PM   #10
nordine is offline nordine  Chile
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Join Date: Aug 2004
Location: antofagasta
no luck here...

installed it in a protoboard ( so i can change components whenever i detect an error), used fresh components, checked every res, cap, everything.... and nothing

i'm feeding it w/ 12Volts... would that be the problem?

thats the max voltage i can feed it with, however..... is there a simple mod that could allow me feed it w/9V?? ( and still be using the 3904's)


thanks
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