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Old 4th February 2010, 02:48 PM   #71
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Quote:
Originally Posted by wahab View Post
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 !!)....
Well, I'm trying that exact same circuit (in bridge mode).
My SMPS has only a 2 conductor ac cord.
I have a 10k potentiometer.
Without anything plugged into the inputs, there's a buzzzzzzz (guitar amp like noise).

Does yours do that when you use bridge mode?

So far, the 17th redo involved:
Replace the TDA1558Q
Replace all resistors
Replace all caps
Replace all wires
Replace the power supply

Exactly the same! BZZZZZZZ!!!
Help?

P.S.
I also get high dc offset when the amp is first turned on and it goes to normal after 2 seconds. But, this is very bad for speakers.
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Old 4th February 2010, 05:51 PM   #72
wahab is offline wahab  Algeria
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[QUOTE=danielwritesbac;2073482]Well, I'm trying that exact same circuit (in bridge mode).

I have a 10k potentiometer.
Without anything plugged into the inputs, there's a buzzzzzzz (guitar amp like noise).

Does yours do that when you use bridge mode?



Exactly the same! BZZZZZZZ!!!
QUOTE]

without input potentiometer, or at least a resistor connected
from input to ground, all amps produce some buzz..
a few centimeters of input cable not grounded by a source
is enough to produce noise..
try a resistor of a few ohm in serial with the positive supply,
as it will give a clue if ever the buzz is due to smps badly
filtered noises...

can you post a schematic showing exactly how you did the
connections ?..
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Old 4th February 2010, 05:52 PM   #73
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This is a brute force method to "turn down the noise" by readjusting the gain.
supplementary feedback resistors

Supplies:
4 of 2.2k resistors

Location:
2.2k from pin 15 to pin 12
2.2k from pin 16_17 to pin 10
2.2k from pin 15 to pin 6
2.2k from pin 1_2 to pin 8

It is still far more than enough gain for the MP3 player.

EDIT:
Working on it still, and testing, but this bit is nice progress. Finally, near silent at idle!
This mod also seems to stop the wide variety of misbehaviors and racket.
1.9k and 1.5k values are even better (smaller figures = less noise).
The RCA Pearl MP3 player has no trouble pushing this amp to clipping with the 1.5k supplementary feedback resistors.

Last edited by danielwritesbac; 4th February 2010 at 06:14 PM.
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Old 4th February 2010, 06:10 PM   #74
wahab is offline wahab  Algeria
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Quote:
Originally Posted by danielwritesbac View Post
This is a brute force method to "turn down the noise" by readjusting the gain.
supplementary feedback resistors

Supplies:
4 of 2.2k resistors

Location:
2.2k from pin 15 to pin 12
2.2k from pin 16_17 to pin 10
2.2k from pin 15 to pin 6
2.2k from pin 1_2 to pin 8

It is still far more than enough gain for the MP3 player.
pin15 is a virtual ground in ac mode..
you cant reduce gain by injecting feedback to this pin...
what you have done is to reduce the gain of the non
inverting amps , making the bridge unbalanced, as the inverters
amps have not effectively reduced gain..
so a half of the bridge provide more output voltage than the
other half...
if there s still noise with a 10K potentiometer in minimal position,
then noise is due to a bad layout , as you said that changing the
power supply didn t change nothing..
a photo of you proto would help, if possible..
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Old 4th February 2010, 07:22 PM   #75
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Quote:
Originally Posted by wahab View Post
pin15 is a virtual ground in ac mode..
you cant reduce gain by injecting feedback to this pin...
what you have done is to reduce the gain of the non
inverting amps , making the bridge unbalanced, as the inverters
amps have not effectively reduced gain..
so a half of the bridge provide more output voltage than the
other half...
if there s still noise with a 10K potentiometer in minimal position,
then noise is due to a bad layout , as you said that changing the
power supply didn t change nothing..
a photo of you proto would help, if possible..
Well, I didn't test in bridge mode until now. The proportions are lopsided. Feedback from pin 15 is only half as effective as feedback from the input. Darnit! No wonder they discontinued this one and made a new one with more reasonable gain setting.
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Old 4th February 2010, 07:43 PM   #76
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Okay, I just bought a tda8561q

Last edited by danielwritesbac; 4th February 2010 at 07:56 PM.
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Old 4th February 2010, 07:53 PM   #77
wahab is offline wahab  Algeria
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sorry that it didn t work according to your wills...
since i didn t test the 8561Q, i m in the waiting of your
experiences, as i surely will go with this one next time..
could it be that i was just lucky with the old fashion ic ?..
generally, ic s work perfectly at first shot, if i except
some that were badly designed like the horrible TDA2005,
the STM concurrent of the 1558Q....
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Old 5th February 2010, 03:41 AM   #78
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Quote:
Originally Posted by irishpatrick33 View Post
I am not sure I understand. There's a bunch of stuff from the data sheet missing, like C5, C3, R1, and R5. I assume your C1 and R1 replace the data sheet's C6 and R6. Also not sure what the TLO72 is mentioned for.

Am I eliminating the R5 connection between pins 4 and 2; as well as eliminating the C3 and R1 connection between pins 5 and 1; and eliminating C5? Because that's what I got out of it.
Wahab,

Could you clarify these issues with the TDA2040 diode schematic you posted?

Considering Daniel's issues with the TDA1558... I think I will focus my efforts on the TDA2040 until I get the TDA8561Q.

How do the THD and gain values compare between the TDA8561Q and TDA2040?



Thanks
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Old 5th February 2010, 07:40 AM   #79
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For TDA2030, TDA2040, TDA2050, LM1875. . .

You set the gain you want.
On a non-inverting amplifier. . .
If the feedback resistor is 27k (inverting input to speaker) and its partner is 820R (0.82k) (inverting input to signal ground) then you can divide the two with the calculator to find the gain (albeit there's a more exact formula and a simple division will be off by "1")

A voltage divider:
Its like a potentiometer, pot, l-pad, except there's no dial. You can divide a voltage divider's two resistor values to find its effect. What it does is divide. You can too.
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Old 5th February 2010, 08:55 AM   #80
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Quote:
Originally Posted by wahab View Post
sorry that it didn t work according to your wills...
since i didn t test the 8561Q, i m in the waiting of your
experiences, as i surely will go with this one next time..
could it be that i was just lucky with the old fashion ic ?..
generally, ic s work perfectly at first shot, if i except
some that were badly designed like the horrible TDA2005,
the STM concurrent of the 1558Q....
I've used the tda2003, tda2005, etc. . . family of chips in bridged design. The efficiency is rather horrible; however, audio performance depends on your design. Being op amps, they'll do almost exactly as you ask; however, much of what you ask for will probably turn to heat instead of speaker output, and we don't want that extra expense.

The TDA1558Q--I do have to report that its not ever going to qualify for high fidelity class audio. The "disqualification" is the noise output, due to its locked in setting of wildly inappropriate gain.

My experience with TDA1558Q was rather cruel, in fact. Its presentation is desirable and to the extent that most amplifiers of any price cannot match it. It does indeed do the "music takes flight" experience (VERY RARE), along with noise. And that is a heartbreaking combination. Normally, it takes at least three of full bandwidth speakers to make the presentation that this amp can do with one or two.

Since the problem is "locked" inside the chip, I have to tell that one goodbye.

Remaining options:
With TDA8561Q, I'll look forward to seeing if Philips, NXP has mastered their symmetry chip technology. After it comes in, its going to face some stiff competition in the form of LA4628 (which is a great performer but heatsink will cost slightly more). Fail: I've already tested Toshiba and KEC's similar offerings and have to report that they don't even meet mid-fi standards. More research: We also need to find out what similar chips are offered by the major players, ST and Natsemi.
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