I dislike the SPIKE protection on the lm3886.Especially since the instantaneous thermal protection kicks in quite early before the chip is hot.
It is not the overcurrent protection ,which triggers later.
Since this design already stresses this chip thermally it does not help to have an overprotective instantaneous themal prtection circuit.I am measuring about 70-75 deg.C on the actual chip when the spike kicks in.Before this temperature the amp more or less reaches maximum power without problems but as it nears this temp the thermal protection starts shutting on peaks which were easily reached before..Probably ghives only 1/2 or 2/3 power like this.Now 75C is not that hot for a chip that may be rated to 130 deg C continuous.Ok maybe there is 5-10C between the junction and case but still...
It is not the overcurrent protection ,which triggers later.
Since this design already stresses this chip thermally it does not help to have an overprotective instantaneous themal prtection circuit.I am measuring about 70-75 deg.C on the actual chip when the spike kicks in.Before this temperature the amp more or less reaches maximum power without problems but as it nears this temp the thermal protection starts shutting on peaks which were easily reached before..Probably ghives only 1/2 or 2/3 power like this.Now 75C is not that hot for a chip that may be rated to 130 deg C continuous.Ok maybe there is 5-10C between the junction and case but still...
As suggested, the high chip temperatures may be due to insufficient heatsinking. A contributing factor could also be insufficient case ventilation, and even poor thermal conduction due to unsatisfactory mounting or the chip on the heatsink. A good heatsink compound such as Arctic Silver will help with the latter, together with lapping of the heatsink mounting surface.
It should be noted that the "My Reference" amp is rated at 40 watts into 4 ohms and 56 watts into 8 ohms.
Of course you will not achieve these output ratings if any of the abovementioned defective conditions exist.
My RevC amp drives large full range five driver floorstanders rated at 4 ohms (dips to 3 ohms) and 90db efficiency, and I achieve very loud volumes in a large living room.
Audie.
It should be noted that the "My Reference" amp is rated at 40 watts into 4 ohms and 56 watts into 8 ohms.
Of course you will not achieve these output ratings if any of the abovementioned defective conditions exist.
My RevC amp drives large full range five driver floorstanders rated at 4 ohms (dips to 3 ohms) and 90db efficiency, and I achieve very loud volumes in a large living room.
Audie.
What I am saying is that because of spike protection this chip requires much more heatsinking than normal to keep its temp when playing loud below 70 deg.
Normally it should be able to play up to 130-140 deg on occasion without a huge problem BUT then the spike will turn on much earlier limiting thermal peaks.
My chip on normal listening levels does not go above 50-55 deg C .However when you really push it with heavy bass type music it heats up very quickly and slowly starts spike clipping more and more as it heats up but with the same volume level.This occurs very noticeably when the chip reaches 75 deg C.There is no clipping before this temperature is reached but as it approaches this temp the spike switches on slightly and then more heavily.So obviously it is not the overcurrent protection but the instantaneous thermal protection.
I agree that if you put a huge heatsink you avoid this problem but my point is that the spike is too sensitive.75 deg c is not that hot for chips-transistors and it should be ok to run at this temp on occasion without having to pay a penalty on max power output.
Normally it should be able to play up to 130-140 deg on occasion without a huge problem BUT then the spike will turn on much earlier limiting thermal peaks.
My chip on normal listening levels does not go above 50-55 deg C .However when you really push it with heavy bass type music it heats up very quickly and slowly starts spike clipping more and more as it heats up but with the same volume level.This occurs very noticeably when the chip reaches 75 deg C.There is no clipping before this temperature is reached but as it approaches this temp the spike switches on slightly and then more heavily.So obviously it is not the overcurrent protection but the instantaneous thermal protection.
I agree that if you put a huge heatsink you avoid this problem but my point is that the spike is too sensitive.75 deg c is not that hot for chips-transistors and it should be ok to run at this temp on occasion without having to pay a penalty on max power output.
Hi everybody 
I'm finishing construction of an integrated Kookaburra and My-Ref. Long building due to box and big heatsinks
This is my first experience with LM3886.
Last night I made a mistake that I think could happend to others and I don't remember this commented on thread, that's why I report it:
I went too enthousiastic with soldering and I found a short from a solder bubble between two legs of the big opamp on the upper surface of PCB
Fortunatelly I discovered it. It was not very apparent.
Maybe it is intended for people that want the amp to live a long and healthy life
Regards
M
I'm finishing construction of an integrated Kookaburra and My-Ref. Long building due to box and big heatsinks
This is my first experience with LM3886.
Last night I made a mistake that I think could happend to others and I don't remember this commented on thread, that's why I report it:
I went too enthousiastic with soldering and I found a short from a solder bubble between two legs of the big opamp on the upper surface of PCB
Fortunatelly I discovered it. It was not very apparent.
Maybe it is intended for people that want the amp to live a long and healthy life
Regards
M
Current Draw
I have most of the parts to build this little bugger and I just etched two boards tonight. I was wondering what the average current demand on a single side of the DC rail measures for a single channel driven hard?
I know there are many variations and many ways to test but I'm looking for an average or serveral peoples measurements to average it myself. Oh,of course I'm talking about 24VAC or 48VAC CT supply transformer (or close).
I think I'll skip work tommorrow and get some transformer action and a few missing bits (relays, enclosure, power cord, beers). and make a go of it. After reading hundreds of posts in this thread a fella has gotta do something.
Ja Bless,
Shawny Boy.
I have most of the parts to build this little bugger and I just etched two boards tonight. I was wondering what the average current demand on a single side of the DC rail measures for a single channel driven hard?
I know there are many variations and many ways to test but I'm looking for an average or serveral peoples measurements to average it myself. Oh,of course I'm talking about 24VAC or 48VAC CT supply transformer (or close).
I think I'll skip work tommorrow and get some transformer action and a few missing bits (relays, enclosure, power cord, beers). and make a go of it. After reading hundreds of posts in this thread a fella has gotta do something.
Ja Bless,
Shawny Boy.
protos - re. spike protection:
When I first used my Rev C and after I set my external speaker protector to 80 watts/channel as a precautionary measure, there were several occasions, spaced well apart, when the music (very loud) was interrupted very briefly. I did not know if it was spike protection or the external speaker protection, but think it was probably the former. The outside ambient temperature was 40C and about 33C indoors with evaporative aircon. I had a small fan blowing on the amp.
I have not have a recurrence since, though I rarely use such loud volumes. Anyway there isn't a problem at any tolerable volume level, with cooler weather.
maxlorenz,
You saved yourself some grief there! It is wise to closely inspect ones work for solder bridges, and also the quality of each solder joint. I use a magnifying glass, as I am not as sharp eyed anymore. Some tracks are quite close together and a fine tipped soldering iron is useful.
Audie.
When I first used my Rev C and after I set my external speaker protector to 80 watts/channel as a precautionary measure, there were several occasions, spaced well apart, when the music (very loud) was interrupted very briefly. I did not know if it was spike protection or the external speaker protection, but think it was probably the former. The outside ambient temperature was 40C and about 33C indoors with evaporative aircon. I had a small fan blowing on the amp.
I have not have a recurrence since, though I rarely use such loud volumes. Anyway there isn't a problem at any tolerable volume level, with cooler weather.
maxlorenz,
You saved yourself some grief there! It is wise to closely inspect ones work for solder bridges, and also the quality of each solder joint. I use a magnifying glass, as I am not as sharp eyed anymore. Some tracks are quite close together and a fine tipped soldering iron is useful.
Audie.
My calculations could be wrong, and I have not actually measured it, but here is my understanding.
The highest power you can get into an 8ohm load with 35V rails is about 8.75A but that is over 600 watts!!! The MyRef amp could never do this for long.
The max continous power into 4ohm is 56W so at 4 ohms the biggest continuous RMS AC voltage would be 15VAC that gives you about 3.5A continous current draw.
:EDIT: typo it is 3.5A not 4.5A
The highest power you can get into an 8ohm load with 35V rails is about 8.75A but that is over 600 watts!!! The MyRef amp could never do this for long.
The max continous power into 4ohm is 56W so at 4 ohms the biggest continuous RMS AC voltage would be 15VAC that gives you about 3.5A continous current draw.
:EDIT: typo it is 3.5A not 4.5A
I f you look at the spike protection datasheets it is quite clear that the the spike limits output power quite drastically on peaks when the chip warms up.At 75 deg C Tc (case temp) there is probably a loss of about 10-20 watts power output compared to Tc at 25deg C.
I have 4ohm 90 db speakers so 95% of the time there is no problem at all but if I want to really freak out on a couple of lets say Massive Attack songs then after a couple of minutes things start clipping wildly.
The darn chip has overvoltage and overtemperature shutdown so the spike is a bit of overkill and a nuisance.
I have 4ohm 90 db speakers so 95% of the time there is no problem at all but if I want to really freak out on a couple of lets say Massive Attack songs then after a couple of minutes things start clipping wildly.
The darn chip has overvoltage and overtemperature shutdown so the spike is a bit of overkill and a nuisance.
protos said:
Protos, I am driving 4 ohm 87db speakers very very hard right this moment, and have been for the last 2 hours or so. My IR thermometer registers 47C at the case. My heatsink is not huge, 4" x 5-3/8" x 1.5" for two channels. If yours are getting very hot I wonder if your HS are too small, or your amp is oscillating or something.
Ancient Overture
I pulled out an old box of National Semi Stuff from back in the day. I would have sworn I had a few LM3886's but I think someone walked away with them, still I have one each LM2876T and LM3876TF. I'll try the 3876 in one of the boards I just finished stuffing. I ordered a pile of samples of the LM3886TF so I'll be rocking harder in a few days.
I also found the orriginal demo board for the series un-stuffed and with full data sheets and extra distortion graphs. See attached jpeg.
Even if I get the amp set up nice, I think I'll order the kits from the Pear Brothers. Those components with the nice boards are too sweet. I'm gonna try to make a nice case first with the prototypes in it and then stuff it with Pears. Hmmm, pears (In a Homer Simpson voice)
I'm gonna go pop some fuses and beers! Goodnight folks.
P.S. What do I do with the Demo Board? Mauro did all the work for me, I just had to wait 12 years! P.S.2. I will put the graphs on flickr and post the link ASAP.
Shawn.
I pulled out an old box of National Semi Stuff from back in the day. I would have sworn I had a few LM3886's but I think someone walked away with them, still I have one each LM2876T and LM3876TF. I'll try the 3876 in one of the boards I just finished stuffing. I ordered a pile of samples of the LM3886TF so I'll be rocking harder in a few days.
I also found the orriginal demo board for the series un-stuffed and with full data sheets and extra distortion graphs. See attached jpeg.
Even if I get the amp set up nice, I think I'll order the kits from the Pear Brothers. Those components with the nice boards are too sweet. I'm gonna try to make a nice case first with the prototypes in it and then stuff it with Pears. Hmmm, pears (In a Homer Simpson voice)
I'm gonna go pop some fuses and beers! Goodnight folks.
P.S. What do I do with the Demo Board? Mauro did all the work for me, I just had to wait 12 years! P.S.2. I will put the graphs on flickr and post the link ASAP.
Shawn.
Attachments
Overture Stuff on Flickr
I guess this will interest some.
http://www.flickr.com/photos/17836073@N00/sets/72057594118049798/
Shawn.
I guess this will interest some.
http://www.flickr.com/photos/17836073@N00/sets/72057594118049798/
Shawn.
Hi all,
Decided to compare the Rev C, which I have been using in my secondary front end, with the Golden tube Audio SE40 stereo valve amp that I normally use. The SE40 is set to the zero feedback setting. The record I selected was Concord Jazz LA4 Just Friends - did not have time for more.
The main difference was that the Rev C lifted a veil from the music - it reproduced clearly some instrumental lines that were indistinct and difficult to follow with the SE40.
The SE40 has a more relaxed feel, but the Rev C was more involving.
Overall I think I frefer rhe Rev C as it reveals everything with clarity that is on the record.
have to go now, as the skirted boss beckons.
Audie.
Decided to compare the Rev C, which I have been using in my secondary front end, with the Golden tube Audio SE40 stereo valve amp that I normally use. The SE40 is set to the zero feedback setting. The record I selected was Concord Jazz LA4 Just Friends - did not have time for more.
The main difference was that the Rev C lifted a veil from the music - it reproduced clearly some instrumental lines that were indistinct and difficult to follow with the SE40.
The SE40 has a more relaxed feel, but the Rev C was more involving.
Overall I think I frefer rhe Rev C as it reveals everything with clarity that is on the record.
have to go now, as the skirted boss beckons.
Audie.
BrianDonegan said:
My heatsinks are not quite as big about 3inchby 2.5 inchby 1inch roughly each.
My aleph x also does not go above 50deg c but if you measure on the mosfet metal case it can be 90degC.
However my point is not that I do not know how to cool the chip better or that I dont have a few bigger heatsinks around the place(as a Pass fan should) but that the overprotective engineers at national -who never want their chip to have any chance of dying -have made this spike protection too sensitive necessitating more cumbersome heatsinking than absolutely necessary.
Anyway - now I got this off my chest I will go and cut some huge heatsinks to keep the SPIKE bogeyman away from my dwellings.
Wrongs value resistor
Hey fellas,
I am in the process of assembling my Twisted Pair RevC amp and noticed that R13 was supplied as a 3.3k ohm resistor rather than the speicified 100k ohm resistor. Has there been a design change or is this an inventory mistake? Thanks. Off to check the other values of components.
Hey fellas,
I am in the process of assembling my Twisted Pair RevC amp and noticed that R13 was supplied as a 3.3k ohm resistor rather than the speicified 100k ohm resistor. Has there been a design change or is this an inventory mistake? Thanks. Off to check the other values of components.
