Time for a stupid question

[kitaristi0]

Can you use an amplifiers head without a cabinet? Heads like Marshalls and Hiwatts?

[BiC]

Originally posted by kitaristi0:

Can you use an amplifiers head without a cabinet? Heads like Marshalls and Hiwatts?

Time for a stupid answer...

 

Sure... if it has a headphone jack!

[KARL FISHER]

Just be careful which amp you only plug headphones into. Most tube amps need a speaker load-headphones are not enough.

 

I practice many late-nights with a Marshall MG10CD? The little 10 watt amp. Works great with its headphone out jack and a cd/tape player plugged in. I've learned many new songs at 1:00 am that way!

 

Karl

[Jedro]

First, only use headphones if a headphone output is supplied. Second, you'll need load resistors on the speaker outs so your head won't fry. Possibly some newer amps have functions to disable the speaker outputs, but I'm not sure.

[Caevan O’Shite]

Whith a tube-amp, unless there's a built-in load of some kind (like if the amp has a "silent record" switch option, or something similar) you would have to have some kind of load connected to the speaker-output, like a Power Soak, GT E Speaker Emulator, Hot Plate, Power Brake, etc. And the load should equal or exceed the impedance that the amp would want to see, i.e. an 8-ohm or 16-ohm load if the speaker was an 8-ohm model, etc.

 

Imagine that you're driving down the freeway, goin'along on cruise-control at 55(+) m.p.h., and suddenly the transmission is somehow completely disconnected from your engine. Your engine will suddenly wind up into some screamin' RPM's, and likely suffer some serious damage, right? The same goes for your amp: its output section needs a work-load, or it will try to drive infinity, and burn up in the process.

 

There are a lot of various loading and attenuating devices on the market right now that are absolutely perfect for direct-recording of your amp, getting a signal to send to headphones or a headphone-amp, drive effects-chains, etc., etc., so you're in luck if you need to do something along these lines. Just don't fry your amp, and always use a bona-fide speaker cable to connect the speaker-out of your amp to said load-device.

[WaterMan]

Originally posted by Caevan O'Shite:

Whith a tube-amp, unless there's a built-in load of some kind (like if the amp has a "silent record" switch option, or something similar) you would have to have some kind of load connected to the speaker-output, like a Power Soak, GT E Speaker Emulator, Hot Plate, Power Brake, etc. And the load should equal or exceed the impedance that the amp would want to see, i.e. an 8-ohm or 16-ohm load if the speaker was an 8-ohm model, etc.

 

Imagine that you're driving down the freeway, goin'along on cruise-control at 55(+) m.p.h., and suddenly the transmission is somehow completely disconnected from your engine. Your engine will suddenly wind up into some screamin' RPM's, and likely suffer some serious damage, right? The same goes for your amp: its output section needs a work-load, or it will try to drive infinity, and burn up in the process.

 

There are a lot of various loading and attenuating devices on the market right now that are absolutely perfect for direct-recording of your amp, getting a signal to send to headphones or a headphone-amp, drive effects-chains, etc., etc., so you're in luck if you need to do something along these lines. Just don't fry your amp, and always use a bona-fide speaker cable to connect the speaker-out of your amp to said load-device.

I had a custom Kingsley made to address this issue. I wanted a headphone option in a great sounding tube amp,which is very hard to find. Simon Jarret at Kingsley added this feature to his Deluxe 50, as well as other features, like a power tube overdrive head , into a 2x12 combo. Sweet -- and silent when it needs to be for the wife

[Jazz Guitar]

Originally posted by Caevan O'Shite:

 

Imagine that you're driving down the freeway, goin'along on cruise-control at 55(+) m.p.h., and suddenly the transmission is somehow completely disconnected from your engine. Your engine will suddenly wind up into some screamin' RPM's, and likely suffer some serious damage, right? The same goes for your amp: its output section needs a work-load, or it will try to drive infinity, and burn up in the process.

That analogy doesn't work for TRANSISTOR amps however. Transistor amps are just fine with no load.

[Caevan O’Shite]

Originally posted by Mr Nice Jazz Guitar Guy:

"That analogy doesn't work for TRANSISTOR amps however. Transistor amps are just fine with no load."

Yes, as far as I understand; (in best "Ed McMahon"-impression) you are cor-rect, sir!

 

Now, if you had a more sophisticated version of "standby" on a tube-amp, where you could selectively put the output-section and its tubes on "standby", you could still take a signal from the preamp section. But this still wouldn't be a fair representative of the tone and response of the overall tube-amp in question. (Hence, specifically designed preamps like your Boogie Formula, or the built-in "dummy"-load and "Silent Record"-switch on a Boogie Mark IV, and the like.)

 

I recall reading an article in a "Hi-Fi" enthusiast type magazine only a few years ago about a monoblock, true class-A, single-ended, all-tube power-amplifier that was designed to drive one single horn-driver with no transformer between the output tube and the horn. (You were expected to buy two of them if you wanted stereo.) It was reputed to have a purity and clarity of hi-fi sound-reproduction that brought rapturous tears to reviewer's eyes, and the vinyl records of Sinatra to their ears. It had better have sounded good- I believe that the price was supposed to be in the neighborhood of, oh, a paltry $85,000.00!! APIECE! Two for stereo! And you still had to buy those special horn-drivers separately. At least they provided you with the output-tubes packed separately, in padded velvet-lined hardwood presentation-grade cases. (Spares were only around $850.00.)

[Jazz Guitar]

Originally posted by Caevan O'Shite:

Originally posted by Mr Nice Jazz Guitar Guy:

"That analogy doesn't work for TRANSISTOR amps however. Transistor amps are just fine with no load."

Yes, as far as I understand; (in best "Ed McMahon"-impression) you are cor-rect, sir!

 

Now, if you had a more sophisticated version of "standby" on a tube-amp, where you could selectively put the output-section and its tubes on "standby", you could still take a signal from the preamp section. But this still wouldn't be a fair representative of the tone and response of the overall tube-amp in question. (Hence, specifically designed preamps like your Boogie Formula, or the built-in "dummy"-load and "Silent Record"-switch on a Boogie Mark IV, and the like.)

 

I recall reading an article in a "Hi-Fi" enthusiast type magazine only a few years ago about a monoblock, true class-A, single-ended, all-tube power-amplifier that was designed to drive one single horn-driver with no transformer between the output tube and the horn. (You were expected to buy two of them if you wanted stereo.) It was reputed to have a purity and clarity of hi-fi sound-reproduction that brought rapturous tears to reviewer's eyes, and the vinyl records of Sinatra to their ears. It had better have sounded good- I believe that the price was supposed to be in the neighborhood of, oh, a paltry $85,000.00!! APIECE! Two for stereo! And you still had to buy those special horn-drivers separately. At least they provided you with the output-tubes packed separately, in padded velvet-lined hardwood presentation-grade cases. (Spares were only around $850.00.)

Sounds good to me. Of course I'm still partial to a pair of Apogee Grands driven by 4 Krells.

 

BTW, I have a pair of Apogee Stages downstairs. Nice speakers but sure don't have the sheer "umphh" of my JBL EON1500s upstairs. I've been known to use the JBLs to punish my neighbors when their 3 little pugs start barking.

[Blue Strat]

Originally posted by Mr Nice Jazz Guitar Guy:

Originally posted by Caevan O'Shite:

 

Imagine that you're driving down the freeway, goin'along on cruise-control at 55(+) m.p.h., and suddenly the transmission is somehow completely disconnected from your engine. Your engine will suddenly wind up into some screamin' RPM's, and likely suffer some serious damage, right? The same goes for your amp: its output section needs a work-load, or it will try to drive infinity, and burn up in the process.

That analogy doesn't work for TRANSISTOR amps however. Transistor amps are just fine with no load.

Actually that's incorrect. Transistor amps are fine with a dead short to ground, but will burn up with an infinite load. You can go lower in impedance, not higher.

[Jazz Guitar]

Originally posted by bluestrat:

Originally posted by Mr Nice Jazz Guitar Guy:

Originally posted by Caevan O'Shite:

 

Imagine that you're driving down the freeway, goin'along on cruise-control at 55(+) m.p.h., and suddenly the transmission is somehow completely disconnected from your engine. Your engine will suddenly wind up into some screamin' RPM's, and likely suffer some serious damage, right? The same goes for your amp: its output section needs a work-load, or it will try to drive infinity, and burn up in the process.

That analogy doesn't work for TRANSISTOR amps however. Transistor amps are just fine with no load.

Actually that's incorrect. Transistor amps are fine with a dead short to ground, but will burn up with an infinite load. You can go lower in impedance, not higher.

Actually you are quite incorrect. Have you ever plugged in a reciever or hi-fi amp with no speakers connected? Have you ever turned on a transistor guitar amp like my good old Acoustic 450 with no load? They work just fine with no load.

 

Transistor amps do not like "shorts to ground" either. People spend big bux on amps that will drive low inpedance speakers, like Apogees. For a time the only amp on the planet that would drive an Apogee Scintilla was a Krell, as the speaker's impedance went as low as about 0.7 ohm.

[Jazz Guitar]

Originally posted by bluestrat:

Originally posted by Mr Nice Jazz Guitar Guy:

Originally posted by Caevan O'Shite:

 

Imagine that you're driving down the freeway, goin'along on cruise-control at 55(+) m.p.h., and suddenly the transmission is somehow completely disconnected from your engine. Your engine will suddenly wind up into some screamin' RPM's, and likely suffer some serious damage, right? The same goes for your amp: its output section needs a work-load, or it will try to drive infinity, and burn up in the process.

That analogy doesn't work for TRANSISTOR amps however. Transistor amps are just fine with no load.

Actually that's incorrect. Transistor amps are fine with a dead short to ground, but will burn up with an infinite load. You can go lower in impedance, not higher.

Got another analogy for you. Ever measure the gain of an op-amp circuit, with a 'scope probe being the only "load"? Funny that op-amp doesn't burn up driving an open circuit. The gain for a inverting op-amp is still Vout/Vin.

 

Also, when op-amp stages are cascaded, the output of one drives the input stage of the next. As most EEs know, output impedance is supposed to be LOW, and input impedance is almost infinite. Therefore, in a cascaded op-amp circuit, one amp would see virtually infinite impedance, which sure is similar to an "open circuit".

[Blue Strat]

Originally posted by Mr Nice Jazz Guitar Guy:

Also, when op-amp stages are cascaded, the output of one drives the input stage of the next. As most EEs know, output impedance is supposed to be LOW, and input impedance is almost infinite. Therefore, in a cascaded op-amp circuit, one amp would see virtually infinite impedance, which sure is similar to an "open circuit".

Not really, because as most EE's know there's a virtual short between the non-inverting and inverting inputs of said opamp, therefore the opamp sees zero impedance to ground.

[Jazz Guitar]

See below!

[Dave da Dude]

bluestrat,

Not really, because as most EE's know there's a virtual short between the non-inverting and inverting inputs of said opamp, therefore the opamp sees zero impedance to ground.

Please don't confuse us with facts

 

Dave

[michael saulnier]

Lots of "headphone" guitar players have tapped into the "modeler" market. Most of the leading modelers have built in headphone jacks, and sound pretty good with headphones for practice. On the low price end, the Johnson J-Stations are going new for under a hundred dollars, and used for about 1/2 that. Digitech has a low priced unit, and used POD's are available for a modest price.

 

You can also run a modeler into a mixer or recording device, which you're also sending a rhythm track... and then listen to the whole "mixed" signal with headphones...

 

Almost "noiseless" except for the "plink, plink, plink" of your guitar strings...

 

I've had many nights where I'm RAGING... it's one in the morning, and everyone else is sleeping peacefully!

 

guitplayer

[Jazz Guitar]

Originally posted by bluestrat:

Originally posted by Mr Nice Jazz Guitar Guy:

Also, when op-amp stages are cascaded, the output of one drives the input stage of the next. As most EEs know, output impedance is supposed to be LOW, and input impedance is almost infinite. Therefore, in a cascaded op-amp circuit, one amp would see virtually infinite impedance, which sure is similar to an "open circuit".

Not really, because as most EE's know there's a virtual short between the non-inverting and inverting inputs of said opamp, therefore the opamp sees zero impedance to ground.

That is completely INCORRECT!!!!! That is only true when one of the terminals is referenced to ground.

Internally the inputs to the amp pose a HIGH impedance to ground.

 

I think you are confused with the concept of a "virtual" ground which occurs when the (usually +) terminal is referenced to ground. With NO signal present, the - and + terminals are at the same potential, even with a very large impedance between the two terminals. Why? Because virtually no current flows between the two terminals.

 

The concept of a virtual ground is very important for deriving the equations for inverting and non-inverting amps. Inverting gain = -Vo/Vin. Non-inverting gain is 1+Vo/Vi.

 

Again, some EEs know the above, even after having been out of school for decades.

[Blue Strat]

Maybe so. I'll have to read up on it again. It's been a full year since I had that class.

[Blue Strat]

Double post, my bad.

[Jazz Guitar]

Originally posted by bluestrat:

Maybe so. I'll have to read up on it again. It's been a full year since I had that class.

Come on man! It's been 26 years for me.

 

Typical impedance between + and - might be on the order of 10 Mohm. Same to ground.

 

Outside of building PCs now and then, I don't see alot of hardware these days. Usually when I do, it's the "throw it out and buy a new one" variety, like today with my erstwhile Uniden phone/answering machine.