Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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
Reply
 
Thread Tools Search this Thread
Old 7th March 2008, 08:18 AM   #1
simsim is offline simsim  British Indian Ocean Territory
diyAudio Member
 
Join Date: Mar 2008
Default My first amp: constant white noise problem

I just finished my first amp, based on TDA1558Q, "2 X 22 W or 4 X 11 W Single-ended Car Radio Power Amplifier"

It sounds great but the problem is that if I connect it to anything else than my old ipod (classic white model with metal back) there is white noise/static at even volume, very noticable when you stop the music or play soft. So far I tried at different friends houses with an ipod shuffle, portable cd player and 2 laptops.

I rebuilt it on breadboard and tried both the 2x22W (Bridged) and 2x11W circuit, same result. I must be doing something wrong. What could be the source of the noise?




TDA1558Q data
  Reply With Quote
Old 7th March 2008, 09:27 AM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
high impedance on the input?
__________________
regards Andrew T.
  Reply With Quote
Old 7th March 2008, 08:10 PM   #3
gfiandy is offline gfiandy  United Kingdom
diyAudio Member
 
gfiandy's Avatar
 
Join Date: Jul 2003
Location: Cambridge UK
Does it do it with nothing attached?

If yes then it is probably as AndrewT has suggested and needs a lower input impedance. You could try a 10K resistor to ground.

If it is not present when no input is connected then this may be due to quite high gain of this amplfer amplifying noise on the ouput of your source. Strange that an iPod would be better than a CD player though.

The other possibility is that it is unstable and the instability is creating noise in the audio range (if it is unstable it is likely that the oscillations will be at several hundred KHz if not into the MHz. If this is the cause the it is likely that you need to improve you power supply decoupling and check that none of the input signlas are tracked close tot he output signals or near the power supplies.

Regards,
Andrew
  Reply With Quote
Old 7th March 2008, 11:05 PM   #4
simsim is offline simsim  British Indian Ocean Territory
diyAudio Member
 
Join Date: Mar 2008
Thanks for replying so quick!

I'm new to this so it's really good to get advice. I'm going to try that thing with the impedance, the amp is very loud, too loud actually and if you pull out the cable from the source there's a terrible sound :-)

This evening I breadboarded another amplifier, using two LM1875 and the suggested circuit from the datasheet. This one sounded perfect, no noise, so I think I will finish this one before I go back to the 1558Q. On this new amp build I noticed something to do with your second suggestion, when I moved the input voltage to a strip on the opposite side of the breadboard, a distortion I heard earlier totally disappeared.

I used another power supply for the new one, the LM1875 needs at least 14 volt I think, the old wall wart I used for the 1558 didn't suffice.

I'll report back :-)
  Reply With Quote
Old 8th March 2008, 03:47 AM   #5
TheMG is offline TheMG  Canada
diyAudio Member
 
Join Date: Jan 2008
Yup, definitely way too much gain then.

Looks to me like you're going to have to add a couple resistors or a pot to attenuate the signal coming into the TDA1558, as the chip has a fixed gain.
  Reply With Quote
Old 8th March 2008, 05:07 AM   #6
simsim is offline simsim  British Indian Ocean Territory
diyAudio Member
 
Join Date: Mar 2008
yeah, I actually had a volume pot in the first build, hastely added, which might have solved the noise issue, the problem was that I naively thought you could use a pot on the supply voltage to regulate the volume, I suppose I heard somewhere you shouldn't interfere with the input signal :-) I think my next idea would have been to put it just before the speakers. But then I googled it.
  Reply With Quote
Old 8th March 2008, 06:13 AM   #7
TheMG is offline TheMG  Canada
diyAudio Member
 
Join Date: Jan 2008
Simplest and most effective way to implement a pot for passive vol control is to tie one end to the audio source, other end to ground, and the wiper (center connector) to the amplifier input.
  Reply With Quote
Old 9th March 2008, 03:25 PM   #8
simsim is offline simsim  British Indian Ocean Territory
diyAudio Member
 
Join Date: Mar 2008
Thanks, I wasn't quite sure what to do with that 3rd connector on the pot :-)

Well, the pot doesn't help so much with the 1558 it turns out. when I increase the resistance the music lowers but instead you get this other horrible loud noise, like when you pull the connector from a guitar sometimes. That makes you almost miss the gentle hissing white noise. That loud noise is there when there is nothing connected to the amplifier too. Only when I short out input and ground there is beautiful silence. I probably misread the schematic somehow and I'm thinking I'll leave it and go back to it when I know more.
  Reply With Quote
Old 9th March 2008, 04:33 PM   #9
TheMG is offline TheMG  Canada
diyAudio Member
 
Join Date: Jan 2008
You did set it up like in the picture below, right?

What value of pot did you use?
Attached Images
File Type: png pot.png (2.1 KB, 183 views)
  Reply With Quote
Old 10th March 2008, 10:33 AM   #10
simsim is offline simsim  British Indian Ocean Territory
diyAudio Member
 
Join Date: Mar 2008
Since you asked what value I used I decided to try some other values. Turned out to be the solution! I had been using 100K pot but I found out that with 2k pots it worked much better. Thanks!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
White Noise Active PSU ANDYLASER Swap Meet 5 12th January 2009 06:37 AM
Trends Audio Ta-10.1 - white noise? dalefog Chip Amps 1 5th May 2008 09:05 PM
HELP: White or Pink noise problem Tedyp Parts 2 26th March 2006 10:42 PM
For sale White Noise Battery Pre Amp chrisbarber Swap Meet 0 15th June 2005 10:06 AM
Review - TC622VAT: Fan-cooling amps without the constant noise OddOne Chip Amps 0 22nd May 2004 10:15 PM


New To Site? Need Help?

All times are GMT. The time now is 04:46 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2