I played a bunch of amps today....

[Lt. Bob]

My issue with low watt amps, and this is just my own observation YMMV, is that they don't get the cab and speakers working in their sweet zones to my satisfaction.

absolutely ..... there's a lot going on with a speaker when it's being pushed including cone deformations that add their own particluar distortions to things.
If you're using a 5 watt amp you kinda want a 5 watt speaker.
But even then if the sound you like is say, a V30 ...... then you need a V30 since every speaker sounds different.

And power tube distortion is a totally different beast than just pushing the pre-amp tubes.
My Mark V, for instance, ...... GREAT pre-amp section and a very usable master volume so you can get a very good sound at any volume.
But in the few cases where I've been able to really crank it and push the power section it becomes a different amp. The thing just roars in a way that it doesn't when I'm relying on the pre-amp.
It just sounds amazing when the power section is pushed while it just sounds very good otherwise. I'd prefer amazing to really good.
But I can rarely run it that loud.

 

[Greg_L]

absolutely ..... there's a lot going on with a speaker when it's being pushed including cone deformations that add their own particluar distortions to things.
If you're using a 5 watt amp you kinda want a 5 watt speaker.
But even then if the sound you like is say, a V30 ...... then you need a V30 since every speaker sounds different.

And power tube distortion is a totally different beast than just pushing the pre-amp tubes.
My Mark V, for instance, ...... GREAT pre-amp section and a very usable master volume so you can get a very good sound at any volume.
But in the few cases where I've been able to really crank it and push the power section it becomes a different amp. The thing just roars in a way that it doesn't when I'm relying on the pre-amp.
It just sounds amazing when the power section is pushed while it just sounds very good otherwise. I'd prefer amazing to really good.
But I can rarely run it that loud.

Attenuator!

I hear good things about the Dr Z Air Brake. And it's not ohm specific.

 

[ecc83]

Can I just put in a few words about loudness, speakers ratings etc?

The numbers mentioned are correct. To double subjective impression of loudness you need to increase power by a factor of ten. This is how the "Bel" was derived and we divide it into ten parts for general usage. It was found, many years ago, that the the "average" person can reliably detect a change of 3dB (double the power) on pure tone*. With some experience 2dB is just detectable but very few people outside experienced balance engineers say, can tell a 1dB diff.

One watt into a good guitar speaker IS very loud! For the V30 that is 100dBSPL.

Running the breasts of speakers. Not required. (respect to those that like the sound but please read on!) Celestion themselves say that this is largely a myth and their speakers sound good at milliwatt levels. In any case it is a dangerous practice..

A valve amp can usually put out 25-50% more distorted power than its specification suggests. Honest amp makers specify power at just observed clipping and at "normal" mains input. At higher input voltages and driven hard a 30watter can deliver 50W. This is even worse for fixed biased amps. There is but one push pull fixed biased 5W amp on the market AFAIK and that puts out just 5W clean but goes onto deliver nearly 10W if pressed (why it sounds bloody good as well!). Bigger fixed biased amps can deliver much more. A well specified, honestly marketed 60 watter (2x EL34) will easily kickout 85 even 100watts.

Celestions (no, I don't work for them!) have always been very conservative on their power ratings (speaker ratings are in any case a bit of a "wet finger in air"!) but many techs will tell you that other manufacturers are not so fussy. Even so, chose a speaker at least 50% over the amp's badge rating.

I understand AC30s have blown the odd cone? A 30watter of my aquaintance uses 2x V30...Never had one fail in 5 years....And remember! An o/c voice coil at top vol' will do your OP traff NO good at all!

*Mind you, music is not pure tone and all this is a bit academic subjectively. "They" also almost certainly did not test people at "gigging" levels, 110dB and counting!

Dave.

 

[Greg_L]

Can I just put in a few words about loudness, speakers ratings etc?

The numbers mentioned are correct. To double subjective impression of loudness you need to increase power by a factor of ten. This is how the "Bel" was derived and we divide it into ten parts for general usage. It was found, many years ago, that the the "average" person can reliably detect a change of 3dB (double the power) on pure tone*. With some experience 2dB is just detectable but very few people outside experienced balance engineers say, can tell a 1dB diff.

One watt into a good guitar speaker IS very loud! For the V30 that is 100dBSPL.

Running the breasts of speakers. Not required. (respect to those that like the sound but please read on!) Celestion themselves say that this is largely a myth and their speakers sound good at milliwatt levels. In any case it is a dangerous practice..

A valve amp can usually put out 25-50% more distorted power than its specification suggests. Honest amp makers specify power at just observed clipping and at "normal" mains input. At higher input voltages and driven hard a 30watter can deliver 50W. This is even worse for fixed biased amps. There is but one push pull fixed biased 5W amp on the market AFAIK and that puts out just 5W clean but goes onto deliver nearly 10W if pressed (why it sounds bloody good as well!). Bigger fixed biased amps can deliver much more. A well specified, honestly marketed 60 watter (2x EL34) will easily kickout 85 even 100watts.

Celestions (no, I don't work for them!) have always been very conservative on their power ratings (speaker ratings are in any case a bit of a "wet finger in air"!) but many techs will tell you that other manufacturers are not so fussy. Even so, chose a speaker at least 50% over the amp's badge rating.

I understand AC30s have blown the odd cone? A 30watter of my aquaintance uses 2x V30...Never had one fail in 5 years....And remember! An o/c voice coil at top vol' will do your OP traff NO good at all!

*Mind you, music is not pure tone and all this is a bit academic subjectively. "They" also almost certainly did not test people at "gigging" levels, 110dB and counting!

Dave.

Interesting. This kind of confirms something I never quite understood before. I had an 18w class A 3 12ax7, 2 x EL84 amp. The people that made the amp told me "yeah, it's 18 watts, but pushed hard it kicks out around 29 watts". I never understood how or why, the math didn't work for me, I was just like "yeah whatever". But that little bastard was fucking crazy loud, and it got there fast.

 

[ecc83]

Interesting. This kind of confirms something I never quite understood before. I had an 18w class A 3 12ax7, 2 x EL84 amp. The people that made the amp told me "yeah, it's 18 watts, but pushed hard it kicks out around 29 watts". I never understood how or why, the math didn't work for me, I was just like "yeah whatever". But that little bastard was fucking crazy loud, and it got there fast.

The "math" is actually fairly simple. You will have seen pictures of sine waves? Well if that amp produced 18 CLEAN watts into 16Ohms that would be an rms voltage of ~17volts (you can take rms to mean the "heating" or real power of an alternating voltage or current waveform). But the rms value is only about 2/3rds the way up the "slope". The peak of the slope is at 24volts. Now, as we push the amplifier harder and harder into distortion we "fill up" the waveform space with harmonics* until in the limit we have a square wave which contains an infinite number of odd harmonics. The power out would then be 36watts.
In practice we cannot produce a perfect squarewave and in any case the power supply will sag and not supply enough juice, so 29W is quite beliveable.

Now there are many tricks to making a modest amp sound loud! Voicing is common one. Put a permanent boost in the response at 2-3kHz, slap in the ear's most sensitive region and it will shout down a same power "flat" amp. Volume tapers are another stunt. If an amp burns the ears at Number 2 or 3 "F! knows what it will do at 9,10 or 11!!" Actually, F 'all more in practice! Yet another dodge is distortion. Some amps just don't "do" clean and people equate distortion with loudness.

But 'tis true. All you need for rock n roll even in quite a big pub is a pair of EL84s and a good speaker, two for preff. But! Only for rock, really clean stuff will demand at least twice the power.

*Most of which, thank F! The speaker filters out. Ever tried a really distorted guitar thru a hi fi speaker!

Dave.

 

[Greg_L]

The "math" is actually fairly simple. You will have seen pictures of sine waves? Well if that amp produced 18 CLEAN watts into 16Ohms that would be an rms voltage of ~17volts (you can take rms to mean the "heating" or real power of an alternating voltage or current waveform). But the rms value is only about 2/3rds the way up the "slope". The peak of the slope is at 24volts. Now, as we push the amplifier harder and harder into distortion we "fill up" the waveform space with harmonics* until in the limit we have a square wave which contains an infinite number of odd harmonics. The power out would then be 36watts.
In practice we cannot produce a perfect squarewave and in any case the power supply will sag and not supply enough juice, so 29W is quite beliveable.

Now there are many tricks to making a modest amp sound loud! Voicing is common one. Put a permanent boost in the response at 2-3kHz, slap in the ear's most sensitive region and it will shout down a same power "flat" amp. Volume tapers are another stunt. If an amp burns the ears at Number 2 or 3 "F! knows what it will do at 9,10 or 11!!" Actually, F 'all more in practice! Yet another dodge is distortion. Some amps just don't "do" clean and people equate distortion with loudness.

But 'tis true. All you need for rock n roll even in quite a big pub is a pair of EL84s and a good speaker, two for preff. But! Only for rock, really clean stuff will demand at least twice the power.

*Most of which, thank F! The speaker filters out. Ever tried a really distorted guitar thru a hi fi speaker!

Dave.

Good info, thanks.