Sneasle said:
Does this also mean that all parts have to be ROHS compliant?
Do you have boards with which to build the prototype? As suggested above, you could use the chipamp.com boards (they will fit nicely) for a prototype.
I'll post the new BOM once I hear back about the ROHS thing, as some of the parts are not currently in that specification.
-David
Changing the parts to ROHS compliant ones was trivial, so I went ahead and did it, it only costs a few cents more per resistor.
The current BOM is looking pretty good. Getting the parts from three vendors down to two has allowed for a more expensive enclosure to be used for no difference in cost.
Not including the PC boards, volume potentiometer, and heatsink; an individual's cost for a chipamp kit as built in the BOM would cost about $90. Add in another $26 for a set of boards and some extra cost for wires, volume potentiometer, and heat sink and the overall project cost for one order would be around $130 +/-$5.
I'll provide a full BOM so that the individual can purchase the parts themselves if they choose. That said, volume purchasing will reduce the cost significantly. How much interest would there be in a group buy of the kits? If we can secure at least 25 kits, the cost drops significantly. I will organize the group buy, all I ask for in return is that I can pay for the prototyping cost (basically a free kit for me).
If the Auburn students do in fact order 20, I am close enough to broker the kits for that group if they want (they are not required to as I have freely provided the BOM, the could order enough in and of themselves to get a discount). If we can stack the Auburn order on top of an additional group buy from DIYAUDIO then everyone will save even more.
Please express interest on the Wiki Page.
The current BOM is looking pretty good. Getting the parts from three vendors down to two has allowed for a more expensive enclosure to be used for no difference in cost.
Not including the PC boards, volume potentiometer, and heatsink; an individual's cost for a chipamp kit as built in the BOM would cost about $90. Add in another $26 for a set of boards and some extra cost for wires, volume potentiometer, and heat sink and the overall project cost for one order would be around $130 +/-$5.
I'll provide a full BOM so that the individual can purchase the parts themselves if they choose. That said, volume purchasing will reduce the cost significantly. How much interest would there be in a group buy of the kits? If we can secure at least 25 kits, the cost drops significantly. I will organize the group buy, all I ask for in return is that I can pay for the prototyping cost (basically a free kit for me).
If the Auburn students do in fact order 20, I am close enough to broker the kits for that group if they want (they are not required to as I have freely provided the BOM, the could order enough in and of themselves to get a discount). If we can stack the Auburn order on top of an additional group buy from DIYAUDIO then everyone will save even more.
Please express interest on the Wiki Page.
I don't want to derail your momentum, but you might consider deleting the enclosure from the group buy BOM, or at least making it optional. Not that what you've selected isn't a fine choice. It is, but the enclosure seems to be a place where "individuality" is king when it comes to DIY electronics and locking in only one choice there might discourage some who would otherwise participate. OK, me, anyway. 
Given that, I'm in.
Given that, I'm in.
ROHS isn't necessary, but we are not allow to solder with leaded solder.
Aside from that, that looks good.
I'll hopefully have a schematic or sorts done this week/weekend.
edit:
Thinking about this some more, I doubt we will get much, if any interest at this price point. I don't have a problem putting this much in myself, but I think a price point this high will be a major hindrance.
Even if the quality of this ends up better what what you can buy at the store, I think we will be hard pressed to convince people that putting in 100+ for a 2ch amp is worth it.
These are college students, the $$$ will be more important to them then anything they may get out of it.
I need to sit and think on this. Even at a $50 price point I think we will be hard pressed to get 20 interested. I need to figure out what the IC was I built that amp in high school with. I don't think I put more then $20 into it, so that I think is easily doable.
more later
Aside from that, that looks good.
I'll hopefully have a schematic or sorts done this week/weekend.
edit:
Thinking about this some more, I doubt we will get much, if any interest at this price point. I don't have a problem putting this much in myself, but I think a price point this high will be a major hindrance.
Even if the quality of this ends up better what what you can buy at the store, I think we will be hard pressed to convince people that putting in 100+ for a 2ch amp is worth it.
These are college students, the $$$ will be more important to them then anything they may get out of it.
I need to sit and think on this. Even at a $50 price point I think we will be hard pressed to get 20 interested. I need to figure out what the IC was I built that amp in high school with. I don't think I put more then $20 into it, so that I think is easily doable.
more later
I appreciate the input, and see where you are coming from.
The big savings would come from the enclosure and power supply parts coming down in cost. If someone wants to build a custom enclosure, they can order the parts from the BOM (freely available) and build their own. The shipping from two vendors isn't prohibitively expensive. The type that are likely to build their own enclosures are also likely to customize many other things about the design and will probably want different power supply capacitors, transformer, and other things which are budget oriented.
This group buy would target those without the inclination or facility to build their own enclosure and who are interested in getting the best bang for their buck without doing alot of extra labor. I'm working on getting some price estimates together.
-David
The big savings would come from the enclosure and power supply parts coming down in cost. If someone wants to build a custom enclosure, they can order the parts from the BOM (freely available) and build their own. The shipping from two vendors isn't prohibitively expensive. The type that are likely to build their own enclosures are also likely to customize many other things about the design and will probably want different power supply capacitors, transformer, and other things which are budget oriented.
This group buy would target those without the inclination or facility to build their own enclosure and who are interested in getting the best bang for their buck without doing alot of extra labor. I'm working on getting some price estimates together.
-David
I wouldn't be too quick to back out Sneasle. Parts cost without the case is only $35, without any volume discounts, another $25 is shipping. If you can get 20 interested, the shipping will be virtually free.
I'd also like to see a volume pot added to the BOM, such that the BOM is enough to build a complete, working amplifier without enclosure. Unfortunately neither Mouser nor ApexJr sell anything appropriate. Passives at DigiKey are a bit more expensive, and they have more minimum quantities, but for such a small BOM the difference is not large. I put one together there, including the volume pot, the difference is about $5.50. DK also has cheaper shipping, so it brings the difference down to $3.50 (for a single order).
See: http://spreadsheets.google.com/ccc?key=pO3ofQox_j8gwk4XqVDw3cQ&hl=en (the original Mouser BOM is on sheet 2 for comparison, and anyone can edit this document)
I'd also like to see a volume pot added to the BOM, such that the BOM is enough to build a complete, working amplifier without enclosure. Unfortunately neither Mouser nor ApexJr sell anything appropriate. Passives at DigiKey are a bit more expensive, and they have more minimum quantities, but for such a small BOM the difference is not large. I put one together there, including the volume pot, the difference is about $5.50. DK also has cheaper shipping, so it brings the difference down to $3.50 (for a single order).
See: http://spreadsheets.google.com/ccc?key=pO3ofQox_j8gwk4XqVDw3cQ&hl=en (the original Mouser BOM is on sheet 2 for comparison, and anyone can edit this document)
error401 said:
Don't get me wrong, I'm not backing out, it just needs to be made cheaper.
I'll need to look at the numbers again, but I doubt it's under $30 for everything including the power supply parts.
Volume pots are easy enough to find. How big of a pot? 50k, 100k?
john blackburn said:
John, honestly, no college kid is going to be swayed by hearing it. Chances are, they won't be able to hear the difference because they won't know what to listen for, how to listen.
It doesn't matter how good it sounds, if they can't tell the difference between it and somethign they can buy retail for cheaper with more 'power' and channels, then they won't be interested in this.
You can use a single supply if you want, there's a schematic for it right in the datasheet. It will add some passives and remove the power supply components, but you still need to find an appropriate wall wart. You're going to need at least 40V @ 2A, and I think you'll have a hard time finding a way to do that cheaper than already suggested. Personally I think the 80VA trafo is already skimping a bit too much.
10K to 50K is fine. You won't find anything worth using at Mouser, but yea if you can find that locally it would be fine.
We're really talking about shaving pennies here, but you can save a few bucks by excluding:
- 2.2K and 1R resistors
- 47uF capacitors (why did we have 4 of these on the bom anyway, the chipamp design only needs 2 or 0 - ditto the 10uF caps of which only one is needed)
- 4 of the 0.1uF capacitors
- Get the $1 binding posts instead of the $2 binding posts
Everything else is pretty much as cheap as it can be. With a quantity of 20, buying from DigiKey and the mods above, you're down to $34.20 per, plus a couple dollars shipping.
Oh, and the current BOM is missing heatsinks. There are lots of ways to do this, aluminum channel sourced locally might be the cheapest, and can serve as a makeshift chassis as well.
I think you're underestimating the students here. It sounds like you're targeting an EE program with this idea, so I think you should find some interest if the cost is 'affordable' regardless of the benefits. The people in the program are hopefully interested in electronics, and it's cool to build stuff, and even cooler when you get to keep it. Add the guidance and learning (and maybe some credits too?) and for $50 it becomes a great weekend workshop or however you were planning to do it. I think you'll also find some (not many) that are interested in the audio quality. Certainly more in EE than anywhere else.
For what it's worth, a local kit supplier sells a 2x20W kit for $30 without any power supply. It's certainly not nearly as good.
10K to 50K is fine. You won't find anything worth using at Mouser, but yea if you can find that locally it would be fine.
We're really talking about shaving pennies here, but you can save a few bucks by excluding:
- 2.2K and 1R resistors
- 47uF capacitors (why did we have 4 of these on the bom anyway, the chipamp design only needs 2 or 0 - ditto the 10uF caps of which only one is needed)
- 4 of the 0.1uF capacitors
- Get the $1 binding posts instead of the $2 binding posts
Everything else is pretty much as cheap as it can be. With a quantity of 20, buying from DigiKey and the mods above, you're down to $34.20 per, plus a couple dollars shipping.
Oh, and the current BOM is missing heatsinks. There are lots of ways to do this, aluminum channel sourced locally might be the cheapest, and can serve as a makeshift chassis as well.
I think you're underestimating the students here. It sounds like you're targeting an EE program with this idea, so I think you should find some interest if the cost is 'affordable' regardless of the benefits. The people in the program are hopefully interested in electronics, and it's cool to build stuff, and even cooler when you get to keep it. Add the guidance and learning (and maybe some credits too?) and for $50 it becomes a great weekend workshop or however you were planning to do it. I think you'll also find some (not many) that are interested in the audio quality. Certainly more in EE than anywhere else.
For what it's worth, a local kit supplier sells a 2x20W kit for $30 without any power supply. It's certainly not nearly as good.
I guess I messed up some of the quantities when I copied my shopping cart to the BOM. I based the BOM off the www.chipamp.com parts list for a stereo pair with single power supply board. I already had the boards so it made for an easy way to prototype the project. I understand the concern about the 80VA transformer, but it's the one I can get the best deal on and it will suit most applications well. I suppose there is always the option to offer monoblock versions or to allow the purchaser to opt out of buying the transformer, but at that point I don't think there is much advantage in buying a kit versus buying the items a la carte.
If <$50 is the price point you are looking for, you probably should stick with a 12-18V single supply chip designed for car audio applications (obtained via sample programs, the ST parts look good and you should be able to get them free). Then you could use a surplus laptop power supply and inexpensive small enclosure and keep the cost down to <$50. There are some interesting surplus switching power supplies out there, like the ones on this page : http://www.73.com/a/0658.shtml . You should be able to get a good 12V 5A or 18V 3A power supply for around $10 (there may be minimum order quantities). That leaves $30 for parts and boards plus some shipping. If you make your own boards and have inexpensive or free facilities to do so you might be able to pull it off.
I'm still moving ahead with the group buy if the external interest is there. I'll start a new thread for that when I get the parts for the prototype and know a little more about the pricing. If you need a hand with the new design let me know, although I'm afraid that I don't have any experience with those chips (I just today ordered some samples to play with). I'm still interested in attending a meeting sometime, just email me through the forum.
Best Regards,
David
If <$50 is the price point you are looking for, you probably should stick with a 12-18V single supply chip designed for car audio applications (obtained via sample programs, the ST parts look good and you should be able to get them free). Then you could use a surplus laptop power supply and inexpensive small enclosure and keep the cost down to <$50. There are some interesting surplus switching power supplies out there, like the ones on this page : http://www.73.com/a/0658.shtml . You should be able to get a good 12V 5A or 18V 3A power supply for around $10 (there may be minimum order quantities). That leaves $30 for parts and boards plus some shipping. If you make your own boards and have inexpensive or free facilities to do so you might be able to pull it off.
I'm still moving ahead with the group buy if the external interest is there. I'll start a new thread for that when I get the parts for the prototype and know a little more about the pricing. If you need a hand with the new design let me know, although I'm afraid that I don't have any experience with those chips (I just today ordered some samples to play with). I'm still interested in attending a meeting sometime, just email me through the forum.
Best Regards,
David
volume control
A tested decent potentiometer is Alpha A20k (or 10k) Dual Gang, and its very low priced.
zobel
You can omit the speaker output zobel on LM3886. If needed (to support very long speaker cables) it can be added to the back side of the speaker output terminals at the chassis.
bypass caps for power
You can use 100nF multilayer ceramic at the amplifier board.
You can use 100nF (or smaller) cheapskate polyester at the power supply board.
I think I've already illustrated about the cheapest power supply going, and it works nicely.
To view the importance of this entrance into hi-fi class amplifiers, have a look at the "47 Labs Gaincard" and other hi-fi amplifiers. See the prices? Just because YOUR cost is low, doesn't mean that the value is low.
The project, as illustrated by gtforme00 and others has considerably more effective educational value than repeating basic soldering skills on kit assembly.
A tested decent potentiometer is Alpha A20k (or 10k) Dual Gang, and its very low priced.
zobel
You can omit the speaker output zobel on LM3886. If needed (to support very long speaker cables) it can be added to the back side of the speaker output terminals at the chassis.
bypass caps for power
You can use 100nF multilayer ceramic at the amplifier board.
You can use 100nF (or smaller) cheapskate polyester at the power supply board.
I think I've already illustrated about the cheapest power supply going, and it works nicely.
To view the importance of this entrance into hi-fi class amplifiers, have a look at the "47 Labs Gaincard" and other hi-fi amplifiers. See the prices? Just because YOUR cost is low, doesn't mean that the value is low.
The project, as illustrated by gtforme00 and others has considerably more effective educational value than repeating basic soldering skills on kit assembly.
However, if you did want an "easy" cheap kit, then here it is:
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=320-212
On 8 ohm speakers it produces 10 watts per channel at max, of which 5 watts per channel is usable for music.
Un-exciting and un-educational, isn't it?
It is usable as a desktop computer amplifier and for learning soldering skills.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=320-212
An externally hosted image should be here but it was not working when we last tested it.
On 8 ohm speakers it produces 10 watts per channel at max, of which 5 watts per channel is usable for music.
Un-exciting and un-educational, isn't it?
It is usable as a desktop computer amplifier and for learning soldering skills.
Well I've run some more calculations, and heard back from more vendors, so I have a better idea of what the end product might cost now.
I found a similar enclosure for close to half the price of the Hammond one from a seller on ebay.
The case is 200mm x 145mm x 70mm (8" x 5.7" x 2.8"). I can get a small volume discount from them.
As an added bonus, the increased height should now clear most of the power supply capacitors available.
I've also worked out a discount with Brian from www.chipamp.com on the printed circuit boards.
With this new information and estimating the shipping savings for a 20 piece group buy, I think we could get the price down to around $80 each + shipping. The biggest uncertainty at this point is the cost of a proper heat sink. My idea right now is to attach a 1/4" thick aluminum plate of about 2"x5" to the floor of the enclosure. The chips would be bolted to this plate. I would definitely have to test this design to see if it dissipated heat sufficiently, but it should be cost effective if it works.
It is certainly possible that we could see another price drop if enough people are interested. I'm reluctant to raise hopes till we gage interest.
In my mind, this kit would target products like the Sonic Impact Amp, which at $70 puts out a third of the clean power that this amp would be capable of delivering.
There is no use comparing a project amp to a store bought receiver. Yeah you could walk into a store and buy a receiver for $100 (I have two of them). I'll even be facetious and say that it might sound better and have more features. That isn't really the point of a project though, right? Some people get it and will spend the money (like that $300+ Leach amp project of mine), others (like my wife) don't see the point.
With all that said, I'm still supporting this project, wherever it may turn. I will let the interest in the chipamp kit group buy judge whether it will be successful or not, but I'll understand if your peers do not want to spend that much.
Best Regards,
David
I found a similar enclosure for close to half the price of the Hammond one from a seller on ebay.
The case is 200mm x 145mm x 70mm (8" x 5.7" x 2.8"). I can get a small volume discount from them.
As an added bonus, the increased height should now clear most of the power supply capacitors available.
I've also worked out a discount with Brian from www.chipamp.com on the printed circuit boards.
With this new information and estimating the shipping savings for a 20 piece group buy, I think we could get the price down to around $80 each + shipping. The biggest uncertainty at this point is the cost of a proper heat sink. My idea right now is to attach a 1/4" thick aluminum plate of about 2"x5" to the floor of the enclosure. The chips would be bolted to this plate. I would definitely have to test this design to see if it dissipated heat sufficiently, but it should be cost effective if it works.
It is certainly possible that we could see another price drop if enough people are interested. I'm reluctant to raise hopes till we gage interest.
In my mind, this kit would target products like the Sonic Impact Amp, which at $70 puts out a third of the clean power that this amp would be capable of delivering.
There is no use comparing a project amp to a store bought receiver. Yeah you could walk into a store and buy a receiver for $100 (I have two of them). I'll even be facetious and say that it might sound better and have more features. That isn't really the point of a project though, right? Some people get it and will spend the money (like that $300+ Leach amp project of mine), others (like my wife) don't see the point.
With all that said, I'm still supporting this project, wherever it may turn. I will let the interest in the chipamp kit group buy judge whether it will be successful or not, but I'll understand if your peers do not want to spend that much.
Best Regards,
David
Ya, I understand David.
I'm still a bit confused to the discrepancies int he prices being given. David, your saying ~$90 each, someone else is saying ~$30 ea... where is this difference coming from?
Well, the issue is only partially that students may not be willing to put the money into, but partially that the department may not approve of a project of such high cost.
We shall see.
I'm still a bit confused to the discrepancies int he prices being given. David, your saying ~$90 each, someone else is saying ~$30 ea... where is this difference coming from?
Well, the issue is only partially that students may not be willing to put the money into, but partially that the department may not approve of a project of such high cost.
We shall see.
I'm not sure where the ~$30 is coming from, but I think it just includes the cost of the components: no boards, no enclosure, and no hardware.
It may very well be that you want that level of kit, but I got the impression that you wanted something more complete, and hence my estimates include all the components, hardware, and an enclosure. Basically I have nailed down the cost of everything except the heatsink, the plan for which is described above. I have several vendors that are quoting the parts, and depending on how successful negotiations are, the price may drop even further from what I have estimated. I'll probably know more tomorrow, but the ~$80 + shipping estimate (which will not necessarily apply to you as you are so close) is what I know for a fact we can get right now.
If you decide to make your own boards, the price can drop another $10 or so. If you decide to use cheaper RCA jacks and speaker terminals as suggested above, the price can drop more. The cycle could go on and on, but you might be surprised how inexpensive $80 will seem to a faculty member for an electronics kit. I know we paid half that much for a bag full of wire segments and cheap logic ICs for our labs!
-David
It may very well be that you want that level of kit, but I got the impression that you wanted something more complete, and hence my estimates include all the components, hardware, and an enclosure. Basically I have nailed down the cost of everything except the heatsink, the plan for which is described above. I have several vendors that are quoting the parts, and depending on how successful negotiations are, the price may drop even further from what I have estimated. I'll probably know more tomorrow, but the ~$80 + shipping estimate (which will not necessarily apply to you as you are so close) is what I know for a fact we can get right now.
If you decide to make your own boards, the price can drop another $10 or so. If you decide to use cheaper RCA jacks and speaker terminals as suggested above, the price can drop more. The cycle could go on and on, but you might be surprised how inexpensive $80 will seem to a faculty member for an electronics kit. I know we paid half that much for a bag full of wire segments and cheap logic ICs for our labs!
-David
gtforme00 said:
Heat spreader technique works nicely with an under-volting like the 18-0-18vac to 22-0-22vac transformers you mention. Adding sufficient holes underneath the enclosure for air inlet and also as much holes in the top of the rear panel for air output, should finish the job of getting the heatsink expense cut. When the bottom panel gets hot from the chips, air will flow through the enclosure, simply because hot air goes up.
Bravo on the planning and pricing!!
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