Help on Preamp

pra3718 · 24th April 2009, 09:13 AM

Attached picture is preamp which is sounding but not stable. Speaker moving up/down with noise when no audio signal.

TDA1554q & attached preamp is powred by ( Single supply PSU )

Regards.

barry4 · 24th April 2009, 02:21 PM

The output capacitor appears to be connected to the wrong end of the feedback resistor. It should connect directly to pin 1 ?

pra3718 · 24th April 2009, 02:28 PM

Yes, it was my drawing fault not is circuit.

AndrewT · 24th April 2009, 04:10 PM

could you re-post the correct schematic?

pra3718 · 25th April 2009, 08:09 AM

Thank you,

This is altered schematic

AndrewT · 25th April 2009, 09:52 AM

Hi,
an opamp has two inputs +IN & -IN.
These two inputs must connect to the flow and return of the input signal, commonly referred to as signal and signal ground. There must be a circuit for the input signal.

connect the non-inverting input (pin3 +IN) to the input RCA barrel.

For best performance the opamp inputs should see the same source impedance.
-IN Rs = 100k // 10k+10uF // 10uF (at DC =100k)
+IN Rs = source resistance of ground return = 0k

Some opamps demand that these two impedances are loosely matched.

pra3718 · 25th April 2009, 11:09 AM

Thank you AndrewT

I read your post but do not understand what to do (sorry I am poor in electronics)

Quote:

connect the non-inverting input (pin3 +IN) to the input RCA barrel.

pra3718 · 25th April 2009, 11:13 AM

Even I have added 100K POT between 10K & Pin 2 (before 100k Joint) to adjust the gain.

AndrewT · 25th April 2009, 12:42 PM

Hi,
electricity flows around circuits.

The source has an output plug. The pin is referred to as line or live, the barrel is referred to as ground or signal ground.
It is more useful to call these flow (pin) and return (barrel). The current must flow down one side of the cable and return back through the other half of the cable. You MUST complete the circuit in the input side of your preamp.
Pin3 (non-inverting input +IN) must go to the RCA barrel to complete the circuit.

pra3718 · 25th April 2009, 12:52 PM

If possible please post best matching example.

Regards.

24th April 2009, 04:10 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	could you re-post the correct schematic? __________________ regards Andrew T.

25th April 2009, 09:52 AM	#6
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, an opamp has two inputs +IN & -IN. These two inputs must connect to the flow and return of the input signal, commonly referred to as signal and signal ground. There must be a circuit for the input signal. connect the non-inverting input (pin3 +IN) to the input RCA barrel. For best performance the opamp inputs should see the same source impedance. -IN Rs = 100k // 10k+10uF // 10uF (at DC =100k) +IN Rs = source resistance of ground return = 0k Some opamps demand that these two impedances are loosely matched. __________________ regards Andrew T.

25th April 2009, 12:42 PM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, electricity flows around circuits. The source has an output plug. The pin is referred to as line or live, the barrel is referred to as ground or signal ground. It is more useful to call these flow (pin) and return (barrel). The current must flow down one side of the cable and return back through the other half of the cable. You MUST complete the circuit in the input side of your preamp. Pin3 (non-inverting input +IN) must go to the RCA barrel to complete the circuit. __________________ regards Andrew T.

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24th April 2009, 02:21 PM	#2
barry4 diyAudio Member Join Date: Feb 2009	The output capacitor appears to be connected to the wrong end of the feedback resistor. It should connect directly to pin 1 ?

24th April 2009, 02:28 PM	#3
pra3718 diyAudio Member Join Date: Jan 2009	Yes, it was my drawing fault not is circuit.

25th April 2009, 11:13 AM	#8
pra3718 diyAudio Member Join Date: Jan 2009	Even I have added 100K POT between 10K & Pin 2 (before 100k Joint) to adjust the gain.

25th April 2009, 12:52 PM	#10
pra3718 diyAudio Member Join Date: Jan 2009	If possible please post best matching example. Regards.

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