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DIY Workshop » β22: A discrete, cascoded, fully complementary, pure class A amplifier (part 3) | 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. |
amb  Headphone Council Joined: Apr. 1, 2004 | Message [#481] posted on: 03-20-2009 03:59 AM CST (US). | | No, it is not necessary to elevate the caps. In fact, the shorter the excess lead, the better (less inductance). |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#482] posted on: 03-20-2009 04:18 PM CST (US). | | Thanks AMB, at this stage with all my boards complete and working, is is worth correcting this or leaving it the way it is? |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#483] posted on: 03-20-2009 05:24 PM CST (US). | | If you cap leads are no longer than 1mm or so, then don't worry about it. |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#484] posted on: 03-21-2009 12:41 AM CST (US). | | Dang, some are in 3.5mm territory - ok, just so I can gauge my decision to replace or leave. What effect could this have on the overall sound? Does the gain setting influence inductance, my build is gain 2 for balanced? Also would it be prudent to try as is to gauge the gain setting anyway. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#485] posted on: 03-21-2009 02:05 AM CST (US). | | Those are compensation capacitors whose purpose is to ensure amplifier stability in the ultrasonic frequencies. As such, you want to minimize any inductance in the leads so that the performance of the capacitor is not impacted at those frequencies. You don't need to replace the caps. Simply heat both pads at the same time to melt the solder, and then apply downward pressure on the caps (pad with a piece of foam or something to avoid burning your finger) to push it down against the board. Reflow the joints if necessary. |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#486] posted on: 03-21-2009 02:19 AM CST (US). | | Thankyou AMB. |
| johnwmclean Member Joined: Dec. 8, 2008 | Message [#487] posted on: 03-21-2009 09:16 AM CST (US). | | Ok that worked as well as could be expected, I lost one capacitor from heavy handedness though. I have yet another query regarding the initial set-up, when measuring in AC mV at the ouput, is it measured across the output and ground? For all my builds Im getting around 0.07v’s not mv’s so that’s 0.00007mv, which is to spec, right? [Edited by johnwmclean on 03-21-2009 at 09:27 AM.] |
| yuk228 Member Joined: Mar. 21, 2009 | Message [#488] posted on: 03-21-2009 11:40 AM CST (US). | | amb, I am going to build a 4 channels balanced beta 22 As some people said the gain 8x is more than enough for K701 and HD650, they never turn the volume knob to 11 o'clock position. Those builder recommend 5x is enough But as I am building a balanced one, if I use 5x, then it will become 10x.....so if I use 2x in each board, add up only 4x Will it be too low for 4x gain?Also is there any degradation on sound quality at this gain?since default is 8x thank you very much~ |
| rhester Member Joined: Aug. 2, 2007 | Message [#489] posted on: 03-21-2009 12:51 PM CST (US). | | I have been running my 3 channel B22 (mounted on e22 board, and transfo and o22 in separate cse) for sometime now with my 701s and sounds great, just the slightest amount of hiss if I convince myself it is there. I recently got a pair of D2000s and hiss is much more noticable. This is on a e22 board mount and RCA ins are connected to the case (tried isolated and connected and made little difference). do not have the e22 board grounded to case except with standoffs. Any ideas on how to quieting this down? Any help would be greatly appreciated. Using TDK pot. Would it help to ground it to case other than with the holding nut? Have 2 RCA inputs tied into a double pole elna switch - so not switching grounds, they go striaght to input. Is that a problem? [Edited by rhester on 03-21-2009 at 01:55 PM.] |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#490] posted on: 03-21-2009 03:40 PM CST (US). | | johnwmclean, yes, it's measured between output and ground. 0.07V is 70mV. But I won't worry about this measurement too much. Many DMMs can't display this properly anyway. yuk228, how much gain also depends on what source you're planning to use with the amp. If you're using a typical home stereo CD/DVD player, then their output is usually around 2Vrms at 0dBFS, which is "hot". On the other hand, some computer sound cards and portable devices put out 1Vrms or less. I recommend a gain of 5-8 for the headphones you have, but for 4-channel balanced, you need to drop the gain in approximately half (so 2-5) is ok. Note that this assumes that your source still puts out 1-2Vrms. Balanced sources are all over the map on this. rhester, your problem is not with grounding. You simply have too much gain for the D2000s. |
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