Orange Micro Terror Clipping when cranked?

[Zarraboy]

Hi, i have just got my Micro Terror. Lovely tone! Well, i am using it with my 1x12 cab with a single Scorpion 4 ohms speaker. When crank the gain up TOGETHER with the Volume knob (both above 12 oclock) the signal starts to clip! When i take the volume back bellow 12 o clock it seems to be ok. What could the problem be?

[jontheid]

It is the amp output stage clipping. With a tube amp this sounds nice. With a transistor output stage this doesn't sound nice. Micro Terrors go into output stage clipping more easily when used with 4 ohm loads.
Quite a few people have mentioned that they don't sound too good when driven hard into 4 ohm loads.

[a.hun]

Clipping distortion. Avoid as it sounds horrible and is really good at wrecking speakers.

While in theory you can usually set most valve amp controls anywhere without any harm coming to the amp the same isn't true of solid state amps. If you are getting output clipping simply lower the volume control. This doesn't have to indicate a fault, only that you are pushing the amp too hard for safety.


Andy.

[Zarraboy]

Clarifying: It is not clipping distortion. It is sound clipping. The best sound i dialed from it has the gain fully cranked and the Volume knob at 2 or 3 o clock. Fantastic overdriven sound. BUT the sound clips (output disappears and comes back at very short intervals)! As if there was some kind of bad wiring contact or something. When i bring the volume back to about 10 o clock, clipping disappears BUT so disappears the great tone i had before. I think i used the wrong word (clipping). The signal would just die out suddenly and come back randomly. Is this a sign of OVERLOAD on the amp? Doesn´t it handle a 4 ohm speaker as stated?

[jontheid]

You are not alone in having this problem, see this thread here:
http://forum.orangeamps.com/viewtopic.php?f=3&t=49503" onclick="window.open(this.href);return false;
It would be nice if Orange commented on this, the amp is spec'd to run into 4 ohms . . .

[jontheid]

Might be the power supply running out of juice, hard to say really.
Very interestingly in the video below Orange's Ade Emsley states you can upgrade the Micro Terror using a laptop power supply . . .
http://www.youtube.com/watch?v=6MmMLL6n2Qk" onclick="window.open(this.href);return false;

I think the original PSU is 15V, 2A. You can get cheap 15V 5A laptop power supplies.
This may help, or might not make any difference, and if it is the wrong polarity could damage things.

Cheers
Jon

[Zarraboy]

OMFG. Dozens of posts of people with EXACTLY the same problem. The amp simply cuts out when cranked up at 4ohms. I have just connected the unit to a friends 8ohm cab and there is no cutting out. ALSO, NO GOOD TONE at all. What is the problem with Orange?? I thought it was a traditional and reliable British company. Why do they lie about the Micro Terror working properly at 4 ohms???

[Randy Bass]

OMFG. Dozens of posts of people with EXACTLY the same problem. The amp simply cuts out when cranked up at 4ohms. I have just connected the unit to a friends 8ohm cab and there is no cutting out. ALSO, NO GOOD TONE at all. What is the problem with Orange?? I thought it was a traditional and reliable British company. Why do they lie about the Micro Terror working properly at 4 ohms???

It's a shame that Orange has released a product that appears to have a flaw, but you seem to be overreacting a bit. It's quite a leap to conclude that you have been lied to and that the reliability (and Nationality) of the entire company is somehow in question now. Once you are able to temper your indignance, I would recommend calling Orange to see what they can do to resolve the problem. They are usually very helpful and they should be given the opportunity to make it right before you write them off as a bunch of kitten murderers. They might end up offering to send you a new upgraded power supply, or at least a couple of dead kittens.

[Jondog]

OMFG. Dozens of posts of people with EXACTLY the same problem. The amp simply cuts out when cranked up at 4ohms. I have just connected the unit to a friends 8ohm cab and there is no cutting out. ALSO, NO GOOD TONE at all. What is the problem with Orange?? I thought it was a traditional and reliable British company. Why do they lie about the Micro Terror working properly at 4 ohms???

Yeah! How did they ever become so awesome!

[Zarraboy]

It's a shame that Orange has released a product that appears to have a flaw, but you seem to be overreacting a bit. It's quite a leap to conclude that you have been lied to and that the reliability (and Nationality) of the entire company is somehow in question now. Once you are able to temper your indignance, I would recommend calling Orange to see what they can do to resolve the problem. They are usually very helpful and they should be given the opportunity to make it right before you write them off as a bunch of kitten murderers. They might end up offering to send you a new upgraded power supply, or at least a couple of dead kittens.

Thank you for your recommendation. You probably live in some country with an Orange Kitten official representative. This is not my case, unfortunately. Left for me is to advise local people against the product.

[jontheid]

We don't actually know that upgrading the power supply would make any difference to this particular problem.
It may actually be caused by some internal protection circuitry kicking in and changing the power supply wouldn't actually make any difference.
The fact that Ade Emsley said that the upgraded power supply "would give more clean headroom" is food for thought though.

[Zarraboy]

We don't actually know that upgrading the power supply would make any difference to this particular problem.
It may actually be caused by some internal protection circuitry kicking in and changing the power supply wouldn't actually make any difference.
The fact that Ade Emsley said that the upgraded power supply "would give more clean headroom" is food for thought though.

Cant see how that could help either. It´s a pity. The amp sounds great when dialed up. Will wait for somebody to come up with a solution. Probably a deep mod.

[jontheid]

The reason an uprated PSU may help is that the original psu can only supply 2 Amps of current at 15V to the Micro Terror.
This seems a bit underrated for a 20W amp.
Let me try to explain why.
Power = voltage x current.
Thus the standard psu can supply 15 x 2 = 30 watts.
However not all of this power is going to go to the output stage of the amp, the tube preamp will take some current from the power supply.
150ma of the supply current is needed just to power the heater of the 12AX7. This only leaves 1850ma.
Class AB amps have a maximum theroetical efficiency around 75%, so for 20W output you need at least a 26.6W supply.

The standard Micro Terror PSU can supply no more than 1850ma to the output stage, at 15V. This gives 1.85x15=27.75W.

In reality it is going to be worse than this, as there will be plate current taken by the 12AX7, there will be circuitry to convert the 15V volt supply to HT for the 12AX7 plate which won't be 100% efficient, even the power LED will take some current.

I get the impression that the standard PSU would not be good at handling transients at high volume levels.

An uprated 15V psu that could supply more current and that had the same polarity as the original PSU could not harm the amp in my opinion

I wish I had a Micro Terror myself so I could try this.
Hope this helps
Jon

[jontheid]

Another much simpler way of looking at it.

Power = current squared x resistance
Let's apply this formula to the 4 ohm speaker itself.

We are using a 4 ohm load, so let resistance = 4 (I know speakers aren't purely resistive and their impedance changes with frequency, but let's keep it simple)
This gives us:
20 = current squared x 4

so current squared = 5
current = 2.236 A

So for 20 watts output into a 4 ohm load, there needs to be 2.236 Amps flowing through the speaker.

The standard Micro Terror PSU is only rated at 2 Amps . . . it can't supply the 2.236 Amps required to give 20 watts at 4 ohms.

Cheers
Jon

[Zarraboy]

Wow! Thank you Jon. Should not hurt to try! I will try to find a 5 amperes power supply with the correct tip polarity. Will be glad to post results here soon.