Markbass F1 not playing well with Acme Low B2

troy mcclure · #1 02-24-2011, 08:39 AM

I bought an older Acme Low B2 from a tber to replace my Avatar 210. The cab sounded much better, but after playing about for 5 mins at a medium volume the Markbass shuts down. I turn it back on and it plays again for a little while and again it shuts down.
I read the manual and didn't see anything about any built in protection in the Markbass. The cab is 300 watts 4ohms and the
F1 is 500 watts at 4 ohms.

Am I missing something?

KJung · #2 02-24-2011, 09:36 AM

The Acme's are an unusual cab, and like the discontinued EA NL210's, there have been reports of shutdowns with those cabs and MB heads. With the NL, the issue was that the nominal impedance of the cabs was below 8ohms (even though they were spec'd as 8ohm cabs), so when you drove two of them with the MB heads, the total impedance was below 4ohms just enough to cause trouble.

With the Acme, I believe it is a combination of being a smidge under 4ohms, combined with the low sensitivity, which can push an amp to full power even at moderate volumes.

So, combination of 'unique' cab and the high sensitivity of the Markbass safety shutoff system when you run that head below 4ohms, even by just a little bit.

I think I have this correct, but there have been other reports of this with the Acme/MB combination. You might PM Peter Murray and see if there is a fix or something, or talk to Andy, who has probably dealt with this before.

Bassman12350 · #3 02-24-2011, 10:18 AM

I'd have to agree. If the F1 is working properly, then the protection circuit is shutting it down because the active load the F1's output sees is well below four ohms. Inefficient cabs will, as was previously mentioned, cause one to drive the amp harder to reach the same output levels as with a more efficient cab. This coupled with a low impedance, is certain to cause problems.

greenboy · #4 02-24-2011, 10:24 AM

One of the reasons I think micro-heads/modules in general are not quite mature yet. Pro power amps have no problems with Acmes. I'm not saying the previously mentioned points don't have merit. Because some so-called por power amps like the Stewart 1.2 are kind of whimps when full duty cycles are required too.

twinfallsbass · #5 02-24-2011, 11:06 AM

I had this problem with the LMII and Schroeder 410L I once had. The cab went back to Jorge twice for speaker replacements, Jorge tought there might be a bad speaker. I was never was able to get those two components to work together, kept shutting down my LMII. Ended up selling the Schroeder cab out of frustration

Fekwood · #6 02-24-2011, 11:22 AM

I have a LMII and a newer 4 ohm Acme Low B2 and just love that combo. However, I never had issues with the LMII shutting down, even when trying to keep up with a heavy hitting drummer. Very interesting to hear Ken mention other reports of MB users having the same issue as you are having. Maybe try to get in contact with Andy, owner of Acme, and see what he says.

KJung · #7 02-24-2011, 12:13 PM

Quote:

Originally Posted by greenboy

One of the reasons I think micro-heads/modules in general are not quite mature yet. Pro power amps have no problems with Acmes. I'm not saying the previously mentioned points don't have merit. Because some so-called por power amps like the Stewart 1.2 are kind of whimps when full duty cycles are required too.

I think for some reason the Markbass heads are particularly sensitive to 'under 4ohms' nominal impedance. It is very cabinet specific. With most cabs (virtually all cabs), you can pound the MB stuff all day at max volume in 100 degree weather in the sun, and no problem (been there, done that

). However, with a few cab designs, they don't seem to be the best choice, and for whatever reason, are very fussy with 'non standard' impedance.

troy mcclure · #8 02-24-2011, 02:00 PM

This is an older Acme. The amp powers right back up and plays fine with my avatar. So if I love the cab I need a new head, and I love the head I need a new cab. Silly me, I thought I was done amp shopping for a while....

BassmanPaul · #9 02-24-2011, 02:11 PM

My Acme B2s work just fine with my Carvin BX1500 with one 4Ω cabinet per output channel. I've had zero problems.

KJung · #10 02-24-2011, 02:14 PM

Quote:

Originally Posted by BassmanPaul

My Acme B2s work just fine with my Carvin BX1500 with one 4Ω cabinet per output channel. I've had zero problems.

This issue is specific to Markbass combined with a few particular cabs, including the Acme's. A head sensitive to under 4ohm impedance, combined with a cab that is low sensitivity and has a unique impedance curve (i.e., lower impedance way down low than many other cabs), and you can unfortunately have trouble. I actually lay the 'blame' on MB more than Acme... safety limiting/shut-off should not be set THAT sensitive IMO. The good news is, for 95% of the Acme and Markbass users, it is a zero issue. Only when the two meet does there seem to sometimes be trouble (probably depending mostly on EQ and volume in determining why it happens with some users and not others).

BassmanPaul · #11 02-24-2011, 02:33 PM

Hey Ken, although I've not played through a MarkBass amplifier, my reading of posts on this site leads me to the feeling that their amps can be quirky at times. I agree totally that the problem lies with MB. I've never had a single issue with any amplifier and my b2s.

mrpackerguy · #12 02-25-2011, 04:42 PM

I'll probably take some flack for this, but I've owned several B2s, B1s and B4s. IMHO, I wouldn't feed a B2 or B4 less than 600W to really get it to shine for you. The 500W and below micro heads just don't open up the Acme like I believe it was designed to. My B4s were regularly fed 900W or more and they sounded great. Those little devil B2s really open up the more you push them, and I think that's > 500W. Only exception I found, was the LMII which I thought sounded pretty good, but was not comparable to a good pre and a Crest CA6 or 9. The Shuttle max 9.0 sounded very nice through the B2 without issue and I always thought that was a really nice compact rig.

oddio · #13 02-26-2011, 05:26 AM

I certainly agree with Ken and BassmanPaul's comments. Like Paul I haven't tried my Acmes with Markbass either, but I have used a wide variety of amps without issue.

As far as the basics go, Ken mentions the EQ - are you running the F1 relatively flat? You shouldn't need to boost the low bass excessively with the Acme. THis might cause thermal shutdown.

Have you tried standard troubleshooting: like the 9v battery test to be certain that both drivers are working properly? Can you measure the impedance of the cabinet with a multimeter? I can state, based on experience, that an Acme with one damaged driver still sounds great.