5E3 uneven frequency response

[Arry]

Hi everyone. I recently built my first amp, a 5E3 Deluxe. I followed the original layout but chose to install different values for the coupling caps in order to reduce the bass response of the amp (.022 for the nomal channel, .047 bright, .01 for the phase inverter, and .022 output coupling caps).
The amp works fine and the voltages are correct, however I'm experiencing a strangely uneven frequency response, compared to all the amps I've played so far (including other 5E3 amps).
The best way I can describe it is that certain notes (especially the notes B, D and E on the guitar third string - and the same frequencies on other locations of the fretboard) have more gain and sound noticeably louder than the rest of the spectrum. I'd like a more even, linear behavior. To achieve that, where would you start?

It's definitely not a guitar related problem, as it does it with different guitars. I thought it might be a room resonance issue but again, no, even when played on a big stage the problem is there.

I believe the wiring is nicely done, I checked (and re-did) all the soldier joints but it didn't make a difference. Rolled different tubes through it to no avail.

Thanks for your help!

[shooter]

in order to reduce the bass response of the amp

did the amp have the same "issue" before you changed the caps?

[PRR]

> certain notes ...have more gain and sound noticeably louder

Speakers can do that too.

[Arry]

> certain notes ...have more gain and sound noticeably louder

Speakers can do that too.

Yes, but I tried the amp with different speakers, and the "loud notes" stay the same unfortunately... I think it is an electrical problem.

[Arry]

in order to reduce the bass response of the amp

did the amp have the same "issue" before you changed the caps?

So, the only caps that I changed are the output coupling caps: I started with the stock .1 caps but quickly went to .022 to tame the bass.

From what I can remember: I started noticing this "resonance" issue after installing a new O.T., I was trying to reduce bass and wondered if a different o.t. would help. The new o.t. didn't do much and so I went back to the stock o.t. and started noticing a louder D4 note.

After some time the amp started producing a loud crackling sound, not always, sort of an intermittent issue. By tapping with a wooden stick I noticed that the taps were amplfied when tapping on the power tubes cathode resistor; tapping on it would also make the power tubes flash... I replaced the cathode resistor and the crackle went away for good.

But, that's when I noticed the resonance issue: not only the D note is louder, B, Eb and E are noticeably louder.

In a situation like this, what are the things you would check in the circuit? It would be helpful to know where to start... 

[shooter]

It would be helpful to know where to start..

i'd start with a sig-gen and scope 80Hz 200Hz 400Hz 800hz, 2Khz 4Khz.  plot the data, verify the data matches my ears, then work my way from input to output, but that just me 

[dwinstonwood]

Just throwing this out there...

I have once or twice noticed an unevenness in the loudness of notes and strings when playing through a new amp.

My solution was to raise and lower the treble and bass sides of the pickups until I got all of the strings balanced.

I found that getting my pickups optimized actually made my other amps sound much better, too.

It's free, quick and easy, and it's just as easy to change them back.

[Arry]

It would be helpful to know where to start..

i'd start with a sig-gen and scope 80Hz 200Hz 400Hz 800hz, 2Khz 4Khz.  plot the data, verify the data matches my ears, then work my way from input to output, but that just me 

Thanks Shooter. Unfortunately I don't have an oscilloscope... Is there any specific part of the circuit that could be responsible for this issue? If I had to try replace some components, where should I start?

[shooter]

I'd try the "option" given in reply #6, seems easy enough.
Shot-gunning a nuanced problem like yours is asking for trouble. 

[pdf64]

… the amp started producing a loud crackling sound, not always, sort of an intermittent issue. By tapping with a wooden stick I noticed that the taps were amplfied when tapping on the power tubes cathode resistor; tapping on it would also make the power tubes flash... I replaced the cathode resistor and the crackle went away for good.

But, that's when I noticed the resonance issue: not only the D note is louder, B, Eb and E are noticeably louder.
…

Did you also replace (or even refit) the bypass cap across the cathode resistor? The original cap may have been damaged by excessive voltage if the resistor was intermittently open circuit.
An unbypassed output valve cathode will tend to result in the amp having a higher output impedance, so be more prone to its stage gain tracking any variations of load impedance with frequency.

[Arry]

… the amp started producing a loud crackling sound, not always, sort of an intermittent issue. By tapping with a wooden stick I noticed that the taps were amplfied when tapping on the power tubes cathode resistor; tapping on it would also make the power tubes flash... I replaced the cathode resistor and the crackle went away for good.

But, that's when I noticed the resonance issue: not only the D note is louder, B, Eb and E are noticeably louder.
…

Did you also replace (or even refit) the bypass cap across the cathode resistor? The original cap may have been damaged by excessive voltage if the resistor was intermittently open circuit.
An unbypassed output valve cathode will tend to result in the amp having a higher output impedance, so be more prone to its stage gain tracking any variations of load impedance with frequency.

Thanks pdf64, I had not thought of that. I did replace the resistor but not the cap, I'll try that and report back!

[Arry]

I'd try the "option" given in reply #6, seems easy enough.
Shot-gunning a nuanced problem like yours is asking for trouble.

Thanks for the heads-up. However, it is not a guitar problem. The same guitar through my other amps sounds just fine with no weird "louder notes". Lowering and/or raising a pickup is certainly going to give the proper balance across the six strings; but the problem I have is that certain notes up and down the same string are louder/gainer than the others when I play through this particular amp...

[sluckey]

The best way I can describe it is that certain notes (especially the notes B, D and E on the guitar third string - and the same frequencies on other locations of the fretboard) have more gain and sound noticeably louder than the rest of the spectrum. I'd like a more even, linear behavior. To achieve that, where would you start?

I followed the original layout but chose to install different values for the coupling caps in order to reduce the bass response of the amp (.022 for the nomal channel, .047 bright, .01 for the phase inverter, and .022 output coupling caps).

I've never noticed that with my 5E3. Nor have I ever heard of this particular problem. Maybe a better starting point would be to use original values for coupling caps and reevaluate the sound.

[dude]

Try going back to the original caps on the schematic, then change one coupling cap you did but one at a time, then play (possible bad coupling cap?). Also check for any poor solder contacts. Tap on the pre-amp tubes, if excessive noise try replacing that tube. You did try another speaker, right? All above and still the issue, try re-tentioning  the tubes pins. You might try lowering the cathode cap on the 12Ay from 25uf to say 10uf, i doubt if this would solve the issue but it will tight'n up the bass more.

[Williamblake]

You tried to have less bess and you chose smaller caps and now you have too much of a good thing. Time to change the caps some more. Smaller caps are a high pass filter being altered, maybe this is too much and you want a shelving filter somewhere instead. That would be a different cathode bypass cap. Other means exist, i wanted less bass and smaller caps and a fitting bypass cap worked fine for me. Still building me first 5E3-clone, this is just food for thought.

[AlNewman]

Have you tried different guitars?  Having volume issues on one string at certain frets might indicate a fret level or nut/bridge issue.

Edit:  seen in your original post it isn't a guitar issue.

[HotBluePlates]

So, the only caps that I changed are the output coupling caps: I started with the stock .1 caps but quickly went to .022 to tame the bass.

From what I can remember: I started noticing this "resonance" issue after installing a new O.T., I was trying to reduce bass and wondered if a different o.t. would help. The new o.t. didn't do much and so I went back to the stock o.t. and started noticing a louder D4 note.

After some time the amp started producing a loud crackling sound, not always, sort of an intermittent issue. By tapping with a wooden stick I noticed that the taps were amplfied when tapping on the power tubes cathode resistor; tapping on it would also make the power tubes flash... I replaced the cathode resistor and the crackle went away for good.

But, that's when I noticed the resonance issue: not only the D note is louder, B, Eb and E are noticeably louder.

In a situation like this, what are the things you would check in the circuit? It would be helpful to know where to start... 

Speakers can do that ...

... it is not a guitar problem. ...

I've never noticed that with my 5E3. Nor have I ever heard of this particular problem. Maybe a better starting point would be to use original values for coupling caps and reevaluate the sound.

... check for any poor solder contacts. Tap on the pre-amp tubes, if excessive noise try replacing that tube.

Quoting a whole bunch of stuff, because:

   -  There's no "place in the circuit" to target individual notes unless you have a parametric or graphic EQ.

   -  Most guitar amp circuits (and certainly the 5E3 Deluxe) can shave the bottom, shave the top, or scoop the middle.  And a 5E3 lacks a Fender blackface tone stack "scooping the middle".  So there's nowhere to turn to tame individual notes as you requested.

   -  Depending on where you set the Tone control (and which channel you're using), the 5E3 Deluxe can have a measurably "flat" frequency response... which then sounds like "too much mids" to many players who are used to other amps whose tone stack scoop a bunch of mid.  That fact can then make other flaws of the guitar stand out.

   -  That tapping produced crackling sounds, flashes of light, etc, sounds like there could be intermittent connections in the amp.  As in poor solder joints.  If "some notes jump out" that makes me wonder if vibration sometimes temporarily corrects a "poor connection" making the note louder.

   -  Speakers are the thing that have a bunch of peaks & dips.  When "some notes jump out" it is often about the speaker's peaks.  However, those peaks/dips are usually up around 1-5kHz and way above the notes you're describing (more like harmonics of the notes you mention).  Though sometimes we might notice one speaker has a lot more "low-mid" than another.

   -  A stock 5E3 is fine except I would agree it could tolerate rolling off some bass; and some folks won't be used to how much midrange it has.  I'd suggest going back to the stock circuit then re-evaluating as Sluckey said.  "Weird resonances" at that point are not the circuit, but the guitar, or the speaker, or intermittent wiring.

[HotBluePlates]

... certain notes (especially the notes B, D and E on the guitar third string - and the same frequencies on other locations of the fretboard) have more gain and sound noticeably louder than the rest of the spectrum. ...

Those notes are about 230Hz to 330Hz.  That's the "not-scooped-midrange" of the Deluxe, where other amps scoop by 15-20 decibels in the range of 200-500Hz.

   -  If "everything around those notes" are too loud, it's the extra midrange.

   -  If "just those notes" (not C at 3rd string 5th fret, not C# at 3rd string 6th fret, not D# at 3rd string 8th fret) the you probably have a setup or pickup-adjustment issue.  The 3rd string has the thickest solid-core in most string sets with an unwound 3rd string, so it tends to be the loudest.  You can back down a polepiece to tame the strength somewhat; there are historical reasons why a staggered-magnet Strat pickup has its G-string pole piece too high.

   -  If it's "just those notes" but you can prove the guitars sound fine through another 5E3-like amp with the additional midrange, then intermittent wiring seems the only likely cause.  Though I would expect a wiring issue to reliable be "fixed" by playing a certain note.