diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Analog Line Level (http://www.diyaudio.com/forums/analog-line-level/)
-   -   GHOST in 3 band graphic equalizer!! SOS! (http://www.diyaudio.com/forums/analog-line-level/225643-ghost-3-band-graphic-equalizer-sos.html)

csom 14th December 2012 09:29 AM

GHOST in 3 band graphic equalizer!! SOS!
 
3 Attachment(s)
First a brief history:
I started to build a 3 band Equalizer using NE5532 as per this website. 3 band EQ

First I tested the second part of the circuit on a breadboard and it worked as expected. ( attachment: graphic eq on bread board.jpg )

Then I made a quick PCB and built it.

Upon first power up it worked nicely but I found 2 problems

1. after some 10 seconds the sound started to spark
2. and gain reduced.

I touched my fingers at the input and it became normal again for another 10 seconds.
I added a 100k bypass Resistor infront of the 10uf/63v Electrolytic cap like this below in the input and the problem was solved! (Kindly see the attachment EQ FIX 1.png )

After some days I replaced the electrolytic input caps with a bigger nonpolar 10UF/100v caps. I found the sound was improved . I was happy. But after some 5 minutes the previous problem reappeared. i.e gain reduced and sparking noise.

I monitored the voltage ... +-15v okay, no over heating of the ICs, No pcb foil line is damaged. I tried my best to solve that but alas...
As a last resort I had to use the electrolytic caps again with the 100k biasing resistor.
Could please help me fix this problem so that I can use the bigger caps instead of the el-caps?
eq question how to solve .jpg

Thank you,
Best regards,
Som.

freax 14th December 2012 09:43 AM

sounds like an earthing issue to me, possibly a ground loop issue.

Reason for thinking this is that you touched the input with your fingers and that fixed it.

Get some perfboard and put the project onto that.

Bone 14th December 2012 09:46 AM

The positive input to the 5532 needs a resistance to earth to give it a reference. Move the top of R15 to the junction of C1 & R1.

csom 14th December 2012 09:46 AM

Thank you freax.
I am lost as the el-caps are working perfectly with the 100k resistor but the bigger nonpolar ones ( which are dramatically improving the performance) fail.

I checked the ground continuity too. No problem there .
:(

csom 14th December 2012 09:49 AM

Quote:

Originally Posted by Bone (Post 3284203)
The positive input to the 5532 needs a resistance to earth to give it a reference. Move the top of R15 to the junction of C1 & R1.

Thank you Bone !
Is the gain of that buffer stage 2? If yes can I use a 47k instead of that 100k ?

csom 14th December 2012 09:59 AM

1 Attachment(s)
Quote:

Originally Posted by freax (Post 3284200)
......
Get some perfboard and put the project onto that.

That was the second thing I did Freax It worked okay . Although the buffer stage was not there. Its the buffer stage that's the culprit here.
Here is the pic

bobodioulasso 14th December 2012 10:09 AM

Your schematic does not correspond to original.
Original shows an inverting opamp config.
You enter into + input. when this one should be grounded.

csom 14th December 2012 10:16 AM

Quote:

Originally Posted by bobodioulasso (Post 3284220)
Your schematic does not correspond to original.
Original shows an inverting opamp config.
You enter into + input. when this one should be grounded.

OUCH!! A "BIG FALE" for me !!!
Thank you so much bobo for pointing out that!
Re-designing the PCB now!
Sigh!

csom 14th December 2012 04:02 PM

1 Attachment(s)
Fixed the prototype. No more sparking or gradual gain reduction now.

Improvement: Noise is minimized to a great extent.

But the stereo image/ sound stage is reduced. weird. Earlier it was better.

Could you please suggest what can be done to increase Stereo image ?

Regards,
Som.

csom 14th December 2012 04:59 PM

Problem solved! One of the pots ( midrange 100k ) had a dry solder joint.
All fixed now! Sound stage restored again !
Working great now! Thank you all!

If any newcomer, hobbyist ,like me, wants a quick, simple yet very effective Equalizer solution and add it to your DIY amp, please go ahead and give it a try, you will be surprised to see its performance. :)


Regards,
Som


All times are GMT. The time now is 09:27 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