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DIY Workshop » M³ headphone amplifier (part 2) | Iggurk Member Joined: Mar. 28, 2007 |  Message [#20] posted on: 03-11-2008 12:55 PM CST (US).   |  |  ok, I'll ask. He told me that at mid range with volume there is saturation, not clipping. |
| Iggurk Member Joined: Mar. 28, 2007 | Message [#21] posted on: 03-14-2008 10:53 AM CST (US). | | ok, found the issue. His power line has no ground... |
| Beefy Member Joined: Feb. 29, 2008 | Message [#22] posted on: 03-17-2008 09:47 PM CST (US). | | Well, I've finished the lion's share of my M3 build with great success - after initially having a heart attack when the LED didn't light up. Thankyou AMB for D1; in my excitement I'd hooked up the power supply lines backwards. Anyway, all three channels work beautifully. OPAMP bias has been set to 0.47V on all three channels, and MOSFET bias is 95-100mV out of the case. I cannot measure any DC offset at all my multimeter, so it is less than 0.5mV. Initial listening tests with a set of sacrifical Koss KSC-75 are VERY promising. And this amp certainly has massive amounts of power on tap - at the lowest gain of 2, I only need 1/6 turn on the volume knob to get the music to the louder side of comfortable.
Now all I need to do is case it all up! |
amb  Headphone Council Joined: Apr. 1, 2004 | Message [#23] posted on: 03-17-2008 10:48 PM CST (US). | | Another M³ lives! (sorry, couldn't resist  )Post pics when you have the casing done. |
| Beefy Member Joined: Feb. 29, 2008 | Message [#24] posted on: 03-17-2008 10:54 PM CST (US). | | Well its a great design, and there is great documentation on your site. Also, this thread has been a massive help. While not remembering specific details of problems over 90 odd pages, I'm sure that other people's experiences have subconsciously swayed my preparation and decisions along the way...... |
tomb Headphone Council Joined: Mar. 1, 2006 | Message [#25] posted on: 03-18-2008 12:00 AM CST (US). | |
The birthing of an amp is an achievement that should be celebrated. You've been helping M3 builders all over the world do that for quite awhile. |
OverTork Member Joined: Jan. 26, 2008 | Message [#26] posted on: 03-23-2008 07:02 PM CST (US). | | Another M3 & Sigma 11 went live Friday March 21st at 9:30 PM EST.   They fit very nicely below the iMac. |
Mister X HeadWize Fanatic Joined: Jul. 23, 2003 | Message [#27] posted on: 03-28-2008 06:16 PM CST (US). | | 
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| Beefy Member Joined: Feb. 29, 2008 | Message [#28] posted on: 03-28-2008 10:29 PM CST (US). | | Very nice, MisterX! * Just a quick question about OPAMP stability in the M^3. I've got a pair of OPA637's here that I bought off eBay, and they should be unstable and begin oscillating under a gain of 5-8, correct? But putting them in and testing them, albeit very briefly, I didn't notice any problems at all - even when I dropped my variable gain down to my minimum setting of 2. So under what conditions will OPA637 begin oscillating? Or have I bought counterfeit chips? |
| Beefy Member Joined: Feb. 29, 2008 | Message [#29] posted on: 03-31-2008 09:43 AM CST (US). | |
...... anybody? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#30] posted on: 03-31-2008 03:52 PM CST (US). | | The OPA637 is not guaranteed to be stable at gain below 5, but whether it will actually self-oscillate depends on the application. It may not oscillate in a gross manner, but it may exhibit parasitic instability (i.e., square wave overshoot/ringing). I would not recommend it to be used with gain of less than 5. |
| Beefy Member Joined: Feb. 29, 2008 | Message [#31] posted on: 03-31-2008 08:12 PM CST (US). | | Thanks AMB. I'll do some longer testing with careful listening, and see whether I get any of the behaviour that you describe. Oh, and I came across your Head-Fi profile the other day, and the fact that you started CDDB. That's just plain awesome [Edited by Beefy on 03-31-2008 at 08:16 PM.] |
| Jon P Member Joined: Apr. 2, 2008 | Message [#32] posted on: 04-03-2008 02:29 AM CST (US). | | Hi there, just completed my M3, Some very strange things happening. i get audio (adjustable with gain pot) its very distorted and if i adjust the bass pot up, the R9 resistors get red hot. biasop and bias have been set to give 0.45 v across r5's and 80 mv ish across R9's with no input signal and minimum on both volume and bass pots. i am powering form 2 12v lead acid batteries in series giving 24.5 overall the sound is garbled with clipping at higher volume ( which is not that high really ) and the bass boost has no noticiable difference on sound but makes the R9's get very hot + it also heats up the mosfets. any ideas? oddley enough i thought i had the opamps around the wrong way, as powering up the amp with no left channel op amp results in sound through both left and right phones. really a bit puzzled. looking at the schematic i am getting what looks correct out of the tle chip (full 24 ish and then half that) any help appreciated.. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#33] posted on: 04-03-2008 02:53 AM CST (US). | | Jon P, hot output resistors and MOSFETs could indicate severe oscillation. Are your DC offsets reasonable? Check your offboard wiring carefully to make sure there are no mistakes. Also double check all parts to make sure there are no solder bridges or cold joints. Is there any chance that the opamps are not genuine AD8610? |
| Jon P Member Joined: Apr. 2, 2008 | Message [#34] posted on: 04-03-2008 03:06 AM CST (US). | | thanks for the speedy response, i will defenetley check the wiring when i get home the opmps had the RS number : 497-1710 have a look at www.rswww.com they were about £5 each, and the datasheet says they are made by "analogue devices" so i just presumed they are ok..
same voltages everywhere, less heat but no sound at all.... mosfets stay warm to touch. i have double checked datasheet and i am pretty sure i had them round the right way to start with.. Oscillation was my guess also, looking at the schematic and voltages going into the opamp seam ok.. its just the output. i will like you say double check the external wiring when i get home.... |
| Jon P Member Joined: Apr. 2, 2008 | Message [#35] posted on: 04-04-2008 02:02 AM CST (US). | | All Good, now. rationalizing and reviewing the schematic lead me to the problem. my headphone jack was the culprit, no visible damage (internal prob) I have to say it really does sound very nice now.. Sound is very good indeed, makes me wonder how much better some of those other opamps are like the opa627 series. |
| Beefy Member Joined: Feb. 29, 2008 | Message [#36] posted on: 04-04-2008 02:43 AM CST (US). | |
Based on this Head-Fi thread http://www.head-...g-m-3-a-136888/ I bought some OPA637AP and OPA627BP. I haven't done extensive testing, but the OPA627BP in L/R and AD8610 in ground gives MASSIVE bass slam. Not any more volume, but massive power. Highs are deliciously smooth with no sibilance - except where the recording actually has it. I was very skeptical of mixing OPAMPs across L/R/Gnd, and it may still be my imagination..... but I really do like this combo. |
| Jon P Member Joined: Apr. 2, 2008 | Message [#37] posted on: 04-05-2008 03:33 PM CST (US). | | I think i will consider the OPA627 / 8610 on ground combo, there are lots of people who seam to like it. attached is a pic of me m3^3 considering a hifi2000 thanks for the advice everyone, |
| Beefy Member Joined: Feb. 29, 2008 | Message [#38] posted on: 04-05-2008 07:06 PM CST (US). | |
Don't get me wrong, I think that the differences between OPAMP combos are quite overstated. But this combo is nice if you can find the 627.
It is missing! |
| Jon P Member Joined: Apr. 2, 2008 | Message [#39] posted on: 04-06-2008 03:34 AM CST (US). | | Sorry here it is again, it was bigger than the 200Kb limit..  Attachment: C3665.jpg |
| Beefy Member Joined: Feb. 29, 2008 | Message [#40] posted on: 04-06-2008 04:09 AM CST (US). | | Very nice! Looks similar to mine with those black UHE(?) caps. But the resistors all look really chunky..... are they all 1/4 watt Vishay Dales pre-MOSFET? And huge films caps on the bass boost, but no resistors. What values are you using at CBB and R3/R4? I'd be interested to see the graphs. |
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