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DIY Workshop » CKČIII: Cavalli-Kan Kumisa III headphone amp (part 2) amb  Headphone Council Joined: Apr. 1, 2004 |  Message [#1] posted on: 01-17-2008 08:29 PM CST (US).   |  |  This is a continuation of the New Cavalli Kumisa III plus Boards thread which reached its post limit. Let's keep a good thing going. |
garo Member Joined: Oct. 27, 2007 | Message [#2] posted on: 01-18-2008 07:49 PM CST (US). | | I've been working on this for a month or so. It's almost done, just a little more wiring to do, then testing. Thanks to all you guys who made this such a fun project to do. I can't wait to hear it!
Attachment: C3367.jpg,C3370.jpg,C3369.jpg |
moodysteve Member Joined: Apr. 11, 2007 | Message [#3] posted on: 01-18-2008 08:19 PM CST (US). | | Well, I just replaced the 7915 regulator, and that did fix the power supply problem; I'm now getting the +/- 15V that I had before. That did not, however, fix the audio problem. The last time I did discover the wiring error that was causing the low-pass filter (AMB guessed it right the first time around) but when I corrected the wiring, I had hardly any sound in the left channel and a lot in the right channel. Voltage measurements from the 4 output transistors indicated that something is seriously funky: Q12c +3V Q13c +2.9V Q25c +11V Q26c -11V Looks like I may be in the market for a new set of matched transistors? Should I replace the BC550C/BC560C transistors as well? I'm aware that I've long since passed the point of being economically intelligent in continuing to troubleshoot this amp, but I'm enjoying the opportunity for hands-on learning. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#4] posted on: 01-19-2008 12:07 AM CST (US). | | moodysteve, your voltage readings indeed don't look right. Are your 0.47 ohm output resistors still good? Have you checked these transistors (as well as the other BJTs) with the diode check mode of your DMM for some sanity? |
| korben69 Member Joined: Nov. 10, 2007 | Message [#5] posted on: 01-19-2008 08:47 AM CST (US). | | Cheking from the begining. Measures between star ground pads, power off : +15 about 35M, and -15 about 35M both decreasing. Voltage : star ground and +15 gives 14.732v, -15.264v with -15. Done operations : When powering, the led is OK. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#6] posted on: 01-19-2008 08:56 AM CST (US). | | korben69, so far so good. Now turn the bias adjustment trimpots up and see if you could set the output stage quiescent current to their target values (Initial setup procedure Step 9 as outlined at the CKČIII website). |
therobbstory Member Joined: May 2, 2008 | Message [#7] posted on: 01-19-2008 01:02 PM CST (US). | | I built one about two months ago. I thought I had some crazy grounding issue because I was getting some nasty buzzing and only hearing left channel audio out of both channels. Re-examined my input/pot wiring this morning and realized I had made a few mistakes, doh! Everything is better now and this thing sounds pretty amazing. Will post pics sometime next year when I get it cased up. |
| korben69 Member Joined: Nov. 10, 2007 | Message [#8] posted on: 01-19-2008 02:48 PM CST (US). | | Step 9 : Turning trimpots up = no effects on voltage. Less than 1mV, near 0mV across R23/R47... same values for R24/R48. R23/24/47/48 are correct about 0.49R. Q12/Q25 : 14.248v Q13/Q26 : 14.804v OG-OL : 200mv decreasing while measuring OG-OR : 200mv decreasing while measuring [Edited by korben69 on 01-19-2008 at 05:51 PM.] |
| garo Member Joined: Oct. 27, 2007 | Message [#9] posted on: 01-19-2008 08:15 PM CST (US). | | Hey Guys, I'm going to solder up the last of my panel components tomorrow, and I want to make sure I get it correct. Amb's drawing of the RK27 wiring is a little hard to decipher, since all the wires are black. Is the drawing I've attached correct? I couldn't find this by searching the forums, looking at alps web page, or a general google search. I imagine that this is standard for pots, and I just don't know it by heart yet. Thanks garo Attachment: C3371.png |
Mister X HeadWize Fanatic Joined: Jul. 23, 2003 | Message [#10] posted on: 01-19-2008 09:37 PM CST (US). | |
Yes an alternate image can be found on tangent's "how to wire panel components" page http://tangentsoft.net/audio/pancomp.html
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| garo Member Joined: Oct. 27, 2007 | Message [#11] posted on: 01-19-2008 10:15 PM CST (US). | | @ Mister X sweet. I like that picture even better. Thanks! g. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#12] posted on: 01-20-2008 12:58 AM CST (US). | |
How far did you turn the trimpot? These are multi-turn and will require quite a number of turns for the voltage across those resistors to begin to go up... |
| korben69 Member Joined: Nov. 10, 2007 | Message [#13] posted on: 01-20-2008 02:30 AM CST (US). | | Trimpots turned from each end to end, still no result. It seems that there is no voltage accross R23/47/24/48. But I'll try again this afternnon. Thanks [Edited by korben69 on 01-20-2008 at 03:02 AM.] |
| garo Member Joined: Oct. 27, 2007 | Message [#14] posted on: 01-20-2008 03:14 PM CST (US). | | It works, and it sounds great!!! I was a little worried when I had trouble getting the right channel trim pot set so that the quiescent current was right. I ended up finally getting the voltages to ~14 mV (I actually ended up with 13.8 mV). It all turned out okay in the end. I'll submit pictures to amb once I get my cover plate on. [Edited by garo on 01-20-2008 at 09:34 PM.] |
| korben69 Member Joined: Nov. 10, 2007 | Message [#15] posted on: 01-21-2008 11:53 AM CST (US). | | No changes, turning trimpots seems to have no effects. There is no voltage accross R23/47/24/48.  [Edited by korben69 on 01-21-2008 at 01:05 PM.] |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#16] posted on: 01-21-2008 07:02 PM CST (US). | |
I suggest that you check your circuit using the operating points PDF file at the CKČIII website, in the "Initial setup" page under "Troubleshooting". All voltages listed are relative to ground. Convert that file into a PNG or GIF image and mark your actual measured voltages on there, and post it. |
| garo Member Joined: Oct. 27, 2007 | Message [#17] posted on: 01-22-2008 10:56 AM CST (US). | | When I touch the volume knob, I hear buzzing. Probably 60 Hz, but how do I get rid of it. It's worse when I touch other metal stuff with my other hand. The knob is metal (which I like), but maybe I should have a plastic knob. Thanks, g. |
| amb Headphone Council Joined: Apr. 1, 2004 | Message [#18] posted on: 01-22-2008 11:17 AM CST (US). | | garo, the volume pot body should be connected to the amp's ground. Normally, in an all-metal case, this would be accomplished simply by mounting the pot to the front panel/case which is already grounded. But if you have a plastic front panel, then you should connect a wire explicitly. On a Alps RK27 blue pot, you could loosen one of the screws, wrap a thin wire around it, and then re-tighten the screw. Connect the other end of the wire to ground. |
| garo Member Joined: Oct. 27, 2007 | Message [#19] posted on: 01-22-2008 01:45 PM CST (US). | | I see what is happening. I'm using the plastic cover plate holders still, and they are isolating the front cover from the main body of the case. I'll clean some of the anodizing off and then when I use the real screws to hold it on, it should be grounded. I'll check it with a DMM anyway to make sure. Thanks for the quick reply! g. |
| moodysteve Member Joined: Apr. 11, 2007 | Message [#20] posted on: 01-23-2008 03:38 PM CST (US). | | An Update: Enough of the BJTs seem to be toast that I think I'm going to replace all of the BC550/560s just to save some aggravation. I have a spare set of output transistors on hand to swap in as well. Guys and gals - When something is weighing heavily on your mind, don't touch your electronics. |
| korben69 Member Joined: Nov. 10, 2007 | Message [#21] posted on: 01-27-2008 04:04 AM CST (US). | | Some measures after 10mn warmup. Does it help ? [Edited by korben69 on 01-27-2008 at 03:30 PM.] Attachment: C3398.jpg |
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