Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Effects => Topic started by: dpm309 on December 11, 2011, 11:40:57 am
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I have an old vintage Univibe on my bench that seems to be bleeding all of the treble off in the chorus position and am getting no effect at all on the vibrato setting. A quick look at the board, connections etc. did not reveal anything out of the ordinary. I have the schematic and will start looking at the components. This thing has 13 transistors, a flashing lamp, and 4 photo-resistors. Has anyone ever worked on one of these? I have attached the schematic for reference.
Thanks,
Dan
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The circuit is dark sounding. RG Keen already has a great page about it. All you could want to know about the Univibe. http://geofex.com/Article_Folders/univibe/uvfrindx.htm (http://geofex.com/Article_Folders/univibe/uvfrindx.htm)
SLW
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SLW,
Thanks for the reply. I have already read the article but have not been able to get the vibrato working properly. When I have the unit on the vibrato setting, I do get some effect if I move the expression pedal back and forth. I don't think this is the way it is supposed to work. Checked voltages and component values and everything seems in line. I opened up thphoto resistoror box and the bulb is flashing. I also checked all of the connections and had to re-solder one of the connections to the input jacks. You are correct about the dark sounding circuit. It appears that the univibe clones have addressed the issues of a true bypass and the treble bleed problem.
Dan
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Do you get the effect when in in "chorus" mode? When in in vibrato mode you should get a pulsating effect. Chorus mode should give you that swirling sound the Univibe is known for. If you get the effect in chorus mode but not in vibrato mode I would look at the output mixer portion of the circuit as well as the switch.
SLW