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
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
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
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
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...?
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.
You might try operating the preamp from a pair of series-connected 9 volt batteries to see if the hum goes away.
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
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
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?
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?
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=products.main&ID=0ed0405324041d8025a955aa6ae2db1c
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=products.main&ID=adf95efc30b88aba043fa8b83343bfb8
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=products.main&ID=0ed0405324041d8025a955aa6ae2db1c
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=products.main&ID=adf95efc30b88aba043fa8b83343bfb8
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
I have to admit, I not really that fanatic, and don't know of "opamp" and such things but thanks anyhow!
/Erik
almost all op amps use 2 power supply rails , u got only 1 rail of 12V , i think thats your problem , maybe the ic is dead also
anyways CREATIVE sound cards are better , there are some companies that making pro soundcards ,i dont remembr the names but those are werry expensive
also
a pre amp can be a simple op amp , nothing special
anyways CREATIVE sound cards are better , there are some companies that making pro soundcards ,i dont remembr the names but those are werry expensive
also
a pre amp can be a simple op amp , nothing special
If you have a look at the schematic of the pre-amp you could see that the PSRR of that circuit is't all that good. It works with a single power-supply and sets the reference voltage at the pos-input of the opamp by a simple devider-network (the bottum one bypassed by a 1µF cap). I think if the 12V you measure is from a switched supply you will have a very distorted signal.
Filtering computer power supplies
I had exactly the same problem, as I was building an HTPC with a bunch of audio circuits in it - a total of 24 dual opamps for starters!! The noise from the computer power supply was unbearable.
But I figured it all out and now there is *NO* computer noise at all in my audio system. The details:
First, all ATX power supplies have both +12V and -12V, which is good
enough for most modern op amps. I did upgrade my power supply to a quality 300 W, which is total overkill since my motherboard draws less than 30 W. (Beware cheap ATX power supplies) But I wanted enough power overhead, since all the power supplies I looked at rated the -12V between 0.8A and 1.0A. I just identified the voltages, cut back the insulation, and soldered wires straight into the cable that goes to the motherboard.
Then I put together a power supply filter for both the positive and negative rails. Something really basic - just strung together a heavy choke, 1A diode, 5 ohm 2W resistor, with 100uF electrolytics between each stage. Don't use a 1/2W resistor - I burned a pair up and that was exciting. The voltage at the end is about 11.8V, but very clean. Unbelievable difference, for $15 in parts.
All my interconnects between analog boards are done exclusively with shielded audio cable. Physically, the boards inside the case are as far away as possible from the DVD drive, IDE cables, and motherboard.
Hope this helps.
Ben
I had exactly the same problem, as I was building an HTPC with a bunch of audio circuits in it - a total of 24 dual opamps for starters!! The noise from the computer power supply was unbearable.
But I figured it all out and now there is *NO* computer noise at all in my audio system. The details:
First, all ATX power supplies have both +12V and -12V, which is good
enough for most modern op amps. I did upgrade my power supply to a quality 300 W, which is total overkill since my motherboard draws less than 30 W. (Beware cheap ATX power supplies) But I wanted enough power overhead, since all the power supplies I looked at rated the -12V between 0.8A and 1.0A. I just identified the voltages, cut back the insulation, and soldered wires straight into the cable that goes to the motherboard.
Then I put together a power supply filter for both the positive and negative rails. Something really basic - just strung together a heavy choke, 1A diode, 5 ohm 2W resistor, with 100uF electrolytics between each stage. Don't use a 1/2W resistor - I burned a pair up and that was exciting. The voltage at the end is about 11.8V, but very clean. Unbelievable difference, for $15 in parts.
All my interconnects between analog boards are done exclusively with shielded audio cable. Physically, the boards inside the case are as far away as possible from the DVD drive, IDE cables, and motherboard.
Hope this helps.
Ben
Is the lack of bass is due to the fact there is no RIAA equalization ? I wanted to use this circuit as a pre-amp with a record deck, but the sound is very tinny...
Is there a way to add this feature to this circuit, or will changing the capacitor values as Frank suggests be adequate ?
many thanks!
Is there a way to add this feature to this circuit, or will changing the capacitor values as Frank suggests be adequate ?
many thanks!
HerrNilsson said:
😀 😀 😀
Who made that junk with 1k trimmer pots in the output to adjust the volume was drunk, for sure.
And they call it "Universal stereo pre amplifier".
To Frank Berry: tone tuning on K2572
Hi Frank,
First time on this forum. I am trying to get the most of my freshly installed K2572. I set it between the TV headphone output and the Hifi amp. Signal was too low compared to the 300mV norm.
As avised, I use 2x9volt batteries for the test. The sound is OK, but still not as good as with my Soundcraft Folio sound mixer...
When you advice to change the capacitors for better bass response, is there a solution for treble response that is quite "noisy"?
Except for this, I could also change the IN cable which comes from cheap headphones.
Thank you for your great participation to this web site,
-Yves.
Hi Frank,
First time on this forum. I am trying to get the most of my freshly installed K2572. I set it between the TV headphone output and the Hifi amp. Signal was too low compared to the 300mV norm.
As avised, I use 2x9volt batteries for the test. The sound is OK, but still not as good as with my Soundcraft Folio sound mixer...
When you advice to change the capacitors for better bass response, is there a solution for treble response that is quite "noisy"?
Except for this, I could also change the IN cable which comes from cheap headphones.
Thank you for your great participation to this web site,
-Yves.
- Status
- Not open for further replies.