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DIY Workshop » β22: A discrete, cascoded, fully complementary, pure class A amplifier (part 3) | Iniamyen Member Joined: Mar. 7, 2008 |  Message [#460] posted on: 03-15-2009 05:30 PM CST (US).   |  | 
Okay, but at least in my environment, the type of interference it picks up is very low-level white noise whose power is so low compared to any type of systematic hum that it's basically negligible. YMMV I guess; it's at least a useful data point for me. |
| oneplustwo Member Joined: Feb. 16, 2009 | Message [#461] posted on: 03-15-2009 08:31 PM CST (US). | | Well, I get a hum no matter what the volume, source connected or not. I get a little bit of something else as the volume goes up that's not really noticeable until the knob gets to like 7 or so. My guess is transformer hum plus amplified noise when the volume knob goes up. Guess it's time to whip out that other tin I have and relocate the trafo at least if not the board as well. Grr... Also is the amp itself supposed to have a hum? Sounds like something is coming from the boards themselves. [Edited by oneplustwo on 03-16-2009 at 02:33 AM.] |
housing HeadWizer Joined: Dec. 16, 2006 | Message [#462] posted on: 03-16-2009 06:19 AM CST (US). | |
Remove your transformer from the tin and place it farther away from the amp. This surely helps. |
| oneplustwo Member Joined: Feb. 16, 2009 | Message [#463] posted on: 03-16-2009 10:47 AM CST (US). | | Sorry, I should probably clarify what I'm hearing. I understand that there is a hum through the headphones as a result of the trafo and that moving it will solve the problem. However, without headphones on and just powering on the amp, I hear a low hum like something on the amp is vibrating. It turns out that the frequency is the same as the hum I hear through the headphones so I was wondering if maybe I wired something incorrectly to make the hum happen or if there's some other problem I need to address. Also, the fact that the frequency is the same could be a coincidence, but perhaps I don't have a trafo problem at all and there is another issue that I need to fix that will eliminate the hum. I don't remember getting a hum when I was testing the sigma by itself, nor when I was doing the beta checks. I think I noticed it first when I put everything in the case. Otherwise, I don't notice anything getting hot and the sound coming out of the headphones is actually very good minus the hum. Thoughts? |
| pidesd Member Joined: Jan. 20, 2009 | Message [#464] posted on: 03-16-2009 11:55 AM CST (US). | | i would try to solve the problems i have solutions to first.sometimes miracles happen  . move the trafo away.put it in your yard but move it away... after that if the trafo is still vibrating try different position inside it s enclosure. i dealt with that specific problem by putting a 1 inch piece of wood between the trafo and the bottom.[Edited by pidesd on 03-16-2009 at 12:21 PM.] |
amb Headphone Council Joined: Apr. 1, 2004 | Message [#465] posted on: 03-16-2009 01:56 PM CST (US). | | Transformers vibrate, some more than others. This is why most raw toroids come with vibration damping pads which are supposed to be used on both sides. |
| pidesd Member Joined: Jan. 20, 2009 | Message [#466] posted on: 03-16-2009 07:34 PM CST (US). | | yeah the pads prevent the vibrations to be transmitted to whatever it s bound to. just to clarify, the piece of wood i use is only to elevate the trafo, which cause the vibration to disappear( or to be inaudible). as i explained a couple pages ago. [Edited by pidesd on 03-16-2009 at 09:09 PM.] |
| oneplustwo Member Joined: Feb. 16, 2009 | Message [#467] posted on: 03-16-2009 09:18 PM CST (US). | | Ah, gotcha. I had no idea transformers vibrated! A couple more questions. 1. So if I just put the sigma in it's own enclosure, does it matter much how far away it is from the beta? It will probably also go in a cookie tin to follow the theme of the beta, just a smaller one. Also, the beta will probably run with the top off to keep it cool (but will have the top on when not in use.) Do either of things indicate the the sigma should be farther away from the beta than normal, (whatever normal is?) 2. I assume it's ok for me to connect all three V+, V-, and G wires from my three beta boards to form one three wire umbilical which will ultimately end up on one of the sigma's connections vs. the three currently occupied? This is what I interpret from the wiring section of the website. 3. I currently have a ground loop breaker installed since everything is in one enclosure. I assume it's totally unnecessary if I put the sigma in it's own enclosure. Or is there any reason to use it at all? |
| pidesd Member Joined: Jan. 20, 2009 | Message [#468] posted on: 03-16-2009 11:28 PM CST (US). | | 1. the farther the better but the dc cable should not be longer than 3 feet or so, as stated in the guide. to keep that nice cover on you could drill holes under and on top for airflow. 2.yes, as stated in the guide 3. not necessary, as stated in the guide. but i m not competent enough to tell you why. [Edited by pidesd on 03-16-2009 at 11:37 PM.] |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#469] posted on: 03-17-2009 12:35 AM CST (US). | | A ground loop breaker is not needed in a 2-box configuration, because AC earth ground and the amp's signal ground will not share the chassis, and therefore a ground loop cannot occur. You simply hook up the amp case to the amp's signal ground (easiest way is to use uninsulated RCA input jacks), and connect the IEC's ground to the PSU/transformer case. This is all shown in the β22 website "Wiring & ground" section. I once wrote a discussion about this topic when I built my 2-box dynahi, you can see it here. [Edited by amb on 03-17-2009 at 12:37 AM.] |
| oneplustwo Member Joined: Feb. 16, 2009 | Message [#470] posted on: 03-17-2009 11:27 AM CST (US). | | Can I mount my trafo bare outside my enclosure? I played around with the amp last night and figured out that if I just move the toroid up 2" and rotate it 90 degrees so it's basically just above the tin itself that the hum goes 99% away. It seems like the tin amplifies any toroid hum and taking it outside the tin eliminates it. So I'm thinking maybe I just mount the toroid outside the tin on a slightly longer board than I was going to mount the tin on anyway. I would put one additional hole in the tin to allow for the input and output wires with appropriate sleeving, strain relief, and grommets. |
| pidesd Member Joined: Jan. 20, 2009 | Message [#471] posted on: 03-17-2009 01:00 PM CST (US). | | we were born to be free arent we? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#472] posted on: 03-17-2009 02:06 PM CST (US). | |
Not pretty, but workable. Just make sure absolutely all AC wiring is insulated/heatshrunk,and mounted in a mechanically-secure fashion so that there is no possibility of an accidental short circuit or shock hazard. [Edited by amb on 03-17-2009 at 02:07 PM.] |
| oneplustwo Member Joined: Feb. 16, 2009 | Message [#473] posted on: 03-18-2009 01:26 AM CST (US). | | I ended up moving the toroid into it's own "enclosure" but still keeping all the wiring, IEC, and on/off switch in the original tin. As luck would have it, I had a round cookie tin lying around so I put it to good use! As such, I present to you the cookie tin/beta 22 hybrid:
I just need to trim and mount everything to that board (scrap piece of shelf from IKEA) and then it should be completely finished. [Edited by oneplustwo on 03-18-2009 at 01:36 AM.] |
| rille Member Joined: May 22, 2007 | Message [#474] posted on: 03-18-2009 02:35 AM CST (US). | | Just use a better transformer with magnetic shielding. I had also some problems with hum at high sensitve headphones and with the new transformer they are gone. See headwize.com/ub...=73798&fpage=11. |
| oneplustwo Member Joined: Feb. 16, 2009 | Message [#475] posted on: 03-18-2009 11:05 AM CST (US). | | If I was to do it again, I definitely would have gotten a shielded toroid. But I'm actually happy with the quirky cookie tin theme I have going on. I still do get a tiny amount of hum though. I can't hear it unless it's totally silent, but it is there. |
| ephrank Member Joined: Dec. 16, 2008 | Message [#476] posted on: 03-18-2009 08:43 PM CST (US). | | woohoo I've got my first beta22 board working! Luckily it was a problem-free initial setup. Was able to set the DC offset to 0.0mv Man the MOSFETs do run hot.3 more boards to go... |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#477] posted on: 03-19-2009 05:26 AM CST (US). | | ephrank, congratulations! Another Aussie! I’m from Blaxland in the Blue Mountains. Is yours a balanced build for headphones or speakers or both? I’ve just completed all 6 boards for my build which includes 2 sigmas (all test perfect). It’s a headphone only amp, I have two par metal 20 series enclosures. This week I picked up my laser cut front and back panels, I’m getting a logo and slogan laser etched on the two front panels on Saturday. I’m hoping to be completed in around a month, I’ve build slowly taking my time. The $$$ that’s gone into this was totally unexpected, things like audio feet, glue guns and terminal blocks etc., that you never account for. Anyway good to see another aussie on their way to Beta heaven... |
| ephrank Member Joined: Dec. 16, 2008 | Message [#478] posted on: 03-19-2009 09:46 PM CST (US). | | Hi johnwmclean, great to know that your amp is up and running My build is similar to yours, 4 beta + 2 sigma boards and it will be headphones only. Where do you have the panel laser cut? I am planning to get two 2U rack mount cases from Jaycar for my amp. BTW I live in Merrylands. |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#479] posted on: 03-19-2009 10:20 PM CST (US). | | ephrank, a company in Chatswood did the laser cutting, as I work in North Sydney. I’m afraid I cannot recommend them as they charged me twice as much as another companies quote which I received too late, the job was great though. And to be fair it was my fault in accepting the quote. As a coincidence I will be in Merrylands tomorrow getting the front face panels laser etched. This company has been great to deal with and can recommend them thoroughly if want your panels engraved. http://www.p4laserengraving.com.au pdf of my design attached, I keep is short and simply. Attachment: C4772.pdf |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#480] posted on: 03-20-2009 02:43 AM CST (US). | | I have a query in regards to multilayered ceramic capicitors, is it preferable to elevate these slightly from the pcb board? This is what I have done with my build, I assumed this was correct, I've seen it done both ways though. |
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