freestompboxes.org

Hey everyone...

I just snagged this pedal off eBay, and I didn't see a thread on this model... so I thought I'd share a bit.
I found this description online when I first saw the listing. It sounded like a pretty interesting concept, so I wanted to have a listen:

AMT Tube Magnum:
The Tube Magnum is in tube the series of effects based on the valve signal limitation principle. A 12AX7(ECC83) tube is used making it possible to obtain a real valve overdrive with a unique warmth and density of tone characteristics parallel to tube driven amps. Tube Magnum is an overdrive style pedal with less gain than the Tube Platinum. It recreates that classic vintage style warm tube overdrive from your favorite, more expensive amplifiers.

The smallest, best sounding tube overdrive pedal on the market. VERY compact design, making it easy to fit that huge tube tone on your not so big pedalboard!

All AMT pedals are designed to sound equally as good through an amp or direct recorded due to built-in cabinet emulation circuitry.Perfect for live performance and in the studio. You must try one to believe it. The first time you plug one in, you will be instantly addicted to the "AMT Tone".

Tube Magnum's frequency-compensated output can be connected not only to a guitar combo but also directly to mixer or a recorder's input.

Features:

* Size: 112mm (4.4"), 72mm (2.8"), 90mm (3.5")
* Weight: 420g (14.8 oz)
* Control: Level, Low, High, Drive
* Ports: IN, OUT
* Power: Included AC Adapter Only (cannot be powered by a battery)

It's nearly all SMD... with a few stand-up resistors and a couple of caps to go with the tube. I decided to get a look at the inside because the description said that it was an AC-only pedal, but the chassis has a battery compartment. I didn't see anything that looked like a

I'll have to drag this thing out to my bench to get a better look under glass, but first... I think I'll put it back together and make sure it actually works.

This is my first attempt at taking some gutshots... be gentle.

Cheers...
Steve

Please note: I goofed a bit on my post above and posted some of my comments inside the quote box with the product description. My apologies.

Also, here's the complete specs from AMT:

Technical Information:
Size: 112mm (4.4") x 72mm (2.8") x90mm (3.5")
Weight: 420g (14.8 oz)
Min. level: -40dB
Nominal: -26dB
Max. level: +17dB
Resistance: 1 kOm
Max. level: +12dB
Current of the consumption: 420 mA with 9V
LEVEL: loudness of distortion.
LOW: regulates the level of low-frequency components.
HIGH: regulates the level of high-frequency components.
DRIVE: regulates the level of tube overloading.
Power: DC 9V PSA (-) center Adapter Included

I woke the wife up out of a sound sleep with this one in record time.

For what amounts to a half-tapped filament configuration, this thing has some really nice tone and a lot of boost. Even at lower volumes (see above ), it gets a really warm-sounding, full overdrive sound. The "Drive" knob gives a lot of control... from very mild overdrive right up to some pretty crunchy distortion and sustain... even with the volume on my little Vox combo and the pedal "Level" turned way down. The "Low" and "High" provide a reasonable amount of control, although I usually use the tone controls on the guitar anyway. With the "Low" about 12 o'clock and the "High" and "Drive" turned up, you get into some really nice Angus Young territory... complete with visits from the police for "Noise Pollution"...

I've never had a big tube amp (see above again... ), but you can get some pretty "big amp" sounds with this thing. I think it'll be on my main board for awhile... Looks like the TS-9 gets a little rest.


Cheers...
Steve

interesting. apparently this thing runs off 300v, but uses a 12v adapter.

https://www.freestompboxes.org/viewtopic.php?f=22&t=7694

thanks for the shots!

that small board sticking out the back is a high speed switching mode dc voltage step up supply - possibly up to 300v dc from a 9v dc input
cheers
bajaman

bajaman wrote:that small board sticking out the back is a high speed switching mode dc voltage step up supply - possibly up to 300v dc from a 9v dc input
cheers
bajaman

Absolutely right. I just double-checked the adapter... 9V ~ 1.11A (10W Max.)

I've been buying up quite a few pedals recently (and I blame each and every of you)... and to ensure my trip to the dog house, I just grabbed an Epi LP Standard for the collection tonight. Can't wait to plug it into this baby and crank it up a bit. That is, of course, if I can sneak the guitar into my office and get it into my guitar rack without my wife noticing. It's tough to get into a riff when you're playing with two broken arms. I bought a Fender Strat about 6 weeks ago... so this may just be the straw that breaks the low E string...

If you don't hear from me for a couple of weeks, you'll all know what happened. Somebody call the police and have them check my backyard.

I've had one of these for some time.. it's a great pedal.
You can see in this thread where I asked if there was any interest in it :
https://www.freestompboxes.org/viewtopic ... &hilit=amt

In the second picture thee is a small pcb just below the valve, this is the switching PSU. Could you please read the identification on the IC for us ? (this is what makes the 9V into 300v.

Greg_G wrote:I've had one of these for some time.. it's a great pedal.
You can see in this thread where I asked if there was any interest in it :
https://www.freestompboxes.org/viewtopic ... &hilit=amt

Actually, I can't Greg. I am logged in, but it says, "You are not authorised to read this forum."

Am I on double secret probation already?

I've only been here a short while, but I consider most of you guys far more an expert on effects than I am (I buy a lot of pedals, but mainly just to plug in and fiddle with).

Since you have one, I am really curious what you think of the sound of this thing. Primarily, I use a little Vox 4W tube combo amp with a 1x12 extension cab. I was stunned at how this little beast gave a really big amp sound at really low volumes. As I turned it up, it got better and better... but even at "quietly noodling in front of the TV" volumes, it was incredibly rich-sounding, IMHO. I also tried it with my Fender Vibro Champ, and it gave that same full tube tone at very low volumes.

I don't have access to a large variety of vintage pedals to compare it to, so I'm curious if there are any overdrives you think outdo this one? I love the sound of various ODs for different sounds, but I can't imagine another stompbox beating this one with a small combo rig.

Ice-9 wrote:In the second picture thee is a small pcb just below the valve, this is the switching PSU. Could you please read the identification on the IC for us ? (this is what makes the 9V into 300v.

Ice ~ I am assuming that you're referring to the far-end of the daughterboard that the tube is mounted to (where the larger caps and little transformer are) in this pic?

Tonetweaker wrote:

SAM_0115a.jpg

I took the pedal back apart and checked the chip on that board for you, but it appears that the top of the IC has been sanded to remove the markings. You can actually see the very top of the top row of digits/characters, but there's definitely not enough left to read. A shame too... I hadn't really thought about it, but identifying that chip could have been pretty useful for other projects involving tube circuitry in a small-box setting.

Sorry...


Cheers...
Steve

Tonetweaker wrote:

Greg_G wrote:I've had one of these for some time.. it's a great pedal.
You can see in this thread where I asked if there was any interest in it :
https://www.freestompboxes.org/viewtopic ... &hilit=amt

Actually, I can't Greg. I am logged in, but it says, "You are not authorised to read this forum."

Am I on double secret probation already?

My aplogies Steve.. it's in the Tracer's Fund which is accessible by people who've contributed funds.. everything that happens there eventually makes it's way to the main board anyway, so you're not missing out.

Basically this:
"Is there any interest in an AMT Electronics Tube Magnum ?..
12AX7 Pre-amp / Overdrive running at high voltage.
Sounds surprisingly nice."

"I see 9V DC on the case ? "

"That's the interesting bit... 9v in and maybe a couple of hundred volts at the tube.. all in a small package.
It's a clever design.
I'm not sure of the numbers on this one, but the current AMT tube designs are 12 volts in and 290 volts Anode !

I've got one. Tracing this one is beyond my skills (quite a bit of smd), but I'm willing to send it to someone who can.. if there's any interest."

Greg_G wrote:

Tonetweaker wrote:

Greg_G wrote:I've had one of these for some time.. it's a great pedal.
You can see in this thread where I asked if there was any interest in it :
https://www.freestompboxes.org/viewtopic ... &hilit=amt

Actually, I can't Greg. I am logged in, but it says, "You are not authorised to read this forum."

Am I on double secret probation already?

My aplogies Steve.. it's in the Tracer's Fund which is accessible by people who've contributed funds.. everything that happens there eventually makes it's way to the main board anyway, so you're not missing out.

Basically this:
"Is there any interest in an AMT Electronics Tube Magnum ?..
12AX7 Pre-amp / Overdrive running at high voltage.
Sounds surprisingly nice."

"I see 9V DC on the case ? "

"That's the interesting bit... 9v in and maybe a couple of hundred volts at the tube.. all in a small package.
It's a clever design.
I'm not sure of the numbers on this one, but the current AMT tube designs are 12 volts in and 290 volts Anode !

I've got one. Tracing this one is beyond my skills (quite a bit of smd), but I'm willing to send it to someone who can.. if there's any interest."

As far as my opinion of it.,. I think it sounds great when set right.
The tone controls really have too much range IMO, and it takes some playing around to get it right.. set at 12.00 doesn't really work for me on this one.
But.. it's versatile and has some really sweet tones in it.

It's the only (pedal) tube pre-amp I've ever liked.

Greg_G wrote:My aplogies Steve.. it's in the Tracer's Fund which is accessible by people who've contributed funds.. everything that happens there eventually makes it's way to the main board anyway, so you're not missing out.

No worries, Greg. Hopefully, I can contribute to the next project so I can keep track of the tracing/de-gooping process...

I can see your point about the tracing on this one, too. It'd be a nightmare.

Greg_G wrote:As far as my opinion of it.,. I think it sounds great when set right.
The tone controls really have too much range IMO, and it takes some playing around to get it right.. set at 12.00 doesn't really work for me on this one.
But.. it's versatile and has some really sweet tones in it.

It's the only (pedal) tube pre-amp I've ever liked.

I usually just put everything to 12 o'clock, dial in a nice basic tone and then start fiddling with the drive/volume settings. This thing had me smiling in a matter of a minute or two.

I take it you prefer some of the solid state ODs to this one? Which ones (if you don't mind me asking, of course)?

As I mentioned, I don't have a lot of real vintage or high-dollar stuff, but I have a few that I was really happy with (Fulltone OCD, TS9)... This thing knocked them all off of my main pedal board for the moment. I have a Tech21 XXL on the way though, so I'll see if that gives this pedal a run for its money.


Cheers...
Steve

Tonetweaker wrote:I take it you prefer some of the solid state ODs to this one? Which ones (if you don't mind me asking, of course)?

As I mentioned, I don't have a lot of real vintage or high-dollar stuff, but I have a few that I was really happy with (Fulltone OCD, TS9)... This thing knocked them all off of my main pedal board for the moment. I have a Tech21 XXL on the way though, so I'll see if that gives this pedal a run for its money.

Cheers...
Steve

Not necessarily Steve.. if it came down to a 'Desert Island' Overdrive I could be happy with this.

Other than that I'm usually using something I've built and tweaked myself.
It took me a couple of years to be able to build stuff I liked better than what I could buy, but I feel that's where I am now... and there's so many more cool projects out there I haven't tried.
Being able to build and tune things myself saved me from endlessly buying and selling pedals trying to find "the one".

Greg_G wrote:Not necessarily Steve.. if it came down to a 'Desert Island' Overdrive I could be happy with this.

Other than that I'm usually using something I've built and tweaked myself.
It took me a couple of years to be able to build stuff I liked better than what I could buy, but I feel that's where I am now... and there's so many more cool projects out there I haven't tried.
Being able to build and tune things myself saved me from endlessly buying and selling pedals trying to find "the one".

That's a great place to be, Greg... I really wish I was at that point. To be honest, I am currently doing just what you described... minus the selling part. I've always been a real amateur in the guitar department, so when I turned 40 a few months ago, I promised myself I would get some real gear and make a serious run at trying to improve my skills. Since then, I've been accumulating quite a stash of gear (3 decent practice amps, 4 new guitars, somewhere in the neighborhood of 75 pedals or so, and assorted accessories) looking for quality tones and sounds to keep me motivated while I practice. I find that nothing inspires me to keep playing than dialing up a really sweet tone for whatever type of music I'm trying to learn/practice.

I also bought some upgraded gear to get back into building some toys of my own, and I've got most of the technical/electronics aspects of building down pat (I was a tech in the military)... so it's mainly a matter of having the time to start building. I'll be moving in the near future, but after that, I plan on restocking my bench and getting to work on some light builds. In the meantime, probably the biggest setback for me is not really knowing which vintage effects will provide "the" tones I really want... without that knowledge, all the technical ability in the world is pretty much useless. That's part of the reason I'm here... I've always found that when you want to learn, you hang out with the guys that really know their s**t. Then, you just try to shut up and listen until you've got something worthwhile to contribute.

Since I joined this site, I've already learned far more about what makes tone tick in a couple of weeks than in 30+ years of collecting and listening to the music I enjoy. I've already decided that my first build will probably be an early Fuzz Face... I was lucky enough to grab a couple of those authentic-looking pre-made PCBs from that eBay vendor while he was around, so it'll really just be a matter of getting some period correct components when I get settled. Then, the real rookie questions will start...

I appreciate the help (and the patience), Greg...


Cheers...
Steve

For the switchmode power supply, check out the thread
https://www.freestompboxes.org/viewtopic ... 41&t=12094
This is just one example of how you can change 9VDC, 12VDC etc, up to a regulated 250VDC

The control ic is TL494, available everywhere.
The only harder things to get are the 6A 600V mosfet & the inductor.
The inductor makes sense to wind your own, if you have insulated wire & ferrite cores.

of course, if you have an AC input available, then the transformer connected backwards method is a much easier way to generate a 250V supply.

Hi there,

But what happens if we take the job to trace the schematic of this unit, and leave the HV supply discussion for another occasion ?

Perhaps this same circuit, if employing a 12AU7 running at lower voltages, has the same sound that a 12AX7 at 300 Vdc.

Its easy to obtain around 70 to 90 Vdc using 12 Vac from a wall wart, and a voltage multiplier: no more than 6 diodes and 6 to 8 electrolytics capacitors is all that need.
Cheers,
Jose

ppluis0 wrote:Hi there,

But what happens if we take the job to trace the schematic of this unit, and leave the HV supply discussion for another occasion ?

If you decide to trace it, just let me know... I'll be happy to get some component values and take some better pics if needed.


Cheers...
Steve

Hi Steve,

I was thinking that if we leave aside for now how to generate high voltage, the rest of the circuit should not be too complicated to understand.

My first impression is that there must be a stage with a opamp buffering the input, then the valve, tone control and another opamp driving the output jack.

Something similar to a Tube Driver, but with the addition of these 300 Vdc to feed the tube plates.

If anybody else feels interest in drawing this diagram, I am gladly willing to participate.

Cheers,
Jose

ppluis0 wrote:Hi Steve,

I was thinking that if we leave aside for now how to generate high voltage, the rest of the circuit should not be too complicated to understand.

My first impression is that there must be a stage with a opamp buffering the input, then the valve, tone control and another opamp driving the output jack.

I tend to agree, but then again, I'm pretty useless without a schematic in hand.

I can troubleshoot the hell out of most circuits, and I haven't had much trouble building them... but reverse engineering is another matter. I'm not very good at taking a PCB and turning it into a schematic. Old eyes, I guess.

If anyone has any interest in the job, though, I'd be more than happy to do what I can on my end (which applies to any of the pedals I have)... short of major-league desoldering work. I don't mind taking pics and identifying components when feasible, but I just hate the idea of ripping apart a working circuit board, especially since the vast majority of my bench equipment is currently packed up in my garage for my upcoming move. Too many years as an old tech, I guess.

I'm kind of strange in that regard. I see threads on some pedals where excellent (and in some cases, necessary) mods are suggested, but personally, I'd much rather build a pedal completely from scratch for those mods than tinker around with a working commercial effects pedal, even a somewhat poor-sounding one. I guess I'm a purist, for better or for worse.


Cheers...
Steve