| |||||||||||||||||||||||||||
| Moderators: cmoy | Welcome. Please log in. | ||||||||||||||||||||||||||
Registration is required to post a new topic or a reply. 
| |||||||||||||||||||||||||||
DIY Workshop » M³ headphone amplifier (part 2) | jackhsu Member Joined: Dec. 9, 2008 |  Message [#280] posted on: 03-18-2009 09:21 AM CST (US).   |  |  AMB, Finally, after installing the new and correct 2N3904, I got my BIAS working fine. Thank you so much for your help. One little thing bothering me is the DC offset between IG and OR, which is 4mV, much higher than that of the other two channels. Is this a problem? Any way I can do to bring down the DC offset inline with the other two channels? |
amb  Headphone Council Joined: Apr. 1, 2004 | Message [#281] posted on: 03-18-2009 12:59 PM CST (US). | | jackhsu, The three channels are independent and DC offsets are not adjustable in this amp. What opamps are you running? Try swapping the opamps between channels to see if the DC offset moves with the change. If it does, then the opamp is the culprit. Depending on what opamp you're using, 4mV may or may not be typical. Regarding the 2N3904 transistors, don't forget to also replace Q5+ with the proper one. |
| jackhsu Member Joined: Dec. 9, 2008 | Message [#282] posted on: 03-19-2009 08:41 AM CST (US). | | AMB, AD8610 is the Op-Amp I am using now. Swaping op-amps between channels does change the DC offset a bit. I will post the findings after trying all the possible combinations. And yes, I changed the Q5+ as well. [Edited by jackhsu on 03-19-2009 at 09:18 AM.] |
| jackhsu Member Joined: Dec. 9, 2008 | Message [#283] posted on: 03-19-2009 08:55 AM CST (US). | | AMB, After trying every possible combination of swaping Op-Amps, I found only one Op-Amp has 1.xxmV DC offset in R and L chnnels. The other two Op-Amps, when put in R or L channel, read 4.xxmV DC offset. And the DC offset of OG is always between 0.3-0.5mV. So is this going to be a problem? [Edited by jackhsu on 03-19-2009 at 09:19 AM.] |
| jackhsu Member Joined: Dec. 9, 2008 | Message [#284] posted on: 03-19-2009 10:38 AM CST (US). | | AMB, another problem is the AC reading between IG and OG/OL/OR. The readings are all around 7.5mV, which is also a lot higher than the <0.1mV you specified. Is this a real problem? Thank you. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#285] posted on: 03-19-2009 12:55 PM CST (US). | | jackhsu, are you measuring the offsets with the volume and bass boost pot turned to minimum? If not, then it would be a problem with test procedure. If that's not the problem, I wouldn't worry about it too much anyway. The offset numbers are low (even though they're higher than typical for AD8610), and perfectly safe. As for AC mV measurements at the output, don't worry about it. Many DMMs can't do this measurement accurately anyway. |
| jackhsu Member Joined: Dec. 9, 2008 | Message [#286] posted on: 03-19-2009 09:05 PM CST (US). | | Yes, I did all the measures with volumn turned down to the minimum. It's good to know everything is OK and I can go on plug in my HD650 now. Thank you very much for the great design and kind help. |
| jackhsu Member Joined: Dec. 9, 2008 | Message [#287] posted on: 03-19-2009 10:19 PM CST (US). | | AMB, Finally I got to plug in my HD650 and this M3 really rocks. I don't have too much experience with different amps but this one is far better than every amp I have heard. And the best part is: I built it. Here are the photos of my M3, just to let you know another M3 is singing happily across the Pacific.  [Edited by jackhsu on 03-20-2009 at 01:23 AM.] Attachment: C4773.jpg,C4774.jpg |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#288] posted on: 03-20-2009 03:55 AM CST (US). | | Congratulations, Jack, that's a nice clean build. Happy listening. |
| a1m80t Member Joined: Feb. 26, 2009 | Message [#289] posted on: 03-20-2009 10:51 AM CST (US). | | I know the dc offset test is to be done on minimum volume/bass boost, but a high dc offset (~30mv) on high volume/bb doesn't damage headphones? btw, thanks for eco|mate connectors recommendation, they are pretty nice |
Mister X HeadWize Fanatic Joined: Jul. 23, 2003 | Message [#290] posted on: 03-20-2009 11:06 AM CST (US). | | The instructions imply that anything over 5mV offset is a problem that needs to be sorted out with this amp. I would say "~30mV" is a major problem and it's time to try some different op-amps.  |
| a1m80t Member Joined: Feb. 26, 2009 | Message [#291] posted on: 03-20-2009 11:54 AM CST (US). | | Thanks again, I had to actually reposition the order of the opamps to get the offset low. Its a little off because i have to have OPA627 in the left channel and the OPA134 on the ground and right but that order is the only way i can the dc offset low. If i change the order up, there will always be one channel with a high dc offset if bb is up. In case you are wondering the suboptimal opamps setup, I have a few buddies who said they could give me some OPA637 samples. |
| niksh Member Joined: Feb. 13, 2009 | Message [#292] posted on: 03-21-2009 11:45 AM CST (US). | | Jackhsu, I have the same problem too with the DC offset. First I swapped the opamp. If the DC offset follow the opamp, then it is the respective opamp that is producing high DC offset. Changing the opamp solve the problem |
| Page << < 15 | Prev Topic | Next Topic | ||||
 (remove _nospam_ ) |
© Chu Moy, 2001.