Low freq. excess in Fender Frontman 25r

[Paul Wegmann]

Hi guys! Greetings from Brazil!
I Always felt an excess in some low frequencies in my Frontman 25r, and using a tone generator into the amp, and an oscilloscope, I can observe that we have an increase of intensity in the range of 100 - 90hz, this frequencies really scream and is so bad because you have to play light that notes, sound like a subwoofer, you know... my question is: Why this exact frequencies "scream", and what can I do to resolve the problem? Thank you very much!

[Jazz P Bass]

Using the tone generator, does the bass potentiometer have any control over the 90-100hz frequencies.
Also the mid potentiometer.

[Paul Wegmann]

Yes, I forgot to say we test with bass potentiometer in 0... the mid potentiometer is a High-Mid control, doesn't affect low frequencies... yo know?

[Jazz P Bass]

does the bass potentiometer have any control over the 90-100hz frequencies.

[Paul Wegmann]

sure, yes.... but the level in ZERO, doesn't solve the problem... we have that frequencies very loud anyway...

[g1]

As long as you are sure the bass pot is otherwise working.
A defective bass pot could act like it was set to "10" even though you turned it right off.

[Jazz P Bass]

Exactly.
What I would do is turn all of the tone controls to '5'.
With a 100 mv input signal, plot the amplitude of the frequencies.

What I would look for is any pronounced boost or cut in the plot.
I would expect a mid dip.

Then run a plot with all controls at 1 (off).
Then run a plot with all controls maxed.

I find it odd that the bass control cannot lower the 90-100 hz signal COMPARED to the higher frequencies.

Which brings up the question: how loud are you playing the amp?
And does this problem occur on the clean & the lead channel?

[J M Fahey]

Oi amigo, todo bem?

I guess 90/100Hz is the speaker resonance and the mixed feedback circuit enhances that.

You could have a narrow peak around 6dB, maybe more.

It is added on purpose and if really necessary, it can be taken out.

Are you trying to play loud and clean?
Do you use humbuckers?
Any pedals?
What kind of music are you trying to play?

[Paul Wegmann]

Exactly.
What I would do is turn all of the tone controls to '5'.
With a 100 mv input signal, plot the amplitude of the frequencies.

What I would look for is any pronounced boost or cut in the plot.
I would expect a mid dip.

Then run a plot with all controls at 1 (off).
Then run a plot with all controls maxed.

I find it odd that the bass control cannot lower the 90-100 hz signal COMPARED to the higher frequencies.

Which brings up the question: how loud are you playing the amp?
And does this problem occur on the clean & the lead channel?

thanks jp bass! I'm playing with volume in 3, and the lead an clean channel have the same problem. We tested with all eq. in zero, all in 5, the results are the same, we have that frequencies screaming all the time.

[J M Fahey]

Ummmmmm are you using the original speaker or maybe somebody (you or an earlier user) replaced it?

Sometimes people uses a Hi Fi type woofer and has that problem, overpowering bass, weak treble, lack of volume.

If not the original one, post a couple pictures, front and back.

[Paul Wegmann]

I'm using an Eminence Copperhead, but the problem is not the speaker because we connect the speaker output directly on the oscilloscope...

[Jazz P Bass]

I will ask one more time.
Does the bass pot do anything to the 90-100hz waveform.
If it does not, then you may have a solder issue.
Flip the board over & touch up the tone circuit.

Note: screaming is not a scientific term.

Amplitude is.


here is a plot of a flat frequency response.
Although not what you expect from a guitar amp, it shows graphically what I am getting at.

If there is a pronounced 'amplitude' bump (higher than any other frequency) then there is either something wrong with the amp or that's the way it was designed.
If the later, you may have to change out one or more of the tone capacitors.