Building a bass amp?

[J M Fahey]

@ joecool: nice build !!

@Roly:

and they have no volume pots !!!

refers to *drummers* !!! 
And they have the volume switch stuck on 11 anyway !!!   :lmao:

That's why I said : "they define the volume level onstage".

Part of mine being considered "good" amps comes from the fact that I do not make small amps.
50/60W minimum.
So many times a brand-oriented guy buys a "famous" amp, such a 30 to 60W Hartke/Laney/Peavey/Marshall/whatever , shows up with it at the rehearsal room, and one of my 100 watters (which by the way costs less than his imported stuff)  blows them off the water.

I also avoid combos and go for "real" cabinets as you see.
As you mentioned before, Acoustic Laws can't be beaten.

[joecool85]

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

Yeah, funny.  No fan and running it full tilt in a 75F room for an hour brought the heatsink up to about 90F on the end with the chip and 85F or so on the other end.  I'd say it won't be an issue :-)

**edit**
I should note that at normal volumes I was unable to get the heatsink to raise more than 5F above room temp no matter how long I played it.

[joecool85]

@ joecool: nice build !!

Thanks.  It used a 330va transformer as well.  WAY more than necessary, but I had planned on adding a second channel (never did though) and wanted to make sure at full tilt it would have enough.  I'd rather build it once and do it such that I can upgrade later.  Who knows, my brother has it now and I may get it back some day and choose to through another channel or 3 in there.

[Roly]

Oh, drummers, yeah, I forgot about them (easy to do).

Still, I rather like the idea of a guitar amp with minimalist controls...




Yeah Joe, looks like you could turn that into a bridge with little trouble.:tu:   Where did you score the chassis metalwork?

[joecool85]

Oh, drummers, yeah, I forgot about them (easy to do).

Still, I rather like the idea of a guitar amp with minimalist controls...




Yeah Joe, looks like you could turn that into a bridge with little trouble.:tu:   Where did you score the chassis metalwork?

Old (dead) CB base station radio. 

Also, I have a guitar amp I made that has no controls but gain (on or off).  It is an LM386 based deal and it clips onto my belt, I built it into a pocket radio that I gutted for that purpose.  It turns on when you plug in.  There is also a green LED where the antenna use to be that lights when the circuit is powered.  Runs on 3 x AA and it's had the same batteries in it for years now.  I don't play it much now, but for a while I used it frequently.

[STDog]

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.

As a brass player (tuba and trombone) I'm well acquainted with that effect.

Firstly it's used for what we call a "false partial", that allows playing notes that don't exist on the horn. Handy in a pinch, but they never sound quite right.

Also I've seen similar effects where you play one note of a triad, sing the another (not the easiest thing to do), and the horn natural harmonics cause the ear to fill in the missing note and hear the full triad. (only works when all 3 notes play with the same "fingering")

Really freaky the first time you hear it.

About the only time you actually hear real fundamental bass these days is at big arena rock shows

Live performances of unamplified music. Nothing like the bass (i don't mean guitar either), tuba, tympani on a proper stage in a hall with good acoustics.

Or stand in front of 20+ sousaphones playing a grove at fff.

{I sometimes wish I had taken up the flute}

You and me both.

[mexicanyella]

While I'm not unhappy with the Siamese W-bin I'm now keen to try one of the Fane J-horns which I think may give just as good results with less building effort (and weight).

http://OzValveAmps.org/cabinets.htm#fane
Get 01-11, and 34-41 bass horns.

attach: Fane-rear-J-15

Roly, I looked through the Fane speaker book--cool stuff--from your links and in looking at the cross-section of that rear-horn-loaded "J-bin" 15" enclosure...it looks like the speaker cone radiates directly through the round hole at the top, while the rear of the cone is radiated out through the folded "J-horn." Am I seeing this correctly?

If so, is the idea that by "delaying" the sound coming off the back of the cone by the length of the horn, the sound reaches the mouth of the horn in time to be "in phase" with the direct-radiated sound coming off the front of the cone? So the extra efficiency comes partly from the horn-loading effect you described, but also from harnessing the sound off the rear of the cone more effectively?

STDog, I think I've experienced something like that "false partial" effect when trying to play lap steel in a tuning that didn't lend itself to minor chords without fancy hand moves that were out of my reach at the time. You could play part of the minor triad without abusing your inexperienced hand, and even if the other instruments were'nt covering the note you left out, sometimes it would still seem to be there. So it wasn't just wishful thinking, huh?

[STDog]

STDog, I think I've experienced something like that "false partial" effect when trying to play lap steel in a tuning that didn't lend itself to minor chords without fancy hand moves that were out of my reach at the time. You could play part of the minor triad without abusing your inexperienced hand, and even if the other instruments were'nt covering the note you left out, sometimes it would still seem to be there. So it wasn't just wishful thinking, huh?

The false partial is a bit different. It's cheating the natural harmonic series on the horn and using the overtones to mimic the note.

Say you have a Bb horn. open partials are Bb, Bb, F, Bb, D, F, etc..
That octave jump between the bottom 2 is the issue. With 3 valves (or a 7position slide) you can play down to the E between them, but no lower. You need 4 valves to get all of that octave. But, you can fake an Eb between them that has zero fundamental and is all overtones. And, many can fake all the way down to the B.

On a stringed instrument, you can play two strings and sympathetic vibrations will sound the third if you have the chord fretted properly. That's similar to the effect I mentioned, in that the missing note has to fit in the tube as played. Say you play Bb, sing F, and the D magically sound in the head. That because if the interactions of the overtones of the 2 real notes, the horn characteristics, and the human ear.

Not sure about other effects on strings. Whatever you are playing would need to emphasize enough of the right harmonics to trick the ear.

[Roly]

Interesting @STDog, didn't know that.  I actually used to roadie a double bass player, but sousaphones are pretty thin on the ground in Australia, the occasional Trad Jazz band, never mind in massed swarms (or whatever the collective is for sousaphones).  Do people still go to orchestral performances any more?  I was sorta thinking of massed German basses when I wrote that, but I thought that most readers wouldn't know what I was talking about.  In my misspent youth I used to go around playing pipe organs and 32 foot Diapasons spoil you for real bass.

@mexicanyella - yes, that's right, the upper frequencies are radiated from the front of the speaker cone, and the rear is loaded by the J-horn.

No; what happens is that the radiation crosses over. Down to the acoustic crossover all the radiation comes from the front of the speaker because the inertia of the mass of air in the horn makes it effectively a sealed box, but as the efficiency of the front radiation starts to drop off so the air mass behind (by arrangement) starts to respond and as the frequency comes down the whole cab acts like a horn, with little radiation from the front of the speaker cone.

It is effectively a combination of both a mid frequency direct radiator and a low frequency horn. {The Siamese 'tho does have some internal vents and makes use of the radiation from them to augment its bass output, but then it's rather more complicated inside.}

Because the replaced fundamental is all in the mind you could actually call it wishful thinking.    I was talking to a techno mate about this topic who pointed out that MP3 encoding makes heavy use of this subjective effect.

This stuff goes some way to explaining why chord inversions, 'tho nominally the same, actually sound a bit different.

[STDog]

Interesting @STDog, didn't know that.

A lot of horn players don't understand it either. They just know those false partials sound bad.

Do people still go to orchestral performances any more?  I was sorta thinking of massed German basses when I wrote that, but I thought that most readers wouldn't know what I was talking about.  In my misspent youth I used to go around playing pipe organs and 32 foot Diapasons spoil you for real bass.

Some do. Not nearly enough.
Speaking of the land down under, I'd really like to go to the Sidney Opera House and hear that organ.

In the States you can always find a good college marching band on Saturday during football season. That's the best place to find lots of sousaphones.
Catch them practicing, inside, for the best effect

And drum corps is still pretty good, though the switch to Bb horns has hurt the bass. The old horns in G have/had a lot more punch.

Because the replaced fundamental is all in the mind you could actually call it wishful thinking.    I was talking to a techno mate about this topic who pointed out that MP3 encoding makes heavy use of this subjective effect.

And OGG Vorbis relies on it even more than MP3.

Gotta love how easily the human mind can be tricked.

Motion pictures rely on that effect (multiple stills looking like motion).
Even our displays (monitor, TV, etc) as you have 3 distinct color points (RGB) that the mind blends into a color.

[J M Fahey]

Do people still go to orchestral performances any more?

Thanks God many still do, specially in Europe.
In Austria , Germany and Czechoslovakia (or what they became now) open air Classical Music concerts rival Rock Festivals in popularity and attendance.
In Buenos Aires , at least once a year, I dress up and go to listen some real music at our Teatro Colón, our Opera House.
It's *incredible* the transparence, brilliance, depth, separation, dynamic range you can hear there.
Back home, I want to smash all Hi Fi equipment with a hammer.
Not even the *best
* Hi Fi equipment even approaches that.
I have friends with as-expensive-as-their-home equipment: still no dice.
Which isn't surprising, their listening rooms are a shoebox compared to the real thing.
So far I have only listened to 2 very believable reproductions (meaning I close my eyes and  "they are there"):
1) string quartets and
2) small Jazz ensembles, meaning, say, a singer accompanied  by a piano, double bass, small drum set, maybe a horn or two.
Or, what's about the same, some Classical or Flamenco guitar players.

*Recording* is very important too, best I've heard is music captured in one take, no processing, just 2 mikes (often in an "X-Y" setup), direct to disc or digital recording.

[mexicanyella]

I took some audio recording classes in school, and before we were turned loose in the multitrack studio, we had to do some field recordings of acts we'd find for ourselves, using the school's two-track field kits (TASCAM portable DAT, small Mackie mixer--better mic preamps than the DAT had--a stand with a clever stereo X-Y mount on it and a pair of Shure SM81 small-diaphragm condenser mics). For the small-ensemble assignments we were supposed to use the mics in the crossed 90-degree XY formation to reduce the variables and ease the grading process. It was very exciting to hear how accurate and spatially defined a recording could be using that arrangement. In the assignment my partner and I turned in, we recorded a electric guitar/upright bass/drums jazz trio in a pretty noisy bar, and while the ice-grinding machine was pretty intrusive every time someone ordered a frozen drink and the upright bass wasn't picked up as loudly as I'd have liked, it was remarkable how you could hear EVERYTHING and it was positioned realistically in the stereo spread when you'd close your eyes and concentrate on it.

Before turning the equipment back in some friends and I messed around with comparing XY formation at 90 degrees, ORTF formation at 110 degrees or something like that and also the spaced pair approach, in a basement, recording a couple of acoustic guitars playing together. I recall the ORTF being even more pronounced stereo, maybe a little more lush, but it seemed a little "hyped" to me somehow. Spaced pair recording in a basement-sized space didn't sound bad but it wasn't as focused and crisp as the XY setup.

Later on we had to record a large classical ensemble in a pretty good-sized hall, using a spaced pair of omnidirectional mics and I think a more distant filler mic...I can't remember the details of that as well but I do recall that it took some experiments in spacing the mics and blending them different ways at the mixer to approach the huge actual acoustic sound we were hearing in the actual space. The final recording seemed to sound pretty good, but nowhere near the real thing! I think it was supposed to be a humbling experience...clearly a long afternoon of moving three mics around and running cables and taping things down to the floor was not enough to really do it right, and while we were borrowing some pretty expensive mics and gear, we were really on the low end, gear-wise, for that kind of thing.

[Roly]

My step-father got to a point where he decided it was better value for money to buy concert tickets than Hi-Fi gear.  As a kid I was allowed to have any LP I wanted - as long as it was classical.  So in my youth I was playing in rock bands and also a subscriber to Melbourne Symphony Orchestra and Australian Opera seasons, and catching chamber recitals of Bach, Vivaldi, &c.  Never been mad on modern composers, or classical dance as an art form, but a good symphony orchestra in a good venue (and Melbourne is lucky to have both) is really an experience.

I've also done a lot of live recording, but never with the kind of equipment I'd like to have, but I've found that if you are prepared to put in the effort to squeeze the best out of what you've got you can still make some pleasing recordings.

I have a group of favorite recordings that I listen to just for pleasure, and they are almost all live recordings of performances in front of an audience, and even though there are the "ice grinder" moments there is also an energy that you simply don't get with studio recordings; there is no chance of a second take here, get it right first time or die live on stage in front of thousands.  That risk seems to lift performers and performances.

So yeah, when I'm talking fundamental bass I'm thinking of a bunch of orchestral basses, or the biggest Diapason on a big pipe organ - that's the sort of chest-vibrating bottom end that a bass guitarists should have at their disposal.

[STDog]

So yeah, when I'm talking fundamental bass I'm thinking of a bunch of orchestral basses, or the biggest Diapason on a big pipe organ - that's the sort of chest-vibrating bottom end that a bass guitarists should have at their disposal.

I think that's what any bass player really wants. Bass should be felt as much (more?) as heard.
And on the very bottom end the human ear doesn't hear the fundamental very well either. While the nominal is 20Hz, that best case in a lab. The low A on a piano is 27.5Hz (just below a 16' C pipe), compared to the 41.2Hz E on a 4 string bass. Tuba parts regularly go down to 24.5Hz G, and at least one piece has 16.3Hz C (32' pipe).

Reproducing anything below 50Hz just takes a lot of air movement, and really needs to be felt.
That's just not easy, never mind trying to do it with small drivers and low power.

[J M Fahey]

Guys, thanks for sharing your personal experiences, that's what I was referring to, the "real" sound of Music.
Nowadays vey little people knows what I'm talking about.
Not usual finding guys with the same kind of experiences I've had, lots of Forums filled with people with *strong* (borrowed) opinions but little to back them with.
:dbtu: