Hey!
i was thinking it should be possible to power my desk speakers trough my headphone amp if i just allow more power to the speakers than what the headphone amp originally allows.
what if i hook up my headphone amp's output to a mosfet for extra power (one for each audio channel) and plug that into my speakers? anyone tried something like this with good results?
my goal right now is to not spend money on getting a dedicated stereo amplifier for my speakers when i already have a good stereo headphone amp (o2). but maybe there will be a significant drop in audioquality taking such shortcuts?
*the speakers i want to power are KEF Q300 with an "amplifier requirement" of 15 - 120W according to product details page. as im planning to use them just for normal speaking volumes and perhaps sometimes a bit higher for a movie (without disturbing neighbours) i doubt that i will need more than 20w.
i was thinking it should be possible to power my desk speakers trough my headphone amp if i just allow more power to the speakers than what the headphone amp originally allows.
what if i hook up my headphone amp's output to a mosfet for extra power (one for each audio channel) and plug that into my speakers? anyone tried something like this with good results?
my goal right now is to not spend money on getting a dedicated stereo amplifier for my speakers when i already have a good stereo headphone amp (o2). but maybe there will be a significant drop in audioquality taking such shortcuts?
*the speakers i want to power are KEF Q300 with an "amplifier requirement" of 15 - 120W according to product details page. as im planning to use them just for normal speaking volumes and perhaps sometimes a bit higher for a movie (without disturbing neighbours) i doubt that i will need more than 20w.
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Not perfectly sure yet, im mostly asking to see if anyone else has already tried this so i can copy their solution
i suppose powering it with the same power used by the o2 headphone amp would be easy but im not sure it would be too happy about that. not sure if the ground would become unstable or if it even has enough power to begin with.
i just checked the ac-ac adaptor the o2 uses, and its rated 20 watt :| so i guess thats a dead end already. i expected the limiting factor would be the dc-ground circutry in the o2 amp but the wall adaptor is too weak already. i could maybe get a more powerful one but im still not sure the o2 power supply would be happy with that. probably better to use a separate adaptor but that introduces new problems with needing a stable ground and stuff, i wonder if im not just making things harder for myself.
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I think you arei wonder if im not just making things harder for myself.
. The power supply is a large part of the cost of an amplifier. What you are wanting to do is put an amplifier after your headphone amp, there really is no point. You would be much better off building or buying a proper amp up to the job in the first placeyea i guess what i would end up with is a headphone amp used as a preamp, then another amp on top of thatI think you are
. in the end i will have 2 amps anyway. i will look for a suitable amp to power the speakers, if i have time maybe i will diy one from the forums. thanks for your feedback
Yes, you can do this - look at MOSFET follower like MoFo. With 24v supply and and a big inductor you can get 11Wrms. But it’s simple and Class A. If you need more power you need to go with Class AB output stage and it’s not a simple single MOSFET anymore. Then you might as well build a full amp. The HPA saves you the first 2 stages of matbe 3 depending on design.
If you have 91dB or higher sensitivity speakers - you only need many 10w and it will be plenty loud.
Even with a simple single MOSFET output, it’s not so simple as heatsinks and PSU gets big.
If you really want to keep things compact just use a small Class D speaker amp that’s smaller than your HPA and drive it with your headphone amp as anpreamp.
A TDA8932 monobloc is smaller than a TO247 MOSFET and a few resistors and cap needed for a MOSFET follower plus it is 30w and costs only $2. Sounds very nice actually.
1pcs Digital power amplifier board module 35w mono amplifier module High power TDA8932 low power consumption-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
If you have 91dB or higher sensitivity speakers - you only need many 10w and it will be plenty loud.
Even with a simple single MOSFET output, it’s not so simple as heatsinks and PSU gets big.
If you really want to keep things compact just use a small Class D speaker amp that’s smaller than your HPA and drive it with your headphone amp as anpreamp.
A TDA8932 monobloc is smaller than a TO247 MOSFET and a few resistors and cap needed for a MOSFET follower plus it is 30w and costs only $2. Sounds very nice actually.
1pcs Digital power amplifier board module 35w mono amplifier module High power TDA8932 low power consumption-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
wow $2 for an amplifier, i never stop getting surprised by how cheap they can make things while still making profits from them in china. that monobloc defenitly seems like a easier solution than using a mosfet. so i guess i could just piggyback 2 of those, one for each channel.
but isnt that 35w for a 4 ohm load? it says "Speaker Impedance: 4-8 ohm, 8 ohm best".
wouldnt the 35w drop to half with a 8 ohm load? (though even at half i bet its enough for my prefered volumes)
Was also checking some other suggestions on the forum and a lot of people seem to like TPA3116, someone linked this and said its a good one:
TPA3116 2.1 Digital Audio Amplifier Board HIFI DC 12-24V BASS Speaker 50W*2+100W 721968958942 | eBay
any idea how these compare? obviously the TPA3116 is more expensive but $20 is still cheap if its a good amplifier.
but isnt that 35w for a 4 ohm load? it says "Speaker Impedance: 4-8 ohm, 8 ohm best".
wouldnt the 35w drop to half with a 8 ohm load? (though even at half i bet its enough for my prefered volumes)
Was also checking some other suggestions on the forum and a lot of people seem to like TPA3116, someone linked this and said its a good one:
TPA3116 2.1 Digital Audio Amplifier Board HIFI DC 12-24V BASS Speaker 50W*2+100W 721968958942 | eBay
any idea how these compare? obviously the TPA3116 is more expensive but $20 is still cheap if its a good amplifier.
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Hi,
To some extent, the demands of desktop speakers aren't vastly larger than headphone amps.
I built a small headphone amp, using a buffer and op amp. The buffer is LH0033, which has continuous current rating of 100mA, peak 250mA.
This on the surface isn't enough, but is adequate for me to drive a small full range driver (86dB/W) at comfortable levels, listening distance 0.7-1metre.
1-2 Watts is fine, unless you want subs and to deafen yourself!
To some extent, the demands of desktop speakers aren't vastly larger than headphone amps.
I built a small headphone amp, using a buffer and op amp. The buffer is LH0033, which has continuous current rating of 100mA, peak 250mA.
This on the surface isn't enough, but is adequate for me to drive a small full range driver (86dB/W) at comfortable levels, listening distance 0.7-1metre.
1-2 Watts is fine, unless you want subs and to deafen yourself!
Im looking at the datasheet for the op amps used in the output stage of the o2 HPA (NJM4556). it says
it also says in the datasheet the dip8 has a power disipation of 700mw, but since the o2 has two amps parallel for the output stage i wonder if that is doubled? its two amps in the same chip used for each audiochannel, so i guess they might heat up a bit if i max it out.
but the speakers im planning to use are 8Ω, not 150Ω. im still waiting to receive the speakers (ordered them online) so i cant try yet but i will give it a try once they are here.
it also says in the datasheet the dip8 has a power disipation of 700mw, but since the o2 has two amps parallel for the output stage i wonder if that is doubled? its two amps in the same chip used for each audiochannel, so i guess they might heat up a bit if i max it out.
For what it's worth, 70mA looks pretty good. Maybe a pair paralleled, or triplet?
The Buffer IC I used got fairly warm at max output with music, and Hot enough to avoid touching when running in the region of 600 mWatt, into 8 Ohms. However a rudimentary heatsink is easier to apply to the metal case (or ceramic case) version.
16 or 32 Ohm would keep those DIP at a lower temperature, being as their in a lower dissipation case. Although cunning copper foil heatsinking could be employed
I'm be following to see how it turns out as I hadn't spotted that IC and might try this myself!
The Buffer IC I used got fairly warm at max output with music, and Hot enough to avoid touching when running in the region of 600 mWatt, into 8 Ohms. However a rudimentary heatsink is easier to apply to the metal case (or ceramic case) version.
16 or 32 Ohm would keep those DIP at a lower temperature, being as their in a lower dissipation case. Although cunning copper foil heatsinking could be employed
I'm be following to see how it turns out as I hadn't spotted that IC and might try this myself!
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I read up a bit more about the o2 and i wonder if i may have to give up the idea of using headphone amp alone.
Max Output 15 Ohms: 337 mW
Max Output 33 Ohms 613 mW
Max Output 150 Ohms 355 mW
Guessing at 8 ohms its even lower? not sure why it has similar wattage at 15 and 150 ohms but almost twice that at 33 ohm. on the website it also says the amp has "active current limiting" to make sure you dont do something stupid and blow up your low impedance headphones with max volume. Not sure how that is implemented, maybe its just refering to the limitations of the IC's themself? but yea, the IC is pretty impressive from what i have read about them, high output, low noise, and low price.
well, time will tell. will give it a try once speakers are here but im leaning towards the TPA3116 i mentioned earlier in the thread or maybe the TDA8932 mentioned by xrk971
Max Output 15 Ohms: 337 mW
Max Output 33 Ohms 613 mW
Max Output 150 Ohms 355 mW
Guessing at 8 ohms its even lower? not sure why it has similar wattage at 15 and 150 ohms but almost twice that at 33 ohm. on the website it also says the amp has "active current limiting" to make sure you dont do something stupid and blow up your low impedance headphones with max volume. Not sure how that is implemented, maybe its just refering to the limitations of the IC's themself? but yea, the IC is pretty impressive from what i have read about them, high output, low noise, and low price.
well, time will tell. will give it a try once speakers are here but im leaning towards the TPA3116 i mentioned earlier in the thread or maybe the TDA8932 mentioned by xrk971
> not sure why it has similar wattage at 15 and 150 ohms but almost twice that at 33 ohm.
Do math. Figure the V and I in each load. (all RMS)
2.25V 0.15A in 15r
4.5V 0.13A in 33r
7.3V 0.05A in 150r
So basically the amplifier will deliver 0.15 Amps and/or 7+ Volts.
Power output might be maximized if the load were exactly 7V/0.15A which is 47 Ohms.
The observed limits "could" be met with three channels of NJM4556 working on +/-12V supply. Dual-12V will give 10V peaks or 7Vrms. Three '4556 gives 3*0.07A or 0.21A peak which is 0.15Arms. (I do not know what is actually inside the box.)
The amplifier appears to be V-I limited. We can also have a V limit plus a series resistor, which gives a more rounded W/Z curve.
As for speakers: anything involving "Power" usually has to be well matched to the load. Do you have enough power? Does it come out at the right rate? A farmer may pull a large plow with a 100HP engine, but a 115HP Mazda MX-5 sports-car would be a terrible plow-puller, just like a M-F 100 won't go 99MPH. Getting more power out of a too-small engine is difficult, generally calls for a bigger engine. Getting a different ratio of thrust/speed (impedance) is "just gears" but gears are a huge part of the cost of a tractor, and the audio equivalent is the Transformer, which is not cheap nor easy to make good. If you want to pull speakers, get a speaker-puller (amplifier).
Do math. Figure the V and I in each load. (all RMS)
2.25V 0.15A in 15r
4.5V 0.13A in 33r
7.3V 0.05A in 150r
So basically the amplifier will deliver 0.15 Amps and/or 7+ Volts.
Power output might be maximized if the load were exactly 7V/0.15A which is 47 Ohms.
The observed limits "could" be met with three channels of NJM4556 working on +/-12V supply. Dual-12V will give 10V peaks or 7Vrms. Three '4556 gives 3*0.07A or 0.21A peak which is 0.15Arms. (I do not know what is actually inside the box.)
The amplifier appears to be V-I limited. We can also have a V limit plus a series resistor, which gives a more rounded W/Z curve.
As for speakers: anything involving "Power" usually has to be well matched to the load. Do you have enough power? Does it come out at the right rate? A farmer may pull a large plow with a 100HP engine, but a 115HP Mazda MX-5 sports-car would be a terrible plow-puller, just like a M-F 100 won't go 99MPH. Getting more power out of a too-small engine is difficult, generally calls for a bigger engine. Getting a different ratio of thrust/speed (impedance) is "just gears" but gears are a huge part of the cost of a tractor, and the audio equivalent is the Transformer, which is not cheap nor easy to make good. If you want to pull speakers, get a speaker-puller (amplifier).
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I was one of the first to build my own TPA3116/3118 on DIYA and have like over a dozen of them and I really like them, but feel that the TDA8932 has better bass authority and is quieter and more natural sounding. It is smaller and had built in anti-thump circuitry which the TPA3116 really has issues with. I would still pick it over 3116 at same price. At this price there is no reason not to try it. Just connect a 19v laptop brick and judge for yourself.
Thanks for the clarification PRR! i guess it makes sense for it to be limited in both voltage and amps. so if my speakers are at 8r and the current is limited to 0.15A then i wont get out more than ~0.180w.
so i guess despite the fact that theres plenty of room left for the voltage to increase, the limiting factor is the current so the output will be low anyway. that explains the amps "active current limiting"
Sadly the price is not as attractive for someone who lives in sweden. when we order something from outside EU it costs ((original shipping price + shipping)*1,25*(possible extra import fees) )+$8.3
so to order one TDA8932 at a cost of US $1.59 i pay a bit over $10 despite the free shipping. and then wait another 2 weeks for it to pass customs...
but anyway, its not like i will order just one. if i decide to go for the TDA8932 route i will probably order a handful, so i have a few extra.
going to read some more about it but im defenitly leaning towards the TDA8932, and i do have a 18.5v laptop brick laying around just waiting to be put to use after years in a drawer.
thanks for the input!
so i guess despite the fact that theres plenty of room left for the voltage to increase, the limiting factor is the current so the output will be low anyway. that explains the amps "active current limiting"
It's kind of hard to belive that a much smaller much cheaper chip is better but im defenitly willing to give it a try hearing this
Sadly the price is not as attractive for someone who lives in sweden. when we order something from outside EU it costs ((original shipping price + shipping)*1,25*(possible extra import fees) )+$8.3
so to order one TDA8932 at a cost of US $1.59 i pay a bit over $10 despite the free shipping. and then wait another 2 weeks for it to pass customs...
but anyway, its not like i will order just one. if i decide to go for the TDA8932 route i will probably order a handful, so i have a few extra.
going to read some more about it but im defenitly leaning towards the TDA8932, and i do have a 18.5v laptop brick laying around just waiting to be put to use after years in a drawer.
thanks for the input!
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