Headroom and Amp Class for Dummies

[rickdog]

Both types of devices can be used to design a wide range of performance goals.

Certainly! I was just trying to make the point that things that come easily, almost for free, with one type of device can take a lot of sophisticated design to achieve with the other.

I think your comment is a succinct answer to the OP's question about amp classes. The design goals and quality of the design affect the sound of the amp more than the amp class or components (tubes, discrete transistors, op amps) used in the preamp. (Of course, there are other considerations like efficiency and weight.)

I'm guessing - and wondering whether you can say anything about this - perhaps some clever op amp circuits are involved in giving the class D power amp in the 800D some of the desirable characteristics of a tube output stage? There has to be more than a basic op amp gain stage involved....

 

[rickdog]

I just opened this thread to this ^^^ post. Contrary to its title, this thread is NOT for dummies .

Dummies beware! Reading this thread could change you forever!

 

[agedhorse]

Certainly! I was just trying to make the point that things that come easily, almost for free, with one type of device can take a lot of sophisticated design to achieve with the other.

I think your comment is a succinct answer to the OP's question about amp classes. The design goals and quality of the design affect the sound of the amp more than the amp class or components (tubes, discrete transistors, op amps) used in the preamp. (Of course, there are other considerations like efficiency and weight.)

I'm guessing - and wondering whether you can say anything about this - perhaps some clever op amp circuits are involved in giving the class D power amp in the 800D some of the desirable characteristics of a tube output stage? There has to be more than a basic op amp gain stage involved....

Correct, I was answering the OP's comments. It can take a lot of work to makes something sound like something else, but if the something else is expensive or is becoming more difficult to obtain, working harder can achieve similar results without the considerable cost (and weight usually).

There are several circuits that work together to achieve the feel of the Bass 800D. They consist of elements used in the other Subway models, plus some additional stuff that brings it all together. This goes back to basic R&D work I have done over 30+ years, I have a catalog of circuits that behave in different ways, I may not have used the circuit for that specific project but that does't mean that it might not be useful down the road... sometimes it's concepts, and sometimes it's actual circuits.

 

[Deloofs]

Cool discussion. I initially got into amplifiers and electronics in general just a few years ago when I was searching for a cool stereo system to match the wood panelling in my living room. I picked up a stack of Kenwood separates and wood panelled tower speakers from the late 80's which I thought looked cool. I plugged them in and was pleased to learn that in addition to looking cool they also sounded bonkers compared to the cheap sound bars and surround systems that I was used to. I got really into it and started learning about amp architectures. I learned about the Kenwood L-series specifically the L-08M power amp. These were 180 watt genuine class A single channel power amplifiers. The design includes vents that look like smoke stacks to dissipate the waste heat. Kenwood offered a feature on some high-end products they called "Sigma Drive" which was an extra set of speaker wires (called "signal wires") which would extend the negative feedback loop all the way to the speaker terminals to account for impedance in the wires. Apparently the most noteworthy thing they did was blow up amps when users would connect the signal wires wrong It seems like the late 80's was a cool time for stereo technology because companies were all trying to outdo each other with specs and performance whereas nowadays it seems like all the emphasis is on connectivity and convenience.

I'm not super well-versed in electronics but class A amps always seemed akin to driving a car by slamming the accelerator to the floor and controlling the speed with the brakes in an effort to improve throttle response.

 

[agedhorse]

Cool discussion. I initially got into amplifiers and electronics in general just a few years ago when I was searching for a cool stereo system to match the wood panelling in my living room. I picked up a stack of Kenwood separates and wood panelled tower speakers from the late 80's which I thought looked cool. I plugged them in and was pleased to learn that in addition to looking cool they also sounded bonkers compared to the cheap sound bars and surround systems that I was used to. I got really into it and started learning about amp architectures. I learned about the Kenwood L-series specifically the L-08M power amp. These were 180 watt genuine class A single channel power amplifiers. The design includes vents that look like smoke stacks to dissipate the waste heat. Kenwood offered a feature on some high-end products they called "Sigma Drive" which was an extra set of speaker wires (called "signal wires") which would extend the negative feedback loop all the way to the speaker terminals to account for impedance in the wires. Apparently the most noteworthy thing they did was blow up amps when users would connect the signal wires wrong It seems like the late 80's was a cool time for stereo technology because companies were all trying to outdo each other with specs and performance whereas nowadays it seems like all the emphasis is on connectivity and convenience.

I'm not super well-versed in electronics but class A amps always seemed akin to driving a car by slamming the accelerator to the floor and controlling the speed with the brakes in an effort to improve throttle response.

Based on the Kenwood schematic, It’s not class A except lower power. This was very common claim back in the day.

 

[Deloofs]

Based on the Kenwood schematic, It’s not class A except lower power. This was very common claim back in the day.

I can't believe it! I'm cancelling my order!

 

[undercutter]

probably not a good look that my first post is piggybacking on this thread in hopes to get an answer to my total newb inquiry.... all of this ohm, watt, class, headroom, etc. makes me want to bang my head against the wall.

I have a sansamp bass DI as a preamp (but am looking for other options, perhaps a traynor ts-50b clone). I have a power amp. This power amp:

LX 1600 | Dynacord

and i am trying to figure out my best course of action for matching definitely one 2x12 cabinet and potentially a second 2x12 cabinet if more volume is necessary in certain situations.

based on my very limited understanding of this type of thing, I should run the A channel of the power amp (800 watts @ 4ohm) into a single 2x12 cab rated for 800w @ 4ohm and if i need more volume, i would do the same on the B channel of the power amp.

BUT

Could i also (alternatively) run the A channel of the power amp (800 watts @ 4ohm) into a single 2x12 cab rated for 800w @ 8ohm (making it roughly 400 to 500 watts? this is where it gets extremely confusing) and if i need more volume, i would add an identical 2x12 cab rated for 800w @ 8ohm?

what about headroom? I'm sure there are plenty of other factors that i'm not even considering. i need HELP.

thanks in advance

 

[agedhorse]

Yes, there is no problem with the speaker being rated with more power handling than the amp delivers.

What speaker? This is important because there are different marketing ways of describing a speaker’s power handling which can lead to incorrect assumptions and ultimately damage.

 

[undercutter]

Yes, there is no problem with the speaker being rated with more power handling than the amp delivers.

What speaker? This is important because there are different marketing ways of describing a speaker’s power handling which can lead to incorrect assumptions and ultimately damage.

and that's what i'm worried about... i feel like there are specs that i'm not considering/don't understand that are important for choosing the correct speaker and it's not as easy as just matching wattage and ohm numbers in such a way that the load does not exceed the output of the amp. i'm not married to the idea of any particular brand. i just want to know exactly what i need to be looking for to work with this power amp.

 

[undercutter]

and that's what i'm worried about... i feel like there are specs that i'm not considering/don't understand that are important for choosing the correct speaker and it's not as easy as just matching wattage and ohm numbers in such a way that the load does not exceed the output of the amp. i'm not married to the idea of any particular brand. i just want to know exactly what i need to be looking for to work with this power amp.

also, i should add that if i had $3000+ to make my ideal setup, i'd get that new mesa d800+ and a couple of subway cabs and call it a day, but alas.... i'm trying to use what i have in tandem with what i might find for a decent price so that i can play out to a larger room without having to rely on a supplied backline 100% of the time if necessary.

 

[agedhorse]

Be sure the speakers are rated in RMS metrics so that you are comparing apples to apples.

Often, trying to get by on the cheap ends up costing more in the long run.

 

[SunByrne]

Often, trying to get by on the cheap ends up costing more in the long run.

The Mesa philosophy in one sentence.

 

[undercutter]

Be sure the speakers are rated in RMS metrics so that you are comparing apples to apples.

Often, trying to get by on the cheap ends up costing more in the long run.

i understand and appreciate that point but sitting on my hands and waiting to be able to afford the long run solution is not a viable option for me, so if i find something that suits my needs now and will allow me to expand in the future that would be good.

really i guess i just need to make sure i understand what exactly i'm looking for so that i can make informed decisions. to be very clear i really appreciate your time and effort in answering these questions that have undoubtedly been spewed here ad-nauseum since 2008

as far as i can tell from the manual, the power output of the amp is 800 watts rms at 4ohms per channel.

for clarity's sake and to say it out loud to a room of professionals so i can see if i understand, if i were to buy two identical cabinets, lets say two 2x12 800w rms at 8ohms cabinets, i could run one of the 8ohm load cabs on the A channel which would cause the amp to put out 500 watts (per the book) and leave me 300 watts of headroom on the cabinet. then if i connected the second 8ohm load cabinet in parallel with the first cabinet on that A channel, that would give me a 4 ohm total load on that 4ohm A channel and would therefor output the full 800watts of power split evenly, 400watts to each 800watt cabinet which would leave 400watts of headroom per cabinet?

alternatively, i could run one of the 8ohm load cabs on the A channel which would cause the amp to put out 500 watts (per the book) and leave me 300 watts of headroom on the cabinet. then if i connected the second 8ohm load cabinet to the B channel it would be the exact same stats as the A channel.

do i understand more than i thought or have i messed up somewhere?

also, assuming that my very basic understanding of the importance of headroom, which of those two scenarios (both cabs on one channel OR one cab on each channel) is "better"? is there a clear "winner" or is it more of a 6 of 1/half a dozen of the other situation?

 

[agedhorse]

Either way will work, but why not buy a single 4 ohm 212 that outperforms 2 x 8 ohm 212’s? You will come out ahead in the long run, and it shouldn’t cost any more.

 

[undercutter]

Either way will work, but why not buy a single 4 ohm 212 that outperforms 2 x 8 ohm 212’s? You will come out ahead in the long run, and it shouldn’t cost any more.

Okay, this is the kind of insight that will help me make better decisions. I’m listening….

It did not occur to me that a single 4ohm 212 could outperform the 2 x 212 8ohm setup. How would that be possible?

Also, assuming that the single 4ohm 212 is 800w rms, then headroom would be a concern right? So I guess I’d want to shoot for a cabinet that is higher than 800w rms? Or am I overthinking it?

 

[agedhorse]

Okay, this is the kind of insight that will help me make better decisions. I’m listening….

It did not occur to me that a single 4ohm 212 could outperform the 2 x 212 8ohm setup. How would that be possible?

Also, assuming that the single 4ohm 212 is 800w rms, then headroom would be a concern right? So I guess I’d want to shoot for a cabinet that is higher than 800w rms? Or am I overthinking it?

There are different classes of 212’s, some are better than others by a wide margin.

You are overthinking the headroom part.

 

[S-Bigbottom]

Most 2x12's are 4 Ohms. They are the same as two single 8 Ohm speaker cabs together. Generally the 8 Ohm version of a single speaker is the most efficient version.

Where you are missing is that each cab will perform differently even at the same power rating. This may be slight or by quite a bit depending on what you are looking at.

More mids that cut through, deep rumbley, can do both at high volume, do not try to go deep at volume, balanced, boxy, boomy, buttery, dark, punchy grindy??? They are all over the place.

Tone profile at volume and can it get there safely for your needs is most important now you have the first part covered.

 

[sears]

I must be misreading something. Why is 500w into an 8 ohm Acme B2 ok, but 500w into a 4 ohm Acme B2 not ok?

Or is it that with the same amp at 4 ohms, you'd be sending 1000w into that 4 ohm cab?

 

[agedhorse]

I must be misreading something. Why is 500w into an 8 ohm Acme B2 ok, but 500w into a 4 ohm Acme B2 not ok?

Or is it that with the same amp at 4 ohms, you'd be sending 1000w into that 4 ohm cab?

Your second paragraph is correct.

 

[JimChjones]

Based on the Kenwood schematic, It’s not class A except lower power. This was very common claim back in the day.

Mind you if its a 180W amplifier being used in a typical domestic situation it probably is only used at lower power unless he has some very insensitive speakers.