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DIY Workshop » β22: A discrete, cascoded, fully complementary, pure class A amplifier (part 3) amb  Headphone Council Joined: Apr. 1, 2004 |  Message [#40] posted on: 08-29-2008 11:26 PM CST (US).   |  | 
Yes, I will. |
| jazzist Member Joined: May 9, 2008 | Message [#41] posted on: 08-30-2008 11:30 AM CST (US). | | Hi AMB, Can you tell me who you use to manufacture your PCBs? At the moment I have a quote from Golden Pheonix which is very good but am interested in other options.
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| amb Headphone Council Joined: Apr. 1, 2004 | Message [#42] posted on: 08-30-2008 01:47 PM CST (US). | | I've used several in the past, but these days mostly use Imagineering. |
| helzerr Member Joined: Jul. 11, 2003 | Message [#43] posted on: 08-31-2008 09:06 AM CST (US). | | I've been working on finalizing the details of my amp, happily listening as I build cable assemblies to replace alligator-clip leads. I have one question regarding biasing the output via VR2. The mosfet current seems to be very temperature dependent. If I set the bias to 160 mA when it's cool, then the bias is too low when things heat up. If I set it when the amp is all warmed up, it's much too high (~ 260 mA) when the amp is cold. Which is the correct setting? I know mosfets are PTC devices, but is it normal for the bias to be this temperature dependent? I've settled on 120 mA measured after warm-up, as that seems to be a good compromise to keep the overall temperature reasonable. [Edited by helzerr on 08-31-2008 at 09:29 AM.] |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#44] posted on: 08-31-2008 01:38 PM CST (US). | | 120mAis ok. 260mA cold leading to 160mA warm is also ok. The MOSFETs can handle up to 17A so you're nowhere near that limit. As long as the heatsink temperature is kept in check while inside the case (no higher than 70°C or so) then you're fine. |
| wnmnkh Member Joined: Apr. 20, 2008 | Message [#45] posted on: 09-02-2008 03:54 AM CST (US). | | Sorry for this long overdue pic. This is finally assembled Beta22. I am happy with this now....
Taken while still in progress..... At night, the blue light from the venting holes of the amplifier is just awesome. [Edited by wnmnkh on 09-02-2008 at 03:57 AM.] |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#46] posted on: 09-02-2008 08:12 AM CST (US). | | Wow. That is massive!  EDIT: What enclosure is that? [Edited by amb on 09-02-2008 at 08:14 AM.] |
| wnmnkh Member Joined: Apr. 20, 2008 | Message [#47] posted on: 09-02-2008 05:12 PM CST (US). | | As I said a while ago on my previous posts, I could not find any commercially available case suitable for two backboards and two power supplies together. So, it was completely custom made, fabricated at my father's factory. The quality is not so excellent compared to what's inside, but still very good IMO. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#48] posted on: 09-03-2008 01:46 AM CST (US). | | wnmnkh, I am very impressed by what your father's factory turned out. What does his factory normally make? |
| tenorsaxophone Member Joined: Feb. 27, 2008 | Message [#49] posted on: 09-04-2008 12:46 PM CST (US). | | Hello! Mr. AMB in β22 and σ22 Part List WebPage indicates for RESISTORS and ELECTROLITIC CAPACITORS many constructor names. Is there a ranking (a classifies) of level of quality between them, considering the price differences. Please, help me to choise. Many thanks. Davide. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#50] posted on: 09-04-2008 03:45 PM CST (US). | |
If it's listed as recommended, then it's good. Which to choose depends on which vendor you're ordering from and what manufacturer(s) they carry, and your own preference/prejudice. |
| MrMajestic2 Member Joined: Jun. 5, 2007 | Message [#51] posted on: 09-05-2008 06:05 PM CST (US). | | Was listening to my b22 today, and it sounds fantastic But, I did something I probably shouldnt have done: Plugged in the balanced headphones with the amp still on. I heard a loud click and now I have lower volume on the right side. The heapdhones are unhurt thank god, so that leaves the amp. Time to go in and troubleshoot again, I hate this part. Any ideas on where to start would be great. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#52] posted on: 09-05-2008 07:14 PM CST (US). | | MrMajestic, that's curious. The amp should not be affected while plugging/unplugging headphones while it's on. I do it all the time (albeit I usually turn the volume down). On unbalanced TRS jacks, there is an opportunity for the left/right amp outputs to be shorted to each other and to output ground while the plug is inserted/removed, but the β22's output stage is stout enough to handle it, as long as the volume isn't cranked way up while playing music. On XLR jacks, there is no such issue at all... Also, if the output stage is to fail from being shorted, the symptom isn't just a reduction in volume. Measure the resistance of the 0.47 ohm output resistors, and check the output DC offsets. [Edited by amb on 09-05-2008 at 07:15 PM.] |
| MrMajestic2 Member Joined: Jun. 5, 2007 | Message [#53] posted on: 09-06-2008 05:13 PM CST (US). | |
Thanks for your reply AMB. I havent started troubleshooting yet, but the click is still there when I plug the phones in so Im guesing that either the + or - board on the right side has some kind of failure or at least some issues. So its probably not due to me plugging in the phones while on that did it. Will try to check it out tomorrow as I miss my amp a lot |
| MrMajestic2 Member Joined: Jun. 5, 2007 | Message [#54] posted on: 09-08-2008 05:03 AM CST (US). | | Turns out that the error in my amp was a power cable to one of the boards not fully plugged in. Must have slipped out just a tad when I was poking around in it. |
| MrMajestic2 Member Joined: Jun. 5, 2007 | Message [#55] posted on: 09-08-2008 05:14 AM CST (US). | |
That is just awesome [Edited by MrMajestic2 on 09-08-2008 at 05:14 AM.] |
| wnmnkh Member Joined: Apr. 20, 2008 | Message [#56] posted on: 09-09-2008 02:22 AM CST (US). | | Both sides were tested using 0404+RMAA, the results were very similar/same as what AMB measured. Check his website for the detail. |
| tenorsaxophone Member Joined: Feb. 27, 2008 | Message [#57] posted on: 09-10-2008 05:15 AM CST (US). | | Hello! Is ε12 Muting/Protect Circuit needed for β22 ampli? Many thanks. Sincerely. Davide. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#58] posted on: 09-10-2008 11:58 AM CST (US). | |
β22 emits almost no-turn on or turn-off thump, so no delay muting is required. Whether you want to add an ε12 for DC offset protection (in case of malfunction) is up to you. |
| jazzist Member Joined: May 9, 2008 | Message [#59] posted on: 09-11-2008 04:24 AM CST (US). | | Today I'm very excited as my first β22 backplane arrived :-) (for active ground unbalanced or left channel balanced, there will be another for the right channel balanced/active ground unbalanced). Well, sorry to be boring, but I had to share my excitement somewhere The boards look very nice. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#60] posted on: 09-12-2008 05:05 AM CST (US). | |
How about posting some pictures? |
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