Why All of the Aggressive Bandpass Filtration in New Amps?

[bob p]

I've had a few people come to me with complaints about their current production amps. A common denominator seems to be that they all bought a new amp, thinking that it sounded great, and after they've lived with it for a while they've all decided that the amp was mid-heavy and didn't have enough LF response, so they brought it to me.

Now I have to admit, I don't particularly like working on new-production amps, and I seriously don't like re-engineering someone else's work, especially when it involves changing the very nature of their device. In recent cases they've designed the amp to act as a bandpass filter and the customer is coming to me asking to design the amp to change it into something new. To me that's kind of like saying, "I bought a cat but now I want a dog."

It's not at all uncommon to see aggressive bandpass filtration occurring in these amps, including things like the appearance of parallel RC circuits in every gain stage to aggressively re-shape frequency response. What amazes me is that these designers put these types of filters one after another in every stage, so that they typically roll off anyting below 500 or 1000 Hz. I can see where this would be useful in a gain channel, where you need to get rid of LF content to avoid fartiness and flubbiness as SPL goes up, but in a clean channel that doesn't make as much sense.

The result is that a lot of the amps I see end up being bandpass filters where LF gets discarded and only the harmonics get amplified. OK, I can see BW limiting at the high end to get rid of supersonic HF content and prevent oscillations under heavy gain, but why all of the fundamental roll-off below 1000 Hz?

I think that this gives the impression of a snappy bright amp, and it probably sells well in the showroom, but to me that tends to be a hard amp to live with as the shrill midrange grates on my ears. I find that I have to dial back the mids and treble on those amps, and dime the bass, and I still can't get any worthwhile LF response because it's all been filtered away.

Anyone else noticing this? On the user boards they seem to refer to this as a "mid-forward" sound, and it's selling a lot of inexpensive amps.

[Enzo]

Overdrive channels - and reverbs - often roll off the bottom, because it often turns into mud when it comes through the amp.

[bob p]

well yeah, i mentioned that. but i'm talking about also doing the aggressive roll-off on clean channels without reverb and without overdrive.

there seems to be a big thing now where people are marketing midrange-enhanced / bass-deficient amps at the low end of the market. I think the reason this is happening is because the amps are voiced primarily to be impressive in the showroom and lead to a sale. Lots of people have the initial love-fest for them, claiming that they have a Voxy sound, but then the honeymoon doesn't last when you realize that everything sounds thin and you can't get full range with the bass control on 10...

I think some of the designers are designing amps this way for 2 reasons: first, to be impressive in the showroom. The mid-heavy amp sounds great at first, but then after a while you come to realize just what's missing. second: they can use a cheaper speaker that doesn't have to have decent bass response.

[darkfenriz]

I think that this gives the impression of a snappy bright amp, and it probably sells well in the showroom, ...

You may have just answered yourself here.
On a more serious note though I'd speculate all the 'djent-iness' factor is tried to be squeezed. In many cases it is critical to aggressively high-pass and roll-off every remaining bit of low-mids and bass before massively clipping, modern shredders/metallers, often using lower tunings or 7/8/9/10/19 strings love it.
The clean channel does not afford to have its own life with its own EQ shaping and is just a side-effect of dropping all the clipping.

[teemuk]

and it's selling a lot of inexpensive amps.

The inexpensive ones are often low power too. Not much headroom for cleans so cleans channel is voiced for overdriven tones as well.

[J M Fahey]

That.
A disturbing trend is that kids all over the place are lying to each other that "Tiny Terror" type amplifiers (include Vox Night Train, Meas Mini Rectifier, Marshall 15W, tons others) are enough to play live besides a drummer ... which they are not, plain and simple.

Trying to reach what they can´t, "clean channel" is effectively turned into s dirt one, just because it needs to be turned full up or else, so "mud cutting" techniques need to be applied to them too.

It was also mentioned above that the amp backbone *is* the distortion channel, and "clean" is simply the same with clipping turned off and less gain (usually bypassing 1 or 2 gain stages).

Proper solution would be either to add a dozen relays to switch a lot of things , what famously Mesa does, some of their amps have up to 25 relays inside, sheer madness, *or* build a full, separate , proper clean channel besides the dirt one.

Another problem is that probably some of those complaining may be "bedroom rockers": at low volume and "playing alone" amps can sound quite thin; exact same sound full blast and mixed in a padded rehearsal room (which mainly kills highs) or a much larger untreated room (natural reverberation boosts lows) sound becomes what´s expected.

You can´t equalize customer´s amps into what they want, it involves building new ones; they should use them loud, and into a large fat cabinet (4 x 12" , 2 x 12" or at least a large 1 x 12" with a *good* speaker)

And cutting Bass is nothing new.
"Voxy" clean sound you said? .... VOX AC30 500pF into 500k volume pot cuts every thing under 600Hz; famous Trainwreck , not exactly a "box of Matal" cuts under 500 Hz (.002uF into a 150k grid resistor) , none of them is regarded as thin buzzy but as sharp well defined sound.

[Leo_Gnardo]

they can use a cheaper speaker that doesn't have to have decent bass response.

Also they can use a small box to house that cheap small speaker & amp, and more amps fit into that trans-Pacific shipping container. Everybody wins . . . for profit, not tone. I get to see a lot of Blues Juniors here, #1 complaint is "why can't I get it to sound like a Marshall 50W & half-stack?" Because you're too lazy to lug around a 4x12 cab Johnny Guitar, and the club manager where you play listens with his eyes "you're not gonna crank that behemoth up in here!"

Juan, on relays. I happened to need some help from Mesa's chief engineer, Mike Bendinelli, on the eve of their release of the Mark V. He mentioned it would be sporting 47 relays. Yikes, that's insane... whatever it takes to make the boss's dream into reality.

[pdf64]

I don't think it's just modern designs that screw up the clean channel, resulting in 2 channels that sound like ass; Fender have a 4 decade history of it, starting I think with the 75 in the late 70s http://schems.com/schematicheaven.ne...r_75_schem.pdf (the top smaller schematic is accurate).
Every stage had a low pass filter, in order to keep the rats nest stable when in 'lead' mode, causing the clean mode to sound like mud unless the 500pF bright cap is switched in.
A friend brought me his 90s Super 60 to try and make it sound like a Fender; it took a crazy amount of work, both channels had to be stripped and re-designed
http://schems.com/schematicheaven.ne...er_60_rack.pdf

At least the dreaded pull boost of the 70s SF amps retained a proper classic Fender normal mode.

[Mike Sulzer]

Yes, bass takes a lot of power so get rid of it. In the show room you locate it in a spot that reinforces bass so it sounds OK.

[Randall]

I can't offer anything regarding why modern manufacturers do anything. But personally, I have a line I have drawn a long time ago. I do repairs, not engineering or design. If the amp is working like it was designed to, then I simply send them away, and I don't think twice. The reason for this is twofold. I'm not an engineer, and I have no interest really in modding anything unless you bring me the mod. But also, because it is so subjective. I could put 3 hrs into trying to please the customer, and he could very easily say, "It's not what I'm looking for". No thanks.

[Enzo]

Amen, Randall.

If someone brings me a published mod and says do it, I will, but when they ask me to "make it sound more like Green Day, " I send them on their way. Likewise, when they ask for "more gain", what they usually mean is they want the distortion to sound different. Not my thing.

[Justin Thomas]

they should use them loud, and into a large fat cabinet (4 x 12" , 2 x 12" or at least a large 1 x 12" with a *good* speaker)

*** or a 2x15"?

<WELL> WORTH REPEATING!
And so we end up back in the same place and the same old argument...
Sound Guy: can you turn the guitar amp off and plug your pedals into the board?
Me: [7th Plane Of Hell Icy Death Stare & "$&@# you] No.
Sound Guy: Why Not?
Me: Am I drowning anyone out? Do I sound like shit? Can you hear me clearly in the mix?
Sound Guy: No, No, Yes.
Me: then, what's the problem?
Sound Guy: I can't control you! [The REAL issue...]
Me: I can live with that.

My amp on 1 then pumped through a PA just ain't gonna give up the goods, either to me, or a listening audience. Sure, it sounds "good," sure, THEY can make it LOUD, but it certainly isn't evocative...

Justin