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vox valvetronix series amplifyer modification

Started by sempri_fi, July 01, 2006, 03:46:28 PM

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sempri_fi

does anyone know how to modify a vox ad50vt to put out more wattage or maby even add a couple more tubes because ive asked a bunch of people and they all say that you cant mod ss amp which i know is bs so can someone help me???

joecool85

Well, for one, you can modify SS amps.  For two, as far as I know, a valvetronix amp has tubes as well, no?  I'd need to see a schematic to give you some good modding suggestions.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

Bob N

I'm with Joe on this.... Anything can be modded, understanding however, all mods have a cost associated with it and space is always at a premium, but we need to know what we're dealing with in order to help out. I have just about every Vox "AC" model schematic under the sun, but have no "AD" models at all. We'd need to see that in order to help out.

My question REALLY is: What do you feel you are lacking? is is just power? or is it tone as well? Based upon Vox's previous numbering scheme, and I may be mistaken, but the AD50VT would be a 50 watt amp, yes? If so, that's not enough power? What would you like to see?

Another question is "Do you ever plan on using it live with a PA?" Reason I ask is simple. Adding more power can actually do the opposite of what you are trying to accomplish. If it's a bigger guitar sound that you are looking for, smaller amps actually have a bigger sound when miked. I know it sounds weird, but it's pretty simple when you factor in many rigs are close miked when going into a PA. The sound only needs to be loud enough for the mike to pick it up and then will be amplified through the console rather than from the amp. If the sound is too loud, the mic and the mic preamp itself will distort and give you crappier sound....

Well, I've rambled enough, but look forward to what your response is.... I'll help out whatever way I can, but hope that you understand what I've laid out....

RDV

Quote from: sempri_fi on July 01, 2006, 03:46:28 PM
does anyone know how to modify a vox ad50vt to put out more wattage or maby even add a couple more tubes because ive asked a bunch of people and they all say that you cant mod ss amp which i know is bs so can someone help me???
Buy another one?
Just kidding!

RDV

sempri_fi

sorry guys i dont have a schematic to give you, ive looked on google and there is nothing. but i wanted to add another tube because it allready has one 12ax7 that its useing half to preamp and half to power amp somehow so would i just take and wire another tube socket in paraell to it or would i have to do some other mods first? and the signal path gos like this it gos through the moddeling chip, then it goes through the preamp half of the tube then it goes through the effects chain chip that moddels the effects, its then shiped off to the poweramp half of the tube and through the output, then it goes through an additional solid state power section that does most of the amplifying and is pretty transperant, and then it goes out through the speaker.

this problably wont help schematic wise but i think it gives a good idea of what is going on.
it also isnt actually 50 watts, it says it is but it only consumes 52 watts so its problably around 30 ish. i wanted to get a more tube like distortion out of it and i figure adding another tube or tubes woud help, so if you guys have any ideas please tell me.
~jacob

Bob N

So you're looking for another gain stage. In order for me to REALLY help out the way you're looking for, I'm going to need the schematics, BUT, there are a bunch of possible solutions in the form of footpedals which don't require you hacking apart your amp.

1. Real McTube - You asked for a Tube Gain Stage.... This is exactly that. A tube preamp built into a stompbox

http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

2. Tube Amp Emulations - These actually sound VERY good and you can build them off of ANY established tube amp design. They're not perfect, but definately give you the character you'd expect from that amplifier.

Example: Marshall Super Lead 100 http://www.runoffgroove.com/thunderchief.html

3. Build a tube amp from scratch with exactly what you are looking for, tone-wise: Sounds crazy? No way.... I've done it and it sounds incredible. There are many people out there on the net that do exactly that and are willing to help you get through it. 2 years ago, I never would have dreamed that I could do ANY of this. Now, I know I can do it and do it regularly. Hi, my name is Bob and I'm a tone junkie.

steve_m

To add to the excellent reply by Bob N:

1. I've built a version of the Real McTube, and to me it only sounds "so-so." If you're looking for lots of tube saturation, you're not going to get it with the Real McTube. It is basically an OD pedal. It is also a high voltage project and therefore inherently dangerous.

2. A better first project might be the Thunderchief. There is also a BSIAB II pedal that nails the saturated EVH "brown sound." Since it is a pedal and operates at low voltages, it is relatively safe.  Info here:

http://www.generalguitargadgets.com/index.php?option=content&task=view&id=150&Itemid=178

You can even buy a PCB.

3. There is lots of good advice for building tube amps. One good beginner's site is the AX84.com site. They have projects there suitable for beginners, and a forum to help with technical issues.

One amp I'm really jazzed about now is the Epiphone Valve Junior head. It sounds pretty good out of the box or you can make a couple of easy component changes to really open up the sound. There are lots of mod sites. Some of the best advice I've seen has been on the 18 Watt forum, about 36 pages discussing mods!

I'm going to buy one, gut it and build in a new circuit using a better output transformer.

Again: tube amps have high voltages in them and are inherently dangerous. You might want to work your way up by starting out with pedals first, a lot of guys do.

HTH,

steve


Quote from: Bob N on July 02, 2006, 10:37:36 AM
So you're looking for another gain stage. In order for me to REALLY help out the way you're looking for, I'm going to need the schematics, BUT, there are a bunch of possible solutions in the form of footpedals which don't require you hacking apart your amp.

1. Real McTube - You asked for a Tube Gain Stage.... This is exactly that. A tube preamp built into a stompbox

http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

2. Tube Amp Emulations - These actually sound VERY good and you can build them off of ANY established tube amp design. They're not perfect, but definately give you the character you'd expect from that amplifier.

Example: Marshall Super Lead 100 http://www.runoffgroove.com/thunderchief.html

3. Build a tube amp from scratch with exactly what you are looking for, tone-wise: Sounds crazy? No way.... I've done it and it sounds incredible. There are many people out there on the net that do exactly that and are willing to help you get through it. 2 years ago, I never would have dreamed that I could do ANY of this. Now, I know I can do it and do it regularly. Hi, my name is Bob and I'm a tone junkie.

Bob N

I'm glad you posted steve. Normally I would have mentioned the precautions of working with tubes but I'm still finishing my first cup 'o coffee. Tube voltages are VERY dangerous as they utilize anywhere from ~100v (in starved tube mode) to 300 - 400 volts. These voltages WILL kill if not worked with very carefully.

I'd take Steve's advice on the McTube as I never finished the one I was working on before gutting it for my Firefly tube amp. It was mainly put there as an illustration that tubes CAN be used in the form of a stompbox.

I've done a number of the Tube Emulation circuits and have them up and operational as we speak. I LOVE these little circuits because they flat out rock! They can be a bit of a B*t*h to dial in, but are a lot more forgiving if you make a mistake and touch one of the hot leads. They won't kill you.

sempri_fi

wow! you guys are awesome, adding an external gain stage is perfect because it doesnt void my warranty, so thats what im going to do, but im useing the eclipse tube booster kit from (http://www.olcircuits.com/olc_eclipsevalve.html). its a pretty good deal for a complete kit that has full costomer support behind it. they even finish the enclosure for you.
~jacob

Ge_Whiz

The 'Valvetronix' series are not your run-of-the-mill amplifiers. They combine a single-valve pre-amp stage with a solid-state output stage, and then feed back and process the output signal to emulate the effect of a valve amp output transformer, plus they have a range of excellent digital amp emulations.

The complexity of the output stage means that modifications are virtually impossible on a DIY basis. If you just want more power, you'd do best to trade-in your 50W model for a 100W - and it won't sound much louder. The amp as it stands has a number of high-gain emulations, and I doubt that you'll be able to improve on them significantly. But you can try.

teemuk

You could try to trace out a schematic of the output stage. As far as I´ve figured from Vox´s advertizements the output stage uses both halves of the 12AX7 to form a push-pull stage that is decoupled to SS power amp stage with a transformer. The ValveReactor pedals do not have a transformer, they simulate it. The power stage utilizes a feedback path after the speaker (not before as usual), which raises the output impedance and mimicks tube amp´s response to a speaker load. Vox calls this technology "reactive feedback" but it is better known as as a mixed mode feedback. This feedback path goes to either valve -or SS power stage. It even might go to both of them. There might be some DSP circuitry somewhere in the signal chain also - very likely there is - but you probably want to limit the examination to analog circuitry and signal path only. Although the circuit might seem and sound like a complex one it can be divided into simpler circuit parts. You do have a fairly good knowledge of what kind of circuitry you are expecting to find from both tube PP power stage and SS power stage since you are ready to modify it, right?

If you just want more loudness try more efficient speakers.