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Old 3rd February 2010, 04:52 AM   #61
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Back to TDA1558Q and its noise problems:

There is no reasonably clean ground for audio input provided by either the chip or datasheet.

Therefore I'm thinking of using a rail splitter much like the popular CMOY Headphone Amplifier. With the TDA1558Q in bridged configuration, there's no heavy current needed for "virtual ground" and so it could simply be a pair of ordinary 1/4 1% resistors, possibly a 2k value.

Any ideas or help would be sincerely appreciated.

Pin 4, the internal rail splitter is emitting:
+6.28
-5.81
(the power supply in use has 12.1v)
There's a 0.47v error in the internal rail splitter, so I don't think its useful, unless, perhaps stabilizing it can reduce the noise?

Reading materials:

Philips/NXP document showing that the company won't help you apply their products: http://www.nxp.com/acrobat_download2...us/AUDIOIC.pdf

The CMOY rail splitter: http://tangentsoft.net/audio/cmoy-tu...angent-sch.pdf and maybe it can make a solution for getting a reliable input circuit ground on a bridged TDA1558Q?
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Old 3rd February 2010, 04:57 AM   #62
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Quote:
Originally Posted by danielwritesbac View Post
Compare the 16w amplifier with the sound you want to crank up -versus- the 64w amplifier with the sound you'd never want to hear again. Only one of these options is useful, so lets make clean amplifiers.
Yes, I am well aware how wattage is the most overstated factor of a quality amp. It seems to be the one that gets all the casual listener's ears to perk up. Them and the mobile audio crowd love them watts. Plus, I can't play music very loud due to neighbors.


I will probably snag a few of those TDA8561Q's. I think it also said there's some "switch on/off pop" protection. Which saves me from extending myself further into an area I am brand new to. The less I have to do the better. In addition there's better THD. Win Win.
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Old 3rd February 2010, 04:59 AM   #63
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Quote:
Originally Posted by irishpatrick33 View Post
. . .
I will probably snag a few of those TDA8561Q's. I think it also said there's some "switch on/off pop" protection. Which saves me from extending myself further into an area I am brand new to. The less I have to do the better. In addition there's better THD. Win Win.
Win-Win looks more like this:
Parts-Express.com:Velleman 30W Stereo Audio Amplifier Kit | velleman stereo amplifier stereo kits kit ic audio amplifier audio audi amps amplifiers amplifier kit amplifier amp kits amp kit amp
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Old 3rd February 2010, 05:44 AM   #64
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I didn't exactly mean it that way. The goal isn't to do as little as possible, exactly. More so strike a nice balance, while trying to achieve the best product possible. But I want to build something myself.

I just realized I screwed up. I thought the TDA8561Q had 2 less wpc than the TDA1558Q, not the other way around like it is. Hence the giving up watts comment. I'm stupid.

The specs for the Velleman aren't for 12V single supply. I wonder how much worse that wattage gets running it that way. Is the THD for the TDA1521Q as good as the Velleman suggests, because I am having a harder time understanding that spec sheet?
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Old 3rd February 2010, 06:59 AM   #65
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Quote:
Originally Posted by irishpatrick33 View Post
I didn't exactly mean it that way. The goal isn't to do as little as possible, exactly. More so strike a nice balance, while trying to achieve the best product possible. But I want to build something myself.

I just realized I screwed up. I thought the TDA8561Q had 2 less wpc than the TDA1558Q, not the other way around like it is. Hence the giving up watts comment. I'm stupid.

The specs for the Velleman aren't for 12V single supply. I wonder how much worse that wattage gets running it that way. Is the THD for the TDA1521Q as good as the Velleman suggests, because I am having a harder time understanding that spec sheet?
Its not exactly for a 12v power supply. It uses the very common 12-0-12vac center tap transformer, which is a 24vct transformer. The power supply circuit is onboard with the amplifier itself, so you don't have to build a power supply. The reputation of the product is MUCH different that what we're looking at (and that's a good thing).

I think the datasheet is interesting because its SO very similar to the amplifiers we're looking at, and comparing it "may" show how to use a split-rail power supply with a bridged TDA1558Q, via a simple rail splitter (2 resistors like the CMOY) to get a reliable and noise-free input circuit.
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Old 3rd February 2010, 09:24 PM   #66
wahab is offline wahab  Algeria
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here a photo of the test circuit using the 1558Q....
it did work at first start...
you can see that there s four electrolytic caps...
two are connected to the supply rails...
the two other are connected like this :
the negative side is connected to earth, and the
positive side is connected through a dual switch to
a half of each bridge, thus reducing the power
delivered by the non relevant amplifiers ,
so i can add a bass box connected from the non inverting
output of higher channel to the inverting input of the lower channel,
so the amp become a 2 X 4 W + 20 W for the boom box...
i m preparing a pic to help explain..
Attached Files
File Type: zip Photo029.zip (542.9 KB, 50 views)
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Old 3rd February 2010, 09:34 PM   #67
wahab is offline wahab  Algeria
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Quote:
Originally Posted by irishpatrick33 View Post
Yes, I am well aware how wattage is the most overstated factor of a quality amp. It seems to be the one that gets all the casual listener's ears to perk up. Them and the mobile audio crowd love them watts. Plus, I can't play music very loud due to neighbors.


I will probably snag a few of those TDA8561Q's. I think it also said there's some "switch on/off pop" protection. Which saves me from extending myself further into an area I am brand new to. The less I have to do the better. In addition there's better THD. Win Win.
8561Q is a little better than the 1558Q, due to reduced gain that
did allow to reduce a little the distorsion...
power output capability is slightly better, in the range of
10% at equal supply voltage...
i can only warn about ground loops if smps are used,
as the negative is connected to earth if there s a safety
earth cable...
power supply with no safety earth, i.E, class 2 insulated in
european norms, don t suffer from these ground loops that
create buzz and hums even all things look perfectly connected..
the ground loop start from the amp which have its ground connected
to negative rail of the power supply..this latter will make
this ground connected to earth..
if the source signal has also a ground connection, then there
will be a ground loop...
suppressing the earth connection of one of the side, amp or
source generally resolve the problem but create another one as
the safety earth is no more adequatly connected...
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Old 4th February 2010, 05:43 AM   #68
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Quote:
Originally Posted by wahab View Post
. . . The ground loop start from the amp which have its ground connected to negative rail of the power supply..this latter will make this ground connected to earth. If the source signal has also a ground connection, then there will be a ground loop.
Suppressing the earth connection of one of the side, amp or source generally resolve the problem but create another one as the safety earth is no more adequately connected...
This is a badly dangerous problem in the UK because outlets there are split-rail AC, much like U.S. Air-Conditioner, Water Heater, Clothes Drier, and Cook Stove 220 outlets--but yet somehow even more dangerous.

This is also a problem in the U.S. if the audio equipment is plugged into more than one outlet. Its really hazardous to musicians if the mixer board happens to be plugged into an outlet (at some distance away) that operates on the "other" rail, and shocks (especially to guitarists) are commonplace here in the U.S. Recently, this problem also causes "mooing" subwoofers for home theater installations.

So, I think that the plastic-bodied (absolutely no touchable metal parts) "wall wart" or "laptop cord" is a really good idea for safer starter projects. Its not totally safe; however, the potential output is considerably decreased, thus increasing safety (decreasing risk) by that same amount.

Ah, well, I suppose I'll go fight with this little amp some more. Gosh, I don't just want to give up on it; however, DIY'ers the world over have had very bad luck with TDA1554/5/8 family of chips. Some get it to work nicely but there are no support circuit or pcb examples to help anyone else.

Last edited by danielwritesbac; 4th February 2010 at 06:01 AM.
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Old 4th February 2010, 08:33 AM   #69
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Quote:
Originally Posted by wahab View Post
here a photo of the test circuit using the 1558Q....
it did work at first start...
you can see that there s four electrolytic caps...
two are connected to the supply rails...
the two other are connected like this :
the negative side is connected to earth, and the
positive side is connected through a dual switch to
a half of each bridge, thus reducing the power
delivered by the non relevant amplifiers ,
so i can add a bass box connected from the non inverting
output of higher channel to the inverting input of the lower channel,
so the amp become a 2 X 4 W + 20 W for the boom box...
i m preparing a pic to help explain..
Could you make a sketch or a drawing of the circuit?
All of my attempts, datasheet, extra load, split rail, single rail, etc. . . make a very annoying buzz! In fact, there's a wide variety of awful noises possible, along with some music that's quite good.
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Old 4th February 2010, 10:46 AM   #70
wahab is offline wahab  Algeria
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Location: algeria/france
here the exact configuration i used..
as you can see, it s the minimal one...
pin3 is connected with the relevant ground pins...
a cap is added to pin4....
the switches allow the left/right channel to work
in non bridge mode, as a bass box can be added..
somewhat tricky, but it works very well...
of course, this particular implementation is of no
use if only two speakers are used...
i can only remind everybody to use a potentiometer
at the input..
also; be carefull with those plastic smps, as the negative side
is often connected to earth..
check if there s 3 wires in the ac input; and measure
the resistance between earth and negative output (the thing being
unplugged, of course !!)....
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File Type: zip TDA1558Q 3 channels.zip (4.7 KB, 43 views)
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