#1
My VJ is now Fender voiced. However I decided I wanted it to be a bit cleaner but also have an option for abit more gain/drive. So I looked around and poked around with the schem. I decided to use R6/R7 seeing as they act as a voltage divider. So I started playing around with R6.

I finally decided on my resistor values, 1.2M and 320K. 1.2M for the Fender side....etc. I select between the two using a DPDT (On-On). That's all cool....I decide the Fender side needed a bit more sparkle and highs, so I added a 250pF cap in parallel to the 1.2M resistor. It works, sounds nice. I might add a switch later to disconnect it.

Anyways on the Marshall side with just a 320K resistor the sound was pretty flat. A good amount of gain but kinda boring. I decided it needed tight bass and more mids like a real Marshall. So taking Mr. Carrot's advice I wired a 1000pF cap in parallel....Yikes way too much treble. So I started increasing the value progressively.

I am currently at 0.22mF and it is still pretty sharp and trebley. But now I have a grounding issue it seems. There is a lot more noise and buzz. It just kinda started happening. Also when I touch the switch or another switch (the other switch isn't even wired) the noise goes away.

So I guess what I am asking is where did the hum come from and how do I get rid of it? I have a few ideas but I am curious to what you guys have to say. Also what value should I try for the Marshall side for tight bass and mids?

Thanks...
#2
Without knowing what the hell R6/R7 are, I'd guess that you've got a crappy solder joint somewhere. You should redo them.
#4
Quote by kurtlives91

So I guess what I am asking is where did the hum come from and how do I get rid of it?
I'll guess the noise was already there, but you're making it more noticeable with the bright bypass on R6.

Quote by kurtlives91
So taking Mr. Carrot's advice I wired a 1000pF cap in parallel....Yikes way too much treble. So I started increasing the value progressively.

I am currently at 0.22mF and it is still pretty sharp and trebley.
I think you're taking the wrong approach. By increasing the value or the brightness cap, you just shift the frequency downward. So now you're not just adding a bit of "sparkle". You're adding bite and mids. I'd put a 1 meg pot in, temporarily to replace R6.

Connect it so the 2 ends are where R6 is now.
Then experiment with cap values between the wiper, and one end of the pot.
Use the pot to dial in how much brightness you add.
Change the value of the cap to change the frequency of where the boost starts.

When you come to a combination you like, you'll have 2 resistors in series for R6.
One of them will be bypassed with your brightness cap.
Meadows
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#5
OK I will try that thanks very much....

I got rid of the 0.22mF cap and the noise seemed to be gone. I was wrong it's still there. I think your right it was probbly always there. I did not notice however when the volume was low. When turned up it becomes quite apparent.
#6
Removing both caps that were in parallel with the resistors helped a lot. Huge decrease in hum. There is still a tiny bit of a grounding issue but I think it has always been there..,

So why did the caps create hum? I really liked the 250pF caps effect but I dont like the noise.
#7
Quote by kurtlives91
Removing both caps that were in parallel with the resistors helped a lot. Huge decrease in hum. There is still a tiny bit of a grounding issue but I think it has always been there..,

So why did the caps create hum? I really liked the 250pF caps effect but I dont like the noise.
I don't believe they did.

The hum is probably not 60 Hz.
It's probably 120 Hz from one of the power supplies.
Could be either the filament supply, if you have them on DC
or from the B+

The caps pass more of the high frequency content of the first stage.
That means the edges of the ripple bleeding into the first stage signal are sharper.
They didn't add to the noise,
they do a better job of passing it from the first stage, on to the second.

Which version of the VJ do you have?
DC or AC filaments?
Any mods to the filament circuit?

If any of your filament circuit is directly connected to ground,
there are some changes you can make, that will probably help.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.