Morgan MP200 cab questions

[bassman_mike]

I've been reading through the amps FAQ throughout most of today. I've learned a few things, but I find myself in a slightly unique situation with a custom amp and I could use some advice. I know there are at least a few other MP200 owners here, so if any of you guys have any advice, it'd be much appreciated.

I have a Morgan MP200 tube amp with the following important features:
- 200watts
- One 8ohm output, two 4ohm, and two 2ohm
- Custom Mercury Magnetics output transformer designed to provide a low end that extends past the audible frequency range (meaning probably as low as 15-20hz). In Joe Morgan's words, "The sub-audible stuff is more of a carrier type signal. Super long wave. Its crazy but you will understand when you can hear the bass anywhere in the room." And I do. It's awesome.

And I have an Ampeg 410HE:
- 500watts
- 8ohms
- Frequency range 48hz-18khz

This rig sounds phenomenal. I'm really happy with the tone and the way it cuts through in a mix live without getting in the way of anyone else's frequency spectrum, but when I play larger rooms I end up with 2 problems once the gain gets to about 10-11 O'clock (volume disengaged from the circuit):
1) Low notes start to make the speakers fart
2) Notes on the G string start clipping if I dig in or slap

It seems a little early for the amp to start clipping, and it seems like the speakers shouldn't be farting since the cab is 500watts and the amp is 200. So based on what I've read I have a few theories as to what's going on here (please confirm this for me or correct me if I'm wrong):

Theory 1 (Fart Theory): Since the cab is rated at 500watts and the amp is 200watts, the speakers are not farting due to being overpowered. They're farting due to the extra cone excursion from the super low frequencies provided by the custom transformer in the MP200. To my understanding, most 10inch drivers used in Ampeg cabs are only rated down to 45-55hz at best, but the fundamental of a low E on a bass rings at 41hz and a low B is 31hz. Since the output transformer on my MP200 is designed to provide that much low end and more, it's forcing my speakers to provide more low end then they're designed to provide, hence, the farting.

Theory 2 (Clipping Theory): The extra low end information from the output transformer drives the amp harder than a typical 200 watt tube amp, so that's why the amp seems to clip earlier than it should. It's also why the amp seems relatively quiet, because all that extra low end information is down near the sub-audible range, so you feel it more than you hear it. Additionally, since my Ampeg cab is 8ohms, I'm not getting as many watts from the MP200 as I would with a 4ohm cab, so that's why I end up needing to push the amp harder to get it to sound louder, right?

Let me know if I'm crazy or of these theories are correct.

Moving forward, if I'm understanding these issues correctly, I'll need a better cabinet capable of handling the low end of this beastly and wonderful amp! If you have any suggestions, let me know. I have a few good ideas in mind already, but I want to be sure that they will solve the issues at hand first.

 

[waltdogg]

Additionally, since my Ampeg cab is 8ohms, I'm not getting as many watts from the MP200 as I would with a 4ohm cab, so that's why I end up needing to push the amp harder to get it to sound louder, right?

Not true. Tube amps put out the same amount of power at any impedance.

Issue number one can be examined further by rolling your bass control back on the amp and hearing how the cab responds. Issue number two is either the horn in your cab is distorting from your string attack or it's the inherent aggressiveness I hear in Ampeg cabs you're also hearing.

As for your theories, the first is a direct relation to your first issue. Roll off your bass and hear your speakers sing with relief instead of fart with indigestion from too much bass. As for thoery two, well like I already said right off the bat you're not losing power at 8 ohms. Low end frequencies eat up power, if the amp produces extra low end you can assume that's where all your clean power is going.

 

[bassman_mike]

Not true. Tube amps put out the same amount of power at any impedance.

Thanks for the correction there. I was wondering about that.

Also I think it's very likely that you're absolutely right that it's the horn distorting, because that clipping occurs before any farting issues occur, and the clipping only occurs on the G string, which is probably the string that's pushing the horn at its hardest. I even A/B tested it with a few other cabs with horns (ampeg 410HLF and aguilar DB 410) and got the same result. Also I'll make note that the tweeter control on the back of each cabinet was rolled down to about 7 or 8 o'clock (and the amp gain is at about 10 o'clock with volume knob disengaged).

Regarding the farting, I've noticed it on a few cabs even with the ultra low disengaged and the bass rolled almost completely off. I'm wondering if it's just the nature of those sub-audible frequencies from the transformer exerting the speakers further than they're designed even with the bass knob rolled down.