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Discussion in 'Shock Brother's DIY Amps' started by James Knox, Oct 10, 2020.
@Lowerleftcoast - great post, mate.
Your excellent Tutorial Post on 5E3 RC‘s has cleared up many questions I have been having. Thank you so very much. I now have an “internet High Pass Filter Calculator” bookmarked, lol. Pointing out the “parallel” RC’s of the Pots on the Schematic was super helpful. As you know, I’m *learning to read schematics to overcome “painting by numbers”.
OK, now I can see that! But where then does this 80k number come from? The knobs turned down?
Knowing this, do you build your 5E3’s with .047 replacing the .1’s?
If you check out almost every vintage Fender amp after the 5e3, you'll find a lot of .022uf caps in place of those .1uf caps in the preamp of the Deluxe. Even the "Bassman" had .02uf caps there. Probably not a coincidence.
I would just love a dumble clone of the 5E3 it seems to be a fantastic amp.
FWIW I gig and practice with a 5e3 with buckers, and run through a JFET preamp that has a bass cut knob on it (in front of the amp). Can't remember where I lifted the bass cut but it's definitely a simple high pass filter. My 5E3 has the .022 coupling cap mod on the bright channel - which I use the most. I think this might reduce the interactivity between the 2 vols, as I don't hear anything more than subtle tone changes with the 2 volumes in different positions. I also have a 3-way switch on the preamp tube which switches the bias cap, or disables it. I never use it and leave it stock. I like T-Top style humbuckers with the neck pickup lowered further from the strings and the bridge just close enough to not pull the strings.
I've been involved and experimenting with audio electronics since I was 9 years old, worked much of my life in the field, and growing up with bands going from little combos, even for Bass, evolving into Marshall 2x4x12 stacks even in the smallest of venues, I learned very early on that Bass Response takes Power. A corollary to that was Bass Boost circuits in the preamp are very often "flabby" or "fart-y". Paul Kossof fascinated me that he'd plug into the Bright Channel of a Marshall head but preferred plugging that into Bass cabs to get distortion but with definition. That just furthered the feel that Treble is easy and good early, can be diminished later, and Bass response is best far down the signal chain.
So I modded and designed amps from scratch using a few overriding design principles.
1) I replace ALL electrolytic (asymmetrical response) cathode bypass caps with non-polarized caps, generally with lower values for bright pre-emphasis. The most common Fender-ish design of a 1.5K resistor with 10-20 uf around them is overkill for guitar. Even a 1.0 uf cap is full range with a 1.5K. 0.47 will barely reduce the lowest fundamentals of a 6 string guitar.
2) Early coupling caps (0.001 - 0.01) for pre-emphasis as signal path moves up to .1 or .2 at driver-to-power coupling and in some cases a low pass shunt around the PI plate resistors (0.0001 - 0.001) around the plate resistors to increase bass response and possibly dump some high end (progressive de-emphasis) works well and can be adjusted to personal taste for tonality with clarity and definition.
3) I don't generally like much negative feedback which always introduces some phase cancellations, so I get clean headroom by increasing either voltage or current or both with gain staging. Just increasding PS filter caps values improves both for more headroom and less noise but does reduce "sag". The sag can be re-introduced by reducing or designing out negative feedback (variable is pretty nice) and/or reducing B- Bias voltage to get closer to Class A. The balance between those final areas is hugely important and effective.
4) I prefer every plate has it's own filter cap for reduced crosstalk and phase effects, both cancellations and sympathetic increases.
There are more but these are the main design imperatives I follow. FWIW David Lindley loved my designs.
You are right... it is no coincidence.
Oh, but now you can't fool JK, he has the RC filter calculator!
JK will simply put the V1 coupling bassman RC numbers into the calculator and find the bassman to have a 7.2Hz cutoff. The interactive 5E3 does not always cutoff that low with .022 on board.
JK now knows we are talking apples to oranges.
Lots of cool ideas in there. Are the Amps you build closer to Fender Tweed Era or Marshall? Or something entirely different?
Only about a million good ideas so far.
Did anyone mention a bigger reservoir cap? I got the idea from @Wally , and sure enough a 30uF there is very nice; you might be able to go up to 40 (yes, 5Y3s can do 40 all day long -- different opera). You can keep 16uF in the other two slots so the preamp stays nice and tweed-y.
My first 5E3 was nice, but not "just right." So after some experiments, my second one (in addition to the reservoir) had .02, .05, and .02 in the normal, bright, and preamp coupling slots. (I tried .02 in the PI, too, but reverted to 0.1). And I *definitely* endorse the 470K PI grid stopper.
Those worked for me, but a few more come to mind. I know folks *did* mention the V1 bypass cap, but a clip-in-parallel trial there, starting from 0.68 or 1uF, is simple and revealing.
Now an odd one. Did someone mention bright and tone caps? A sneaky cause of too much 5E3 bass can be too much treble (and wonky tone knob behavior). First, the tone knob is kind of a gain knob; second, diming the treble can actually give your farty bass an icepick accompanist. So folks are reluctant to turn the tone up too much, which leaves Signore Flubbo alone on stage.
Not a cure for bass directly, but putting a 100-500pF 'bright' cap on the *normal* channel gives that channel a more nuanced tone control. And (even more indirectly) a smaller (680-1000pF) tone cap will leave more mids in your tone, so you can cut the icepick but leave the altos and tenors on stage.
But, all that said, the best single cure for 5E3 bass issues is to build a different amp next time (my second 5E3 was my fifth build). A PR should do the trick...
Now, where is that Bassman Schematic?
- Put a 12AY7 in the first socket like Leo intended.
- try different speakers. They make a HUGE difference.
- if its not loud enough, plug it into a 2x12 or 4x12
- play it in tandem with a Harvard. Love the Harvard. Good gain, no flubb, pretty loud. Under rated amp.
- back off the volume to edge and use a stomp box.
You don't always have to warm up an iron to change the tone of an amp. People go down that rabbit hole and think if they just keep going..., but it doesn't happen. It's like learning all this theory to be a better player and then BB hits just one note and nails it. That's what I got.
More Good Stuff Bro! I especially love the experiential advice in this thread. I’m basically using my first 5E3 as a Science Experiment. Listening and learning prior to starting a “keeper” Deluxe.
Thanks for bringing this up. I know our OP will need to understand your post and more to get his head wrapped around any particular guitar amp design. He has already asked *why reduce bass early in a guitar amp*? I am not sure how to quickly teach him the ins and outs of amp design. He seemed to be ready to learn about RC filters and probably cathode bipass caps. Maybe the teaching must be done with understanding the placement of filters as well.
in response to this and others talking about "losing the magic"...
one of the real beauties to me of the 5e3 as a platform is that you could very easily turn it into a 6g2 princeton, or a 5e5/5e5a pro, but stripped down and in a smaller form factor (like a form fitting head). and people don't seem to think those amps are stinkers when you change the lettering on the front panel...
this is why it's my only small amp, i change it around from time to time when i get bored.
To be frank. 80K is a hypothetical number. I used it to show the 5E3 will cutoff low guitar signals. I based it on complaints that .022 cuts signal. If those complaints reflect *real data* the *R* would have to be low. To get *R* that low the 5E3 amp with it's particular tone/volume arrangement either drops more signal to ground (remember it does drop signal to the B+ side as well as to ground) than is easily calculated or it is turned down by the user.
I bet a normally cranked 5E3 with .022 caps will not have user complaints.
The ones I have built have .1 caps. I chose the .1 caps as a selling point. The buyers I have talked with don't want the circuit changed much.
That being said, as I pointed out, I am trying an additional RC filter before the interactive controls of the 5E3. I suppose it would be equivalent of cutting lows with a bass cut on a guitar or from an EQ pedal. I have not spent enough time with this design to determine whether it will stay in the circuit.
Making a 5E3 into a 5E5A Pro would be a big stretch. The 5E5 Pro is already in essence a 5E3 Deluxe circuit with transformers and biasing for 6L6s, but the 5E5A is a much more complicated circuit in comparison to the 5E3/5E5 amps.
There're many reasons Rob's 5E3 mods page has become so long it's now visible from space.
Many articles (some of them full of beans, some perfectly accurate) have been written about the 5E3's flaws, but those 'flaws' also gave it its iconic sound.
As our smart friend @Nickfl said, it's also a super-popular early amp build, so folks expect it to sound like other amps. Some of them walk away, some of them start to mod, and some of them learn to love it and play it the way Leo built it. Rob himself shows us the spectrum, from suggesting ways to "leave in" the stock sound, to a hundred ways to alter it or correct each and every flaw. In fact, IIRC, a good deal of Rob's early focus on the 5E3 involved his first build, his ProLuxe (which he built from a popular early Boothill kit).
No wrong answers in either staying stock or modding. I see great players and builders who wouldn't change a thing from stock; I see others who've moved their amp all the way to the other side of the sonic globe. A lot of us land in the large space in between.
But it's too bad we end up with the (not small) disappointed crowd who 'can't get a decent tone out of the thing' or 'never bonded with it' or find it a 'one-trick pony.' One more reason we maybe should encourage new builders to look elsewhere -- and I'm not sure my beloved 5F1/5F2a are the best alternatives. It'd be nice if more BF Champ / VibroChamp kits were available and widely built; Rob himself suggests folks considering a 5E3 look at a 5F11 or 6G3; the 5F10 Harvard is also a great amp that gives players a nice tweed (but more mainstream) sound.
oh yeah damn, why did i think it was 4 stages instead of 5? sorry about that.