I'm not sure whether it belongs in the Class D section but ist seems to be most appropriate at this time.
I've used several of the Sanwu TPA3118 PBTL boards. They perform fine in general although the're sometimes a little noisy if you keep the high gain in combination with a high efficiency loudspeaker. Also the potentiometer is sometimes critical but that is not what this thread is about.
I'm helping out someone who is building a small cabinet fro amplification of instruments. The amplifier is a sanwu board but this time the amplification is for accoustic instruments and possibly voice.
A dynamic microphone is used (old sennheiser and an old shure I believe)
In general dynamic microphones require no phantom voltage but do need high gain pre amplifiers.
I found on ebay preamplifier boards based on NE5532 opamp. In general this is not a super opamp but should be quite useful for the purpose. The adavnatge of the board would be that it also has reverb as a plus and includes inputs. The board runs on DC (between 12-24 volts) so it can use the same voltages as the amplifier (in this case 12 Volts, for 4 ohm 20W loudspeaker)
This is the peamplifier: DC12-24V Karaoke Sound Board PT2399+NE5532 Preamplifier Microphone MIC Amplifier | eBay
After installing the preamp the Sanwu board immediately starts to oscillate with a approx 1 Hz frequency and is unusable. Without the preamp the TPA3118PBTL works fine from a music source.
After a few attempts I declared the board DOA and ordered a new one. Unfortunately the new board has the same issues so it is the type/configuration of the circuit and not the board itself.
I've ordered a new preamp. Now a different one without inuts/potmeters and without the PT2399 reverb. This one: NE5532 Dynamic Microphone Stereo Preamp Amplifier Board + Signal Shielding Wire | eBay
I hope this works of course but I have my doubts. These Sanwu TPA3118 PBTL boards seem very sensitive to what you put in front of it.
I noticed that in another thread (noise with BT Sanwu TPA3118 board) that the NE5532 is removed but as far as i could establish that was because of wrong design in the differential input.
Do any of you have experience with a good preamp topology for this purpose?
Am I overlooking something?
I've used several of the Sanwu TPA3118 PBTL boards. They perform fine in general although the're sometimes a little noisy if you keep the high gain in combination with a high efficiency loudspeaker. Also the potentiometer is sometimes critical but that is not what this thread is about.
I'm helping out someone who is building a small cabinet fro amplification of instruments. The amplifier is a sanwu board but this time the amplification is for accoustic instruments and possibly voice.
A dynamic microphone is used (old sennheiser and an old shure I believe)
In general dynamic microphones require no phantom voltage but do need high gain pre amplifiers.
I found on ebay preamplifier boards based on NE5532 opamp. In general this is not a super opamp but should be quite useful for the purpose. The adavnatge of the board would be that it also has reverb as a plus and includes inputs. The board runs on DC (between 12-24 volts) so it can use the same voltages as the amplifier (in this case 12 Volts, for 4 ohm 20W loudspeaker)
This is the peamplifier: DC12-24V Karaoke Sound Board PT2399+NE5532 Preamplifier Microphone MIC Amplifier | eBay
After installing the preamp the Sanwu board immediately starts to oscillate with a approx 1 Hz frequency and is unusable. Without the preamp the TPA3118PBTL works fine from a music source.
After a few attempts I declared the board DOA and ordered a new one. Unfortunately the new board has the same issues so it is the type/configuration of the circuit and not the board itself.
I've ordered a new preamp. Now a different one without inuts/potmeters and without the PT2399 reverb. This one: NE5532 Dynamic Microphone Stereo Preamp Amplifier Board + Signal Shielding Wire | eBay
I hope this works of course but I have my doubts. These Sanwu TPA3118 PBTL boards seem very sensitive to what you put in front of it.
I noticed that in another thread (noise with BT Sanwu TPA3118 board) that the NE5532 is removed but as far as i could establish that was because of wrong design in the differential input.
Do any of you have experience with a good preamp topology for this purpose?
Am I overlooking something?
What is the p-to-p output voltage of the pre-amplifier? Does the same pre-amp work with a different amplifier?
Well, I had not until you posted this question. I had to dig up some cables and get the hot iron out but now found some time to fix some temporary cables.
The preamplifier is working with a different amplifier. In this case a ready made and enclosed Yuan Jing TPA3116 stereo amp.
No problem at all. I'm listening to music through it right now.
I'm now wondering why this preamplifier is driving the Sanwu TPA3118 PBTL board into heavy oscillation.
Could this be a ground problem? I dod not pay specifically attention to the grounding because I have not encountered issues with the Sanwu boards before and the Sanwu Board is also working fine with just a potmeter and direct input.
If it is a grounding problem than it should be easily solved by making a star ground. I will try to do so but somehow don't think that is the solution. Grounding problems ussuly cause hum and noise and not heavy oscillation
After yesterdays test with the preamplifier on a different amp (the Yuan jing stereo amp) I'm (again) going to try to solder the preamp to the Sanwu TPA3118 PBTL board.
This time I will make a star ground but might need some reflection/confirmation whether I use the right topology.
There will be 3 connections to the star on the chassis/casing
1: the power ground taken from where the power ground is connected to the Sanwu TPA board.
2: the signal ground between the NE 5532 pre amplifier and the TPA Sanwu board
3: the power ground where it enters the chasis
Al of them will be connected to the star through a resistor unless you guys think that I can connect all of the wires to just one resistor and the resistor to the star ground.
I have plenty of 0,5 watt resistors but I'm somewhat limited in 1, 2 and 3 watt resistors. I recall that for heavy amps I used 5 watt resistors but this is a very small amp with relatively low currents. Would 2 ohm 3 watt be sufficient for this purpose?
I have not yet used supply caps with these small amplifiers as I, in this case, use a smal walwart (2A 12 Volt) Would a supply cap make a difference in the performance in this case? I think I have some low ESR Panasonic FR caps rated for 16V and 4700uF or is that much too large for such a small amp?
This time I will make a star ground but might need some reflection/confirmation whether I use the right topology.
There will be 3 connections to the star on the chassis/casing
1: the power ground taken from where the power ground is connected to the Sanwu TPA board.
2: the signal ground between the NE 5532 pre amplifier and the TPA Sanwu board
3: the power ground where it enters the chasis
Al of them will be connected to the star through a resistor unless you guys think that I can connect all of the wires to just one resistor and the resistor to the star ground.
I have plenty of 0,5 watt resistors but I'm somewhat limited in 1, 2 and 3 watt resistors. I recall that for heavy amps I used 5 watt resistors but this is a very small amp with relatively low currents. Would 2 ohm 3 watt be sufficient for this purpose?
I have not yet used supply caps with these small amplifiers as I, in this case, use a smal walwart (2A 12 Volt) Would a supply cap make a difference in the performance in this case? I think I have some low ESR Panasonic FR caps rated for 16V and 4700uF or is that much too large for such a small amp?
Two steps forward, one step back
I made a star ground and resoldered the preamplifier. Unfortunetely to no avail.
Before messing with Low ESR supply caps I decided to try a different power source (12V 12A) and found out that the original power source was the problem.
I did test the initial powersource before use both with no load and with a load and it was stable at that moment. Appearantly the load of the amplifier and preamplifier together initiates the powersupply to oscillate.
Well, it was an El cheapo 2A powersupply so that figures.
My brother (originally it was more his project than mine) has found a better 12V powersource (6A, respectable brand) so I'm going to try that.
I consider this as 2 steps forward
The step back is the huge thump when the amplifier is switched on. The (test) speaker moves in and out with max amplitude a couple of times before it comes to rest in the neutral position.
In principle there is a mute function on this board which I'm not using currently. I have read it somewhere in one of the 10000 of posts sow il try to find it
I made a star ground and resoldered the preamplifier. Unfortunetely to no avail.
Before messing with Low ESR supply caps I decided to try a different power source (12V 12A) and found out that the original power source was the problem.
I did test the initial powersource before use both with no load and with a load and it was stable at that moment. Appearantly the load of the amplifier and preamplifier together initiates the powersupply to oscillate.
Well, it was an El cheapo 2A powersupply so that figures.
My brother (originally it was more his project than mine) has found a better 12V powersource (6A, respectable brand) so I'm going to try that.
I consider this as 2 steps forward
The step back is the huge thump when the amplifier is switched on. The (test) speaker moves in and out with max amplitude a couple of times before it comes to rest in the neutral position.
In principle there is a mute function on this board which I'm not using currently. I have read it somewhere in one of the 10000 of posts sow il try to find it
doctormord, thanks
I finally had a chance to dig out a switch that was small enough for the housing and make the connections. When the mute is on there is no thump on or thump when switching of.
I noticed in another thread that you also indicated an RDC network for muting ats power on and power of. Would that work in this case as well? I mean the 1uF, 750kohm values?
That would be even more convenient.
Now that I solved the oscillation and the power off thumps I feel that the noise is too high to be usable. The combined gain of the premplifier and the amplifier is just too high i guess. The >95db speaker doesnt help for hearing noise of course.
I will see if I somewhere have a smaller tip for my soldering iron and remove R27 to lower the gain to 20 In the TPA3118 amplifier and see if that works.
After the previous experiences with this little amplifier I thought it would be a straightforward project but ist is nothing of that sort.😀
I finally had a chance to dig out a switch that was small enough for the housing and make the connections. When the mute is on there is no thump on or thump when switching of.
I noticed in another thread that you also indicated an RDC network for muting ats power on and power of. Would that work in this case as well? I mean the 1uF, 750kohm values?
That would be even more convenient.
Now that I solved the oscillation and the power off thumps I feel that the noise is too high to be usable. The combined gain of the premplifier and the amplifier is just too high i guess. The >95db speaker doesnt help for hearing noise of course.
I will see if I somewhere have a smaller tip for my soldering iron and remove R27 to lower the gain to 20 In the TPA3118 amplifier and see if that works.
After the previous experiences with this little amplifier I thought it would be a straightforward project but ist is nothing of that sort.😀
Slow pumping effects often are caused by unstable supply voltages, i.e. supply voltage coupling to pre-amp. In such a case the first step I take is monitoring the supply voltage(s) with an oscilloscope.
Voltwise thanks.
I cracked open this brand new powersupply to find that it was only the plastic shell that was new. Inside were old, salvaged components where some parts were bypassed and some were new.
Lesson: don't go to cheap on your powersupply. (I wouldn't do that ussually but this was originally not my project)
Today I grinded a soldering tip to a needle point and have removed R27 to lower the gain of the TPA amplifier to 20 db. The operation was succesfully executed 😀.
I soldered SMD components before but not as small as these ones. Luckily it was desoldering but I don't think I could solder such small components.
The noise has reduced by lowering the gain. The levels are not yet as I hoped but they are acceptable for the application (accordeon amplification in small venues/bars)
When using 85 db speakers the noise is very low and practically unaudible from a few meters away but that all changes if you use a 95 db speaker.
For home hifi audio you will definetly need a low noise pre-amp if you use a pre amp.
I cracked open this brand new powersupply to find that it was only the plastic shell that was new. Inside were old, salvaged components where some parts were bypassed and some were new.
Lesson: don't go to cheap on your powersupply. (I wouldn't do that ussually but this was originally not my project)
Today I grinded a soldering tip to a needle point and have removed R27 to lower the gain of the TPA amplifier to 20 db. The operation was succesfully executed 😀.
I soldered SMD components before but not as small as these ones. Luckily it was desoldering but I don't think I could solder such small components.
The noise has reduced by lowering the gain. The levels are not yet as I hoped but they are acceptable for the application (accordeon amplification in small venues/bars)
When using 85 db speakers the noise is very low and practically unaudible from a few meters away but that all changes if you use a 95 db speaker.
For home hifi audio you will definetly need a low noise pre-amp if you use a pre amp.
Sorry for reviving this post. But it took me weeks to solve the same problem you have.
The only thing you need to do is put a low pass filter at the output of the preamp.
Try 6.8nf and 1.5k, that would be around 17khz.
I solved the same problem on my guitar amp with that same power amp board. But using 10nf and 1.5k (around 11khz)
Sorry again for reviving the post (and for my English)
Hope you try it
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