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Thread: Crown IC 150 Preamp popping noise - source of problem?

  1. #71
    Join Date: Oct 2012

    Location: NE England

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    I'm Jez.

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    Quote Originally Posted by jimkarl View Post
    Don't have any of those but can order them. I have BC549B's and BC547's.
    Can't find hardly any info on a TZ81. Only thing I saw on a data sheet was hfe value of 60. Google search on alternatives yields only 2 or 3 mentions of alternatives. One said 2n9249 was the alternative but now defunct. Another said people have used 2n3904 with success. Those seem to be readily available too. Thoughts on that vs the BC550c (or my 549 or 547) given the limited info on the TZ81 spec? I confess I'm a novice with respect to understanding transistor specs (and a lot of other electronic related things too lol but i like to learn.)
    Pretty much any NPN transistor should work. The BC550C is a low noise very high gain device. The BC549B is of the same family and should work great. Any similar spec USA part should work just the same as well.
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  2. #72
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 468
    I'm Andrew.

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    Quote Originally Posted by jimkarl View Post
    I misstated - open circuit, not zero ohms. Confirmed on two meters and a continuity tester as well. To clarify, that only reads open circuit if I lift the ground leg off R20 (R13 leg is already lifted from main board). If I leave R20 in place I get about 280-300K+ and climbing resistance between traces where C12 was (100K from R20 through ground, and the rest from someplace else in circuit that ultimate goes to the same ground that R20 does. I assume one the the caps since the resistance is climbing as I measure. Again, this is reading between the two points that C12 was. I have 100% confidence there is not a dead short between those points.

    I don't have a separate power supply to rig up the suggestion in post 37, but I have confirmed readings on two meters, one is a fluke (which although very accurate I don't regularly use because it doesn't have auto range and that's a pain!). There is nothing wrong with my meter.
    I wasn't suggesting there was a dead short between those points - there doesn't have to be to cause a problem. A high resistance of a few hundred ohms would create a DC offset.
    Could you post a few photographs so we can see the physical layout of the boards etc? That might be useful.

  3. #73
    Join Date: Apr 2017

    Location: maryland

    Posts: 32
    I'm jim.

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    Quote Originally Posted by RothwellAudio View Post
    I wasn't suggesting there was a dead short between those points - there doesn't have to be to cause a problem. A high resistance of a few hundred ohms would create a DC offset.
    Could you post a few photographs so we can see the physical layout of the boards etc? That might be useful.
    To clarify my comment If I leave R20 in place I get about 280-300K+ and climbing resistance between traces where C12 was... That was really 280K* - 300K.

    Board pics attached though it's messy to look at. Keep in mind, it was doing this long before my soldering iron ever touched that board! Also attached the board layout from the service manual, but it's so poor not sure that will be much help. My pics are laid out in the same format to match.

    I did replace that channel transistor pair with the new BC549B's I had, and those seem to work just fine. Seems even compare to the the other channel with no issues there. Didn't resolve the voltage post C12, but I didn't expect it to either. Really not sure how the channel worked at all given those previous transistor readings, but now there is at least a fresh pair there and those are verified good transistors

    Crown_phono_layout.jpgIMG_4850.jpgIMG_4851.jpg

  4. #74
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 468
    I'm Andrew.

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    Actually, in my previous post when I said "a high resistance of a few hundred ohms would create a DC offset" I meant to say "a high resistance of a few hundred kilohms would create a DC offset". Sorry for the typo.
    Imagine 200k in parallel with C12: in conjunction with the 100k of R20 you would have a DC potential divider leaving you with one third of the DC offset on C12.

    Thanks for the pictures but what I had in mind was more of an overall shot. I was wondering if it's all laid out on one PCB or if there are lots of individual PCBs and whether or not the controls are on PCBs etc. I still think there's something odd about the way the sections are linked.

  5. #75
    Join Date: Oct 2012

    Location: NE England

    Posts: 3,847
    I'm Jez.

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    Jim. Can you be more specific as to the nature of the problem please... Is it a continuous repetitive popping? a single pop?

    Also what test gear do you have available?
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  6. #76
    Join Date: Apr 2017

    Location: maryland

    Posts: 32
    I'm jim.

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    Just two pcbs - the phono board (pics I posted) and the main board. Main board has all the controls mounted. Pic attached for that board. You might have something about that resistance though. With everything back in circuit, all connected etc. as well as to the main board. I'm seeing about a 110K resistance across C12 on that problem side, whereas it's about 185K across C12 on the other channel.


    Crown Main Baord (1).jpgCrown Main Baord (2).jpg

  7. #77
    Join Date: Apr 2017

    Location: maryland

    Posts: 32
    I'm jim.

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    Quote Originally Posted by Arkless Electronics View Post
    Jim. Can you be more specific as to the nature of the problem please... Is it a continuous repetitive popping? a single pop?

    Also what test gear do you have available?
    Initially, it was popping heavily on the RIGHT channel when switching to or from the phono input, as well as continuous popping when phono was selected. It was identified there was a large unexpected DC voltage on the other side of C12 (4 - 5 volts, C12 on the left channel also had an issue of about 0.5 volts but just not as bad). Also confirmed this voltage is being sourced by the phono board itself, as it is measured with the main board disconnected from it on that channel. A number of components were replaced (per spec) on both boards in effort to reduce the popping and voltage. Ultimately, I found the negative source voltage to the phono board was far too low (should have been -18v, was -15v). That was adjusted via main board trimmer and eliminated the problem on that channel (post C12 DC voltage now ok on that channel)

    So that brings us to the LEFT channel with it's unexpected DC voltage post C12. This time, the source voltage (+18v) was correct and did not need to be adjusted. A number of components checked/replaced to spec, found a couple leaky transistors as well which have been replaced but nothing has resolved it yet. However, the popping is not as bad as it was on the left channel. Neither as much in volume when switch to/from phono (but is present and obvious), nor is it continuous anymore once selected. That may simply be because the Post C12 DC voltage is substantially lower than the other case.

    As far as test equipment, I have a voltmeter (two actually), capacitance meter, ESR meter (which also does capacitance). I just picked up an oscilloscope last week at an auction but I have to find some leads for it, confirm it even really works, and relearn how use one, since I haven't used one since I was a kid in high school (decades ago LOL)

  8. #78
    Join Date: Apr 2017

    Location: maryland

    Posts: 32
    I'm jim.

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    To clarify the above - It's a single pop now on select or deselect of phono (or power on/off with phono preselected) with a Post C12 DC voltage that starts initially about 0.5v and ramps to about 1.5v quickly

  9. #79
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    After an exchange yesterday on another thread I think Jez may be reluctant to offer any more help and advice on the forum. Shame, because his input would have been valuable here. I'm afraid I'm running out of ideas.

  10. #80
    Join Date: Apr 2017

    Location: maryland

    Posts: 32
    I'm jim.

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    That is a shame because his input has been helpful and I've learned something new from both his posts and yours. I may just have to live with the pop. Perhaps you could help me move forward with figuring out why the tone section doesn't seem to be working on that channel? I failed to mentioned that in lieu of me getting an oscilloscope up and running, I've always had an audio tester that has served me well for tracing audio circuit - just not always sure where to put it to check LOL.

    So I get audio all the way through on that channel whether tone controls are engaged or not but when they are engaged the audio is "muffled" and the bass/treble controls don't have any effect. Disengaged, audio is nice and clear, just like the other channel's when disengegaged.

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