What makes the power section sound like it sounds?

[shocki]

I was wondering why some amps like Marshalls sound better the more you turn them up. They stay really tight. Other Amps like Blackface Fenders don't really sound good when turned all the way up. At least for my taste! Slightly overdriven with a pedal they sound nice. But if you push them harder with the volume past 4-5 I don't really like the way they break up. To me the distortion sounds rather kind of "broken" and the bass does not stay tight. For rock riffs this does not sound good.

Well actually this is why no Metall or Rock Band would use a Fender. I think with the Tweed Amps it is quite different. A Bassmann does have a nice breakup. Also it is really similar to the JTM45 (or the other way around) which also has a great, tight breakup sound which could be used in any rock band.

What is it that makes the power section sound differently? I am pretty sure the tubes are only a small factor. I have heard amps like the OD100 which 6l6 that did not sound like Fender Amps at all.
I think the Feedback circuit has some impact. Other than that. Is it the circuit, the voltages or the type of OT ?

[Steve Conner]

I believe the difference is not in the power section, but what it gets fed by the preamp. Hard rocking amps like the JTM45 filter out some bass by using undersized cathode bypass and coupling caps, and have different tone stack values that emphasise the midrange. When this signal is distorted by an overdriven power amp, the result is an aggressive crunch. The big 4x12 cabinet then puts the bass back in.

Fender preamps boost bass and treble, and when this is distorted by the power amp, the result is a more farty distortion, unless you turn the bass right down.

The cathode follower in the Marshall preamp also clips more smoothly and symmetrically, which could explain why the distortion doesn't sound "broken".

[shocki]

Hey Steve. Thanks for the input.

Now that I think about it I might have something to do with the tonestack before or after the gain stages. I think this could play a massive roll when I drive the amp with a pedal. This is also different in the Tweed Amps.
I could try modding one channel of my Silverface Amps to a tweed Tone Stack or actually no tonestack and see what it does.

[Alan0354]

I have the Marshall Plexi in the 70s. It sounded good at 4 or 5. But if you push pass 6, the sound gets very ugly. The preamp tube get driven too hard and the grid start conducting and pump up the DC. It starting to have a harsh cracking sound. My problem with the silver face fender is more because of the lack of gain in the preamp that it hardly breakup even when crank high.

[shocki]

My problem with the silver face fender is more because of the lack of gain in the preamp that it hardly breakup even when crank high.

Maybe I should note that I use pedals to push the preamp. There is no other way with the Fenders I think

Also I will try a pot with the feedback resistor to make it variable.

[Alan0354]

I agree with Steve, the sound is mostly from the preamp. I can make the over driven distortion sound totally different by changing the preamp. Even when I drive it all out and know for sure it's the power amp that distorted, it is still control by the preamp.

Marshall has less bass, it might sound good in distortion, it sounds not that good clean. I would not say the old Marshalls are all around amps.

[shocki]

Ok. You guys are right. I am still wondering why there is still no Marshall/Fender Sound in one amp kind of Amp. Putting a Fender and Marshall Preamp into one amp and make the feedback resistor selectable should not be a big problem.

[madkatb]

Check out Duncan Amps Tonestack Calculator at this site:
TSC
Then put in the values from your tonestack in the appropriate circuit. Adjust the pots to get the flattest response. Then try those settings on your amp. You'll be surprised at how good it sounds.
(for treble/mid/bass it usually works out around T=0, M=7, B=1)

[Alan0354]

Ha ha, the early Marshall is really a copy of the old Fenders!!! They did use different components though.....Down to the cathode follower section. Don't ask me how Marshall could get away with this!!!! Fender change their design since then.

I actually experiment with my Bassman 100 with modified power amp and a Bandmaster OT. I have two distinct front end section that are not cascade high gain. I drive through a THD Hotplate to lower the sound. I can assure you the two front end sound different when I drive the power amp into distortion. I am sure that the distortion is not from the front end as I scoped to make sure they both are not clipping. Only the power amp distorted. I can make one channel sound more fatter Fender and the other lean and mean Marshall type. I am not saying the power amp don't make a difference, I just don't have two power amp and compare with the same front end yet.

[Alan0354]

Check out Duncan Amps Tonestack Calculator at this site:
TSC
Then put in the values from your tonestack in the appropriate circuit. Adjust the pots to get the flattest response. Then try those settings on your amp. You'll be surprised at how good it sounds.
(for treble/mid/bass it usually works out around T=0, M=7, B=1)

I have Window 7, I click the first one and bunch of garbage fill the screen!!!

[Enzo]

Don't ask me how Marshall could get away with this!!!! Fender change their design since then.

It is easy, Fender "stole" many of his circuits right out of the RCA tube guide. The RCA circuits were provided free from restriction for use by all.

All the component values are mere details. Most amps are extremely similar to the others.


I have an ongoing philosophical argument going with a fellow. I maintain that amps are amps and they are all the same under the skin. He cries OH NO, they are all different. I am looking at the circuits, he is looking at the details. Certainly no one would ever confuse a Corvette and an old lady's Buick, yet you could hop into either one, and instantly know how to drive it. SO in a sense cars are all the same. I can sit down in the tavern with a pen and a blank napkin and draw you a complete amp schematic, one that would function if you built it. If you were to ask me if it was a Marshall or a Fender or some other brand, I;d have to say it was all of them and none of them at the same time. Change a cap here and a resistor there, and you can have your Marshall or your Fender. Doesn;t matter, they all work the same way.

I service amps for a living, if someone asks me "do you know how to work on Fenders?" (or Peaveys or Gibsons etc) I have to think it is a meaningless question. You work on all of them the same. Sure there are certain caps in a Fender I might not see in a Marshall. MY Marshalls will have 1k screen resistors instead of the 470 ohm ones in my Fenders, but so what? I am going to look for and correct a bad one, whichever value it might be.

So when it comes to a push pull amp with a tone stack and a long tail pair PI, I sure don;t care which brand it was, nor do I expect the circuit to change much brand to brand.

[Alan0354]

Hey Enzo, I don't know what to think. I used to look at amps are the same, just a few values different. But since I started working on amps and pedals, the value is everything. I was totally surprised by how much a value change can totally change the characteristic of the amp or pedal. This is one area that context is everything.

Yes, circuits are basically the same, but just that little detail.

BTW, I thought the cathode follower driving the tone stack is a very unique feature that Marshall copy from Fender. Yes, each stage are very common like common emitter, common collector or common base BJT. But the combination is unique here, don't you think? That's one stage that seems to give a little of the Marshall sound. It's just don't think it's particular improving the clean sound and is one extra stage the signal has to go through. Maybe Fender drop that because Fender was going for the softer clean sound.

[Enzo]

I never argue that they don't SOUND different, of course they do, but the circuits are still all the same. I can;t accuse someone of stealing a classic stock circuit that was GIVEN to the industry by the tube sellers, nor can I really call in "innovation" when someone changes a cathode bypass cap from 25uf to 0.68uf.

I think it is unfair to accuse Marshall and Fender of copying each other. They don;t NEED to copy, the designs are obvious. Just as I need not copy anyone to draw a scematic on the counter in my kitchen. It is common knowledge in amp design that a low impedance cathode follower driving a tone stack will have different characteristics than one coming right off the plate of a preceding stage. No one needs to "steal" that.

I don't offhand remember a Fender tone stack driven by a cathode follower, which model do you have in mind that Marshall might have "stolen" it from?

Why would Fender reduce the tube count by one triode to eliminate a cathode follower? Because it costs less. Simple as that.

[Alan0354]

bassman_5e6a_schem.pdf

bassman_5f6_schem.pdf

Particular the 5F6, the front end is so similar to the Plexi. I think Fender remove the CC to get a softer sound, more mellow. My impression is with the CC is because of the lower impedance drive, it sounds more brawny.

Well, I am just speculate here, the circuit is very well known today, we have 50 years looking at it and experiment with it. But in the early 50s, these were all very new and different from hifi amps. Not necessary that Fender can patent the circuit as this is just standard CC stage or the value of the components, but with a good attorney, you never know.

If you look back at the same period of time, there were very few guitar amps around, the circuit in Gibson amps are totally different. You can see in 5E6-A, it did not even have the differential amp stage ( long tail) that is so common now. Now a days you cannot tell who copy who as they all look very similar.

[Enzo]

But they were not new, they were like hifi amps. Difference being they didn;t try to get hifi performance, as they didn't need hifi performance. Fender designed an amp to complement the pickups in their guitars. They based it on industry common circuits. In the 1950s Fender had no interest at all in what young Jim Marshall might be doing.

Look at your 5F6 drawing, the input stages share a cathode resistor. If they had separate resistors, each would be about 1500 ohms. (They didn;t have 1640 ohm resistors then, parts were 20% anyway) and the plate loads were 100k. This is straight out of the charts in the RCA manual. I used to design amplifiers as a kid in the 1950s, for my record player. I used those same charts myself. I had never even HEARD of Fender or Marshall.

The 5E6A has a split load phase inverter - needs only one triode instead of two - cheaper. Those are still common, the Peavey Classic series is full of them. And the sample circuits in the RCA manual? All three power amp use them.

If I design an amp, I will want tone controls. I will probably chose to have three controls. I could have one tone knob or two, or for that matter five or six. But three works well, so I will go there. AM I "copying" Fender because they also have three band EQ? Or have I simply come to the same conclusion they did? What self-respecting engineer at one company like Fender is going to sit down to design a new amp and start by copying one from Marshall? Fender amps are clean and strong, Marshall amps are all distortiony and razzy. What does a Fender designer even WANT from a Marshall? I myself don;t like the sound of a Marshall, I sure as hell don;t want Fender to start making them.

Copy, schmoppy.