Old Vox 1900 phaser (not original but I 'fixed' and having problems)

[jable1066]

Hi there - Just fixed an old vox 1900 phaser with a new switch. Previously it didn't work at all, no LED etc then I installed a new DPDT switch and it works like a charm... HOWEVER, when I put it in the effects chain with other pedals the thing just doesn't work at all. No sound when the pedal is engaged. It's running off the same power supply, it is 9v and negative ground just like my other pedals. I know how to debug but I've no idea why this would happen...

[jable1066]

SO I have the schematic here... I just can't get my head around the wiring. There is a really peculiar looking output jack - it has loads of connections. Like... 8 solder tags but in a standard closed chassis config. The wiring of the footswitch does not follow anything I've ever seen before. There seems to be wires coming off the board that are... input, output, ground, 9v, LED positive and then one more strange wire that's attached to the output jack and then footswitch. I'm still not sure why it won't play with other pedals - I may have to look at the grounding on this and just play around and see what works over the weekend. Because I can't read schems it's quite hard to know what that extra blue wire going from board to output jack is doing. If anyone could help with layouts on how it should look from the schem - I mean the footswitch and jack wiring then I'd be very greatful. Pics are coming - I just need to wait till the weekend to find time and steal my lass's camera!

[jable1066]

Forgot the schem link...

http://www.voxamps.com/downloads/circuits/1900phas.jpg

This is how I assume I'll be wiring the footswitch - it's a dpdt with an LED... http://www.generalguitargadgets.com/diagrams/switch_lo_dpdt_led_in.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

[DougH]

It would help to see a print that didn't look like it was dragged through the mud, however-

That doesn't look like a DPDT switch to me. It appears to be 4 switches ganged together- a 4P4T?

What kind of switch did you pull out of it when you replaced it?

[jable1066]

Yeah, it's the only available schematic unfortunately. If needs be I'll redraw the shematic and upload it, but I'm hoping when I have pictures it'll make things more clear. I pulled a DPDT from the pedal - other gut shots I've seen from the same series use a DPDT. It's really the output jack that's confusing me, I'll upload detailed pictures when I get the camera. Coming out from the board there is more than 9v, input, output, LED, ground and pots. It's one wire going to the output jack - I tried removing it but no love. I understand it'll be hard to help without pictures so that is my priority for the weekend to get some. I'll also do a drawing of the wiring layout and upload that because that should help too. Thanks for the reply.

[Rob Strand]

I think your problem is that effect needs an 18V DC supply, not a 9V.

You are probably using an unregulated 9V supply which is putting out about 11 to 12V, the Vox unit is just able to work.
When you put the other effects in it loads the power down and the DC rail drops, then the Vox unit doesn't work.

I have a redrawn schematic (traced independently) As far as I remember it agrees with the manufacturers schem, except that
there was no Zener diode in series with the LED on my early unit.

[jable1066]

Thanks for the reply - that is curious indeed! On the unit it says that it's 9v and from what I can see on the schem, towards the bottom right it looks like it says 9v too. I will however, try 18v if you think that is the correct voltage it should be working at. There are also one or two 16v capacitors in there too. If it is an 18v circuit, would these things not... fry or something. Hmmmm.

[Rob Strand]

NOOOOO!!! If it's says 9V don't plug in 18V.   

I've screw up my 18V Vox unit was a Flanger.

Perhaps a better plan is to try:
- first separate power supplies (9V and )
- then a single power supply (9V) but measure the voltage when working and not working.
  The effect could be as I mentioned.

[zombiwoof]

I saw a couple of pedals from that series on Ebay, one was a distortion that used a 9 volt supply, the other was a flanger that took 18 volts (18 volt supply or two 9 volt batteries).  I would guess if the battery compartment only has room for one 9 volt then your pedal is meant to take a 9 volt supply.

Al

[jable1066]

Thanks for the replies guys - I'm still having no luck with this however I have made a discovery... And somebody above touched upon this about having 2 switches ganged together. The output jack actualy has enclosed, 2 SPDT switches. Like this http://www.musikding.de/product_info.php/info/p1143_6-3mm-Stereo-jack-isolated-with-2-SPDT-switches.html. Now... what on earth is this switching!!!! I will post my pictures up later on to try and keep this thread alive and remotely interesting!

Thanks again for your replies.

Jonny!

[jable1066]

http://s867.photobucket.com/albums/ab236/jable1066/Vox%20Phaser%201900/

I thought it would be easier to post a link to my album because there was 14 photos - uploading these would be a bit of a pain but if for any reason anybody wants them uploading, I will do so!

Now... I hope they are clear enough - bear in mind the jack on the right hand side is the output jack which I've established acts as a switch of some sort - 2 SPST or DTs like in the link above maybe? I will describe where the connections from the jack are going anyways...

Looking at the picture we have starting from the far left - which would be the side of the jack - a green wire which runs to the DPDT switch. Then on the bottom row of lugs, from left to right we have a RED wire coming form the DC jack - a RED wire going to battery snap. Looking from left to right on the top row there is nothing on lug 1. Lug 2 has 2 black wires which I assume are ground connections. Third lug - this is the confusing part, which differs to most circuits I've built. There are 2 blue wires. One of these wires goes to the board and one goes to the switch. There are more grounds to be found at the top of this jack also.

http://i867.photobucket.com/albums/ab236/jable1066/Vox%20Phaser%201900/DSC_0691.jpg

Looking at this photo, from what I can gather from the schem - one red wire on the board is LED, the orange wire is 9v, white and yellow wires belong to a potentiometer; the white wire runs to a cap which is attached to lug 3 of the pot and then goes to switch, black is ground, green is circuit INPUT, grey is circuit OUTPUT (this is found at the bottom of the circuit board, obscured by the orange wire, but just beneath). Oh and brown wire appears to be from the pot lug, as does the grey wire to the left.

I will take another look at the schem and pedal to try and work more out but maybe somebody could enlighten me on the switch/jack sittuation.

Thanks, Jonny.

[Rob Strand]

I know you tried hard but there is too many connection and wires to get the message across.

I can tell you what the original circuit does and hopefully you can piece the puzzle together with the unit in front of you.

The first thing that is different on that unit is the battery power is switched by two separate switch contacts on the output jack.
Both the positive (red) and negative (black) wires are switched.

- The battery positive runs through the DC jack then through a switch contact on the output socket; that's the upper contact on the schematic.
  The switched side of the output socket switch then runs to PCB connection point 7 on the schematic - positive supply.
- The battery negative (and DC jack negative) runs through a switch contact on the output socket; that's the lower contact on the schematic.
  The switched side of the output socket switch then runs to PCB connection point 5 on the schematic - negative supply/ground.

I would check both switches are working because these can fail.

I suspect most of the wiring matches the schematic but I can't work out what color is what, I've run out of my lunch time.
There looks like two blue wires to the output socket.  Based on the schematic I'm not sure why there are two wires, I can
think of a connection different to the schematic which would use that wiring method.

[jable1066]

Hi Rob - thanks so much for taking the time to have a look at this and reply! I will draw up a wiring diagram tomorrow I guess to try and make things more clear. What I'll do is PM you when I get it up just so you don't have to keep checking back to this thread. I still can't get my head around why this thing works but doesn't work with another pedal in the chain. crazy.

[Rob Strand]

Hi Jabel,

I've traced the switch wiring and it looks like it follows the schematic:

Following uses top, bottom, left, right as shown in your pics...

The top three terminals of the switch are for the LED,
and the bottom three terminals of the switch are for the audio switching.
Center contacts are the pole/common connection of the switch.

In bypass mode contacts on the left of the switch are closed,
top contacts: blue (0V) connects to the white (cap)
bottom contacts: green (output socket) connects to green (input socket)

In effects mode the right side of the switch contacts are closed:
top contacts:  blue (0V) connects to black (LED negative).
bottom contacts;  green (output socket) connects to grey (phaser output, schematic terminal

The blue wires are the negative supply to the PCB, which are switched via the output socket contact.
On the schematic this is the lower wire of the lower switch contacts which is wired as follows:
- Light Blue Wire,   Output socket to switch to the PCB 0V/ground,
 effectively going to connection 5 on the schematic.
- Dark Blue Wire,    Output socket to centre (pole) of the switch S1-2

- Green wire, from input socket to lower left switch contact,
 at the switch this picks up a second green wire which wires back to the PCB at
 connection pin 2 shown on the schematic
- Green wire from lower centre contact of switch this is the pole of the switch wired
 back to the output socket tip

(Note the input socket is always wired (bypassed & non-bypassed) to the circuit input via the two green wired)

It all looks OK to me, and it matches the schematic.   The only assumption I'm making is that the switch contacts are in fact operating as I explained at the top - if not you need to rewire so it is.

You need to check of the PCB is getting power and take it from there.

Do you have a multimeter?


What are your other effects?  Do you have any positive ground units?  That will cause problems.

[jable1066]

Hi Rob - I can't keep thanking you enough for putting your time and effort into answering my questions and helping! I'm going to go over all the wiring and match it up to how you described, and I will order 2 new jack sockets. For a 20 year old unit, if they've never been changed, the price of £1.50 to possibly fix a problem isn't much to pay. And I suppose, there'll come a day in the next 50 years when I own the thing where they'll need to be changed anyway!

As for the other effects - I don't have any positive ground pedals. I'd put it in the chain with other pedals I've built like the Stage 3 clean boost, crackleboost (SHO clone), tubescreamer and ghetto stomp. It did the same thing with all pedals, placed before or after the phaser. I then thought I could have messed up all of my wirings so I tried it with a few Boss units I have i.e. tuner, chorus and it did the same thing. I then tried to run the boss pedals of batter and phaser off power supply and it did the same again.

I'm hoping there's just one or two wires that are switched - I'm going to try and really trace the schematic and wiring on my unit and match every thing up. I do have a DMM, yes. I will plug the unit in by itself - trace the voltages etc then put a pedal in the chain and trace the voltages again and see where they differ. What I hope is that there's a point on the circuit, the earlier the better!, where something is being grounded/shorting. I may print the schematic off and trace over it in sharpie to make it more clear - then I can write the voltages down on here. I've started drawing out the wiring scheme last night, but my services today are lent to my parents as they're throwing a party, so it'll be tomorrow before I can finish that. I'll get some better pictures too and post it all tomorrow afternoon/evening.

If/when I get it working fully I'll probably send all the info to discofreq on his website so he can update with all the new info and hopefully it'll help someone else if they have a broken one. I know someone on eBay just won one the other day, I think it's the guy I outbid! He may even check here for advice...

Thanks again, Jonny!

[Renegadrian]

Found this googling...
http://cgi.ebay.co.uk/Guyatone-PS-101-Rolly-Box-Phase-Sonix-VINTAGE-Japan-/150529163570

PLEASE NOTE: It cannot be powered from a daisy chain
or multi-output PSU where the outputs are linked...
a dedicated (or isolated) power supply is required.
[This is not a fault but is due to the design of the circuit -  it wasn't an issue
back when these were made as daisy chaining effects wasn't common practice.]

[crrollyson]

Hi, I just got a Guyatone Rolly Phaser (non working) and have been looking for a schematic. From what I've read this schematic follows that of the Vox 1900 Phaser.

The only schematic I've found is also the one mentioned here: http://www.voxamps.com/downloads/circuits/1900phas.jpg

@jable1066 did you ever draw up a new one by chance? Or does anyone else know of any site that might have such?

Thanks,

CR