Burning smell from VX351

The Moog Forum Minimoog Forum
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I was sending CV from my arturia beatstep to my voyager for hours and all was fine. I then sent the beatstep CV to my CP251 mult and sent it to both my filter and vol CV inputs on my voyager. All seemed fine. Then I patched out from the X touchpad out and square LFO from the VX351 to my moogerfooger mf103. After a few seconds (and possibly after I swapped the X touchpad output to the Y touchpad output) the screen on my voyager went blank - still with the backlight, but completely blank. I rebooted and got the same thing, backlit but blank screen - and the panel keys would light accordingly if I pressed them, but no sound. Then I smelt burning. I immediately turned off the voyager. Rebooting did nothing to change this.

I thought the smell was from the voyager, but it was from the VX351. Once I disconnected the main VX351 cable the voyager powered back on and all seems fine again, however, I’m too nervous to connect the VX351 again. Im just wondering does anyone know what might have happened or have any experience of this?

Im so relieved that I dont seem to have blown my Voyager, but Im kinda surprised the VX351 would burn up

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Not the best.

You can certainly mult voltages in a less than safe way either directly or if using the wrong cables or if using TRS to TS converters from Voyager or MoogerFooger expression input jacks, each of which supply +5V, do the math! Very glad your Voyager didn’t blow but you should open up your VX-351 and have a look. (see pic below) To remove, take off back panel, wood blocks, two nuts from the DB connectors, then remove each of the ‘jack fronts’ which are black plastic nut-looking caps, each of which require a partial (1/4 turn maybe) to be removed.

If the smell/smoke really came from the VX-351, my money is on the electrolytic capacitor blowing up. you’ll see the top of it split open and some crap inside. If not, look for burn marking around the voltage regulator (assuming that’s what it is). I neglected to ID this component when I took the picture so if you get in there, have a look for this. If not, I’ll rip mine apart.

You should call tech support just for fun and tell them exactly what you patched. If you find a blown component, they may be able to do a deal for you to have it replaced. If not a friendly DIY guy around here, I’m sure, would be happy to address for you. : )

Looks like:

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Thanks EMwhite, I really appreciate the reply. I’m definitely out of my depth here in trying to determine why this happened. I bought the unit from Thomann so I think it’s safest for me to return it to them.

There is a strong smell of something having been burnt inside the VX, but rather worryingly, there is also a burnt smell from my voyager. It seems stronger where the VX interface port is on the voyager, so Im hoping it’s only the small card I installed inside the voyager that’s burnt. I’ll check in the morning.

I am now going to be paranoid with any connection I make to the voyager / moogers. The beatstep, from research online, gives out up from 5v up to 8v - though I’ve read differing results from various users, who also report varying voltages when the Beatstep is powered from a PC and from a plug, and different results with different synths.

Would it be possible that when I put the CV output from the Beatstep into the mult of the CP251, and then sent 2 copies of that separately to both the filter and volume CV inputs of my Voyager, that this in turn sent these voltages to the VX when I inserted a cable into some of the VX outputs, and that this was too much power?

Also, as you kindly advise, cables can be an issue - what cables should I use - mono ones? They are TS right? I think I had a few stereo (TRS?) patch cables in the CP251 (small ones, both ends in the CP251). I also used a (mono) minijack to quarter inch jack adapter directly from the Beatstep to the mult in on the CP251, might this have been a bad move?

Finally, are there any safeguards I can take to prevent this from happening again, while I can make sounds I like in a somewhat pre-meditated manner, I clearly don’t have a handle on the ins and outs of CV voltages :slight_smile:

Oh, and the CP251 is fine - works prefectly and no burnt smell!

Thanks a mill for chiming in,

Cheers,

Simon

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I don’t have a CP-251 but the diff between it and the mult on the VX-351 or a passive modular multi is that the red jack (or the jack with the circle around it) is powered such that +5V is supplied to the ring so that you can plug in an expression pedal then send a variable voltage to the other jacks on the mult via ‘tip’.

Haven’t seen a schematic or an internal shot of the circuit board so can’t tell if the other 3 are TRS or just TS. Hard to say if this even matters.

As for cables, I have plenty of TRS and TS but I don’t have any that convert from one to the other like Mono to Stereo or non-balanced to balanced. If there was a problem with using either, I would expect a big warning in all of Moog documentation. They do warn about mult’ing waveforms (voltage) vs mixing, however, one “in” and multiple “outs” as you describe is very common.

You didn’t say anything that sounds off or dangerous but in general, you should be wary of putting 3 power sources into a multi and taking the resulting output from the 4th connection and apply to an input of any device because it will contain the sum of the other 3 and 15V is pushing it.

Many of the components within analog synths such as Op-amps or caps are rated upwards of 25V or higher so that should be plenty of headroom. I think that Moog says that even 10V is getting a bit hot but still OK and then of course there are diodes in various places to prevent patching of voltage ‘in’ where it shouldn’t be.

It may be a good idea to get some paper and draw out the patch beginning to end before you forget what you did. I can’t wait to hear what actually blew, could be a perfect storm that just pushed things beyond limits but if I’m being honest, you really have to go out of your way to create a scenario that will damage this gear; there is so much of it out there and not much in the way of reported problems of this nature. Could have been defective from the start!

I’m going to rip apart my VX-351 tomorrow to see what the TL082 is tied to. Otherwise, most of the connections are wired direct to jack from the Voyager.

Considering that you had to open your Voyager in order to put the output adapter in there, maybe crack it open again and look/smell for something blown. The analog board, as you know is packed but a good look may reveal something.

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Thanks again EMwhite!

I will be opening up the Voyager this evening, will report back. Hopefully it’s only the VX daughterboard that’s fried and not the part it connects to in the Voyager.

Excuse my ignorance, but how exactly does one mult more than one source in the CP251. I thought that the left input was the only input and the other 3 connections took a mirror of that signal for distributing the same CV signal to other devices. I know you can use the mixer to add multiple sources together - and then possibly patch that to the mult input - but how would one combine more than one source in the mult area?

I read that combining multiple sources of CV might create too high a voltage, but I’m struggling to remember what I did that would have caused this. I wonder if there is any way to create too high a voltage inside the voyager between the various mod sources and the touch surface etc. which in turn gets sent to the VX351 and is too high for it? More so if there is external CV also coming in from the CP251 / Beatstep - does the voyager limit any of this?

I wonder would it be a good idea to buy a voltmeter and measure the voltage being produced by a patch before connecting it to the voyager / VX in future - as I’m struggling to understand how to prevent this from happening again :slight_smile:

Cheers,

Simon

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In a standard mult such as the pair inside of the VX-351 or on a modular synthesizer, the tip and sleeve is simply connected across each of the four jacks. It’s literally just 4 jacks and wire. So if you connect a powered jack with +3V in any of the four jacks, that voltage will show up in the other 3.

I believe the CP-251 is identical with the exception that the red or circled jack has a 3 conductor jack (TRS) and the ring has +5V on it with the idea being that if you plug in an expression pedal (and for your information all that passive Moog type expression pedals do is attenuate the voltage from heel to toe and return the attenuated voltage on the tip of the plug), the 2.5V or 1.1V or whatever (up to the original +5V) is sent to the other 3 jacks on the Tip of jack #1.

I’m not sure if there is any diode protection to prevent voltage from other sources to going to jack #1 or not. I doubt it.

But if you take the Mod wheel output of your VX-351 and plug it into Jack #2 of a Mult and take an output voltage of the touch pad into Jack #3 of the mult then take a patch cable from Jack #4 and plug it into your a Filter Cutoff on your Voyager; with the Mod wheel fully up and the touchpad position fully on (e.g., either up or to the right), you’ll have +10V heading into the Voyager. If you do the same on the CP-251 and then plug an expression pedal into Jack #1 and put it to TOE with the trim attenuator all the way open (CCW), you can have +15V arriving at your Voyager. Will that blow something up? Hope not, don’t think so, but it’s not advisable.

If you were to Mix these instead and possibly had an LFO as one of the sources, you could have some combination of voltages which might be interesting from a performance point of view and you would be assured that you would not exceed the max of any one; the mixer ought to max out at unity. Some mixers, however will actually BOOST. They have gain in the channel, or an overdrive which in some cases is desirable (in the case of audio signals of waveforms which are pushed up to the voltage rails to create waveform distortion; such is common on the Moog Modulars and to some extent on some of the modules sold today; on particular Mixer module which is based on the Moog CP3 design is calibrated to hit unity at the 2 o’clock position). Have a read here, just out of interest. This particular mixer also has capabilities to ADD or SUBTRACT a given amount of voltage to the mix on normalled jacks [e.g. only if nothing is plugged in] - http://stgsoundlabs.com/products/mixer_mu.htm

I’ve used Mults to add voltages in interesting ways for instance, to take Keyboard CV Pitch + Mod wheel output properly attenuated to offset/transpose. The important thing is to take Moog’s recommendations on what max voltage you should keep an eye out for and certain to get a Volt meter so that you can read where things sit as you experiment until you get comfortable.

Important to note that voltages are also added within the voyager, for instance if you set an LFO with a destination of OSC3 wave, but set the wave of OSC3 to pulse width towards the higher end of the potentiometer (near full CW) in order to do some pulse width modulation, you might end up pushing the circuit beyond limits in which case you will hear a dropout of the oscillator frequency (dead spot). Likewise, voltage into the Filter cutoff jack is ‘added’ to the position of the cutoff potentiometer and that which might be added via Modulation bus routing. From that standpoint, it will be the net effect of having the Filter cutoff FULLY open and beyond the range of the pot on the panel. Whether or not this is safely limited within the Voyager circuitry is another matter; I would think so, else you would see many folks with lots of issues but I have not seen this documented;

As I said in my prior message, many of these components are rated at 16V, 25V or higher so it will not have a useful effect in the audio realm but might not be detrimental to the electronics. Even diodes which are meant to protect against current flow in the incorrect direction (and polarized caps for that matter) have ‘breakdown’ voltage and will eventually pop (smoke). But to give two examples of the type of components you are likely to see on the Voyager analog board: A 1N4001E-E3/73 diode is rated with a peak reverse voltage of 50V and a standard 1% tolerance metal film resistor is rated at hundreds of volts. It’s really the ICs and the capacitors that you need to watch out for.

FWIW, the output adapter that you installed with the VX-351 contains a resistor network (e.g., a pair of components each of which act as a single resister for a signal); this is required for the Voyager, but not so for the Voyager Old School. I remember looking up the value/tolerances of the component a few years ago and I thought I took a picture of it but it doesn’t spring to mind now.

At this point, I’m talking in circles :laughing: happy to continue the dialog but I think you have plenty to go on. Give Andy Hughes a call @ P: (828) 251.0090 ext. 221 and explain what you’ve experienced. He’s a really good guy so can answer any questions you might have. I’m just a customer with more gear and spare time than talent.

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Ahah, OK, I think I understand the mults now, so all inputs are added and sent to whatever the outputs are, be it 2 in 2 out, 1 in 3 out, 3 in 1 out etc

I opened up the voyager to check. Most of the burnt smell definitely came from the VX351, yet I think I can smell some kind of burning from the voyager - though my mind could be playing tricks on me. The VX daughterboard is fine, but then I noticed what I think is the fuse - the big brown box in the attached photo labelled CA2A106040 - does this look normal to you? All that brown goo - might be innocent glue, or maybe it blew? Any ideas?

The voyager is working fine, but of course if there might be an issue I wont power it up till I can sort it.

I’ve emailed Andy

Thx again

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I re-read what you wrote at the top of this thread, this time with a clear head.

Beatstep says it has a Gate output of 8V. This is a little hot but I’ll let Andy tell you if that is a problem. I would attenuate it down to 3V or 4V (whichever works) just to be safe. Doubt this was your problem.

Voltage CV won’t be your problem, despite the range being upwards of 7V, you’ll only hit that if you generate an extremely high frequency and based on Bob’s original 1V per octave standard, it can be assumed that the range of a non-limited (e.g. not Minitaur) instrument is 6 or 7 or 8 octaves.

BeatStep CV into a mult and to the two inputs not he Voyager is also no problem.

Two outputs from VX351 to a MoogerFooger; Well, provided that one of them was not the LFO OUT of the Phaser, I don’t see a problem. Obviously you would want the OUTPUT of the Voyager touch pad and an LFO to go into one of the expression pedal inputs on the Phaser (the top row with reverse text). If you plug pan LFO (voltage out) from the VX-351 into the LFO OUT of the Phaser (voltage out), there is no telling what would happen but I’m fairly certain that Moog has protection on these circuits to prevent incorrect patching.

Overall, I don’t see anything that you did as harmful; If the digital board of the Voyager locks up, it may not ‘boot’ to the extent that it will allow any of the keys to play the analog board and produce audio; despite being 100% analog signal path, the CPU is between the keyboard and the analog board (everything is attenuated by ICs and patch settings until you get to panel mode as far as I’m aware).

Challenge Andy/Tech Support to reproduce your patch and see what results he has; regardless of whether or not they have Beatstep, I’m sure he can produce comparable voltages with other gear that they have there. Lessons learned or as they say in England, ‘learnt’ : ) none really. Always good to learn more about this wonderful gear as time marches along and we all are doing some extent of that. But definitely get your hands on a voltmeter or if you have access to a low cost, refurbished scope even better… it’s lots of fun to watch voltage/waveforms on a screen and if you know somebody local that is savvy, he/she might be able to recommend a particular model for $100 or so;

I have a module on my Modular which does this; it’s was not inexpensive, I likely could have gotten a more full featured scope for the same $$ but I use it all the time to debug patches and see the effect of modules and filters on audio and control voltages. There are scope apps that you can run on your iPad or Mac/PC but of course you are then back to ‘what is a safe voltage’ again.

Please update this thread as you come upon the root cause.

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All these problems of voltages adding up in multiples, trigger polarity incompatibility, imprecise tuning with pitch CV between different devices, and all other quirks of analog control, that’s exactly why Dave Smith came up with the MIDI standard in the early eighties…

And since MIDI is opto-isolated, there is absolutely no danger of busting anything up…

BTW, that “brown box labeled CA2A106040” is not brown, it’s yellow. And it’s a high frequency, high voltage transformer (hence it’s yellow color to indicate high voltage danger). And the brownish stuff on it is simply varnish (to prevent mechanical vibrations of the wire coils inside).

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^yes, Andy in Moog had come back to me about that, seems the issue is with my VX351 and thankfully not the voyager. Both he and an official Moog tech in the UK were both surprised at what happened and seem to think it a freak occurrence with my VX351.

I have sent it back to Thomann, so let’s see if they honour the warranty, or blame me…

Yes, of course midi is safer and easier to use in a studio, but CV is a lot of fun!

I really appreciate the responses in this thread, thanks!

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By combining MIDI for the precise control of the notes, and CV modulation for the sound exploration, you get the best of both worlds…

But sometimes CV can cause strange things to happen. Although it never resulted in burning smell, or smoke, for me luckily.
I do remember something about a grounding issue between two of my analog devices, causing a terrible hum when patch cords were interconnected between the two. But They weren’t of the same manufacturer. And I did finally managed to resolve the issue…

Anyway, I hope your VX was really defective and that they fix it under warranty, and that your beloved Voyager is okay.

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I guess the signal can be quite hot from the VX351. It manage to blew the soundboard on my Voyager when I accidently did a patch with plus to plus.
Had to change the soundboard.

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Hi moogsound, what do you mean “plus to plus”?

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Hi Sofine!

I meant output to output.
Sorry for the mistake…

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Most analog gear does not feel very happy when you connect outputs to outputs. Even God frowns upon it so they say… :slight_smile:

Fortunately this is difficult to do. Except for when using a Multiple… The general rule is never connect two outputs to the same Mult. Use a mixer for that. There are audio mixers and CV mixers, sometimes one mixer will do both even though it may be optimized for one or the other.

With Serge synthesizers, everything is patched with banana cables, CV and audio alike. These banana cables are stackable, hence no need for Mults. It’s especially important to keep your head straight when patching on a Serge as the potential for BSU is higher.

Stephen




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