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.
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.
That would be:
Operating Ratings (Notes 1, 2)
Supply Voltage |V+| + | | 20V ¡Ü VTOTAL ¡Ü 84V
http://www.national.com/ds/LM/LM4780.pdf
Operating Ratings (Notes 1, 2)
Supply Voltage |V+| + | | 20V ¡Ü VTOTAL ¡Ü 84V
http://www.national.com/ds/LM/LM4780.pdf
Peter Daniel said:
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.
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.
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.
Attachments
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.
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.
karma said:you making a toaster oven
ya 84v is the maximum
|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.
sangram said:
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.
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).
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 Daniel said:
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.
Well, I'm just about finished with my lm3875 amps and should be starting the all-in-one dac kit in the next week or two.
The new buffer boards caught my eye, as have TVC's and AVC's.
If I wanted to use the buffers between the dac and gainclone, would something like intact audio's AVC work well at the input of the buffer?
I also had a question about heatsinking.
With an 18V-0-18V 160VA transformer per channel, would a 4" long 1 1/2" square aluminum bar work for both shielding and heatsinking?
Thanks
The new buffer boards caught my eye, as have TVC's and AVC's.
If I wanted to use the buffers between the dac and gainclone, would something like intact audio's AVC work well at the input of the buffer?
I also had a question about heatsinking.
With an 18V-0-18V 160VA transformer per channel, would a 4" long 1 1/2" square aluminum bar work for both shielding and heatsinking?
Thanks
mcamolin said:
Maybe he is overloading the amp's input. Without more info on source equipment it's really hard to comment.
mcamolin said:
The choice of transformer depends on the speakers. If they are easy, 8 ohm load, 2 x 25V will work fine. I'd rather prefer 2 x 24V but it's harder to find trafos with that rating. Personally, I'm using 2 x 22V, 300VA toroids, as this gives me better compatibility with most setups.
sdedalus said:
Such bar seems a bit small, even for one channel, but if speakers are easy to handle it may be still OK. However, a square tubing of that size would be more efficient in heat dissipation. Unless the bar is connected to other, metal, chassis parts.
Regarding buffer, I'm not familiar with intact AVC, but I find that the buffer works very well at the DAC's output and resistive attenuator directly at amps input. I think that it may be equally suitable to replace resistors attenuator with TVC or AVC.
I don't really feel like I need a buffer after the attenuator. The buffer has 6 ohm output resistance and improves substantially driving capabilities of any source.
I will soon have all the required semiconductors and buffer kits will become available.
I'm also working on an attenuator project that will complement the buffer for a nice line stage: http://www.diyaudio.com/forums/showthread.php?postid=839425#post839425
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