Where best to post about diff between Fender and Dumble?

[WhopperPlate]

I did an AES keynote a few years ago and the presenter after me(Eric Valentine--brilliant!) did his speech on quantitatively proving that aural testing is a flawed methodoogy. I know a lot of builders of high end studio audio(mostly vintage varietals) and though they definitely value high quality components and understand material types for resistors and capacitors, they really seem to understand a level of audio tuning that is much more practical. /my opinions on resistor and cap brands(within composition types) are that this is mostly a non factor, and the only real consideration would be quality of components(such as ESR for caps). To that regard, this is where I wonder if Dumble was a putting a little bit of pretend fairy dust on things. I just think if you are talking about a touring rig, unless you are bundling unlike cables together with some awareness that I haven't yet seen or heard, I need some true convincing.

There are two types of people…those who take others word s for gospel …and those who have their own experience to develop their own gospel ….

If I listened and believed every know it all who ever told me that “this” or “that” won’t make a difference , or “you can’t hear or feel that”, well at the very least I’d be wrong too lol

Let’s get real folks . Listening is a developed skill . Some people can identify and remember every note within a musical progression , others can’t identify a single note if they wanted to at any point in time … even if they tried really hard for years on end….same goes for every skill in life . Experiment and develop as much experience as dumble did, and then maybe dare to make conclusions .

This ain’t about dick measuring and seeing who can hear what , but it’s about understanding that not everyone hears the same .

I remember growing up hearing an overdriven power chord and assumed it was more than two notes becomes of the complexity of the harmonic overtones . now I know better.

I remember listening to the album Friday night live in San Francisco for the first time as a teenager and all I heard was nonsense . Too many notes . Took me about 10 listens to break it down .

Listening is a developed skill .

[martin manning]

Martin. My tone stack is actually taken from the Two Rock, which is .1, 047, and .001. Since, aside from the treble cap, this is similar to most of my Fenders, that is an easy sub to check.

Well, this changes things. The 47n mid already goes a long way toward the Fender stack, but note that the cap on the preamp board (where an AB763 Fender has the treble cap), is actually the mid boost cap. With mid boost off, the treble cap value is nearly the one on the mid boost switch. Those two are in series, so the combined value is something less than the smaller of the two. Only when the one on the switch is shorted does the cap on the board become the treble cap. TR seems to use values similar to Dumble (~330p) rather than the Fender standard 250p.

I normally put in the feedback defeat switch for that first stage, and generally have preferred that, though I would like to spend more time really listening to each.

You're leaning Fender there, too, I guess.

One of the biggest things that I love about Fender style amps is the pull when you hit a note hard and bend it, and the amp seems to "bend" in a way.

This may be a combination of compression (including voltage sag) and EQ effects. Harmonic content changes when the signal gets clipped, and if you are at a frequency where the EQ curve is steep, like near the scoop, and adding frequency variation with a bend, you might get something like that.

[martin manning]

My tone stack is actually taken from the Two Rock, which is .1, 047, and .001. Since, aside from the treble cap, this is similar to most of my Fenders, that is an easy sub to check.

PS You can still try shorting the bottom of the bass pot to the top of the middle in your TR stack and see what that does for you.

[imo1]

Martin. My tone stack is actually taken from the Two Rock, which is .1, 047, and .001. Since, aside from the treble cap, this is similar to most of my Fenders, that is an easy sub to check.

Well, this changes things. The 47n mid already goes a long way toward the Fender stack, but note that the cap on the preamp board (where an AB763 Fender has the treble cap), is actually the mid boost cap. With mid boost off, the treble cap value is nearly the one on the mid boost switch. Those two are in series, so the combined value is something less than the smaller of the two. Only when the one on the switch is shorted does the cap on the board become the treble cap. TR seems to use values similar to Dumble (~330p) rather than the Fender standard 250p.

I normally put in the feedback defeat switch for that first stage, and generally have preferred that, though I would like to spend more time really listening to each.

You're leaning Fender there, too, I guess.

One of the biggest things that I love about Fender style amps is the pull when you hit a note hard and bend it, and the amp seems to "bend" in a way.

This may be a combination of compression (including voltage sag) and EQ effects. Harmonic content changes when the signal gets clipped, and if you are at a frequency where the EQ curve is steep, like near the scoop, and adding frequency variation with a bend, you might get something like that.

Martin,

Ok, this is a good example of where my brain farts out, and I appreciate you pointing it out. So, the treble cap is actually going in series with that mid boost cap, and without the boost switch engaged, the capacitance is right at 250p! So, in theory, this is exactly a classic fender stack, and it is the mid boost that shifts that frequency down to the .001. Am I tracking this correctly? This is exactly why I am posting this stuff. I’m doing my due diligence with Merlin’s books and the end of chapter with formula after formula keeps bucking off my non-engineer brain!

If this is indeed true, regarding the tone stack, I might play with that .022 mid cap that the super reverb uses to see what that does.

[imo1]

Im a max guy and my recent m2 makes it really hard to run windows in parallel. It was really nice to be able to use the Duncan tone stack calc to be able to simulate tone stack changes.

[martin manning]

So, the treble cap is actually going in series with that mid boost cap, and without the boost switch engaged, the capacitance is right at 250p! So, in theory, this is exactly a classic fender stack, and it is the mid boost that shifts that frequency down to the .001. Am I tracking this correctly?

Exactly.

It was really nice to be able to use the Duncan tone stack calc to be able to simulate tone stack changes.

Here's an alternative: https://www.guitarscience.net/tsc/info.htm

[martin manning]

So, the treble cap is actually going in series with that mid boost cap, and without the boost switch engaged, the capacitance is right at 250p! So, in theory, this is exactly a classic fender stack, and it is the mid boost that shifts that frequency down to the .001. Am I tracking this correctly?

Exactly.

Except for one thing...

The Two Rock topology is like the Skyliner, where the middle and bass controls are separated. Here's a comparison with all pots at noon... Still doesn't have the Fender scoop:

Screenshot 2024-01-28 at 2.53.56 PM.png

If you short the bottom of the bass pot to the top of the middle as I suggested above, you get this:

Screenshot 2024-01-28 at 2.55.22 PM.png

Turn the bass pot down one click, and they will match right across.

[rootz]

Martin, would you get close to mid scooped Fender with a 50k or 100k log pot in a classic Dumble stack?

[Mr. dB]

Listening is a developed skill .

Some people are operating at a different level. For example, watch Eric Johnson spend an hour biasing his Marshall, playing the same lick over and over whilst making minute turns on a trimpot, he's hearing something in the sustain, touch and texture that us mere mortals may miss, but when you hear him do it the changes are real, and the result is worth the effort.

[WhopperPlate]

Listening is a developed skill .

Some people are operating at a different level. For example, watch Eric Johnson spend an hour biasing his Marshall, playing the same lick over and over whilst making minute turns on a trimpot, he's hearing something in the sustain, touch and texture that us mere mortals may miss, but when you hear him do it the changes are real, and the result is worth the effort.

And some people still choose to bag on the guy as if he just completely hallucinates everything . If years of experience and fame and acclaim for virtuoso accomplishments aren’t even considered a benchmark for a qualified opinion …

[martin manning]

Martin, would you get close to mid scooped Fender with a 50k or 100k log pot in a classic Dumble stack?

My question is, is there a defined "Classic" stack? I've seen 100k and 250k mid pots, taper not always specified. Generally, a larger mid cap, and the bass-mid pot connection is the path to a Fender EQ.

[rootz]

Probably not Martin, though there seems (or should I say is for clarity) to be some common ground between different types of stacks Dumble used. #94 has a stack that I would define as a classic stack, but with a 150k slope resistor. Might be half an update to a Skyliner stack? Who knows? Maybe Had built it that way and couldn't care less about what name we would apply to that stack.

But it is beside the point really, IMHO. imo1 made the point that Dumble's and derived designs do not do the Fender Funky stuff that well and they have got a lot of low end. I read his posts a bit like: I like the Dumble amps, but is there a way to make them suit my style of playing without giving up the Dumble goods? If I understand him correct that would mean a bit less low end, a bit more scoop, a little less direct/more give in the feel of the amp. Please correct me where I misunderstand.

One way to do this would be, IMHO, bring the stack more to Fender values, but also keep Dumble possibilities. One way I tried to do that is lower the treble cap a bit to 330pF so with the mid boost cap you land more in the direction of 250pF when the mid boost is off. Also tried a 100k logarithmic pot instead of linear in a Dumble stack. 250k J-taper for treble, 250k log for bass, other caps 100n and 47n, 100k slope. With the mids on 3 this gets very close to standard Fender stack like in a AB763 Vibrolux.

Off course it means less mids going to the OD section when you do not use PAB. So it's a compromise. Unless you turn the mids up to 7 or 8. Then it does the same thing the Dumble stack would normally do.

Another tweak point would be the grid stopper on V1b. I haven't experimented a whole lot with it, but maybe Martin can comment on the effect of that mod. I'd think the 220k grid stopper would drastically alter the overdrive character of V1b. Before overdriving V1b the 220k/470p combo is pretty transparant; there is not much alteration of the frequency response.

Next Fenders typically use 25uF bypass caps, where Dumble's and derivatives use 5uF. This should give less low end. I think in the preamp Fenders have more low end than Dumbles, at least the components and tone stack should lead to that.

Increasing your slope resistor a bit to 150k like in ODS #94 would also give a bit less low end. Something like 2 or 3dB. Not much but very noticeable.

So if you want less low end from your Dumble and make it a bit more Fender and Funky, these are the points where I would look. Changing that mid pot to log goes a long way and is where I'd start. Attached is plot comparing both stacks/preamps. Mids at 3 in this simulation.

[WhopperPlate]

Next Fenders typically use 25uF bypass caps, where Dumble's and derivatives use 5uF. This should give less low end. I think in the preamp Fenders have more low end than Dumbles, at least the components and tone stack should lead to that.

Imo a lot of the funkiness comes from here . Dumbles have a tight low end , not necessarily more low end . Higher filtering , cleaner phase inverter, and bold midrange interact well with the 5uf value to increase this effect. As you said , 25uf is more bass, and all the extra lower harmonics definitely make things looser and funkier . Even just increasing from 5uf to 10uf like 124 is enough to bring some of that back .

I don’t know if it has been mentioned yet , but definitely remove the local nfb on v1 if you want more funkiness . I personally hate the effects of that design aspect for playing . Never inspires me , but that’s just me

[martin manning]

imo1 is using a Two Rock stack, which is very similar to the D Classic. I'm hoping he can give the "short bottom of bass to top of middle" experiment a try. Very easy to do (tack in a 3" piece of hookup wire), and it should be pretty conclusive as to whether it's the Fender Scoop that he's missing or not.

[rootz]

Next Fenders typically use 25uF bypass caps, where Dumble's and derivatives use 5uF. This should give less low end. I think in the preamp Fenders have more low end than Dumbles, at least the components and tone stack should lead to that.

Imo a lot of the funkiness comes from here . Dumbles have a tight low end , not necessarily more low end . Higher filtering , cleaner phase inverter, and bold midrange interact well with the 5uf value to increase this effect. As you said , 25uf is more bass, and all the extra lower harmonics definitely make things looser and funkier . Even just increasing from 5uf to 10uf like 124 is enough to bring some of that back .

I don’t know if it has been mentioned yet , but definitely remove the local nfb on v1 if you want more funkiness . I personally hate the effects of that design aspect for playing . Never inspires me , but that’s just me

My observations exactly, Fenders actually have more low end. Nfb around V1b might not work for funkiness, but I love it eiher way. Have it on a switch in all my amps, but it's always on.

Agree Martin, just a short piece of wire is the faster method. Mind you, it would have a more extreme mid scoop than say a Vibrolux. but if you like the effect, it is a way to go forward. Putting your mid control barely on 1 would also do the trick to bring the scoop in.