AudioSector-chip amp kits, dacs, chassis

[Peter Daniel]

Yes, it seems to be correct.

You will usually get more on secondaries than specified, as the rating includes regulation margin and the voltage is given for maximum current draw, which when you masure is not applied. Also, you need to allow for mains voltage fluctuation.

The voltage you are currently getting from transformers is still within limits for LM4780 chip.

[safetyman]

Originally posted by Peter Daniel
Yes, it seems to be correct.

You will usually get more on secondaries than specified, as the rating includes regulation margin and the voltage is given for maximum current draw, which when you masure is not applied. Also, you need to allow for mains voltage fluctuation.

The voltage you are currently getting from transformers is still within limits for LM4780 chip.

Thanks Peter, I am relieved and more confident now. How do I look for the voltage to work with in the LM4780 datasheet? I mean which is the section that has this information?

[Peter Daniel]

That would be:

Operating Ratings (Notes 1, 2)
Supply Voltage |V+| + | | 20V ¡Ü VTOTAL ¡Ü 84V

http://www.national.com/ds/LM/LM4780.pdf

[safetyman]

Originally posted by Peter Daniel
That would be:

Operating Ratings (Notes 1, 2)
Supply Voltage |V+| + | | 20V ¡Ü VTOTAL ¡Ü 84V

http://www.national.com/ds/LM/LM4780.pdf

Peter, does this mean I am operating at very close to the max allowable?

Are there any downside to this? Like I need a bigger heatsink or something? I am deliberating to mount each chip to the side of the amp wall which is a flat piece of aluminium 0.5" thick and 4" in height and about 10" long. One side is exposed to the ambient but has no fins. Would this be good enough?

Thanks.

[karma]

you making a toaster oven


ya 84v is the maximum im runing half that and my amp gets hot.


|V+|+|V-| = 80V
Supply Voltage |V+|+|V-| 20V = VTOTAL = 84V

Differential Input Voltage (Note 13) 60V

Output Current Internally Limited
Power Dissipation (Note 3) 125W Note: Operation is guaranteed up to 84V; however, distortion
may be introduced from SPiKe protection circuitry if

ESD Susceptability (Note 4) 3.0kV

proper thermal considerations are not taken into account.
ESD Susceptability (Note 5) 200V Refer to the Thermal Considerations section for more
Junction Temperature (TJMAX) (Note 9) 150°C information.

[sangram]

I don't think the chips will work properly with such low heatsinking, even if you are within the normal limits for voltage. I have my 4780s mounted to 5" Alu profile of 4 mm thickness and flower finning and extrusion. I estimate around 1.5 C/W for the heatsinks, and they do get quite toasty. Not enough to burn but not comfortable to hold. I'd say around 60 degrees C. And my DC voltage is just 32 volts (22VAC oversized transformers so as to not sag under load).

You should be fine with the voltages though, as long as your load is around 8 ohms. I'd say you drop a volt or two once you load up the secondary, and you should get a DC voltage of about 37-38 Volts per rail. Though high, it should be OK.

But you definitely need better heatsinking. 0.5" Aluminium is definitely too slim of a margin (pun intended). At best Spike circuitry may cut in in a few minutes.

[safetyman]

Originally posted by karma
you making a toaster oven


ya 84v is the maximum im runing half that and my amp gets hot.


|V+|+|V-| = 80V
Supply Voltage |V+|+|V-| 20V = VTOTAL = 84V

Differential Input Voltage (Note 13) 60V

Output Current Internally Limited
Power Dissipation (Note 3) 125W Note: Operation is guaranteed up to 84V; however, distortion
may be introduced from SPiKe protection circuitry if

ESD Susceptability (Note 4) 3.0kV

proper thermal considerations are not taken into account.
ESD Susceptability (Note 5) 200V Refer to the Thermal Considerations section for more
Junction Temperature (TJMAX) (Note 9) 150°C information.

karma, the problem is that the torroids available here have either 18V secondaries or 25V secondaries. !@#$ Don't tell me I wasted 2 new transformers.

Originally posted by sangram
I don't think the chips will work properly with such low heatsinking, even if you are within the normal limits for voltage. I have my 4780s mounted to 5" Alu profile of 4 mm thickness and flower finning and extrusion. I estimate around 1.5 C/W for the heatsinks, and they do get quite toasty. Not enough to burn but not comfortable to hold. I'd say around 60 degrees C. And my DC voltage is just 32 volts (22VAC oversized transformers so as to not sag under load).

You should be fine with the voltages though, as long as your load is around 8 ohms. I'd say you drop a volt or two once you load up the secondary, and you should get a DC voltage of about 37-38 Volts per rail. Though high, it should be OK.

But you definitely need better heatsinking. 0.5" Aluminium is definitely too slim of a margin (pun intended). At best Spike circuitry may cut in in a few minutes.

What if I attach fins to outside of the 2 flat side panels? Would that work? This LM4780 is in a parallel configuration? And BTW, what value resistors do you use to place across the output during the running in period?

Thanks guys.........Opinion most welcome.

[mcamolin]

Hi Peter, you think work fine your kit dual mono xlm3875x with a transformer x300VAx that have secondaries 25 0 25.
Thanks

[Peter Daniel]

2 x 25V, 300VA transformer will work fine (providing the speakers are easy load). It is my observation that the higher the voltage, the better the sound.

If amp runs too hot, just encrease the heatsinks (adding fins is fine), but even temperatures of 50-60 deg C are OK (Yes the chip amp can run that hot if pushed).

[safetyman]

Originally posted by Peter Daniel
2 x 25V, 300VA transformer will work fine (providing the speakers are easy load). It is my observation that the higher the voltage, the better the sound.

If amp runs too hot, just encrease the heatsinks (adding fins is fine), but even temperatures of 50-60 deg C are OK (Yes the chip amp can run that hot if pushed).

Peter, thanks for your response. Actually, my casing will be aluminum on all 4 sides. The left and right side where the amp is going to be attached to is 4" (H) X 8.5" (D) X 0.5" (thick), and the front and back is 4" (H) X 11.5" (W) X 0.25" (thick). I would rather not add fins if possible. The bottom will be a piece of wood off a nice chopping board and to show your beautiful PCB, the top will probably be acrylic.

My speakers are a pair of Epos ES11 which I believe they are about 87-88 dB sensitivity. No idea on impedance though, but I guess it will depend on the music played too.