Post cathode follower Dual Eq's

[nandrewjackson]

Hello all,


I have this EQ setup up and running in my amp.  The circuit comes off of the FX loop return cathode follower.  Everything works fine, but I'm trying to get a balance between the 2 EQ's volumes.  The "Marshall" EQ is much louder than the "Fender" EQ.  I knew it would be that way prior to the build, thanks to the tone stack calculator, and other research.


When I first built this amp, I didn't have the 500K resistor coming off the "marshall" EQ treble pot swiper in series.  I originally put Resistance to ground from the treble pot swiper, finding about ~20K to ground from the treble pot got the 2 EQs volumes similar to one another.  However, when I had ~20K to ground, it threw the whole science of the EQ out the window and it was nothing like it should've been.


The 500K in series with the treble pot swiper knocked a few dB off of that EQ, but it's not enough.  Will more resistance in series be OK in this location to shave off some more dB's without changing the functionality of the EQ?


I'm starting another amp build, and I plan on using this dual EQ setup on the new build.
thanks in advance.
Noah.


https://drive.google.com/open?id=1og7Z7cbVIQ54O88qykJiH1cYDvGdjH_q

[sluckey]

The 500K in series with the treble pot swiper knocked a few dB off of that EQ, but it's not enough.  Will more resistance in series be OK in this location to shave off some more dB's without changing the functionality of the EQ?

Probably. Give it a try.

Another option would be to stay with the 500K series resistor and change the MV1 to 500K.

Can't you balance the volume between channels using the MVs? Does it matter that the knobs aren't set to the same number?

[shooter]

maybe a quick-test with something like this 

[nandrewjackson]

Sluckey,
MV1 is for clean channel.  MV2 is for distortion channel. the Eqs switch independent of the  channels.
As the amp is now, you can  be playing the clean channel(1) and switch between the 2 eqs, or you could be playing the distortion channel(2) and switch between the two eqs. Whichever channel you're playing, there is volume difference between the eqs.


My goal would be to play channel 1(clean) and switch between the 2 eqs with no noticeable volume change.


Play channel 2 (distortion) and switch between the 2 eqs without hearing volume change.


Shooter, yeah, drawn out like that makes sense.


I'll try higher series Resistance after the marshall eq, I just wasn't sure if it would start to affect the eq curve like the resistance to ground did.


Thanks

[Willabe]

I'd try leaving the 500K series R in place and put an R to ground after the 500K R.

Then you have a voltage divider and the 500K might isolate the R to ground from the treble wiper.

Need more signal loss, decrease the R to ground value.

[nandrewjackson]

Willabe, you might be on the right track,


I changed it today, the majical, non-scientific, listening by ear resistor value I settled on is 1.2M in series with the treble pot swiper output.


The Eq does retain 98% (that's 98 scientific percent %  )  of it's intended functionality, but it seems the high end is being attenuated more than the rest of the spectrum.  The 2 EQ's are now very similar in apparent volume when switching between them.


I suppose I'll try 500K off the swiper in series, and then some resistance to ground, maybe that can save the little bit of high end that 1.2M seems to be eating up.

[Willabe]

The higher the series resistance the more high end will be attenuated.

You can try putting a small value cap in parallel (||) across the 1.2M R. It will bypass the highs around the 1.2M R. You'll have to play with the cap's value, might start with as small as 100pF?

But 1st I'd try a voltage divider like I described above, with the series R before the R to ground.

You might have to bypass the series R in the voltage divider.

[d95err]

Try this: split the cathode of the cathode follower into 47k + 47k. Take the input to the Fender eq from the cathode and the input to the Marshall eq from between the two cathode resistors.

[nandrewjackson]

Will abe,  d95err , I'll try both of those ideas,  but not in this amp. I'm building a new, 4 channel, 2 Eq amp, I'll try those ideas in there.


This 2 channel,  2eq, chassis is a mess, it's going on a shelf for a bit. It sounds good, but it was my first build combining terminal strip / point to point,  with vactrol(LDRs), and there's spaghetti flying everywhere in there. My new build has more LDRs, but it won't be such a mess of wires inside, it will still be terminal strips / point to point, but a new switching system for the  vactrols(LDRs) will reduce the amount of spaghetti.



Thanks.