Walkabout limiter?

[willashe]

I like the overdrive/distortion the Walkabout has with very high gain and low low master (for bass and guitar). But I always experience/hear/fell what I think is a limiter of some sort.
Is there a limiter in a Walkabout and if so where is it? Before or after the preamp, before or after the power block?
If there is a limiter, I would like to be able to bypass it or turn it off.
My concerns would be harm to the amp. Mesa customer service won't comment on any questions about the limiter.
I will probably see if Mesa will send a schematic and then take it to an amp tech to see about a by pass.
What I am after is to be able to get the over drive the preamp has without the limiter kicking in. I tried overdriving the preamp and reducing the input to the power amp by using an effects processor set clean but with reduced volume to reduce the signal through effects the loop. This did reduce the volume. I tried this thinking the limiter was in front of the power amp section and not part of the preamp. Still hit the limiter. So the limiter may be somewhere in the preamp.
I am not sure if the limiter is there to protect or for effect or both.
Anyone have suggestions about by passing the limiter and possible harm to the amp?
Thanks

[KJung]

I believe every solid state amp has some sort of limiting to protect if from being driven to the point of damage (heat, bad distortion in your speakers, etc.). Some brands let you run it hot all the way to the 'trouble point' and then just shut down (like the GK amps). Others put a limiter that kicks in and compresses the signal when the amp starts to be pushed beyond its set distortion specs, etc. (like the Markbass and TecAmp heads). Others have a sort of tube emulation type limiting that allows distortion (and hence volume) to increase beyond the normal distortion spec of the amp in a musical way (like Genz and TC amps). Not sure which approach is used by Mesa.

However, more often than not, players confuse the input stage of the amp clipping/compressing and attributing that to running out of power. So, if you are putting a very hot input signal into the gain stage of the amp, use the active/padded input setting, and turn the gain down, then compensate with the master. If you are still hitting the power amp safety limiting, then you need a more powerful amp (i.e., bypassing the safety limiting on a low powered amp like the Walkabout will just result in bad sound.

IMO!

[RickenBoogie]

+1 I think you need more than the 300 generous watts the WA can give you. Maybe look into a Big Block 750, or Titan. You'll get alot more dirt with either of those, as well.

[willashe]

Thanks for your reply.
Actually the signal I am putting in is passive so not hot at all. And over all volume is not an issue.
I set the gain about 3 or 4 oclock and the master very low, sometimes for practice or recording purposes the master is barely on.
So I get plenty of overdrive which I like and can control the volume by the master. But I experience what I think is a limiter. Good tube guitar amps (Mesa) overdrive and do not produce this limiter effect. I was hoping to see if there is something in the design that is a limiter and is it to stop damage or to act as a limiter. Sometimes, but not often, I use a limiter or compressor. Just want the option to not have it.
I guess I need a schematic and to bring it to a tech.

[naturalkinds]

Originally Posted by willashe

Thanks for your reply.
Actually the signal I am putting in is passive so not hot at all.

The hotness of an input signal is often independent of whether it's passive or active. My passive P-bass is *considerably* hotter than my old active J-bass.

[KJung]

Originally Posted by willashe

Thanks for your reply.
Actually the signal I am putting in is passive so not hot at all. And over all volume is not an issue.
I set the gain about 3 or 4 oclock and the master very low, sometimes for practice or recording purposes the master is barely on.
So I get plenty of overdrive which I like and can control the volume by the master. But I experience what I think is a limiter. Good tube guitar amps (Mesa) overdrive and do not produce this limiter effect. I was hoping to see if there is something in the design that is a limiter and is it to stop damage or to act as a limiter. Sometimes, but not often, I use a limiter or compressor. Just want the option to not have it.
I guess I need a schematic and to bring it to a tech.

Yeah, then you are just hearing that input tube gain stage squash the low end a bit. That is just the nature of the beast, and many like that 'give and compression' you get when you push a tube gain stage with a bass guitar. There is no limiting in the gain stage, just the natural compression of that tube stage.

The Walkabout is really not voiced (IMO) for big overdrive.... it's meant to stay warm and relatively clean. If you want a Mesa head that is designed to really grind and grunt, than the BB750 is probably more of that.

However, most 'distortion units' (whether pushing an onboard tube pre or dialing it in with a pedal) will reduce low end and compress the signal a bit.

You are correct that with the very 'trebly' input signal of a guitar, you don't really hear/feel this much.

Edit: And, +1 to the above... there is no real relationship between active/passive and how hot the bass output is. There should be a law keeping amp manufacturers from listing the padded input (or input setting) as 'active' (although to be fair, some amp companies actually vary the input impedance also between these two settings, which does kind of impy 'active versus passive' basses).

[willashe]

I am primarily a bass player but in the trio I work with I double quite a bit on guitar and because we often fly and with freight/baggage what it is I have to use the same amp for guitar and bass. The walkabout actually sounds pretty good for guitar with the right settings, especially clean.
I do experience the "limiter effect" with bass or guitar with high preamp overdrive, regardless of eq, master volume, again plugged straight with passive selected. Also tried over drive with active selected with the same limiter effect.
Maybe Mesa designed the tube preamp to reach a point in the overdrive that produces what I hear as a limiter. Customer service won't comment.
Seems I read in the forum here a reference to limiter in the Walkabout. I will look to see if I can find it.
If anyone has a Walkabout schematic please forward.

[sunbeast]

I agree that you are probably just hearing the compression of the preamp- I've noticed it does almost sound like a limiter when the volume is set very low and gain very high, and I would get that same effect with my Mesa 400+ if I kept the preamp cranked and the Master just barely on. I've never experienced anything that sounded like a limiter to me at high volumes with my Walkabout though, until it is obviously at the end of the power amp's headroom (which sounds like unpleasant distortion, and I've never needed to push it that hard to get the volume I needed in the real world!). I imagine it being a weird relationship between the attenuation of the Master at really low settings and the extremely hot signal from the pre- it's probably just not really designed to play with Master volume set that low (I've noticed that there seems to be an added level of distortion when it is played with the Master just barely on, which also suggests that it is not the ideal way to run that amp).

I'm no tech, so this is just my theory!

[willashe]

Thanks for your input. I don't often go up to an extreme overdrive and when I do I reduce the signal to the power section by having an SE 70 effects processor in the effects loop with the volume set at 1/4. I will update if I find out more from an amp tech.

[willashe]

Did find out from Mesa today there is a limiter on later versions (not sure when later is) in the preamp circuit with a trim pot set by them. Their disclaimer is do not adjust. Would not make a schematic available.