Paralleled Amp4? Same as Amp11?

[krilli]

Hi,

What do you have if you take the stereo outputs of an Amp4 and parallel them into a 4 Ohm load?

Excluding the relay, isn't this essentially the same amplifier as an Amp11, topology- and power-wise?

[krilli]

Interesting! Thanks for the answer. What would you say is the main significance of the AOUT1 -> INV1 connection? Can't wrap my head around it.

[krilli]

OK now I get it. Thanks.

I would be feeding it with ... hmm. Depends :) This was more of a gedanken-forum-posten.

It's mostly that I like flexibility, when it comes for free. E.g., instead of getting an Amp11 to use as a mono amp, I was wondering if it would make sense to get an Amp4 instead, which can be the same mono amp when summed, or a stereo amp with stereo channels, or a biamping-amp, with a mono signal crossed over high/low.

... edit: and to me, it would make sense, for my personal amp, because I understand what's going on in it. I'd question if it made sense when building for electronics-naive people.

[mikechw]

I am building a pair of AMP4 with DDX2240.

Planning to use 39VDC, need to upgrade several components on the board.
2x10000uF 35V bulk caps
2x1500uF 35V close in caps
1x330uF 35V caps near the 1st LM317 regulator

DDX2240 is rated 6A compared with ST505's 3.5A
From the datasheet it says 1%THD 100W into 6ohm.
I think it could drive 4ohm loads 2 x ~60WRMS 1%THD

Now I am sourcing the power supply, either get a 28VAC transformer or a switch power supply.

[krilli]

I am very much looking forward to hearing more of that amp, mikechw.

But isn't it more like 2 x 4 Ohm loads at 100W, at 0.01% THD?? I'm calculating it back and forth and I always get around 100W.

http://www.google.com/search?q=60%25+of+45%25+of+%2839V+*+39V+%2F+4+Ohm

That's a 200W+ Amp11!

[mikechw]

Well,

DDX2240's datasheet stated that <1% THD 100W 39VDC into (6ohm Full Bridge)
I x I x R = Power
so I calculated the current = square root of ( Power / R )
= sqrt( 100 / 6 ) ~= 4A

I just assume 4A's current will render <1% THD, so
4A x 4A x 4ohm ~= 64W
May be a little conservative...:D

For AMP11 ==> Parallel output ==> (4A x 2)x(4A x 2)x4ohm ~= 250W

:)

For AMP4
I suppose 39V / 4 is 9.75A, so I think over current protection will trip over with 4 ohm load. (My speakers impedance is 6ohm)
6ohm load ===> 39V / 6 is 6.75A.
8ohm load ===> 39V / 8 is ~5A.

[mikechw]

Actually I compared ST's STA505 with APOGEE's DDX's range chip.

STA505's datasheet specified THD value much lower than APOGEE's DDX2100

May be they are measured with different evaluation boards and the chip that is driving the power chip are different.

[krilli]

We shall see :)

Yeah, I looked at the datasheets, not too much, but to me it looked like it was mostly the driver chip that caused the lesser performance numbers.