GCs and ESL

[Nuuk]

well, apart from the current output. I currently have +12 spare LM3875TF chips and no idea what to do with them?

Better get over to Decibel Dungeon straight away!

 

[nina]

If you want power, you can use the STK4048xi chip! It gives you at least 150W per chanel

I had tried the STK4046 (w/ DC servo) over the 4 Ohm speakers, and the result was awful. I don't think the STK404x is suitable for low impldence load at all.

However, I once saw a schematic they use a STK4048 (as Voltage gain) with 8 external power MOSFET as a 200Wrms PA amp!!

 

[nina]

Better get over to Decibel Dungeon straight away!

Just visit the "Decibel Dungeon " site. There are many interesting things to read on. BTW, what project/pages you actually refering to?

 

[Nuuk]

BTW, what project/pages you actually refering to?

Take your pick - it's all free!

The GC pages were what I was thinking off, or how about the active speakers in the DD project section? That would use up four of your chips!

 

[carlosfm]

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

I_F

I know, in bridge mode it will, but only at almost the full PSU voltage rating.
Not what I would use for this type of speaker.

 

[I_Forgot]

But can I ask what are your rail voltages as I am informed that the maximum voltage swing (p-p) when driving the Quads should be no more than 36 volts?

I believe its +/- 25V. Where does the 36V figure come from?

I_F

 

[carlosfm]

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

While some are recommending you power, power, power... I recommended you to use a slightly lower voltage PSU and parallel chips if needed.

Check this out:
http://www.quadesl.com/quad_main.shtml

Quote:
"But the Quads also have some downsides. First, they are fragile. They need about 15 Watts of the best amplification you can get your hands on (see the Heathkit UA-2 EL84 (6BQ5) or Fisher SA-16 amps). If you use a larger amplifier or try to overdrive the speakers, you risk arcing. Arcing occurs when the potential across the stator panels is sufficient to ionize the air and spark across the gap and through the membrane. Arcing will ruin the panels, if it occurs enough times or is severe. The Quads will play up to about 100 dB, which is much louder than I play music even when playing loudly. The second downside is that they are a difficult load for the amplifier to drive. They are highly reactive loads (primarily capacitive). Their impedance drops as the frequency increases."

 

[Nuuk]

Thanks Carlos, it was partly due to reading that , that I started this thread!

I_Forgot, here is something that a Quad ESL57 owner sent to me. I hope that he won't mind me quoting him here!

Bear in mind that anything over 36V with arc the Quad ESL, causing (repairable) damage to the panel. Therefore the amplifier power supply should be configured so as to limit the maximum voltage swing (p-p) to voltage below this.

 

[I_Forgot]

"But the Quads also have some downsides. First, they are fragile. They need about 15 Watts of the best amplification you can get your hands on (see the Heathkit UA-2 EL84 (6BQ5) or Fisher SA-16 amps). If you use a larger amplifier or try to overdrive the speakers, you risk arcing. Arcing occurs when the potential across the stator panels is sufficient to ionize the air and spark across the gap and through the membrane. Arcing will ruin the panels, if it occurs enough times or is severe. The Quads will play up to about 100 dB, which is much louder than I play music even when playing loudly. The second downside is that they are a difficult load for the amplifier to drive. They are highly reactive loads (primarily capacitive). Their impedance drops as the frequency increases."

That blurb is about the older ESL 57s, not the 63s. The 57s did not include any protection circuits to prevent arcing as do the 63s. They had separate bass and treble panels and the diaphragm to stator spacing of the treble panel was very small, on the order of a mm, if I recall correctly, making it very easy for the diaphragm to hit the stators and to get arcing between the stators. Hence the warnings about limiting amplifier power.

Don't worry about having too much power available in your amp. Remember, you can't drive more power into the speaker without the sound getting louder. There are very few ESLs, both amateur built and commercial, that won't get uncomfortably loud before any damage occurs. If it's too loud, turn it down.

Before my lm3886 amp, I used a 200W/ch amp to drive both my home-built and Quad ESLs. I never damaged either, though on one occasion I did manage to trip the protection circuit in the Quads.

I_F