5e3 coupling caps to reduce bass

[BluesDude]

Now that I am getting familiar with my amp (5e3)... I am discovering that it is a little heavy on the bass.


I read about swapping the coupling caps with lower values.

This is a basic question. What does people normally swap out?

Coupling caps going to the 2nd preamp stage or both 2nd preamp and power amp stage?

Likewise, do people normally make these changes on both normal and Bright inputs?


One other question. Since I am not afraid to break out the soldering iron... I assume that this is preferable (cheaper) that trying to attack the situation with a speaker replacement (I have the weber Sig 12s). Or do I have those mods mixed up? Perhaps someone could compare and contrast these two mods.

Thanks. This forum has been a wealth of information. I really appreciate the help.

[fyl]

Coupling caps going to the 2nd preamp stage or both 2nd preamp and power amp stage?

You can try different combinations, depending on your guitar and playing style.

If you use single coils and play old style, lower the preamp coupling caps to 47n. Or try 47n in the pre and 47n in the power amp.

If you use humbuckers and play more aggressively, you may consider using 22n for the preamp and 47n for the amp, or 22n everywhere.

You may also lower the value of the first cathode bypass cap, going from 22 or 25µ down to 10 or 4.7µ.

Likewise, do people normally make these changes on both normal and Bright inputs?

Both.

[tubeswell]

Even for single coils, 22nF is appropriate for the 1st stage coupling caps in a 5E3, whilst still having a good broad audible freq response.

IMHO, you won't get any bass rolloff going down to 10uF on the Ck, or even going down to 4.7uF; you have to go down to 2.2uF or lower (on the first stage) before you start to notice anything much in the way of less boominess as far as geetar frequencies are concerned. 2CW

[fyl]

IMHO, you won't get any bass rolloff going down to 10uF on the Ck, or even going down to 4.7uF; you have to go down to 2.2uF or lower (on the first stage) before you start to notice anything much in the way of less boominess as far as geetar frequencies are concerned. 2CW

Agreed, but a 10µ or 4.7µ cap also lowers intermodulation, thus leading to a somewhat tighter sound.

[hasserl]

I favor 4.7uf cK on the 1st stage. There is definitely a reduction in and a tightening of the bass from that value, quite a bit to be honest.

[cminor9]

I like .022 on the channel tied to the tone control, and .033 on the other channel. .047 for the other three coupling caps.

That setup can go from fat, bassy, but muddy with humbuckers (aka classic) to sharp and cutting to all points in between.

[BluesDude]

Anybody have any idea of how I can calculate the changes that will occur by modifying bypass caps and coupling caps to different values. I am aware of the RC formula.

If possible could someone reference a 5e3 schematic (perhaps the original fender) and identify the components and values for both bypass and coupling so I can get an idea (at least) from a numbers angle of the frequency that will be cut and the rate of drop-off. I assume the frequency that is reduce will taper down at an angle (as opposed to a vertical cutoff).

I do not have the test equipment to measure it and compare the original state to the modified state.

Of course, I will listen and make a subjective judgment (which is important). But if I try several variations... it is easy to get lost and confused. Plus since the speaker comes into play it will color the information somewhat (and I might wind up switching speakers later).

I am intending to record some tests so I can play back the various modded values several times to analyze the outcome. I was thinking about doing this with a mic through the speaker and just straight out of the amp (using the Mass as a dummy load) with the speaker removed from the equation.

If I record these tests, does anyone know of some good software to analyze the results? So I can see the difference? Has anyone done this or approached the comparison that way? There seems to be quite a bit of recording software that can analyze mp3 and wav files.

Any recommendations would be appreciated.

[tubeswell]

Anybody have any idea of how I can calculate the changes that will occur by modifying bypass caps and coupling caps to different values. I am aware of the RC formula.

This really requires a few hours of heavy reading, for which there are two really good chapters (1 & 2) in this book.

Designing Valve Preamps for Guitar and Bass by Merlin Blencowe in Engineering

A free (pre-publication) version of Ch1 is on Merlin's website, which explains basic triode functions and DC load lines, which is not that hard to plod your way through if you re-read it a few times (but even so, its a lot easier than reading RDHB4). See:

http://www.freewebs.com/valvewizard1...Gain_Stage.pdf

Ch2 builds on the first chapter and goes on to explain AC load lines and coupling and how each stage's input and output impedance play a role, together with coupling, in shaping frequencies between stages. You really need to become familiar with this sort of stuff to attempt to understand how to break it down into calculations. I am only a beginner on this journey, but I recommend the book.

[ThermionicScott]

BluesDude, here's the schematic/layout if you didn't have it yet: http://www.ampwares.com/schematics/deluxe_5e3.pdf

- Scott

[Bruce / Mission Amps]

Quite a few years ago, (hard to believe it... but it was a ways back)
after reading a bunch of stuff on Randall Aikens killer website,

Aiken Amplification

I did all the math and whipped up a chart showing the 3dB points of a 12AX7 with a 100K plate load resistor and a whole slew of cathode resistors and cathode bypass caps.
Although not deadly accurate, this should help you quite a bit.

[BluesDude]

Appreciate it Bruce. I am sure a number of people can take advantage of that information.

[BluesDude]

Here is a site that has a coupling cap calculator and some other useful information and calculators.

Here is the Coupling Capacitor Calculator with a brief explanation of what occurs.

There is also a Bright Cap Calculator, a Bypass calculator with brief explanations. Very helpful for newbies like me. It helps to do the calculation and see how the numbers change (for me). The visual feedback helps me to better understand the dynamics based on the sensitivity. This in essence provides a data point in Bruce's grid... which was very helpful showing how things change.

[d95err]

Anybody have any idea of how I can calculate the changes that will occur by modifying bypass caps and coupling caps to different values. I am aware of the RC formula.

Due to the backwards wired volume controls, the cutoff frequency will change with the position of the volume control. The lower volume, the less bass will be let through. With the standard 0.1u coupling caps it is probably not that noticeable. However, if the coupling caps are made smaller, the amp should get brighter at low volume.

[Dave H]

Anybody have any idea of how I can calculate the changes that will occur by modifying bypass caps and coupling caps to different values. I am aware of the RC formula.

Any recommendations would be appreciated.

It is possible to do the calculations but a full circuit analysis is going to involve a lot of tedious mathematics involving complex numbers. It makes my head hurt just thinking about it. These days I wouldn't even attempt it. My recommendation would be to model it in LTSpice. It's a free download. If you want to try it I could give you the tube models and a circuit similar to the 5E3 that could be modified but it won't tell you how it's going to sound

Dave H.

[wizard333]

Whats LTSpice?