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Group order of non-inverted LM4780 pc boards? Anyone interested?

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Well, with a prototype made with the board layout, I am considering organizing the order based on the current layout.

As for pricing, it looks like 1 pcb set would cost $20, and include:
- 2 power supply boards
- 2 amplifier boards
- 1 bridging board (DRV134)

This price would be for 4 oz copper (for the extra current handling), and the boards would be put together with scoring, as with my current LM4780 boards. (boards to either be red or black)

The amplifier pcb would be a single LM4780 chip hardwired in paralled configuration.

One pcb set would allow for these configurations:
- 2 channel amplifier (one amplifier pcb per channel) with a single or dual power supplies. (dual monoblock setup possible with one pcb set)
- bridged setup producing 150-200w for one channel

Remember that the LM4780 is hardwired in parallel mode, so one chip = 1 channel.

The non-bridged board should put out around 50-100w, depending on the power supply voltages and the load driven.

Kits will also be offered, and pricing will be announced soon. Pricing should be just a bit more than the current LM3875 group order.

I modified the Wiki for a new list to see the interest out there. If the interest is fairly substantial (100+ pcbs being the target to get the price), I will go through with the order, and offer kits. Please sign-up again here:
http://www.diyaudio.com/wiki/index.php?page=LM4780+Eval+PCB+Group+Order

Please indicate your initial interest. This will allow for me to determine the kit pricing, and the whether there is enough interest for me to put time into this.

Drop me an e-mail if you have any questions. PCB set pictures will be posted soon.

--
Brian
 
Brian, if you do go ahead with this, and are offering a component kit, is it likely you will be using the Mills MRB-5 power resistors at all? Just if you are I would also be interested in buying a bunch of these seperately, to use as output resistors for my Aleph-X (preferably 0.33 or 0.22 ohms).

Alternatively, if anyone knows where you can buy these off the shelf I would really appreciate it if you could let me know.
 
I'm curious - looking forward to seeing the prototypes. Personally, I like red.

But is there an option to order just the LM4780 PCBs? For my application, I won't need the rectifier boards. I guess the answer to this might be "no", as I guess you get all 5 boards made on one piece of FR4...

BTW, hams, I'm not sure that you'd get 150W from one PCB. To get 150W into 8 ohms, you need an RMS voltage swing of 35V, which is 50V peak. The highest supply rails you can put into an LM4780 are +/-42V, and these will fall under load to perhaps around 35V (this is hard to predict, of course). Allowing for other losses, I reckon you'd get around 30V peak, or 21V RMS, which is 55W. The parallel configuration will reduce some of these losses, so you might get nearer to 65W - I reckon that 60W is a fair guess of the continuous RMS power output of one of these PCB's.

Bridging a pair of these boards will give you double the voltage swing, which is 4 times the power in theory. Unfortunately, losses will reduce this to perhaps 3 times the output, so say 150-180W. But, these numbers are for continuous RMS outputs - dynamic or short-term "peak" outputs will be substantially higher. I reckon that a bridged setup will drive my ATC's quite well ;)

When sizing the torroid, a factor of two is a good starting point. But, it depends on the application - for a PA amplifier, you might want to increase it. For home use, you might get away with a smaller one. Unless you listen to heavily compressed music, you rarely need the full output power - it's there to deal with peaks. For the stereo bridged amplifier amplifier I'm thinking about (using 4 PCB's), I reckon 500VA will be enough ;)

Cheers,

Mark
 
me me me me me
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me too

and I like black. black is cool. imagine black pcb, black heatsinks, black case, black toroid :D



yeah, and another point... what is a kit?
one channel bridged? or two channels bridged?
 
Retired diyAudio Moderator
Joined 2002
bigparsnip said:
Brian, if you do go ahead with this, and are offering a component kit, is it likely you will be using the Mills MRB-5 power resistors at all? Just if you are I would also be interested in buying a bunch of these seperately, to use as output resistors for my Aleph-X (preferably 0.33 or 0.22 ohms).

Alternatively, if anyone knows where you can buy these off the shelf I would really appreciate it if you could let me know.

I will keep this in consideration when ordering parts. This shouldn't be a problem if I go for the Mills resistors.

--
Brian
 
Retired diyAudio Moderator
Joined 2002
mhennessy said:
I'm curious - looking forward to seeing the prototypes. Personally, I like red.

But is there an option to order just the LM4780 PCBs? For my application, I won't need the rectifier boards. I guess the answer to this might be "no", as I guess you get all 5 boards made on one piece of FR4...

Bridging a pair of these boards will give you double the voltage swing, which is 4 times the power in theory. Unfortunately, losses will reduce this to perhaps 3 times the output, so say 150-180W. But, these numbers are for continuous RMS outputs - dynamic or short-term "peak" outputs will be substantially higher. I reckon that a bridged setup will drive my ATC's quite well ;)

Mark,

You can find the prototype pcb pictures in this thread, where the idea of the layout was created:
http://www.diyaudio.com/forums/showthread.php?postid=391330#post391330

The pcb set will be created on a single pcb set, with scoring to allow for the boards to easily be broken apart, just as with my current LM3875 order:
http://www.briangt.com/gallery/nigc-kit
It will consist of 5 boards on one, instead of 3. Having 2 power supply boards will easily allow for building monoblocks from one pcb set. The bridging pcb hasn't been finalized yet.

When bridging with the LM4780 layout, keep in mind that it is actually a bridged-parallel configuration, which seems to be the optimal high-power solution with the chipamps.

Here is a picture of the amplifier board layout. The power supply board will be similar to the last one from the LM3875 group order.

Wiki signup:
http://www.diyaudio.com/wiki/index.php?page=LM4780+Eval+PCB+Group+Order

--
Brian
 

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peranders said:
Brian, I like what I see BUT the signal ground (red) trace should go more left and directly to the OG pad. Than you have got a perfect pcb!

BTW: Where are the decoupling caps? Can't see any.


Wouldn't connecting SG and OG pads with bottom layer trace trace take care of that?

There is no coupling caps, as they are not required here. All the amps I build now don't have coupling caps either. I used them before though.
 
Something that's crept in to later versions of this layout - the connection between pin 7, R1 and the output. I'm not happy about the noding here. The connection on the other half of the chip is a perfect textbook example of how to do it, but the "T"ing of the output connection worries me slightly. I can see the space constraints that have caused you to shape the track in the way you have, but could you not run a track on the red (top?) plane from pin 7 to R1, and then take the output from R1? The via shouldn't cause a problem here, as it will have the wire and solder from R1 to "beef up" the connection.

I also agree with peranders about the track linking the earth planes - it doesn't need to be so long, and would be better connected to the middle of the earth plane. I also think that the OG would be better if you moved it to be between OUT and SG - the symmetry would definitely improve performance - easily measured (if not necessarily audible;)). However, this is only an issue if you're not bridging a pair of boards, so I don't feel that strongly about it.

Have you considered moving R6 and R7 around to the right of the IC, behind the cap? It would reduce the length of the input traces, and these are at a higher impedance than the input node, so slightly more susceptible to pickup. You might even be able to make the board slightly smaller as a result. (Although, is the spacing of the caps chosen so that you can easily get to the screws holding the IC to the heatsink?). Also, the trace from R6 looks very close to the R9 output node, and as this is a non-inverting amplifier, the chances of positive feedback are very real.

Another small thing - the spacing of the resistors R3 to R7 looks to be non-uniform - is this the case in reality, or a screen-draw issue? Moving them all closer together so the spacing matches R6 and R7 will make it look a bit neater, and you will be able to tidy up the blue SG trace slightly (and the trace to R3, which looks as if it "misses" the centre of the pad).

Sorry if all of this seems unduly critical, but these are the sorts of details that I ask myself when I'm nearly ready to declare my designs "finished". I normally find that the critical analysis can take longer than the basic layout. But, I'm a perfectionist, which isn't always easy ;)

Finally, is it an option to purchase the resistors along with the PCBs?

Best regards,

Mark ;)
 
I would be much more concerned with via than a T. There is no problem running this trace directly between pads, without the need for a T. I wouldn't recommend mixing 2 layers for that.

As to the output ground 200mill won't make a difference in performance, but it will make big difference in how easy it is to run the connection wire. I don't care for perfect symetry. I care much more for convenience.;)
 
mhennessy said:


Another small thing - the spacing of the resistors R3 to R7 looks to be non-uniform - is this the case in reality, or a screen-draw issue? Moving them all closer together so the spacing matches R6 and R7 will make it look a bit neater, and you will be able to tidy up the blue SG trace slightly (and the trace to R3, which looks as if it "misses" the centre of the pad).


The spacing it's done here on purpose. Those are not Krell (or Kristian's boards for that matter) where everything is lined up and spaced perfectly. Looks were not considered to be the goal, but performance. The board accomodates Caddocks, but I have strong feeling that Rikens will be better here, so this extra space allows to mount Rikens as well (in vertcal position). You wouldn't mind putting them this way? After all those extras on the leads are part of 3-D layout, (popularasied by Jonathan Carr);)
 
mhennessy said:

Have you considered moving R6 and R7 around to the right of the IC, behind the cap? It would reduce the length of the input traces, and these are at a higher impedance than the input node, so slightly more susceptible to pickup. You might even be able to make the board slightly smaller as a result. (Although, is the spacing of the caps chosen so that you can easily get to the screws holding the IC to the heatsink?). Also, the trace from R6 looks very close to the R9 output node, and as this is a non-inverting amplifier, the chances of positive feedback are very real.

Even if you place those resistors closer to the chip, you still have to run the connection wires around the board (this makes those wires longer) so I don't see much difference here. And anyway, there is no space to place those resistors there. Again having conveniently placed input access points on the board was major deciding point.

I would rather modify the traces (less square) and this would further reduced their length.

Regarding the "trace from R6 looks very close to the R9", look how close those are on IC pins;)
 
mhennessy said:
Sorry if all of this seems unduly critical, but these are the sorts of details that I ask myself when I'm nearly ready to declare my designs "finished". I normally find that the critical analysis can take longer than the basic layout. But, I'm a perfectionist, which isn't always easy ;)


It took at least 5 days and countless hand drawings to finalize that layout.

I'm still working on a DAC (for almost a month) before committing to final layout.

So be asured that a lot of thought went into those amp boards. Also, we ride on experience gained with a previous version, which tested by hundreds brought only positive feedback;)
 
Retired diyAudio Moderator
Joined 2002
roibm said:
what is a kit?
one channel bridged? or two channels bridged?

A kit will consist of the components for 2 amplifier boards and 1 power supply board. Additional components will be available for the bridging board, and the extra power supply board at additional cost.

My estimate on the kit price for the basic kit will be $40-45, and the premium kit will be $70-75.

Here is a list of components for the kit to contain:
2 - LM4780 chips
1 - PCB set
6 - 22k resistors
4 - 1k resistors
4 - 680 ohm resistors
4 - 0.22 ohm 3w resistors
2 - SMD resistors for mute
4 - 1500uF 50v Panasonic FC capacitors
2 - 4.7uF capacitors for power supply pcb
8 - MUR860 diodes for power supply pcb

The difference between the premium and basic kits is the choice of components. The premium kit will use Caddock MK132 resistors and 4.7uF BlackGate N capacitors for the power supply board. The 1500uF 50v Panasonic FC capacitors will be used for both kits for now. I am considering offering BG 1000uF STD capacitors in the future, but they are rather expensive costing $12.50 each (with quantity discount), making the price $50 for the capacitors needed fo a kit.

As for the upgrades to the kit, it will cost $5 to add the components for an extra power supply for the basic kit and $10 for the premium kit. I haven't determined the pricing for the bridging board components yet, as the design is being finalized.

I will post more details when everything is finalized.

--
Brian
 
joensd said:
roibm,
would you mind ordering 2 additional sets of PCB´s and send them to me. Just to save a bit of shipping cost.
Your email adress is not available through the forum, can you drop me a mail?
Neither is your email address. And this is not normal, as it has worked just fine previously.
I could do just that, even for other people if interested(as long as the quantity is not that high, otherwise we will have to pay customs + our lovely mwst)


If there is someone from romania that wants to order I could take the order for you as well. You will have to send the money to a romanian bank account so this way you will save some money. For more details contact me when the email contact function gets back.
 
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