OMG! Accugroove Accuswitch / Markbass combo question
Okay TB gearhead genius nerds... I have a couple of different but overlapping questions here.
Being the owner of a pair of Accugroove Whappo Jr. cabs, I sorta followed the Accuswitch (a magic switch to change impedance from 4 to 8 ohms) controversy wayyy back in the day. I dropped off Talkbass somewhere along the way, but left with the notion that the Accuswitch does not really perform as intended. With the configuration of my rig (powered by a Crest CA9) there were no pressing issues to worry about.
Fast forward to today. I'm using a Markbass CMD 121P for most gigs, and putting one of the Whappo Jr. cabs under it for bigger gigs. The Markbass is supposed to put out 500w when used with an 8 ohm extension cab, and with the Whappo Jr. it sounds every bit as wickedly good as I might hope - I haven't turned it all the way up, but I haven't heard any hint of distortion.
That said, my bandleader said he thought he heard distortion during a bass solo. I told him I was pretty sure he was hearing some crunchy fret buzz from me digging in here and there, but I wasn't about to dismiss his concerns entirely.
He looked at my gear and remarked that the Markbass might not be pushing enough power to drive the Accugroove. My ears tell me otherwise, but if there is transient distortion I can't hear or other issues I'm not savvy to, I certainly don't want to abuse the cab.
And now the icing on the cake... I'd always left the Accugroove set to 8 ohms and assumed the switch made no difference, but my bandleader flipped it while I was playing and I was surprised to learn that the rig sounded better (better mids and highs) with the cab set to 4 ohms. No noticeable difference in volume, just tone.
So, to try to wind up and distill this down... 1. Is my Markbass combo insufficient to power its internal speakers plus the AG cab? 2. Given the "voodoo" of the Accuswitch, am I risking harm to the Markbass amp by running the AG cab set to 4 ohms, since that would (in theory) reduce the total load to below 4 ohms. 3. What other issues and concerns might I be neglecting here.
Okay, thanks for reading... (whew) :o
Crunchy distortion doesn't mean you don't have enough power for the cab. If distortion is originating in the cab, it can only come from too much power.
That said, I have a LMII that I used regularly for a couple years. What I found was that when it was pushed hard enough I would get some distortion in the mids and upper mids if I was playing at decent volume and digging in a bit. It entirely is the amp that produces the distortion when you're pushing it to its limits.
Don't have much to offer other than I "think" (IIRC) WJR's were all pretty much 4ohms regardless of switch position. If that is true, you will eventually fry the MB head....just a matter of time. That head is not safe below 4 ohms. I can not comment on tone phenomenon you are describing. I just wanted to drop in to mention you are prob putting your head in dangers way. Again, I'm not 100% on the 'real' impedance of switch equipped WJR's....but if I were you, I would take heed to this warning and find out what the 'real' resistance of that cab is before you initiate an expensive mistake. If you have a volt/ohm meter at the house, it's as simple as taking a reading off the +\- terminals.
The subject of the Accuswitch and Andy Lewis' debunk with the "Acmeswitch" has been done to death. In your place I'd rip the circuitry out of the cabinet and be done with it. I don't feel that it's safe for you to use the cabinet as an extension to a 4Ω minimum combo. I think that you may well end up damaging the amplifier.
If the WJR is indeed 4ohms, I'd prob just invest in a stand-alone head to power it. In fact, due to time alignment and comb filtering, it will prob sound better as a stand-alone anyway. From what I can recall, the WJR's like power....prob what you need is a more powerful head to drive the jr. Or perhaps a quiter band. Either one would prob work.
Thanks guys! FWIW I don't believe there was any distortion - I played and listened at the same volume and could hear fret buzz cleanly reproduced - which (hopefully we agree) can sound like distortion.
And I'll assume you're correct about the 4 ohms, G4string, unless I learn otherwise. I played two sets with the switch at 8 ohms, the last set with the switch set to 4 ohms. At no point did the amp seem to run any hotter than it gets without the extension cab. Had the master volume no more than halfway up. I'm hoping that bodes well - I'm sure you guys will let me know if temperature is irrelevant here. :)
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