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 .....
Also true amplifiers double when Imp Half's , a bonus on the SPL side 2 .....
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?
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?
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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!!
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
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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
Mark
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 ...
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do not try to drive <4ohm speakers with chipamps, not even paralleled ones.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 ?
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.
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?
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?
The extra cable, the extra cable runs by labour, extra mains outlets to plug in all these amp, extra harnesses to hook everything up, more extra labour extra, extra.... It's never as simple as it seems.
Fix has his Krell up and running , all seem well there , Hmmm it even made 700 watts into 1 ohm ...
Methinks he finally heard the screech of the amps that are special made for loud clear voiceband in tv use. Yes, the majority of chipamps are either severely underpowered and/or should be bolted to their own dedicated speaker because of other performance issues (such as sounding like a tv amp).
Instead of having a big chip amp run in parallel mode to turn its own screech into heat (LM3886's don't make that noise at exactly the same time, so that triple-parallel removes the noise on PA150), thus eventually resulting in clean audio. . .
Even though that works just fine. . .
I'd prefer to do it a different way.
Since the majority prefers the sounds from LM1875, why not bridge it so that it becomes a pre-drive for a reduced parts count solid state amp? Is it impossible to do a nice job with this? I've never seen it fully implemented. It seems that this would be a useful introduction (springboard) into projects that aren't fully sealed shut inside a chip.
P.S. ABS Max volts for long life LM1875 is 26.5+26.5vdc regardless of load. However, that's still a pretty healthy shove as a pre-drive. It can scale to a massive amp. Howabout it?
I've had both of my Krells up and running for at least a couple of years now but hardly ever use them. I prototyped the first batch of PCBs for both of those amplifiers. No stability problems at this end on either of them and the Krells are well known for their excellent stability into any load. Not sure what you did especially considering your easy loads there.
Just because the chip amp chips are cheap doesn't automatically deny them from being the high quality performers they really are. You can't discount the reviews that Peter Daniels gets with his Patek 3886 based amplifiers!! Parallel as many as you like just as Nelson Pass parallels gobs of tiny fets... You can do anyhthing with any device if you put your mind behind it! The BPA 300 running here in stereo mode is certainly far superior to all the amps I have here and by a long shot. You can do all the math or what ever you want, spend alot or a little but the only thing that matters in the end is how it sounds.
Mark
Just because the chip amp chips are cheap doesn't automatically deny them from being the high quality performers they really are. You can't discount the reviews that Peter Daniels gets with his Patek 3886 based amplifiers!! Parallel as many as you like just as Nelson Pass parallels gobs of tiny fets... You can do anyhthing with any device if you put your mind behind it! The BPA 300 running here in stereo mode is certainly far superior to all the amps I have here and by a long shot. You can do all the math or what ever you want, spend alot or a little but the only thing that matters in the end is how it sounds.
Mark
The TI hybrid can do 2 ohms in single channel BTL and it only costs about $7 each in quantity. Then there's the very significant savings from the reduced power supply and heatsinking requirements. (Unfortunately, if you buy a kit, the hybrid premium cuts into the savings. But the lower operating costs mean you'll be saving anyways.)
Any more power than that and a discrete hybrid or pure digital makes the most sense. After all, the main motor inverter in an EV is basically a very big digital amplifier that outputs up to hundreds of kilowatts.
If you're looking at high power, a hybrid or pure digital using discrete power electronics is the most cost effective. FDPF52N20T MOSFETs (200v, 52A) only cost $1.37 each in small quantities! FDPF52N20T Fairchild Semiconductor MOSFETs
I was going to try to argue with this and say that output transistors cost less for big amps. That idea failed somewhat.
However, parallel does make for cancellations, in this case used to quite good effect in making LM3886's fight off their own noises (that don't occur precisely at the same time). Unfortunately, if you were to cause enough cancellations then you also erase audio that is similar to the cancellations.
That is the point (beyond a carefully made pa150/bpa300) where output transistors start to get obviously more competitive on making clean audio.
The cancellations from paralleling can be reduced as well as the heat when the output devices are matched. Matched Lm3886's scale to pa200/bpa400. UNmatched output transistors scale to pa200/bpa400. Matched output transistors scale upwards of 1kw. Heatsink expense is decreased in proportion to cleaner audio from output transistors. And, the thermal interface area is considerably larger.
I'm not talking about a complex and dizzying time analyzing all of the possible options of a discrete preamp/predrive. What I'd like to see is a ready solution involving a chip-based bridged predrive running 8 output transistors per channel (bridge+parallel). Preferably, it can be "bugsplat" wired without a circuit board, in 20 minutes or less to result in a very powerful high fidelity amplifier. Design? Anyone?
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