Question about adding caps with this bright switch

[cap217]

This is the vox ac30 I have another thread about but this is more specific and I hope I can get answers. This all has to do with the normal channel.

I attached a stock layout that was from a web site with mods. Mine is modded by pisonic and has a push pull pot so keep that in mind. The stock layout shows the normal volume pot with a 220pF from the middle lug to the bright switch top lug. Mine was switched to 68pF but I recently put it back to 220.

1-Stock shows the volume pot right lug to a 330k resistor split to the bright switch middle lug and then to 10m resistor to ground. Mine doesn't do that. Mine goes from volume pot right lug to bright switch middle lug then to the turret board but I assume 10m to ground. The 330k resistor isn't there and I read that people remove the resistor to make the normal channel achieve more of a Brian May drive. I have also read that it can be dropped to 160k. How would I add the resistor back in? Is it the same if I put it from the right lug to the 330k resistor to bright switch middle lug to 10k r to ground or does it need to split from the 330k resistor right away? I hope I explained this correctly.

2-Next, in the stock layout, the bright switch bottom lug doesn't have any connection but on mine the bottom lug goes to an added resistor on the turret board. The resistor colors are brown-black-green-gold which is 1M. What is this doing?



I added a 120pF cap from the volume pot middle lug to the right lug to brighten up the normal channel with the bright switch off. With the bright switch off I get a big full sound and a good balance of highs and lows. I would like a little more highs and I might make this a 150pF when I order some. But when I switch the bright cap on, the tone gets really bright (which is ok) and losses fullness and body. It's almost a scooped mids sound. I actuall like it if there were a way to add in more bass. I do use the cut but it doesn't do what I am looking for but gets close.

I would just like someone to explain what is going on here vs the stock circuit and if there are things I can do to add low end or anything else.

[cap217]

I might have found the 330k resistor although it's a 220k. Since the volume pot is a push pull I think it was made to switch in and out this resistor. The resistor is in the bottom right of the pic and soldered to the board. There is also another wire from the pot to the board as well.

Can someone explain this?

[Reeltarded]

The 330k. Remove it. The 220p is a peaker over it with the 330k as a mixer. That is an RC circuit that works all the way up and down the volume control. It totally revoices the amp.

I would remove the 120p. I would defeat the switch. Remove the 330k and the 1M. I would put the 220p across the wiper and input lug where the 120p is now.

Try that. If you need more brite after that you can go up to maybe 500p as long as it's not over a resistor.

[Reeltarded]

Oh, and when you have that switch free we'll do two things. The mixers after that stage we'll raise the ground side to double, then we'll put a resistor half that value on the switch and over that side of the mixer.

You will have an identical sound and drive as you have now with that switch on, but more drive than you have now when it's off.

[cap217]

The 330k. Remove it. The 220p is a peaker over it with the 330k as a mixer. That is an RC circuit that works all the way up and down the volume control. It totally revoices the amp.

I would remove the 120p. I would defeat the switch. Remove the 330k and the 1M. I would put the 220p across the wiper and input lug where the 120p is now.

Try that. If you need more brite after that you can go up to maybe 500p as long as it's not over a resistor.

Totally re voices the amp in what way?

I just put the 120 on and changed the 220 from a 68. I like what that did so far.

What is the barite switch doing now? I know it's more than just introducing a cap.

[Reeltarded]

RC. There are calculators all over the web. 120p is .00012MFD. 330k is 330000 ohms. Or did you say it turned out to be a 220000 ohm resistor?

That corner frequency you see in the calculator is where the high-pass filter starts. If you make it pass above 500hz you will be tragically unhappy. AC with no ass might as well be a tiny Line6 Spider with a DOD Glassbreaker in front of it.

You actually told me what you wanted in the original post. You said in lots of words that you wanted to have a simple brite cap. I read between the lines. Brite caps are black art. Imma brite cap ninja.

Try 220/250p and then 500p if you gotta have more. These caps are all but defeated by around 7 on the volume and good, because that is where the amp is brite enough to stand on it's own.

[Reeltarded]

http://www.muzique.com/schem/filter.htm

There is a place to look at the cutoff of simple filter networks.

[cap217]

It is a 220k in there now. Sorry I confused you but I mentioned 330k because that's what it is in stock form.

With bright caps, does it have an inverse effect on the bass and mids? I don't think it does and just acts as a high pass filter, right? So if I wanted to add more bass to the channel, what are my options?

[cap217]

http://www.muzique.com/schem/filter.htm

There is a place to look at the cutoff of simple filter networks.

This helps. Thanks



I have 220k resistor and 120 cap and a corner freq of 6,000 hz. If I go to a 220 cap I can get this down to 3,200 hz. I am starting to get this.

[Reeltarded]

More bass? Less brite. A cap over a resistor is a peaker that bypasses everything above, and cuts everything below, normally -6dB per octave.

Remove all connections from the switch to the volume and throw a 220p over the center and right outer lugs. It will take you less time than reading this reply. Bet ya. Go!! You'll say "Oh!! Why didn't you tell me??" but did telll you.



Peakers revoice the whole damned thing. You want normal with a little brite addon. That's all. A volume control with a brite cap.

[cap217]

Thanks. Too late to mess with this now and then play the amp. I wish I had an identical amp to compare these changes. I might get one just to see.

Is my peaker only in the circuit when the bright switch is on or push/pull activated? Or is it always in the circuit? I think it's the push pull that changes it.

Now can you help me with my other thread in the vox section? It's about the filter caps not matching.

Thanks in advance

[Reeltarded]

Yeah I'll look, but please defeat all of that and only use a 220-250p over the volume knob for a naturally full tone with a tilting hint at highs, all you need and all you'll ever want again. Search is over. Trust me. Makes it sound like what you'd expect.

[cap217]

Can you tell when this peaker is active? Does it have to do with the push pull? When it's not active, is it working as a normal volume pot bypassing this resistor and cap?

[Reeltarded]

For examination let's look at what I am most familiar with. Marshall 4 input models.

The bright channel has a 470p to 5000p cap over the volume control, and a 470k split mixing network between the first stages and the second. The bright side of the mixer network has a 470p over it. This creates a peaking effect for that channel. (It also affects the normal channel, but we are not worried with that)

Someone check my maths (because I am not using any) but the 470k//470p bypasses everything above a midband frequency. (Around 700hz.. I am thinking) because the lows aren't sent over that bypass the outcome is a boost at all frequencies above the cutoff.

This is antismooth. Ganky kerrang. It's the face of the amp.

Volume control

The amps with a 2000p to 5000p cap over the volume control are too touchy to use at your grandmother's house. She will shoo you off with a broom by the time you get the amp on 2 because once you crack the volume most of the signal is already present at the wiper. Turning the control up only makes the amp more fat and distorted. That is because as you approach a virtual infinity of resistance the cap has less effect. A 100p is very Voxy. A 250p is very JTM. A 470p sounds like the Marshall I expect.

These circuits do similar things, so this is a place to balance carefully.

If you really want to know, please remove the switched components and use only a 220p cap over the volume. Put a 220k resistor on the switch in parallel with that cap. When you switch in the resistor the ass will fall off and your gain will go up.

To get away with what you have I would bet you are using 85 to 90% cut with the bass cranked. Silly. Out of range. No fine control. The goal is to get the controls in the middle when it's awesome. Controlled headroom is king.

[cap217]

I will try taking everything off like you are saying. And I cant crank the bass on this because just the volume and cut work on the normal channel. That is why finding the balance here is very important to the overall sound.