Building a bass amp?

[Roly]

Well you can put a horn on anything, or anything in a horn, but horn or not there are a few physical realities that must be recognised and paid due homage.

Big speakers are used because they pump more air for a given cone throw.  They are also used because they normally will have lower mechanical self resonance frequencies, and once you come below the driver resonance the output starts to drop like a rock.

From my discussions with bass players it seems that groups of 10's are favored for two reasons, one is that some players like the more trebly "ga-dang", but it also seems that many bass players are willing to compromise on real fundamental "ommph" for the sake of portability.  I remember one discussion that ended on me asking if they were a bass player first, or a driver first, and if they were a bass player first then maybe they needed a bigger vehicle.

As a keyboard/synth player I have a foot in this camp because I want real bass from my left hand, and smaller speakers simply don't cut it.

There is a thing that all small speakers such as "bookshelf" and computer speakers depend on, and it's called the "replaced fundamental".

If you present the human ear with a group of third harmonics it is possible to fool the brain into thinking that it is hearing not harmonics but the fundamental note, even though there may be no fundamental there at all.

If you do a sinewave sweep (no harmonics) of typical computer speakers you won't hear anything until you get above 100Hz, perhaps well above, yet if you play music through them you will get an impression of the bass line.  This is an example of the "replaced fundamental", and to some degree this is what you are getting with 10-inch speakers.  But no matter what you do you are never going to get that feel-it-in-your-chest thump of a genuine fundamental.

If we compare two 10's with a single 18, the cone area for a single 10-inch is about 78 sq inch so two are about 157 sq inch.  A single 18 has a cone area of about 254 sq inch, so already a pair of 10's will have to throw nearly twice as far to move the same volume of air.

When we look at the driver free air resonance we find that a 10-inch has a typical resonant frequency of about 60Hz, while an 18-inch will be down around 30Hz, so the ten is starting to roll off even before we get to the open bottom E on a four string bass (41Hz).

If that were not enough, as soon as you put any speaker in a cab its resonant frequency is pushed right up.  You can minimise this effect by making the cab very large, but you then end up with a cab that is as big as a family fridge (or bigger) and the loading on the driver cones is reduced to the point where they are easy to turn inside out.

When it comes to bass the basic physics is not kind, and there is no such thing as a free lunch.

What horn loading does (for any speaker) is it creates an acoustic impedance transformer (or gearbox if you like) between the stiffness of the cone and the floppy compliance of the air at the horn mouth, and provided it is big enough for the desired low frequency cutoff it loads the cone and limits the throw for a given SPL output - it couples the speaker to the air better; and that is where the big increase in efficiency comes from.  (for a given cab volume a J should produce a "better", less compromised, horn than a W)

The other way to go is to put your drivers in a way undersized box and flog the living daylights out of them with huge power (e.g. most commercial bass rigs).  You end up with a rig that is fairly small and transportable, but terribly inefficient (i.e. most of those watts go into heating up your speaker voice coils instead of into the air).

This really only scratches the surface of what is a major and interesting problem in physics.  The key word (unless you have a very large truck) is "compromise", and no matter what the salesman tells you, the old saying is still true - "There ain't no substitute for cubic feet".

"Doof" boxes, so-called sub-woofers, are a whole other nasty topic all of their own.

{I sometimes wish I had taken up the flute}

[mexicanyella]

This is very interesting and is presented in a condensed-enough form for me to grasp; thank you for taking the time to write this. I have probably experienced a lot of the "replaced fundamental" phenomenon without knowing it! Maybe I need to get some time in playing my bass and listening through some larger speakers to get a feel for what some real fundamental feels/sounds like.

[Roly]

My pleasure, because it has long been a special interest to me as a key player and soundie/mixer.

We are all boiled frogs.  About the only time you actually hear real fundamental bass these days is at big arena rock shows with rows of W-bins the size of double beds along the front edge of the stage, and you can actually feel the kick drum in your chest - fooom!

My son is typical of the iPod and doof generation, and you should have seen his face the first time I played him some Toto through the Siamese.  "Never mind you don't like the naff music - listen to the bottom end".  Once you have the illusion explained, and actually experience real fundamental bass guitar bottom-E, sound systems never sound the same again. 

[mexicanyella]

Actually, it's been years since I've been a gigging musician, but after reading and re-reading your post it got me thinking about nights when my band lucked into playing some of the bigger clubs around here (like, when two or three bands in front of us on the list were sick or something, and we eventually got the call).

Hearing the familiar sound of our drummer's kick and low tom and the bassist's Peavey TNT combo suddenly booming through a row of subs and nice monitors, out into a mostly empty club, was pretty exciting.

I meant to say in my last post that your likening the horn to a gearbox was helpful to me; also, in another thread here I mentioned recently picking up a little Line 6 Lowdown 110 bass amp cheap and used. I think that would be a good example of "flogging the living daylights" out of a small (10") speaker in a too-small box (12" x 12" x 12" cube, plus subtract however much the chassis cuts into the internal volume...probably reduces the internal depth by at least 1-1/2" or 2").

To me that little amp sounds pretty good on at least two or three of the models, but I wonder how hyped the models are in the lows to partially overcome the acoustic limitations of the amp's physical configuration? It would be interesting to use the amp to drive a larger, more "neutral" enclosure and drivers and see what that sounded like.

[J M Fahey]

Well, *my* customers go the big box, high power route.
As in 4  Ampeg 8x10" boxes driven by 4 of my 300W heads or same cabinet setup with 2 of my tube rackpreamps driving an AB Systems 1500 into 2 cabinets, plus a QSC900 (later replaced by an AB1000) driving other 2.
Of course, they play Stadiums and have armies of Roadies, forklifts, the full Monty.
My heads are the white front ones, with the very visible HP bright red Leds.
http://youtu.be/LpGu0XscQ-o  <-- click to see the You Tube video.

These are the silver and light blue Tube Preamps driving the Rack Power Amps:

and

In case you wonder, the unconnected Rack mount Ampeg SVT400 you see in the middle, is the "backup amp".

[Roly]

Well, to be frank @mexicanyella, I consider any speaker for any use in a 1 foot cube to be a practical joke.  The 15 that is in the Siamese came out of a commercial vented enclosure, intended for bass, that I came to call its "carry crate" 'coz as a speaker cab it was a bust, and as a bass cab doubly so.

Let me quote some actual numbers to hand.  A Dai-1Chi "instrumental" 10-inch (94dB/W, 400Wmax) has a free-air resonance Fo of 63Hz.  From a different table, a 10 with an Fo of 52Hz has a resonance of 105Hz in a 1 cu ft enclosure.

That's roughly the open-G or top string, leaving the rest of the bass guitar down a mineshaft (and that's before you scale it up 20% or so).

This is about the same size as the Roland Cube series, and I know from painful experience that they start to roll off about Middle-C, or 250Hz odd - and these get sold as "keyboard" amps cor blimy!  Computer keyboard maybe, 'cause they are totally bloody useless as synth amps - shreeking lead guitar is the only thing they are good for (and door stops).


(_{Counts up on fingers...}) I make that 32 drivers and 1.2 (or 2.5) kilowatts for the backline bass alone.

I think I rest my case.   

{should we ignore the mike in front of the bass bins and the rather large bins behind which I assume are only part of the on-stage foldback - what do the FoH bins look like JM?    And we're not fooled by you using dwarfs to make the bins look bigger either.  :lmao: }

Of course all this depends on the playing style and desired effect.  If the bass player uses a popping and gar-dang style then the fundamental may be a lot less important.

But for those bass guitarists who;
- are not frustrated lead guitarists
- are not rich
- are not (yet) famous
- don't have a road crew that gets mistaken for a small invasion force
- don't play stages that are so high they need oxygen
- play venues where the majority of the audience are still in the same State, and
- want actual fundamental bass notes

...some compromise and cunning are required. 

[mexicanyella]

Good points all, and in general a great thread that has affected how I look at things.

Now, taking a brief break from bass amps, I think I've left my "tube amp snob" days far and long behind me, but check out that green Matchless head on that check-fronted Marshall cabinet. If a guy was going to play through a half-stack, I bet that'd be a pretty nice-sounding one to play through!

We used to split gigs with a band whose guitarist ran a Matchless Clubman head through a Fender Bandmaster cab, and and it really sounded great. Ahh, memories...

[J M Fahey]

Well, these guys play LOUD. http://en.wikipedia.org/wiki/La_Renga
The guitar player uses 6 100W tube heads into 4x12" Marshall cabinets.
Heads being a mix of Marshall, Matchless and Mesa Boogie.

So against 600 guitar tube watts , 2500 Bass watts are proportionate.
Which is not unreasonable when playing outdoors, in a 48000 seat Football (USA "Soccer") Stadium.
Which actually held 74000 people because the Football field was chock full, besides the actual seats.
The still empty River Plate (Buenos Aires) Stadium, the night before:

Same, slowly filling up, 4 hours to the actual concert.


Ah !!! , the "midgets" are my kids ... and the right size for their age.
As you see, I take them everywhere (if possible), to see what "Dad's work" is about.

[polo16mi]

Ah !!! , the "midgets" are my kids ... and the right size for their age.
As you see, I take them everywhere (if possible), to see what "Dad's work" is about.

I would love to be "uncle polo"    also to see what "dad´s work" is about.

[mexicanyella]

Yeah, going to work with Dad under those conditions would have to be pretty interesting!

Does the guy blend all those amps for a composite tone, or switch between them for certain things, or all of the above?

[J M Fahey]

This is a basic Rock'nRoll band, they just plug, turn everything up and go.
No keyboards, nothing.
A basic trio plus a sax player on some songs.
Problem is, they draw so much people that they can not play for less than, say, 5000 people (usually over 10000).
Now , to be able to pack more inside a stadium, they build a large circular rotating stage in the middle of the fiels, some 40 meters diameter.
In such a huge stage, amps get lost, because they are spread all around:
http://youtu.be/lV5Jlcn_v-I  <--- click for a video
http://youtu.be/lMxZoAdRWWU <--- similar in another Stadium.

EDIT: please do not think I sell these big amps every week, or that I recommend you to follow such path, let's get back to the original idea behind this thread.
My "bread and butter" amps , the ones which have paid for my house, car, Family, whatever during the past 43 years have been good and simple 100W, 2x12" Bass and Guitar amps.
Why 100W? : easy to get in SS; loud enough with power to spare to play along any normal drummer, who is the guy who really sets the sound volume reference onstage.
And they have no volume pots !!! ; they play as they play.
For me, roughly equivalent to, say, 50/60W amplifiers.
So in my experience, 60W is the minimum onstage; 100W can easily be turned down, of course; 50/60W is just on the drummer's level, some guitar players may get by with 40W (or 25/30W but *very* good speakers).
I see *lots* of kids lately trying to play onstage with 15W amps (Orange Tiny Terror/Vox Night Train/Marshall Haze 15/etc) but they have no dynamic range, always at the edge of overdrive, no reserve power left for *clean* sound, so ......
They usually have to play into a Marshall 4x12" cabinet to be heard, so, what you save on amp you spend (lots more) on the cabinet.
While guys with around 50W and a 12" speaker play hgappily.
We are talking guitar here.
For Bass, 100W is better, driving a good 15".
Yet I use 2x12"   Why?
I make my own speakers: when I started with this over 40 years ago, tried the classic 1 x 15" against 2 x 12" in similar cabinets: 2 x 12" won hands down so ......
These are my standard heads:

these the standard 2x12" cabinets
Front:

and back (showing the Bass tuning port)

The 2x12" cabinets are light and easy to carry in any car, either in the trunk or, worst case, in the back seat.

As I said, I live thanks to the *regular* Musicians, Pro or advanced enthusiasts; big Stadium packing bands are cool, but not that many, and can't sustain me.
Of course, they polish my name and help bring in the regular folks !!

Back to what you want to build: a 50/60W chip amp, a good speaker and any preamp you fancy will carry you a long distance.
Start by building a simple SS preamp like the one Rodd Elliott recommends for guitar, but pull the clipping diodes.
You will have a "Fendery" sound, not bad at all.
Build it, use it, play a lot , you will soon know what it can and what it can not do, your own practical experience.
Later, if you wish, you may build a hybrid: a tubed "Ampeg fliptop" (B15N) preamp, driving your chipamp and speaker.
You'll have quite a good chunk of "Motown sound", still you won't have power tube compression ... but not bad for a homemade project.
Good luck.

[mexicanyella]

JMF, I really like the clean, simple looks of your 2 x 12" cabinet. I'd love a chance to try one of your amps out someday. I don't think a trip to Argentina is in my budget right now, but never say never...

Thanks for the La Renga clips too. That big circular stage is pretty wild.

Re: power levels, amp features and bass...I am only just learning to play bass, on a P-bass copy, but what I've found is that I'm happiest with a clean, uncompressed and fairly bright tone, which I can darken "to taste" with the bass guitar's tone knob. I set the amp loud and try to play fairly softly and evenly with my hands, fingerstyle that is, and "compress" myself by managing my "attack" on the instrument. I am a ways from mastering this, but when it works it's a lot of fun, and one thing about this approach that really appeals to me is that I don't seem to need any pedals or anything special from the amp. Just loud, clean and no special EQ features.

I realize that my own idea of what sounds good with bass might not apply to others, but I think it's a valid point that a simple, clean-toned and fairly neutral amp can sound decent with bass, good enough to have some fun with, if my experience is any indication.

[Roly]

As you see, I take them everywhere (if possible), to see what "Dad's work" is about.

I think that's brilliant JM; they will grow up with some great memories,  and understanding how shows are put together, all the background work required.  :dbtu:

After my son was born I often had to combine work with child minding, so I would take him on jobs such as office computer repairs and mixing gigs wherever possible, but I would also take him to visit nearby small factories and ask to show him around, so he got to see glass works, sheet metal, various textiles, and an iron foundry that was a favorite - and never got knocked back once.

and they have no volume pots !!!

But what is "volumen"?  Are we evolving to a guitar amp that just has a switch marked "off" and "11"?   :cheesy:  Nice looking gear.

a clean, uncompressed and fairly bright tone

I agree with JM, a fairly basic amp of 50/60 or 100 watts, and I would suggest the AES rear-loaded J-horn with a suitable 15 inch speaker will cover both a rich bottom end and still allow brights from the front, and be practically portable.

I would either build your amp as two units, preamp and main amp, or at least include Fx send and return.  Even if you don't intend to include Fx this is still the place you can experiment with external graphic or parametric EQ's and such.

Apart from cost I see two important advantages in building your own gear; satisfaction that "my" rig really is my creation; and when it needs repair (as they all do at some time), or you feel you want to modify it in some way, you are fully in charge, you know exactly what is inside the boxes and the compromises are all yours to own or to change.

Rod's amp designs are as good as you will find anywhere, but two important points, don't skimp on the power supply, or the heatsink - it is hard to have too much heatsink in a gigging amp (and you always seem to need more than you initially think).

[joecool85]

... it is hard to have too much heatsink in a gigging amp (and you always seem to need more than you initially think).

I managed to do it:



That is a single LM3886 on there btw.

[Roly]

Nope, looks about right to me (as long as it also has a fan somewhere out of sight)  :lmao: