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Old 6th December 2012, 04:06 AM   #11
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Well duh on my part, thanks for that info. The 30D was staring me in the face and I went with the H number. The H number turned up a tant reference.

Lots of duh here lately. This board has some J309 jfets among the transistors. Eight up by the dipswitch end, and two above each outer bias pot (Q13, Q14, Q36, Q37). One of the left channel jfets has some different readings than the other on the right channel. I also learnt that the adjustable pots at the middle of board must be for nulling DC. Nulling the DC on the left channel with the pot helps reduce the hum, but it is still present.

Luckily my DAC enclosure arrived so I can leave this phono board alone for a while.

Last edited by SCompRacer; 6th December 2012 at 04:12 AM.
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Old 6th December 2012, 08:31 AM   #12
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Chances are if it's the first jfet in circuit, that's the one that has gone.
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hoping to pick up some things.
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Old 31st December 2012, 03:26 AM   #13
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Thanks again for all the tips. I finished my DAC and got back to the phono board. Some progress made but more needs to be done. I replaced the old Sprague caps on the phono board with new 105C Vishay BC's. No change in left channel noise, but all caps measure similar uf now (measured with Fluke set to uf) where the old ones varied from 5-20%. I’ll have all new caps on the way this week for the pre amp.

I got some NOS J309 jfets. I used a 9 volt battery/multimeter set to mA to match them. (Neg of DMM to Drain, Pos of DMM to B+, jumper B- across G and S). They ranged from 2.04mA - 2.07mA. The second of the two removed jfets measured 2.08 (the first is my flaky one). I installed two new jfets in the left channel and powered it up.

Now I never touched the right channel bias pot and I would get different readings from time to time. It usually measured ~.370, every now and then .440. I just ever so slightly turned the adjustment and it snapped to .608. Turning right or left now gradually increases or decreases bias. It would take many turns to get to .369 so I am guessing ~.600 is where it should be.

IF I attempt to adjust the left channel bias over .369 to .600, that left channel circuit that measures .072 increases which means more DC to null out at the left channel output. (With the new jfets, that .072 dropped to .026). I left the left channel bias at .369 and get much less noise out of the left channel now. I'm thinking I'll have to replace some or all of the transistors like sq225917 did for a total fix.

If I did replace all transistors (16 - MPS8599, 18 - MPS8099, no longer manufactured) should I procure some NOS MPS8099/8599 transistors or their replacements (MPSA56/MPSA06)?

Last edited by SCompRacer; 31st December 2012 at 03:29 AM.
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Old 4th January 2013, 04:26 AM   #14
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Some closure here. On board testing wasn't that reliable so I removed every transistor and jfet from the left channel and tested them; none failed. Out of frustration I reassembled and adjusted bias (pots at sides of board) until I got zero DC in that one what I call bias circuit (cause I don't know what else to call it) in each channel. That bias circuit sets bias for a transistor by the null DC pot (by center of board) and sets transistor E voltage at end of board (follow the .072 measurements in previous pic; the R channel bias circuit was .006 and quiet). While I could null that DC at the output, the left channel hum was still there.

I don't know if I did it right but the left channel is quiet now. So the right channel ends up at -.612, and the left channel at -.560, zero DC in that ‘bias circuit’ and all voltages are pretty square from side to side. L and R volume sound identical, vocals centered. Some test tone tracks and output voltage tests could confirm all is well. All due to dirty or sustained transfer spots in the pots.
Attached Images
File Type: jpg kslphono_recapped.jpg (259.1 KB, 149 views)

Last edited by SCompRacer; 4th January 2013 at 04:32 AM. Reason: add the pic
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Old 19th January 2013, 04:25 PM   #15
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Finally got around to recapping the KSL main board and power supply. Some measured close on the Fluke set to capacitance, some were up to 27% over spec. I don't have an ESR tester. A friend that I helped once helped me with 22 United Chemi Con KME's. Digi key supplied two 4700uf UCC KMH's for the power supply, and four really long life 470uf UCC LXY's for the hot spot between the sinks.

He parted with some Siemens Styroflex polystyrenes to replace the four .033uf caps on the phono board. I don't know if they are part of the RIAA filter or some signal feedback loop? I'll look for some .0016uf's to replace the two remaining poly's. It still works and sounds pretty good! Thanks again for all the help and tips.
Attached Images
File Type: jpg kslrecap_1.jpg (165.1 KB, 109 views)
File Type: jpg kslrecap_2.jpg (136.0 KB, 102 views)
File Type: jpg kslrecap_4.jpg (166.2 KB, 94 views)
File Type: jpg kslphono_recap_2.jpg (101.5 KB, 93 views)
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Old 19th January 2013, 08:44 PM   #16
kamis is offline kamis  Serbia
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SCompRacer, which are mc phono input transistors?Could you describe phono circuit or rev. eng. schematic? KPE phono clone would be interesting.
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Old 19th January 2013, 09:01 PM   #17
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Sorry, I'm not a tech or that smart kamis. I don't have a schematic and have not been able to get one. Due to the multi layer board it is difficult to follow the circuit....for me anyway.

EDIT: An added note, I have a friend that works in the electronics business. For what its worth he said the parts count per gain stage seems high for a balanced discrete design but would need to see a schematic.

Last edited by SCompRacer; 19th January 2013 at 09:23 PM.
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Old 19th January 2013, 09:32 PM   #18
kamis is offline kamis  Serbia
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Quote:
Originally Posted by SCompRacer View Post
Sorry, I'm not a tech or that smart kamis. I don't have a schematic and have not been able to get one. Due to the multi layer board it is difficult to follow the circuit....for me anyway.

EDIT: An added note, I have a friend that works in the electronics business. For what its worth he said the parts count per gain stage seems high for a balanced discrete design but would need to see a schematic.
Boards are double-sided, not multi layer. You could read down transistor markings on 8 transistors in row near DIP switches. I would be grateful.
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Old 25th January 2013, 05:15 PM   #19
TNT is offline TNT  Sweden
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I have a KSL without RIAA but with the hum. I had to put the PSU in an external box in order to get rid of it.

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Old 26th January 2013, 06:43 PM   #20
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Quote:
Originally Posted by kamis View Post
Boards are double-sided, not multi layer. You could read down transistor markings on 8 transistors in row near DIP switches. I would be grateful.
Well it looks multilayer to me as 1) there are traces visible with a strong backlight that are not on either side of board. 2) There is a seam at the side of board. I don't have close up capability to show that well enough.

Here are some pics, best I can do.

http://i417.photobucket.com/albums/p...ps7f874d8a.jpg

http://i417.photobucket.com/albums/p...ps25002355.jpg

http://i417.photobucket.com/albums/p...psa8948606.jpg

http://i417.photobucket.com/albums/p...psfe5419e4.jpg
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