vox ad 100vt

[adv]

Hello , Ive recently had a noise out of this amp. Without a guitar plugged in it makes a noise. I will descibe the sound which may have  some humor.It sounds like a ticking or farting sound and then like a zooooooot sound. then it will quit and repeat the process.It does it on any channel or manual switch, pre-set,etc!!!Can anyone help a struggling muscian out on this probelm. Any help will be a great help.     Thanks adv

[Roly]

 

How often?  Any chance of a sound sample?  All gains/volumes at zero, all tone/EQ at 12o'clock.

If the amp has an FX Send and Return try plugging a jumper lead across these two and see if it makes a difference.

[adv]

Hello, Thanks for the response.I went ahead and did what you said to do. Heres what happen when I jumped the return and send.The sound got louder and I can put my hand on top of the left side of the amp and a pronouce flange sound comes out of the vent on top of the amp.When i first plugged in and powered up it took about 3 mins. for it to make the noise.I have already reset the amp to factory settings.(No change).Im just wondering if a tube could be at fault or a IC going bad.Once it starts making the noise after warm up, The noise is constant( Like a loop).Even though I set the gains , master at zero or on ten and the eqs on 5 it still does the same thing.I have to go to work now so I will read my post tonight. Thanks again for your help.I really appreciate your response. ADV

[Roly]

Well I read a review, and oh dear, its got a silicon Fx wunderbox.  So I went for a look with no real hope in my heart - and got lucky straight away (find service manual attached).

If you can bring this one together with another amp that also has an Fx loop you can try cross-patching them, i.e. Fx Send on one to Fx Return on the other, and this way you can determine if the problem in yours is in the output stage or, more likely, in the preamp (and it sounds most likely in the internal effects unit).

You can check that the supply voltages are correct and getting to the Fx unit, that all internal connectors are properly seated, and the IC themselves too if they/any are socketed.

PS - it looks like all signals go through the A/D-D/A conversion.    The manual shows how to enter test mode but gives no details of what to expect. 

[Enzo]

Look in the owner manual for reinitialize or restore factory settings.  Try it.

[adv]

Hello Roly, I thank you for the service manual.Our computor has been down, Im just now getting a chance to reply.Do you know if that was for the 2 channel or the 4 channel. Mine is the 2. I will figure that out looking at the schematic. Im a newbie to the solid state amp scene so I may have to ask more question.LOL! I have tried re-setting to factory settings.( no change) I put another ax-7 in it, took awhile for it to start acting up again. Maybe that original tube has some issues as well. I think that 1981 super champ i have has a send and return on it. I will try out what you said.Well Im going to start lookig at the scematic so once again thanks, adv

[Roly]

Even as a tech I'd find your amp a bit daunting since it basically converts the input signal into a digital stream which is then operated on by its computer before being converted back to analogue.  This makes it a bloody nightmare to service, HOWEVER since removing and replacing the 12AX7 made some change to the fault it is possible that it could simply be the valve/tube making poor contact with its socket, something very common in valve/tube amps.  I therefore suggest that you try scrubbing the connector contacts by working the 12AX7 in and out a few times.  If its not something simple like this, as a newbie I don't think you have much chance of servicing this amp - sorry.   

[Enzo]

ANother couple years, and I will have been soldering for 60 years.  I got into guitar amps and such about 45 years ago.  I have run a pro audio repair facility for over 25 years now.  I am an experienced professional.   And I absolutely HATE working on Vox Valvetronix stuff.   My best wishes to the novice who wants to wade into one.

[phatt]

Thanks Enzo and Roly,,, that tells me I'm not going nuts when (as a novice) 
I bork at working in that kind of equipment.

I get lucky with some stuff, often just bad connections but when it's terminal digital most of it is way beyond the novice.
Which is why I stick to analog simple Systems.
@ ADV,,, I was almost sucked into the Valtronics stuff but one simple A/b test and I dropped the idea fast,, IMO,, they are nothing like a real Guitar Amp.
Phil.

[Roly]

Nah; ever since I first got an eyeful of the Fender Cybertron (or somesuch?) as somebody who has built microprocessor-based systems for industry my first thought was "Who/how is going to fix it when it breaks?"

I'm often dealing with valve/tube amps that are 50 years old and still very repairable, but I'm also dealing with modern digital stuff of all sorts that use in-house and application-specific IC's that were literally unrepairable even when brand new.  It's totally uneconomic to even take the back off for a look, and it gets worse from there.   :duh

You know that the repair depot would simply have swapped the brain module, and once its more than a year old you can't even get that done.

You walk in to a repair shop (or Dick Smith) and ask for a "NEC D720101GJ/0340EPA12" 80-pin SMD* and may wonder why they fall over laughing.  Even specialist suppliers like Wagners don't carry spare parts at this level. (* a real multi-USB controller)

So with these "Wunderboxes" you are generally a long way up a well known waterway in an unseaworthy vessel with no means of propulsion.   xP

[adv]

Hello, I thank all of you for your experience and input.y es, I agree that its above my knowledge to even try to work on this type of amp and I would take it to an experience person.I have tried to reset to factory settings and I went ahead and cleand and lubed any thing and every thing.I have noticed though that the noise gets louder when I turn up the wattage on the back of the amp. I went to trusty you tube and found were other people have the same probelm with thier vox.One peron freeze sprayed a IC and had some luck with it I think he said it was the final amp near a heat sink? I know you get what you pay for.I didnt pay much. Ive made a few dollars with it so its all good. I just dont want to have to pay more to repair it than I  payed for it .Well I need to get back to ,As the amp turns. Thanks again. adv

[adv]

Hello,I tried crossing FX with another amp and the noise came through that amp also. So It must be in the pre-amp stage.Hell, I feel sorry for the people that have to assemble this amp in the first place. On youtube,under vox probelms or vox siren noise there is a sample of a amp doing almost what mine is doing, The helocopter is the same, but the siren sound on my amp is not as prominent. That is if anyone wants a sample of sound. Thanks ADV

[joecool85]

Hello,I tried crossing FX with another amp and the noise came through that amp also. So It must be in the pre-amp stage.Hell, I feel sorry for the people that have to assemble this amp in the first place. On youtube,under vox probelms or vox siren noise there is a sample of a amp doing almost what mine is doing, The helocopter is the same, but the siren sound on my amp is not as prominent. That is if anyone wants a sample of sound. Thanks ADV

Sounds like it's time to build your own preamp and bypass the "fancy" one Vox used.  Power amp, PSU and speaker should all be fine as is and you'd have a decent amp again.

[Roly]

Hello,I tried crossing FX with another amp and the noise came through that amp also. So It must be in the pre-amp stage.Hell, I feel sorry for the people that have to assemble this amp in the first place. On youtube,under vox probelms or vox siren noise there is a sample of a amp doing almost what mine is doing, The helocopter is the same, but the siren sound on my amp is not as prominent. That is if anyone wants a sample of sound. Thanks ADV

Sounds like it's time to build your own preamp and bypass the "fancy" one Vox used.  Power amp, PSU and speaker should all be fine as is and you'd have a decent amp again.

:dbtu:

@adv - could you post the link to the YT example please?

[J M Fahey]

adv said:

Hell, I feel sorry for the people that have to assemble this amp in the first place.

Don't worry that much, *this* is the "people" who builds such amps:
http://youtu.be/OO0c_PKDw7g

And this is the one who "hand solders" what can't be wave soldered:
http://youtu.be/AIwF1Hg65mg

Bye, I'm going to watch again my collection of "Terminator" movies.
I want to get used to the day when Machines Rule the Earth.
(A few years at most).