Altering a valve guitar amp for bass usage.

Rocker

I have a vintage Nolan 50 watt guitar amp that I would like to use for bass. What is the difference between guitar and bass amps? Is it possible (in other words, easy) to change it for use with my bass. It will be connected from my Markbass minimark 802 via the Di out. Thanks. The reason will be revealed later.

JezWynd

I'm interested in this issue too. I've been using a Laney Cub 10 to practice bass. I used to feed the speaker out to a 15" but I'm currently toying with fitting a 10" bass speaker in the combo instead. The only noises (I think) I'm hearing when I turn up is the speaker being driven too hard. Thinking about a 10" neo 100w speaker or thereabouts.

The tone I get on bass from the little Lavey valve amp are very pleasing, no issues there, it's just the speaker. If you're playing loud then vibration might become an issue in a combo.

steamabacus

There's nothing inherently different between a guitar amp and a bass amp, The only issue is likely to be whether the speaker (you don't say whether the Nolan is a head or combo) can handle the bass frequencies and has enough power handling (the higher rated the speaker is, the better). At lowish volumes there's no problem.

Chris_J

What's wrong with just using the 802? 

Rocker

steamabacus said:

There's nothing inherently different between a guitar amp and a bass amp, The only issue is likely to be whether the speaker (you don't say whether the Nolan is a head or combo) can handle the bass frequencies and has enough power handling (the higher rated the speaker is, the better). At lowish volumes there's no problem.

It is a head, I have a 12" Eminence Alpha speaker in an old open backed cab that I hope to use.

Rocker

Chris_J said:

What's wrong with just using the 802? 

We have a gig coming up and I would like to spread the bass sound 'a bit'. Both sides of the drumkit...

I am not sure of the spec of the PA system. If it is good I could send the DI output to the PA, which would solve the volume and spread  question.

steamabacus

Rocker said:

steamabacus said:

There's nothing inherently different between a guitar amp and a bass amp, The only issue is likely to be whether the speaker (you don't say whether the Nolan is a head or combo) can handle the bass frequencies and has enough power handling (the higher rated the speaker is, the better). At lowish volumes there's no problem.

It is a head, I have a 12" Eminence Alpha speaker in an old open backed cab that I hope to use.

A closed back cab would be better for bass response  however an open backed cab will be less strain on the speaker. What is the speaker rated at? Also worth noting is that the more distorted the bass frequencies are, the more strain will be placed on the speaker (fuzz bass is known to be a speaker killer). This is why, in PA applications, you will often see higher powered amps (run well within maximum output, ie very clean) into lower power rated speakers.

Personally, I'd want to see a 100w speaker on a 50w valve amp to feel comfortable (with bass). And keep it clean.

EricTheWeary

steamabacus said:

There's nothing inherently different between a guitar amp and a bass amp, The only issue is likely to be whether the speaker (you don't say whether the Nolan is a head or combo) can handle the bass frequencies and has enough power handling (the higher rated the speaker is, the better). At lowish volumes there's no problem.

There's a reasonable history of bassists using guitar amps and vice versa. Dusty Hill, of ZZ Top, has usually used guitar heads into bass cabs as an example. 

steamabacus

EricTheWeary said:

steamabacus said:

There's nothing inherently different between a guitar amp and a bass amp, The only issue is likely to be whether the speaker (you don't say whether the Nolan is a head or combo) can handle the bass frequencies and has enough power handling (the higher rated the speaker is, the better). At lowish volumes there's no problem.

There's a reasonable history of bassists using guitar amps and vice versa. Dusty Hill, of ZZ Top, has usually used guitar heads into bass cabs as an example. 

LEMMY!  \m/

Funkfingers

The amp EQ controls of a guitar amplifier will be focussed on different frequency bands. The pre-amp gain structure may also be different.

JezWynd

Rocker said:

steamabacus said:

There's nothing inherently different between a guitar amp and a bass amp, The only issue is likely to be whether the speaker (you don't say whether the Nolan is a head or combo) can handle the bass frequencies and has enough power handling (the higher rated the speaker is, the better). At lowish volumes there's no problem.

It is a head, I have a 12" Eminence Alpha speaker in an old open backed cab that I hope to use.

Useable freq range is 51hz - 4.3 Khz. Is that broad enough for bass guitar?

Specs here: http://www.eminence.com/pdf/Alpha_12A.pdf

ICBM

Connect to bass cabinet.

Plug in and play.

JezWynd said:

Rocker said:

It is a head, I have a 12" Eminence Alpha speaker in an old open backed cab that I hope to use.

Useable freq range is 51hz - 4.3 Khz. Is that broad enough for bass guitar?

Specs here: http://www.eminence.com/pdf/Alpha_12A.pdf

Yes. There won't be a sharp cut-off at the low end, and a (standard 4-string) bass goes down to 41Hz, where the response is only about 3dB down, so you'll still easily hear the lowest frequency it can produce.

The Alpha 12A is described as a mid-bass driver to distinguish it from true bass/sub bass drivers - it will be fine for bass guitar, in fact better than a true bass driver which are more useful in multi-way PA systems and normally sound too dull for bass guitar.

fretmeister

Rocker said:

Chris_J said:

What's wrong with just using the 802? 

We have a gig coming up and I would like to spread the bass sound 'a bit'. Both sides of the drumkit...

I am not sure of the spec of the PA system. If it is good I could send the DI output to the PA, which would solve the volume and spread  question.

Each side of the kit would actually result in horizontal phase cancellation if they are at the same level. Not as bad as if the 2 were next to each other but still there.

Far more efficient to go upwards in an array format instead. Increases the spread for better.

So stick one on top of the other instead. Everyone will hear it including you as it will be closer to your ears.

Just don't over do it on the guitar amp with the bass EQ and maybe even cut it a bit and let the MB do the lows properly.

Rocker

Thanks guys. Good to know it will work. Another option that occurs to me is to use the Eminence speaker as a second speaker for the MB802. I will try these options out towards the end of next week.

ICBM

fretmeister said:

Rocker said:

We have a gig coming up and I would like to spread the bass sound 'a bit'. Both sides of the drumkit...

Each side of the kit would actually result in horizontal phase cancellation if they are at the same level. Not as bad as if the 2 were next to each other but still there.

Far more efficient to go upwards in an array format instead. Increases the spread for better.

So stick one on top of the other instead. Everyone will hear it including you as it will be closer to your ears.

Missed this earlier but this is true. Counterintuitively, a vertical array produces much better horizontal dispersion than a horizontal one does. That's why old fashioned PA speakers were made as column cabinets, and also one of the reasons the Ampeg SVT was designed with a tall but narrow 8x10" cab.

fretmeister

Rocker said:

Thanks guys. Good to know it will work. Another option that occurs to me is to use the Eminence speaker as a second speaker for the MB802. I will try these options out towards the end of next week.

Check your impedances!

ICBM

fretmeister said:

Rocker said:

Thanks guys. Good to know it will work. Another option that occurs to me is to use the Eminence speaker as a second speaker for the MB802. I will try these options out towards the end of next week.

Check your impedances!

I think it should be OK, the Eminence is most likely an 8-ohm driver - but yes, important to check.

If you're using the Nolan to drive the second cab it doesn't matter - if you set the amp correctly for the cab of course.

This also throws up another possible problem though - phase. It's not impossible that the Nolan inverts the phase - quite a few amps do. If so the two speakers will then be out of phase which will cause major problems with loss of low-end. It's easy to fix if you can swap the speaker connections, or use a phase-reversing speaker cable, but it would be wise to check this out beforehand...

ecc83

Stand by for deep pedantry!!

The 'column' or 'line source' speaker system only has the HORIZONTAL dispersion of a single speaker, no better. The VERTICAL dispersion is however restricted and it is this that give them their acoustical advantage, they do not spray sound at the ceiling or floor and the radiation can be concentrated on the largely non-reflective audience.

The V restriction also gives them a directional 'gain' over a single unit (Google 'Yagi' aerial) and so a column speaker is more sensitive than the individual drive units that make it up.

But, these advantages are frequency/size dependant. To get any benefit even at speech frequencies you need a 5-6foot column.

They say "there is nothing new under the sun"? Dunno but it is interesting that after years of seeing grotty sounding 12 and 15" 'tubs' with glass cutting tweeters in them either side of stages, the line source seems to have been re-invented?

Dave.

Rocker

@ICBM, @ecc83, Guys the Eminence Alpha 12" speaker I have has a yellow label stuck on the back of the speaker.  I want to use it as a second speaker powered from my Markbass Minimark 802 [we have a gig on Sunday week (28th)].  I Googled Eminence Alpha 12" speaker and it suggested that it is 8 Ohm and 150 Watt RMS.  I did, briefly, connect the Alpha to the Minimark and it works fine but am uncertain the speaker impedence is 8 Ohm or higher [no mention on the speaker itself and the Alpha mentioned on the websites has a black label].

Thanks.

ICBM

It's unlikely it's anything other than 8 ohm. On Eminence speakers there is usually a paper label on the edge of the magnet with some code numbers on it - that may give a clue.

ecc83

ICBM said:

It's unlikely it's anything other than 8 ohm. On Eminence speakers there is usually a paper label on the edge of the magnet with some code numbers on it - that may give a clue.

Get a *&%%g! test meter! (not you IC!) An 8 Ohm 'hi-fi' woofer would have a DC resistance of about 6 Ohms. Some guitar speakers have a DC R close to their nominal impedance but an 8'er will be under 8 Ohms. (BTW headphones usually have a DC R very close to stated impedance)

Dave.