Orange Micro Terror

Ichabod_Crane · Post by **Ichabod_Crane** » 27 Apr 2020, 17:41

Yes, I didn't analyze the schematic with much careful. I need to look that well.
Indeed, it was strange even if I didn't thought about it.

Tha guy who drawn the schematic said that is tracked from the original amp, but of course he admits some mistake can be there.
It's suspect the Tone section. Some mistake is possible, but I guess we can't "read" the Big Muff tone style instead a Vox Style by mistake.
And the Volume pot value? 100k or 25k is just supposed?
Even the two last stages, those drive the Aux In jack and the Phones jack, but it's possible that two stage need to the signal tracking.

mojorootietootie · Post by **mojorootietootie** » 07 Jun 2021, 19:16

This is an old thread but I have to set the record straight. Valiant effort by camljenkins94 but the original schematic posted in https://gitlab.com/jofirel/uterror-amp/ ... master.zip is >90% correct. The board has 2 layers and many of the traces are covered by the components making it impossible to trace from the photos alone.
I was able to trace the board from micro terror SN 10131-1112 by using a combination of visual and multimeter probing so I am quite certain of the results.
Kudos to José Relvão who did the original tracing. The following are where his and my tracings differ:
1. R2 wired to Vbias and not GndRef
2. Gain circuit C7 connected to VR1A wiper not to R8-C6 node.
3. R17 is 220k instead of 100k
4. R20 is 47k instead of 150k
5. R22 is 220k instead of 1M
6. Several discrepancies in power section. Most notably, Tube heater powered via 12V regulator. See attached schematics for more details
7. STA540 pin 6 connected to C32 47u cap. This is missing in the original.

Of special note is the tone control circuit which is 100% correct including the dubious short across R24. I suspect this was added by the original designer as a means of detecting if the design was copied since it makes no sense. Of course, it could always be an oversight by Orange

. I would just leave out R24.
I have modified the original schematic and attached it below.

mojorootietootie · Post by **mojorootietootie** » 08 Jun 2021, 20:04

Oops. Forgot to update speaker out jack JK3.

orcl2 · Post by **orcl2** » 13 Jun 2021, 02:53

thx Man, i'll test It skin.

J0K3RX · Post by **J0K3RX** » 14 Jun 2021, 13:10

@mojorootietootie

Take a look at R24/R25. It appears R24 is shorted as member deltafred pointed out in the Orange Terror Stamp post.

mojorootietootie · Post by **mojorootietootie** » 15 Jun 2021, 00:36

See my original post wrt short across R24.

Cactusjack · Post by **Cactusjack** » 03 Jul 2021, 15:47

Hi guys. Got one for a couple of days, so I checked the schematic (it is fine) and redraw the PCB from the original.

mojorootietootie · Post by **mojorootietootie** » 03 Jul 2021, 18:17

Excellent job Cactusjack. It is almost identical to the original and to one I am working on.
Some suggestions I have:
1. Relocate C100 to the front of the PCB. If you move D1 behind DC jack JK5, there is space between JK5 and spkr out, JK3 to place C100. It looks to me that C100 was added by Orange as a mod after PCB's were designed. This would clean things up a little.
2. Note that C35 is only rated for 16V. This is too tight for the power supply voltage of 15V. I would suggest upgrading to 25V which has a slightly larger footprint so some slight adjustment would be required.

I believe C35 and STA540 are the only components limiting the input voltage to 15VDC. The 4558 should be good for 18V so an interesting experiment could be to replace the sta540 class AB with something like an Aliexpress tpa3118 class D power amp module. That would get this puppy up to the 25-30 watt range with significantly less heat in the box.

Again, great work!

Juarocks · Post by **Juarocks** » 11 Nov 2021, 15:25

Not completely unrelated to this topic:

Has anyone got some uDARK gut shots?
I'm currently tracing a Stamp, that seems to be the same circuit, but it uses all unmarked smd caps.

thx