Velleman K2572 Preamp

HerrNilsson · 9th April 2004, 09:38 AM

I have a Vortex 2 sound card in my computer which have a quite low line out level. When I connect it to my home audio system I have to turn up the volume quite a lot, getting a noisy signal as result. Also when I change source to my cd-player forgetting lowering the volume my loudspeakers are about to explode.

I therefore bought the Velleman K2572 preamp kit intended for "low noise, audio/hifi stereo use". I take the power supply directly from my computers 12V wires. BUT I get a very noisy signal with a hum. I use very short wires from the sound card except for the power cables. The quality of the soud is also very bad, no low tones are amplified. (The frequency of the preamp is 40Hz-30kHz, should't that be enough?) The power seems very stable at 12.21-12.23 V. Is it impossible to use such pre-amplifier near the computer or what is the problem?

/Erik

Bas Horneman · 9th April 2004, 09:52 AM

I don't know how well the chip of your preamp rejects power supply noise...

But I think that the power supply from the computer is of the switching type...good enough for a computer... but not for an audio preamp..

However I don't think that is your problem...why not try the preamp in your home setup first. If you don't have the problem in your audio system...it might be because of the noise inside the computer and / or the psu.

In other words try to isolate your problem by taking the preamp somewhere else and / or using a different psu...

Regards,
Bas

sss · 9th April 2004, 10:41 AM

computers power supply got only one rail of 12V
can your pre amp work with single supply?

HerrNilsson · 9th April 2004, 10:48 AM

Well, I don't know, I just use one of the wires which isn't in use (on the power chain for 3,5" IDE units). I measure the voltage to 12.21-12.23 V. I think +/-0,01 V should be enough...?

Frank Berry · 9th April 2004, 10:51 AM

The output coupling capacitors (there are 2 of them in each channel, one before the level control and one after the level control) are rated at 1 ufd. You can improve the bass response by increasing their values to, perhaps 4.7 ufd.

Frank Berry · 9th April 2004, 10:53 AM

You might try operating the preamp from a pair of series-connected 9 volt batteries to see if the hum goes away.

HerrNilsson · 9th April 2004, 11:44 AM

Thank you for suggestions! Maybe i get rid of the hum, but not the noise i think. To me it seems that the Velleman K2570 is crap. Maybe it's easier to buy another sound card. Does any know of of soundcard with higer output level? The ideal would be a soundcard with hardware adjustable level.

I have also tried to gain the level in software with the Winamp preamp but the sound become crappy. And none of the problems has to do with my stereo or wires because I listen to the source directly with earphones.

/Erik

rho · 9th April 2004, 08:01 PM

Looking at a picture of that pre-amp module it is just a 8pin DIP dual opamp with a trim-pot at the input.
What type of opamp do they use? What is the value of the caps by-passing the supply? they could be closer to the opamp in my oppinion. They also use plain electrolites for inout caps.

An other thing I'm afraid of is that there is some feed-trough from the switching power-supply of the computer, to the pre-amp board. Ddi you use shielded cables for the audio-signals?

neutron7 · 9th April 2004, 08:57 PM

most of the noise is probably from d/a converter and related circuitry on the sound card before the amplifier stage.

so if you amplify it with anything else the noise will still be there.

you might be better off getting a different sound card instead.

m-audio soundcards have lower noise than most soundbl***s

http://www.m-audio.com/index.php?do=...a955aa6ae2db1c

that is their consumer offering. I used one to replace the on-board sound on my shuttle PC and the sound is much much better and quieter(noise wise).

I think the output level must be higher as well becuase the shuttle is connected to my mixer via a very long cable and it used to be quite bad. this one seems to drive it a lot better.

this one looks good too
http://www.m-audio.com/index.php?do=...3fa8b83343bfb8

HerrNilsson · 10th April 2004, 06:54 PM

I didn't use sheilded cables, because the cables from the sound card to the preamp are less than one inch long. And the noise is not from the D/A converter because the sound directly from the sound card doesn't have much noise. I think the combination of bad power supply (even it seems ok with my multimeter, which isn't probably fast enough) and a low cost preamp is the problem.....

I have to admit, I not really that fanatic, and don't know of "opamp" and such things but thanks anyhow!

/Erik

9th April 2004, 09:38 AM	#1
HerrNilsson diyAudio Member Join Date: Apr 2004 Location: Stockholm	Velleman K2572 Preamp I have a Vortex 2 sound card in my computer which have a quite low line out level. When I connect it to my home audio system I have to turn up the volume quite a lot, getting a noisy signal as result. Also when I change source to my cd-player forgetting lowering the volume my loudspeakers are about to explode. I therefore bought the Velleman K2572 preamp kit intended for "low noise, audio/hifi stereo use". I take the power supply directly from my computers 12V wires. BUT I get a very noisy signal with a hum. I use very short wires from the sound card except for the power cables. The quality of the soud is also very bad, no low tones are amplified. (The frequency of the preamp is 40Hz-30kHz, should't that be enough?) The power seems very stable at 12.21-12.23 V. Is it impossible to use such pre-amplifier near the computer or what is the problem? /Erik

9th April 2004, 10:51 AM	#5
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	The output coupling capacitors (there are 2 of them in each channel, one before the level control and one after the level control) are rated at 1 ufd. You can improve the bass response by increasing their values to, perhaps 4.7 ufd. __________________ Frank

9th April 2004, 10:53 AM	#6
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	You might try operating the preamp from a pair of series-connected 9 volt batteries to see if the hum goes away. __________________ Frank

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9th April 2004, 09:52 AM	#2
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	I don't know how well the chip of your preamp rejects power supply noise... But I think that the power supply from the computer is of the switching type...good enough for a computer... but not for an audio preamp.. However I don't think that is your problem...why not try the preamp in your home setup first. If you don't have the problem in your audio system...it might be because of the noise inside the computer and / or the psu. In other words try to isolate your problem by taking the preamp somewhere else and / or using a different psu... Regards, Bas

9th April 2004, 10:41 AM	#3
sss diyAudio Member Join Date: Jul 2003 Location: Israel , haifa	computers power supply got only one rail of 12V can your pre amp work with single supply?

9th April 2004, 10:48 AM	#4
HerrNilsson diyAudio Member Join Date: Apr 2004 Location: Stockholm	Well, I don't know, I just use one of the wires which isn't in use (on the power chain for 3,5" IDE units). I measure the voltage to 12.21-12.23 V. I think +/-0,01 V should be enough...?

9th April 2004, 11:44 AM	#7
HerrNilsson diyAudio Member Join Date: Apr 2004 Location: Stockholm	Thank you for suggestions! Maybe i get rid of the hum, but not the noise i think. To me it seems that the Velleman K2570 is crap. Maybe it's easier to buy another sound card. Does any know of of soundcard with higer output level? The ideal would be a soundcard with hardware adjustable level. I have also tried to gain the level in software with the Winamp preamp but the sound become crappy. And none of the problems has to do with my stereo or wires because I listen to the source directly with earphones. /Erik

9th April 2004, 08:01 PM	#8
rho diyAudio Member Join Date: Sep 2003 Location: Peer, Belgium	Looking at a picture of that pre-amp module it is just a 8pin DIP dual opamp with a trim-pot at the input. What type of opamp do they use? What is the value of the caps by-passing the supply? they could be closer to the opamp in my oppinion. They also use plain electrolites for inout caps. An other thing I'm afraid of is that there is some feed-trough from the switching power-supply of the computer, to the pre-amp board. Ddi you use shielded cables for the audio-signals?

9th April 2004, 08:57 PM	#9
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	most of the noise is probably from d/a converter and related circuitry on the sound card before the amplifier stage. so if you amplify it with anything else the noise will still be there. you might be better off getting a different sound card instead. m-audio soundcards have lower noise than most soundbl***s http://www.m-audio.com/index.php?do=...a955aa6ae2db1c that is their consumer offering. I used one to replace the on-board sound on my shuttle PC and the sound is much much better and quieter(noise wise). I think the output level must be higher as well becuase the shuttle is connected to my mixer via a very long cable and it used to be quite bad. this one seems to drive it a lot better. this one looks good too http://www.m-audio.com/index.php?do=...3fa8b83343bfb8

10th April 2004, 06:54 PM	#10
HerrNilsson diyAudio Member Join Date: Apr 2004 Location: Stockholm	I didn't use sheilded cables, because the cables from the sound card to the preamp are less than one inch long. And the noise is not from the D/A converter because the sound directly from the sound card doesn't have much noise. I think the combination of bad power supply (even it seems ok with my multimeter, which isn't probably fast enough) and a low cost preamp is the problem..... I have to admit, I not really that fanatic, and don't know of "opamp" and such things but thanks anyhow! /Erik

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