vox valvetronics head

[Gunn_Slinger]

I bought a vox valvetronics head used.
The sound is good except that there seems to be a lot of break-up when I let a palm muted note ring.
I tried 3 different 4x12 cabs.....same sound.
Could vox have engineered the amp modals with this break-up?....or is there a problem with the head?
thanks for any help
Clay

[olddawg]

Originally Posted by Gunn_Slinger

I bought a vox valvetronics head used.
The sound is good except that there seems to be a lot of break-up when I let a palm muted note ring.
I tried 3 different 4x12 cabs.....same sound.
Could vox have engineered the amp modals with this break-up?....or is there a problem with the head?
thanks for any help
Clay

If it does it on all of the modeling modes the first thing I would suspect would be the single 12AX7/ECC83 tube in the preamp since the amp is used. From what I have heard the factory tube is a cheap Chinese one that may rapidly deteriorate and replacing it with a better quality tube improves the amp significantly.

[Gunn_Slinger]

thanks old-d
I changed the ax7 when i encountered the prob with a mesa ax7...best ax that guitar center had....I dont know?
The tone was better but the problem continues.
the head is an AD60VHT.
STILL LOOKIN...LOL...THANKS AGAIN....IM NEW HERE AND THINK THIS SITE IS GREAT.

[Enzo]

First, try to determine if it is a defect or a characteristic. Find another one to play through to see if others sound the same. The 120 is the same except power output, so try it if no 60s emerge.

Isolate the problem: Does it sound like this in the headphones? How about the effects send? Play into the effects return, does it make this noise that way?

You could have a missing or stuck low significance bit.

[Robert M. Martinelli]

Hi,
the first thing I would do is to try to determine if the failure is located in the preamp or the power amp section, so I' d try to connect the guitar, or an audio signal generator ( or an MP3 player, starting at low volumes ) to the effects return ( power amp in ) and/or connect the effect send ( preamp out ) to another amp, as per Enzo' s advice, either way way you should be able to ( approximately ) locate the problem.

Looking forward to hearing about your test results

Hope this helps

Best regards

Bob

[Steve Conner]

As far as I know, the Valvetronix amps are analog, so I'm not sure about stuck bits

Given that the original poster talks about letting a palm muted note ring, and muted things don't ring by definition, I think there may be some confusion over what the problem really is. Does the guitar volume affect it? the amp volume? Does it happen on both clean and dirty models?

[Enzo]

The Valvetronix series amps have a single tube floating in a sea of DSP crap. Tiny-lead-pitch LSIs and custom ICs abound. The things are laid out in some insane fashion that makes a PV Classic 30 seem downright convenient. I hate when they come in my shop.

I tried to post the schematics on the AMpix, but the file was too large. If you are interested, STeve, send me your email and I will forward the drawings to you. My PMs are off but my email is on.

[Steve Conner]

The Valvetronix series amps have a single tube floating in a sea of DSP crap.

Oh no! Silicooties! The guitarist in my old band had the Valvetronix combo and I honestly thought they were analog. My bad.

Try thumping it with your fist, and if that doesn't cure it, unload it on Ebay

[Robert M. Martinelli]

I own an AD120VT too, and I can only confirm that they' re very nice as long as they work.... when they don't....oh my God! I bought a GPS not to get lost while repairing mine , and it' s still out of order, maybe one of these days I' ll start a new thread about it, meanwhile, it gave me a good reason to go back home to my old AC30....

[Gunn_Slinger]

Thanks guys
the next sound you hear is me cocking the hammer on my s&w 357....bye bye valvetronics....lol
ok....i did all the tests Enzo suggested and the problem is before the power amp. The clean amp models are ok at low volume but at 6+ the noise is there on them also. The compression pedal setting really brings out the noise on all models. When you pick a note , the sound is great....if you let it ring and die ,here comes the noise ( sound is like s swoosh-ing noise ) stop the note....stops the noise.
In another post I read that the impedence switch ( 4-8-16 ) could corrode and cause noise..???
I bought this amp with a 400 watt 4x12 b52 8 ohm cab.
When i got it home i found that the former owner had used a guitar cable to hook the amp to the cab....aaarrrggggggg. + the cable has an intermittent short or open....double aaarrrgggggg.
The cab seems to be ok....put a marshall and a crate 100 watt head to it...ok
I love the sounds this head has and hope I/We/You guys can fix it...lol
or......cocking s&w 44 mag.
thanks for the replys
and........HHHEEELLLPPPPPPPPPPPPPPP

[Enzo]

You could also try reinitializing the thing, what is there to lose?

Initialization

Switch the amp off.

Switch the amp on while holding down the UP and DOWN BANK buttons, and TUNER/CANCEL button. If you've done this correctly, a "P" will be flashing in the BANK Display.

Press the WRITE Button and watch the BANK and the four CHANNEL LEDs do a little dance as they indicate each one of the 32 programs being reset to its factory preset. Once they both stop "dancing," you're done. The amp will automatically enter Program Select Mode with Program 1 - 1, "Flying High," selected.

[Enzo]

And there Steve is the evidence... The thing has a reinitializtion function.

[Gunn_Slinger]

wheee.....the light show was great...not as good as the 60's though...lol
But....it didnt help the problem.
I did notice that the higher string notes, when plucked and held, seem to wah slightly tone wise...or it could be volume wise....
Got to get a bigger gun...lol
Dump on ebay sounded good...but i cant sell anything thats not right...never could....soooo...where do i go next.....i have the chassis out of the box....

[Robert M. Martinelli]

The "power selector" too can oxidize and cause some problems, but the symptoms you' re describing make me think some signal gets lost before the A/D converter, I get ( uhm....well...used to get when the damn thing was working ) a similar sound on some presets when I turn(ed) down the volume knob on the guitar, and probably the signal getting to the A/D was no longer enough to be sampled properly..... I would check the signal path starting from the input jack, chances are some signal gets lost along its way to the A/D section.

I would not recommend anything less than a .460 Weatherby Mag. to get rid of the amp, but, if you don' t manage to fix it, it makes more sense to sell it on ebay "as is" for spare parts, or "cannibalize" it and sell the parts ( speakers, cab, handles, logo, knobs etc. ) separately to get the most out of them.

[Gunn_Slinger]

thanks mr vox
I figured i would be taking this thing apart. I like the sounds so much that im determined to fix this rascal....so im sure ill be screamin for help soon...lol
thanks again
Clay

[Gunn_Slinger]

hey guys
havent gotton into tearing the head apart yet.
i read about old amps being affected by house voltage over 110....mine is 123.
any chance this amp/computer doesnt like the higher voltage?
i also read that a weber browner is a good voltage reducer.
any thoughts would be good......im lazy till it gets cold here in virginia and runs me off the golf course...lol
thanks
Clay

[Enzo]

That's fine when you talk about amps from the 1950s, but this is not an old amp. Many are still under warranty even. other than teh power amp which doesn't care, all the inner voltages are regulated anyway. Mains voltage is not an issue.

[Robert M. Martinelli]

Originally Posted by Enzo

That's fine when you talk about amps from the 1950s, but this is not an old amp. Many are still under warranty even. other than teh power amp which doesn't care, all the inner voltages are regulated anyway. Mains voltage is not an issue.

Hi Enzo!
How are you doin'?
Well, I would say mains voltage is not an issue if it falls within reasonable limits, otherwise it could stress the transformers and voltage regulators....
( Here in Italy the Electric Co. wise guys, to lower the substations' number, used to start with a very high voltage, and run the same line for miles, this way the "poor guys" close to the substation got 260 VAC instead of 220, while the guys at the end of the line got 200 VAC, this way the Electric Co. destroyed a good number of TV sets and VCRs, and later lost a lot of money in courts ).

In this case 13V more represent some 11 percent, this means 23 percent more power to be dissipated on the PT and regulators, so i would expect them at least to run at a higher temp, which can decrease life expectancy....

OTH it is true that other amps are more forgiving than the Valvetronixes, whose reliability record is unfortunately very poor, ( such a pity because they' re otherwise very versatile and good sounding amps ), so generally a 10-15 percent higher mains voltage is not an issue.

How I wish Vox was still building their amps in the UK! Imagine a good idea, ( like the Valvetronix is ), turned into a versatile, sturdy, rugged, well built amp with no reliability issues whatsoever - a guitar player's dream! Sixteen amps in one plus effects, without having to worry about a thing! - Stop dreaming, Bob!

[Enzo]

Yes, a rise of 13v in the mains would mean more dissipation in the unit, but the point that was raised was comparing the old 110VAC mains for 50 years ago with the 120v mains of today - 123v being a common level for it. The Valvetronix was never designed as a 110v amp, so the 110/123 issue is moot. The difference discussion arises when someone looks at schematics for a 1950s era amp and finds all the voltages are higher because the mains are now higher. His house has 123v on the mains, and the amp is designed as a 120v amp, so that is well within the range of proper voltage.

Obviously if the local mains are unreliable or not consistent, that is an issue to pay attention to, but it is a separate issue from the one brought up.

[Gunn_Slinger]

thanks guys
so power is ok
latest tests : went line out of the vox to the receive of a borrowed marshall head.....the signal was pretty clean, but i did notice that the amp emulations were not as prononced....more on that
Then i went from the marshall line out to the receive of the vox....surprisingly
((( spell check!!!...lol ) the signal was pretty clear.
Started read manual about the vox using the 12ax7 into a dummy load as a power amp emulation along with the pre amp emulation.
Sounds like the line out on the vox bypasses the dummy power amp and the receive in also bypasses it?
I cant find the schzo on it ( only the newer 50 and 100 watt are on their website )
Could the dummy power amp be the problem?
thanks again
Clay

[Enzo]

SIgh...

Reread the last paragraph in post #7 Gunn.

[mr.jetski]

gunslinger vox and enzo, hi all,

if that thing is at all like a peavey tubefex the noise gate threshold is set to low. I found that the hard way!

[Enzo]

There you go, a different direction to try. From your description it sounded to me like a stuck low bit, first impression anyway, but certainly other avenues are worth exploring. I am familiar with fixing them, but I don't know about their features. I'd be surprised if it didn;t have a gate.

[Gunn_Slinger]

thanks guys
it has an adjustable noise gate which ive tried in many positions ....it works to take away noise at idle but has no effect on the signal noise.
enzo, i read post #7 and i dont know much about the parts you talk about.
i dont know how the 12ax7 power amp into a dummy load works, i built some tube amps in the 50's and havent done anything with amps till now ( becomming sorry i did...lol )...so im not sure to what you are referring.
just a note ,i put an mxr smart gate in the effects loop and it nakes the amp playable ( for now ). What do you think a shop would charge to work on this amp?
thanks for all the support
Clay

[Enzo]

I was referring to the last paragraph, wherein I mentioned that sending me an email would get the drawings in return.

I cant find the schzo on it

You'll have to find a shop willing and able to work on it, and then ask their rates.

[Gunn_Slinger]

thanks enzo
i emailed you .
where would i start looking for a stuck bit?
later
Clay

[Enzo]

REmember it is only my notion that is the problem.

I would be looking in the A/D-D/A areas first I guess.

[Gunn_Slinger]

hey enzo
got the sczho...thanks
was reading about the self test modes
do you know how to use it and how to read the output codes?
thanks
Clay

[Enzo]

You now have the same service manual that I do. All I know is from that.

I think I already posted this:

AD60 / AD120
Initialization

Switch the amp off.
Switch the amp on while holding down the UP and DOWN BANK buttons, and TUNER/CANCEL button. If you've done this correctly, a "P" will be flashing in the BANK Display.
Press the WRITE Button and watch the BANK and the four CHANNEL LEDs do a little dance as they indicate each one of the 32 programs being reset to its factory preset. Once they both stop "dancing," you're done. The amp will automatically enter Program Select Mode with Program 1 - 1, "Flying High," selected.

Mounting the "Amp Type" knob

The Amp Type knob is not keyed. So mounting it correctly requires knowing what Amp Type is currently selected. The factory setting for patch program 1 - 1 has an amp type of "UK Modern". The following procedure uses this fact combined with the Original Value LED to find the correct orientation for the knob.

Reset the unit.
With patch 1 - 1 selected, turn the Amp Type knob until the "Original Value" LED lights.
When this LED is lit, install the knob with the arrow pointing at "UK Modern".

[Gunn_Slinger]

yes you did post that and i did that
i was referring to page 12 of the sczho that talks about self test.
it outlines a number of tests but no info on what the readouts mean.
maybe voxrules or someone who has one of theses " monsters " has been thru this. as i said before my knowledge of amps is 50 yrs old and tubes only.
thanks again
Clay

[Enzo]

Beats me, I just run tests when it seems they might relate to the problem at hand, and then I interpret whatever results I obtain as best as I can. And I ain;t too proud to call the factory and ask when i get baffled.