Building a bass amp?

[oleskool]

Hello everyone. I am new to this fourm. I have a question that I haven't seen answered using the search function, although i'm certain it has been asked. I am probably not searching correctly. I want to build a bass amplifier and separate cabinet. I would like to go with 350- 500 watts. If this is dumb i'll just step back off this. The safe bet is SS, I don't want to try tubes, well , because I enjoy life, and i dont own a O'scope. First are their kits available for something like this, that you are aware of? I'm not too worried about the cabinet, l'll most likely go with one of the fearful designs if you are familiar with those.

[J M Fahey]

300/500W is doable, but not suggested as a first project.
Rather than *electronic* problems, the "mechanical" problems will arise finding a suitable big heavy chassis to hold it all, the big power transformer, big cooling fins plus probably adding some cooling fan, etc.
Notice the repeated use of the word "big" and not by chance.
Cost may easily add up.
I would start by building a nice Bass preamp, your choice, plus a 50/70W chipamp.
You can use it with a 15" speaker or a 2x10" cabinet.
You are not wasting your time, that amp will be kept for rehearsals and recording, plus being easily portable anywhere.
Later on you can either build a 300/500W kit, if available (remember the "mechanicals" I mentioned, just the PCB and a transformer which is what kits offer is far from a practical working amp) or plain get a cheap 300/500W rack amp and building a suitable cabinet 2x15" at least or 2 of 4x10" style.
Forget a single 8x10", impossible to carry.
Also forget a "500W" single 15" ; they promise but do not deliver.
You need a lot of cone surface to move air.
I forgot: you drive your rack amp frrom your 50/70W amp, which you still keep and use.
As I said, you do not waste it  :tu:

[oleskool]

Thank you for the quick reply. I really like the idea of building a bass pre, and a 50/70 chipamp.
Are threads here that cover these? I'm using a 90w combo at the moment. It just sounds like junk to me. I like the sound of the old Ampeg b-15. The Motown sound is good to me. I'm a bottom end guy.
Is a 50/70 chipamp kit out there? Please point me in the right direction. My electronic background is from a trade school called R.E.T.S., pretty good 2yr. trade school in it's day. I worked as a field service tech in the copy machine industry for a while. If you have ever worked repairing things in the field you know i was more likely to snatch a board, and install a reworked one in its place. Component level work in the field was a no-no for me. I can adapt though. Thanks again for the reply.

[Roly]

I think JM is being kind.  I'm an experienced builder and I would have a long hard think before attempting a build of this class.  Just re-creating an Acoustic 361 at the (genuine) 160 watt level took the best part of a year.

I'd also suggest that while brute force is popular with bass guitarists, my own experience strongly suggests that cunning beats brute force every time.  I have built some horn-loaded speakers for bass and found that they can more than deliver in a moderately sized, powered, and priced package.

I can vouch for the fact that this guy's designs are not hyped but realistic, and deliver what is claimed;

http://www.billfitzmaurice.com/

The Fane back-loaded J-horn design looks good too.

The basic point is not watts but dB_SPL, and when you discover that you can get more dB with 50 watts and a good horn, you are going to wonder about others flogging 8x10's with 500 watts for fewer dB Front of House.

[polo16mi]

Dont know about your spanish skills, but, here something that looks promises...
http://www.construyasuvideorockola.com/proy_prebass.php

What you think?

[oleskool]

Thanks for the reply Roly. I have seen Bill on other fourms. He has boatloads of knowledge. I did spend a lot of time looking at his designs. I want that Motown like sound. From what I have seen so far he likes the mid-range sound. It does cut through better though. I think Jm was telling me the samething you are saying in a very tactful manner. I love his idea but I haven't seen those as kits.

Polo thank you also. I'm a single language guy, and i don't always do so great with that one.
I'm in bed on a tablet pc so i had to save the page and i will try and use google translate shortly.
Thanks again and if you guys come across plans for jm's suggestions please post them.

[Roly]

I cut my teeth on Tamla-Motown the first time around (I'm still gigging this stuff in my 60's).

400 Watt Columbian bass rig.  Yes, very impressive.

So is this;



...but you would be nuts to try and learn to drive in one.

IMPORTANT: This project is not for beginners. The voltage and current management are quite high, not counting the cost of components. For this reason you should have good knowledge and experience in electronics assembly projects of this magnitude. If you have no experience in the assembly of electronic projects, we recommend starting with a simple amplifier, such as the 40W amplifier. Otherwise any mistake can cost you money. {my emph.}

To be blunt, these amps are for advanced builders only. The preamps, sure, but the main amps are serious engineering.

It also has to be said that these are adaptions of stereo amps to guitar service, and as such are not intended to deliver their rated output continuously as is required of stage gear.

There is nothing wrong with the idea of getting high power by running several lower power amps in parallel, in fact there is a lot to be said for it, but how ever you do it you have to deal with some very serious questions of component capacity and sufficient cooling.

The power transformers, big as they are, are only for intermittent output at these power levels.  Rack amps designed for concert use have power transformers twice this size for the same power, and look more like welders than amplifiers.

The multi-amp method has a couple of real advantages; one is that lower powered amp modules make use of more commonly available components, thus they are cheaper and easier to build and to repair, and they also give you diversity in that if one amp blows up at a gig you still have the other(s), all your performance eggs are not in one basket.

As a keyboard player who uses a homebrew Twin-50, and as a soundie who has used multiple amps, I can tell you this diversity has saved the show on more then once occasion.  Even the classic Acoustic 360/361 used a single preamp, but independent power modules in each W-bin - and I would strongly suggest to you that they knew what they were doing going this way.

A speaker in a direct-radiator cab is about 3% efficient in converting electricity into sound.  In a J- or W-bin that jumps to 25 to 30% efficient; in other words it makes 50 watts sound like 500 watts - without having to use a genuine 500 watt driver.  Bill's "Siamese", one of his earlier designs I modified a bit, has ample slap thanks to having tweeters, but I wouldn't call it "mid-range" by any means, going down flat to the low-E on a four string bass it makes your guts shake.

[oleskool]

So it looks like the consensus is "keep it simple stupid"!!!??? I'm very interested in everything that has been said. Roly what would you suggest as a start .... can you point me in a good direction for a buildable ( <---- is that a real word? Aww you know what i mean. ) amp for bass? I love the idea of less watts, but better sound. I've looked around the net for some of the things mentioned here, and it's kept me busy. Here's proof.

I can get one of these Peavey series 300 things for about $40 but it reads Musicians where this one reads bass. It reminds me more of a preamp than a amp though. It yells a minute when you turn it on.
Good idea? Bad idea. Please help!!!

[J M Fahey]

That Peavey Musician, if working properly, is an excellent Bass amp too.
Just don't use its reverb of Fuzz !!!
*Many* old amps e+were designed that way: same big PCB where for Bass "ffects" were simply not fitted.
And for $40 each ...... *I* would buy a dozen, and I'm not kidding.
Real difference between Bass and Guitar versions, besides effects, was speakers, as in 2 or 4  x 12" instead of 1 or 2 x 15".
And 10" were for Guitar .
Check old Kustom, Acoustic, Randall, etc. catalogs (and schematics).

[Roly]

Yeah, "buildable" is certainly a word, and not a bad concept if you want to actually finish something and use it. 

Ah, so you found my Siamese.  The amp just happened to be what was around at that time and it has been driven by all sorts of things since it doesn't really have an amp of its own.  It's nominally a couple of hundred watt 15-inch Etone driver but normally gets driven with about 50 watts (and I dread to think what would happen to the back wall if I drove it with 200 watts).

Like most of my stuff this was build mostly out of scrounge, the cloth covering and corners were bought but most of the rest were scraps gathered from here and there.  I did an earlier, smaller Mid-Ranger that was built entirely from wood that had been pile up to burn in a bonfire, warped ply and the like.

A criminal amount of good ply &c gets thrown out at building sites as "offcuts" or used formwork that has a bit of cement residue on one side, and for a bit of dumpster diving after quitting time, and a bit of cleaning, you can have all the materials you need to build guitar speaker cabs - leaves more money to spend on the actual driver(s).

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).

Any box with knobs you can get for $40 has to be worth serious consideration - all the better if it's actually working.  :dbtu:  If it doesn't suit your needs, or you can't adapt it, you can always flog it again (to JM  :cheesy: ).

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

attach: Fane-rear-J-15

[mexicanyella]

This thread is making me want to build a W-bin or a J-horn cabinet for my old 60-watt Univox tube bass head! Off to follow links...

[oleskool]

Any ideas as to why this peavey musician is screaming when it is turned on??? It stops after it's been on a few minutes.

[joecool85]

Any ideas as to why this peavey musician is screaming when it is turned on??? It stops after it's been on a few minutes.

Is it a high pitch whine, a low pitch rumble, some other noise?

[Roly]

Here's an Audio Engineering Society J-horn for 12, 15 or 18 inch driver, similar to the Fane.

I'm posting this one here because it's out of my private stash (not on-line) and the book is way out of print now.

If you look closely at the response curves the main difference as the diameter goes up is you get that extra bit just above 50Hz, but at the expense of some top end roll-off.  I'm considering a pair of these with 12-inch drivers, and maybe a low-reach tweeter horn in each for use with synth/keys.


Circuits for the Musician 300 series appear to be available here;

www.audio-circuit.dk/schematics_o-r.php

re: Peavey Musician screaming

Q: Do any of the controls have any influence, louder, softer, change tone or pitch?

[mexicanyella]

1. Have J-bins or W-bins been built that use 10" bass drivers? I'm wondering how a single- or dual-10" compact folded horn arrangement might work with a low-wattage head like mine...or does that compactness/small driver approach begin to negate the efficiency benefits of a design like that?

2. Does the "screaming" of the Peavey Musician occur even if nothing is plugged into the input? Or does it only happen when you plug in an instrument or just a cable? If the latter, does plugging something else into it still make it scream?

I have an old Valco tube amp that screams like crazy if I plug my lap steel into it, but it doesn't act up with my guitar. My lap steel is fine plugged into other amps. I haven't traced this problem down and dealt with it yet.