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gwertman

Valve Junior Head Preamp Bypass?

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Hi all,

 

I wanted to bypass the preamp in my VJr head for use with my Damage Control Demonizer. Some info at amptone.com said you can wire into the master volume pot -specifically the middle lug. Would this work on the VJr? I don't need an effects loop and I can solder pretty well so can I wire the input jack right to the volume knob?

 

Any thoughts?

 

Thanks,

Gary

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How does one do that?

 

:-)

 

Also, Wiring into the center lug bypassed the volume control. Wiring into the outside lug made the volume work again. Is there a tonal difference between the two?

 

Thanks!

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If you add a second jack for the loop (or it your case, the power amp-input), the original guitar jack will take care of grounding the input first preamp tube stage. Otherwise, just short the two input wires together to ground it.

 

Here's the scoop on loops. http://www.sewatt.com/files/sewatt/VJr_FX-Loops.JPG

 

Here's another interesting way to use both preamp stages in parallel as your input buffer.

http://www.sewatt.com/files/sewatt/PA_IN.pdf

 

Tonally, volume pots tend to sound a little dark as you roll off from 10, and yet you can compensate for that rather transparently with a 150pf bypass cap. But it's a very good thing to have a volume control if you need to match levels, set limits, or mute things quickly for a phone call or whatever. The rest of the time, I run my slave amps on 10 and the volume pot is completely out of the way.

 

Gil...

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Thank you Gil! I guess that means I can place a jumper across the 2 connectors where the input jack previously plugged into the board. The amp sounded a little brighter when I was tied into the center lug - because the volume pot wasn't loading the signal at all I guess.

 

As for the buffered input schematic - how different is that from stock? Meaning, can you point me to the stock schematic so I can visualize the difference? I'll probably have my amp tech do the work since I'm so new at this...

 

Thanks again for all your help!

 

-Gary

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Here's the schematics for all three versions of the VJr in one file.

http://www.sewatt.com/files/sewatt/StockVJ_1-3.pdf

 

Loops need buffer circuits. Most amp manufacturers and a lot of techs add this extra buffer circuit to an amp's already existing circuitry as an 'enhancement'.

 

In the case of the VJr, it just wasn't practical or even necessary to add more circuitry, because if you look at the big picture, you realize the amp already has what you need. So, you simply insert the loop jack between the two preamp stages, and the whole preamp becomes the loop driving circuit for the power tube.

 

Gil...

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Hi Gil,

 

How do I know which version my VJr is? Also, if I'm wiring to the volume pot doesn't that signal go through the second half of the preamp tube before it goes to the power tube? And if so, doesn't that mean I already have a buffer?

 

Of course, I do IT support so schematics and 'real' electronics aren't my thing. Which is probably why my amp tech makes 60 and hour while I make 35...

 

:-)

 

-Gary

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Hi Gil' date='

 

How do I know which version my VJr is? [/quote']

 

That's easy. If your circuit board is black, it's version 3. If your circuit board is green, it's either a v1 or v2. If the front panel graphics stripes are on the same horizontal line as the jack and volume, it's version 1. If the jack is lower on the panel than the volume pot, and the graphics line is up near the top with the Epiphone logo, it's a version 2.

 

 

Also' date=' if I'm wiring to the volume pot doesn't that signal go through the second half of the preamp tube before it goes to the power tube? And if so, doesn't that mean I already have a buffer?

 

Of course, I do IT support so schematics and 'real' electronics aren't my thing. Which is probably why my amp tech makes 60 and hour while I make 35...

 

:-)

 

-Gary[/quote']

 

Right, as long as the fx signal sent to the amp hits a preamp tube first so that it can be amplified to a level useful to the power tube, it's buffered.

 

Gil...

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Hi all,

 

I'm abit of a newbie when it comes to guitar tech, but am interested in adding an 'FX loop' to my epiphone VJ head for more versatility. I'm currently using a Korg multi fx unit. Though will probably use other pedals too...

 

From what I understand (correct me if wrong) an 'FX loop' is generally designed to BYPASS the VJ preamp stage. I've heard this is prefered for effects like modulation & delay as it sounds better to have preamp distortion before the effects instead of after.

 

So do either of these designs do the job, or is a more advanced solution required? Note I don't want to compromise sound quality.

 

http://www.sewatt.com/files/sewatt/VJr_FX-Loops.JPG

http://www.sewatt.com/files/sewatt/PA_IN.pdf

 

And whats the deal with the following thread? Are they saying the VJ doesn't need an fx loop?

 

http://www.ultimate-guitar.com/forum/showthread.php?t=799492

 

 

thank you

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actually I may not bother with the fx loop. I read that modulation/time fx are best done after being miked at the speaker.

 

What might be better for me is to have an optional 'clean channel' on the VJ, so instead of using the VJ's preamp distortion, I can use fx unit/pedal to get the preamp distortion for a more modern/heavy sound. The reason being I heard that the VJ's preamp distortion might sometimes be too 'vintage' sounding? Ofcourse I don't want to lose the sound of the VJ's breaking up power-amp stage...

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Needs are determined by the user, not the peanut gallery. In regards to that ultimate guitar forum, well, armchair quarterback opinions will vary! Folks consult a player if they really want to know what's going on in the huddles.

In regards to the poor fool with the Boss GT-8... he should simply try the loop if he needs a line input. He'll find out it works!

 

In terms of more advanced solutions, yes. There are many ways to skin a cat; but most often, the simplest method is the most effective. Fancier overengineered versions in the big money amps often have their own driver and recovery tube (or SS) stages to handle the loop duties, but all that is really not necessary. The VJr loop versions are integrated into what's already available.

 

The PA-IN version works great if you don't need an fx-send cuz it saves the expense of a jack, but it still requires the expense of a switch and is a little more complicated to install. I designed the VJr-FX-Loops to be the simplest, most direct method possible. It works great with the PODS, Lexicon G2, Digitech 1101, and others I've tested it with.

 

Gil...

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The VJr doesn't really have any preamp distortion. It's all in the power tube. And you're right in that delays and reverbs sound best placed after distortions. So if you really want to preserve your tone and do it right...

 

Get a second VJr. Add a post-OT line out on your primary amp to provide the tone in all its glory to your processor. Install an fx loop return on the second VJr and feed the processor output into that. I've got 3 VJr's that I use this way. One has the post-OT line out, and two with loop returns for a stereo wet side of life. And it's freeking AWESOME!

 

Gil...

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cool thank you,

 

I'm a bit over my head here, but I'd like the VJ to have an optional clean channel, so that can use the FX unit (before the VJ preamp) to get the preamp distortion instead of the VJ's preamp distorting so much. But sometimes I might prefer to use the VJ's preamp distortion instead of the FX unit! But either way I don't want to lose the power-amp stage break up.

 

So I guess what I want is variable VJ preamp distortion (ie clean to heavy) but not want to lose the sound of the power-amp stage breaking up (thats why I bought the VJ-break up at low volume) Maybe some of the kits like Bitmo etc will provide this?

 

Edit; I wrote this before reading your last post.

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Does anyone make a high gain preamp circuit for the VJ (for more metal sound)' date=' but also allows to dial in a clean sound by not overdriving the preamp? Maybe one isn't really necessary..[/quote']

 

The easiest way to get what you want is probably with a pedal in front of the VJr. But sure. DIY'rs make high gain preamps all the time for their own amps, but as far as I know, there are no "mod kits" like that other than an entire amp kit. Check out AX84.com's HiOctane schematics and their sponsor's HO kits

 

http://www.ax84.com/hioctane.html

http://shop.dobermanamps.com/

 

 

Gil...

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thanks for the links,

 

I think I'm starting to nut it out, yep I think will just use a distortion pedal to get high gain sounds (metal), drive (distortion knob) to get what like, and then set the level just before the VJ preamp starts getting buzzy.

 

And I'll stick with the 12ax7...

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got any good recomendations for OD and distortion pedals for the VJ?

 

I've tried a few Boss distortion and OD pedals for the Valve Junior. In fact, a modded VJ head is my main amp right now. I run Boss pedals into the front end for my sound.

 

For OD pedals, I like the OD-2 Turbo OD and the SD-1 Super OD. I have a Digitech Bad Monkey and a Boss BD-2 Blues Driver, but they don't sound as good to me. The BD-2 works better as a clean booster: volume all the way up, gain all the way down, EQ to taste.

 

For distortion I like the Boss MD-2 Mega Distortion and the DS-1 Distortion pedals. Unlike most people, I like the sound of the stock DS-1 through the VJ. The MD-2 takes a little tweaking to get a good distortion sound dialed in.

 

HTH,

 

tung

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I noticed that some of the Bitmo kits have 'gain' 'boost' 'voicing' switches etc...

I wouldn't need all that if have fx pedal, right? Just want to make sure I'm not missing out on anything, lol.

 

I bought the VJ already fitted with a spanky mod & tweed tone control, new OT... My FX unit is an AX1500G, its got a dual channels per effect, good for clean and dirty I guess..

 

thanks

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got any good recomendations for OD and distortion pedals for the VJ?

Keeley/Boss BD-2. My Keeley modded BD-2 is a great clean boost as 'tung' has said' date=' but I also like the gain settings especially if running it [u']after[/u] my compressor. To my ear, the BD-2 is a bluesier OD in that it has more punch and definition in bass-mid ranges than the tubescreamers (which are probably better for higher freq. soloing).

 

Many positive comments here in prior threads on a myriad of pedals & amp modelers w/VJr. Try a search.

 

Hit every BLUE NOTE baaaby..., I'm going to play on:-"

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Hi,

 

I have a epiphone valve junior, I'm looking at replacing the tubes in my amp.

From my understanding (correct me if wrong) its the power tube break up I'm after, the preamp tube break up I can simulate pretty well with a pedal. Ive seen a few people use lower gain tubes in the preamp section, what is the advantage of this? I mean if someone wants less preamp dist all they have to do is use less level output from their pedal (before the VJ preamp), right?

 

What I basically want to know is will using a lower gain preamp tube (such as a 12at7 instead of a 12ax7), give me the same, more or less power tube distortion?

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The 12AT7 or a 5751 will reduce the gain by about 30%. Personally, I don't think they sound like there's that much of a reduction in the power tube grind. I prefer the 5751 because of its slightly brighter tonal character and its oh-so-smooth distortion character when overdriven. The 12AT7 sounds a little stiff to me, and more like just a lower gain version of it's more powerful cousin the 12AX7.

 

Gil...

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