Problem with 1965 Vox Continental

[jakobsongs]

Hello there, not sure if anyone here can give me some advice or tips, I am trying to put the wiring back as it should be,
it had been messed about with years ago where someone added a bass circuit. this has now been removed.
I have just got hold of a schematic but my electronics knowledge is quite basic, I have put the connections back as they look, but I think i've misread something somewhere as the organ is making a noise as though all the keys are being depressed.
If anybody has any photos of their Vox Continental V301J preamp and drawbar connections it would be brilliant.
Thanks in anticipation.

[52 Bill]

If anybody has any photos of their Vox Continental V301J preamp and drawbar connections it would be brilliant.

The Vox Showroom site has lots of photos of the internals of this organ, have you looked there?

I own an V301H so I can't directly help you with photos, but let me know if there is anything I can assist with.

[jakobsongs]

The Vox Showroom site has lots of photos of the internals of this organ, have you looked there?

I own an V301H so I can't directly help you with photos, but let me know if there is anything I can assist with.

Thanks Bill, I have looked at The Vox Showroom, there are some great pictures, but unfortunately the only one I can see of the preamp circuit is not very clear, and the connections on the bottom of the board are not visable, does anyone know if there is such a thing as a layout diagram available for the preamp board?

[Tom Phillips]

Thanks Bill, I have looked at The Vox Showroom, there are some great pictures, but unfortunately the only one I can see of the pre-amp circuit is not very clear, and the connections on the bottom of the board are not visable, does anyone know if there is such a thing as a layout diagram available for the preamp board?

I have some original V301J service information. It was published by the Thomas Organ company ~1967 and is a mix of poor quality copies of Jennings Musical Industries schematics and a nice clear Thomas drawing number 38-5495-0. That drawing is an 11" x 35" fold out that includes a combination of block diagrams and schematics of the power supply, Tone generators, pre-amp and vibrato unit. Does that description match the schematic that you have? The one you mentioned in Post #1? The one I have shows a ten terminal connector on the pre-amp board and 7 of the 10 are used. Between the block diagram section and the pre-amp schematic section there seems to be enough information to cover the connections for the 7 terminals used including wire colors.

Let me know if the 38-5495-0 drawing I described would be useful to you and, if so, I figure out a way to post a copy. (Maybe in two or three parts)
Tom

[jakobsongs]

I have some original V301J service information. It was published by the Thomas Organ company ~1967 and is a mix of poor quality copies of Jennings Musical Industries schematics and a nice clear Thomas drawing number 38-5495-0. That drawing is an 11" x 35" fold out that includes a combination of block diagrams and schematics of the power supply, Tone generators, pre-amp and vibrato unit. Does that description match the schematic that you have? The one you mentioned in Post #1? The one I have shows a ten terminal connector on the pre-amp board and 7 of the 10 are used. Between the block diagram section and the pre-amp schematic section there seems to be enough information to cover the connections for the 7 terminals used including wire colors.

Let me know if the 38-5495-0 drawing I described would be useful to you and, if so, I figure out a way to post a copy. (Maybe in two or three parts)
Tom

Hi Tom, I have seen a copy of the drawing you're referring to, the model I have does not have a terminal connector, just point to point wiring, with components mounted on a tag board, I also can't rely too much on wire colours as I think they have been messed around with in the past.
Many thanks for the offer though, I shall keep searching.

[Tom Phillips]

OK. But note that the drawing just really just shows "connections." I don't know if they are connectors, terminals or wires soldered to the PCB.

[52 Bill]

...the model I have does not have a terminal connector, just point to point wiring, with components mounted on a tag board...

The photo at the North Coast Vox Showroom shows the preamp tag board with the two transistors coming off the top of the board and a trim pot on the right side of the board (looking from the back of the organ). Is this what you have?

The preamp consists of two transistor stages, one that connects the output from the footage drawbars to the tone section. This is on the left side of the board. The second stage connects the output from the two mixture drawbars to the organ output via the volume control. This is on the right side of the board.

If you have a constant output from the organ, then perhaps you have the two stages mixed up.

You could post a photo of your board and we may be able to help you that way.

[jakobsongs]

The photo at the North Coast Vox Showroom shows the preamp tag board with the two transistors coming off the top of the board and a trim pot on the right side of the board (looking from the back of the organ). Is this what you have?

The preamp consists of two transistor stages, one that connects the output from the footage drawbars to the tone section. This is on the left side of the board. The second stage connects the output from the two mixture drawbars to the organ output via the volume control. This is on the right side of the board.

If you have a constant output from the organ, then perhaps you have the two stages mixed up.

You could post a photo of your board and we may be able to help you that way.

Hi, thanks everyone for your advice so far, yes Bill my preamp is the same as the North Coast photo, I will arrange to post some photos later today, thanks for your patience as I'm very slow at reading schematics.

[jakobsongs]

Hi, thanks everyone for your advice so far, yes Bill my preamp is the same as the North Coast photo, I will arrange to post some photos later today, thanks for your patience as I'm very slow at reading schematics.

Here's the pictures.

[52 Bill]

The first thing that I can see is that you have the input and output of the first preamp stage reversed. The cap at the far left side of the board is the input the third electrolytic cap is the output. The wire that connects to the 5K6 end of the footage drawbars should go to the input and the output from the stage should go to the 5K6 end of the mix drawbars.

The two wipers from the mix drawbars should connect to the two tone filter circuits that are between the drawbars and the preamp board. I can't tell from your photo if this is correct or not.

The output from the tone networks should then connect to the 2nd preamp stage whose input is the next cap over on the tag board. It looks like there is nothing connected to that terminal other than a short cut off black wire.

The output of the 2nd stage then goes to the volume control. It looks like a red wire may be the output going to the control.

[jakobsongs]

Brilliant stuff, cheers Bill! I will work my way through your info and report back, I can't thank you enough for your help.

[jakobsongs]

Right, thanks to Bill's help I now feel I'm getting somewhere, I am getting notes sounding loud and clear, but only the first 18 up to and including the 2nd F, the rest of the notes can be heard very faintly, has anyone any ideas where I should look to resolve this? Thanks again in advance.

[52 Bill]

...but only the first 18 up to and including the 2nd F, the rest of the notes can be heard very faintly...

So the first 18 means the leftmost lower octave keys?

On the keys that do work, are you getting all of the different voices on each note (4-8-16)?

If the leftmost keys are working fine, and the upper end of the keyboard is dead, then look to see if the bussbars for the upper octaves have been disconnected. On some of these, the bussbars only cover sections of the keyboard and are wired together to form longer keyboards.

[jakobsongs]

Thanks Bill, you're an absolute star! It's pretty much sorted now, the only issue I have is the D# tone generator, but I think it's probably just a dry joint or the bias pot may need replacing, you've really made my day, thanks again.

[52 Bill]

Thanks Bill, you're an absolute star! It's pretty much sorted now, the only issue I have is the D# tone generator, but I think it's probably just a dry joint or the bias pot may need replacing, you've really made my day, thanks again.

Glad I could help you out. I like to hear that another one has been saved.

I do have a question for you. In one of your photos, it looks like there is an added drawbar loaded with 10K resistors. Is this so, and what was it supposed to do?