Projects for next hollidays (the world smallest VBITNGC??)

[Franz G]

Ok, what about using +-12v instead of +-25v ?

No! Why?

This is the limit of the "undervoltage protection" from the LM3875, the muting point.

And with +/-12 V, I get less output.

Dont forget: it is absolutely theroetically, to play a 1kHz sine 10 minutes.

When I use the amp under normal conditions, nothing is getting hot or warm.

Franz

/edit: this amp is designed for about 20W, this is depending on the Vcc, the gain and the input voltage.

[Upupa Epops]

Franz, it is norm about home audio and video electronic. Warm up of amp is there defined : Load amp at 8 % of nominal power and let him run four hours. After this time upwarming of any by finger touchable part ( heatsink ) can't uprise over 40 °C above temperature of surroundings, but not more than 60 °C. Little explanation : nominal power is power declared by manufacturer, what is in your case 22 W .

[Franz G]

Thanks, Upupa

This is interesting!

And my amp can run many days under this conditions! Easily.

Franz

[janneman]

Originally posted by Upupa Epops
Franz, it is norm about home audio and video electronic. Warm up of amp is there defined : Load amp at 8 % of nominal power and let him run four hours. After this time upwarming of any by finger touchable part ( heatsink ) can't uprise over 40 °C above temperature of surroundings, but not more than 60 °C. Little explanation : nominal power is power declared by manufacturer, what is in your case 22 W .

Upupa,

Interesting indeed. Do you have an idea where this spec comes from? The only one I am familiar with is the IHF (USA) preconditioning, which states (IIRCFTTOMH) 1 hour at half of max output power. That is quite hard on the amp, because at half output power the actual dissipation in the output stage is approximately at it's highest.

Jan Didden

Edit: Not sure, maybe it was 1/3 or even 2/3 of output power?

Edit2: It's 1/3 power for 1 hr:

"After checking for continuity and the optimal grounding between the device under test and the Audio Precision System One test gear, my usual routine for an amplifier review is to run the amp for 60 minutes at 1/3 power into 8 ohms. This preconditioning both thermally stresses the amplifier and makes sure its operating conditions have stabilized.

With the Bryston 14B-SST, however, not only was its chassis too hot to touch after just 20 minutes of driving 200Wpc into 8 ohms, it turned itself off after 25 minutes. While this IHF-recommended test is very much the worst case for a design with a class-B output stage and it is unlikely the 14B-SST will get this hot under normal use with music, it does suggest that the amplifier's heatsinking is underspecified for continuous use at high levels. "

[Tekko]

Ah i forgot the under voltage protection Sorry Was thinking of the STK series that has no protection circuits at all that could run on a button cell. I am such a stupid idiot.

[PMA]

Originally posted by janneman

1 hour at half of max output power. That is quite hard on the amp, because at half output power the actual dissipation in the output stage is approximately at it's highest.


Edit: Not sure, maybe it was 1/3 or even 2/3 of output power?

Edit2: It's 1/3 power for 1 hr:

And great many amps fail during this test - not only for heatsink temperature reason, but their temperature protection switches them off. These are only "products for pleasure", nothing serious, even if they cost thousands of USD. Funny world, try this in an industrial automation project. You get 10x less money and you need to fulfil 100x better reliability.

[Upupa Epops]

Curve of thermal dissipation is relatively very flat in " middle area " of output power, so I mean, that in this norm is good rendered upwarming of amp by relatively low volume levels.

[demogorgon]

Originally posted by Tekko
Ah i forgot the under voltage protection Sorry Was thinking of the STK series that has no protection circuits at all that could run on a button cell. I am such a stupid idiot.

Now, dont be so hard on your self, we all forget or missplace things!

[digi01]

Spring coming,my mood is very good.

[Franz G]

Boahh, looks very fine with the new boards, Digi!

But there seems to be a problem with the picture.

I am looking forward, to see a mini gainclone in Bejing!

Franz