Mesa 2:90 - using one channel

Shredzilla

Member
Messages
3,582
So until I pick up a second cab, I plan to use only one channel of the 2:90. Is it safe to use the 2:90 with no load connected to the second channel ? I assume it is, but want be sure before I try it and fry something.
 

fusionbear

exquirentibus veritatem
Platinum Supporting Member
Messages
11,341
No, it is not safe, use a shorting jack on the unused channel, or make your own.
 

logdrum

Member
Messages
2,121
The manual is confusing. It sounds like you can. But call mesa first


"LEVEL A/B

These two pots control the volume level of each side or channel of the 2:90. Since there's
only one Standby Switch on this unit they may also be useful as channel muting controls.
NOTE: If only one speaker is to be used on one channel and no speaker load on the other,
always turn the unused channel’s Level Control to zero
. To prevent oscillation (motorboating)
turn the Presence Control of that channel all the way up"
 

Guinness Lad

Member
Messages
15,853
If thi si sthe 4-6L6 rack power amp I had one, and yes it's perfectly fine to use one channel, you just need to be sure to turn the volume off. I ran a Quinn SDO preamp into this amp and had no issues.
 

fusionbear

exquirentibus veritatem
Platinum Supporting Member
Messages
11,341
If thi si sthe 4-6L6 rack power amp I had one, and yes it's perfectly fine to use one channel, you just need to be sure to turn the volume off. I ran a Quinn SDO preamp into this amp and had no issues.


You got lucky. Most manufacturers, including MESA recommend a shorting jack. Some tube power amps have a separate HT power switch, that works too...
 

Shredzilla

Member
Messages
3,582
The manual is confusing. It sounds like you can. But call mesa first


"LEVEL A/B

These two pots control the volume level of each side or channel of the 2:90. Since there's
only one Standby Switch on this unit they may also be useful as channel muting controls.
NOTE: If only one speaker is to be used on one channel and no speaker load on the other,
always turn the unused channel’s Level Control to zero
. To prevent oscillation (motorboating)
turn the Presence Control of that channel all the way up"


Yep a bit confusing. I know generally the rule is you must always have a load, but the manual leads one to believe it's not required.
 

logdrum

Member
Messages
2,121
That is why I prefer the Peavey classic 50/50. 2 power switches and can be bridged mono. It also has 8 E-84 and much linear in operation. I use it as a power amp for my turntable, The 50 watt per channel rating may be too optimistic though
 

Tone_Terrific

Silver Supporting Member
Messages
36,558
No signal, so no power passed through the OT, so no load needed.
However I would be tempted to plug in a resistor, short the input to avoid any signal, or remove the power tubes just in case.
 

Guinness Lad

Member
Messages
15,853
You got lucky. Most manufacturers, including MESA recommend a shorting jack. Some tube power amps have a separate HT power switch, that works too...

Maybe so but I did what Mesa said in their manual. I bought the amp from a friend who plays for a living and he's owned this thing two or three times, this is how he always used it.
I just sold it because it was so heavy, otherwise I never had any issues. I do dislike having to remember things like this in order to not have a failure. For example imagine a buddy coming up and cranking the wrong side, that would suck.
 

GasMask

Member
Messages
3,419
The (discontinued) Mesa 50/50 power amp manual specifically says it's OK to use only one channel. Just turn the other volume to zero. I've owned one for decades, and done this many times. Not sure if the design of the 2:90 would make this unwise though. Maybe just contact Mesa- they are pretty cool to deal with.
 




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