Help on Preamp

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pra3718

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#1
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.
 

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#6
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.
 
#9
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.
 
#14
That would be the virtual earth created by connecting two 4.7R resistors across the single power supply. If it is connected incorrectly to the next stage, this would mean that there is no effective negative supply to the amplifier.


Barry
 
#16
Thank you AndrewT

you are trying to help me that "connect the non-inverting input (pin3 +IN) to the input RCA barrel." but I am not a technical person to understand what is "RCA barrel" If you post which component where to connect, I would try my level best.

Thank you barry4

"How is it connected to the next stage?" As I understood attached preamp's output is the input of tda1554q amp.

Apart from above preamp I want to know more about operational amplifier.

1) Is there any output sound improvements OR differences between SINGLE SUPPLY OP-AMP (+),(G) and SPLIT SUPPLY OP-AMP (-),(+).

2) In which situation I should use inverting OP-AMP and non-inverting OP-AMP. ( Sound related )

3) Inverting OP-AMP delivers more gain THAN non-inverting OP-AMP Is that right ?

4) Inverting OP-AMP is usefull for Lower frequencies. Is that right ?

5) When PSU is single supply, I need to BIAS and I have to use two resistor WHAT IS THE BEST VALUE I SHOULD USE ? Example I am using 10K+10K WHAT HAPPENS IF I INCREASE OR DECREASE THE VALUE ?

6) When using non-inverting amp, as per my knowledge
GAIN = (FEED BACK resisistor / GAIN resistor)+1
5.68 = 22 K / 4.7 K +1

If I decrease the value of GAIN resistor I achive more gain but more sound disterbance.

WHICH IS THE BEST VALUE TO GET CLEAN SOUND AND MAX GAIN ?

7) I am using NE5532 which has two channels and I am using only one channel, Is there is any idea to use both channel to achive more gain i.e. 1st channel output is 2nd channel input and 2nd channel output is power amps input.

8) If NE5532's output is not suitable to me I want more output. Can I add output transistor to increse output IF YES, HOW ?

9) If I want to add more BASS ( in general WEIGHT ) in over all sound, I should increase the capacitance at PSU. As well as is there any requirements for PRE-AMP ?

Thank you in advance

Regards.
 
#19
pra3718 said:
you are trying to help me that "connect the non-inverting input (pin3 +IN) to the input RCA barrel." but I am not a technical person to understand what is "RCA barrel"
A] the RCA also known as phono socket/plug is the input to the amplifier case.

I want to know more about operational amplifier.

1) Is there any output sound improvements OR differences between SINGLE SUPPLY OP-AMP (+),(G) and SPLIT SUPPLY OP-AMP (-),(+).

A] no, both sound the same. It's the same opamp receiving the same signal and feeding the same load.
But adding extra capacitors to one topology and not the other may make them sound different.

2) In which situation I should use inverting OP-AMP and non-inverting OP-AMP. ( Sound related )

Some say the inverting produces less distortion.
Some say inverting is quieter.
I don't believe everything poster write.

3) Inverting OP-AMP delivers more gain THAN non-inverting OP-AMP Is that right ?

A] no.

4) Inverting OP-AMP is useful for Lower frequencies. Is that right ?

A] no.

5) When PSU is single supply, I need to BIAS and I have to use two resistor WHAT IS THE BEST VALUE I SHOULD USE ? Example I am using 10K+10K WHAT HAPPENS IF I INCREASE OR DECREASE THE VALUE ?

A] no best value.
Low values give less noise.
Low values give a lower input impedance.

6) When using non-inverting amp, as per my knowledge
GAIN = (FEED BACK resistor / GAIN resistor)+1
5.68 = 22 K / 4.7 K +1

If I decrease the value of GAIN resistor I achieve more gain but more sound disturbance.

WHICH IS THE BEST VALUE TO GET CLEAN SOUND AND MAX GAIN ?

A] gain formula is correct.
"Sound disturbance" what?
no best value for clean sound and maximum gain.
You set the gain to what the circuit needs
You set the input voltage to ensure the signal is not clipped.
You can build in an overhead to reduce distortion but that lowers the signal to noise ratio.

7) I am using NE5532 which has two channels and I am using only one channel, Is there is any idea to use both channel to achieve more gain i.e. 1st channel output is 2nd channel input and 2nd channel output is power amps input.

a] no.

8) If NE5532's output is not suitable to me I want more output. Can I add output transistor to increase output IF YES, HOW ?

the 5532 is similar to most opamps. it's open loop gain >100000times. You don't need any more.

9) If I want to add more BASS ( in general WEIGHT ) in over all sound, I should increase the capacitance at PSU. As well as is there any requirements for PRE-AMP ?

A] no. Listen to it the way the music performer wanted you to hear it. Why distort it with added bass?
Click to expand...
 
#20
If you have built this circuit to your diagram. One problem that could be causing the problem is that you have one of the opamps floating, i.e nothing is connected to the inputs. Its behaviour in this situation is undefined and it is probably oscillating. This will upset the other channel and could be causing the low frequency distrurbance you are seeing on the other channel.

If you are not using one channel. You should connect the +ve input to ground and connect the output to the negative input. This defines the state of the opamp as a grounded inverting buffer.

Some basics on opamps here:

http://web.telia.com/~u85920178/begin/opamp00.htm

If you have good maths and alot of time all you need to know about opamps can be found here:

http://www.analog.com/library/analogDialogue/archives/39-05/op_amp_applications_handbook.html

http://focus.ti.com/lit/an/sboa092a/sboa092a.pdf

Regards,
Andrew
 
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