The high and low boost switch on the amp. I was told is to boost the frequency at low volumes so you don’t have to annoy the neighbors by increasing the volume to get descent bass production. Everything I have in reality is my practice Riggs. I just ordered the Fuchs tube amp and notice it does not have a low boost. So to use my brain I would conclude. That I am just going to have to boost these frequencies with the usual tone shaping controls. I’m worried I will have new gear remorse and not like it cause I can’t use this amp for my particular needs. I just sent back the Phil jones raved about solid state amp. The class D ampegs I have sound way better. But they also got that hi/low boost. So after to much explaining. What does the low boost actually do. And is it absolutely necessary when playing low volumes to have good bass. Thanks
Every preamp is a different electronic circuit, and “low boost” is just some kind of generic label that indicates that it will somehow boosts the low, but every preamp will do it differently. Speaking about Ampeg (and that’s what I play), the “Ultra low” switch boosts the lows a lot but also cuts a lot of higher frequencies, it’s a totally different voicing. Generally, such switches can be considered as different voicing options but again it depends greatly on the circuit itself.
Don’t overthink this. Just set your playing volume and set your tone using the available controls, EQ and maybe switches. It’s not a big deal if there is a “low boost” switch or not.
Now that you mentioned that about ampegs. That’s seems right. I’ll have to mess around a bit to find what I like to hear. I seem to get stuff that seems to be a bright idea at the time. Like buying those semi aluminum paper cones cause I seen geezer butler standing in front of a wall of them.
Anyway thanks.
Wouldn’t that diminish the “Ampeg sound?” To me, the Ampeg sound is all about the mids at the cost of low end. Or is that mostly about the SVT vs B15?
The Ultra Low boosts the low end by about 15dB we saw, it’s nuts. And then puts in a big low mids notch, and follows up with a high shelf-like effect. it’s basically an asymmetric bandstop filter centered in the low mids biased towards the low end.
For comparison, the boost range on most EQ are +6 to +12dB at full deflection. 15dB is a lot, about 2.5x in perceived volume (though at those frequencies you won’t notice it nearly that much).
Actually the B15 is more midrange-focused than the SVT. But even with the “Ultra low”, those Ampeg’s sound like Ampeg’s, somewhat. They could call that the “motown switch”, almost 
But yeah it changes the sound a lot. It’s barely useable for me (I don’t use it really). The “Ultra high” is what we call a treble-cap, it’s even less useable for me as it totally changes depending on the gain (“Volume”) setting.
yeah @howard is right, this filter is really extreme.
yeah that’s the motown muddy tone. extremely fat.
Yeah, with the B-15 especially, I feel like the “B-15 sound” is more of a range of sounds rather than just one “hey, that’s obviously a B-15” type of thing. It’s an amazingly versatile amp.
For the rocket bass combos they’re selling now can’t you get a big low mids bump by turning on ultra lo, turning down the bass knob, and turning up the mid knob? Pretty sure it’s something like that to take advantage of the filter behavior.
(I just use graphic EQ on pedals)
Not sure how it’s voiced there, I was just talking about the SVT.
The Rocket amps also have an SVT mode.