• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Mesa D800 - 2ohm stack with switch to 4/8ohm. Bad?

mcnach

mcnach

Jun 16, 2007
8,721
9,563
Edinburgh, Scotland
#1
I'm considering getting one of these little beasts.

I had one loaned to me a while ago and I really liked it, but at the time I was not looking for a new amp, being very happy with my LM3.

Now I'm considering getting a head that can do 2ohm to be used with my two 4ohm cabs, so the D800 is right at the top of my list.

One thing that concerns me is that it's very easy to forget to turn the switch to 2ohm, or easily switched by careless handling. If it's something that can cause trouble, I would like a more fool-proof mechanism as I've been known to sometimes be a fool ;)

I'm assuming that using a 2ohm stack with the switch at 4/8ohm will be a bad thing, but the amp's protection circuit will probably kick in and switch it off, no harm done. Similarly, with the switch at 2ohm, if I connect a 4ohm cab, the amp might not suffer but I'd just not get the most of the amp.
Am I right?
 
#2
mcnach said:
I'm considering getting one of these little beasts.

I had one loaned to me a while ago and I really liked it, but at the time I was not looking for a new amp, being very happy with my LM3.

Now I'm considering getting a head that can do 2ohm to be used with my two 4ohm cabs, so the D800 is right at the top of my list.

One thing that concerns me is that it's very easy to forget to turn the switch to 2ohm, or easily switched by careless handling. If it's something that can cause trouble, I would like a more fool-proof mechanism as I've been known to sometimes be a fool ;)

I'm assuming that using a 2ohm stack with the switch at 4/8ohm will be a bad thing, but the amp's protection circuit will probably kick in and switch it off, no harm done. Similarly, with the switch at 2ohm, if I connect a 4ohm cab, the amp might not suffer but I'd just not get the most of the amp.
Am I right?
Click to expand...

I've done stupid things with (and even without) amps. I'd think that the head would protect itself in the case of running a 2 Ohm load with the switch in the 4/8 Ohm position -- whether this would happen right away or only if the amp became stressed enough, I don't know -- and of course you wouldn't want to run it that way habitually -- but I can't say for certain if or to what degree that would put your amp at risk. Pinging @agedhorse on this.

The other way (4/8 Ohm load with the switch in the 2 Ohm position) should be safe, though the max power will be less and it might change the feel of the amp a bit. I have tried this with my GBE 1200 (equipped with a similar switch).
 
#5
The 2 ohm mode is necessary for driving a 2 ohm or 2.67 ohm load. Unlike with a linear amp where the voltage and current are not directly related (because of the phase shift between voltage and current into a reactive load) a class D output stage isn't impacted in the same way. The 2 ohm mode monitors the peak current and limits it to a safe value in the event that it approaches dangerous levels. This approach does not work with linear amps because of the phase shift that offsets the current with respect to voltage.

Operating the Subway with a 2 ohm load anddthe inpedance selector switch set to 4 ohms is likely to trip the protection circuit and shut the amp down as the current moves into dangerous territory.
 
  • Like
Reactions: tombowlus
#6
agedhorse said:
The 2 ohm mode is necessary for driving a 2 ohm or 2.67 ohm load. Unlike with a linear amp where the voltage and current are not directly related (because of the phase shift between voltage and current into a reactive load) a class D output stage isn't impacted in the same way. The 2 ohm mode monitors the peak current and limits it to a safe value in the event that it approaches dangerous levels. This approach does not work with linear amps because of the phase shift that offsets the current with respect to voltage.

Operating the Subway with a 2 ohm load anddthe inpedance selector switch set to 4 ohms is likely to trip the protection circuit and shut the amp down as the current moves into dangerous territory.
Click to expand...
Andy, is there much of a chance of actually damaging the amp if one does this, or does the protection circuitry make it unlikely?
 
#7
MarkA said:
Andy, is there much of a chance of actually damaging the amp if one does this, or does the protection circuitry make it unlikely?
Click to expand...
The protection circuitry makes it very unlikely, but not impossible. Just like seat belts and crush zones on cars, they dramatically improve safety but nothing is 100% effective IME.
 
  • Like
Reactions: revroy and Munjibunga
#9
mcnach said:
switched by careless handling.
Click to expand...
Tape.

agedhorse said:
The protection circuitry makes it very unlikely, but not impossible. Just like seat belts and crush zones on cars, they dramatically improve safety but nothing is 100% effective IME.
Click to expand...

Just like cars, best to let the product engineers do the testing of safety features IMO :D

If you are switching between impedance modes, masking tape the power cord socket as a reminder to verify the switch. Otherwise tape the switch in 2 Ohm. Maybe use 2 Ohm all the time if that's safe with a 4 Ohm load.
 
#13
S-Bigbottom said:
With this great power comes great responsibility. Just make checking the Ohms switch part of your pre-power on check routine.
Click to expand...

Indeed, I have to come up with some obvious way to ensure that I check (or that anybody else checks/doesn't interfere etc... rare, but if it can happen, one day it will)...
I just feel happier if I know that there's a built-in mechanism that will likely protect the amp in case of "fool-proof failure" ;)
 
  • Like
Reactions: S-Bigbottom
#14
agedhorse said:
The 2 ohm mode is necessary for driving a 2 ohm or 2.67 ohm load. Unlike with a linear amp where the voltage and current are not directly related (because of the phase shift between voltage and current into a reactive load) a class D output stage isn't impacted in the same way. The 2 ohm mode monitors the peak current and limits it to a safe value in the event that it approaches dangerous levels. This approach does not work with linear amps because of the phase shift that offsets the current with respect to voltage.

Operating the Subway with a 2 ohm load anddthe inpedance selector switch set to 4 ohms is likely to trip the protection circuit and shut the amp down as the current moves into dangerous territory.
Click to expand...

Thank you! It's what I expected but it's great to hear it first-hand from the person who should know. :)

Great amp, by the way. I had the opportunity to test the MarkBass LM3 and a Streamliner 900 I owned next to the Mesa D800 through the same cabs in the same location... and they all sounded good, they all had their 'thing', but the Mesa was a notch above the others. :thumbsup:
 
  • Like
Reactions: agedhorse
#15
Well... I've been thinking about this, and I was offered an old Fender 800Pro head at a very attractive price...

In the end I have decided not to but the Mesa D800.

No.

I just ordered a Mesa D800+ ;):hyper:

I really like having an adjustable HPF built into the amp (one more external box I no longer need, probably) and semiparametric low mids in particular... so for a little extra why not?
I have only used the D800, and I have not even seen a D800+ in person, for some reason I thought it was bulkier than it is but it's still pretty compact. So... done! It should be with me next week sometime. Then the weekend of the 23rd/24th I have a busy one that include a variety of gigs: outdoors, indoors big and small... can't wait to use this beast with a couple of Barefaced Two10 (4ohm each).

Thanks everybody, and especially agedhorse... very impressed with having a reply by him so quickly as well. Awesomeness. :thumbsup:
 
  • Like
Reactions: dazmond and agedhorse
#16
I have a little label above the switch (8/4 2). As I'm setting the amp up, speaker cords, etc., I check for correct position of the switch.
Also, being somewhat anal about such things, I can easily confirm the switch is in the correct position during performance.
 
#17
Alivefor5 said:
I have a little label above the switch (8/4 2). As I'm setting the amp up, speaker cords, etc., I check for correct position of the switch.
Also, being somewhat anal about such things, I can easily confirm the switch is in the correct position during performance.
Click to expand...

That's what I'll probably end up doing. I was more concerned about the possibility of someone else flipping the switch when I'm not aware... sound person maybe replacing the DI cable on the back and accidentally hitting it, or something along those lines. It's happened with the pre/post switch of my LM3, but that's a simple push/push switch placed right by the DI output, so maybe not so much an issue as the impedance switch is far from the DI socket and switches...
 
#18
... and it arrived! :hyper:

Just a quick test at home, and I'm loving the variable HPF. Very glad I went for this over the smaller D800. The bright switch is also a welcome addition.

Can't wait to get this thing out and make some serious noise.

Here it is... only connected to a single cab. The other is still in the car (I often use just one, as a stage monitor is all I need most times). This combination sounds very good.

20170612_141901.jpg
 
  • Like
Reactions: jongor and S-Bigbottom

Latest posts

Top Bottom
Back