Wanting to build a bass amp from scratch

[Bruce / Mission Amps]

By the way.... the last 813 amp I built used four of them at around 2800 volts.... Big RF deck and lots of power... easily a 1000 watts output at 1.8MHz to 21MHz.
And the damn safety lock out switch on the deck cage failed... I blew the meaty tip of my finger off while touching the plate cap, with the plate supply fully loaded and the amp unplugged from the power supply.
That really put me in a bad mood.
That and my Parallel 2x4-1000a amp were the last big amps I've messed with and don't miss them and their 100lb power supplies at all!!

Some of us have talked about using a couple old Eimac 4x150a tubes at audio.
With 350 watt power supply and some forced air cooling, two of these should easily hit 250 to 300 watts dead clean at around 1200vdc to 1500vdc.
I wonder what one would sound like in Class A at around 50-70 watt output.??
I still have a bunch of them and their sockets but no motivation or drive to build one up.
Comments?

[Chuck H]

If I had the stuff on hand to build a 60watt Champ I think I'd have to do it on principal alone.

[Chuck H]

Oh, I suppose I should just cobble up some kind of a preamp for it, just to see what it would sound like.
Besides, I don't like to see it half finished just sitting there in my lab.

-g

So, get the preamp built... Then you need one of those giant speakers like the one in Back to the Future.

[Bruce / Mission Amps]

If I had the stuff on hand to build a 60watt Champ I think I'd have to do it on principal alone.

You send me your address and I'll send you a tube and socket... I probably have a couple dozen of them.
You'll be broke buying the output tranny though! ha ha

[Chuck H]

OOOh. You got me. I guess I'd need to have ALL the parts on hand. After the holidays I can't even afford to pay attention. Much less the iron for one of those tubes.

[J M Fahey]

Some of us have talked about using a couple old Eimac 4x150a tubes at audio.
With 350 watt power supply and some forced air cooling, two of these should easily hit 250 to 300 watts dead clean at around 1200vdc to 1500vdc.
I wonder what one would sound like in Class A at around 50-70 watt output.??
I still have a bunch of them and their sockets but no motivation or drive to build one up.
Comments?

COOL !!!!!!!!!!!!!!!!!!!!

I would build it on principle too .... and would mail news of it to the Guinness Records people.
Not kidding.

Would also mail Eric Clapton producers and suggest he uses this "World Record Champ" to play "Layla" live, on a Big stage, driving a 4x12" or something.
Not kidding either.
Publicity never hurts, even less so to a performing artist, and *he* would also get in the Guinness Book.(if heīs not already there for some other feat)

[mooreamps]

So, get the preamp built... Then you need one of those giant speakers like the one in Back to the Future.

Alright... I do have "all the iron"...As far as the "speakers"... I could do a 2x15, complimented with a pair of 10's...

-g

[J M Fahey]

@ Steve Conner.
No, I donīt have the U$200K (or more) hydraulic presses, yet I managed quite well:
It all went step by step.
In the very beginning I bought **excellent** Argentine made LEEA speakers, (they made Altec Lansing clones under licence, plus the JBL123), tore them apart and built my own on those frames.
It was "the easy solution" but crazy expensive !!!!
Then I disassembled one of them, used its frame as a mold, had "plates" made and cast the frames in sand.



Did the same with Altec Lansing horns.
This is one of my quite battered "half horn" models, for sandcasting.
Halves are later soldered using TIG or MIG machines (itīs aluminum)





Better and more reasonable, but still slow.
The frames still needed some surfaces turned in a lathe, because sandcasting is rough and inexact.
Then I made lathe turned frames, the technology used to make kitchen pans, which leaves characteristic concentric marks on the metal surface.
I only needed to make some hardwood molds plus a relatively cheap 3" round punch die set, to make the frame holes plus the center one for the voice coil.
Ugly as Hell, but since I sold complete cabinets, not speaker components, fine .



I envied those nice Jensen or Celestion stamped frames, but one day I was visiting a Car Parts factory and saw what, for me, were unfinished speaker frames.
They were stamped Car Wheel parts.
I asked for permission to search the "old and unused" dies deposit, and found one used to make trapezoidal holes, with a surrounding reinforcing rib, in car door inner panels.

Here you see what I managed to get, compared side by side to a Celestion Greenback.





To be delivered tomorrow:

[Chuck H]

That'll do.

Back on subject, and somewhat related. I can't say why 12's never caught on for bass. They sure seem popular for woofers in just about all other areas audio. Lot's of monitors and even small PA cabinets use them. Isn't a 12" woofer the standard in home and car audio? I suppose for a bass amp you would want a full range speaker. But a real beefy one leaning toward the low end. I'd be interested in what JM is doing.

I've played with a two bassists that used a Peavey 1820 cabinet. 2x10" Scorpion's and an 18" Black Widow. Sounded great as I recall. Other than giant PA cabs you don't see 18"s either.

[Chuck H]

Tha't just cool as hell. Do you just experiment until you find a formula that sounds good? Or do you test with high grade amps, spectrum analyzers, dB meters and such to get some on paper specs? How much does one speaker cost you, including labor? Really great. I'm awed.

[J M Fahey]

Thanks a lot.
A mixed bag of resources.
Speakers are " a mystery", nobody knows nothing, the ones who do fiercely hide their "secrets", most have strong and very peculiar ideas often not backed by reality, itīs a jungle or an unknown world out there.
A lot of respected (or at least famous) makers just keep on doing things a certain way, just because "they always did so".

I started by offering to repair everybodyīs speakers, no matter what.
Learnt *a lot* that way, although much of the knowledge was empyrical, "XXXX brand does things *this*way; brand YYYY something very different, both sell and work, not even themselves can justify why".
As in comparing a Strat and an LP.
Worlds apart, both killers.
Also studied a lot.
I formally studied Industrial Engineering, but asked for a "career change" *just* to take the "Electroacoustics" Course, which consisted entirely in spending the full year studying Leo Beranekīs "Acoustics".(1954).
Lots of info, way too much, but often impossible to apply in practice because no seller knew the parameters of what they sold.
Then I studied Olsenīs "Acoustics" (late 1940's) on my own.
Itīs everything there, but you have to read each chapter 100 times, and every time you find something new.
Similar to reading RCA's Radiotronīs Designers Handbook.
Also have a Genius friend, who never got to the University, but who studied on his own twice as much as me, who manufactures Hi Fi speakers equal to the best in the World, but whose only clientele are Jazz and Symphonic Musicians, (not Audiophools), who along the years has amassed an impressive Lab, think HP, Brüel & Kjaer,Neumann , etc. which he lets me use.

Cost? Unit "parts" cost is very low; think a "Twin speaker" around 15/20U$ ; a "Celestion" between $25/35 , but that is only part of the picture.
Time, energy, dies, machinery investment along the years has been *huge* and way surpasses mere parts cost.
I even had to buy and learn to operate a Lathe, have my own Magnetizers, a short in a speaker drying oven burnt 25% of my house, I usually "do everything" (PCBs, transformers, chassis, silkscreening) but when I set up my own Galvanizing Tanks, I noticed *every* single bath contained Sodium Cyanide , some Cadmium salts, etc.
Got rid of it after a week, losing a lot of money .... decision for which I'm happy now, specially after seeing lung X-Rays of the guys who work on that trade.
How can I put a price on all of this?.

Yet Iīm very happy for making my own speakers, they are 50% (or more) of the final sound.
Even more, I donīt rely on a supplier's whims or have to stand his ignorance.
Mind you, If my Country were USA Iīd use Eminence, period: cheap and good; if it were UK I'd use Celestion, and not give it a second thought, but under my reality .... well worth the effort.

[loudthud]

Building your own speakers, that's what I call building from scratch. Very impressive. Just one question... do you play an instrument?

One comment about the 2x12 thing. In the early 60's, the Blackface Fender Bassman had a 2x12 (non-ported) cabinet. It was miserable. The tone was ok, but no volume. The Ampeg B15 was just as loud and it was only half the power. A Dual Showman worked better for bass. This situation gave birth to the Sunn 60W 2x15.

[J M Fahey]

Thanks.
As my friends always joke: "Juan Manuel does not play ... not even the Play-Station".
So thatīs about it.
Most people in this profession are Musicians who got interested in the Enginering side of it; I guess I was an Engineer mind which happened to love Music a lot.
*In a way* (although it might be a post-facto rationalization), I guess not actually playing let a lot of unused Energy free to be re-applied to the technical side.
Or something like that.
Thanks again.

[dai h.]

JM,

wow, that is amazing!

FWIW, re: spk. sound, a guy who used to "play" "Dr.Decibel" (the "question answering guy" for Celestion) related that in the end (despite having all the anechoic chambers, laser interferometry devices or whatever) the ear was the best judge of a speaker's sound. (I'm sure that doesn't mean that the science and test/measuring equipment doesn't have its uses (to obtain exactness, repeatability, etc.), more to use that inner sense of (subjective) "correctness" informed by history, taste, context, and so on.)

[jmaf]

That is some impressive stuff right there, JM. Congrats and thanks for sharing that bit of behind the scenes work there

(Off Topic)
Edit: I wish there was a way to bookmark specific posts on this forum so that I can have a compilation later. Is there a way? I'd like to save this Fahey post, also a recent RG post on bias and some others which are definitely reference work.

It'd be nice to have a zeitgeist of this forum to go back to and share around on the WWW as in "click here and read all there is to know about X or Y".

Pardon if it's there and I just didn't see it, if it is please somebody tell me how to do it, thanks.