Mesa Boogie Walkabout Mega-thread Part 10

[ImTheOnlyOne]

I don’t want to see players modify their amp only to discover that the modification missed it by “that much”.

I've not touched the fan in my stock WD-800, and I'd volunteer to send it in for an experimental manufacturer's quiet fan mod while it's still in warranty...

 

[agedhorse]

...good advice and I really liked the Get Smart reference, which interestingly enough is also good advice as well as a classic TV show...

One of my favorite shows of all time, my dad's too. YOU have experienced the dome of silence though

This is an interesting point. Back in the day there were many of us on TB who replaced the factory fans with quieter, but lower air flow spec'd options. That was mostly prior to MESA's chassis modification which added a LOT of extra venting to the top of the amp. To my knowledge MESA kept the same fan even after the additional venting was added.

Would the added venting change the operational static pressure the fans see? If so, would the final generation Walkabouts with added venting be better suited to make use of these quieter fans that are rated at 0" static pressure?

We have seen amps with such fan modifications in for service, and it usually involves the output section. Since a few years back, these repairs have gotten really expensive and there's no reason to taunt that bear. Good rule of thumb, if it's not broken, don't break it!

I've not touched the fan in my stock WD-800, and I'd volunteer to send it in for an experimental manufacturer's quiet fan mod while it's still in warranty...

View attachment 5127643

There's a ton more thermal engineering in the Subway amps, because they are designed to be able to provide solid 2 ohm operation without excuses, the thermal modeling is very thorough and the fan class that was used is extremely reliable with precision ball bearings. There is a trade-off though, ball bearings is a couple dB noisier yet has an incredible lifespan. Since we offer a 5 year warranty on our amps, there's not room for guessing or half-assing the design and the reliability record speaks for itself.

 

[amper]

I found the old thread about fan replacements, and after reviewing it, I think I'm fine with the stock fan, since there don't seem to be any better alternatives.

 

[MarkA]

I read back over a few pages, starting here, but couldn't find a conclusive answer.

I understand that the preferred replacement driver in a 4 Ohm WA Scout combo (barring finding an appropriate Mesa original) is the 8 Ohm Eminence Deltalite II 2512. If one makes the swap, are any changes to the crossover or horn necessary?

I understand that the 4 Ohm driver is thought to offer no real advantage (less sensitive/efficient, more easily over-driven) and that an 8 Ohm driver is preferable if running the combo with an extension cabinet (so as not to run the head under 4 Ohms), but, if one is going to run the combo solo, does the 8 Ohm driver offer a significant (or even noticeable) performance advantage? Does the voicing or character of the amp change much?

While I'm at it, is the preferred woofer replacement for a 4 Ohm Scout 15 a Deltalite II 2515?

I don't have a Walkabout right now (and have never played the Scout combo). I'm just... curious.

Thanks, all, and take care.

 

[amper]

I can't speak to the specs of the original 4 ohm driver, but I can say that Andy did unequivocally state that the WA head is perfectly capable of damaging the original driver, and I will say that even before I read that, I always got a bit nervous when trying to eke too much volume out of my 4 ohm Scout 12.

The head puts out 165 W (I think?) into 8 ohms, or 300 W into 4 ohms, so if the 8 ohm Deltalite is 3 dB more sensitive and less prone to overexcursion, I would feel pretty comfortable with that.

I no longer play at volumes that would stress the Scout 12, in any case. And since that is the case, I will continue to use the original 4 ohm driver.

 

[agedhorse]

No changes to the crossover are required.

The 8 ohm DeltaLite II 2515 is the best replacement for the 4 ohm Scout 15 as well. We still have the factory 8 ohm Scout 15" in stock. IIRC, there were few 4 ohm Scouts sold.

There isn't much of a change when updating to the 8 ohm driver.

 

[amper]

IIRC, there were few 4 ohm Scouts sold

I was under the impression that the 4 ohm was the standard config, but it has been over 20 years since it was introduced. Maybe mine isn't even 4 ohms? I haven't looked at the back of it in a long time.

 

[agedhorse]

I was under the impression that the 4 ohm was the standard config, but it has been over 20 years since it was introduced. Maybe mine isn't even 4 ohms? I haven't looked at the back of it in a long time.

The 15" version wasn't as popular and I don't know how many of 4 and 8 ohm versions were made.

 

[mikeswals]

This is an interesting point. Back in the day there were many of us on TB who replaced the factory fans with quieter, but lower air flow spec'd options. That was mostly prior to MESA's chassis modification which added a LOT of extra venting to the top of the amp. To my knowledge MESA kept the same fan even after the additional venting was added.

Would the added venting change the operational static pressure the fans see? If so, would the final generation Walkabouts with added venting be better suited to make use of these quieter fans that are rated at 0" static pressure?

Among the 7 Walkabouts I owned, I had one of the last models with the super vented lid and the fan noise was way louder.

Another blackface one I had afterward had a solid lid, I had sent it in for repairs & update around 2017, and they didnt have any of the vented lids left.

 

[Christophe C]

I am still very happy with my Walkabout Scout 12 combo (4 ohm version). I have the opportunity to buy a second hand 12" additional walkabout cab (8 ohm) (these are rare as hens teeth on the old continent )
Question : will it be ok for the head to run the two cabs (the external 8 ohm and the combo 4 ohm) ? I think yes (2.7 ohm) but what about sound ? Should I also upgrade the combo internal speaker to a DeltaLite 2512 in 8 ohms ?
Thank you

 

[MarkA]

I am still very happy with my Walkabout Scout 12 combo (4 ohm version). I have the opportunity to buy a second hand 12" additional walkabout cab (8 ohm) (these are rare as hens teeth on the old continent )
Question : will it be ok for the head to run the two cabs (the external 8 ohm and the combo 4 ohm) ? I think yes (2.7 ohm) but what about sound ? Should I also upgrade the combo internal speaker to a DeltaLite 2512 in 8 ohms ?
Thank you

Mesa used to wink at sub-4 Ohm operation of the Walkabout, but the official stance for some time now has been to keep it to 4 Ohms, minimum. Beyond that, I think that, for speaker longevity and performance both, it would work better to have two 8 Ohm woofers than an 8 and a 4.

 

[Christophe C]

Mesa used to wink at sub-4 Ohm operation of the Walkabout, but the official stance for some time now has been to keep it to 4 Ohms, minimum. Beyond that, I think that, for speaker longevity and performance both, it would work better to have two 8 Ohm woofers than an 8 and a 4.

thank you. No cheap route then not too expensive but not as cheap as I thought

 

[StayLow]

I am still very happy with my Walkabout Scout 12 combo (4 ohm version). I have the opportunity to buy a second hand 12" additional walkabout cab (8 ohm) (these are rare as hens teeth on the old continent )
Question : will it be ok for the head to run the two cabs (the external 8 ohm and the combo 4 ohm) ? I think yes (2.7 ohm) but what about sound ? Should I also upgrade the combo internal speaker to a DeltaLite 2512 in 8 ohms ?
Thank you

Mesa used to promote & encourage it. IME it’s fine. Depends on how hard the amp’s working - overall volume, ambient temperate and air flow. Same for any amp, really.

That said, go for it! *AND* get the 8-Ohm speaker in there. Alternately get one of these or similar: Palmer CAB M | Signal Splitter & Switcher | Palmer

 

[agedhorse]

It's not recommended to drive the WA below 4 ohms. You will probably get away with it, but there were enough issues that it was later changed to 4 ohms minimum total load.

Note that if the WA needs to be repaired, the cost is pretty high. The MOSFETs are becoming hard to get is the Vgs threshold ranges that we typically used and if we are out of that band than all MOSFETs need to be replaced with whatever bands the manufacturer/distributor has in stock.

 

[donhank]

Question : will it be ok for the head to run the two cabs (the external 8 ohm and the combo 4 ohm) ? I think yes (2.7 ohm) but what about sound ? Should I also upgrade the combo internal speaker to a DeltaLite 2512 in 8 ohms ?

Mesa used to wink at sub-4 Ohm operation of the Walkabout, but the official stance for some time now has been to keep it to 4 Ohms, minimum. Beyond that, I think that, for speaker longevity and performance both, it would work better to have two 8 Ohm woofers than an 8 and a 4.

Here is the actual statement from the final revision of the Walkabout owner's manual:

"The optimum speaker load for your WalkAbout is 4 Ohms. You may use a cabinet (s) of a higher rating safely (8 Ohm) with
no degradation in tone, however the amplifier will not produce its full rated wattage. Minimum load rating is 2 Ohms and while the WalkAbout will handle this lower load condition - and in fact produce more than its rated power, it is not recommended. Prolonged use of a 2 Ohm load will cause the power mosfets to run hot causing the protection circuit to trigger and mute the output signal until such time as the mosfets can return to a safe operating temperature. Avoid using 2 Ohm loads whenever possible."

CAN you run at 2.7 ohms? Well, yes. SHOULD you? Not factory recommended. And if you don't mind a little anecdotal evidence: both my 1x12 Scout and extension cab are loaded with Eminence Deltalite 2512-8 drivers. This rig sounds great and has never let me down.

 

[agedhorse]

The MOSFETs were not consistent enough across production lots to be confident that what we were receiving was actually met all of the specs all of the time. Some lots had higher than acceptable failure rates, and ultimately this was the primary reason these amps were discontinued.

You can always try, but the repair costs are very high for amps with these parts and at some point if we can't get the Vgs bands that we need to repair them, we may find that we simply can't. There is only one source, they are a repackager of die, and they have already discontinued the TO-3 versions of these parts (that I used in a previous life). Also, the market is flooded with fakes and counterfeits that are not only different parts but different semiconductor process parts and do not work correctly even though they are labeled the same (they do test completely differently).

 

[Christophe C]

Thank you. As I want to keep my walkabout as long as possible, then I will play it safe and follow the experienced advises.
I am going to upgrade the scout with the Delta Lite 2512 8 ohm and buy the extension cab.

 

[agedhorse]

Thank you. As I want to keep my walkabout as long as possible, then I will play it safe and follow the experienced advises.
I am going to upgrade the scout with the Delta Lite 2512 8 ohm and buy the extension cab.

Good choice, I think you will find this an improvement too.

 

[ImTheOnlyOne]

A Scout Cab question about tweeter hiss.

My understanding is that you generally only get out of a cab what you put into it. My Scout cab, with any lone amp I've tried, emits truly excessive hiss from its tweeter, tweeter setting engaged at or beyond the 9 o'clock position. No hiss with the control fully CCW.

Could there be an issue in the cross over circuitry causing this?

 

[agedhorse]

A Scout Cab question about tweeter hiss.

My understanding is that you generally only get out of a cab what you put into it. My Scout cab, with any lone amp I've tried, emits truly excessive hiss from its tweeter, tweeter setting engaged at or beyond the 9 o'clock position. No hiss with the control fully CCW.

Could there be an issue in the cross over circuitry causing this?

Probably not, though it’s possible that tweeter L-pad is damaged.

Proper troubleshooting will identify the cause.