My Marshall JCM2000 DSL401 1x12 combo has a 16 Ohm internal speaker (upgraded to a Celestion G12 Classic Lead 80):
- With just the 16 Ohm internal speaker - the impedance selector is set to 16 Ohm
- When connecting to a 16 Ohm cab PLUS the internal 16 Ohm speaker - impedance selector is set to 8 Ohm
- An 8 Ohm cab on its own, with NO internal speaker - impedance selector is set to 8 Ohm
But I'd like to connect it to a separate 1x12 Laney Cab that has an 8 Ohm Celestion Seventy-Eighty and accordingly only an 8 Ohm out. Is it safe to connect this in addition to the internal 16 Ohm speaker and if so, what's the correct impedance selector setting?
I started out with nothing..... but I've still got most of it left (Seasick Steve)
Comments
(Although the popular belief is correct for solid-state amps, which shouldn't be run below their minimum impedance - that's why it's described as a *minimum* rather than a *matching* impedance.)
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I must say that adding the 1x12 extn cab to both my Laney Cub 12R and DSL401 (both have 100dB internal speakers) makes a noticeable difference re perceived volume/fullness - more noticeable with the Cub actually but probably because it has a smaller cab than the DSL401.
To be fair, I haven't yet seen a DSL401 with a blown output transformer, which would be the most likely failure other than a valve. The 201 will blow transformers even when run at the *right* impedance though… so I'm just inherently cautious with them!
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Although the popular belief is correct for solid-state amps, which shouldn't be run below their minimum impedance - that's why it's described as a *minimum* rather than a *matching* impedance.) "
Yes ^ The term 'matching' when applied to amps and speaker impedance (aka 'Z') IMO needs dragging out to the pub car par, soaking in petrol and burning and the remains stamped on and hosed away!
The internal, source Z of an amplifier, valve OR transistorized is never* anywhere near the value of the speaker. Valve OP stages are generally much higher than load and transistors much lower, near buggerall most times.
True signal source/load matching only happens at RF and with digital and video signals.
*A big, ~100W valve amp might have an internal Z of around 10 Ohms but that is just serendipity.
Dave.
I'm sure that was a brilliant post Dave - if only I had the brains to understand it!
In fact, that's how you can identify the correct impedance on an unmarked amp, or the taps on an unknown transformer - measure the power output at 4, 8 and 16 ohms and see which produces the most. Start with 8, then 4, then 16 - if you get more power at 4 than 8 then don't try 16 since it's more risky to run a 4-ohm amp at 16 than a 16-ohm amp at 4.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
http://blog.hughes-and-kettner.com/ohm-cooking-101-understanding-amps-speakers-and-impedance/
Am not quite sure what bee has got into ecc83's bonnet regards matching ;-))
The only other thing I can think of that's worth mentioning is that if you're ever presented with a cab of unknown impedance which you have to use and you have no way of measuring it, just assume it's 8 ohms - because running an amp set to 8 ohms into either a 4-ohm or a 16-ohm cab is less risky than running either of them into the opposite one...
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"
Am not quite sure what bee has got into ecc83's bonnet regards matching "
The 'bee' sm chap is because the term 'matching' in electronics refers to a signal transmission condition that is never now used for audio signals (and never was for valves or transistors) .
Yes, the transformer reflects a load to the valves but this is ideally the 'Optimum Load' and this is chosen for best power output at minimum distortion. It is NOT a 'match' to the anode resistance of the valve.
I agree these matters are a bit esoteric in the rough-ass world of guitar amps but these questions DO come up in other forums and 'matching' e.g. S/PDIF signals, Word Clock are also discussed and I feel it important to keep the differences in mind?
Dave.[i
A bit off-topic from the basis of the thread, but am i assuming correctly that you are are referring to 'impedance matching' for audio connector issues regards the s/pdif and word clock ?
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
'RMS power' is actually very commonly used, despite being nonsense. It seems to be defined as the continuous maximum clean power of an amp - I assume it's derived from the RMS voltage output into the load impedance. Peavey do actually state that, but most other companies use 'W RMS'.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
http://www.n4lcd.com/RMS.pdf
Another good explanation ?
http://www.n4lcd.com/RMS.pdf
and to get mathematical about it
http://www.skm-eleksys.com/2011/06/instantaneous-average-and-total-power.html
That does sound like the explanation, anyway.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
It's a back shot of a '63 Fender Tele which i bought in the noughties from an ex-player/collector. It's original and very light in weight but with the worst paint/tippex 'job' around the side to make it look like a 'Custom' whilst on stage (carried out by an earlier previous owner)....and, yes, it's been played ;-))
The original dowel marks should be visible if you look closely enough.