Orange Tiny Terrors gutted and rebuilt

[hermannbjorgvin]

Tale of two Terrors

Time to introduce a new project here from Iceland, we are two friends who are into guitar gear and electronics, one of us has an education in electrical engineering (or something) and I am just good with a soldering iron when I am not burning myself with it. I recently finished my own Steel String Singer #002 build based on Ryan Colgan's plans and was looking for a smaller project. After looking online we happened to both purchase Tiny Terrors at a great price, but we like to tinker with shit and this seemed like it could be a great project. The plan is to take two Orange Tiny Terror amplifiers and gut them and rebuild with turret boards and beautifully handwired construction and all those expensive components we know and love. Not because we are unhappy with PCB but for the love of building, Orange really knocked it out of the park with this amplifier and we have 0 complaints, in fact I'll list out below how awesome Orange are.

To give this project a bit more context, here in Iceland the Tiny Terror was a hugely popular amp and sold like hot pancakes, now they are not quite as popular and so the secondhand market has flooded with secondhand Tiny Terrors. The going price right now is between $150-180 USD, what do you get for that kind of money? You get a chassis, 2xEL84 valves, 2xECC83s valves, a power transformer, an output transformer. That's better value than any amp kit I've seen and especially for a modern classic design like the Tiny Terror.

Breakdown of our plan so far

* Trace the PCB boards and design a turret board (unclear if it will be a single board or one for high voltage and another for the preamp)
* Order 3mm FR4 white glass epoxy fiberboard to CNC cut custom turret boards.
* Add a Hammond 159P choke into the circuit for... added tone (right?)
* One of us is planning on using the "Orange Glory" mod from Gear Upgrade
* Sprague Atom and Mallory is probably our cap choice
* Undecided on resistors, what is everyone's favorite 1W/2W resistors?

An ode to Orange

Here is what we love about this amp after tearing it apart to inspect it

* Long transformer leads, US leads tied up nicely in case anyone wants to switch mains.
* Chassis cutout for a potentiometer index locator pin even though they don't seem to use them
* Transformers are clearly labeled for voltages and primary/secondary wire color
* All resistors and capacitors are 1% spec-ed, except for the electrolytics
* Nicely finished powder coating on the inside

Orange are clearly crying out for this amp to be hotrodded and we are here to oblige!

[hermannbjorgvin]

Teardown

So it begins... we are starting by tearing down and tracing out, figuring out what components we want and how to make a turret board fit in this thing. You can see how awesome Orange are here with labeling, thank you whoever did this, if you see this you are awesome.

[Guy77]

Great project! Excited to hear your thoughts on how you like the final results compared to the original!
I played a Micro Terror recently and was also surprised at how nice it sounded. Just 1 12ax7 and the power section is transistors.

Cheers
Guy

[xtian]

Looking forward to your build!

Just FYI, I did a DIY Tiny Terror build a few years ago: https://ampgarage.com/forum/viewtopic.php?t=28411

[hermannbjorgvin]

Great project! Excited to hear your thoughts on how you like the final results compared to the original!
I played a Micro Terror recently and was also surprised at how nice it sounded. Just 1 12ax7 and the power section is transistors.

Cheers
Guy

The micro terror looks awesome too! I think the Tiny Terror definitely takes the cake as the last great all tube amp (solid state rectifier aside).

It will be interesting but I'm afraid I probably won't have any A/B samples available unless I manage to get another amp. If I had to guess I would say the biggest difference would be the choke smoothing out the high voltage, and the "orange glory" mod on at least one of the amps which of course totally changes the sound. I'm guessing the noise will be about the same.

Looking forward to your build!

Just FYI, I did a DIY Tiny Terror build a few years ago: https://ampgarage.com/forum/viewtopic.php?t=28411

That looks awesome! Especially clean for point to point wiring.. as clean as you can get at least

[ChopSauce]

I LOVE these hot rodding projects...

I'm not sure I understand your plans really well, though.

The schematic seems to be available on the internet so I don't see the need to trace it...

If you already didn't do it, I highly recommend that you look at Aaron "xtian'" builds - not just its Orange clone - for inspiring original layouts.

I'm sure you're not as unskilled with a soldering iron as you claim, anyway...

[Stevem]

I have gone thru more then a few of these amps that where modded for more gain and they oscillated like mad above 3/4 volume and were useless!

This root cause of the issue is the placement of the input and outout jacks too close to each other in that small chassis. My cure was to first wrap the jack in a layer of black tape and then fully shield the input jack in foil that was of course grounded out. The layout of your build will be critical to the amp working right and your happiness with it!

[hermannbjorgvin]

I have gone thru more then a few of these amps that where modded for more gain and they oscillated like mad above 3/4 volume and were useless!

This root cause of the issue is the placement of the input and outout jacks too close to each other in that small chassis. My cure was to first wrap the jack in a layer of black tape and then fully shield the input jack in foil that was of course grounded out. The layout of your build will be critical to the amp working right and your happiness with it!

Thanks for the advice. We don't plan on increasing the gain on ours but we are creating our own layout so it's good to know what to watch out for. Grounding and shielding will be important for the lowest noise floor definitely.

I LOVE these hot rodding projects...

I'm not sure I understand your plans really well, though.

The schematic seems to be available on the internet so I don't see the need to trace it...

If you already didn't do it, I highly recommend that you look at Aaron "xtian'" builds - not just its Orange clone - for inspiring original layouts.

I'm sure you're not as unskilled with a soldering iron as you claim, anyway...

Yeah we have a schematic and a diagram but my friend wants to trace the board to get it 100% right

Well you can be skilled but still keep burning yourself, clean joints, nasty burns

[ChopSauce]

Tweezers are my friends, in that respect. They may be yours too...

[sneakers563]

While you're at it, could you measure the impedance of that OT? There are a couple OTs out there that are listed as replacement/upgrades, but they vary somewhat in specs. I'm going to be attempting a subminiature version of the TT soon and it would be good to know what the load line in the original is like.

[sneakers563]

I LOVE these hot rodding projects...

I'm not sure I understand your plans really well, though.

The schematic seems to be available on the internet so I don't see the need to trace it...

If you already didn't do it, I highly recommend that you look at Aaron "xtian'" builds - not just its Orange clone - for inspiring original layouts.

I'm sure you're not as unskilled with a soldering iron as you claim, anyway...

Yeah we have a schematic and a diagram but my friend wants to trace the board to get it 100% right

Well you can be skilled but still keep burning yourself, clean joints, nasty burns

I think tracing it out is a good idea. There seems to be some question around the dropping resistor immediately after the second gain stage. The most common schematic that you come across has it listed as 68K, but there are posts where people claim that it is actually 100K. I'd be interested to see what the value is in yours.

[sneakers563]

Sorry for monopolizing the thread this morning, but there is one other thing that I've always wondered about the Tiny Terror, which is the (to my mind) somewhat odd gain pot circuit. Specifically, does anyone have any thoughts about why Orange puts a resistor in parallel with the potentiometer, rather than just adjusting the size of the series dropping resistors? I suppose it could be to adjust the load impedance seen by the prior stage, as the first gang is equivalent to a 243K pot, and the second is equivalent to 153K, but when you add in the series resistors, and the effect of paralleling it with the load resistor, the AC load lines really aren't all the different.

Technically, this isn't even specific to the Tiny Terror. The Rocker 30, for instance, has a dual-gang 1 Meg gain pot, with 470K resistors in parallel with both gangs. It seems like it's just a hallmark of the modern Orange amps, but I don't really see what purpose it serves.

[hermannbjorgvin]

There seems to be some question around the dropping resistor immediately after the second gain stage. The most common schematic that you come across has it listed as 68K, but there are posts where people claim that it is actually 100K. I'd be interested to see what the value is in yours.

We have two different revisions of the circuit board February and June 2008 if I recall correctly so we can let you know if we find differences between them, what's interesting is that the PT specifications that are labeled on the amps differ as well, one is 238V and the other is 250V, whether that is just a difference in how it's labeled or actual specs I'm not sure, but we'll let you know as well when we measure the live amps. There's plenty of reason now to trace and figure out what's really going on with this.

[Njall_L]

Hi everyone!

I'm the friend who hermannbjorgvin meantions in his original post, the same post where he describes me as an electronic engineer, but I'm only a mere electronic technician for the time being. My background is mostly in digital electronics but I do have some fun with analog circuits in my spare time. I will be joining hermannbjorgvin in updating you guys on the process of the project and answer some questions and thoughts.

The schematic seems to be available on the internet so I don't see the need to trace it...

Yes, some TT schematics are available but I have not found one that seems to be correct, for our models at least. All I have found are for example missing the "hum balance", some place fuses in wrong places, some have wrong values for components, others have no numbering on components and some even show capacitors in the wrong rotation.
After discovering this I decided to just make my own schematic but it is handy to have some other ones for reference.

There seems to be some question around the dropping resistor immediately after the second gain stage. The most common schematic that you come across has it listed as 68K, but there are posts where people claim that it is actually 100K. I'd be interested to see what the value is in yours.

For clarification, aren't you describing the resistor that is circled in red on the image below? (Schematic found here: http://www.prowessamplifiers.com/schema ... error.html)
If so, this is R19 in the amp and I can confirm that both our amps have a value of 100k Ohms for this resistor.

TT_R19.png

While you're at it, could you measure the impedance of that OT?

Are you looking for the input or output impedance, or even both? I don't have a decade box or a power variable resistor available in order to do this measurement, but I want to look into getting some.


Now, some update on the project.
- The tracing of the PCB is going well but I wonder about how to transfer it from a schematic to a chassis layout drawing. Any software someone can recommend?
- We have ordered white FR4 plates for the turret board and they will hopefully arrive soon.
- Some caps have been ordered but we have not finalized the BOM list so some components still have to be ordered
- The Hammond 159P chokes have been received and installed in one of the amps in order to get voltage measurements before we tear everything apart. The choke replaces R3 (150 Ohm / 5W) in the power supply of the amplifier. With the choke installed on the chassis it is pretty crowded on the power-side of things. It also add's a noticeable amount of overall weight to the whole amp.

TT_Choke.PNG

[sneakers563]

For clarification, aren't you describing the resistor that is circled in red on the image below?

Yes, that's the one. Thanks, that's a big help!

Are you looking for the input or output impedance, or even both? I don't have a decade box or a power variable resistor available in order to do this measurement, but I want to look into getting some.

I'm interested in the primary impedance. I'm not sure you actually need a decade box or power resistor. With the speaker and power tubes removed, I think you can just feed a small (~1v) 1 kHz signal across the primary, and measure the voltage that appears on the secondary. Dividing the primary voltage by the secondary voltage gives the turns ratio which can then be squared to find the impedance ratio. In the past, I've used an iPhone / iPad with a function generator app to generate the 1 kHz signal on the headphone jack. The iPhone can put out about 1V RMS, which will probably result in around 33 mV on the transformer secondary.