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DIY Workshop » β22: A discrete, cascoded, fully complementary, pure class A amplifier (part 3) | tedsmith Member Joined: Feb. 3, 2009 |  Message [#340] posted on: 02-07-2009 11:48 AM CST (US).   |  |  This was very difficult as it was a 3.6 Ohm short, not a dead short, so impossible to see even with very high magnification, bright lights, and many many hours looking. Eventually I decided to "carve" out all of the output track, it looks a little messy though  where is my short? Not around the output pad..
[Edited by tedsmith on 02-07-2009 at 11:48 AM.] |
amb  Headphone Council Joined: Apr. 1, 2004 | Message [#341] posted on: 02-07-2009 05:26 PM CST (US). | | tedsmith, I'm glad you found it!  |
| mrmajestic2 Member Joined: Jun. 5, 2007 | Message [#342] posted on: 02-08-2009 11:56 PM CST (US). | | Just want to check something with you guys. I built a balanced B22 with 8x gain and using a Joshua Tree for volume control. I have to turn the knob to 12 and beyond to get reasonable listening levels with Senn HD600s. I didn't think much about it, thinking this was normal, since I don't have anything else to compare with. So I'm asking, does it seem normal? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#343] posted on: 02-09-2009 02:53 AM CST (US). | | mrmajestic2, I don't know what kind of attenuator "taper" the Joshua tree has, but it's possible that it has very gradual volume change in the first half of the pot rotation. If you can get more volume than you could bear by turning it up further, then there is nothing to be concerned about. Oh btw, if I am not mistaken, the JT wants a linear taper pot to control it. If you used a log or "audio taper" pot, then that could be a reason for the low volume in the first half turn. If you're really curious about whether the amp has the correct gain, you could measure it. Unplug your headphones/speakers, play a steady-state sine wave test tone from your source with the volume turned to maximum. Measure the input voltage with your DMM in AC V mode (across the + and - input pins), and then measure the same across the + and - outputs. The output should be approximately 16x the input. |
| MrMajestic2 Member Joined: Jun. 5, 2007 | Message [#344] posted on: 02-09-2009 03:04 AM CST (US). | |
Thanks for your reply. I actually sold the unit and the buyer was wondering about this. It didn't worry me that much, i thought it was fine. The pot is a 10k linear RK27 so thats ok. Not sure what "taper" the JT has, but Im sure its somewhere in the JT thread on Headwize. No point for me looking there as it would really only be Greek to me |
| pidesd Member Joined: Jan. 20, 2009 | Message [#345] posted on: 02-12-2009 11:27 AM CST (US). | | [Edited by pidesd on 02-12-2009 at 02:15 PM.] |
| pidesd Member Joined: Jan. 20, 2009 | Message [#346] posted on: 02-12-2009 01:16 PM CST (US). | | - [Edited by pidesd on 02-12-2009 at 02:29 PM.] |
| pidesd Member Joined: Jan. 20, 2009 | Message [#347] posted on: 02-12-2009 01:17 PM CST (US). | | hi, i just cased up my balanced beta 22 and got a problem since then. i have unbelievable hum coming from my phones. i checked the signal and supply wiring and everything seems ok. i also noticed hum from my 2 transformers(in a seperate chassis with psu) when i connect any beta 22 board to it.i did the initial setup for the beta22 and psu and everything is ok except i get psu output AC voltage reading of 100 micro volts unloaded and 1 to 2 mV when loaded. the AC offset is 40 mV. also i noticed the voltage between the output and input pad on the beta 22 is 13 V AC. is that whithin acceptable levels? i tried to put the trafos away from the psu without any good results. meanwhile i ll try to put a steel pipe around the trafos to see if it helps but i doubt it. can anybody help me please? [Edited by pidesd on 02-12-2009 at 02:43 PM.] |
| pidesd Member Joined: Jan. 20, 2009 | Message [#348] posted on: 02-12-2009 01:18 PM CST (US). | | - [Edited by pidesd on 02-12-2009 at 01:45 PM.] |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#349] posted on: 02-12-2009 03:39 PM CST (US). | | pidesd, do you have the inputs shorted to ground (i.e., volume turned all the way down) when you listened for hum? Without a source connected, if the input isn't shorted it will pick up noise. Also please describe how you have done the input, output and power wiring, including the grounds. There definitely shouldn't be 13V AC between the input and output pads. |
| pidesd Member Joined: Jan. 20, 2009 | Message [#350] posted on: 02-12-2009 04:55 PM CST (US). | | i tried to solve the 13V ac between the input and ouput pads seperately by only connecting two b22 board to 1 power supply with one trafo, just to make a simpler setup, and i get pretty much the same readings as before(no signal wires are connected nowhere)on the 2 boards. ac offset on beta 22: around 15 mV if that matters. between the output pads of the psu i get .5 mV AC loaded. i just cant see what i did wrong. my trafo is avel lindberg y23. blue and violet together(neutral).gray and brown together(live). yellow and black live. red and orange ground. then my two beta 22 are connected to the psu terminal blocks. could it be emi from the transformer alone? i switched the trafos, psus and b22 and nothing will do. [Edited by pidesd on 02-12-2009 at 06:06 PM.] |
| fc911c Member Joined: Jun. 6, 2008 | Message [#351] posted on: 02-12-2009 05:08 PM CST (US). | | Hi Will a ballanced B22 with two S22 ps drive Polk LSi9 speakers ok? |
| pidesd Member Joined: Jan. 20, 2009 | Message [#352] posted on: 02-12-2009 05:12 PM CST (US). | |
yes but 4 psus with 4 traffos are recommended. it s all written on AMB s website [Edited by pidesd on 02-12-2009 at 05:12 PM.] |
| pidesd Member Joined: Jan. 20, 2009 | Message [#353] posted on: 02-12-2009 05:54 PM CST (US). | | - [Edited by pidesd on 02-12-2009 at 06:01 PM.] |
| fc911c Member Joined: Jun. 6, 2008 | Message [#354] posted on: 02-12-2009 06:13 PM CST (US). | |
ok thanks I just read it. looks like I will need two more then. |
| helzerr Member Joined: Jul. 11, 2003 | Message [#355] posted on: 02-12-2009 08:27 PM CST (US). | | My Y23 primaries are wired as you describe, but the secondaries are wired yellow(~) black (G) orange (G) red (~)
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| pidesd Member Joined: Jan. 20, 2009 | Message [#356] posted on: 02-12-2009 09:20 PM CST (US). | |
are you sure it s the right way? it didnt solve my problem at all [Edited by pidesd on 02-12-2009 at 09:20 PM.] |
| helzerr Member Joined: Jul. 11, 2003 | Message [#357] posted on: 02-12-2009 09:36 PM CST (US). | | This post would indicate your initial transformer wiring configuration was correct and I am wrong: headwize.com/ub...d=74679&fpage=1 [Edited by helzerr on 02-12-2009 at 09:54 PM.] |
| pidesd Member Joined: Jan. 20, 2009 | Message [#358] posted on: 02-12-2009 11:42 PM CST (US). | | is it normal i get 12v AC between the psu center tap and the power entry s earth pin? when i connect the input signal the "13V AC" problem disappears because the inputs are shorted.maybe it was normal after all...i ll test again tomorrow. [Edited by pidesd on 02-13-2009 at 01:31 AM.] |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#359] posted on: 02-13-2009 01:55 AM CST (US). | |
That is a meaningless measurement if your PSU's center tap is isolated from AC earth. The two have no reference in common. |
| 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". |
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