Orange Micro Terror

Tube or solid-state, this section goes to eleven!
User avatar
schastleevo
Information
Posts: 2
Joined: 10 Feb 2015, 21:59

Post by schastleevo »

I've demo'ed the Micro Terror a couple of times in a store, & thought that it's an interesting "little" amp. Maybe I can't help myself, but I was trying to think how much better it would sound with some tweeks. I've listened to the YouTube that demos some tube swaps, & gives a nice impression but to really hear the change in person is always better. Swapping the tubes is good for a little change, & a nice place to start.

I was also thinking about replacing the OpAmps for an added improvement. I've swapped out the OpAmps in my Jolida turntable preamp along with the tube swap, & really noticed an improvement in the sound.

I've been trying to search for the circuit schematic, but am surprised that I haven't been able to find one yet. I'm also surprised that I haven't read of anyone changing the OpAmps either. I thought that someone on this forum would have tried this by now with the Micro Terror. Maybe I've missed this, or searched using the wrong phrases.

User avatar
FiveseveN
Cap Cooler
Information
Posts: 591
Joined: 25 Oct 2009, 21:20
Location: Romania
Has thanked: 215 times
Been thanked: 116 times
Contact:

Post by FiveseveN »

schastleevo wrote:really noticed an improvement in the sound.
In what way?
I'm also surprised that I haven't read of anyone changing the OpAmps either.
What's wrong with the original ones?
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

User avatar
Groovenut
Resistor Ronker
Information
Posts: 299
Joined: 07 Jan 2011, 16:31
Has thanked: 60 times
Been thanked: 100 times

Post by Groovenut »

The chances are very good that this is basically a tube driver type arrangement. Starved tube for overdrive/distortion, opamp for buffer then boost, hits the tube then opamp for buffering and driving the tone controls then driving the power amp. All along the way filtering the signal to achieve the Orange sound. I haven't looked in depth at the traces on the pcb but thats my guess as to archetecture.

User avatar
schastleevo
Information
Posts: 2
Joined: 10 Feb 2015, 21:59

Post by schastleevo »

In what way?
The Jolida is a really good turntable preamp with a 12AX7 tube output for each channel. When the opamps were installed and I sat down for a listen it had even better detail and definition as well as depth of soundstage.

With the OEM opamps in place the Jolida is still a good preamp, but when the opamps were swapped it really helped make a noticeable improvement. So this has me wondering about the opamp swap in the Micro Terror, then trying some tube rolling for a little fine tuning. It's a nice amp, I like it's small size & the price is nice.

As I mentioned it's too bad that my searches for the circuit schematic isn't having much luck.

User avatar
FiveseveN
Cap Cooler
Information
Posts: 591
Joined: 25 Oct 2009, 21:20
Location: Romania
Has thanked: 215 times
Been thanked: 116 times
Contact:

Post by FiveseveN »

schastleevo wrote:had even better detail and definition as well as depth of soundstage.
I asked because people are usually fooling themselves. And while a proper test can be done, few do and it seems to be the case here as well.
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

User avatar
dimitarmk
Information
Posts: 1
Joined: 23 Feb 2014, 11:19
Location: Skopje, Macedonia
Been thanked: 1 time
Contact:

Post by dimitarmk »

First let me apologize for writing on an old thread, but I'm really interested in making this amp.

I couldn't find any schematic available, but the pictures posted really help. Probably nobody bothered as this amp is cheap to buy. But some of us that are on the end of the world can't even order it - shipping, customs and duties would be crazy.
I also think shitty amps like Frontman 15 and so on are perfect candidates for converting to hybrid - tube/solidstate amp as they already come with a speaker, transformer that can be reused and so on.

From the pictures as I can see, the STA540 is wired into Dual bridge mode but only OUT1 and OUT2 are used, where OUT3 and OUT4 are left out as this is a mono guitar amp, not a stereo.

Image

Image

Image

STA540 is a really simple and cheap power amp - $1.2 on eBay.

Can somebody provide higher-quality pictures where the we can see capacitor and resistor values ?

User avatar
Coldwindofnowhere
Information
Posts: 1
Joined: 24 Apr 2016, 16:23

Post by Coldwindofnowhere »

Here are some high quality pictures of the pcb :

https://www.mediafire.com/folder/aywpiig6zbid3/Orange

Anyone there would be able to make the schematic based on these pictures ?

User avatar
orcl2
Information
Posts: 18
Joined: 16 Dec 2013, 20:49
Has thanked: 11 times

Post by orcl2 »

Is dificult in this way, i'll try.

User avatar
kciuq
Information
Posts: 3
Joined: 26 Aug 2013, 09:16

Post by kciuq »

Hi, schematic be found?

User avatar
kciuq
Information
Posts: 3
Joined: 26 Aug 2013, 09:16

Post by kciuq »

Some picture micro terror pcb.
https://drive.google.com/drive/folders/ ... sp=sharing

In my version, do not have 7812 stabilization has bypassed.

Preamp is not exactly tiny terror preamp, micro terror in both the cathode connected to the ground without RC.

User avatar
camljenkins94
Information
Posts: 17
Joined: 27 Aug 2017, 20:20
my favorite amplifier: My Custom 18-Watt Marshall Bass Amp
Completed builds: Fuzz Face Diy Clone
Boss DS1 gain mod
Location: USA
Been thanked: 17 times

Post by camljenkins94 »

I know that it's been more than a year since this thread was messed with, but I couldn't help myself. I went ahead and carefully studied the pictures of the Micro Terror pcb in order to try and make a schematic.
This is what I was able to get.
This is what I was able to get.
I traced it as far as I could before I got to the giant blob of hot glue by the Aux-in jack. It was here where I lost both the trace and my will to live. :( Mind you, the Part numbers on my schematic aren't the same as on the pcb.

User avatar
Ichabod_Crane
Resistor Ronker
Information
Posts: 354
Joined: 26 Apr 2016, 15:11
Has thanked: 83 times
Been thanked: 36 times

Post by Ichabod_Crane »

Hello, I have four questions:
1) The stupider one: the schematic above and the parts value are just assumed or those are accurated?
2) The zealous one: where to place the JRC4558 and where the 4560 (I see it in the picture)? Maybe the 4560 is a low noise version, so it could be better used in the gain stage?
3) The simple one: the Volume is place in the end of the circuit, right?
4) The hardest one: how I can replace the tube stage with a jfet stage? I need the jfet schematic, please.

Thank you!

User avatar
camljenkins94
Information
Posts: 17
Joined: 27 Aug 2017, 20:20
my favorite amplifier: My Custom 18-Watt Marshall Bass Amp
Completed builds: Fuzz Face Diy Clone
Boss DS1 gain mod
Location: USA
Been thanked: 17 times

Post by camljenkins94 »

Well,
1. The only part value that I guessed on the schematic was C7, since I couldn't make out the part value in the pictures. However, if we compare with the values from https://gitlab.com/jofirel/uterror-amp/ ... master.zip, we can see that I was spot on, despite the fact that their schematic almost seems to be of a different revision of the circuit from the one that I traced.

2. Not all Micro Terrors use NJM4560's, but the best place to put them is in the early gain stages, since any noise there will get amplified by successive stages.

3. Yes, the volume is at the end of the circuit after the aux in and before the power amp.

4. I'm not exactly sure why you'd want to do that, but it is possible. However, because I don't have a Micro Terror to play with, I can't do a proper comparison test.

User avatar
Ichabod_Crane
Resistor Ronker
Information
Posts: 354
Joined: 26 Apr 2016, 15:11
Has thanked: 83 times
Been thanked: 36 times

Post by Ichabod_Crane »

Thanks for all your answer camljenkins94! :wink:
The thing I would like to do is to replace the tube stage with an easier (for me) JFET stage, but I'm not sure how I can convert this tube stage exactly using the JFET.
I could use a simple JFET stage Fetzer Valve style, or echoplex or something like that, but if it's possible to redraw this stage more similar to the original is better.

User avatar
camljenkins94
Information
Posts: 17
Joined: 27 Aug 2017, 20:20
my favorite amplifier: My Custom 18-Watt Marshall Bass Amp
Completed builds: Fuzz Face Diy Clone
Boss DS1 gain mod
Location: USA
Been thanked: 17 times

Post by camljenkins94 »

Okay, so this is what I've come up with:
Micro Terror JFET.pdf
(109.44 KiB) Downloaded 1260 times
Knowing my luck, it probably won't be perfect as is, but you'll probably be able to get it the way you want with some tinkering.

If you want more gain from the JFET stages, decrease the values of R39 and/or R40.

The 12-volt supply is provided by an LM7812 regulator in the Micro Terror, so using a 78L12 here would probably be just fine.

-Cameron Jenkins

User avatar
Ichabod_Crane
Resistor Ronker
Information
Posts: 354
Joined: 26 Apr 2016, 15:11
Has thanked: 83 times
Been thanked: 36 times

Post by Ichabod_Crane »

Thank you. It seems exactly what I was looking for. :D

I noticed just some difference with the other schematic above.
A 1M resistor in the Vbias after the input cap and resistor. And the cap between the lug 1 to the ground is 100nF instead 22nF.
The voltage is 12, in the first schematic is 15v. It doesn't matter, I guess.

User avatar
camljenkins94
Information
Posts: 17
Joined: 27 Aug 2017, 20:20
my favorite amplifier: My Custom 18-Watt Marshall Bass Amp
Completed builds: Fuzz Face Diy Clone
Boss DS1 gain mod
Location: USA
Been thanked: 17 times

Post by camljenkins94 »

Yeah, there are some differences between my schematic and the uterror schematic. I'm not sure if the uterror schematic is supposed to be an accurate tracing of a real Micro Terror or if it is supposed to be a design for building your own Micro Terror. Either way, there are some errors with the uterror schematic, such as with how half of the gain control potentiometer isn't wired up in a way that would work for controlling gain. Also, the tone control on that schematic seems questionable, since the Tiny Terror uses a Vox-esque top cut tone control, which my schematic has while the other one has a big muff-style tone control.

Either way, I should buy one so that I can know for sure what the schematic is.

User avatar
orcl2
Information
Posts: 18
Joined: 16 Dec 2013, 20:49
Has thanked: 11 times

Post by orcl2 »

Hi everyone, follows the site from the schematic -> https://gitlab.com/jofirel/uterror-amp

User avatar
Ichabod_Crane
Resistor Ronker
Information
Posts: 354
Joined: 26 Apr 2016, 15:11
Has thanked: 83 times
Been thanked: 36 times

Post by Ichabod_Crane »

This schematic https://gitlab.com/jofirel/uterror-amp/ ... terror.pdf has indeed some important difference schematically speaking and a lot of difference in the frequencies. I don't know about the sound. In my emulator software the first version of schematic here with flat settings appears to me pretty mid-bump with smooth low end and high end.
This uTerror schematic has more gain/volume (more db), mid scooped, so more bass, and much high end/presence. It remember me the same graphic of the Marshall tonestack in flat when I use it with some emulation. Has it sense? :hmmm:

It's true, the gain pot wiring looks pretty funny. In the emulator the dual action works, but the first half doens't effect if it has set at min or at max. All the action is in the second half.

uTerror schematic has two further stages, and the Volume pot is between the two. In the first is connected the AUX IN and in the second the PHONES. Nevertheless, I really think that the signal pass through this two stages until the power amp. These two stages give more output (or more gain) if we compare uTerror version with and without these two stages. But without the two stages probably we will not get low output, I suppose.

Of course I emulate it with the conversation of the tube stage in the JFET stage designed like camljenkins94 shown me early.

I've done my best and I drawn a few of days ago a veroboard layout based on the schematic by camljenkins94, so this is it:

Image

It's UNVERIFIED, so tell me if you seen something wrong.

I hope somebody want to look at it, maybe to try to build it, because I can't do it now.

User avatar
orcl2
Information
Posts: 18
Joined: 16 Dec 2013, 20:49
Has thanked: 11 times

Post by orcl2 »

Hi Ichabod_Crane, did you noticed that marked on the picture?
confused.PNG
confused.PNG (4.33 KiB) Viewed 9942 times
Something wrong hehe.

Post Reply