| |||||||||||||||||||||||||||
| Moderators: cmoy | Welcome. Please log in. | ||||||||||||||||||||||||||
Registration is required to post a new topic or a reply. 
| |||||||||||||||||||||||||||
DIY Workshop » β22: A discrete, cascoded, fully complementary, pure class A amplifier (part 3) | tedsmith Member Joined: Feb. 3, 2009 |  Message [#320] posted on: 02-03-2009 12:17 PM CST (US).   |  |  I think I need to remove the components covering the output trace's snake down the top side of the board. I've looked at the schematic and the resistance to ground is higher at the other side of every component directly connected to the output, so I think this must be the problem.. but 3.62 Ohms it is going to be a /tiny/ under-etched point or bridge  Thanks. [Edited by tedsmith on 02-03-2009 at 12:17 PM.] |
| tedsmith Member Joined: Feb. 3, 2009 | Message [#321] posted on: 02-04-2009 09:02 AM CST (US). | | I have removed R34, R35, D9, D10, C1, R4, VR2, VR3, and I still cannot find the short I tried to desolder as neatly as possible but discoloured the PCB slightly on the underside by VR3 due to the heat (I used a SMD rework station, hot air station, as it's difficult to heat all three legs of the VRs with a soldering iron, must have set the air temp a little high).Still can't find the short, will look again and again though.
I spent several hours wearing an opti-visor and cannot see anything. Hoping the short was under the top layer silkscreen (so hidden from view), I made incisions all along the output track's snake along the top layer of the board, still the short persists [Edited by tedsmith on 02-04-2009 at 03:21 PM.] |
amb  Headphone Council Joined: Apr. 1, 2004 | Message [#322] posted on: 02-04-2009 03:37 PM CST (US). | | tedsmith, keep looking. This is a two-layer board so there is nothing hidden inside. If you measure a short, there has to be one somewhere. |
| zhang_junyang Member Joined: May 19, 2007 | Message [#323] posted on: 02-04-2009 06:46 PM CST (US). | | It may be a component short, not a solder short. A part may be spoilt. |
| zhang_junyang Member Joined: May 19, 2007 | Message [#324] posted on: 02-04-2009 06:48 PM CST (US). | | It may be a component short, not a solder short. A part may be spoilt. |
| ZMN Member Joined: Nov. 13, 2004 | Message [#325] posted on: 02-05-2009 03:55 AM CST (US). | |
Hi amb, It took some time to try all options, with grounding and wiring in both chassis. In the end, the only way to reduce the noises to null, was to reinstall the potentiometer as you suggested. For this, the best solution so far, was to replace the potentiometers with fixed resistors (atm: well matched, Vishay-Dale 1/8W RN55, 10k to GND & 6.6k to +), and continue to apply volume control digitally. I think this is the best I can get out of it without changing the IVY I/V stage or source. Thanks for the help and advice. I can continue to enjoy the beta22s wonderful head-amp performance! [Edited by ZMN on 02-05-2009 at 03:56 AM.] |
| juswyq Member Joined: Feb. 5, 2009 | Message [#326] posted on: 02-05-2009 11:51 PM CST (US). | | I'm thinking of ordering a 4 channel b22 kit from glassjaraudio. i'm ordering a kit because sourcing each part individually and shipping them to this part of the world will cost a lot, so a kit will be more cost effective. however, my question is that can i build a 3 channel b22 first? i dont have any balanced source right now, so i will have to run the b22 in 3 channel first. will modifications be substantial if i change it between 3 and 4 channel b22? Thanks. Really looking forward to listening to this beauty of an amplifier. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#327] posted on: 02-06-2009 12:03 AM CST (US). | | juswyq, there are a few resistor and capacitors that will need to be changed to convert a 3-channel active ground board to one of the balanced 4-channel boards, but it's not a big deal. See the β22 website parts list for details. The more important things you need to keep in mind are that the casing/cabling/connectors/volume pot requirements for 3-channel and 4-channel are different, the PSU power transformer should be sized for four boards, and optionally (depending on your preference), the power supply may be upgraded from a single σ22 to twin σ22s. |
| juswyq Member Joined: Feb. 5, 2009 | Message [#328] posted on: 02-06-2009 12:28 AM CST (US). | | amb, is it possible then to use an SE headphone on a balanced b22? Instead of changing configurations, Maybe i could just build a balanced b22 and just run it single ended? I was thinking XLR -> TRS converter for the headphones, but maybe its not that simple? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#329] posted on: 02-06-2009 12:44 AM CST (US). | | It's risky using a "converter" unless you know exactly how it's wired inside, and how it might integrate with your balanced output jack wiring. A balanced headphone has four active outputs L+, L-, R+ and R-. An unbalanced headphone has three signals L, R and G. You could drive the L and R with the L+ and R+ outputs, but without recabling your headphone to 4 wires, the G cannot simply be connected to both of the L- and R- outputs. If you don't want to recable the headphone, then you need to wire the G to the power supply ground. Which, of course, means you're not using the L- and R- amps. All the discussion above is just for the output side. You also need to deal with the inputs... If you don't have a balanced source, then you need to decide what to do. There are several possibilities, one of which I mentioned in this post. You can also look at the "Other options" section of the β22 for another idea. |
| juswyq Member Joined: Feb. 5, 2009 | Message [#330] posted on: 02-06-2009 12:57 AM CST (US). | | I don't mind reterminating my headphones to four wires.(Stupid question: This means the ground wire of the 3 pin XLR connector isn't used, right?) However, regarding the unbalanced source. From what I've read in the article, it's fine to connect the inputs of the L ground and R ground to the L- input and R- input, but they will simply act as active grounds for each channel.. does this means I can use a TRS to XLR connector? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#331] posted on: 02-06-2009 01:25 AM CST (US). | |
That's correct.
It depends on what the TRS-to-XLR adapter does. If it grounds the L- and R- inputs to the amp, then yes, you could use it, but the L- and R- amp boards will still "see" the volume pot in the path, with varying resistance depending on where the pot position is. It would increase the noise floor when the pot is not at minimum or maximum positions. If you look at the post I linked to above, the balanced/unbalanced switching scheme will ground the L- and R- amp boards' inputs directly without going through the pot when set to unbalanced mode. |
| juswyq Member Joined: Feb. 5, 2009 | Message [#332] posted on: 02-06-2009 01:47 AM CST (US). | | I see.. So it's a matter of a simple modification to the b22, rather than using an XLR to TRS adapter. Thanks amb, I think i'll go ahead with the balanced b22  |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#333] posted on: 02-06-2009 06:47 AM CST (US). | | AMB could you please have a look over the attached pdf diagram for wiring. I found doing this immensely helpful. Attachment: C4637.pdf |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#334] posted on: 02-06-2009 06:58 AM CST (US). | | johnwmclean, nice work. The only things I would add are: 1. You should bridge the grounds of all four channels at the volume pot together. As it stands, the input XLR jack grounds are wired only to the L- amp board, but none of the others. 2. Even though your drawing says "connected" at the input XLR jacks, pin 1 should be explicitly wired to the chassis (you can use a ring terminal on one of the XLR jack's mounting screws). Most XLR jacks' pin 1 is isolated from the body. |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#335] posted on: 02-06-2009 07:53 AM CST (US). | | Thanks AMB, not sure if I need to connect both PIN 1 inputs to the chassis or just one. The real amp will have the cables grouped and shielded accordingly (doing this has got my head around that). Revised pdf attached, please let me know if there’s anything to improve on. |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#336] posted on: 02-06-2009 07:56 AM CST (US). | | Sorry here’s attachment. Attachment: C4638.pdf |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#337] posted on: 02-06-2009 02:18 PM CST (US). | | Looks fine now. The pot wiring is correct if the pins shown are pointed toward the base of the chassis (and you're looking from above). |
| Johnwmclean Member Joined: Dec. 8, 2008 | Message [#338] posted on: 02-06-2009 02:52 PM CST (US). | | That’s correct, pins are located on the underside of the pot. Thanks again AMB! |
| Johnwmclean Member Joined: Dec. 8, 2008 | Message [#339] posted on: 02-06-2009 02:52 PM CST (US). | | Please delete! Sorry! [Edited by johnwmclean on 02-06-2009 at 02:53 PM.] |
| 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.] |
| Page << < 15 16 17 18 19 20 21 22 23 24 25 | Next Page | Prev Topic | Next Topic | ||||
 (remove _nospam_ ) |
© Chu Moy, 2001.