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Old 1st July 2002, 04:18 PM   #1
diyAudio Member
Join Date: Jun 2002
Location: UK
Default Artificial floating ground

Hi All,

This is my first post, so I hope it works ok!

While reading this thread:

much less crazy idea

I noticed the talk of generating floating grounds with big resistors, which reminded of the scheme that Quad used for their 306 amplifer (amongst others, I'm sure). By putting 2 smoothing caps in series, the voltage at their midpoint is roughly equal to half the total supply voltage. To ensure that it remains close to this point, two transistors are used to steer the point to the required voltage. This then forms the signal ground for the whole amplifier.

This arrangement offers DC protection for the loudspeaker - if one of the output devices saturates. the midpoint will be allowed to rise to the appropriate tail, thus avoiding damage to the speaker. The only drawback of this is both capacitors must be rated to the total supply voltage (unlike a conventional split supply, of course)

Hopefully, this might be useful if you happen to have a large mains transformer with a single winding...? Apologies if everyone already knows this!

BTW, click here for the
complete Quad 306 schematic
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Old 1st July 2002, 04:36 PM   #2
e96mlo is offline e96mlo  Sweden
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Join Date: Apr 2002
Location: Helsingborg, Sweden
The problem is that this is the same as a capacitor coupled speaker, only the capacitors are placed differently. All the speaker current still have to go through the capacitors and they need to be highly ripple tolerant.

But it is an interesting schematic.

I didn't get the quad link to work, though.

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Old 1st July 2002, 05:07 PM   #3
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Join Date: Jun 2002
Location: UK
Sorry about that!

Try this instead

The Quad306 link is towards the end of the list...

I wondered about the sonics, as it does appear to be equivelent to a simple series capacitor at a first glance. But, as the signal is referenced to this floating ground, I guess that feedback should help...
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