Anyone know what the "tiny terror" circuit is?

[FatGaz]

Hi all,

I've got a old project amp that I want to rebuild - I was never happy with the design i tried SO i want to strip it down and try again.

Anyhow, the amp has two 12ax7's and 2 EL84s plus an EZ80 or EZ81. At the moment it has the power stage arranged as one 12ax7 as a phase splitter into the two el84's using i think the circuit of a marshall 18 watt amp. The pre is the two triode stages of the other 12ax7 in series with a tone stack in between. The preamp was my own design; unfortunately it sucked !

I happened to try an orange tiny terror amp in a shop last week - WOW this is just what i want my amp to sound like !!!

anyone know what circuit it uses ? it's got the same set of tubes - but uses a SS rectifier.

(also my amp happens looks very similar to the tiny terror - it's a shoebox sized metal head with a handle on top)

Anyone know if orange are in the habit of including schematics with their amps ?

Peace and Season's greeting,

Gareth.

[FatGaz]

http://www.orangeamps.com/tinyterror/

only info i have been able to find on the web is from this link (and it's a very interesting description of an amp design possibly closer to the kind of tricks 'london power' amps use than a basic circuit from an ac15 or 18-watter etc.)

http://www.musicianshotline.com/issu..._orangeusa.asp

from which i quote :

"Inventing Terror
The Tiny Terror utilizes class A valve technology with a 100% analog signal path that eliminates any and all digital clipping output characteristics. Driven by a pair of EL84 power valves and a front end that utilizes a duct of 12AX7 preamp valves. Switchable from 7 to 15 watts of output, Orange designers have designed the gain structure of the Tiny Terror to work in a very unique way; utilizing a dual gang gain pot, one side turns up the first gain stage to the point of very heavy compression, while the other side changes the impedance of the second gain stage so that it to compresses to the same degree.

It utilizes a five section fully filmed interleaved output transformer that is very closely balanced to primary. The EL84 output tubes are cathode biased to around 90% in the 15w position, and 96% in the 7w position. In short, the Tiny Terror is designed to produce as much gain as a four stage gain pot, but the output tubes are driven evenly all the way through. The tone control is also designed in a unique way, where the tone circuit is not on the preamp side, but actually part of the phase inverter (power amp) so the gain structure of the amp is unaffected by the tone control. "

[AdmiralB]

It's an AC15, with an extra gain stage cascaded on the front end. PI and power amp are 100% AC15. The gain pot is a dual 500K that serves as simultaneous voltage dividers after each gain stage.

The amp is actually biased at over 15W per tube static. It's insane. I swapped the 100 ohm cathode resistor for a 180 ohm, made no difference in the sound but made the tubes a lot happier.

[steve]

Admiral,

How does the 7/15 watt switch work?

steve

Originally Posted by AdmiralB

It's an AC15, with an extra gain stage cascaded on the front end. PI and power amp are 100% AC15. The gain pot is a dual 500K that serves as simultaneous voltage dividers after each gain stage.

The amp is actually biased at over 15W per tube static. It's insane. I swapped the 100 ohm cathode resistor for a 180 ohm, made no difference in the sound but made the tubes a lot happier.

[AdmiralB]

It selects a different HV tap on the PT secondary. One leg remains tied to one side of the bridge rectifier, the other side has two taps and the switch selects between them. The result is something like 250VDC rather than about 325VDC.

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

I replaced the power switch with a DPDT and also switched a second cathode resistor in parallel when I selected 7W. That made both modes idle happily.

[steve]

Cool. Thanks for the info.

steve

Originally Posted by AdmiralB

It selects a different HV tap on the PT secondary. One leg remains tied to one side of the bridge rectifier, the other side has two taps and the switch selects between them. The result is something like 250VDC rather than about 325VDC.

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

I replaced the power switch with a DPDT and also switched a second cathode resistor in parallel when I selected 7W. That made both modes idle happily.

[Steve Conner]

That's "underbiased" as in running too hot, I guess? I always think of underbias as meaning cold with a lack of idle current.

BTW, thanks for the info, I played through one of these in a guitar shop a while back, and was wondering how they were made. It struck me as a real dirt machine of an amp. I read all the PR blurb on the Orange site, and it gave me the impression of some top secret cutting-edge technology, not an AC15 clone ;-)

[bob p]

Originally Posted by AdmiralB

It selects a different HV tap on the PT secondary. ... the switch selects between them. The result is something like 250VDC rather than about 325VDC.

didn't Randall Smith/Mesa claim a patent for B+ switching back when they first used that in the Mark series amps? I know that my Mk IV uses a toggle switch to tap different coils on the PT for its lower voltage "tweed" mode, and its higher voltage "full power" mode. IIs Orange licensing that, or has that patent expired already?

[AdmiralB]

Originally Posted by bob p

didn't Randall Smith/Mesa claim a patent for B+ switching back when they first used that in the Mark series amps? I know that my Mk IV uses a toggle switch to tap different coils on the PT for its lower voltage "tweed" mode, and its higher voltage "full power" mode. IIs Orange licensing that, or has that patent expired already?

Smith's patent selects different taps on the primary - in practice, one is 120V and the other is around 160V, which when fed 120V gives the result of 120V variaced down to about 90V. It browns out the whole amp, HV, heaters, bias, etc.

The TT switches the HV secondary only. Heaters don't change.

[drewl]

Judging from the assesment, it seems pretty close to the rocker series....here's one I had to bring back from the dead.....it blowed up real good!

http://img.photobucket.com/albums/v3...1/100_1918.jpg

http://img.photobucket.com/albums/v3...s/100_1917.jpg

[gtrboy]

please post the schematic on this one... it kicks butt!!! i played one. its gotta have 3 gain stages and not be push pull. the dual pot thing has been on ax84 forever. no news there.

[AdmiralB]

Ask and ye shall...

gotta have 3 gain stages and not be push pull.

Why do you say this? It is neither of those things.

[gtrboy]

thats one sexy circuit!!

[mak]

so, has anyone tried to mod the tone circuit to brighten the mid/hi response? great amp, but a really foggy tone and not much authority in the tone circuit
Cheers
mak

[FatGaz]

Hi All,

I've not been here for a while after posting my query - but ampage proves what a fantastic set of people post here ! both the circuit and constructive critisism of it !

I am now spurred-on to get the soldering iron out and turn my failed project amp in to a terrible-tot !

I using a hammond universal PP OT, 125E i think is the model number. I have a tube recto too (ez80 i think) so the amp will probably feel fairly different.

Questions for A.B. re the schematic....

I notice that there is the 7/15w hv switch is not shown and that there is also no master vol shown - which master vol circuit is used ? post PI ?

I will mod my preamp to match that of the circuit and put two preamp gain controls in. I will leave my poweramp as is - it has switchable NF and a post PI master vol that shorts across the power tube outputs. I'm not sure if i'll bother putting in the ac-15 alike top-cut.

I don't have any dual 500K or 1mge pots at the moment - maplin don't do them worst luck - so i'll need to think what els i need for a big enought mailorder.

If anyone has any ideas about tweaks i might want to do or where I may need to tweak component values to suit my particuar tubes/ ot/ B+, post them here !

Gaerth.

PS
since i last posted i've hot rodded my jap squire strat (kinman woodstock plus pups and a switch to put the bridge pup in series) and finally set it up properly with a new bone nut, bridge bits and I read a decent book and borrowed an imperial feeler guage to set it just right - it's such a better guitar now - bridge and neck in series is a great new tone too.

[AdmiralB]

You're right, I omitted the master from my drawing. It's a 500K dual-pot post-PI master with an extra set of .1uF caps.

The power switch is on my drawing, it's on the HV secondary. It selects between two 'ends' of the winding - HV winds up with about 325V and LV about 250V.

[AdmiralB]

I fixed the drawing. Standard post-PI master, but since it's cathode-bias it doesn't need the extra set of blocking caps.

[ElTeye]

I picked up a TT, and was very pleasantly surprised with the build quality. It sounds nice; now on to the fine tweaking!

1) The 7/15Watt switch:

Originally Posted by AdmiralB

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

Would it be an improvement if the 7/15W switch just lowered the power tubes and left the pre-amp in hi-volt mode? That would be tricky to achieve, right?
Cathode bias R is R5? I read somewhere it would be better a 180-Ohm resistor. Would it not be better to switch this value also when switching from 7 to 15 Watt?
Admiral, what values of cat resistor and bypass cap do you suggest for the 7 Watt, and which for the 15 Watt position?

2) The resistors seem to be metal film in the first stages - nice - but all caps are little square blue boxes. Would it be a big improvement if I replaced a bunch with SoZo caps? If so, which ones to replace for max effect?

3) On every single TT I've seen, one of the transformers sits crooked. Does this have a reason? Seems weird for such a neatly built amp!

Thanks so much,

El Teye

[AdmiralB]

I don't know how you'd affect only the voltage in the power amp since the switch selects a different HV tap on the power transformer.

180 ohms is a good choice at 15W power; I replaced the power select switch in mine with a DPDT (Mouser sells the same switch brand and family) and used the other pole to place a 100 ohm resistor in parallel with the 180 when I went down in power. Worked great.

I don't think there's much to gain with cap swaps, myself. And both of my transformers were crooked too!

[ElTeye]

Hello Admiral and thanks for your quick reply! The soldering iron, as well as my modding desires, are itchy!

Originally Posted by AdmiralB

I don't know how you'd affect only the voltage in the power amp since the switch selects a different HV tap on the power transformer.

Theoretically, you could leave the voltage drop resistor circuitry hooked up to the 325? And run a new wire that switches the power section and its resistor only? Would probably involve some doubling of some parts. Might affect the whole sound of the whole thing and thereby defeating the concept.
Perhaps a TPDT 7/15Watt switch, altering (or shorting) voltage drop resistor to the pre-amp, as well as transformer tap and cathode resistor?
Or is that just going too far?
(i)I'd thought this beast was a single-ended amp, and you could just pull 1 EL84 ! (At these power ratings, impedance matching does not worry me too much: I've built a AC15 w AC30 front end, put two 10" speakers in series to connect to the 16Ohm tap, and really the thing sounds MUCH better running them parallel into the 8-Ohm tap. Have been doing so for many years now. OT doesn't even get warm.)(/i)

Originally Posted by AdmiralB

180 ohms is a good choice at 15W power; I replaced the power select switch in mine with a DPDT (Mouser sells the same switch brand and family) and used the other pole to place a 100 ohm resistor in parallel with the 180 when I went down in power. Worked great.

Fantastic tip! Thanks! Saves a lot of guessing and trying. Thank you so much!

Originally Posted by AdmiralB

I don't think there's much to gain with cap swaps, myself.

The thing sounds really good as is! But it's all PCB mount so then I wonder: do those blue box caps sit there for sound, or for reasons of easy mounting? Have rebuilt several amps with better caps and the result has been very pleasing, without exception. If I do so, I will let you know my findings OK?

Originally Posted by AdmiralB

And both of my transformers were crooked too!

I straightened out mine last night. It's just the final touch, but.... weird.

Thanks Admiral!

Teye

[AdmiralB]

The voltage selection isn't choosing "both ends" of a winding, one side is always connected to the bridge and the other is selected by switch. I don't know how well adding a second bridge, as well as filter bank(s), would work. IMO, not worth the trouble considering what it is.

The box caps are there I suspect because they're easy for machines to stuff.

[ElTeye]

Originally Posted by AdmiralB

The voltage selection isn't choosing "both ends" of a winding, one side is always connected to the bridge and the other is selected by switch. I don't know how well adding a second bridge, as well as filter bank(s), would work. IMO, not worth the trouble considering what it is.

The box caps are there I suspect because they're easy for machines to stuff.

Of course! It's not switching the DC but AC voltage! Oh man, the brain... sorry.

Still, I could experiment with altering the voltage drop resistor to restore at least some of the voltage back to the pre-amp section... Interesting thing is that I HAVE some TPDT switches at the house (big ones, not micro...)

I'll give the amp some burn-in time and then probably put SoZo caps in, just for giggles.

Hey Admiral, do you hav e that schematic please? Can you e it to teye@teye.com? I'd be helped big-time!

Thanks,

Teye

[ElTeye]

Originally Posted by AdmiralB

The amp is actually biased at over 15W per tube static. It's insane. I swapped the 100 ohm cathode resistor for a 180 ohm, made no difference in the sound but made the tubes a lot happier.

I did the recommended mod to let the tubes run a little cooler: put in the 180 Ohm cathode resistor, switching in a parallel 100 Ohm when giong to 7 Watts. My amp lost punch, bite, and some volume in the 15Watt setting. Even trying some in-between values (connecting a few parallel resistors: i did all of this while the amp was on and I was all plugged in) still did not restore the full blast.

I quickly moded it back to original. Can't believe it: ME happy with the stock version?

Sound-wise: the pre-amp tubes are good quality JJ ECC83's. No reason to not experiment though!
I got a slightly more Ampeg feel by using a 7025 long plate for V1 and 12AU7 for the PI (little surprise there, really). Tried a 12AT7 for PI and was not happy.
My favorite: a Watford tubes Cyrogenically treated ECC83 for V1, and... a long plate 7025 for V2. I would describe it as a middle-of-the-Atlantic sound....

[haripotna]

Originally Posted by ElTeye

I did the recommended mod to let the tubes run a little cooler: put in the 180 Ohm cathode resistor, switching in a parallel 100 Ohm when giong to 7 Watts.

Why don't you put a 360 E resistor in parallel to the 180 E cathode resistor in 7 Watt mode - in this case the overall value would be 120 E for 7 Watt mode ?

I wanna mod the circuit by building in a solo-switch and clean-(less gain)-switch...
...any suggestions ?

[AdmiralB]

That's what I did - I put a new power switch in (DPDT, replacing the stock SPDT) and brought in a second resistor. But I used 100 ohms, which got me in the right spot dissipation-wise. 120 is too high for 7W mode.

I can't explain why he heard such a dramatic difference. I heard none at all.

[ElTeye]

Originally Posted by AdmiralB

That's what I did - I put a new power switch in (DPDT, replacing the stock SPDT) and brought in a second resistor. But I used 100 ohms, which got me in the right spot dissipation-wise. 120 is too high for 7W mode.

I can't explain why he heard such a dramatic difference. I heard none at all.

Yes it is weird. Because I heard it immediately, and at an ungodly hour too! So, to be certain, I wired it all up so that I could switch back and forth between the 180 Ohm and the 120 (and also some in-between values, by means of some parallel resistors, All soldered together on one side, and hook-uppable via clamps).

When going from the 120 to 180, I lost (very audibly so): power, some edge/bite, and all-in-all the eagerness of that amp that I love so much. Even on the in-between valkues, I could not get the result that I got from the 120.

I used a 1993 Tony Zemaitis Custom Deluxe guitar for the tests. Very responsive guitar. And plugged it into a Scumback "Pre-Rola" Celestion loaded 1x12 GenzBenz closed back cab. All very hi quality stuff, and with the Tiny Terror back to stock, a delight to play thru.

Normally, I cannot wait to get the soldering iron into modern stock stuff cause I know that upgrading it is usually just a matter of removing cost-cutting factors (like a SPDT switch....)
But in this case, I'll just keep it stock. I'm very happy for Admiral that in his TT there is no sound difference so that you can run those tubes cooler! Wish I could too! Mine (probably due to many other tolerances in the amp) cannot, so I'll just run it HOT baby yeah!

Next up, I will replace the coupling caps with SoZo's. Will let you know how that goes (it'll be some time though).

Greetings to all!

Best,

Teye

[Justin]

I was wondering if someone could repost the schematic the link to it is broken. Thanks

[AdmiralB]

It works now, my ISP is a little flaky at times.

[tbryanh]

Originally Posted by bob p

didn't Randall Smith/Mesa claim a patent for B+ switching back when they first used that in the Mark series amps? I know that my Mk IV uses a toggle switch to tap different coils on the PT for its lower voltage "tweed" mode, and its higher voltage "full power" mode. IIs Orange licensing that, or has that patent expired already?

A large number of patents are bogus.

The patent office is mostly a record-keeping office. They generally let industry fight it out to see if a patent is valid, otherwise it sits there uncontested.

The patent office generally does not decide if a patent is valid unless it is extremely obvious that it was already invented or is not novel.

Take the wheel for example.

If the patent office already recorded a patent for someone for inventing the wheel, they would not record a patent for you for this. It would be extremely obvious that the wheel was already invented. And, it they hadn't recorded a patent for someone else yet, they still would not do it for you. It would be extremely obvious that inventing the wheel is not novel.

A patent search to see if the "invention" already exists or is similar to one that already exists is required before a patent can be issued. But the patent office does not do the search. They require that the person applying for the patent to do the search.

Bottom line: If you are not "inventing" the wheel, you fill the paperwork out correctly, and you pay the fee, you get your "patent."

Most of the protection for electronic circuits comes from copyrights, not patents. The foil patern on a printed-circuit board is unique and can be copyrighted as art. Most companies copyright their artwork on their PC boards because it is easy to prosecute someone who copies it. When someone duplicates their PC boards, it is blatently obvious.

Randall Smith's patents are probably bogus.

[Steve A.]

Originally Posted by AdmiralB

It selects a different HV tap on the PT secondary. One leg remains tied to one side of the bridge rectifier, the other side has two taps and the switch selects between them. The result is something like 250VDC rather than about 325VDC.

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

I replaced the power switch with a DPDT and also switched a second cathode resistor in parallel when I selected 7W. That made both modes idle happily.

Aunt Bea, er, I mean *Admiral B*:

So the 325vdc and 250vdc voltages you mentioned would be the B+ from the first node of the power supply? Just checking...

I like the idea of using separate taps rather than padding the voltage with a resistor, which can get downright mushy. Then again we could always use the Bruce Collins 10v/5w zener diode trick to cut the B+ down a little bit...

Thanks!!!

Steve Ahola

[AdmiralB]

Right. Since it's a bridge rectifier, there are no 'symmetry' issues around a center tap (there is no center tap), and only one side of the HV winding is switched.

[Wicksy]

Hey AdmiralB, i just though i'd pop by and say thanks for the schem! I'm building a handwired clone. I'm going the whole hog using TAD mustard clones etc... From your schem i managed to draw up a nice layout. Cheers!

[haripotna]

Greets.

I'd like to add an eq after the input stage to the curcuit, in order to have more control over my tone (take some mids out, etc.).

I would build out the resistors R22 (68k) and R23 (470k) and put an eq like used in the mesa/boogie caliber 50 instead of it.

What would you think about this modification ?
Any suggestions for a built in eq ?

[Steve A.]

Originally Posted by haripotna

Greets.

I'd like to add an eq after the input stage to the curcuit, in order to have more control over my tone (take some mids out, etc.).

I would build out the resistors R22 (68k) and R23 (470k) and put an eq like used in the mesa/boogie caliber 50 instead of it.

What would you think about this modification ?
Any suggestions for a built in eq ?

My drawing for a .50 Caliber + shows both a BF style tone stack and a graphic equalizer. What did you have in mind?

Adding a regular tone stack to the TT would cut the overall gain something like 20dB. If you need additional control over the tone I'd suggest a tweed deluxe style tone control, wired up to a switch to be able to remove it from the circuit completely.

The thing I liked about the TT was that it was so simple and direct- without all of the BS that you typically find in a Mesa Boogie amp...

Good luck!

Steve Ahola

[haripotna]

Well, I'd like to add a traditional tone stack to the circuit in order to have more control over the sound. I love the basic sound of the amp, but I'm more the rock/metal head, so I need to shape the sound (just a bit).

I consider, adding a switch to cut the mid-pot of the ground for having a solo switch (without eq in solo mode).

I've put 4 leads instead of the 68k(100k) and the 220k resistor before the second stage of the gain pot - now I can try out several circuits without having to dismount the amp each time I try out an other mod.

I think, I'll give the deluxe tone control a try, for it is very simple and has got good reviews for its "versatility".

Greets from Austria !