Bass amps vs guitar amp

lincolnblue

I don't know what got me thinking about this, but guitar players (me included) always strive to find the perfect tone, and it's often sought in valve amps. Solid state amps have their fans, but many guitarists will only play valves.

However, every guitar amp I've come across has always been solid state. Do you get bass valve amps, and if not, why?

I assume there is some practical reason but I'm just curious as to why.

Cirrus

Yeah you get valve bass amps - before solid state technology kicked off there was no alternative really. In fact some old guitar amp designs were originally intended for bass - the Fender Bassman being the obvious example.

There are valve bass amps being produced to this day, the Ampeg SVT probably being a fine example.

So why are bass players more happy to use SS amps?

A few reasons. Firstly, Bass guitar sounds like bass guitar basically as soon as the signal has left the instrument. You could plug it straight into a PA system and it'd be a usable sound in most instances. So bass amps don't need to alter the tone of the instrument in the same way guitar amps do - guitar plugged straight into a PA sounds nothing like a guitar should sound. So for Bass, solid state does the job pretty much fine. All it needs to do is take the input signal and make it louder, any tonal change can be through choice rather than necessity.

Secondly, valve amps are heavier than solid state amps as a rule. Even a 30 watt guitar amp might weigh 50lbs+ because of the necessity for big transformers and a suitably strong chassis to support them. Bass amps need much more headroom to reproduce the low frequencies, so you end up with 200w+ valve bass amps with equally massive transformers that weight absolutely loads.

ecc83

You mean every BASS guitar amp I think?

Plenty of valved bass amps. Most famous I guess is the Ampeg SVT? never seen one but I HAVE lifted the Bstar 200 watter* and that effer is heavy enough!

Does that give you aclue as to why peeps want sstate??? Then, bass need lots of power, 100W is almost a "practice" amp and past 100W valves do get bloody heavy and bloody expensive both to buy and maintain (4 KT88s 300quid?) .

*Can be used in extremis for bass.

Dave.

Danny1969

I love the Ampeg SVT, it's my fave rock bass tone - especially through an 8 x 10". But the things weigh a ton without a hardcase, put one in a decent road worthy case and it's now a 2 man lift just for the head. There's a few bass amps with a valve pre but the only all valve ones I see tend to be Ampeg

steamabacus

Have a look at this thread - it may go some way to explaining why bassists love tiny class D amps .... unless they have roadies - then, they just LOVE those big old SVT stacks!

Phil_aka_Pip

As well as the weight & reliability & power o/p capability, isn't it something to do with valves being voltage amplifiers whereas transistors are current amplifiers? At bass frequencies, are the current supplying capabilities of the o/p stage under greater stress than compared to when amplifying guitar signals? There's more area under the curve and the signal changes direction less often which means the o/p stage has to be shifting current for all of that time.

edit having said that the only difference between the bass & guitar channels in a Selmer Treble'nBass 50 is that the preamp stage of one goes through a 0.47 cap and the other through a 0.22 before reaching the phase splitter.

martinw

ecc83 said:

(4 KT88s 300quid?)

Dave.

No, a mere £120 and up

ICBM

I still think valve bass amps sound the best too. But as already said, since any serious bass amp normally needs to be powerful and have a good bass response (duh.. ) and hence needs big transformers, they end up heavy and expensive, and expensive to re-valve. Most bass players want a clean sound too, which means even more power to avoid any unwanted distortion - much more so than for the same volume with a guitar amp. You need around four times as much power for bass as for guitar even for a slightly dirty 'rock bass' type sound, possibly up to ten times as much for a truly clean sound at the same volume.

Typical bass amps start at 200W, which needs four KT88s or 6550s, or up to eight 6L6s or EL34s. Compared to the same volume from a cranked 2-EL84 20W guitar amp (if the guitarist doesn't use a clean sound), you can see why bass players tend not to go for valve amps unless they can afford both them and someone else to move them…

That said, with modern very-high-efficiency speakers, 100W and possibly even 50W bass amps become a viable idea again, particularly if you don't need a truly clean sound. Like guitar amps, valve bass amps sound louder than similarly-rated solid-state ones as well, although not to the same extent.

fretmeister

I have a couple of SS heads and a great valve amp, the Mesa Bass Prodigy 4:88.

The four KT88 put out about 245w and is way louder than my 900w ss amps!

fretmeister

The rear of a Mesa 400+

http://www.talkbass.com/threads/fs-ft-mesa-boogie-bass-400.523411/

jpfamps

ICBM said:

I still think valve bass amps sound the best too. But as already said, since any serious bass amp normally needs to be powerful and have a good bass response (duh.. ) and hence needs big transformers, they end up heavy and expensive, and expensive to re-valve. Most bass players want a clean sound too, which means even more power to avoid any unwanted distortion - much more so than for the same volume with a guitar amp. You need around four times as much power for bass as for guitar even for a slightly dirty 'rock bass' type sound, possibly up to ten times as much for a truly clean sound at the same volume.

Typical bass amps start at 200W, which needs four KT88s or 6550s, or up to eight 6L6s or EL34s. Compared to the same volume from a cranked 2-EL84 20W guitar amp (if the guitarist doesn't use a clean sound), you can see why bass players tend not to go for valve amps unless they can afford both them and someone else to move them…

That said, with modern very-high-efficiency speakers, 100W and possibly even 50W bass amps become a viable idea again, particularly if you don't need a truly clean sound. Like guitar amps, valve bass amps sound louder than similarly-rated solid-state ones as well, although not to the same extent.

I concur, although extended bass is in my opinion in not conducive to good live sound (or indeed recorded sound).

I regularly gig with a Bassman 100 in a band with a noisy drummer with an efficient 4 x 10 cab and have never been found wanting for power.

ICBM

jpfamps said:

I concur, although extended bass is in my opinion in not conducive to good live sound (or indeed recorded sound).

I regularly gig with a Bassman 100 in a band with a noisy drummer with an efficient 4 x 10 cab and have never been found wanting for power.

Interestingly I once tested a Bassman 70 (admittedly fitted with 6550s, but still really only 70W) into a modern high-efficiency 4x10", and the amount of bottom end on it was staggering - it was easily capable of making the speakers flap, and the cab was supposedly rated for 800W. It was also perceptively louder than the cab's matching "400W" Class D head… and I'm not kidding. Maybe not in terms of clean headroom though.

I seriously considered using the Bassman and a Mesa 'Powerhouse' cab I had (1x15"+1x10"+2x6"+horn) but the problem was that the cab weighed exactly as much as me and was one of the most awkward things to move I've come across. I took it out of the house twice - once to try it at a band practice, and once when I got rid of it! But it did sound amazing with the Fender, and it would have easily been giggable if I could have shifted it.

fretmeister

After this thread I got my Boogie out again.

I don't usually use it in the house as at really low volume the fan noise is a little annoying (watching telly type noodling).

But when it's opened up it's just brilliant, has a real fullness to the tone.

But I have to say, I'm pretty sure the "secret" is in the preamp and not the poweramp. I have an Ampeg valve preamp that can sound just as good even when I use a Class D power amp with it. Even if it's not as loud.

ecc83

Hi Frets,

Re the fan noise. The next time you have the amp serviced you could have a "normally open" heat switch fitted to the fan. One that closes at about 50C. That is a bit oversafe and would probably cut in anyway after an hour or so even just noodlng but better save than,,,eh?

Could be a useful mod to anyone who has a fan cooled amp and needs a quiet background, recording say.

Dave.

ecc83

http://www.rapidonline.com/electronic-components/auto-reset-thermal-switches-35569

Why ca't I insert that link as an edit?

Dave.

jpfamps

ecc83 said:

Hi Frets,

Re the fan noise. The next time you have the amp serviced you could have a "normally open" heat switch fitted to the fan. One that closes at about 50C. That is a bit oversafe and would probably cut in anyway after an hour or so even just noodlng but better save than,,,eh?

Could be a useful mod to anyone who has a fan cooled amp and needs a quiet background, recording say.

Dave.

I'm always wary of amps with thermally controlled fans, as it could be too late when you find out the thermal switching has failed.

Better that the fan is always on, so you have time to switch the amp off if it doesn't come on.

If the fan is too noisy, install a quieter fan.

ICBM

I've found that a really good trick is to use a 220/240V fan and connect it to the 120V tap on the transformer, if it has one. The fan then turns slowly and as close to silently as anyone could want, even in a recording studio or a quiet bedroom.

It's surprising the difference even a slow-running fan makes to heat build-up, unless the enclosure is really closed up. I admit those Boogie 400s - and other rack-mount amps - are likely to be a problem, but in general well-designed valve gear shouldn't need cooling much beyond normal convection anyway.

ecc83

jpfamps said:

ecc83 said:

Hi Frets,

Re the fan noise. The next time you have the amp serviced you could have a "normally open" heat switch fitted to the fan. One that closes at about 50C. That is a bit oversafe and would probably cut in anyway after an hour or so even just noodlng but better save than,,,eh?

Could be a useful mod to anyone who has a fan cooled amp and needs a quiet background, recording say.

Dave.

I'm always wary of amps with thermally controlled fans, as it could be too late when you find out the thermal switching has failed.

Better that the fan is always on, so you have time to switch the amp off if it doesn't come on.

If the fan is too noisy, install a quieter fan.

I understand and expected your concern but the thermal switches I had in mind are the type fitted in microwave ovens as a safety device and are extremely reliable, probably have a MTBF 100 times better than the fan which why they are fitted, to backup the fan when it gets crapped up and stops!

If makers were that concerned about heat they would fit an N/C type to mains in!

Dave.

ecc83

Note, If you ever have one trip out in your MWO there are two types.

Those that reset at just below trip temp and others that need to be cooled below 0 C. A can of freezer can save you an expensive trip to the white goods man!

But clean the bloody fan as well!

Dave.