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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 [#360] posted on: 02-13-2009 01:57 AM CST (US).   |  | 
Not only must the power supply be beefed up, you must also run larger heatsinks on the amp and the power supply. All the concerns are described at the β22 and σ22 websites, under "Board & heatsinks". |
| pidesd Member Joined: Jan. 20, 2009 | Message [#361] posted on: 02-13-2009 03:20 PM CST (US). | | ok i solved the problem. one of the volume pot's ground was not soldered properly. as for the transfos that were humming, the only action of lifting them an inch or so in the air inside my steel chassis made them silent. i dont know why though. there is just one thing that is a little annoying: i m hearing an unbearable hiss at low and high volume on my 52 ohms sennheisers and not on my k701. i thought that lowering the gain to 10 combined(balanced) and the choice of a 10k pot would have taken care of that. is that normal for sensitive headphones with that amp or is it still a connection problem of some sort i might have? edit: just added the zobel and it s fine now thanks amb and helzerr [Edited by pidesd on 02-14-2009 at 10:32 PM.] |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#362] posted on: 02-15-2009 05:03 PM CST (US). | | Can I solder a terminal block for V+ G and V- inputs to the underside of the board. Is this what is normally done? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#363] posted on: 02-15-2009 05:29 PM CST (US). | |
Most people just solder wires directly, or use inline socket/receptacle assemblies (such as Molex .062 or .093 series). If you have terminal blocks that fit, then sure, why not. |
| ivant Member Joined: Feb. 16, 2009 | Message [#364] posted on: 02-16-2009 12:42 AM CST (US). | | Hi, I got a problem with high DC offset (about -6V).R9-R12 and R34-35 measures alright. Q23 gets very hot though. D9 and D10 are around 12V. Any ideas? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#365] posted on: 02-16-2009 12:52 AM CST (US). | |
Did this board work properly before? Or is it a new build? Check all MOSFETs for shorts, between all combinations for the three pins. |
| ivant Member Joined: Feb. 16, 2009 | Message [#366] posted on: 02-16-2009 05:26 AM CST (US). | |
Thanks for the reply. Its a new build. I tried to resolder all points on the board and finally problem solved. |
| ivant Member Joined: Feb. 16, 2009 | Message [#367] posted on: 02-16-2009 05:45 AM CST (US). | |
Anyway, any idea what could cause r10 to measure 5.5V while r9, R11 and R12 to be around 4.5V? I noticed Q15 to be very hot also. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#368] posted on: 02-16-2009 05:56 AM CST (US). | |
Q13-Q16 should all be similarly warm. If Q15 is hotter than the others then something is not right. You should use the troubleshooting PDF found on the β22 website "Initial setup" section as the reference, and do some voltage measurements to see if there are other locations where things are way off. |
| Sunday Member Joined: Feb. 16, 2009 | Message [#369] posted on: 02-16-2009 09:03 AM CST (US). | | Hi, I'm starting to build my β22 and have a source that is fully differential i.e. not ground referenced and would like to connect it to the β22. What provisions I have to make for it? |
| housing HeadWizer Joined: Dec. 16, 2006 | Message [#370] posted on: 02-16-2009 10:15 AM CST (US). | |
Go to amb's site and read the part on β22 first. It contains all the details. |
| Sunday Member Joined: Feb. 16, 2009 | Message [#371] posted on: 02-16-2009 11:42 AM CST (US). | | Thanks for the pointer. Maybe I should clarify something that my original post only implied. I'm planning use the amplifier in balanced mode. The balanced mode in β22 requires (+), (-), and ground. Not all sources are ground referenced. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#372] posted on: 02-16-2009 04:36 PM CST (US). | |
What source do you have that would be missing the ground on a standard XLR 3-pin balanced line connection? |
| oneplustwo Member Joined: Feb. 16, 2009 | Message [#373] posted on: 02-16-2009 06:42 PM CST (US). | | Hey folks, I just ordered my b22 and s22 from glass jar. I'm now thinking ahead to my enclosures. In the interest of conserving some cash and making a unique piece, anyone have thoughts about a DIY enclosure that's easy on the wallet? I'm not picky about things looking fancy, but do want everything to be safe and functional. Maybe the equivalent of the CMoy altoids tin? Actually, I was measuring out my Sennheiser HD650 case and it looks like it would be perfect for the amp part of the build. That might be just stupid though. Anyway, appreciate any thoughts or opinions you might have. Understand if many of them are "Stop being a cheap-ass" but if you could add a creative solution or two as well, that would be great! Cheers! |
linux-works Member Joined: Jul. 20, 2008 | Message [#374] posted on: 02-16-2009 08:40 PM CST (US). | | first idea for cheap-ish case: check out any used computer stores (if you have any 'junk stores') or even 2nd hand music stores. any place that might have surplus 2U rackmount gear. you might get lucky and find a box that is re-usable. there's a pro audio shop near me and I check that store out periodically to see if any 'non functional box-only' deals can be had also look on fleabay for old junker audio gear where you can gut it and salvage the box. |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#375] posted on: 02-17-2009 03:31 PM CST (US). | | I connected my first β22 board up to σ22, but stupidly didn’t pre-set the trimpots to their minimum positions. Have I caused any harm? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#376] posted on: 02-17-2009 04:51 PM CST (US). | |
If your MOSFETs did not overheat and your R34 and R35 resistors did not smoke, then you're probably fine. Preset the trimpots now before applying power again. |
| housing HeadWizer Joined: Dec. 16, 2006 | Message [#377] posted on: 02-18-2009 01:59 AM CST (US). | | Hi Ti, Is there an industrial standard for XLR panel-mount 4 pole male receptacle connection? Couldn't find useful info after googling. Just guessing :
[Edited by housing on 02-18-2009 at 02:00 AM.] |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#378] posted on: 02-18-2009 03:42 AM CST (US). | | I don't think there is a formal "standard", but the AKG K1000 scheme seems to be the convention that most people use for 4-pin XLR balanced headphones: 1: L+ |
| housing HeadWizer Joined: Dec. 16, 2006 | Message [#379] posted on: 02-18-2009 03:58 AM CST (US). | |
Hi Ti, Thanks. I'm close with my guess. |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#380] posted on: 02-18-2009 06:39 AM CST (US). | | Just checking in with some results, from my first board: LEDS turn on R34 64.8mV DC Offset 0.00mV I was a unsure where to measure the voltage at the output, but guessed it was the same pads as the DC offset (output and signal ground) I got 0.063V. Dang this thing runs hot. Thanks AMB for all your help so far! |
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