Wanting to build a bass amp from scratch

[Dennis]

Hello,

I'm new to your forum.
I did a few searches and I didn't find exactly what I was looking for, so I'm going to try to ask.

I have recently switched from playing guitar to bass guitar, and am liking it.
I have an amp that is ok, its an old KMD 200 watt 15" combo. It's loud for now, but I am worried that it wont last to terribly long as the more I play through it the sloppier it sounds and the low end seems to be slipping away from it. It was made in the 80's.

So I am wanting to build a tube amp. I was looking at building a kit/clone amp of a SVT but as I started ordering parts here and there I am wondering if that's a cost effective and smart idea. The amp is complex, not to bad though but it's not a beginers design.

Is there a quicker and easier way to build a tube amp that can power one 15" speaker and a four 10" cabinet? and be loud and strong enough to actively gig with, and have plenty of headroom, or is continuing with the SVT a pretty good choice?

These are the 10" speakers I was thinking about putting in the 4x10" cabinet
Speaker Detail | Eminence Speaker
unless there is a better sounding speaker for the price of course.

I'm basicly trying to round out my sound and plan out the upgrades for down the road.
My idea sound goals are to have the low end covered well and tighten it up with the 4x 10" cabinet.

Thanks for any feedback.

[jrfrond]

I don't know what your level of skill and expertise is, but a simple 200W bass amp design e.g. Marshall Major would not be technically hard to execute. However, a high-power tube amp needs big iron and a hefty chassis to hold it all.

[Billy R aka DynaFreak]

check out the AB200 Weber Kit: https://taweber.powweb.com/store/kits_weber.htm#ab200

[Dennis]

I'm pretty good with electronics. I'm pretty sure I can tackle a building project, and I have a local amp shop owner who makes his own line who has offered to assist if I get stuck.
I'm looking for the best bang for the buck.

[Dennis]

check out the AB200 Weber Kit: https://taweber.powweb.com/store/kits_weber.htm#ab200

I've actually been debating that weber kit. Do you know anyone who has built that kit?

[Billy R aka DynaFreak]

No, but the girl that sings in one of my bands is also a bass player and I built her a 100W bass amp using the 6S100 as the starting point. It ended up a 4 X EL34 amp. I am a Weber dealer so I often use their kits to supply the basic parts (chassis, cabinet, spkr,) for custom builds. You might want to post your question on the Weber bulletin board.

[Chuck H]

IMHE... Tube bass amp means 1)big iron (=$$$), 2)big, high quality power supply w/choke (=$$$), 3)big, high quality power tubes (=$$$).

I don't think there's a way to ever "save" money building your own tube bass amp. You can probably come out even and still get the "I built this" satisfaction. If you follow good advice (which you have here and local via your amp tech) your bound to get a great amp, and possibly taylored somewhat to your specific whimsy (=cool). But a good used amp is a pretty valid option when you consider cost exclusively.

JM2C but there are some really good bass amps available (though not tube) for reasonable prices. The GK800RB and Peavey MegaBass come to mind. Effects loops, compression, built in crossovers, etc... Why play through some rudimentary and expensive tube circuit when, for what is usually a clean signal anyway, a transistor and MOSFET circuit could do the job with more features for less money??? Just sayin'.

This from a guy who's transistor illiterate. My guitar amps use all tube circuits as much for aesthetics as because I don't know enough about transistors to incorporate them. But I have no illusions about the advantages of tube and SS technologies. Unless your clipping the signal, tubes barely matter with instrument amps.

JMHO and JM2C

[Billy R aka DynaFreak]

I tend to agree with Chuck. A good approach, and the one I used for the 6S100-based amp, is to make an amp that sounds great, is loud enough for practice and can drive a cabinet on stage for a monitor, and incorporate a transformer driven balanced line out (XLR) for sending the bass signal to the PA. I also do sound, and the most common problem (besides the drummer showing up late) is TOO MUCH BASS FROM THE BASS AMP.

[Chuck H]

Scratch that on the GK 800rb... Too popular, even used. Too expensive. The GK 400rb is valid though. Both the Peavey MegaBass and the GK 400rb can be found used on line all day for under $300.

[R.G.]

My bass playing friends tell me they prefer to have an amplifier (and speakers!) capable of 10 watts for each 1 watt the guitarist's amp will do. This gets rapidly out of hand, as that says you need a kilowatt to keep up with a guitarist who has a 100W amp. When I say that, they look me back with no sign of humor and say "Yes, it does."

I know you can do tube amps with more than 200W available, but I'm guessing that half to one kilowatt is out of the question. Long before I got to that point, I'd start doing 50W to 100W amplifiers each in the cabinet with one speaker so I could (a) carry them a piece at a time and (b) only take along as many as I thought I needed. Not to mention the advantages in dispersion by placement.

[jrfrond]

Call me crazy, but it is my firm belief that bass amp design has gotten too far carried away, and helped many bassists hack their sound to death, as opposed to dialing-in exactly what they need. I mean really folks, THE classic bass tone is a P-Bass with an Ampeg B15N. I am not trying to say that this is the ONLY bass sound, however a majority of bassists, particularly jazz, blues and rock just do not need all of the bells and whistles in their signal path. In addition, 100W of tube power through an efficient cabinet with at least one 15" driver for low-end projection (sorry, but 15's sound different in the low-end than multiple 10's, even if the cone area of the 10's exceeds the 15's) can blow away solid-state and especially Class-D ("D" is for "deceiptful") designs of several times the wattage, due to the lower damping factor. Lastly, bass sound that is just too "hi-fi" inevitably gets lost in the mix. You need some harmonic dirt and grit to stand out a bit. Sure, it sounded GREAT by itself at Sam Ash or GC or at the sound check, but mix in a band and GOODBYE bass!

[GregS]

Lastly, bass sound that is just too "hi-fi" inevitably gets lost in the mix. You need some harmonic dirt and grit to stand out a bit. Sure, it sounded GREAT by itself at Sam Ash or GC or at the sound check, but mix in a band and GOODBYE bass!

I agree totally.

Also, I find clean undistorted sound is an area where tubes really shine. I play bass part of the time and guitar part of the time in the band I play in. I always play the bass clean and I play the guitar clean at least 50% of the time. Tube amps really seem to "warm" up the clean sound. It also works great in the band mix.

I would use the B15N copy I built for my bass if it had more headroom (and the speaker cabinet weren't so big!) because the sound is so much better than my 200W solid state combo. I'm putting up with the SS 200W combo for the time being until I can get to my next project - a high power all tube bass amp.

Greg

[jrfrond]

I agree totally.

Also, I find clean undistorted sound is an area where tubes really shine. I play bass part of the time and guitar part of the time in the band I play in. I always play the bass clean and I play the guitar clean at least 50% of the time. Tube amps really seem to "warm" up the clean sound. It also works great in the band mix.

I would use the B15N copy I built for my bass if it had more headroom (and the speaker cabinet weren't so big!) because the sound is so much better than my 200W solid state combo. I'm putting up with the SS 200W combo for the time being until I can get to my next project - a high power all tube bass amp.

Greg

I really hate to sound like an old fart (even if I am) spouting "tube this.....analog that" but far too many bassists (AND guitarists) do not know what they are missing with modeling guitar amps and Class D bass amps. Sure, it VERY cool to have a 300W amp in a 5lb. package, right? Well, it all depends on what you are looking for when you start pushing the watts. Class D power ratings are for instaneous signal only, and won't reproduce repeated high-power transients like those encountered in high-volume bass playing. At low volumes, the sound can be somewhat sterile, making tone controls and EQ that much more critical. But a good ol', simple tube bass amp with passive tone controls is more "plug & play", and the lower damping factor coupled with higher harmonic content will fill the room and "wrap around" the band easier.

In an era when everyone seems to want "smaller, lighter, cheaper", tube bass amps often get a bad rap and go unnoticed, but I totally get it. I've actually been working on a somewhat unique-yet-simple 100W and 200W design for myself. The Weber design looks cool, though a bit overly-complex for my taste in the output stage. A simpler UL design e.g. Marshall Major is all that is really necessary. Leave the hi-fi tube design to the SVT.

[dpacek]

Yep, my son was in need of a bigger amp for gigging and while the B15 sound is great he need more power than
the stock B15. So I took the Joe Piazza 1968 B15-N schematic and lots of tips from KOC TUT3 B15 design and created a
100W version with 4 6L6GCs instead of 2 that easily drives an Ampeg HLF 4X10 (not to the Max of course
since that cab is rated at 500W but still very impressive volume .

Total cost was about $400. If your curious you can see some of the build photos here:
MobileMe Gallery

KOC also has a stripped down 300W SVT schematic (simpler pre amp) in TUT3 that can be
built on a standard 17x10x3 Hammond chassis but the transformers and chassis alone
will run you $500. Then add in 6-6550s and other parts and you'll probably push the cost to $700-$800.
That will be my next Bass amp build.
You could probably a good used SVT head for that amount but the experience of building your own amp
and understanding how it works and how to repair it yourself is pretty satisfying.

Not to mention all of KOC designs have very useful improvements like individual bias controls on each power tube.
No more worrying about finding "matched pairs" of output tubes.

[Bruce / Mission Amps]

Very nice... for a friend's son, I also built a version of this using reissue transformers for a Super Reverb, two 6L6GCs and a 2x12 cab... not very powerful but it had a wonderful vintage warm tone that even the metal head kid learned to love!!