Bass Amplifiers

I spent my first couple of years playing bass borrowing bass amps.  I also used to practice through a little ex-keyboard 10 watter that I was “borrowing”.   My highschool had an old Fender Bassman bass amp which we used to be able to borrow sometimes.  It was a combo and looked something like this.

It was an old amp probably made in the 1970’s sometime which is awesome, because in the 70’s amplifiers were made with TUBES!!! Tube amps are the way to go – especially for Bass.  Tubes give more warmth and growl and you can overdrive them for awesome bass distortion. You’ll find tube amps provide a more pure and richer sound for your stock tone. As with everything over time in this world, bean counters and greedy pricks sought to make things cheaper to maximise profits and tube amplification began to disappear through the 80’s and 90’s.  Solid State or Mosfet amplifiers are cheaper as they use semiconductors and circuit boards to power and create sound.  The good news is you can still buy tube amplifiers or amplifiers which at least use a combination of tube and solid state components to power them.

There are two “stages” in the amplification in bass amps  (well all guitar amps really)

1)    “PRE-AMP”  stage and a

2)    “POWER-AMP” output stage.

You can have either tubes or solid state components powering each of these stages. Having Tubes powering both is the way to go, however this also costs mega bucks. The  legendary and super sweet Ampeg SVT is well known to be the ultimate in this type of bass amplification set up.  Ampeg were the first to provide high powered tube bass amplifiers loud enough to drown out those pesky guitar players.  In the early 70’s the Ampeg SVT (Super Value Technology) was the only bass amp at the time which had more than 100 watts of power.

So a good compromise  is to get an amplifier which has Tube power (12AX7) on at least the PRE-AMP Stage. Many amps are sold now with a tube pre-amp and a mosfet power output stage. This way you are able to project the nice warmer tube sound into a high powered and hopefully lower distortion (high quality) mosfet power output stage. Most  of the mosfet/mosfet pre and power amped bass amplifiers I’ve played in the shops are very ratshit. I think its not even worth bothering about amps set up like this.

If you’ve got the money to spend (AUS$8,000) go straight for the Ampeg SVT.  I’d get two 4×10 cabs or one 4×10 and a 1×15 over the bigarse “fridge” 8×10 cab.  Those mothers are great, they’re just a bugger to transport around.  For most venues, well if your a regular club and pub gigger its over-kill lugging around an 8×10.  I watch many bass dudes huff and puff shifting them.  One day when you’re a pro you can let the roadies do that for you.

By chance more than design I bought my first bass rig  –  a Hartke VX series. I got a 4×10  cab and 1×15 cab powered by a “mighty” Hartke HA2500 250 watt amp.  Hartke are good value for the money however they are also well known and loved for their aluminum speaker cone design. The aluminum cones have a faster response than paper cones and some say the tone produced is also clearer.  The head unit has a tube and solid state pre-amp stages with a solid state power stage.  There is also onboard compression and a 10 band eq.  Its a reasonable set up for regular pub gigging.   Hartke have recently put out their new range of Hydrive Bass Amplifiers which have proper 12AX7 tubes on the pre-amp stage and solid state output.  Bass legend Victor Wooten currently uses the Hydrive range. When I was upgrading my rig I looked at this set up and I still think the Hydrive is a good mid range rig if for less about a third of what you’d pay for the Ampeg SVT.

I decided instead to go for the Ashdown EVO III ABM series.  Ashdown is a British manufacturer although now most of their gear is made in China.  I don’t think this makes them any worse than other brands. I love the retro automotive design of their amps and cabs but even better is the vintage tubey tone.  They sound very similar to the Ampeg but I liked the extra onboard controls the Ashdown EVO have over the Ampeg. There is  rotary variable tube/grind control which gives you some great tone options from warm valvey vintage tube to a tubey grind overdrive.  I like it.
It also has a good EQ control with separate Bass, Mid and Treble dials along with boost/cut sliders at 180Hz, 340Hz, 1.3kHz and 2.6kHz. There is a usable sub-harmonic generator ( a case of less is more) and compressor.  All of these functions are foot switch controllable. If you have a listen to “Talking To” on the Stellas Kitchen website you can check out the bass sound which I’m using the Ashdown rig with the 4×10 cab miked up. I’ve got a bit of grind happening on track with the tube drive set at about 1 o’clock.
Bass AmplifiersThe Ashdown cabs are great and are relatively light to transport.  The “little” 1×15 I have is about 3/4 the size of a regular 4×10 and it still sounds mint.  Its especially good because the Ashdown cabs are 8 ohms and the Amp’s power is supplied at 4 ohms.  So if you hook up the two cabs in parallel you’ll get the full 4 ohms of 575 watts power.  Running  cabs in parallel means you have a separate lead going from the amp to each cab. Another way to hook two cabs is to run another speaker lead from your first cab to the 2nd cab. Most speaker cabs have and “external” output jack on them which will let you “daisy-chain” the 2nd cab to it.  If you want to run two cabs in your rig set up you have to make sure the total impedance load is great enough to match your amp’s impedance.

As a general rule, if you have cabs of the same impedance:

Amp Impedance = Impedance of a Single Cab / Number of Cabs 

My Ashdown Amp = Ashdown Cabs@8 ohms/2 cabs
4 ohms@575w  

4 Ohms               = 4 Ohms 

You need this figure to be the same as your amp’s ohm rating.  If it is less than your amp’s, your amp will burn up and die. If its more you won’t be extracting all the juice from your amp. So if your amp is 4 ohms then you’ll need two 8 ohm cabs in parallel.  I dunno why this all works this way, you’ll have to ask the Ohms Law dude.

Another way to understand this is to look at it starting with your amp. Most bass amps produce their rated power at 4 ohms. Some amps are also built to pump their power out at both 2 ohms and 4 ohms.  This is great as it means you’ll get more power out of your amp for starters, but also you have more flexibility with the cabs you can use. Your typical starter amp+cab setup will give you the amp, say 300 watts @ 4 ohms and a single cab which is 8 ohms.  Straight away you will be losing power you should be getting.  What happens is the power coming from your amp at 4 ohms hits a brick wall of 8 ohms of higher resistance.  So the real power out of your cab and ears may be something like 170 watts.

While this sucks, the benefit of starting with this set up is if you were to then add another 8 ohms cab to create your cool amp stack, you’ll then “equalise” your amp and speakers. You’ll have 4 ohms of the full power of your amp hitting a total resistance of 4 ohms in your cabs. Sweet!  The other way to do this is to straight out buy a cab which already is rated as the same resistance as your amp. This is good and saves your back lugging around all those cabs, however there’s no substitute for volume. By volume I mostly mean the amount of sound waves –  you are always gonna sound louder the more speakers you have.  You’ll find a lower powered amp running in “equilibrium” will sound louder with more speakers connected to it than a higher powered amp which is being throttled by a higher resistance (single) cab.

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