Onboard tremelo

[lowell]

Anyone know where to get a schematic for a harmony Vibrajet tremelo? If not, know of any kits that can be put in a guitar?

[Mark Hammer]

Yikes!! Vibrajet H66 guitar - made by Harmony

Why exactly do you want to do this? Are you restoring one, or is it simply a matter of funkiness/coolness?

In any event, there's this one: Onboard True Optical Analog Tremolo Modboard- Complete Kit!

[lowell]

the guitar comes stock w/ tremelo. it's not working and I drew my own schematic but couldn't figure out why it didn't work. customer wants it fixed or something else installed in its place.

[Mark Hammer]

The picture of the Vibrajet guts suggests the circuit is kind of big and cumbersome for an onboard. If there is no real requirement for historical authenticity, then the GFS modboard strikes me as a reasonable sub. Certainly it will weigh a lot less than the original, and will be easily powered by an onboard 9v, which is a lot safer than the original.

[JHow]

Mark Hammer: What was unsafe about the original circuit? The link you posted above says the orginal was powered by 1.5 V battery. I'm just curious. I didn't see the schematic so I don't have a clear idea of how this works.

[Mark Hammer]

My apology/bad. I posted the link in a hurry, primarily for the pix and did not read the accompanying text. What I saw looked like it would have been powered externally. I may have mistaken the battery socket for a tube shield, and seeing the onboard transformer jumped prematurely to some unwarranted conclusions.

So, we'll rule out safety but the weight aspect is still probably something worth considering.

[JHow]

There are not a lot of components in the picture. You might be able to construct a schematic on pencil and paper. If those are small-value electrolytics I might try to replace that real quick and see if it fires up. Often works for transistor radios.

[lowell]

already tried that Jhow. I also measured DC resistance of the transformer/choke or whatever it is as well as all resistors and even the transistor etc...

[JHow]

When it did work, did you have to switch it to the "battery on" position and play the guitar a bit to get it to start oscillating and then put on the tremelo?

[lowell]

It never worked unfortunately.

[Remus103]

I'm about 6 years late to the ballgame here but Lowell do you still have the schematic drawing that you made?

[52 Bill]

I fixed one of these a few years ago, and I thought that I had found a schematic somewhere online. I just searched, but couldn't find it. I may have drawn one or printed one out, so I'll check my files.

[Remus103]

The only helpful pictures I've found over time are here http://music-electronics-forum.com/t33856/ on this forum. It looks pretty sound but I'm trying to cross check everything in the pictures. I still don't know the value of the transformer. And I'm not sure of the diode coming from the input. And in the picture of the guts I don't know what the component is between the transformer and dwell pot that is an oblong oval with a black border/white center, must be the 10 uf cap, or the component between both pots that is a copper circle with the wire in the center of it. I would guess the circle is the transistor but I can't see any other leads on it, and it would be an odd looking transformer. Also the switch has a "battery off", "battery on" and "tremolo on". What would be the reasoning for having 3 instead of "battery off" and "battery and tremolo on"? Help with any of these would be greatly appreciated. Thanks.

[52 Bill]

That's the schematic that I had seen before. It's gone from the Harmony database site.

And in the picture of the guts I don't know what the component is between the transformer and dwell pot that is an oblong oval with a black border/white center, must be the 10 uf cap, or the component between both pots that is a copper circle with the wire in the center of it. I would guess the circle is the transistor but I can't see any other leads on it, and it would be an odd looking transformer. Also the switch has a "battery off", "battery on" and "tremolo on". What would be the reasoning for having 3 instead of "battery off" and "battery and tremolo on"?

The oblong oval is the transistor, the copper circle is the end view of an electrolytic capacitor. The transformer is actually a choke or a coil that is being used as the emitter load for the transistor.

The three position switch is so that the circuit is in a standby mode with the battery on. When the circuit is first powered up, it might take a few seconds for the oscillator to get up to speed and for the circuit to stabilize. So by having a battery on mode, the circuit is ready to go as soon as it is turned to the on position.

[Remus103]

Wow, thanks so much for the help. I didn't get it from the Harmony database so it's nice to know its validity. The switch makes sense and thanks for the component clarification. The coil then is just a single coil transformer to add a large quantity of resistance?