Is this the PI coupling cap?

[KeithC]

In trying to tame the boomyness on a Fender I hear that changing the PI coupling cap to a lower value will help.

If so is the cirlcled ceramc disc cap the right one?

http://i43.photobucket.com/albums/e365/blueprintk/supercopy3.jpg

Thanks

[Swarty]

Yes

[KeithC]

So if that cap is .01 and I change it to the old BF value of .001 it might help that?

Or I understand that using a 100k bass pot might do the trick too.

BTW: Thanks :)

[scottl]

You could also change it to a .002uf or any in between size.... Maybe reduce the bypass caps on V1a and V1b to 10uf or 4.7uf as well...

So if that cap is .01 and I change it to the old BF value of .001 it might help that?

Or I understand that using a 100k bass pot might do the trick too.

BTW: Thanks :)

[TheAmpNerd]

In trying to tame the boomyness on a Fender I hear that changing the PI coupling cap to a lower value will help.

If so is the cirlcled ceramc disc cap the right one?



Thanks
The first thing I would do is fix the cold solder joint that you have
where the 2 x 220K resistors meet the cap.

Not sure why it would be bommie, try turning down your bass
and turn up the treble. Also make sure the caps you have upstrream
are working properly.

Make sure the little treble caps haven't drifted from value nor are
micro phonic.

Good Luck

[KeithC]

I'll check that. The cap was changed before I got it to .001

Next time I have it open I will suck out the solder and re solder that point.

I can turn the bass to about 2 3/4 - 3 and get it sounding great.
Really for my ears that is how I like Fenders anyway.

But, it seem to have some ghosting/boomy stuff going on when the bass is up pretty far. Not that I run it that way but I was thinking maybe the filter caps are not filtering well and causing ripple?

They say a little knowledge is dangerous! And, I have just a little ;)

Thanks,
Keith

[John Phillips]

That's normal for BF Fenders. The bass response is actually too deep (too low-frequency, not just too much of it), so turning up the bass control too far (typically above 4) makes the sound boomy and a bit overloaded-sounding without actually adding much more useful bass.

SFs are actually slightly better in that respect, the bass is just a little tighter, just enough to make it useful - even though SFs use the .01uF cap. But it's not just the cap that's different - the PI grid and plate resistors are different, which are probably the more important change.

What you have is BF PI resistors with an SF input cap, which is probably the worst of both worlds. The easiest fix is to replace the cap with a .001, definitely.

[KeithC]

John,
Thanks for the info. But, I'm not following on which cap is the SF input cap you refer to.
I will gladly change it out!

I thought I looked at the caps around the PI circuit and they are the BF values.
I also have a 100K pot I got to try as the bass control pot.

But, if I am missing an easy cap change I will try that first.

Thanks
PS: here is a look at the whole board.
Note that I have already changed out the bias circuit to a bias adjust pot but this pics is before that was done.


http://i43.photobucket.com/albums/e365/blueprintk/Super/SuperChassis003.jpg

[John Phillips]

John,
Thanks for the info. But, I'm not following on which cap is the SF input cap you refer to.
I will gladly change it out!The cap we are already talking about, of course!

I thought I looked at the caps around the PI circuit and they are the BF values.Exactly. You have BF PI values with a SF (.01uF) input cap. Change one or the other - the cap is easier. Personally I think changing the whole PI to SF values would be more effective, but it's more work.

I also have a 100K pot I got to try as the bass control pot.Don't. It will just give you a restricted control range and won't change anything about the actual bass response at all.

[KeithC]

OK...the ceramic disk cap I circled in the first post is already a .001 which should be BF value.

The only other things that were changed were the 47k resistors to 100k and 82k.
Other than those changes the only other thing changed was the bias adjust mod.

The thing is I looked on the AB568 layout and it does show that cap as being a .001 anyway.

The AA270 SF SR layout shows the .01 cap.

But, looking at the bias circuit mine definitely has (had) the layout of the AB568.

Besides the extra caps and resistors on the 6L6's the only other differences between the AB568 and AB763 circuits I see are the bias circuit and the 47k PI resistors.


While I am picking your brain. Would you advice changing out the brown turd tone caps? I don't use input 1 so I would just be changing the Vib input.

If so what caps are recommended for these?
I hear good and bad about orange drops.

Or, in am I worrying over minutia?