I recently bid on a couple of LM 4780 IC's on eBay for $0.99 and won to my suprise. I didn't really want or need them (I'm an eBayaholic) but know I need to do something with them. I have tried to purchase some Beta's from a well known supplier of chip amp PCB's but have had a real hard time getting the individual to actually tell me how much and where to send the money to. I have given up on this source. I am wondering if anybody out there knows of a good PCB for this chip and how to get it. I would like to consider a standard 2 channel config from one IC as well as a paralleled or bridged version thus utilizing both IC's for 2 channels. I have considered a point to point but the more I look at all those pins crammed so close together the more daunting the task becomes. I am sure somebodys done it but I haven't seen it. Anyone out there got a good PCB for sale? Know of a source? If not, anybody need a couple of LM4780's, I know were they could find 2 for pretty cheap!
Thanks to all!
Jeff M.
Lawton, USA
Thanks to all!
Jeff M.
Lawton, USA
http://www.tech-diy.com/Audio_Designs.htm for either a specifically parallel or bridged setup, with the bridged not needing a balanced input. I'm currently using the bridged board from here.
http://www.audiosector.com/lm4780.shtml is a nice design that allows for dual channel, parallel or bridged all on one pcb design. The only reason I'm not using it instead of the above is the bridged setup requires a balanced input.
http://www.audiosector.com/lm4780.shtml is a nice design that allows for dual channel, parallel or bridged all on one pcb design. The only reason I'm not using it instead of the above is the bridged setup requires a balanced input.
The one problem I had was that R11 is not listed in the parts list, so I didn't buy it at the same time as all the rest of the parts. He still hasn't updated the parts list (even though I emailed him about it probably a year ago). That was for the bridged amp. Make sure you compare the parts list to the schematic!
According to the diy-tech web site the bridged boards are out of stock. He still has the Parallel and dual mono. You can always use the dual mono in a bridged mode with an external bridge adapter, or you can put it in bridge mode with two resistors added to the board.
(Tie a resistor equal to RF between the output of one amp and the junction of Rf the inverting input of the other amp. Then add a 100 ohm resistor from the non-inverting input of the amp whose inverting input you just added the new RF resistor. Details here:
http://sound.westhost.com/project20.htm)
(Tie a resistor equal to RF between the output of one amp and the junction of Rf the inverting input of the other amp. Then add a 100 ohm resistor from the non-inverting input of the amp whose inverting input you just added the new RF resistor. Details here:
http://sound.westhost.com/project20.htm)
I just received an email from the Tech-DIY store...they have boards available now, guess the site was not updated. How has y'alls experience been with the bridged mode of the LM4780. Is the quality of sould as good as BrianGT's Chipamp? I am hoping for better actually. What type of filtering capacitance have you used on the PSU as well as the trafo voltage? I have a 29-0-29 trafo out of a Denon that I am thinking might work but it will push the chip to the limits if my calculations are correct.
Thanks,
Jeff M.
Lawton, USA
Thanks,
Jeff M.
Lawton, USA
jmillerdoc said:
I haven't yet tried the LM4780, though I do have some samples and plan on buying some boards. I'll probably get either the parallel or the dual mono. The 29-0-29 transformer will give you almost 41 volts per rail which leaves almost zero safety margin as these chips will self destruct above 42 volts with ANY signal applied. 35 volts per rail is really the MAX you should use.
If you measured the voltage out of that transformer rather than saw the rating stamped on it you are quoting the no load voltage, in which case the actual working voltage might be more like 28 or 27 per leg. In this case you would have some more safety margin. I'd connect a bridge rectifier and 10,000uf 63v cap to it and measure the rectified DC voltage. If it's under 38v you will get away with it (BARELY!) any more than that I'd look for another transformer OR use a voltage regulator to drop the voltage down to 30-35 volts. Many have reported that these chips sound better powered off a regulated voltage supply with snubbers. There is a thread somewhere on this site about that.
It sounds great, but I've never built anything else to compare it to. I chose my own components based on quite a bit of research and leaned toward good value. I used 2x 15,000 uF caps on the power supply board (1 board for 2 channels, really abusing the power supply when I turn it up all the way) and 2x 1,000 uF on each amp board. I compared a couple of different power supply setups. You can read about it here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=129306
In a couple of weeks I will have built a LM3886 DC servo design to compare it to.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=129306
In a couple of weeks I will have built a LM3886 DC servo design to compare it to.
is it really a 29-0-29 transformer?
Measure the input mains voltage and the output secondary voltage with the secondaries unloaded.
Calculate the unloaded voltage for the nominal mains input voltage.
This answer is the rated voltage times the regulation factor of the transformer.
Vac unloaded = Vac Rated * [ 1 + regulation ] * Vac mains actual / Vac mains nominal.
Now calculate the Vac unloaded for maximum tolerance mains supply voltage (in the UK this is 254Vac for a 240Vac supply).
Use this to determine the worst case voltage that will be applied to the rectifier.
Measure the input mains voltage and the output secondary voltage with the secondaries unloaded.
Calculate the unloaded voltage for the nominal mains input voltage.
This answer is the rated voltage times the regulation factor of the transformer.
Vac unloaded = Vac Rated * [ 1 + regulation ] * Vac mains actual / Vac mains nominal.
Now calculate the Vac unloaded for maximum tolerance mains supply voltage (in the UK this is 254Vac for a 240Vac supply).
Use this to determine the worst case voltage that will be applied to the rectifier.
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