GCs and ESL

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The problem with some ESLs is that they have very low impedance at high frequencies, and that can cause some solid-state amps to trigger the protection circuits.
Maby a 3//LM3886, with 0,47R in series with each output would work fine.
And a PSU voltage at around +/-24V, no more than that.
Nuuk said:
Do you really think that it would take that much? I have heard of an LM3386 with just 1000 uF caps running Martin Logans without problem.

Yes, it depends on the speaker.
Some ESLs have less than 1 ohm impedance near 20Khz.
For some amps this is a short.:hot:

Try it first with a single chip, and a big heatsink.
If it gets very hot and kicks in the over-tempreature protection, you know you have to do something.
I drive a pair of Quad ESLs with my LM3886 amp daily. I put the standard parallel LR in series on the amp output and have never had the amp complain about the speakers at all. It sounds great, except that the 30W or so I am getting from the amp per channel is a little low for those speakers, limiting the distortion-free playback volume to something a little below bleeding ear drums level.

My amp is in an aluminum box with 1/4" thick sides and a cover that is all 10" x 13" heatsink with numerous fins. The amp chips are bolted to the cover of the box. I have never been able to detect more than 1 or 2 degree rise on the amp's cover, no matter how loudly or how long I play the amp. If I recall correctly, the transformer is a 320 VA and supplies both channels. I have about 112,000 uF in the power supply.

It is not necessarily true to say that ESLs are low Z at high frequencies. It is true that capacitors are low Z at high frequencies, but ESLs are much more complicated than a simple capacitor. If you test the impedance of an ESL with its transformer(s) you'll find that the impedance varies all over the place, inductive at some frequencies and capacitive at others. Typically it dips pretty low at some frequencies, and tends to go quite high at low frequencies. The impedance of the speaker also varies somewhat with the amplitude. None of that should make much difference if the amp has a low output impedance.



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I_Forgot said:
Sure it will, but why use multiple chips in parallel when you can make a much simpler circuit with one or two chips that provides the same output power?

Sure, the same output power, but only at 8 ohms.
Two or three paralleled chips is as much as it could be needed for driving low impedance loads, even the most demanding like some ESL speakers.
Current output is more important, paralleling chips makes the amp have more power at low impedance loads.
The power figure is the same at 8 ohms, but it's not the same at 4 and 2 ohm loads.

I_Forgot said:
You can get 120W out of a single LM4780.

With a single chip you can't.
XELB said:
If you want power, you can use the STK4048xi chip! It gives you at least 150W per chanel :cool:

That chip is recommended to work with 8 ohm loads.
Do you think this is a good match for an ESL speaker?
I see plenty of misleading ideas about power, really.
It's not the solution for everything.
Besides... 150w is only double the power of 15w.:clown:

I don't think you are reading this thread, are you?
You need good current to drive difficult speakers, power is not the miraculous solution.
Do you always follow recomendations ? :dead:
( Try the chip in 4Ohms ;) )

But you are right! I think it's the hour I should be in bed, here is 2:30 AM :D What that is there ? :clown: :p

As I told before, ESL need a lot of current.
Sanyo have an STK ideal for 3/6 Ohms, it's the STK401-330.
I don't know where this idea about ESLs needing lots of current comes from. I suppose it must be from the simplistic view that an ESL is a capacitor. Think about it for a minute. Even if the impedance dropped to a low figure at very high frequencies, the energy in music at those frequencies is not so high, so the current required will not be so big.

If you want to play low frequencies loudly with a dynamic speaker, the impedance is typically low at low frequencies, and the music tries to drive lots of current into the speaker. An ESL is just the opposite- at low frequencies it is usually pretty Hi-z (and inductive), so it doesn't need a lot of current. It needs a large voltage swing. That is why people try to use high powered amps with full range ESLs. High powered amps are capable of higher output voltage swing. Esls are not known for their high sensitivity.

The impedance of ESLs is "all over the place" when you look at it over the entire audio band, as is the impedance of most "conventional" drivers. Sure, ESLs may have some points where they look more capacitive than your typical dynamic speaker, but I don't think it is reasonable to make a blanket statement like "ESLs need high current".

I drive ESLs with relatively low powered amplifiers all the time, and like I said in an earlier post, the 30W per channel I am driving my ESL-63s with now is OK unless I really want to crank it up- and I do mean to ear bleeding levels.

The real issue in driving ESLs is amplifier stability. That is usually handled by the old standard parallel RL on the output.

Oh yes, the front page of the data sheet of the LM4780 says it WILL drive 120W in bridged mono.

As ever, there is no substitute for experience and I_Forgot has 'been there, done that, and got the postcard'!

The recommendation for Quad ESL's does seem to be for a lower powered amp with something like the Quad 33 quoted as 'ideal'.

I_Forgot, what LR are you using on your 3886? Is it the 10R/0.7uH from the data sheet or something different?

I see my old Arcam A60's came with 2R2/2.2uH! :att'n:

It may be a good experiment to try a 3886 GC with both a lower voltage supply, eg 27 VDC and higher, eg 35 VDC to see (or hear) if there is any difference.
BRIANGT GC and Hybrid

I do use a chipamp gc with a set of hybrid speakers (van Medevoort, best described here (http://www.tnt-audio.com/casse/vanmedevoort150_e.html))

It does run warm, touchable still, without heatsink, just a Al sideplate, size comparable to the original size of 47-labs. It does run at little higher temmperature compared with using it on my celestions 3.

As far a sound concerned it does sound substantially better then my 15 year old Rotel 850 bridged monoblocks (leaky capacitors?! at PSU).

At the moment I am in the process of changing over to snubberized PSU of the GC.

Next step in mind is to change to active crossover. I once build and enjoyed extensively the Old Linkwitz Design of the early 80's. The imaging (espacially depth) of that system I have never heard again. The satelites were housed in cast concrete and dampened with bitumen to get rid of the ringing of the concrete. In the end they had a low WAF and the dedicated 5-channel PA did cease.

Back to the main topic, can you drive an ESL with a GC: as far as I am concerned yes. The ESL range of these speakers is 400 Hz and higher. At high levels (I don't know dB's or Watt's) the GC turns the protection on. Happened only once and I just retried to see wheter it was a one time occurance or not; it was not. Music played was female voice, so lots of energy required in the mid-high end of the frequency range.

My question is what an additional inductor/resistor is supposed to accomplish, giving a "fake" impedance for the amp to "see".
You get your amp under control, but do you get your speaker under control?

I do think straight paralelling is an interesting idea, not being an EE, what would be the best way for PSU setup?

Nuuk said:

The recommendation for Quad ESL's does seem to be for a lower powered amp with something like the Quad 33 quoted as 'ideal'.

I think that idea arose because when Quad first started selling these speakers that was the amp they had available, and so the speakers were designed with sufficient sensitivity to be driven by that amp. I don't think it is optimal to use low power. I think this is also where the myth about tube amps and ESLs comes from.

I_Forgot, what LR are you using on your 3886? Is it the 10R/0.7uH from the data sheet or something different?

I am using the data sheet values.

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