GC SuperSymmetry

[jh6you]

Originally posted by stappvargen

a net shop

I have no idea. I bought it at a shop (Busan, Korea) where music lovers often visit.

Regards

[Mikett]

From a DIY perspective, the 4780 looks very tempting. Using the spreadsheet that National provides one sees that the 4780 requires good heatsinking and simple screws may not suffice and clamps are recommended.

I think that using two 3886s may provide a good compromise. Why? the pinout is not as dense as the 4780, thus more tolerant of sloppiness 2. You can get insulated and noninsulated versions 3. You get more surface area to dissipate the heat. This will tolerate non ideal heatsinking and provides that extra margin.

Don't forget that with the GCSS, the bridging arrangement provides for nearly doubling the apparent rail voltage. So operating the GCSS at 20-25 volts provides for apparent high rail voltages.

http://www.national.com/appinfo/audi...gn_Guide14.xls

[Russ White]

I definitely think either the dual LM3886 or single LM4780 per channel is the most ideal. Having build both the 3875 and 3886 I find the 3886 is able to drive hard loads much better. The 3875 really limps on the 4 ohm loads I have tested. Don't get me wrong, they both sound great. But a lot of us really need that extra current the 3886 can deliver.

Ultimately a think two paralleled 4780s per channel would be an incredible solution able to drive most anything, but some may find it complex.

FWIW I have found that heat disapation for the 4780 is not a problem for most uses, it seems really that only when you start bridging them that heat can be a significant issue. I have 6 channels of parraleled 4780s running on a single 12"x4"x1" 16 fin passive aluminum heatsink with no overheating issues whatsoever. So heat dissapation should not be a major consideration here.

I do a agree that the 3886 pins are much easier to work with, those pins on the 4780 are really close together, but on a PCB I really find it not to be a big deal. Now for P2P on the other hand....

[jh6you]

Richard Bona
Reverence


GCSS/ MSS(paralleled): GCSS has bass guitar sound, which tails fade quickly. I do not know why. It is as if to be due to thin sound waveform near the crossover line. It sounds as if the diminishing amplitude of the sound wave suddenly disappears near the crossover line. By the way, voice quality of GCSS has more charm than MSS(paralleled).

Regards

[Peter Daniel]

For some reason I missed that thread (and the recent developments). I would definitely like to try that circuit. My latest LM4780 board may come quite useful here, as it allows bridge configuration now (as well stereo and parallel), providing completely separate two channel inputs and outputs. One only needs to add the input circuit, which I would be very tempted to build around 2SK389.

[vinay]

[QUOTE]Originally posted by Russ White
[B]I
FWIW I have found that heat disapation for the 4780 is not a problem for most uses, it seems really that only when you start bridging them that heat can be a significant issue. I have 6 channels of parraleled 4780s running on a single 12"x4"x1" 16 fin passive aluminum heatsink with no overheating issues whatsoever. So heat dissapation should not be a major consideration here.

Russ,

when you say 6 channels of parralleled 4780, do you mean 6 chips or 12 chips. Also what voltage are you running this at?

Thanks, Vinay

[Russ White]

I have six of Brian's LM4780 boards each with one LM4780 with its two channels paralleled. I am running two snubberized PSs each with an Avel 500VA 25V dual secondary toroid. So three on each PS.

[Russ White]

I don't remember the exact rectified voltage but it was in the mid 30s.

[vinay]

Russ,

what is the thermal resistance of the heatsink you are using?

vinay

[Russ White]

I have no idea what the thermal resistance is, because I do not know how to measure it. I bought the heatsink at a scrap metal shop.