Have you got a Vintage Vox Phaser?

[Scruffie]

Cause i'd sure like some gut shots!

Got a dead one and the Vox 1900 schematic out there does not quite apply to it, this has a transistor input buffer, buffered LFO and, well it's this one (there is another model that does apply to the schematic in the same case).

http://www.modezero.com/vox-1900-phaser.htm



I've managed to get audio running back through and the LFO going (although not quite sure how it hooks up but I think I have the idea but confirmation would be nice for debugging) but all i've gotten is thumping, as there was a burn mark, broken OpAmps and transistor... i'm guessing this got reverse power and that the FETs are dead too.

Another thing is from the gut shots i've seen, I can't work out the bypass wiring, seems to only use an SPST but there's no on board switching set up of any kind and I don't know where the wires hook up... i'm guessing it must just short the wet signal to ground...

Anyway, if you can help out and save me tracing and guess work it'd be appreciated.

[Scruffie]

No one able to lend a hand?

[armdnrdy]

I don't own a Vox phaser....but I found these gut shots:

http://s867.photobucket.com/user/jable1066/library/Vox%20Phaser%201900?sort=3&page=1

[Scruffie]

I don't own a Vox phaser....but I found these gut shots:

http://s867.photobucket.com/user/jable1066/library/Vox%20Phaser%201900?sort=3&page=1

Ah I should have pointed that out, I did find those, sadly they're for the early version that does match the schematic 

Thanks for taking the time to dig though

[R.G.]

I have an old Vox phaser schemo somewhere. If you have a model number off the case, I'll look.

Failing that, if you take the necessary detailed photos, someone will trace out the schemo.

Failing that, make note of your diagnosis - reverse current, and lots of it - and get together a list of the reversable parts, then remanufacture it, replacing everthing with a junction, and all reversable electro caps. This last may be needed anyway. Your description fits "fed AC power" better than "fed a reverse voltage", so it may have killed most or all of them.

[Scruffie]

I have an old Vox phaser schemo somewhere. If you have a model number off the case, I'll look.

Failing that, if you take the necessary detailed photos, someone will trace out the schemo.

Failing that, make note of your diagnosis - reverse current, and lots of it - and get together a list of the reversable parts, then remanufacture it, replacing everthing with a junction, and all reversable electro caps. This last may be needed anyway. Your description fits "fed AC power" better than "fed a reverse voltage", so it may have killed most or all of them.

The generic number for these was the Vox 1900, I believe built by guyatone and then reboxed by Vox, there is this hard to read schematic which doesn't apply to this specific circuit/PCB revision available which may be the one you have - http://experimentalistsanonymous.com/diy/Schematics/Phasers/Vox%20and%20Guyatone%201900%20Phaser.jpg otherwise the box only has a serial number.

Yeah I came to the AC conclusion as well after more poking (at first through some mistakes of my own I thought I might have replaced some parts unnecessarily but I looked at the legs of the opamps in day light and they've seemingly all been hit with excessive heat) after audio probing the first phase stage might be working but after that it's just thump so i'm just going to replace the lot rather than try and match 3 x 2SK30A to the possibly one or two working and damaged FETs.

The electros seem fine, all signal passing through and voltages held steady where need be so far, but I have already replaced all of them related to power, it's 30 years old so... I can't tell if they've been replaced before as they look very new compared to the rest of the parts and someone had replaced one OpAmp in a socket (the one with massive burning under it) then seemingly given in fixing... i'm putting money on that person also owning a Digitech Whammy with a certain power supply 

I certainly can trace it, most of it's unsurprisingly quite standard FET phaser but a shot of the wiring would remove some of the brain power, lots of tight tracks and some unused wire traces confusing things.

I'm going to replace those FETs then get back here, i'll post up gut shots as well for those who might want them in future.

[R.G.]

Yeah, that's the one I saw, but I found it at Korg's Vox "vintage schematics" page. Looks a lot like our friend the Phase 90.

If one opamp's had a massive burn, I would not trust the others. Opamps are too cheap. FETs may have lived. You may be able to check them out of circuit. Tossing them into the JFET matching circuit would tell the tale.

[Scruffie]

Yeah, that's the one I saw, but I found it at Korg's Vox "vintage schematics" page. Looks a lot like our friend the Phase 90.

If one opamp's had a massive burn, I would not trust the others. Opamps are too cheap. FETs may have lived. You may be able to check them out of circuit. Tossing them into the JFET matching circuit would tell the tale.

I actually found a different Korg phaser schematic that looked a bit more similar, the only thing that has me scratching my head a bit is there is a trace for a wire going through a 2M2 resistor, a bit like the 3M3 goes to the Phase 90 gates and a trace that connects to the sources like the Phase 90 LFO, then a trace from the buffered LFO & the Zener voltage... my head tells me, depth 3 goes to LFO out, depth 2 to the sources and depth 1 to the 5v6 zener to blend between LFO output voltage and a fixed voltage... but the unconnected 2M2 seems odd.

Yup, all OpAmps have been replaced, I think the LFO one survived and my mistake was that the rate pot wire fell off without me noticing as I just tacked it in case I made a mistake, also the input & output one may have as it used a BCE transistor buffer input and I twisted a 2N3904 to fit and despite checking again and again, two of the legs were touching even if I couldn't see it and that OpAmp was providing a very weak output... but it would with a weak input, not so important now they're gone.

Anyway, at the moment I tacked rate direct to the sources and have tremolo, at the 1st phase stage a tremolo with dry signal, at phase stage 2, just wet tremolo, FET bias did have an effect at one point but I can't remember how I had it all hooked up and I think that was because of a mistake and there was a lot of oscillation with certain setting, with voltage moving erratically on every pin of the FETs, I think they might be a tad dead.

I may throw the FETs in a matcher to see if they're worth keeping but it's probably easier to match 4 FETs from a fresh batch than 2 or 3 to the original ones with stubby de-soldered legs

[Scruffie]

4 new matched FETs, all new op-amps, new transistor, all electrolytics replaced... still only getting tremolo and the trimmer has no effect 

[Govmnt_Lacky]

How close is your pedal to the schematic you linked above?

I am wondering about the mechanical "Feedback" switch listed in the schematic. Is that on YOUR pedal somewhere? (perhaps internal)

[Scruffie]

How close is your pedal to the schematic you linked above?

I am wondering about the mechanical "Feedback" switch listed in the schematic. Is that on YOUR pedal somewhere? (perhaps internal)

Nothing like it, completely different circuit and no feedback.

[ilcaccillo]

Hello,
were you ever able to fix your pedal or draw a schematic of the circuit?

Didn't know that there were 2 different circuits for the Vox 1900.

[Scruffie]

No in the end I put it away and forgot about it as other projects got in the way, for a £5 pedal I felt like i'd spent enough time and I didn't feel like tracing it out.

I still have it though if you need some information from it although i'm not sure what help it'll be.

[ilcaccillo]

No in the end I put it away and forgot about it as other projects got in the way, for a £5 pedal I felt like i'd spent enough time and I didn't feel like tracing it out.

I still have it though if you need some information from it although i'm not sure what help it'll be.

Hi
I have the Vox 1900, but my unit corresponds to the schematic that is around it uses 3x 1458, 1x 741 and 4 Fets.
My unit is working fine, and I did a chart with the voltages on the opamps and Fets. I will post it around here so people could use it for future reference.

I'm sorry you were not able to fix it, wish you are able to fix it in the fufutre.

[990]

My apologies for bumping an old thread (also, I'm new here, hi!) but I too have an older version of this pedal and it does not correspond to the schematic available only.

The thing with mine is that some wires are missing or are just disconnected, so I'm not sure how the jacks, switch, DC jack, pots, etc. wire into the PCB.

I still have it though if you need some information from it although i'm not sure what help it'll be.

I don't know if this offer still stands, but it would be great help if you could post some pictures of yours and how everything is wired to the PCB.

Thanks!
(If I get mine working I'll try to trace it and post a schematic)

[Scruffie]

Guess what one of the problems with was mine... all the wires had been disconnected. I was never sure I put them back in the right places because there was more pads than connections and I never got round to getting it going again so I don't think i'll be of much help i'm afraid.

If you trace yours out as it stands though it shouldn't be too hard to work out what goes where.

[ilcaccillo]

Well you should post photos of your unit and also pcb and circuit.
You have to find the proper schematic for it. After that the correct wiring will be pretty straightforward