While we are on the subject, I was tooling through Digikey the other day, putting together a BOM for a project I am working on and noticed that the Rohm resistors were literally half as much as the Vishay/Dale resistors. Have you ever used the Rohm resistors? Heard anything about them?BWRX said:
Not that there would be that much difference in cost for a few parts, but it definitely made me wonder what was up and whether the Rohm parts were to be trusted.
I'm not entirely sure why there is such a difference in price between something like the Vishay/Dale CRCW resistors and the Rohm MCR10 since both are thick film types and have similar specs, but it could be due to differences in construction and composition of the resistive element. It could also be that Rohm makes such a large quantity that they can offer them for cheaper (economies of scale at work).
The resistors I like to use are the Susumu RR series. They are categorized as thin film and they have a metal film resistive element. Priced at $1.40 for 10, they have low 0.5% tolerance and low TCR (the RR????P... resistors have a TCR of 25ppm/C). Or if you feel like spending a little more for 0.1% go with the Panasonic ERA6AEB???? resistors which are $2.04 for 10. As always, if anyone knows of good resistors for less, we'd all love to hear what and where to get them
The resistors I like to use are the Susumu RR series. They are categorized as thin film and they have a metal film resistive element. Priced at $1.40 for 10, they have low 0.5% tolerance and low TCR (the RR????P... resistors have a TCR of 25ppm/C). Or if you feel like spending a little more for 0.1% go with the Panasonic ERA6AEB???? resistors which are $2.04 for 10. As always, if anyone knows of good resistors for less, we'd all love to hear what and where to get them
Thanks for the suggestion, but the Susumu's don't seem to come in 1206's (which is what I need)--at least not at Digikey.
Not to veer too much more off course, but do you notice any difference between the thin and thick film resistors? I have seen the "more direct conduction route" argument for thin film, which is voodoo as far as I am concerned, but if you have a reason you prefer one over the other, I am all ears.
Either way, I am certain any of these resistors should work just fine, but now is the tweaking stage!
Not to veer too much more off course, but do you notice any difference between the thin and thick film resistors? I have seen the "more direct conduction route" argument for thin film, which is voodoo as far as I am concerned, but if you have a reason you prefer one over the other, I am all ears.
Either way, I am certain any of these resistors should work just fine, but now is the tweaking stage!
1206 is huge man!, you need to be over 60 to have to have to use those.
I see you are designing double sided, maybe you can copy my idea of useing SMT electrolytics, mounted on the bottom layer, which allows you to shorten the board drasticaly...
After the clever quip above, I reduced my board to 1.3inch square.
useing moslty 0805, they are quite easy to work with I find, even when soldering them with an iron like a caveman.
It seems a shame to make them this small as the suggested heatsink (if it will be exposed - isolated)is quite big, 10 x 10 x 3cm per channel.
I see you are designing double sided, maybe you can copy my idea of useing SMT electrolytics, mounted on the bottom layer, which allows you to shorten the board drasticaly...
After the clever quip above, I reduced my board to 1.3inch square.
useing moslty 0805, they are quite easy to work with I find, even when soldering them with an iron like a caveman.
It seems a shame to make them this small as the suggested heatsink (if it will be exposed - isolated)is quite big, 10 x 10 x 3cm per channel.
dfdye said:
As Nordic indirectly said, why are you using 1206 size resistors? Is it for the slightly higher power rating? If not, use 0805.
dfdye said:
Honestly, I haven't AB tested amps with thick film versus metal film resistors, but I probably wouldn't be able to tell the difference. Technically, the metal films are better so I prefer to use them.
Yea, the 1206's are indeed huge, but they have part numbers on them!
Actually, the reason I like them is because I can use 1/4W parts and not think about the conversion from "OLD" designs to SMP's. I know I should use 0805's, but I guess I am just slow to convert, and, though I don't think I am near the limit for any parts. the 1/10W thing sort of puts me off. Also, with the 1206's I can run traces between the pads, which I don't feel comfy doing with 0805's.
This really helps when making double sided boards at home since vias on small signal traces are notoriously hard to line up and I generally try to avoid them at all cost! The exception obviously being vias going from small traces into a ground plane that you don't have to align carefully.
Plus, that heat sink is INSANE overkill IMHO. I know what the recommendations are, but who in their right mind would push this chip to get hot enough to need THAT heatsink??? If you need that much power, use a different chip (or a grown up amp! )
Actually, the reason I like them is because I can use 1/4W parts and not think about the conversion from "OLD" designs to SMP's. I know I should use 0805's, but I guess I am just slow to convert, and, though I don't think I am near the limit for any parts. the 1/10W thing sort of puts me off. Also, with the 1206's I can run traces between the pads, which I don't feel comfy doing with 0805's.
This really helps when making double sided boards at home since vias on small signal traces are notoriously hard to line up and I generally try to avoid them at all cost! The exception obviously being vias going from small traces into a ground plane that you don't have to align carefully.
Plus, that heat sink is INSANE overkill IMHO. I know what the recommendations are, but who in their right mind would push this chip to get hot enough to need THAT heatsink??? If you need that much power, use a different chip (or a grown up amp!
)
Most 0805 size resistors have values on them too The Susumu and Panasonic resistors do.
If you design the footprint well you can comfortably run up to a 16 mil trace between the pads of an 0805 size part.
I have some sections of that heatsink Nordic posted a picture of. It would work well as the heatsink for many LM1875s!
The Susumu and Panasonic resistors do.If you design the footprint well you can comfortably run up to a 16 mil trace between the pads of an 0805 size part.
I have some sections of that heatsink Nordic posted a picture of. It would work well as the heatsink for many LM1875s!
I hate you so much right now. Now all of my excuses are out the window. . . .BWRX said:Most 0805 size resistors have values on them too
If you design the footprint well you can comfortably run up to a 16 mil trace between the pads of an 0805 size part.
Still, I'll be building one last project that's underway with 1206's, so I have a little reprieve before I have to bust out the microscope.
motherone said:
I sent an email to expresspcb asking to place an order for some boards using the gerber files generated by eagle and they said they only accept boards designed and routed using their software!
I have no idea why they would turn down business like this when every other board house known to man will accept regular gerber files... Needless to say, I won't ever be doing business with them again.In the meantime I stared at the layout some more, saw ways to rearrange components, and shrank the size of the full version board down to 1"x1". Since there isn't much point in having the basic version made anymore, the plan is to put 2 LM1875 boards and 2 differential buffer boards onto a 2"x2" board and see what kind of pricing I can get from some other places even though they will charge an extra fee for more than one part number per board.
Hmm. . . . . If you tie the signal traces between the inputs of the chip board into the outputs of the buffer board and tie some of the power leads together, you could almost make this "one" part. You can always cut through the leads when you separate the boards.
Again, this is clearly trying to skirt the rules, but it may work. . . .
Worst case, you can go with Olimex. Talk about long turn around time, but the price is right!
Again, this is clearly trying to skirt the rules, but it may work. . . .
Worst case, you can go with Olimex.
Talk about long turn around time, but the price is right!
I've already tried that before with multiple little layouts on one board and most places aren't that dumb. Just like any other business, they won't miss out on a chance to charge you more!
Olimex may be the best way to go pricewise but I'd have to check to see if the boards meet their minimum requirements. Either way, I'm also looking at having them made by pcbex. They make great quality 2 layer boards with a pretty fast turn around for pretty cheap. The multiple layout fee might be like $50 though.
Olimex may be the best way to go pricewise but I'd have to check to see if the boards meet their minimum requirements. Either way, I'm also looking at having them made by pcbex. They make great quality 2 layer boards with a pretty fast turn around for pretty cheap. The multiple layout fee might be like $50 though.
BWRX said:
Hi Brian! I just wanted to mention that, in practice, these LM1875 max at 32.5v, but do it well. In the U.S. that would relate closely to a 40vct (20+20) transformer. . . and Nordic's heatsink.
For an economical, yet well made, center tap, there's a Stancor, White Rogers 40vct available with sufficient amperage for several LM1875.
The heatsink won't be economical unless its a "recycle" like a thrifty shop discovery.
At max voltage, the power caps onboard with the amplifier would be in the neighborhood of 100uF to 330uF, because larger "may" promote heat. I don't have details on that observation.
Reason to use the maximum. . . there are some configurations possible to "promote" dynamics to an unusual extent. Personally, I find this helpful for popular music and/or stubborn (inefficient) speakers that the other chip amps drive poorly. In my opinion, there's no such problem with LM1875's.
That's all I've got for now, except. . .
The mention of such voltages has me curious about safer, lower, voltage, but a parallel layout.
Hi Daniel. Quite right about the supply voltage. I was thinking about the LM3875 when I mentioned 35V rails! The max recommended voltage is +/-30VDC for the LM1875.
Most any transformer will work. That rating you would want would depend on how many circuits it will be powering. 30VA per chip is what I would use as the minimum. 50VA per chip would yield a nice beefy supply.
The value of the electrolytic caps on board shouldn't have anything to do with power dissipation in the chip. If different caps yield different amounts of power dissipation than you are probably having oscillation problems. The footprint I've used is for a 5mm lead spacing, 10.5mm diameter cap. I selected a 220uF 35V Panasonic FM to use because it has a height of 15mm which will leave room for a screwdriver to access the screw that will hold the LM1875 to the heatsink. If you have another way of fastening the chip to the heatsink you can use up to a 560uF 35V Panasonic FM (which is 25mm high). If you use lower voltage rails you can use a lower voltage cap and get more capacitance in the same size. For instance, 560uF 35V is the same size as 820uF 25V or 1200uF 16V for the Panasonic FM series.
Most any transformer will work. That rating you would want would depend on how many circuits it will be powering. 30VA per chip is what I would use as the minimum. 50VA per chip would yield a nice beefy supply.
The value of the electrolytic caps on board shouldn't have anything to do with power dissipation in the chip. If different caps yield different amounts of power dissipation than you are probably having oscillation problems. The footprint I've used is for a 5mm lead spacing, 10.5mm diameter cap. I selected a 220uF 35V Panasonic FM to use because it has a height of 15mm which will leave room for a screwdriver to access the screw that will hold the LM1875 to the heatsink. If you have another way of fastening the chip to the heatsink you can use up to a 560uF 35V Panasonic FM (which is 25mm high). If you use lower voltage rails you can use a lower voltage cap and get more capacitance in the same size. For instance, 560uF 35V is the same size as 820uF 25V or 1200uF 16V for the Panasonic FM series.
Daniel, what you are saying about the caps at the chip doesn't make any sense. Those caps merely serve to clean up the power and to provide "quick" reserve, but the power dissipation (heat) of the chip would not be affected by changing those values.
(Woops, didn't see Brian's post there before I posted)
(Woops, didn't see Brian's post there before I posted)
BWRX said:
At from $12 to $14 each, 36va, 36vct (18+18ac), Canadian made Allied store brand, #227-2060 looks good for Monoblocs. No rice paper, no gaps. Actual amperage, well, she'll hold 1x LM1875 quite well with about 4400uF per rail. Pairs of Mallory 2200uF SEK or something nice from Nichicon, are quite economical performers for $1.
There's also MR. . . oh heck no! They've only got OnSemi--ridiculous variances per sample. I was hoping for Motorola Litespeed goodies. Oh well, at least there's a lot of KBPC bridge rectifier units, perfectly matched inside, at about $2 (per bridge).
So, power for two monoblocs would be about $38 + shipping.
The local smoothing cap size makes difference in oscillation problems? Oh thank you! I had no idea why there would be a difference in heat. I was just reporting an observation and hoping for an explanation.
Thanks!! Also, thanks for leaving room for the screwdriver!!!
If someone's looking for a speaker idea, then a possible speaker partner for LM1875 might be W6-789S, Tang Band, 91db, 6-1/2, 8R (DC6R). Despite specs saying large box and 15w, its perfectly happy with small ported box (from 0.5 to 1 cubic foot), works fine sealed or ancheloc (can't spell it)--and a LM1875 with the above 36vct (18+18) transformer matches closely on power handling, as I am testing it right now. Its got that high crossover point, extra fast lightweight coated paper, and, a non-screech fiber dust cap--so practically no effort for the crossover. Anyway, like the LM1875 amps, there's power and fidelity with not much labor to get it.
P.S. That little driver, can't stand up to the "highly optional" 32v rails hotrod LM1875's, but its a can-do with a efficiency-based Harbeth Monitor 40 clone, like this one: http://www.partsexpress.com/projectshowcase/indexn.cfm?project=MagnaCumLaude or similar. But, hey! see what the normal stuff will do, unless you're one of those people accustomed to removing drywall in high fidelity.
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