High Power Chip Amp

[a.wayne]

Andrew are you saying this in relation to chipamp's or in general ? If in general i would have to disagree. Horse's for courses and it would be difficult to build a large speakers system with a full and balanced bandwidth and maintain a Zmin of 8 ohms , well unless you started with 16 ohm speakers .

Also true amplifiers double when Imp Half's , a bonus on the SPL side 2 .....

[AndrewT]

Let's take a small PA example.
The Tannoy B950 has two 18inch 8ohm drivers in the cabinet.
A previous owner has added a second Speakon, now having a Speakon to each driver.
The Tannoy literature says to use a 1kW to 2kW into 4ohm amplifier.
Now that the twin inputs are in place, the speaker can be driven by a pair of 500W to 1kWinto 8ohm amplifiers or the cable could parallel the drivers and one bigger 4ohm amplifier could be used.

I now use a pair of 170W into 8ohm amplifiers to drive this speaker.
I know that a 340W into 4ohm amplifier of the same quality and topology will not perform as well as the twin 170W amplifier set up.

If I had designed the cabinet, I would have ensured each driver had it's own chamber and dedicated port, so that in the PA situation it would keep playing even if one driver or one amplifier had failed to off. If all of the chips were selected to have ~10A maximum current capability rather than the specification >=7A, then this triple chipamp setup could deliver upto 30A when cold and be suitabel for driving 4ohm reactive speaker loading if kept no hotter than warm.

I also know that the twin 170W into twin drivers produces exactly the same +6dB as a 340W into the twin paralleled drivers. So this is the introduction of a spurious argument that gets us no further forward.

Finally, re 8ohm nominal impedance, a real reactive 8ohm speaker can demand short term transient currents that are equivalent to three times the expected current that an 8r0 resistive load would demand. That would be saying that if the current demand never be worse than 8r0 then 24ohm drivers should be used for the speaker.
That is not my philosophy.
I design so that the amplifier can supply three times the rated nominal rated resistive maximum current into reactive loads, i.e. 60degree phase angle 8ohm loading at somewhere between DC SOAR and 100ms SOAR de-rated for maximum operating temperature.

Is it coincidence that I use three times the current of a resistor as the demand that must be met and that the PA150 (Rowland) also uses three parallel chipamps for three times the current demand?

[Mark Allen]

why put four 8ohm drivers in parallel and then drive them with a 2ohm capable amplifier? It makes no sense other than economy.
A four amplifier system driving four individual 8ohm drivers will be far more resilient if any component fails during a performance. This applies especially to PA, where the sound MUST GO ON.

Sure, it would be nice if the budget was typically there for it, I guess in your world there is no set budget!!! Welcome to the real world Andrew... I've installed many many 2 ohm and 4 ohm surround arrays and am usually able to obtain 115db spl with ease. You need to be able to reach at least this level for D-Cinema since it is uncompressed 96 khz digital audio. The surround channels in Digital Audio unlike Cinema DTS systems which drop out at 100 hz are full range. I'd have to go back in my files to show you some of the surround array response graphs as measured with my R-2 four mic system but they are generally very good (+/- 3to 4 db) as long as the room is treated properly. My experience has dictated that in cinema applications if you aim to meet THX specifications for Cinemas you'll enbd up with a killer sound system. Since aI service mainly independent theaters and Cinemas I have had the opportunity to creat some amazing sound systems. I have to confess that many of my customers sound systems sound better out in in their lobby then the average Large Multiplex sound system does in the theater!!

I know that a 340W into 4ohm amplifier of the same quality and topology will not perform as well as the twin amplifier set up.

If you purchase an amp that is designed to work into a low impedance load you will find it's specs and sound reproduction more or less identical as if you were driving an 8 ohm load. The Krells are good examples of the sound staying the same and still being able to drive low impedances or should we just say you can mor or less forget about what impedance you are driving with a Krell.

Mark

[a.wayne]

OK Andrew , now series the drivers as first suggested .....



We digress , will this chipamp in any of it's illustrious configurations drive a 1 ohm Load ?

[Mark Allen]

They would probably drive anything if you parallel enough of them. Say 8 or ten should easily drive a 1 ohm load. Each chip is capable of about 7 amps at operating temperature and a bit higher when cold. You'd also need to increase the power supply capacity as well. Andrew could work the math on this for us because he is fairly familiar with the 3886. Stop and think though that paralleling 8 or 10 or 12 of them would still be very cheap! They cost about 3 bucks each in quantity... I believe the three paralleled that I am using might actually do a 2 ohm load, for sure 4 ohms with ease... might need to go to four chips though for 2 ohms. I'm not the math expert here by any means...

Mark

[a.wayne]

Originally Posted by Mark Allen

They would probably drive anything if you parallel enough of them. Say 8 or ten should easily drive a 1 ohm load. Each chip is capable of about 7 amps at operating temperature and a bit higher when cold. You'd also need to increase the power supply capacity as well. Andrew could work the math on this for us because he is fairly familiar with the 3886. Stop and think though that paralleling 8 or 10 or 12 of them would still be very cheap! They cost about 3 bucks each in quantity... I believe the three paralleled that I am using might actually do a 2 ohm load, for sure 4 ohms with ease... might need to go to four chips though for 2 ohms. I'm not the math expert here by any means...

Mark

Then it would appear 8 would be necessary for 1 ohm operation ....

[AndrewT]

Originally Posted by Mark Allen

If you purchase an amp that is designed to work into a low impedance load you will find it's specs and sound reproduction more or less identical as if you were driving an 8 ohm load. The Krells are good examples of the sound staying the same and still being able to drive low impedances or should we just say you can mor or less forget about what impedance you are driving with a Krell.

I cannot comment specifically on the Krell's performance into different load impedances.
I have only heard my Krell Klone and was very disappointed.

But, all amplifiers perform better when presented with a higher load resistance. Few divulge specifications for any reactive impedance testing and certainly not for a range of differing reactive impedances.

I don't know how many speakers are used in a cinema set up. Let's suppose 40 speakers. in groups of 4 for 2ohm loading. That would require 10amplifiers of say 2kW into 2ohm. Now adopt the philosophy of one 500W amplifier for each 8ohm speaker. That would change the amplifier part of the budget from 10off 2kW into 2ohm to 40off 500W into 8ohm. An extra X dollars in how many hundred thousand dollars? Are we talking about 1% extra or 5% extra?

[a.wayne]

Originally Posted by AndrewT

I cannot comment specifically on the Krell's performance into different load impedances.
I have only heard my Krell Klone and was very disappointed.

But, all amplifiers perform better when presented with a higher load resistance. Few divulge specifications for any reactive impedance testing and certainly not for a range of differing reactive impedances.

I don't know how many speakers are used in a cinema set up. Let's suppose 40 speakers. in groups of 4 for 2ohm loading. That would require 10amplifiers of say 2kW into 2ohm. Now adopt the philosophy of one 500W amplifier for each 8ohm speaker. That would change the amplifier part of the budget from 10off 2kW into 2ohm to 40off 500W into 8ohm. An extra X dollars in how many hundred thousand dollars? Are we talking about 1% extra or 5% extra?

Andrew ,

How were you disappointed in your krell clones ? Did it perform better or worse than your chipamp?


PS: your analogy above does not add up ...

[AndrewT]

Originally Posted by a.wayne

OK Andrew , now series the drivers as first suggested .....



We digress , will this chipamp in any of it's illustrious configurations drive a 1 ohm Load ?

do not try to drive <4ohm speakers with chipamps, not even paralleled ones.
Series connect the drivers? certainly, or chipamp each driver. Chipamping each driver costs the same in PSU resources and the same in heatsink resources and the same in chipamp resources, as providing lots of chipamps in parallel to drive paralleled speaker loads/voice coils.

[AndrewT]

I put chipamps at the bottom of my ranking. They are designed for cheap mass production assembly to eventually power speakers in TVs and radios etc.
The Krell problem that I found was a stability problem, possibly brought about by my selection oc components. I awaited all the other builders testing their Klones, but to date, some two years later, very few have actually got any Klones running.
My Sugden ClassA is at the top of my ranking, all the ClassAB are between these extremes.

OOPS, I did buy a Cmark PA amp, but I daren't connect it to any of my speakers considering the quality of design and assembly inside that chassis. I suppose that is the lowest of my ranking. Doesn't say much for the chipamps though.

ps,
which analogy? Was there one?