Micro terror cutting out at high volume/gain

[rwfelton]

This is undoubtedly the situation.

As already pointed out in graphs earlier in the thread, although that was just one speaker type, it is common and indeed likely that the dc resistance of any and all 8 Ohm speakers to be less than 8 Ohm.. I would hazard a guess that somewhere between 6 and 7 Ohm is typical.
So, get any two "8 Ohm speakers" put them in parallel and your minimum impedance is likely to be between 3 and 4 Ohm

The maximum power demand on any amplifier is when it is supporting a transient, so just like the poster said it cut out when he hit the strings.. that's when all the power is used. Though your average power consumption may be more like 0.5-1W, that 20W is all being used in the milliseconds when you bang that power chord.

I suspect avoiding 4 ohm load is the way to go.. put a 16 and 8 ohm in parallel would work.

An extract from the Micro Terror instruction manual which can be downloaded from the Orange website may shed some light on this:

1. SPEAKER OUTPUT
Connect to a speaker cabinet with an absolute minimum impedance of 4 Ohms. 8 or 16 Ohm cabinets will work fine at reduced output power. In some conditions, the MT20 may cut out when heavily overdriven and exceeding the rated 20 watts output when using a 4 Ohm cabinet. This is due to a protection circuit built into the output stage.

do you mean to put a 16 or an 8 in parallel? not a mix matched set right?

[Randy Bass]

This is undoubtedly the situation.

As already pointed out in graphs earlier in the thread, although that was just one speaker type, it is common and indeed likely that the dc resistance of any and all 8 Ohm speakers to be less than 8 Ohm.. I would hazard a guess that somewhere between 6 and 7 Ohm is typical.
So, get any two "8 Ohm speakers" put them in parallel and your minimum impedance is likely to be between 3 and 4 Ohm

The maximum power demand on any amplifier is when it is supporting a transient, so just like the poster said it cut out when he hit the strings.. that's when all the power is used. Though your average power consumption may be more like 0.5-1W, that 20W is all being used in the milliseconds when you bang that power chord.

I suspect avoiding 4 ohm load is the way to go.. put a 16 and 8 ohm in parallel would work.

An extract from the Micro Terror instruction manual which can be downloaded from the Orange website may shed some light on this:

1. SPEAKER OUTPUT
Connect to a speaker cabinet with an absolute minimum impedance of 4 Ohms. 8 or 16 Ohm cabinets will work fine at reduced output power. In some conditions, the MT20 may cut out when heavily overdriven and exceeding the rated 20 watts output when using a 4 Ohm cabinet. This is due to a protection circuit built into the output stage.

do you mean to put a 16 or an 8 in parallel? not a mix matched set right?

I don't think he was responding to your post since you weren't using a 4-ohm cab. He was basically saying that a 5.33-ohm nominal load (16-ohm cab and 8-ohm cab together in parallel) is as low as you'd want to go with the stock power supply. Your issue seems to be different from the 4-ohm circuit protection issues others have mentioned in this thread.

[rwfelton]

i figured he wasn't talking about my situation. i did some more research and found that my problem was a microphonic preamp tube. got it replaced and all is well. i had just read his post and interpreted it saying to "put a 16ohm and 8ohm in parallel." which can confuse others and then they may mess their amp up. i am running the MT through a laney cub cab 212 8ohm cab and it sounds amazing compared to the other cabs that i used. but i did replace my preamp tube with an EHX russian made tube and it sounds amazing. seems like the cleans and and the high gains are sounding much better. thanks for all the advice and help.

[Randy Bass]

I'm glad it was a simple fix.

[Mystic38]

Indeed I was addressing the OP's issue, and following up from the post in the thread which pointed out that speakers present a load lower than their rated impedance, hence giving potential problems to an amp like the uT that is spec'd at its limit of 4 (real) ohms.

As a technicality, FYI putting a 16R and 8R in parallel in no way will mess any amp up. Of course there are other factors such as power dissipation (1/3 & 2/3 respectively) but the amp is blissfully unaware that there are two cabs. The amp simply sees the combined load, which in the case of the uT would be a safe load and allow the uT to optimize its power output.

i figured he wasn't talking about my situation. i did some more research and found that my problem was a microphonic preamp tube. got it replaced and all is well. i had just read his post and interpreted it saying to "put a 16ohm and 8ohm in parallel." which can confuse others and then they may mess their amp up. i am running the MT through a laney cub cab 212 8ohm cab and it sounds amazing compared to the other cabs that i used. but i did replace my preamp tube with an EHX russian made tube and it sounds amazing. seems like the cleans and and the high gains are sounding much better. thanks for all the advice and help.

[alexislabastida]

Hi there
it's really really easy to solve your problem I have two micro terrors and at first thought like you but there is no problem in the head it self.

It is because in the first configuration your cab was in series but
Now if you change it it's called parallel and then it's when it cuts off
You see more simple
Series = 2speakers 8ohms--> turn in to 16ohms that means 8ohms per speaker
Parallel = 2speakers 8ohms --> turn in to 16ohms but you're giving 16ohms per speaker

That is why you hear it better but (more tight) but you over load the speakers in parallel and it can only take 50% of the power or just passing 12 o'clock on the volume and gain

I hope this helps anyone that may be having the same problem

[bclaire]

Hi there
it's really really easy to solve your problem I have two micro terrors and at first thought like you but there is no problem in the head it self.

It is because in the first configuration your cab was in series but
Now if you change it it's called parallel and then it's when it cuts off
You see more simple
Series = 2speakers 8ohms--> turn in to 16ohms that means 8ohms per speaker
Parallel = 2speakers 8ohms --> turn in to 16ohms but you're giving 16ohms per speaker

That is why you hear it better but (more tight) but you over load the speakers in parallel and it can only take 50% of the power or just passing 12 o'clock on the volume and gain

I hope this helps anyone that may be having the same problem

You are two years too late.

Why are you resurrecting old threads as your first post?

[Randy Bass]

Your post is also totally inaccurate and incoherent. Other than that, welcome to the Forum!