dreamie 0 Report post Posted August 30, 2003 THe OPA134 on mine got hot. anyway, i also tried to modify the circuit. 1) Removed input capacitor (save $$.. blackgate too ex. ) 2) Output load resistor value is 49.9ohm instead of 50ohm to 100ohm. 3) LED using 150ohm resistor from positive and grounded to 0V (not 10K across +4.5 and -4.5). May need to change the resistor value if i decide to use 2x 9V. Using the gold stereo jacks (female) u can get from Kaichin. $0.80 each. Still in development stage. Size is about 1 3/4 of a 9V battery. Any comments on the modifications? Thx for reading. Share this post Link to post Share on other sites
jasonhanjk 0 Report post Posted August 30, 2003 Hot... Is it still touchable? Share this post Link to post Share on other sites
dreamie 0 Report post Posted August 31, 2003 Hot... Is it still touchable? I smell of the burnt smell soon after it was switched on. Only touched it after a few minutes of shutting down. It could be due to oscillations, cause i did it on project board. Share this post Link to post Share on other sites
jasonhanjk 0 Report post Posted August 31, 2003 Nope. Seems like a short circuit. You need to inspect carefully. I burnt one buffer before. $10 one... Share this post Link to post Share on other sites
dreamie 0 Report post Posted August 31, 2003 Nope. Seems like a short circuit. You need to inspect carefully. I burnt one buffer before. $10 one... btw, i just realised i used 10k as the resistor to ground from pin 3 of OPA134. this wasnt the one i tested though.. this was the one i soldered. .. i think this will result in louder sound.. Share this post Link to post Share on other sites
jasonhanjk 0 Report post Posted August 31, 2003 I had OPA134 connect to +-12V but they don't get hot; just warm. Did you short the output to the ground, +V or -V? Really scare me..... To get louder, should try changing higher value resistor between pin 2 and 6. Share this post Link to post Share on other sites
dreamie 0 Report post Posted August 31, 2003 I had OPA134 connect to +-12V but they don't get hot; just warm. Did you short the output to the ground, +V or -V? Really scare me..... To get louder, should try changing higher value resistor between pin 2 and 6. Heh.. i reckon it got hot because I did them on a project board and they oscillated. Anyway, how would changing R2 (Pin 2 to ground resistor) to 10K from 100K affect the whole circuit? thanks. Share this post Link to post Share on other sites
jasonhanjk 0 Report post Posted August 31, 2003 Heh.. i reckon it got hot because I did them on a project board and they oscillated. Anyway, how would changing R2 (Pin 2 to ground resistor) to 10K from 100K affect the whole circuit? thanks. KK... I you use non-inverting amplifier. Gain = Rf/Ri + 1 Rf is the resistor between pin 2 and 6. Ri is the resistor between Pin 2 and ground. Increasing that resistor will give you louder sound... Share this post Link to post Share on other sites
Firefox 0 Report post Posted August 31, 2003 Heh.. i reckon it got hot because I did them on a project board and they oscillated. Anyway, how would changing R2 (Pin 2 to ground resistor) to 10K from 100K affect the whole circuit? thanks. It's pretty difficult to get the OPA2132/ 2134 series of opamps to oscillate. Guess you got a short or wrong connection on the opamp somewhere. If you used dual voltage rails, you MUST connect the virtual ground (or PS ground) to the audio ground. It's not advisable to change R2 to 10K unless you don't have a pot for volume control. Share this post Link to post Share on other sites
dreamie 0 Report post Posted August 31, 2003 Heh.. i reckon it got hot because I did them on a project board and they oscillated. Anyway, how would changing R2 (Pin 2 to ground resistor) to 10K from 100K affect the whole circuit? thanks. It's pretty difficult to get the OPA2132/ 2134 series of opamps to oscillate. Guess you got a short or wrong connection on the opamp somewhere. If you used dual voltage rails, you MUST connect the virtual ground (or PS ground) to the audio ground. It's not advisable to change R2 to 10K unless you don't have a pot for volume control. i Dont have a pot for volume control... Share this post Link to post Share on other sites
dreamie 0 Report post Posted August 31, 2003 Heh.. i reckon it got hot because I did them on a project board and they oscillated. Anyway, how would changing R2 (Pin 2 to ground resistor) to 10K from 100K affect the whole circuit? thanks. KK... I you use non-inverting amplifier. Gain = Rf/Ri + 1 Rf is the resistor between pin 2 and 6. Ri is the resistor between Pin 2 and ground. Increasing that resistor will give you louder sound... Hmm.. according to this forumla i should be getting a gain of 2, if i followed the original one which used 100k, the gain would be 1.1. am i correct? Thanks for all your inputs. Share this post Link to post Share on other sites
jasonhanjk 0 Report post Posted August 31, 2003 (edited) If both are same value.... yes Edited August 31, 2003 by jasonhanjk Share this post Link to post Share on other sites
Firefox 0 Report post Posted August 31, 2003 Hmm.. according to this forumla i should be getting a gain of 2, if i followed the original one which used 100k, the gain would be 1.1. am i correct? Thanks for all your inputs. The resistor from Pin 2 to ground is NOT R2!!! R2 is from In(+) pin to ground. ie. Pin 3 to ground on single-opamps! Share this post Link to post Share on other sites
dreamie 0 Report post Posted August 31, 2003 Hmm.. according to this forumla i should be getting a gain of 2, if i followed the original one which used 100k, the gain would be 1.1. am i correct? Thanks for all your inputs. The resistor from Pin 2 to ground is NOT R2!!! R2 is from In(+) pin to ground. ie. Pin 3 to ground on single-opamps! ops.. 2 wrongs make a right R2 on this image i meant. Correct? Thanks for all your inputs too Share this post Link to post Share on other sites
jasonhanjk 0 Report post Posted August 31, 2003 You may want to omit the C1 and R5... Share this post Link to post Share on other sites
