Here it is: http://www.metalsupermarkets.com/
Also, this place stocks copper bars: http://www.mcmaster.com/
Also, this place stocks copper bars: http://www.mcmaster.com/
Peter Daniel said:
the diagram provided shows the jumper in place for parallel work. Looking at the National LM4780 datasheet i need to tie the inputs (in and in ground) for bridged mode so that i only have one input. This suggest i need to put the jumper in place for bridged setup.
can anyone confirm this ?
The jumper is in place for parallel setup only. For bridged operation we want to keep inputs and outputs separately, as they are run in opposite phases.
but i require only one input per chip. Sorry i'm getting abit confused over the bridged setup.
I understand the schematic in the datasheet where one internal amp is non inverted, the other is inverted resulting in the output opposite phases, doubling the available signal 'swing'.
Looking at the instructions with the kit i can't see how this is achieved.
Sorry if I'm being stupid
I understand the schematic in the datasheet where one internal amp is non inverted, the other is inverted resulting in the output opposite phases, doubling the available signal 'swing'.
Looking at the instructions with the kit i can't see how this is achieved.
Sorry if I'm being stupid
Ted205 said:
My kit is configured in a such a way, that even in bridged setup none of the amps is inverting: that way, with those boards, you can use half of the kit only, with a single chip wired for stereo operation. Of course, bridged configuration requires balanced signal to the amp, as it will not convert unbalanced to balanced.
If you require one input per chip, you have the option of using each chip in parallel for more current output, or one chip only (non parallel) with two separate channels.
http://www.diyaudio.com/forums/showthread.php?postid=636565#post636565
If using a 10k pot should I just omit the 22k R2?I will also be including an input cap after the pot and R1 will be 1k.
THanks
THanks
The 22k input shunt resistor is there for a reason: with simplified GC schematic (and 22k feeedback resistor) it limits the output DC offset.
If you use the coupling cap after the pot, that resisotor is neccessary. If there is no cap, you could omit the R2 resistor, but in case a pot fails the resistor is there for protectioion.
If you use the coupling cap after the pot, that resisotor is neccessary. If there is no cap, you could omit the R2 resistor, but in case a pot fails the resistor is there for protectioion.
Member
Joined 2006
Hi Peter,
I understand that the power supply filter caps should be close to the chip's pins.
From your experience, would positioning those caps with PC board traces that are 2 to 3 cm away from the chip make a sonic difference? Just curious.
Thanks!
CFT
I understand that the power supply filter caps should be close to the chip's pins.
From your experience, would positioning those caps with PC board traces that are 2 to 3 cm away from the chip make a sonic difference? Just curious.
Thanks!
CFT
Thanks Peter ,yeah I guess with no R2 and if the pot opened up that would be problematic.Peter Daniel said:
I have a couple of more questions if I may.
1.)Assuming apropriate heatsinking and an easy 8 ohm load, is 2x36 volts DC fine?
2)Would the inclusion of a feedback cap have any affect on the inherent offset in the chip, or is its only purpose being to keep DC gain at zero?
Thanks
2 x 36V DC is actually recomended (with 8ohm loads); in my experience the amp sounds best with such supply.
Regarding your second question, it could certainly have effect if the source produces some offset, otherwise I don't know, as I never measured offset with and without Ci (using same source).
I just measured the traces on my board and the caps are 2.5 and 1.5 cm from the pins, so I guess 3cm wouldn't make much difference 😉
Regarding your second question, it could certainly have effect if the source produces some offset, otherwise I don't know, as I never measured offset with and without Ci (using same source).
CFT said:
I just measured the traces on my board and the caps are 2.5 and 1.5 cm from the pins, so I guess 3cm wouldn't make much difference 😉
Hi Peter,
For the 330pf cap across the inputs (as mentioned here: http://www.diyaudio.com/forums/showthread.php?postid=1516522#post1516522), could you suggest a digikey part number for that?
Thanks!
For the 330pf cap across the inputs (as mentioned here: http://www.diyaudio.com/forums/showthread.php?postid=1516522#post1516522), could you suggest a digikey part number for that?
Thanks!
Hi peter I just purchased one of you lm4780 kits. Right now I am about 98% sure I am going to run them as a bridged stereo amp. I have read that it is better to use only one rectifier board when only using one toroid. do you believe that a 250VA 2x25V toroid would be sufficient?
While 250VA toroid should be fine, I would still recommend at least 300VA, or even better, 400VA transformer for bridged configuration. Also, you may consider lower voltage in case of bridging: 22V AC should be fine and that's what I'm using myself.
Please note that the amp needs balanced source to work in bridged mode, the load impedance should be 8ohm.
Please note that the amp needs balanced source to work in bridged mode, the load impedance should be 8ohm.
balanced source...hmmm
i was planning on running the amp off of the following
- a 73 kenwood turntable (don't know much about it, dad gave it to me)
- an iPod classic 80 gig using the monster cable version of this http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=181-594
- a sony 50 disk changer (forget the model but its from the mid 90's)
seems like i may have to rethink my decision a bit.
i was planning on running the amp off of the following
- a 73 kenwood turntable (don't know much about it, dad gave it to me)
- an iPod classic 80 gig using the monster cable version of this http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=181-594
- a sony 50 disk changer (forget the model but its from the mid 90's)
seems like i may have to rethink my decision a bit.
In regards to safety when experimenting with the PSU board, I assume the LED (slowly) drains the caps on the positive rail, but what about the negative? If testing the PSU with caps installed but no amp connected, how should I drain the caps so I can hook up to the amp without risk?
Also, you mentioned WAY back in this thread that the LED causes a lower voltage reading on that rail. When you measured that voltage, it was with no caps installed. Do I correctly assume that there will not be a noticeable voltage drop from the LED once the caps are installed?
Also, you mentioned WAY back in this thread that the LED causes a lower voltage reading on that rail. When you measured that voltage, it was with no caps installed. Do I correctly assume that there will not be a noticeable voltage drop from the LED once the caps are installed?
I usually short caps with 10R resistor (across the pins)
The LED will cause voltage drop in one of the rails if only 10uF caps are present on rectifiers board. With main caps connected (1500uF) both rails are at the same voltage.
Hi Peter,
You mentioned a while back in this thread stat R1 on a the LM3875 amp pcb can be replaced by (a wire or) a small electrolytic to filter for dc in the input.
I'm running your lm4780 kit in stereo configuratin, and I've got some dc in my input. Can I do something similar with this kit, like replacing R6 and R7 with 10uf caps?
You mentioned a while back in this thread stat R1 on a the LM3875 amp pcb can be replaced by (a wire or) a small electrolytic to filter for dc in the input.
I'm running your lm4780 kit in stereo configuratin, and I've got some dc in my input. Can I do something similar with this kit, like replacing R6 and R7 with 10uf caps?