Lowering the bass in 124 power amp

[Joost]

I love my 124, but there is just too much bass in the power amp, even if I use my axe fx 2 preamp.

What are the best ways to cut the bass in the power amp? Take the 0.1 caps to 0.05? What caps are best? Most efficient and transparent?

Btw, I also have a built-in dumbleator so that may factor in on the return side

[tubedogsmith]

Changing your PI caps would help but may not do all you need. do you have a schem of what you've got so we're all looking at the same thing?

[Joost]

Thanks. I have the standard 124 phase inverter and this dumbleator built inside: http://ampgarage.com/forum/viewtopic.ph ... c&start=15

[aflynt]

Maybe try lowering the .1uF coupler on the loop return pot to .047uF or .02 if the PI caps don't taper enough off?

-Aaron

[markusw]

You could try to reduce the 20n cap feeding the PI to e.g. 1n....maybe even 500p or lower.


Peace,

Markus

[crbowman]

Some version of the 2nd generation 'James Configuration' on the bass pot might help.
I know that once I omitted this on my #40 build, bass response increased dramatically!

[Structo]

I love my 124, but there is just too much bass in the power amp, even if I use my axe fx 2 preamp.

What are the best ways to cut the bass in the power amp? Take the 0.1 caps to 0.05? What caps are best? Most efficient and transparent?

Btw, I also have a built-in dumbleator so that may factor in on the return side

Does the AxeFX2 have any provision to alter the tone or treble/ bass?

[Joost]

I love my 124, but there is just too much bass in the power amp, even if I use my axe fx 2 preamp.

What are the best ways to cut the bass in the power amp? Take the 0.1 caps to 0.05? What caps are best? Most efficient and transparent?

Btw, I also have a built-in dumbleator so that may factor in on the return side

Does the AxeFX2 have any provision to alter the tone or treble/ bass?

Yes, the axe fx 2 has many options to do that. It has several graphic EQ options, both globally and per patch. However, there still is a lot of bass in my amp when I don't use the axe fx 2. And I think the bass sounds wooly even when I use the graphic EQ on the axe fx 2.

But, most importantly, instead of surgically removing the bass on every patch, it made more sense to fix the problem at the source.

[markusw]

To avoid unsoldering any caps you could just add e.g. a 1n-2n cap between master (in your case this should be the recovery pot after the built in D'lator) and the 20n PI entrance cap and see (or hear) if you like it.
This way you just have to unsolder one wire from the wiper of the master pot. You could just solder the cap to the wiper with one leg and solder the wire to the other leg of the cap.

2n in series with the 20n entrance cap will yield a net capacity of 1.8n.
1n in series with the 20n cap will yield a net capacity of 0.95n.

So, in both cases the knee of the PI entrance high pass will be shifted to higher frequencies.

Peace,

Markus

[Structo]

I've always thought my 100w clone had a lot of bass.
When I moved it more towards #183 specs, such as the PI output caps at
.05uF from .1uF it helped calm the bass.

I set the bass pot at about 10:00, mid pot at 12:00 and treble at 2:00.

I also changed the tail resistor on the bass pot from 10K to 1K which helped
a bit but really helps when PAB is on.

Also speaker cab placement has a huge effect if the back is open or semi-closed.
I use a vintage VOX 2x12 30" x 22" x 11.5" with two EVM 12L Classics.
The back has a five inch open slot.

It sits sort of in the corner of my room so I'm sure that adds to the bass response.

If you are just using the power amp I would suggest you try lower value coupling caps
on the PI.

And you could experiment with the presence circuit components.
Or even give Martin's Presonance control a try.