hi everyone
I have a pair of 6 ohm passive speakers that I'd like to use and not throw away.
could you suggest me a good preamp+power amp (or kit) that I could build to use it with PC line out and those speakers? I don't have the actual specs of those speakers other than impedance, but if needed I could find some info.
many thanks and sorry for my bad english
Dimitri
I have a pair of 6 ohm passive speakers that I'd like to use and not throw away.
could you suggest me a good preamp+power amp (or kit) that I could build to use it with PC line out and those speakers? I don't have the actual specs of those speakers other than impedance, but if needed I could find some info.
many thanks and sorry for my bad english
Dimitri
There is nothing unusual about powering 6 ohm speakers or analog input from a PC line out, you can pick among most of the designs here.
A better starting point might be the level of complexity you want or feel capable of, what the budget is, how many watts you'll want, whether you want to use something premade or a kit (which you prefer).
The generic answer would be get a "LM3886 Stereo Kit" from chipamp.com, and of course a toriodal transformer of about 300VA, 24V-0-24V, and a case, heatsink, switches/knob/jacks/etc of your preference from an electronics supplier in your area.
LM3886 Amplifier Kit | Chipamp.com
A better starting point might be the level of complexity you want or feel capable of, what the budget is, how many watts you'll want, whether you want to use something premade or a kit (which you prefer).
The generic answer would be get a "LM3886 Stereo Kit" from chipamp.com, and of course a toriodal transformer of about 300VA, 24V-0-24V, and a case, heatsink, switches/knob/jacks/etc of your preference from an electronics supplier in your area.
LM3886 Amplifier Kit | Chipamp.com
Remember , your supply voltage determines the lowest load you can drive ......
A 2x24v transformer might be a bit high for 6 ohms I think a 2 x 20v or 2 x 22v might be better ......
A 2x24v transformer might be a bit high for 6 ohms I think a 2 x 20v or 2 x 22v might be better ......
^ I'd rather build with 24-0-24, the heat level is still manageable and it leaves more headroom for 8 ohm speakers should the need arise.
I think you have it backwards ..... there would be more headroom (run cooler) if he built it to handle 4 ohms but used it at 6 ohms ......
If he builds it to 8 ohm specs (+/-35v DC) and runs it at 6 ohms then he runs the risk of trying to disapate more heat than the chip and heatsink can handle which will cause the Spike protection to kick in and shut down the Chip ......
If he builds it to 8 ohm specs (+/-35v DC) and runs it at 6 ohms then he runs the risk of trying to disapate more heat than the chip and heatsink can handle which will cause the Spike protection to kick in and shut down the Chip ......
I don't assume someone tries to use the bare minimum heatsink necessary, as it seems misguided, if building something that costs dozens of dollars.
I don't have it backwards though, running higher voltage has no limit on output power if you keep the chip cool. "headroom" isn't really a factor if you consider this a low power amp, which anything under a few hundred watts is in my opinion. It is very easy to dissipate the heat at the max rail voltage spec'd, with any low ohm speaker.
If we were trying to economize like a manufacturer would, then I would agree to conserve the budget, but until then, if you run it at the max rail voltage things will be fine, IF you don't skimp on the heatsink.
Spike protection, as you wrote, is about heat. Music seldom if ever is continuous sine waves so I advocate designing for real world use.
In the end, we might as well build for max output and then see if "spike" kicks in.
Now I am opening a can of worms but ok... It's a little bit crazy to DIY design an amp to only barely be capable of the load. To do bare minimum voltage, leaves lots of people doing silly things like adding on multiple times as much capacitance as an amp needs and still failing to see why they didn't get a good performance:cost ratio.
I don't have it backwards though, running higher voltage has no limit on output power if you keep the chip cool. "headroom" isn't really a factor if you consider this a low power amp, which anything under a few hundred watts is in my opinion. It is very easy to dissipate the heat at the max rail voltage spec'd, with any low ohm speaker.
If we were trying to economize like a manufacturer would, then I would agree to conserve the budget, but until then, if you run it at the max rail voltage things will be fine, IF you don't skimp on the heatsink.
Spike protection, as you wrote, is about heat. Music seldom if ever is continuous sine waves so I advocate designing for real world use.
In the end, we might as well build for max output and then see if "spike" kicks in.
Now I am opening a can of worms but ok... It's a little bit crazy to DIY design an amp to only barely be capable of the load. To do bare minimum voltage, leaves lots of people doing silly things like adding on multiple times as much capacitance as an amp needs and still failing to see why they didn't get a good performance:cost ratio.
Last edited:
Look at the charts in the Datasheet , it specifies heat dissapation and output power based on supply voltage , it clearly shows that at full power with +/-35v into 6 ohms that the chip will put out over 80w....
Even with a heatsink as big as fort knox the LM3886 can not dissapate that amount of heat , thats why it isn"t a 80w amp .....
The chip will have to try to dissipate about 60w of heat which is impossible no matter the size of the heatsink ......
Those datasheet charts are there for a reason .....
Now if he built it to 4 ohm specifications it could drive 6 ohms or 8 ohms all day at full blast without any problem .......
So he follows your advise and buys the transformer and cranks up his new amp with his 6 ohms speakers and listens for a while and all of a sudden the sound goes all distorted and it starts cutting out and he realizes that his heatsink is hot enough to fry an egg and thinks to himself "now I gotta buy a new transformer because the spike is kicking in" ......
It is much better to be safe than be sorry .....
Even with a heatsink as big as fort knox the LM3886 can not dissapate that amount of heat , thats why it isn"t a 80w amp .....
The chip will have to try to dissipate about 60w of heat which is impossible no matter the size of the heatsink ......
Those datasheet charts are there for a reason .....
Now if he built it to 4 ohm specifications it could drive 6 ohms or 8 ohms all day at full blast without any problem .......
So he follows your advise and buys the transformer and cranks up his new amp with his 6 ohms speakers and listens for a while and all of a sudden the sound goes all distorted and it starts cutting out and he realizes that his heatsink is hot enough to fry an egg and thinks to himself "now I gotta buy a new transformer because the spike is kicking in" ......
It is much better to be safe than be sorry .....
To save on any argument I would just make sure you use a good heatsink and possibly a small quiet fan that kicks on when it gets to warm.
A little bit of movment of air makes a big difference ,when and if you are cranking it, you won't really hear the fan that much anyhow.
I would suggest build building a PA100 or PA150 version and atleast -/+ 35v this would give you an amp with ample amount of power for what ever you hook to it.
And would be good should you have two pairs of speakers you want to power.
The extra cost isn't any thing to worry about considering the design and what you would have in the long run.
It just depends on what your budget is.
Just consider that you will need at least a 400 watt transformer to have ample enough current to run them.
Or else they will just run out of omph and distort like any other amp would.
I am sure that you won't be running them full bore 24/7 all of the time ,although I maybe wrong. he,he
Just my friendly two cents!
jer 🙂
A little bit of movment of air makes a big difference ,when and if you are cranking it, you won't really hear the fan that much anyhow.
I would suggest build building a PA100 or PA150 version and atleast -/+ 35v this would give you an amp with ample amount of power for what ever you hook to it.
And would be good should you have two pairs of speakers you want to power.
The extra cost isn't any thing to worry about considering the design and what you would have in the long run.
It just depends on what your budget is.
Just consider that you will need at least a 400 watt transformer to have ample enough current to run them.
Or else they will just run out of omph and distort like any other amp would.
I am sure that you won't be running them full bore 24/7 all of the time ,although I maybe wrong. he,he
Just my friendly two cents!
jer 🙂
That is incorrect on several counts.
1) People don't run their amps at 100% output power continuously. The average is not 80W nor does the heatsink need be capable of that.
2) The reason the dissipation goes up is that the amp would be outputting more power too. We don't have to consider this! If you argue, use less voltage, I can fairly argue that using 35V, if the extra voltage isn't needed for a particular load then the volume isn't at "100%" figure used in the graph, let alone continuous output being 100%, so again the average dissipation is far below 80W. Further, if your gain is not set higher than appropriate for the lower voltage transformer, you won't even reach 100% on 35V rails compared to lesser voltage, but you'd be less likely to have any clipping and possible speaker damage.
3) It is not impossible to dissipate 60W, but even if it were, plenty of people have built LM3886 chipamps with 35V rails. Myself included, they work fine demonstrating that you have overlooked enough variables that there really isn't any reasonable case where it would be true that ONLY raising rail voltage to 35V will be a problem.
4) It's not an 80W amp because the output transistors can't handle enough current. Just because a higher voltage allows more current through a given resistance, that does not mean someone is compelled to keep raising gain until they fry something. This is true no matter what voltage, or heatsink, you choose for the design.
Can't we let the myth about voltage die already? While in the strictest sense you don't "Need" 35V for 4-6 ohm load, so long as the amp isn't married to the speakers, like integrated into a speaker's housing forever, it is far more reasonable to build an amp able to drive 8 ohm loads better, particularly when there may be no difference in transformer cost.
The difference in power dissipation at the higher voltage is very small. Comparing 20V transformer you suggested, resulting in 27V rails, and 35V rails for example (per the datasheet supply current graph) here is the difference:
35V rails: 45mA * 35V * 2 rails = 3.15W
27V rails: 43mA * 27V * 2 rails = 2.3W
I'm not even certain that you need to multiply both rails, the difference could be half that shown above.
Conclusion: If the amp builder does nothing different except pick a 35V rail voltage instead of 27V, total power dissipation goes up less than 1W... a trivial amount, but in return you get roughly 70% higher output capability should you ever want to drive 8 ohm speakers (output power vs load resistance graph in the datasheet). It really doesn't make much sense to build a standalone amp with rails below 35V unless you happened to have parts lying around you wanted to use like a transformer with lower voltage or expensive 35V capacitors you didn't want to run so near their limit, OR you are 100% certain that nobody would ever connect it to speakers over 6 ohms... not even a future owner or your grandchildren years from now.
Last edited:
I agree, ! !
That is why a PA100 with a 28V-0-28V transformer appeals to me as a very decent and versatile amp.
And won't break any extreme budget if that may be the case.
jer
That is why a PA100 with a 28V-0-28V transformer appeals to me as a very decent and versatile amp.
And won't break any extreme budget if that may be the case.
jer
oh my
Here's my take..........
my first diy project was a chip amp, it used the lm3875. psu traffo was 18v - 225va, basic build in strip board using standard components - this was from an artical in 1997 HI-FI World magazine - a short while later they reviewed the battery powered Final Audio product...........at £1500 (1600eu) BUT i had about 3/4 of that 'perfomance' for a tenth the cost.
my basic build got powered from batteries and made glorious sounds through my freinds Harbeth Hlp3 speakers from both big black discs, little silver discs, tuners and tape. it then morphed into mono channels, built another pair of mono's to bi-amp my first pair of diy speekers.
an awful long way from not much initial outlal.
14yrs later they reside with my mother after her 'plastic trashbox' died, as do my first 'speekers.
so, search BrianGT - amp and psu kit and pcb, basic or the upraded - read the instructions, go by his recomendations, get basic tools and you wont go far wrong. i think he has a thread in this forum.
learn, have fun ect
Here's my take..........
my first diy project was a chip amp, it used the lm3875. psu traffo was 18v - 225va, basic build in strip board using standard components - this was from an artical in 1997 HI-FI World magazine - a short while later they reviewed the battery powered Final Audio product...........at £1500 (1600eu) BUT i had about 3/4 of that 'perfomance' for a tenth the cost.
my basic build got powered from batteries and made glorious sounds through my freinds Harbeth Hlp3 speakers from both big black discs, little silver discs, tuners and tape. it then morphed into mono channels, built another pair of mono's to bi-amp my first pair of diy speekers.
an awful long way from not much initial outlal.
14yrs later they reside with my mother after her 'plastic trashbox' died, as do my first 'speekers.
so, search BrianGT - amp and psu kit and pcb, basic or the upraded - read the instructions, go by his recomendations, get basic tools and you wont go far wrong. i think he has a thread in this forum.
learn, have fun ect
- Status
- Not open for further replies.