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Possibly stupid question about amps and cabs

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Possibly stupid question about amps and cabs

Postby SecretSam » Sat Sep 05, 2020 2:45 pm

I am writing this while hiding behind the sofa, awaiting the incoming teasing as I would a malignant Dalek.

If I wanted to play a 120w SS amp through a 65w cabinet, on the grounds that I would almost never use more than 25% on the master volume, would I be making a dreadful mistake?
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Re: Possibly stupid question about amps and cabs

Postby MOF » Sat Sep 05, 2020 3:02 pm

I wouldn’t recommend it as normally you’d want it to be the other way around i.e. sufficient headroom at the speaker.
However I can’t see a problem except for a switch on ‘thump’ from the amplifier if you’d left it at the 25% setting.
I say this from a Physics up to A level stage and it was a long time ago, so an electronics engineer might chip in and say no.
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Re: Possibly stupid question about amps and cabs

Postby Sam Spoons » Sat Sep 05, 2020 3:39 pm

Neither an electronics engineer or malignant Dalek here, just a guitar player and sound guy for a lot of years. Guitar amps are a slightly unusual case and what would be the normal safety margins are often ignored*. I used a 65 watt speaker in my MusicMan RP100 combo (valve power stage) for many years with no ill effects. I suspect most guitar speakers are well over-rated to take into account the extreme distortion guitarists like to use. Also consider a solid state power amp's output will be related to the impedance if the speaker, if you use a 16 ohm speaker that 120 watts will probably be down to around 50 watts., and into an 8 ohm load around 80 watts

In practice I'd say there is a small risk of damage but, at listenable levels, very unlikely.

* For PA/monitor speakers we usually specify an amp of 1.5-2.0 x rated max wattage of the speakers because distortion is often more damaging than loud but clean and overdriving an underpowered amp creates distortion.
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Re: Possibly stupid question about amps and cabs

Postby John Pinchin » Sat Sep 05, 2020 3:49 pm

It should be fine.

But what model are the amp and cab?

Probably worth noting that turning the knob a quarter of the way doesn't mean the amp is giving a quarter of the power and different amps will respond very differently in gain and volume as you turn up the master.
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Re: Possibly stupid question about amps and cabs

Postby John Egan » Sat Sep 05, 2020 6:10 pm

SecretSam wrote:I am writing this while hiding behind the sofa, awaiting the incoming teasing as I would a malignant Dalek.

If I wanted to play a 120w SS amp through a 65w cabinet, on the grounds that I would almost never use more than 25% on the master volume, would I be making a dreadful mistake?

I think you should be fine. The original Vox AC30s often used to put out substantially more than 30w and had two 15w Celestions with very flimsy cones. Mine was used for around 6 nights a week at mostly full volume or close. It took eight years to die.
Regards, John
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Re: Possibly stupid question about amps and cabs

Postby al_diablo » Sat Sep 05, 2020 7:28 pm

One lovely thing about this particular guitar forum is that nobody has jumped in just to make comments about SS amps...

I just wondered, does it make a difference playing clean vs distorted, on the basis that distortion smooths out the spiky transient attacks, and feels subjectively louder for lower output levels? Or is that all wrong?
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Re: Possibly stupid question about amps and cabs

Postby SecretSam » Sat Sep 05, 2020 7:57 pm

That's encouraging, gents. Sounds like it's worth the risk.

What prompted the question was 90 minutes in the local Marshall dealer this morning trying out various 20w heads.

My conclusion: the 20w Plexi is utterly fantastic if you dial everything to 11 and shove a Tubescreamer up it. A one trick pony, but what a trick. The others ...I could live with them, but... meh. No improvement on the Night Train. And I would have to find a proper rehearsal room to use the Plexi, because it doesn't do quiet.

So I poked around the shop and found some Orange stuff. I liked the Tiny Terror more than I expected. It doesn't have the excitement of the full-on Plexi, but it sounds better at lower volumes and doesn't need much dialling in. Then I found their Crush Pro SS stuff. It sounds convincing either loud or quiet, it's light, well constructed, and costs half of what the Plexi costs. I already have a good cab with a Creamback in it, so don't want a combo. The head only comes in 120w, hence the question.

Should I be ashamed of liking a SS amp?
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Re: Possibly stupid question about amps and cabs

Postby CS70 » Sat Sep 05, 2020 9:27 pm

SecretSam wrote:Should I be ashamed of liking a SS amp?

If it sounds good it sounds good.

My old Trace Elliot SuperTramp 100W has a SS power section and it's a fantastically versatile amp. Nothing to be ashamed of.
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Re: Possibly stupid question about amps and cabs

Postby Sam Spoons » Sun Sep 06, 2020 10:31 am

al_diablo wrote:One lovely thing about this particular guitar forum is that nobody has jumped in just to make comments about SS amps...

I just wondered, does it make a difference playing clean vs distorted, on the basis that distortion smooths out the spiky transient attacks, and feels subjectively louder for lower output levels? Or is that all wrong?

For a given amp/power setting the peaks will still be at the same level but distortion will generate more energy (effectively/visually filling in the gaps in the spiky waveform until it's flat topped). The speaker has to handle this energy so will get hotter. Guitar speakers can handle short transients at a much higher level than their nominal power handling but continuous distortion will increase the risk of damage.
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Re: Possibly stupid question about amps and cabs

Postby ef37a » Sun Sep 06, 2020 10:56 am

https://orangeamps.com/products/guitar- ... 20h/#specs

That is an oddity these days, a Solid State amp with a minimum speaker load rating of 8 Ohms. I assume Secret Sam that the Creamback is 8 or better, 16 Ohms? If the latter you really have nothing to worry about since the amplifier is unlikely to deliver more than 70/80W into 16R and that would be a terrifying 120dB ish, jet plane level!

Eight Ohms is more problematic but, as others have said, guitar speakers ARE tough* and if sensible there should be no problem. The tight suspensions on git speakers means they are almost immune from damage from switch on thumps but if it bothers you, switch the amp on before you plug in the speaker (NOT recommended for valve amps!)

Valves and transistors destroy speakers in different ways. Valves 'keep on giving' when the speaker is into thermal compression and saying "no more please!" Transistors run out of volts but not current and tend to destroy suspensions and spiders with LF.

For guitar amplifiers my opinion is that the speaker should be rated at at least 50% above amplifier and better 100%.

*Celestion, almost alone in the speaker world it seems, are conservative with their power rating (which in any case can only be a statistical specification). Mention was made of the long lived 15W Alnico Blues in the AC30. The originals were Goodmans, still 15W rated but did not like it up 'em!

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Re: Possibly stupid question about amps and cabs

Postby John Egan » Sun Sep 06, 2020 11:18 am

ef37a wrote:https://orangeamps.com/products/guitar-amp-heads/crush-pro-series/crush-cr120h/#specs


*Celestion, almost alone in the speaker world it seems, are conservative with their power rating (which in any case can only be a statistical specification). Mention was made of the long lived 15W Alnico Blues in the AC30. The originals were Goodmans, still 15W rated but did not like it up 'em!

Dave.

Thanks, Dave,
I didn't know that Vox used Goodmans originally. When did they swap to Celestions in the AC30?
Regards, John
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Re: Possibly stupid question about amps and cabs

Postby SecretSam » Sun Sep 06, 2020 11:52 am

ef37a wrote:https://orangeamps.com/products/guitar-amp-heads/crush-pro-series/crush-cr120h/#specs

I assume Secret Sam that the Creamback is 8 or better, 16 Ohms? If the latter you really have nothing to worry about since the amplifier is unlikely to deliver more than 70/80W into 16R and that would be a terrifying 120dB ish, jet plane level!


For guitar amplifiers my opinion is that the speaker should be rated at at least 50% above amplifier and better 100%.

Thanks for the detailed reply Dave.

It's 8 ohms. So will extract the full Monty.

That amp looks less of a bargain if I need to build a new cab for it. What if I daisy chain two 65w cabs?

"65 watts," I said to myself. "Who really is ever going to use more than that in the 21st century ?"
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Re: Possibly stupid question about amps and cabs

Postby ef37a » Sun Sep 06, 2020 11:59 am

Hi Jon, I am NO Vox historian! Just picked up a few things over time. I think the switch to Blues was done very early on. To be fair to Goodmans, the guitar speaker industry was in its infancy and I guess Celestion just got to a reliable product that bit sooner?

Today of course Cellies have pretty much cornered the UK market for gitamp speakers with Jensen doing much the same over The Pond. Some people bemoan the fact that a lot of production has left these shores but I can tell you from personal experience that doe not mean any loss of quality control.

You might also be interested to know that the very early AC30s used an EF86 pentode as the front end valve? Yes it gave oodles of gain but was noisy and prone to microphony. They soon switched to the standard ECC83. Nothing wrong with the EF86 of course! Especially as back then they would have been Mullards but the valve was designed for more genteel use in hi fi RIAA pre amp stages not the rough ass world of guitars!

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Re: Possibly stupid question about amps and cabs

Postby ef37a » Sun Sep 06, 2020 12:10 pm

SecretSam wrote:
ef37a wrote:https://orangeamps.com/products/guitar-amp-heads/crush-pro-series/crush-cr120h/#specs

I assume Secret Sam that the Creamback is 8 or better, 16 Ohms? If the latter you really have nothing to worry about since the amplifier is unlikely to deliver more than 70/80W into 16R and that would be a terrifying 120dB ish, jet plane level!


For guitar amplifiers my opinion is that the speaker should be rated at at least 50% above amplifier and better 100%.

Thanks for the detailed reply Dave.

It's 8 ohms. So will extract the full Monty.

That amp looks less of a bargain if I need to build a new cab for it. What if I daisy chain two 65w cabs?

"65 watts," I said to myself. "Who really is ever going to use more than that in the 21st century ?"

Don't need a new cab just a 16 Ohm Creamback! I still think you would be very safe if a bit careful. Things that will destroy speakers are open circuit cable screens causing a massive hum and possibly instabilty, driving the amp with a distortion pedal but again, you would have to be making a hell of a noise!

If you are handy with a solder iron get an inline fuse holder from Halford and make up a jack2jack cable with the fuse in the live line. Start with 1.6A slo blo and if you haven't popped it in a month, go down to 1A SB.

NB! Do not fuse a cab if fed from valves unless you bypass the fuse with say a 22 Ohm 10W resistor. (you can even get really clever and fit a 'blown indicator' LED! )

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Re: Possibly stupid question about amps and cabs

Postby Sam Spoons » Sun Sep 06, 2020 12:29 pm

Or stick a suitably rated polyfuse into the line between the jack socket and speaker, with the 'safety resistor Dave suggests. Probably easier to solder than fitting the bits inside the plugs.
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