5E3 tone mods

[lowell]

I built a 5E3X2 not too long ago... love it. It is a great sounding amp. I recently decided that the low end was too much and I was getting that farty speaker thing going on. I reduced the first stage coupling cap to .047, both bypass caps on preamp tube and gain tube to 10uf instead of stock 25uf, and both phase inverter coupling caps to .047 instead of .1. I also changed the screen dropping resistor in the power supply from the 2.7k to 5k, and in doing so I also changed the C+ dropping resistor to 47k to keep the ratio constant.

After these mods the low end is great, however I now have reduced high end...?? I don't understand how that happened... could the power supply resistor changes cause this?

[Rob Mercure]

Lowell,

Yeah, your problem is probably in the B+ supply. And I want to let you know that in tube electronics the "C" notation is reserved for the bias supply. Just about the only time you see a "C+" supply is in high powered transmitters. I think you're referring to the "C node of the B+ supply."

Rob

[lowell]

ok thanks Rob, I'll undoing that mod, I don't like what it has done to the amp.

[lowell]

Ok I reverted back to the original power supply resistor specs... it still seems like it has lost that sparkle though. I even have a bright cap across the volume pot! How might one inject some sparkle into this amp? I'm thinking of lowering the grid stopper resistors yet still considering their roll in muting oscillations.

[jrfrond]

I think you overshot the runway with your mod. My first step would have been reducing the cathode bypass cap on the first stage even further (my personal favorite is .68uF) and leave the subsequent caps alone and power supply. That is usually sufficient to squash low-end problems.

You can simulate brilliance in an amp with RC HP shelving networks, but that open, airy tone that it sounds like you had before is, to me, part of amplifier mojo. If you have it, you can take it out, but if the amp DOESN'T have it, you cannot really put it back in. Some amps have "it", and some don't. If you amp had "it", you may have squashed it with mods.

Yes, I know this concept sounds vague, but I've built EXACT amps side-by-side with the same components, and most times, one has "it" and one doesn't, and there's no explanation except for component tolerances and the Amp Gods.

[hasserl]

The tone mods he did would not have reduced high end.

I suspect you may just have a bit of an aural memory problem, you may be remembering the amp having some sparkle that was never there, I see lot's of complaints about 5E3's being too dark. Also, adding a bright cap around the volume pot is just screwing around with the tone control. Take a good look at the tone control circuit, you'll see it incorporates a bright cap around the volume control (the .0005 cap). If you wanted to increase the brightness you could increase the value of that cap.

[lowell]

Yes it is most likely my aural memory... damn that aural devil! He gets me all the time!

As far as bass reduction I had read someone's post stating that they liked bass reduction in small doses throughout the amp which summed into a pleasing end result... more so than an extreme reduction in only one spot. I might try that .68uf in the first preamp though and see if I dig it. Only one way to really find out and that is to try these things right?

On another note. The bass is DEFINITELY reduced in this amp, however, the low end that remains is quite farty. This is the case mostly when I turn the amp up or when I play loud on the low E string. At bedroom levels it sounds great. Does reducing low end in an amp also tend to "weaken" the amps ability to keep the low end tight? On side note I'm using a Peavey sheffield 1350 for a speaker, not sure if relevant.

[pdf64]

Perhaps your aural memory is fine, but the environmental conditions have changed, see
http://www.rane.com/pdf/ranenotes/En...of%20Sound.pdf
The ambient temperature / humidity has a considerable effect on tone in the rehearsal room I use, week to week, season to season. But listening back to the close miked recordings doesn't show this variation.
Yet another variable to throw in the pot! Peter.

[Chuck H]

IME increasing the B+ will help tighten the bass and add top end. So will reducing sag in the screen supply. I might try changing the screen R in the rail to 1K and add a pair of 470R screen resistors. This will also increase preamp voltage, which is a very good thing for tightening up bottom and adding bite in a 5E3. I don't know if your using stock values for the filters, but increasing the UFs will make the power supply more stable and that can only help too. Oh, if your using a 5Y3 tube or copper cap you can pickup some voltage and reduce sag by changing it out for a 5AR4 type. That will also tighten the bottom end.

FWIW when I use the term "tighten" I actually mean tighten, and not reduce.

HTH

Chuck

[lowell]

Chuck,
Thanks, all good info. Yes I'm glad you actually mean tighten and not reduce, big difference.

Couple q's:

-What affect/s does larger filter caps have? I see it helps w/ stability and power reserve because larger caps have more joules etc... but how does this translate to the sound of the amp?

-I read in TUT that the PI can cause grid current to flow in the output tubes to a certain extent. (Is that grid blocking distortion?) What do you all find are the main differences in sound w/ a Concertina PI vs a long-tail differential pair?

-Can an amp still have sag w/ tight bass? I really like the 5y3 sag-factor, but want to tighten up the bass when the amp is cranked.

[Chuck H]

-What affect/s does larger filter caps have? I see it helps w/ stability and power reserve because larger caps have more joules etc... but how does this translate to the sound of the amp?

If the power supply is more stable it will struggle less trying to keep up with the extra current needed to prduce the low end.

-I read in TUT that the PI can cause grid current to flow in the output tubes to a certain extent. (Is that grid blocking distortion?) What do you all find are the main differences in sound w/ a Concertina PI vs a long-tail differential pair?

Too much drive to the power tube grids can cause them to "try" to draw grid current. I say try because most guitar amps aren't designed to allow much current to be drawn by the power tube grid circuit. When this happens you get blocking distortion.

I have never designed with, and hardly ever used the concertina type PI. So I can't comment on the tonal differences. But it's my notion that most popular amps, and probably all modern ones, use the LTP for a good reason. It's suppose to have more headroom and dynamics. Depending on your tonal goals, that may not actually be a good thing.

-Can an amp still have sag w/ tight bass? I really like the 5y3 sag-factor, but want to tighten up the bass when the amp is cranked.

It's a trade off. You can have some of each, but not all of both. Different rectos will give a different balance between the two, but all will provide some sag because they add resistance to the power supply.

HTH

Chuck