Hepl me! Nice amp but noisy

thanh · 31st December 2006, 05:35 AM

Hi !
My amp is quite noisy when
- it is connected to my computer
- computer is operating but there are'n any media software which is playing music
- volume is set at maximium level

If I don't connect my amp to my computer, speaker is silent. I tried to connect the amp to the computer directly but problem is still remains

I don't know where noise come from .

I have no 2SC3281/2SA1302. I'm using 2SA1227/2SC2987 instead of. I don't use C7 and C8 for real circuit but amp still works. Even I use these capacitor, noise still doesn't decrease
I'm using sound card CMI 8738
http://www.cmedia.com.tw/?q=en/pci_audio
Bye!

Twaksak · 31st December 2006, 06:07 AM

Hi Thanh

I experienced the same with my first ever amplifier that I made and ran from my PC soundcard. The problem was that the soundcard output impedance did not match the 22K input of my power amplifier. How I corrected this was to use a preamp between PC soundcard and amplifier input. Maybe this might help for you. I am assuming that the power amplifier plays ok with normal source such as CD etc.

Chris

thanh · 31st December 2006, 06:17 AM

oh! Really ?
So how ohms is input impedance of your pre-amp ?

When I intend to turn off computer, I see your name.
Thank for replying !

analog_sa · 31st December 2006, 06:25 AM

Quote:

Nice amp but noisy

Maybe you should change this to "nice computer but noisy"

AndrewT · 31st December 2006, 09:14 AM

Hi,
If I have understood your description correctly then I agree with Analog,
Nice amp, terrible (is it typical?) soundcard.

What if the soundcard is turn right down? Does that reduce the noise?

Alternatively, attenuate the output of the sound card (which also reduces the noise) and then run the sound card near maximum.
This should improve the signal to noise ratio.

Twaksak · 31st December 2006, 02:28 PM

Hi Thanh

I don't know the output impedance from my preamp but it surely must be made from Op amps. Look on Rod Elliot esp site for hi fi preamp circuit.

Chris

darkfenriz · 31st December 2006, 02:58 PM

Mute 'line-in' and 'microphone' at valume settings if you use MSwin.

jaycee · 31st December 2006, 03:45 PM

The CMI 8738 is a dreadful chip. Good for running computer speakers, but not much else.

Original Burnedfingers · 31st December 2006, 04:08 PM

thanh

Have you tried an issolation transformer between the computer's
sound card output and your amplifier? I have found this seems to take care of most problems.

The amplifier is a stand alone unit I assume?

Moshirio · 31st December 2006, 04:57 PM

i think u could use a filter bettwen the SC out and Amp in, like the monitor and other devices u connect to pc have, to filter that HF noise, just a tought, i never tried that for that use, only in mics that catchs rf noise

31st December 2006, 06:17 AM	#3
thanh diyAudio Member Join Date: Jan 2004 Location: ho chi minh city	oh! Really ? So how ohms is input impedance of your pre-amp ? When I intend to turn off computer, I see your name. Thank for replying ! __________________ Justice for Victims of Agent Orange http://www.petitiononline.com/AOVN/Thank all of you!

31st December 2006, 09:14 AM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, If I have understood your description correctly then I agree with Analog, Nice amp, terrible (is it typical?) soundcard. What if the soundcard is turn right down? Does that reduce the noise? Alternatively, attenuate the output of the sound card (which also reduces the noise) and then run the sound card near maximum. This should improve the signal to noise ratio. __________________ regards Andrew T.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Noisy Amp	vento	Solid State	13	16th January 2009 08:45 PM
Hepl me circuit 6h30	dia thien thai	Tubes / Valves	8	2nd December 2008 01:53 PM
plugged in 220v by mistake, hepl pls?	goliath6900	Solid State	25	16th October 2007 03:53 PM
hepl finding thread...	moray james	Subwoofers	0	25th April 2007 06:30 AM
noisy noisy noisy noisy noisy tube	dsavitsk	Tubes / Valves	50	20th February 2006 04:07 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

31st December 2006, 06:07 AM	#2
Twaksak diyAudio Member Join Date: Apr 2005 Location: Mpumalanga South Africa	Hi Thanh I experienced the same with my first ever amplifier that I made and ran from my PC soundcard. The problem was that the soundcard output impedance did not match the 22K input of my power amplifier. How I corrected this was to use a preamp between PC soundcard and amplifier input. Maybe this might help for you. I am assuming that the power amplifier plays ok with normal source such as CD etc. Chris

31st December 2006, 02:28 PM	#6
Twaksak diyAudio Member Join Date: Apr 2005 Location: Mpumalanga South Africa	Hi Thanh I don't know the output impedance from my preamp but it surely must be made from Op amps. Look on Rod Elliot esp site for hi fi preamp circuit. Chris

31st December 2006, 02:58 PM	#7
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Mute 'line-in' and 'microphone' at valume settings if you use MSwin.

31st December 2006, 03:45 PM	#8
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	The CMI 8738 is a dreadful chip. Good for running computer speakers, but not much else.

31st December 2006, 04:08 PM	#9
Original Burnedfingers diyAudio Member Join Date: Nov 2002	thanh Have you tried an issolation transformer between the computer's sound card output and your amplifier? I have found this seems to take care of most problems. The amplifier is a stand alone unit I assume?

31st December 2006, 04:57 PM	#10
Moshirio diyAudio Member Join Date: Oct 2005	i think u could use a filter bettwen the SC out and Amp in, like the monitor and other devices u connect to pc have, to filter that HF noise, just a tought, i never tried that for that use, only in mics that catchs rf noise

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)