Two Bose 802 questions

[drew gandy]

Re: Two Bose 802 questions

Fireball (I mean, ahem, JR),
would I be correct to say that back then you weren't concerned about "running out of" wall power when designing power amps? Now it seems like managing the draw from the wall is one of the biggest concerns.

 

[Ron Kimball]

Re: Two Bose 802 questions

Not only was the CS800 considered a powerful amp, but at $1 a watt (List price) it was considered cheap, and was for back in the day. Now the Watts/$ ratio is watts per dollar and not dollars per watt like it was before the CS800. 250W @ 8 Ohm is now considered a small amp. Only the fixed instal business still uses modest sized power amps (I think).

I still use amps ~250w/ch for monitors - 115dB peak at the ear is plenty to burn out anyone's ears IMO (and worse case I can double up as I can carry eight monitors). I prefer not to play the extra-stoopid-loud game - but then again I'm not trying to make a living at this so don't need to cater to idiots .

 

[Ivan Beaver]

Re: Two Bose 802 questions

Fireball (I mean, ahem, JR),
would I be correct to say that back then you weren't concerned about "running out of" wall power when designing power amps? Now it seems like managing the draw from the wall is one of the biggest concerns.

Technology has changed a lot over the last several decades. Back then there was not much choice regarding current draw.

Of course one of the big differences is that the old amps (like the CS800) could run at full sine wave output for quite awhile. They did not dip down in power (like modern amps), they would just cut off due to thermal overload.

 

[John Roberts]

Re: Two Bose 802 questions

Fireball (I mean, ahem, JR),
would I be correct to say that back then you weren't concerned about "running out of" wall power when designing power amps? Now it seems like managing the draw from the wall is one of the biggest concerns.

I was actually product manager over power amps at peavey, when we broke through the apparent line cord power limit of around 3kW. I was surprised to see a larger power amp (QSC) at a trade show with a normal line cord, and immediately upon getting back to my office, confronted our in house UL guy and asked what is going on? The confusion continued when the east coast UL office confirmed the 3kW limit??? After some more digging it turned out that the west coast UL office had relaxed the power limit, allowing more peak output power than continuous input (line cord ) power. After some back and forth we got the two UL offices on the same page and higher power amps that plug into Edison outlets continued their power march higher. Before that we were forced to use camper plugs for higher power points that customers immediately cut off and plugged into Edison outlets with no apparent problems.

I also recall when QSC started hitting higher and higher power points despite popular wisdom that there weren't any customers or speakers for that much power, but in classic "build it and they will come" fashion, they built them and they sold.

JR

PS The real Fireball was active in racing when I was just a motor-head HS puke. The name seemed to fit and stuck with me for my childhood friends. It seemed fitting for me to register as Fireball at the drag race (where I won a trophy).

 

[drew gandy]

Re: Two Bose 802 questions

Technology has changed a lot over the last several decades. Back then there was not much choice regarding current draw.

Of course one of the big differences is that the old amps (like the CS800) could run at full sine wave output for quite awhile. They did not dip down in power (like modern amps), they would just cut off due to thermal overload.

In my early years as a bench tech I repaired a number of CS800s as well as some Crown, Crest, Carver & Ashly amps. It seemed like they all would run close to the limit with sine waves into my dummy load. Then I got a QSC in (USA series I believe) and I found it wouldn't run a 1Khz sine wave for very long before going in some kind of protect mode. But, everything else seemed fine about the amp so I called QSC and got the story about the difference in crest factor for music vs my sine wave test. It made sense to me at the time (and still does). (I think some of the AB brand amps scaled back their power supplies and heatsinks in similar fashion.) I ended up testing the QSC with pink noise and all was fine. I sent that unit back to the carnival having learned something. And of course now almost everything is a scaled for higher peak voltages vs long term current.

 

[drew gandy]

Re: Two Bose 802 questions

PS The real Fireball was active in racing when I was just a motor-head HS puke. The name seemed to fit and stuck with me for my childhood friends. It seemed fitting for me to register as Fireball at the drag race (where I won a trophy).

The mental image I have is you as a young man working on a power amp on the bench while it goes up in flames. But I'm sure that's complete make believe.

 

[Ivan Beaver]

Re: Two Bose 802 questions

The mental image I have is you as a young man working on a power amp on the bench while it goes up in flames. But I'm sure that's complete make believe.

I have had a number of amps 'in flames". However never a "flame linear" They just caused the speakers to go up in flames.

The BGW7000 (the white cheap ones) were really bad.

And a few tube amps. I remember one new Years eve gig that the bass players amp was throwing out flames and he was still playing----But not for very long.

And I have had a number of amps that with one little slip of a o'scope probe would take out ALL the output transistors. Phase linears were famous for that.

 

[John Roberts]

Re: Two Bose 802 questions

The mental image I have is you as a young man working on a power amp on the bench while it goes up in flames. But I'm sure that's complete make believe.

I was actually immortalized in a song by a local group of musicians who worked at Peavey for "stinking up the lab", when I tried to design a mosfet power amp using switching power mosfets in their linear region. The switching mosfets did not like being used that way, and I released a lot of mosfet smoke over several weeks before abandoning that project. I could make an amp work with them, but had to slow them down so not very Hifi. I wouldn't sell a product that wasn't good enough for me to use, so I bailed on it.

JR

 

[John Roberts]

Re: Two Bose 802 questions

In my early years as a bench tech I repaired a number of CS800s as well as some Crown, Crest, Carver & Ashly amps. It seemed like they all would run close to the limit with sine waves into my dummy load. Then I got a QSC in (USA series I believe) and I found it wouldn't run a 1Khz sine wave for very long before going in some kind of protect mode. But, everything else seemed fine about the amp so I called QSC and got the story about the difference in crest factor for music vs my sine wave test. It made sense to me at the time (and still does). (I think some of the AB brand amps scaled back their power supplies and heatsinks in similar fashion.) I ended up testing the QSC with pink noise and all was fine. I sent that unit back to the carnival having learned something. And of course now almost everything is a scaled for higher peak voltages vs long term current.

Yup, QSC gets credit for beginning the slide down the slippery slope from continuos duty. The bottom line was you can remove copper, and iron, and aluminum, and devices, while still advertising the same top line power output number. For the vast majority of customers who weren't driving high duty cycle applications, the amps seemed to work as well as their heavier brethren, while costing a bunch less.

Peavey could not afford to ignore cheaper competition, and responded with the old PV series. When I got involved as product manager a little later after that I added some output devices back into the bigger PV amp, that was a borderline hand grenade, but the custumer is always right and they embraced low duty cycle amps with both arms.

The rest is history.

JR

[edit- the CS series did not get gutted, but using the same philosophy the CS amps had the current limiting opened up to support 2 ohms loads.. so more power from same platform. [/edit]

 

[drew gandy]

Re: Two Bose 802 questions

And I have had a number of amps that with one little slip of a o'scope probe would take out ALL the output transistors. Phase linears were famous for that.

The digital Gallien Krueger amps had notes about where you were not supposed to put your scope probe. I thought I would eventually blow one up by bumping something but never did. I don't remember actually creating flames either. I've put some holes in speakers with screwdriver tip drills but that just made me feel cruddy inside; no fireworks or crazy sounds to numb the pain.

On the topic of power amp duty cycle (and this is now pretty far from the 802 thread topic), I was not opposed to the duty cycle shift idea. I thought of it this way: Would I rather have an amp that can do sine waves all day long or an amp of the same size, weight and cost that can do higher peak voltage swings? After all, the vast majority of music has at least a 10db peak to average ratio. There aren't many music styles that use high level sine waves in the music and none, that I'm aware of, that do so above a hundred Hz or so. I agree with JR that, in the context of sound systems overall, high duty cycle is only needed for fringe use cases. In the end the amp companies figured out that you could make a lower cost amp and sell it with higher power ratings than previously which wasn't exactly the way I was thinking about things. But that's economics. I'm interested in the new CAF system that Pat Brown is pioneering. If it can see widespread use it should help put some of the differences between amps into perspective.

As far as Bose 802 goes, I'm surprised there isn't a measured raw response on the web somewhere. Google image search isn't finding it, at least in the first few searches I've tried.

 

[Ivan Beaver]

Re: Two Bose 802 questions

I'm interested in the new CAF system that Pat Brown is pioneering. If it can see widespread use it should help put some of the differences between amps into perspective.

.

The problem is that you have to get manufacturers to agree to have the products measured as such. Just like the CLF (common loudspeaker format), if they are not measured the same way (and not all the products that are "CLF" are measured the same way), then the results can be different.

Not every body wants to have their products examined and made public. So they don't and won't have data available. So it makes it a bit harder to compare-when you aren't sure what the "standards" are.

 

[John Roberts]

Re: Two Bose 802 questions

The problem is that you have to get manufacturers to agree to have the products measured as such. Just like the CLF (common loudspeaker format), if they are not measured the same way (and not all the products that are "CLF" are measured the same way), then the results can be different.

Not every body wants to have their products examined and made public. So they don't and won't have data available. So it makes it a bit harder to compare-when you aren't sure what the "standards" are.

I discussed this ad nauseum back around the time of Bink's amp shootout. While there probably needs to be a handful of amp duty cycle standards (representing musical genres) any industry standard metric will cause ripples in the market as amp makers position themselves based on how the customers will percveive their ranking. Next generation amp designs will target any metric that the customers consider of value for comparisons.

I wish consumers could be trusted to interpret technical specifications. I need to stop posting about this now before I say what I really think.

JR

 

[John Roberts]

Re: Two Bose 802 questions

As far as Bose 802 goes, I'm surprised there isn't a measured raw response on the web somewhere. Google image search isn't finding it, at least in the first few searches I've tried.

Pretty much look at a mirror image of the EQ curve minus a little boom-sizzle. The old 901 EQ was pretty much flat in one of the positions (not the middle position IIRC).

JR

 

[drew gandy]

Re: Two Bose 802 questions

Pretty much look at a mirror image of the EQ curve minus a little boom-sizzle. The old 901 EQ was pretty much flat in one of the positions (not the middle position IIRC).

JR

That's what I was doing earlier in this thread but:
A) I would like to have an SPL reference point.
B) I'm not sure how dramatic the "voicing" is(how much boom-sizzle).

As far as the amp spec thing goes, I really should have used a different term than "widespread". Since there are several metrics in the CAF there is a lot of opportunity for eyes to glaze over. What I see happening is that uneducated customers will be no more interested in understanding the CAF than they are in educating themselves, therefore shielding the primary sales impact of a new metric. The crowd that will have a better chance of making use of the in depth data (and therefore possibly affecting manufacturer sales of install specific amps) is the install contractor crowd. I hope that there will be some way for reliable 3rd parties (like Pat) to make complete CAF measurements for the majority of the interesting amplifiers on the market. Perhaps a consortium of contractors can pay for the measurements? I can imagine that many would be interested in the details and be able to apply them to system designs so it would have value. btw, I recognize that this is wishful thinking but hey, it's still Thanksgiving weekend.

 

[Ivan Beaver]

Re: Two Bose 802 questions

What I see happening is that uneducated customers will be no more interested in understanding the CAF than they are in educating themselves, therefore shielding the primary sales impact of a new metric. .

I bet if you asked the "average" user how much power they could pull from "the wall" they would not have a clue.

And then if you asked them if it made any sense that the device hooked to the wall (the amplifier) could produce more power than it was pulling-you would be met with a blank stare.

The whole idea of something that could produce more power than goes into it would be so far over their heads----------------.

But yet they would STILL talk about how much power it "puts out" without any sort of time constraint.

OH well-the marketing guys LOVE that type of customer. The one who does not question the spec and just believes everything they read.

The guys who dig a little bit deeper trying to get a real understanding are in the very small percentage of purchasers.

 

[John Roberts]

Re: Two Bose 802 questions

And even smaller yet is the number consumer who understands what a specification says, and has the judgement and perspective to relate that to an application. It almost always comes down to a decision tree involving is this spec good or bad with a bigger/smaller number, and is this amp more or less than that amp.

I am not aware that this is really a huge problem. Amp designers have been actually making these design decisions for decades, and consumers have learned which amps work or not.

As a design engineer I am very much a proponent of empirical objective metrics that can be used in design. It would sure make my job easier. The elephant in the room is that music is a bit of moving target.

If somebody wants to invest some brain cells on an industry standard define Q for me. .

@Drew... Look for the old 901 EQ curves, as I recall you could see the boom/sizzle more easily.

re: CAF again I am not aware of any problem with suitability of install amps to work as expected.

@ALL this will be moot as soon as the world goes completely powered speakers and the speaker engineers (like Ivan) get to spec the power amps inside.

JR