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Old 1st January 2013, 11:48 AM   #161
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Default 20W@10%THD (16W@1%THD) to 8 ohms monobloc Parallel amplifier

Hey, solid state gurus! The contest parameters are posted in the chip amp forum where it is popular to use 10% distortion figures when expressing output power of lower voltage chips. So after a few hours and much help (thanks!), I've listed the same power specs, described more appropriately at post 1. And, there is the option of building a more interesting, higher powered, higher quality monobloc with parallel chip or parallel output devices. See also the following extract from the TDA7265 datasheet.
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Old 1st January 2013, 01:47 PM   #162
qusp is offline qusp  Australia
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Quote:
Originally Posted by Kindhornman View Post
jmFahey,
I'll look forward to see what you propose. I told my daughter about the little tin amplifier and she jumped at the chance to build something like that. She wants to become an engineer so perhaps this will help her decide what type she may want to be. The one that bobodioulasso posted was running on a 9v battery.
I would not recommend running from a single 9v battery plus rail splitter, particularly with lowish impedance headphones, a real split supply is recommended. assuming an impedance of 33ohms these days would be a guess. being sonys they probably arent too bad, but headphones these days get down under 20ohms and a power supply using a rail splitter here simply wont cut it, it will add to the return impedance of the amp and power supply.

if it can be a small AC powered supply (say 9VA with 0-10-0-10vac secondaries) I have some excellent PCBs for 'the wire' which has quite superb performance that pretty much defies proper measurement with audio precision system 2. I might even be able to rustle up a kit for her, has she done any soldering before?

ahh just looked at the link, yeah a cmoy.. hmm tbh unless the headphones really need the higher voltage gain, the iphone/ipad will have better performance than a standard cmoy with split battery PSU

Last edited by qusp; 1st January 2013 at 01:57 PM.
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Old 1st January 2013, 02:38 PM   #163
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qusp,
My daughter has no real experience except watching me building boards myself. I understand that amplifying the signal coming from the Ipod or phone probably won't help that much if at all in the sound quality for headphones. I am just trying to give her something to wet her appetite for electronics and see if that interests her. She has good math skills and that seems to be one of the requirements here to do real electronic designs though she could also use those for mechanical design. Myself I would love to see an amplifier that was taking the un-amplifiied signal as a wave file or whatever output you could get from an Ipod and convert it and amplify it but that is another animal completely. If you are stuck with an ac power supply you are also stuck to that wall wort, you won't be walking around with that. JM's idea is interesting but I do see a problem with the impedance match to the LM386 device. Who would want to have to have 4 sets of headphones attached to have low enough impedance? Is there anything else that could be used or should the whole design just use a discrete circuit so you could actually drive the 33ohm load of a standard headphone? Are we just talking about the dc impedance of the headphones, I could easily measure their Sony headphones and see what the real dc impedance is? I know this is way off topic here, perhaps this should be a new thread and start a new challenge?

Steven
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Old 1st January 2013, 03:08 PM   #164
qusp is offline qusp  Australia
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Hey Steven,

OK i'll shoot you an email after this, we are talking AC impedance, not resistance, if you know the model it will be easy to find online, its probably written on the box. actually with a decent design there is improvement possible, but not with the cmoy IMO

yeah the boards i'm talking about are tiny, its a pretty simple build, I run mine portable, but its a bit power (current) hungry due to the output buffers. 9v cells wouldnt cut it for long and it would need 2 in series at a minimum, while still only lasting ~2hrs. I use 4 x A123 LiFePO4 2300mah cells, 9v are usually 200-400mah. so its not going to cut it portable. unless you're a bit loco like me.

it depends on what shes willing to carry, the cmoy honestly I would avoid it, it may be an educational exercise, but you still want a result thats better than the ipod is already. it has to pay off or its not very interesting is it?

there are quite a few designs, of which I have numbers on file. the O2 is probably the best bet for portable, but its a bit large too. runs on battery, but probably not what your average girl is going to want to have to carry. I have a spare PCB for that too if shes keen though.

there are some variations on the cmoy theme that are passable, with 2 x 9v and output buffers, but then you may as well build something really decent.

anyway enough OT, sorry guys. been watching the thread, dont have the time to devote to an entry at the moment, not a lot of action here lately.

Last edited by qusp; 1st January 2013 at 03:12 PM.
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Old 1st January 2013, 03:26 PM   #165
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qusp,
Thanks for the response. Yes I wouldn't expect much from one of those 9v batteries myself. Reminds me of my high output bike light, I changed the batteries to a larger array of NiMh cells so I could actually ride for more than a little over an hour and still get home safe without a headlight! Since this isn't part of the contest here she wouldn't be held to the Altoids sized tin anyway but that just seemed like a nice size and form factor. Your right that if it doesn't sound better than the internal amplifier it isn't worth much as a project, but she will have to learn something and get her feet wet. Better sound is always the object so I will look forward to your input. Perhaps one of the chips meant for an automotive application is the way to go, but this is so out of my purview, I would be learning as much as she is at this point. Not really but I am a noob in circuit design.....

I hope you had a great New Years down under and that everything else has settled down there for you. Send me a PM and I'll talk to you.

Steven

Last edited by Kindhornman; 1st January 2013 at 03:28 PM.
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Old 1st January 2013, 03:43 PM   #166
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Is fashioning the top out of a pair of peltier devices legal?

You can get really decent thd out of a pair of lateral mosfets with no thermal runaway, use an LT1166 w smt parts and the small MKS-2 16V Wima caps.
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Old 1st January 2013, 03:59 PM   #167
qusp is offline qusp  Australia
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OK Steve, we'll take it to email, will send something through within the hour. need to see if I can search out where the old headwize forum projects are being hosted since the forum closed, pretty sure Kevin Gilmore is hosting them somewhere. the headphone section here of course has a few of interest.

thanks for the well wishes mate!
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Old 1st January 2013, 05:12 PM   #168
JMFahey is offline JMFahey  Argentina
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Quote:
I would not recommend running from a single 9v battery plus rail splitter,
Who ever mentioned a rail splitter?
I'm talking *battery* power , 6 to 9V single rail of course.
What's the point of listening to an MP3 player on the go, strolling Nature while pulling a 220V line cable around ?
Or a couple pound batteries

Quote:
JM's idea is interesting but I do see a problem with the impedance match to the LM386 device. Who would want to have to have 4 sets of headphones attached to have low enough impedance?
Maybe you didn't get it.
This headphone booster can drive *up to* 4 x 33 ohm headphones (or 3 x 20 ohm ones, if that worries you ) ..... even one pair of 8 ohm ones, if you find such dinosaurs at Salvation Army
It will be very happy driving just a single 33 ohms set ... or none at all, if you want to use the output as, say, a line driver or something or simply pull al headphones and forget to turn it off.

Quote:
9v cells wouldnt cut it for long and it would need 2 in series at a minimum, while still only lasting ~2hrs. I use 4 x A123 LiFePO4 2300mah cells,
Ouch !!, sorry but I guess you are , say, overdesigning here.
Mine will happily run idle over 60 Hs on a humble 9V Duracell, shorter depending on listening level, which will be quite low because this amp an be *deafening*.
Under real world use, and a single pair headphones, I estimate around 20 hours continuous music playing.
And using 4AA Duracells, multiply that duration by 5 or 6 , how's that?
Your Daughter will become *bored* with this before that

Of course, you can always use rechargeables there, a sensible move.

Last edited by JMFahey; 1st January 2013 at 05:15 PM.
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Old 1st January 2013, 05:50 PM   #169
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JmFahey,
Thanks for straightening me out on the impedance match. I took from your statement that you need to have 4 headphones running in parallel to get the impedance low enough! I am all for rechargeable NiMh or lithium batteries. I'm sure that most of us have chargers laying around to do that these days. I am all ears for suggestions on all sides.
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Old 1st January 2013, 07:22 PM   #170
qusp is offline qusp  Australia
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Quote:
Originally Posted by JMFahey View Post
Who ever mentioned a rail splitter?
I'm talking *battery* power , 6 to 9V single rail of course.
What's the point of listening to an MP3 player on the go, strolling Nature while pulling a 220V line cable around ?
Or a couple pound batteries
yep, you sure are confused... but have a great knack for exaggeration

the Cmoy, which was linked in the post I quoted was what I referred to, not you, or your as yet unknown design..... the cmoy most often calls for a split rail using a single battery, usually with plain resistors, but some versions use a rail splitter. both are a bad idea

I asked if AC was acceptable, IE was portable completely necessary, because I have spare PCBs and parts for 'the wire SE-SE' which I was pretty much offering to gift to Steven; I wasnt suggesting AC for portable...

a couple pounds of batteries? guess its a while since you looked at modern battery tech...


Quote:
Maybe you didn't get it.
This headphone booster can drive *up to* 4 x 33 ohm headphones (or 3 x 20 ohm ones, if that worries you ) ..... even one pair of 8 ohm ones, if you find such dinosaurs at Salvation Army
It will be very happy driving just a single 33 ohms set ... or none at all, if you want to use the output as, say, a line driver or something or simply pull al headphones and forget to turn it off.
A capacitively coupled portable amp that will drive 7 ohms in a linear fashion on a 9v battery? its clear you are not familiar with some of the modern headphone loads.

Quote:
Ouch !!, sorry but I guess you are , say, overdesigning here.
that battery powers a portable Balanced ES9018 dac, balanced headphone amp with ~2.5Wpc @ -110dB THD+N for ~8hrs and the whole thing including batteries, >10 linear regulators, transformer coupled electrical spdif (mini BNC), toslink spdif, battery monitor and digital volume control fits in a case 25 x 120 x 160mm, while weighing significantly less than 1lb.

overkill? yeah but not in the way you thought. its overkill in the manner that I built a very high quality home dac and headphone setup into a portable unit. (pics linked below)

Quote:
Mine will happily run idle over 60 Hs on a humble 9V Duracell, shorter depending on listening level, which will be quite low because this amp an be *deafening*.
Under real world use, and a single pair headphones, I estimate around 20 hours continuous music playing.
And using 4AA Duracells, multiply that duration by 5 or 6 , how's that?
Your Daughter will become *bored* with this before that

Of course, you can always use rechargeables there, a sensible move.
ahh yes, deafening, the age old yard-post of headphone amp drive quality...

i'm looking forward to seeing the 'headphone booster' too

what sort of output caps are needed for driving 7ohm loads? I presume it needs output caps with single rail? I calculate 1000uf or up to 10000uf for a 7ohm load.

but yes lets post a thread in the headphone amps forum.

Last edited by qusp; 1st January 2013 at 07:45 PM.
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