A cap question for designers & builder in the know

[Howlin' Mad Mac]

I'm a father of crazy teenagers & like many other teens they tend to suffer from brain damage & like to listen to (c)rap music, build "Fast & Furious" tuner cars & install insanely high decibel, ear drum shattering stereo systems you can coming from 4 blocks away. Now before I get "flamed" for going off topic here's my question. In these stereo systems they install these huge electrolytic caps... I think a typical value would be like 1 farad with a gazillion wvdc rating placed behind a bevy of power amps shunted to ground. With these babys in place you get enough bass to make a Lincoln jump around like it was one of those tiny little plastic football player figurines on the metal vibrating playing fields my childhood friends & I would play with after school (c'mon, I know some of you guys have to remember those.) Anyway I was wondering if anything like this (on a smaller scale of course... I'm not wanting to be heard in orbit, just a nice "thump" especially for a tube bass amp) has ever been incorporated into an instrument amps design & what formula you would use to calculate the value of the cap needed for the desired effect? So ok ye great & powerful wizards of amps... any thoughts here? Oh & before you ask, remember I stated I'm the father of teenagers & I grew up in the 70's, so yes not all of my synapses are still firing these days.

[loudthud]

For a while in the 70's The Who were known as the loudest band on Earth. They toured with trucks to generate enough power for their shows. It's not really practical to make tube amps that big.

As far as generating insanely big bass, it sounds just as stupid when adults do it.

[Phostenix]

So, you're wondering how much capacitance you need to put into a bass amp to get more punch? Is that generally the question? I would guess it would be enough to maintain the voltage rail(s) during high current transients. I have no idea how to calculate that, but I would think it would be easy enough to test with an analog voltmeter. The problem you'll run into when adding more & more caps to the power supply is that you will eventually have to add inrush limiting circuitry to keep the power transformer & rectifier(s) from being damaged by the huge current surge when you turn the amp on.

[kleptocracy]

...enough bass to make a Lincoln jump around like it was one of those tiny little plastic football player figurines on the metal vibrating playing fields my childhood friends & I would play with after school (c'mon, I know some of you guys have to remember those.)....

Oh, yeah. I had one of those. I loved that thing.

[Phostenix]

Oh, yeah. I had one of those. I loved that thing.

The thumper Lincoln or the electric football game?

[kleptocracy]

The football game. Sorry for the unclear quoting.

[Enzo]

Those have been around for ages, I remember playing that buzzing football game back in the mid 1950s. SOme players went downfield, some circled, and always a bunch of them backed into a corner and vibrated there.

Lancaster, PA? What, you got AMish with thumping stereo in their buggies? "Dig thee this, Jakob."

Car stereo can get the bass that vibrates a Lincoln, and it sounds like crap. But keeep in mind car sound runs on 12v, not 120v, and thus substituting current for voltage. SO the power connection from the battery and alternator to the amp matter a great deal. COnsider the voltage drop when 50 amps comes through as little as half an ohm. or even 1/10 ohm. SO a huge cap holds the supply power up.


"Stiffening caps" I see come in like 1farad or 2 farad, with a 16 or 20v rating. The car system never makes high voltage, so you don;t need HV caps.

In a tube amp, you are not going to see more than 300-400 watts very often, so we don;t need caps that would hold up 4000 watts in them. High power solid state amps DO have high capacitance power supplies, or multiple power supplies. But no more than is needed to do the job.


YOu want strong convincing bass? DOn't use a 100 watt amp when you need 100 watts of power. Get a 1500 watt amp to go with your preamp. it isn;t about seeing how loud you can get, it is about plucking a string on the bass and having the amplifier effortlesly put it in your speaker.

[Steve Conner]

Those big capacitors are stupid anyway. If you wanted to get properly loud, get a Prius and hook a couple of PA amps up to its 200 volt battery. A lot of newer PA gear has switchmode power supplies, so it should run fine off DC.

Someone recently posted a Youtube clip of an amp that had been riced up with a big capacitor bank: http://music-electronics-forum.com/t15627/

When it comes to tube amps, they really don't need it. The energy stored in a capacitor is proportional to the square of the voltage, so at 450V or 600 or whatever, the capacitors don't need to be that big to pack a punch. And the limitations of tube technology mean that tubes just can't suck down huge peak currents, like transistor amps will do.

Besides, tube bass amps don't really do thump. They don't come any bigger than about 300 watts, and the kinds of cabinets people use them with are tuned for high SPL in the midbass and lower midrange. There aren't many bass cabinets that will produce their rated SPL at 40Hz, which is low E on the bass guitar. If you wanted one that did, it would either be the size of a truck, or really inefficient, needing something like Enzo's 1500 watt amp to get a decent stage volume. But that is a valid choice that quite a few modern bassists will go for.

[Howlin' Mad Mac]

Hmmmm...

I've been getting a great kick out of reading some of the posts. Wondering what I may have started here.

Now in one of the posts someone called this a stiffening cap & that kind of makes sense. I'm really not sure of the voltage ratings on these things as I know they're used but I've not actually looked at them. I also was not clear as to what my intent to try something like this would be. In a bass rig such as the one I own I've a 200w Acoustic head driving a 410 w/ horn & a 115. Use of such a cap would be between the amps output & the 115 cab only. My understanding of this is the cap would ignore all but frequencies below a cutoff with (I'm guessing) a fairly steep slope with the caps discharge driving the 15 much harder than normal (though hopefully not so hard as to fry the VC or seperate the cone from the basket) which I'm guessing would be the tricky part. The rusult I'm looking for is a very deep "thump" that'll knock you on your a$$. But unlike my teenagers I'm after a loud but not uberloud very low punch... not so much my stack starts bouncing around the stage but more like something that could be switched off/on & used kinda like an fx pedal if that makes any sense.

[Chuck H]

By your description of the caps position it sounds like these caps are part of a frequency crossover system. Like the ones built into many old console type speakers. The caps may be used to pass frequencies above their knee and block lower frequencies. Inductors (those big coils of copper magnet wire) are used pass low frequencies and block higher ones. Either may also be used as shunts sometimes.

If you have a 1x15, a 4x10 and a horn on your bass rig a crossover system could improve the clarity and thump by making the whole system more effecient but it won't actually make any extra power. I'd be surprised if your horn, at least, doesn't already have a high pass cap in place to protect it from too much current.

There's all kinds of info available with a google search on how to make speaker crossovers. Different types, pro's and con's, online part value calculators, etc.

Chuck

[Phostenix]

Mac, which Acoustic 200W amp do you have? The older Acoustic amps already have a large capacitor between the amp output & the speaker(s) due to the design of the amp. I don't know what effect changing the value of that cap would be.

It sounds like you should try to find a cab like the old Acoustic cabs. Everything I'm reading claims that the 18" Cerwin Vega speaker in a folded horn cab was what really gave those amps the punch & projection that made them famous. I noticed that Musician's Friend carries a similar item now:

Buy Cerwin-Vega JE-36C Junior Earthquake 18" Subwoofer | Unpowered Subwoofers | Musician's Friend

You'll need to trade your Lincoln in to buy a pickup with a liftgate to move it around, though....

[Phostenix]

If you wanted to get properly loud, get a Prius and hook a couple of PA amps up to its 200 volt battery.

Oh great, I can't wait 'til the thumper crowd figures this out.

[guitician]

Those big Farad caps are for power storage in low voltage(12v) amps. They need them for those hideously low efficiency thumper speakers. Get a 15 rated at 104db SPL at 1 watt and put in a big horn loaded cab and thump away.

Remember the movie "Earthquake"?
http://www.cerwinvega.com/history.php

[cminor9]

Remember the movie "Earthquake"?
Cerwin-Vega - The LOUD Speaker Company

Too bad the movie wasn't called Brown Note.

[guitician]

Too bad the movie wasn't called Brown Note.

So, did you see it in the theaters in the 70's? I didn't, I just remember hearing all the hype. I was just pointing out how loud(106db/1w/1m) those folded horn enclosures are for low bass.

Oh, just wiki'd "Brown Note".....
http://en.wikipedia.org/wiki/Brown_note