m00dawg Posted April 20, 2011 Report Share Posted April 20, 2011 So I was thinking about running the Sammich on a 9V battery for while but opted to just put in my 12VDC supply (similar to the one I used on my sammichSID). I was worried heat might be an issue but, so far, the 78L05 is cool to the touch and the heatsinks are just a tad bit warm for the 7805. This is when basically sitting idle and occasionally diddling on my keyboard. So far, though, it seems to be throwing off far less heat than my sammichSID. Is that expected or am I missing a potential source of heat somewhere? By the way, the thing is fully functional and appears to be working as advertised! I was worried I might have had a bad solder joint on the SMD chips (found one while doing voltage tests that I fixed, but my tests previous came out ok for the other pins). I haven't quite figured out how the audio routing works - seems like I can route all audio to just one audio out if I so desired? Haven't tried making patches yet - the default patches are typical cliche FM sounds which are fun but I want to see about adding more dynamics at some point. The drum section is fun once I figured that out. This thing basically owns face! Quote Link to comment Share on other sites More sharing options...
Flemming Posted April 20, 2011 Report Share Posted April 20, 2011 My SammichFM is a LOT cooler than the SammichSID, indeed. Using same wallwart for both Quote Link to comment Share on other sites More sharing options...
m00dawg Posted April 20, 2011 Author Report Share Posted April 20, 2011 The highest temp I saw was 35C which was recorded towards the top of the inner heatsink of the 7805. I can't get my temp probe on top of the 7805 without taking everything apart and taping it directly to the reg (which I may do later). I'm not worried about it though I am still going to buy the 9VDC adapter mentioned in the other thread. Good to know I have a working solution that doesn't get super hot for the moment though. Quote Link to comment Share on other sites More sharing options...
Wilba Posted April 20, 2011 Report Share Posted April 20, 2011 It is a lot less current draw than sammichSID. nILS did some adding up once and I forgot the total. I put an extra heatsink in there to be sure, and kept the ventilation the same as sammichSID, because people will probably try to run it on 12V AC 500mA plugpacks. Quote Link to comment Share on other sites More sharing options...
m00dawg Posted April 20, 2011 Author Report Share Posted April 20, 2011 Oooh yeah 12VAC is quite a bit. So far 12VDC seems to be ok but I'm going to get a proper linear 9VDC brick just the same. I think my 12VDC is a switchmode anyway :/ Need to replace my sammichSID power supply too with a proper linear brick while I'm at it. Quote Link to comment Share on other sites More sharing options...
imsplitbit Posted April 21, 2011 Report Share Posted April 21, 2011 Yeah 12v is seriously way too much. I am curious as to why you don't have more heat. Voltage regulators give off greater heat the further you get away from it's rated output voltage. That extra voltage has to be shed somehow. I try to stay within 1 to 3 V of my rated needs. I have a 6V wall wart for my project. Quote Link to comment Share on other sites More sharing options...
m00dawg Posted April 21, 2011 Author Report Share Posted April 21, 2011 Seriously too much may be a slight stretch. The input voltage for the regulators (after passing through the bridge rectifier) is going to be around 11VDC, so they have to dissipate around 6VDC in the form of heat. However, the amount of heat is related to the load. Little load, little head. Now 9VDC will throw off less heat than 12VDC, but it doesn't seem to be enough to really cause any heat related issues. Even using 12VDC, the sammichFM runs much much cooler than my sammichSID. It depends on the brightness of the LCD too and mine is set a tad low. Now if we are talking 12VAC that's a different story since you can actually end up with higher voltage after the AC is rectified to DC. How much depends on a number of factors (such as load) but the magic number is around 1.4x of the input, so 12VAC can end up being close to 17VDC. Still, low current means low heat but it's certainly going to be more than you would get from 12VDC. On the flip-side, be careful about getting too close to the output voltage of the regulators. Too little and you can end up with drop-outs since most regulators need 1-2V (1.5V being the value I tend to see the most) to operate. The rectifier is going to remove about .7V from a DC input voltage. Quote Link to comment Share on other sites More sharing options...
imsplitbit Posted April 21, 2011 Report Share Posted April 21, 2011 Yeah I noticed after looking at the pcb that wilba is using a bridge rectifier. Very nice touch that most people overlook. Voltage drop will be about 1.2 to 1.5V through that so 6V won't be good enough. But 9V will be perfect. Quote Link to comment Share on other sites More sharing options...
imsplitbit Posted April 21, 2011 Report Share Posted April 21, 2011 I still say 12V is too much though. I mean current draw really is whats important and it *will* work but it seems like overkill. I have ordered a 9V wall wart and will just use my benchtop dc power supply to provide power until it gets here. I should be finished with my sammy tonight. Cant wait to play with it!!!! Quote Link to comment Share on other sites More sharing options...
m00dawg Posted April 21, 2011 Author Report Share Posted April 21, 2011 Yeah me too. 9V from Jameco is in the mail - the 12VDC is just so I can play around with it for now. Heck it's a switchmode PSU, and an old one at that. I didn't notice any audio issues with it though, but I haven't done a noise test with it or anything. No point really if I'm going to replace it in a few days anyway. For now, I turned the brightness down lower than I would ideally like, just in case. Although, I think Wilba is taking the input before the regulator for the high voltage option LCD? I could be totally wrong there though :) I know he does some trickery there. On that note, a total aside, but the negative LCD looks hot! I'm basically sold on those now. Quote Link to comment Share on other sites More sharing options...
m00dawg Posted May 10, 2011 Author Report Share Posted May 10, 2011 Adapters came in! The 9VDC works great, though I haven't yet tested temps yet. After a few hours the sammichFM was cool to the touch all around and I felt no heat on the sides (maybe a teeny tiny bit on the right side where the regulators are). This is the one from Jameco that mazatta recommended in post. Wilba also added a link to it on the sammichFM wiki page. I haven't tested the audio noise yet either but I was able to hear some artifacts before that I am no longer noticing so that's a good sign. I bought a similar wallwart for the sammichSID and noticed no difference there - I did do a recording test but not a particularly accurate one. Quote Link to comment Share on other sites More sharing options...
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