I'm tired of anemic guitar amps!

[scruffy]

Holly shit that's a lot of info! Bookmarked.

To complete the picture, here's Scruffy's theory of thump.

In my opinion a good guitar amp is "thumpy" which means it's dynamic. If you pop the guitar strings with your palm you get this big huge sucking sound out of your speakers, and your ear interprets it as a thump because the excursion of the speaker cone is so extreme and so fast it creates a pressure wave and the air comes at you like a projectile.

And, if you rake the strings with your pick, you get a nice fat raking sound out of the speakers. I don't happen to think Jim Marshall was a particular genius, I rather think he got very lucky and here's why.

So, "thump" comes mainly from two places. The first and most important is the speakers. The early Marshall cabinets are underrated, they're practically airtight, he used different tolerances back then but even with 4 cheap speakers moving in phase, the airflow was such that a lot of pressure built up inside the cab when the cones moved backwards, and it was all released when the cones moved forward again. So, very fast, as long as it takes for sound to bounce off the back wall of the cabinet.

In fact there was so much air pressure inside those cabs that sometimes it would actually blow the speaker plug right out of the jack. Which then caused the amp to operate without a load at 200 watts, after which it would promptly light on fire. All those stories about burning amps are true, this is what happened

Then a more obscure but equally important source of thump is "blocking distortion". This is an interesting phenomenon, it starts occurring long before you can hear it. But basically if the overdrive signal is so strong that it causes the tube to go into cutoff, then it takes a small amount of time to recover from that condition, and meanwhile there's no "sound" to speak of, anything you can hear is at low volume and it doesn't sound at all like it's supposed to. The recovery time is typically a fraction of a second to a second, but it could be longer. Here's how to make it longer: drive the hell out of a cathode follower. Think Black Sabbath, and once you think you have enough gain, double it. You get a delicious sound while you're playing, but the instant you stop playing you get a very strange muffled sound for about half a second till the hum and noise from the overdrive kicks in. That time, is about the same time as the recovery from blocking distortion .

If that time happens to coincide with the cabinet delay you get a very interesting sound that you can control with your guitar. Which is why I say Jim Marshall got lucky, because I've read interviews with him where he doesn't even realize this issue exists. It turns out that in his Plexi amps the combination of blocking distortion and cabinet delay is just about perfect, it results in a very nice "thump" even outdoors at 100 feet away.

 

[CrusaderFrank]

I'm going to build an amp. And post the whole thing on YouTube. Show the world how it's done.

My ear has had it with anemic amps. I like thump, I like an authoritative sound. I like the power tubes to break up at full volume, none of that saggy blues stuff.

My other requirement is it has to be bulletproof. It has to be able to fall out the back of a truck and survive. So no PC boards, all old school point to point wiring. The worst thing that happens is a tube blows and then you replace it and you're done.

If you're into guitar amps, check out the schematic of this 200 watt Marshall. Notice the 12AU7 driver, in front of the power tubes. That's there because the KT-88's require 50 V rms to reach full power. They sound great when they do, they're thumpy and they have great dynamics, but they need some beef backing them up.

https://schematicheaven.net/marshallamps/major_1967u_lead_200w.pdf

So I'm going to have a 400 VA toroid that can supply almost an amp at 560 volts (the tubes draw 640 mils at full power), but it weighs less than half as much as a big metal power transformer.

And I'm going to make it a dial-an-amp, so you can get any sound you want just by flipping a few switches. If you want a Fender sound with reverb and the tone stack up front you can get that, and if you want a Marshall sound with the tone stack in back you can get that too. And anything in between, and above and beyond.

By using a 12AU7 as a phase inverter, ahead of the driver, I get a combined gain of about 60 for the power amp, which is just about perfect, that means about 0.8 volts will drive it to full power. With a long tailed pair, it'll have the same sparkle as a Marshall Major about halfway up, and then it'll get really aggressive when it's cranked.

I want to blow some windows out this year. It's one of my New Year's resolutions.

And a volume knob that goes to 11!

 

[toobfreak]

In fact there was so much air pressure inside those cabs that sometimes it would actually blow the speaker plug right out of the jack. Which then caused the amp to operate without a load at 200 watts, after which it would promptly light on fire. All those stories about burning amps are true, this is what happened.

You are describing an absolutely intolerable, verboten condition, which is why I eschew using 1/4" phone plugs in certain critical applications. What you describe above would be a huge liability on any system a company installed for a professional venue.

Here is one situation where, while taking the integral crossover out of one of my bass cabinets, I also converted it to using Neutrik Speakon connectors. Neutrik connectors don't just pop out.

They are crazy, complicated foreign-made things hard to understand when you first get one, but really, very well designed.

Here is a picture of the input panel on the back of one of my bass cabinets after I converted it to using them.

 

[Chuz Life]

To complete the picture, here's Scruffy's theory of thump.

In my opinion a good guitar amp is "thumpy" which means it's dynamic. If you pop the guitar strings with your palm you get this big huge sucking sound out of your speakers, and your ear interprets it as a thump because the excursion of the speaker cone is so extreme and so fast it creates a pressure wave and the air comes at you like a projectile.

And, if you rake the strings with your pick, you get a nice fat raking sound out of the speakers. I don't happen to think Jim Marshall was a particular genius, I rather think he got very lucky and here's why.

So, "thump" comes mainly from two places. The first and most important is the speakers. The early Marshall cabinets are underrated, they're practically airtight, he used different tolerances back then but even with 4 cheap speakers moving in phase, the airflow was such that a lot of pressure built up inside the cab when the cones moved backwards, and it was all released when the cones moved forward again. So, very fast, as long as it takes for sound to bounce off the back wall of the cabinet.

In fact there was so much air pressure inside those cabs that sometimes it would actually blow the speaker plug right out of the jack. Which then caused the amp to operate without a load at 200 watts, after which it would promptly light on fire. All those stories about burning amps are true, this is what happened

Then a more obscure but equally important source of thump is "blocking distortion". This is an interesting phenomenon, it starts occurring long before you can hear it. But basically if the overdrive signal is so strong that it causes the tube to go into cutoff, then it takes a small amount of time to recover from that condition, and meanwhile there's no "sound" to speak of, anything you can hear is at low volume and it doesn't sound at all like it's supposed to. The recovery time is typically a fraction of a second to a second, but it could be longer. Here's how to make it longer: drive the hell out of a cathode follower. Think Black Sabbath, and once you think you have enough gain, double it. You get a delicious sound while you're playing, but the instant you stop playing you get a very strange muffled sound for about half a second till the hum and noise from the overdrive kicks in. That time, is about the same time as the recovery from blocking distortion .

If that time happens to coincide with the cabinet delay you get a very interesting sound that you can control with your guitar. Which is why I say Jim Marshall got lucky, because I've read interviews with him where he doesn't even realize this issue exists. It turns out that in his Plexi amps the combination of blocking distortion and cabinet delay is just about perfect, it results in a very nice "thump" even outdoors at 100 feet away.

I'm a very percussive player. I deaden the strings for that extra thump for certain songs. But I'm not much into metal, overdrive and distortion. LoL, I have the effects, features on my marshall etc. I just can't fake it till I make it. So, I like a little reverb, sometimes delay. I still get a little crunch by adding a little gain on the input. Probably will never see the kind of thump you are describing tho.

 

[Fort Fun Indiana]

Oh - it probably goes without saying, "stay away from Chinese tubes"! They're horrible, awful. When they break they're likely to take the rest of the amp with them.

Which is about all you get, anymore, when purchasing an amp.

 

[ReinyDays]

Do you often have the problem of equipment falling off your rig? ...

 

[scruffy]

Do you often have the problem of equipment falling off your rig? ...

Other than someone else's beer?

 

[scruffy]

And a volume knob that goes to 11!

I'm going to strip the paint off the front and back panels this weekend. After that I'm going to repaint them. They'll be black as before, but with white chicken head knobs. And then I'll paint on the labels for each of the controls. Yes it is possible the volumes could go to 11.

 

[Chuz Life]

I'm going to strip the paint off the front and back panels this weekend. After that I'm going to repaint them. They'll be black as before, but with white chicken head knobs. And then I'll paint on the labels for each of the controls. Yes it is possible the volumes could go to 11.

No fair, you get to work on your amp. I'm stuck rebuilding a stone hearth and drywall

 

[toobfreak]

No fair, you get to work on your amp. I'm stuck rebuilding a stone hearth and drywall

Surprise your wife and wire it up with a few built-in tube sockets for pentodes then tell her they are mood lights for her birthday.

 

[Chuz Life]

Surprise your wife and wire it up with a few built-in tube sockets for pentodes then tell her they are mood lights for her birthday.

You aren't far from some of the thoughts I had. There are two huge voids in the wall on both sides of the fireplace. (wasted space) I've been brainstorming ways to take advantage of that space with either speaker enclosures, shelves or even other electronics. (heat shielded, of course.) For now, I'm just walling it in. :/

 

[scruffy]

No fair, you get to work on your amp. I'm stuck rebuilding a stone hearth and drywall

Agonizing over how to finish the front panel. After the black paint goes on it still needs white lettering. That part is hard with DIY, requires an exact printed image, inverse templated. Silk screening would be an option except the panel is big, it's 23x8. Vinyl is hoaky looking and doesn't work well with control nuts. So far the only attractive option is two tone engraving on the back of a thin lexan panel, so it comes out looking like a Marshall faceplate except white-on-black. Then that goes over the existing stainless steel panel.

I'm trying to find a company that will do this as a one-off for less than an arm and a leg. In theory 23x8 is smaller than a quarter size panel so it should be doable on someone's existing equipment. The DIY laser engravers are slightly too small for the job, they're okay for A4 size but this is bigger. Can't use the front panel designers, they only go to 17".

Meanwhile yeah, I get the special treat of drilling the chassis, I use stepper bits followed by Greenlee punches, and a mototool with a grinder for oddly shaped things like IEC sockets. Keeping the existing tube sockets saves a whole ton of work, it's worth desoldering them.

I can't figure out how they kept the hum out of this amp, it's a stainless steel chassis with 70's style grounding practices, nothing is shielded and there are audio controls sitting right next to the PT. If this were a Fender it would be humming like crazy. In my builds I put a big huge grounding strap lengthwise across the whole chassis, the AC/PT ground is on one side of it and the input jack ground is on the other, so it ends up being (loosely) a "star" configuration. But like, there's no random ground points on the chassis, everything goes to the strap. You'll see it, I'll post pics.

 

[toobfreak]

You aren't far from some of the thoughts I had. There are two huge voids in the wall on both sides of the fireplace. (wasted space) I've been brainstorming ways to take advantage of that space with either speaker enclosures, shelves or even other electronics. (heat shielded, of course.) For now, I'm just walling it in. :/

Wire it up with a bunch of lamps behind various colored gel filters and cover it all with that prismatic lenticular stuff they used to put in front of light organs, then wire it all to a mic-fed circuit that picks up sounds and divides them into three channels for low, medium and high frequencies so that it flashes in variegated colors and patterns to the sounds of you and your woman making love in front of the fireplace.

 

[Chuz Life]

Wire it up with a bunch of lamps behind various colored gel filters and cover it all with that prismatic lenticular stuff they used to put in front of light organs, then wire it all to a mic-fed circuit that picks up sounds and divides them into three channels for low, medium and high frequencies so that it flashes in variegated colors and patterns to the sounds of you and your woman making love in front of the fireplace.

Flashback to my old highschool project!

 

[Chuz Life]

Agonizing over how to finish the front panel. After the black paint goes on it still needs white lettering. That part is hard with DIY, requires an exact printed image, inverse templated. Silk screening would be an option except the panel is big, it's 23x8. Vinyl is hoaky looking and doesn't work well with control nuts. So far the only attractive option is two tone engraving on the back of a thin lexan panel, so it comes out looking like a Marshall faceplate except white-on-black. Then that goes over the existing stainless steel panel.

I'm trying to find a company that will do this as a one-off for less than an arm and a leg. In theory 23x8 is smaller than a quarter size panel so it should be doable on someone's existing equipment. The DIY laser engravers are slightly too small for the job, they're okay for A4 size but this is bigger. Can't use the front panel designers, they only go to 17".

Meanwhile yeah, I get the special treat of drilling the chassis, I use stepper bits followed by Greenlee punches, and a mototool with a grinder for oddly shaped things like IEC sockets. Keeping the existing tube sockets saves a whole ton of work, it's worth desoldering them.

I can't figure out how they kept the hum out of this amp, it's a stainless steel chassis with 70's style grounding practices, nothing is shielded and there are audio controls sitting right next to the PT. If this were a Fender it would be humming like crazy. In my builds I put a big huge grounding strap lengthwise across the whole chassis, the AC/PT ground is on one side of it and the input jack ground is on the other, so it ends up being (loosely) a "star" configuration. But like, there's no random ground points on the chassis, everything goes to the strap. You'll see it, I'll post pics.

I wondered how you intended to do the lettering.

I'm a rat rodder when it comes to these things (you can tell by my speaker build pics.) I'll take function over beauty every time. That said, if I can make something look nice, too? That's a plus and worth trying.

This method looks slick, and check it out, you'll get more power! It goes up to 12!!!

 

[toobfreak]

Agonizing over how to finish the front panel. After the black paint goes on it still needs white lettering. That part is hard with DIY, requires an exact printed image, inverse templated. Silk screening would be an option except the panel is big, it's 23x8.

Good luck with that. Here is a narrow rack panel I made for a switching circuit with just a few lights and several switches I made about ten years ago that I needed to label up because it is actually pretty complicated in use and central to the operation of my system, and getting it to look halfway professional looking was hard enough. This is just about the best photo I have of it when I was just beginning to wire it up. It ended up with a LOT more wiring.

Here it is completed before installation:

I can't figure out how they kept the hum out of this amp,

I had the exact same thought looking at your original pictures of the circuit wiring.

 

[toobfreak]

I wondered how you intended to do the lettering.

I'm rather old school myself. I've never been too fond of laser etching because it looks too shallow like it could just scratch or rub off.

I have a set of lettering punches in my machine shop and I like to hand punch the lettering deep into the metal with a hammer, then fill the lettering in with paint flush with the surface, bake it rock hard, then carefully sand it out flush so you end up only seeing the lettering as if they were just printed on.

It may look just printed, but I know the lettering is much more substantial than that.

 

[Chuz Life]

I'm rather old school myself. I've never been too fond of laser etching because it looks too shallow like it could just scratch or rub off.

I have a set of lettering punches in my machine shop and I like to hand punch the lettering deep into the metal with a hammer, then fill the lettering in with paint flush with the surface, bake it rock hard, then carefully sand it out flush so you end up only seeing the lettering as if they were just printed on.

It may look just printed, but I know the lettering is much more substantial than that.

Kind of like how they letter bowling balls.

(That lettering has to be durable too)

 

[scruffy]

Well, the good news is, most of the paint came off the back panel. Took about an hour. The bad news is, it didn't work at all on the front panel. In both cases I'll have to do some sanding.

Got some of the major holes drilled, you can see both transformers mounted along with the punch holes for the capacitors.

The underside looks like this, you can see the terminal strip between the transformers, that's for the main and bias diodes. The wires from the toroid aren't in yet (I'll have to take everything off again to punch the capacitor holes and get the rest of the paint off, it just helps to see where everything is so I can mark the rest of the holes). You can see the primary ground point and the first of the terminal strips for the tubes. The power tubes are real simple, they only have the top of the OT directly to pin 3, the ultralinear tap through the 250 ohm screen resistor to pin 4 (which takes up 2 points on the terminal strip), and the 5.6k grid stopper that goes to the bias circuitry (which is two more terminal points). The cathode goes to ground, that's the fifth point in the middle of the terminal strip.

Things are going to get tight in certain areas once everything goes in. I'm going to install another terminal strip near the top of the chassis for the heater wires, otherwise the area around the main power switch gets cluttered (because it contains the pilot light, standby switch, and HT fuse). The construction has to be done in layers, that's the only way to maintain neatness because things never look the way they do in the drawings.

 

[Chuz Life]

You are describing an absolutely intolerable, verboten condition, which is why I eschew using 1/4" phone plugs in certain critical applications. What you describe above would be a huge liability on any system a company installed for a professional venue.

Here is one situation where, while taking the integral crossover out of one of my bass cabinets, I also converted it to using Neutrik Speakon connectors. Neutrik connectors don't just pop out.

They are crazy, complicated foreign-made things hard to understand when you first get one, but really, very well designed.

Here is a picture of the input panel on the back of one of my bass cabinets after I converted it to using them.

View attachment 1149195
View attachment 1149196
View attachment 1149197

I have some of these. Love em.