Hey Tweety, check out this post
http://www.diyaudio.com/forums/showthread.php?postid=1170936#post1170936]usb dac
Gives a price for the DAC. Peter said that the USB dac was the same price as this.
http://www.diyaudio.com/forums/showthread.php?postid=1170936#post1170936]usb dac
Gives a price for the DAC. Peter said that the USB dac was the same price as this.
I am building one of your 4780 kits, but am having a problem.
I hooked up one of the power supply boards to make sure that everything is hooked up and working, but it smoked a few of the diodes and blew the capacitors off of the board. I can't see my error, the only thing that I can think of would be the caps being on backwards, but I am pretty sure that they're on correctly. Can you look at the picture and tell me if you can see my problem. I haven't connected the power supply board and chip board, and didn't on the one that I smoked either. I am using this transformer. The picture is of the board that I haven't hooked up yet.
I hooked up one of the power supply boards to make sure that everything is hooked up and working, but it smoked a few of the diodes and blew the capacitors off of the board. I can't see my error, the only thing that I can think of would be the caps being on backwards, but I am pretty sure that they're on correctly. Can you look at the picture and tell me if you can see my problem. I haven't connected the power supply board and chip board, and didn't on the one that I smoked either. I am using this transformer. The picture is of the board that I haven't hooked up yet.
An externally hosted image should be here but it was not working when we last tested it.
phatcenter77 said:
The black stripe indicates metal tap on the diodes, yours are reversed. This is how they supposed to be mounted: http://www.diyaudio.com/forums/attachment.php?s=&postid=636576&stamp=1115409640
I understand where the confusion may be coming from. I didn't post the pictures of rectifier board for LM4780 chip, only for LM3875 and those have diodes mounted opposite way. Just look for black stripes indicating proper orientation.
Transformer selection; interaction between speaker impedence/supply voltage/power out
Hello,
I'm trying to decide what power supply voltage (and thus transformer rating and heat sink) to use with one of Peter's LM3875 kits.
He posted previously that the higher the rail voltage, the better the amp sounds. My speakers are nominally 8 Ohm, 96db/1W, two-way passive. Although I don't have a Z-curve to see how far Z varies, I am aware that it could be well below 8 Ohms in places.
Page 10 of the datasheet for the LM3875 (http://www.national.com/ds.cgi/LM/LM3875.pdf) shows the attached graph of output power vs supply voltage, for R=4,6 and 8 Ohms, but for a purely resistive load.
Now, 2x25V transformer will give ~±35V rail voltage (1.4 x Va, minus diode losses I put at zero).
Let's assume that Z drops to 6 Ohms from, say, 300-1000Hz, but is higher elsewhere - leading to the nominal 8 Ohm rating.
With rail voltage at 35V, one infers from the R=6 Ohm curve that the chip could supply only 20W at those frequencies, but nearly 60W at frequencies where Z was 8 Ohms.
I don't fully understand the interactions between these variables or whether this inference is well founded. (Or if I should be concerned at all - no-one seems to experience this
)
Any comments?
I've contacted the speaker manufacturer for a Z curve, but if one is not forthcoming, how could I measure it myself?
Back to transformers, here in Switzerland I can source Block, Intronic, Sedlbauer and Toroid. Any comments on these manufacturers?
And finally, is 300VA overkill for dual monoblocks? My speakers roll off quite high and I have an active mono sub (which won't be powered by a GC, for now). I'm looking for dynamics/detail with the GCs and understand that a lower VA transformer might be more apt if weighty bass is less of any issue...
With thanks to Peter for sharing his expertise, and to anyone who can comment.
Steve
PS BTW, National say the non-isolated LM3875T (Peter supplies the isolated LM3875TF) will be obsoleted in favour of the LM3886T next year: http://www.national.com/pf/LM/LM3875.html#Datasheet
Hello,
I'm trying to decide what power supply voltage (and thus transformer rating and heat sink) to use with one of Peter's LM3875 kits.
He posted previously that the higher the rail voltage, the better the amp sounds. My speakers are nominally 8 Ohm, 96db/1W, two-way passive. Although I don't have a Z-curve to see how far Z varies, I am aware that it could be well below 8 Ohms in places.
Page 10 of the datasheet for the LM3875 (http://www.national.com/ds.cgi/LM/LM3875.pdf) shows the attached graph of output power vs supply voltage, for R=4,6 and 8 Ohms, but for a purely resistive load.
Now, 2x25V transformer will give ~±35V rail voltage (1.4 x Va, minus diode losses I put at zero).
Let's assume that Z drops to 6 Ohms from, say, 300-1000Hz, but is higher elsewhere - leading to the nominal 8 Ohm rating.
With rail voltage at 35V, one infers from the R=6 Ohm curve that the chip could supply only 20W at those frequencies, but nearly 60W at frequencies where Z was 8 Ohms.
I don't fully understand the interactions between these variables or whether this inference is well founded. (Or if I should be concerned at all - no-one seems to experience this
)Any comments?
I've contacted the speaker manufacturer for a Z curve, but if one is not forthcoming, how could I measure it myself?
Back to transformers, here in Switzerland I can source Block, Intronic, Sedlbauer and Toroid. Any comments on these manufacturers?
And finally, is 300VA overkill for dual monoblocks? My speakers roll off quite high and I have an active mono sub (which won't be powered by a GC, for now). I'm looking for dynamics/detail with the GCs and understand that a lower VA transformer might be more apt if weighty bass is less of any issue...
With thanks to Peter for sharing his expertise, and to anyone who can comment.
Steve
PS BTW, National say the non-isolated LM3875T (Peter supplies the isolated LM3875TF) will be obsoleted in favour of the LM3886T next year: http://www.national.com/pf/LM/LM3875.html#Datasheet
Would should I order from you to replace the parts that I ruined, and what would it cost? All I need is a single power supply board and parts.
I need just one power supply board, and related parts. If I need to order a complete PCB set that's fine.
Can I just pay-pal you the money with a note about what i am ordering as well as an address and such?
I need just one power supply board, and related parts. If I need to order a complete PCB set that's fine.
Can I just pay-pal you the money with a note about what i am ordering as well as an address and such?
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