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#1
I am planning on modding my bro's VJ, and had a couple questions.
I want to add a bright switch, fender style. I'll I need to to is hook up a small cap with a spdt, correct?
I want to add a master volume, I can just use a pot over R5 right? Do I take out the resistor or leave it in? what value pot do I use?
I have seen some modded VJ's with a gain switch, how do I install one?
Is it worth changeing the 500 volt 22uf caps to 40uf caps?
Thanks a lot!
#2
Use a 250K pot for the mater volume and when you install it remove R5. I think it sounds better when you ditch R15 as well.

For the gain switch you need to bypass R6. Could do this by removing the resitor and adding a little wire instead, or you could leave the resistor in and and a switch with wire running from each side of the resistor to the switch. That way when the gain switch is on the electricity will bypass the resistor and when it's off it'll be forced through the resistor.

You could also add a crunch switch my wiring a switch with a 100K resistor in series with r4

If you want to make the amp sound more like a fender you can change R8 and R9 to 1.5K (rather than the 2.2K that is stock) This will darken the tone but give you more gain and smoother distortion. You could also opt to simply change R9 and leave R8 stock. This will give you better gain and smoother distortion but won't take away so much high end.

You could change R1 to a 1M resistor (from the stock 68K). This will give you more gain and more sparkle in the high end.

A fender style bright switch would have a 120pF cap that connects the middle lug of the volume pot with the lug that is connected to the grid of the next stage. When you are looking at the back of a standard pot with the lugs facing up, it would be the lug on the right hand side. Your switch would be set up so it connects and disconnects one side of the cap.

Finally for the filter caps. I'd ditch the stock caps and replace them with sprauge or TAD caps but If it were me, I wouldn't change the value of the caps. Larger caps gives you more low end and a more solid tone. Smaller caps give you a more compressed, spongey, brighter tone. Only increase the cap value if you get an out of tune note over the top of whatever note you are playing.
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Last edited by CorduroyEW at Jun 4, 2008,
#3
Another way to install a bright switch is to wire one parallel to R6.

For the master volume if you just remove R5 and replace it with a pot you will get a terrible master volume control. In my VJ mod thread I suggested a better way. I cant remember it exactly right now but have a look.

I would also replace the coupling caps with nicer ones, C1 and C2.
#4
Where on the board does the bright switch connect? And CorduroyEW, R1 is 1m stock on the V3 head, which I have. My bro is happy with the voicing of the amp for the most part, he just wants a little more headroom and some more options.
#8
Quote by SVStee



I think that is actually backward. The cap runs between the right and middle lugs when the lugs are facing up and you are looking at the back of the pot.

When the lugs are facing down the cap would need to jump the left and middle lugs.

or you can do the same thing over R6


That will give a nice treble boost but it wouldn't be the fender style boost. A cap over R6 will give you the same amount of treble boost all the time. Fender style treble boosts become less effective as you turn the volume up. The boost on the volume pot is good for people that want thick lead tone and open clean tone. The boost over R6 is better for people that just want to have more treble.
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#13
one other thing, can I use spst's or do I need spdt's for the gain and bright switches?
#14
Sorry, one more thing again. Can I use that bright switch cap on the 250k pot I'm putting in, or does it have to be on the origanal 1 meg volume? Thanks for all the help!
#15
The earlier you add the bright switch the more effective the bright switch will be and the more blanced your tone will be at the end. Valves amplify and compress the signal. The extra amplification means the bright tone is more noticeable and the extra compression means it blends with the rest lower frequncies leaving you with a smoother tone.

Try both and see which one you like better.
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#16
Curses! I did eveything the way I drew it in the layouts, with the sole exeption that I used spst switches for the bright and gain switches. when I turned it on, connected to a speaker, I got no sound. I flipped all the switches and tunred all the pots but nothing. I turned it off so i wouldn't burn it up. any ideas?
#18
Things it could be...giving us the little details you did.

Cold solder joint
Loose wire
You forgot to put back one of those push on wire things
Loose tube
You screwed up a trace
#19
^+1

Did you just do the gain switch and the bright switch?
When you did the gain switch did you remove the resistor or just solder to it?
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#20
I added a volume pot replacing R6 and hooked the bright switch to that. And I just soldered to th resistor, I pulled on leg ou like in my paint drawing.
#21
^you shouldn't have pull one leg out. Put the leg back in and resolder the joint from under the board and see what happens.

As a side note, it's a good idea to only do 1 mod at a time so that you can know exactly where things go wrong if they go wrong.
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#24
The wire on the left needs to be in the middle.


On second thought... That still isn't right! The signal runs in on the right, out in the middle, and grounds on the left. I'm assuming that is the master volume you are going us which means that the right lug comes from C2 the middle lug connects to the side of R15 that leads to the output tube, and the left lug connects to R5 on the side that went to ground. You must phisically remove R15 and R5 for this mod to work properly AND you have to be sure you are connecting the correct holes. If you don't, they won't make sound.

Have you restored the thing back to original yet? You need to put it back to original so that we can be sure you didn't burn up the circuit board. Only after you get it working again should you try and change stuff. Change 1 thing, see if it works, and if it doesn't tell use what you did and ask how to fix it. Don't do 2 mods at once. For example, that pic you showed use has a bright switch and a master volume. That counts as 2 mods.

Another note, by installing the pot as a variable resistor (which is what you tried to do) rather than a voltage devider (what I suggested you do) the cap across the pot will act as a trebble bleed rather than a treble boost.
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Last edited by CorduroyEW at Jun 14, 2008,
#25
OK, I'll restore to original.
Last edited by SVStee at Jun 14, 2008,
#26
OK, I have it working and tried to put the 250k pot in, taking out the resistor, to act as a volume. the amp works fine, but the pot I added has no effect. I have lugs 1 and 3 soldered were the resistor was, and nothing coming out of lug 2. do I need to ground it or anything?
#27
^thats because you have just installed an adjustable impedance and NOT a volume knob.

I have already taken the time to tell you how you should wire the pot. Go back and re read it! I tell you what to do with each of the 3 lugs. (yes, you have to use all 3)
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Last edited by CorduroyEW at Jun 18, 2008,
#30
Quote by SVStee
Sorry, but I looked back through the thread, where did you say how to do it as a voltage divder. I looked at all your posts


Quote by corduroyew
the right lug comes from C2 the middle lug connects to the side of R15 that leads to the output tube, and the left lug connects to R5 on the side that went to ground. You must phisically remove R15 and R5 for this mod to work properly AND you have to be sure you are connecting the correct holes. If you don't, they won't make sound.


The best way to figure out which side of C2 you need to connect to and which side of R5 to connect to is to look under your board and follow the copper trace... If you simply play a game of guess and check that won't hurt anything either.
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Last edited by CorduroyEW at Jun 18, 2008,
#31
How did I miss that... V3 is a solid black board, and I won't be able to see the traces. guessing time!
Kurtlives, just wondering, why a 500k pot instead of a 250k?

Thanks to both of you for putting up with me.
#34
1. If you don't use lug 2 of the pot then the resistance is set and cannot be adjusted. The middle lug is the wiper, it is what controls the resistance. It is the mechanical "arm" that moves across the carbon track inside the pot. So basically what I am saying is use lug 2 and one outside lug. Figure out how you want the control to function then select the proper outside lug.

2. That resistor is actually in parallel. And yes you can do that, I personally did something similar.
#35
So on the gain pot I solder lug 2 to lug 1 or 3?
Also when I attach lug 2 of the master volume pot to r15, do I remove the resistor? I don't think I do.
#36
You lift one end...I think the end that is attached to one of the coupling caps. I explained that in my thread.

I think the gain is increased as the resistance goes up. Position your pot as it would be on the chassis. Now place one lead of a multi meter on lug 2 place the other on lug 3. As you turn the pot CW does the resistance go up. If so use those lugs, if not use the other lugs.
#40
tried and got no sound... I think i'll try it without the gain pot... any thoughts?
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