Vox Valvetronix Mod?

[E***@spamblock.panix.com]

Hey - Never been here, so I'm not even sure I'm in the right place. I
posted the stuff below to alt.guitar.beginner but nobody there could help.
Anybody here got any ideas?




[ This is a repost of the following article: ]
[ From: ***@spamblock.panix.com ]
[ Subject: Vox Valvetronix Mod? ]
[ Newsgroups: alt.guitar.beginner ]
[ Message-ID: <d45rct$afp$***@reader1.panix.com> ]

I have the 15 watt Vox Valvetronix amp. Its a lot of fun.

It seems to be pretty much identical to the 30 watt model, at least as far
as the preamp/effects section goes. Except for one important difference:
The 30 watt model has a knob on the back of the cabinet, which allows you
to cut the output power of the amplifier section. This is so you can
crank the tube, but keep the output low enough to play in small rooms.

So here's my thinking: It might make sense for Vox to make one model,
which they would sell as the 30 watt with the adjustment knob, or as a 15
watt model with the adjustment knob turned down and inaccessable to the
user. (There are differences in the case and the speaker too, but I'm
thinking that maybe the electronics are the same).

If this is true, then I could simply open up the amp, giving myself access
to the knob, and crank the power.

Does anybody know? Has anybody compared the guts of these two amps? Do
they use the same PC board? Is there a pot installed on the 15 watt PC
Board? If not, is there a place to cut a jumper and install a pot?

Are there any other newsgroups where I can ask this same question?

Thanks in advance for any pointers or suggestions.

[Phil S]

I think this is wishful thinking. Do you think for a minute that Vox or any
other mfg would actually do what you suggest...and that word wouldn't be on
the street before the model hit the streets?

[E***@spamblock.panix.com]

Post by Phil S
I think this is wishful thinking. Do you think for a minute that Vox or any
other mfg would actually do what you suggest...and that word wouldn't be on
the street before the model hit the streets?

I think it is entirely possible. Indeed, I think it likely that they
would make manufacturing as efficient as possible, using the least number
of circuit boards, and the least number of different components possible.

But the reason I ask is because the preamp sections are identical.

[oasysco]

Well, I can't attest to whether or not Vox " makes one model, which
they would sell as the 30 watt with the adjustment knob, or as a 15
watt model with the adjustment knob turned down and inaccessable to the
user", but I do know in the world of mainframe computers, that's
exactly what is done. IBM endows mainframes with various features that
make it extend well beyond the price you paid. If you want a feature,
you pay IBM, a tech comes in and enables the feature (whether it's
adding another CPU, upgrading the mainframe to another one in its class
or whatever).

So what you say certainly is possible. If they did that, my guess is
that they would remove the knob and all connections it had to the amp
such that you could not upgrade it.

Greg

[Tim]

Check out the forum at www.patchtronix.com - a Valvetronix site. It's
not something I've read about there but mods on these amps are
discussed, mostly speakers and adding speaker out sockets etc.

http://www.patchtronix.com/modules.php?op=modload&name=phpBB2&file=index

Tim

Post by E***@spamblock.panix.com
Hey - Never been here, so I'm not even sure I'm in the right place. I
posted the stuff below to alt.guitar.beginner but nobody there could help.
Anybody here got any ideas?
[ This is a repost of the following article: ]
[ Subject: Vox Valvetronix Mod? ]
[ Newsgroups: alt.guitar.beginner ]
I have the 15 watt Vox Valvetronix amp. Its a lot of fun.
It seems to be pretty much identical to the 30 watt model, at least as far
The 30 watt model has a knob on the back of the cabinet, which allows you
to cut the output power of the amplifier section. This is so you can
crank the tube, but keep the output low enough to play in small rooms.
So here's my thinking: It might make sense for Vox to make one model,
which they would sell as the 30 watt with the adjustment knob, or as a 15
watt model with the adjustment knob turned down and inaccessable to the
user. (There are differences in the case and the speaker too, but I'm
thinking that maybe the electronics are the same).
If this is true, then I could simply open up the amp, giving myself access
to the knob, and crank the power.
Does anybody know? Has anybody compared the guts of these two amps? Do
they use the same PC board? Is there a pot installed on the 15 watt PC
Board? If not, is there a place to cut a jumper and install a pot?
Are there any other newsgroups where I can ask this same question?
Thanks in advance for any pointers or suggestions.

[l***@aol.com]

You are dreaming. But I can tell you that if you have a garden-variety
2.5HP dinghy outboard by Nissan or Tohatsu (same motor), if you pull
out the small aluminum restrictor plate in its carb you will have the
3.5HP motor without a neutral shifter and it will run like a raped ape.
;-)

[E***@spamblock.panix.com]

Post by l***@aol.com
You are dreaming.

I'm good at that :)

[E***@spamblock.panix.com]

Sorry to reply to my own post, but I have more info.

I took the amp apart last night, after checking out the position of the
"back panel" control on the 30 watt Valvetronix.

I now think even more strongly that the two amps are identical, except for
the control.

The metal case for the amp has a hole in it at the place where the 30 watt
model has the shaft from the knob coming through. The hole is covered by
the silkscreened black stick-on cover that you see when you look at the
back of the amp. So the two amps use the same chassis for the PC boards,
and they both use the same preamp section.

The printed circuit board has holes drilled to mount a pot. There is a
jumper soldered into place which would be directly under the pot, which
could not be there on the 30 watt model, since it would be in the way, and
would interfere with mounting the pot.

The silkscrrening on the circuit board (at least, the portion of the
silkscrrening I could see through the holes on the back of the 30 watt
model) is exactly the same as my 15 watt model.

So the two amps use the same preamp section, the same metal chassis, and
the same printed circuit board.

So.....

Where can I get my hands on a wiring diagram for these amps, so I can know
for sure?

Or alternatively, is there anybody out there who can tell me which pot is
used on the 30 watt model? Anybody willing to take apart their AD30VT to
look at the markings on the pot? Are there any VOX service centers in the
US who might tell me the value of the pot?

BTW, I was not impressed with the build quality. I used to do electronics
assembly work, and if I were to turn in a job like what I saw inside my
amp, I'd have been fired. For example, one of the screw holes holding the
amp to the case was bashed in and stripped. Several of the caps were bent
over from rough handling. There was a lot of sloppy glue holding stuff in
place.

The circuit board looked (from the top) like it had been hand assembled,
rather than populated by a robot. I say this because many of the leads on
the components were improperly bent, so they didn't line up with the holes
in the board, and the components were crooked. I didn't take the board off
the case, so I didn't see the bottom. But I suspect that there's some cold
solder joints there, which will eventually fail.

Nevertheless, I love my little amp. I just want to make it better...

[Stephen Cowell]

Post by E***@spamblock.panix.com
Sorry to reply to my own post, but I have more info.
I took the amp apart last night, after checking out the position of the
"back panel" control on the 30 watt Valvetronix.
I now think even more strongly that the two amps are identical, except for
the control.

The PT is going to be smaller, and there's probably a different
final output circuit. Pennies to be shaved...
__
Steve
.

[E***@spamblock.panix.com]

Post by Stephen Cowell

Post by E***@spamblock.panix.com
Sorry to reply to my own post, but I have more info.
I took the amp apart last night, after checking out the position of the
"back panel" control on the 30 watt Valvetronix.
I now think even more strongly that the two amps are identical, except for
the control.

The PT is going to be smaller, and there's probably a different
final output circuit. Pennies to be shaved...

Thanks. I'll be sure to look into it. Got any more ideas about likely
differences? I sure want to go to the point of no return without
sufficient certainty.

[Teemu_K]

Post by E***@spamblock.panix.com
The metal case for the amp has a hole in it at the place where the 30 watt
model has the shaft from the knob coming through. The hole is covered by
the silkscreened black stick-on cover that you see when you look at the
back of the amp. So the two amps use the same chassis for the PC boards,
and they both use the same preamp section.
The printed circuit board has holes drilled to mount a pot. There is a
jumper soldered into place which would be directly under the pot, which
could not be there on the 30 watt model, since it would be in the way, and
would interfere with mounting the pot.
The silkscrrening on the circuit board (at least, the portion of the
silkscrrening I could see through the holes on the back of the 30 watt
model) is exactly the same as my 15 watt model.
So the two amps use the same preamp section, the same metal chassis, and
the same printed circuit board.
So.....

So... It's the most common way to save production costs known to
industry: Use the same chassis, same parts and same PCB (with less
parts for "lesser" models). This has been common in typical hifi amps
since inventing of mass producted PCBs.

Post by E***@spamblock.panix.com
Where can I get my hands on a wiring diagram for these amps, so I can know
for sure?

I wish i could answer that because i have looked for them too.

Anyway, i used to think like you few years ago. However, getting more
power requires some more than just couple extra parts: You need a
bigger and more powerful transformer (this thing can easily cost as
much as all the parts together or even more), bigger and more
efficient speaker (again a part that is a dominant factor for the cost
of the whole amp), more powerful power amp stage (more expensive
transistors that can dissipate more power etc.) plus a more powerful
power supply section: New rectifier and bigger capacitors (they cost
quite much too).

Post by E***@spamblock.panix.com
Or alternatively, is there anybody out there who can tell me which pot is
used on the 30 watt model? Anybody willing to take apart their AD30VT to
look at the markings on the pot? Are there any VOX service centers in the
US who might tell me the value of the pot?

Schematics for these amps are quite hard to find. If you find out how
to get one please tell me how you did it. I'm quite interested how the
ValveReactor (tm) circuit is built....

I'm sure you can't just fit in a potentiometer and upgrade your amp.

Post by E***@spamblock.panix.com
Nevertheless, I love my little amp. I just want to make it better...

Forget it. That would mean a complete rebuilding.


Teemu K

[Tim]

Post by Teemu_K
Anyway, i used to think like you few years ago. However, getting more
power requires some more than just couple extra parts: You need a
bigger and more powerful transformer (this thing can easily cost as
much as all the parts together or even more), bigger and more
efficient speaker (again a part that is a dominant factor for the cost
of the whole amp), more powerful power amp stage (more expensive
transistors that can dissipate more power etc.) plus a more powerful
power supply section: New rectifier and bigger capacitors (they cost
quite much too).
Teemu K

My inclination if you want more power is to sell the AD15VT and upgrade
to the AD30VT. I've seen these new Valvetronix amps sell for close to
the new price on eBay. I'm no electronics expert but I know the speaker
on these amps is not that great. I very much doubt the 8" speaker will
handle the extra power and give you the tone you want. You could just
end up with a white elephant that no one, including yourself, wants. I
changed the 10" speaker on my AD30VT because it's one area Vox have
shaved costs. That made a huge difference. Save yourself the time and
probably money and upgrade.

[E***@spamblock.panix.com]

Post by Tim
My inclination if you want more power is to sell the AD15VT and upgrade
to the AD30VT. I've seen these new Valvetronix amps sell for close to
the new price on eBay. I'm no electronics expert but I know the speaker
on these amps is not that great. I very much doubt the 8" speaker will
handle the extra power and give you the tone you want. You could just
end up with a white elephant that no one, including yourself, wants. I
changed the 10" speaker on my AD30VT because it's one area Vox have
shaved costs. That made a huge difference. Save yourself the time and
probably money and upgrade.

Where's the fun in that? If I just wanted a better amp, I could buy one,
but I enjoy taking stuff apart and putting it back together in a way
that's better than it used to be.

[E***@spamblock.panix.com]

Post by Teemu_K

Post by E***@spamblock.panix.com
Where can I get my hands on a wiring diagram for these amps, so I can know
for sure?

I wish i could answer that because i have looked for them too.
Schematics for these amps are quite hard to find. If you find out how
to get one please tell me how you did it. I'm quite interested how the
ValveReactor (tm) circuit is built....

I just called Korg at 631-390-6500 and asked about schematics. The nice
guy who answered the phone emailed me the service maual in .pdf form.

I haven't gotten the chance to look closely at it, but it does include a
schematic and parts list.

WooHoo!

If you want, I'd be glad to farward it to you.

[e***@grapevine.net]

Post by E***@spamblock.panix.com

Post by Teemu_K

Post by E***@spamblock.panix.com
Where can I get my hands on a wiring diagram for these amps, so I can know
for sure?

I wish i could answer that because i have looked for them too.
Schematics for these amps are quite hard to find. If you find out how
to get one please tell me how you did it. I'm quite interested how the
ValveReactor (tm) circuit is built....

I just called Korg at 631-390-6500 and asked about schematics. The nice
guy who answered the phone emailed me the service maual in .pdf form.
I haven't gotten the chance to look closely at it, but it does

include a

Post by E***@spamblock.panix.com
schematic and parts list.
WooHoo!
If you want, I'd be glad to farward it to you.
--
In the councils of government, we must guard against the
acquisition of unwarranted influence, whether sought or unsought,
by the military-industrial complex. The potential for the
disastrous rise of misplaced power exists and will persist.
-- Dwight David Eisenhower

Sorry for not taking the time to post to this thread earlier!

AFA 'converting' a AD15 to a AD30; FYI the three main differences
amount to:
Power transformer : the 15 has +-20 volt power amp rails, the 30 has
+-30 volt
The output IC : the 15 uses a LM1875, the 30 uses a LM3886
...and the speakers (of course, already mentioned) 15 = 8", 30 = 10"
(there are some other minor passive component value differences between
the two, all in the power amp circuit)

Sorry, no internal switch to go between the two versions!
HTH,
-Robert
QTS
http://www.Braught.com

[E***@spamblock.panix.com]

Post by e***@grapevine.net
Sorry for not taking the time to post to this thread earlier!
AFA 'converting' a AD15 to a AD30; FYI the three main differences
Power transformer : the 15 has +-20 volt power amp rails, the 30 has
+-30 volt
The output IC : the 15 uses a LM1875, the 30 uses a LM3886
...and the speakers (of course, already mentioned) 15 = 8", 30 = 10"
(there are some other minor passive component value differences between
the two, all in the power amp circuit)
Sorry, no internal switch to go between the two versions!
HTH,
-Robert
QTS
http://www.Braught.com

Thanks. I think that just about settles it.

[E***@spamblock.panix.com]

Post by e***@grapevine.net
Sorry, no internal switch to go between the two versions!

A huge omission on Vox's part, IMO! :)

And if you don't mind another question, what do you make of this engrish
note, which was included on the AD15's schematic?

---
How to adjisut the output power (WATT)
1. Delete R67 and R68 ->6dB UP
2. Delete R74 and R78 ->11dB UP
3. Delete R72 and R77 ->16dB UP
4. Delete R71 and R76 ->21dB UP
5. Delete R12 and R75 ->26dB UP
Please try to increase the power by above order(1-5).
Even doing above modification ,If POWER is not go
to correct wattage, please exchange the TUBE itself.
---

What's this all about? These instructions refer to a couple of banks of
resistors which are in the AD15, but are not included in the AD30. In
what sort of situations would one do this? Only when the amp isn't within
spec?