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Avondale NCC300 Monos Underway

Discussion in 'd.i.y.' started by Mike Hanson, Jul 5, 2021.

  1. Mike Hanson

    Mike Hanson Lovely!

    Thanks for jumping in. I had to take a break myself, as my mother "shuffled off her mortal coil", so I've been busy with all of that.

    I did manage to get the holes drilled for the front panel switches, then assembled the fronts, sides, and backs:


    I've also drilled the holes in the bottom plate, but the transformer and power supply module haven't been attached yet. (Waiting on some brass screws for the transformers.) I'm also waiting for some wire from eBay. I probably won't make much more progress until September.
    Last edited: Jul 30, 2021
    chiily, 337alant and Mynamemynaim like this.
  2. Mike Hanson

    Mike Hanson Lovely!

    As you can see, I'm using the same enclosures as you. Les felt that those heatsinks were adequate to supply a slightly higher voltage transformer. (I didn't take note of the specs at the time, and I haven't had a chance to hook them up to the NCM to see what the resulting voltage is.)
  3. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Hi Mike.. sorry to hear about your mum
    Much more important to have been with her than messing about with a soldering iron
    I lost my mum 40 yrs ago...a very unexpected, early and untimely end:(

    Your switch and fixture fitting is so neat !
    Perhaps you can post a picture of the tool you use?
  4. Mike Hanson

    Mike Hanson Lovely!

    My mom had a good life, and it was a good time for her to say good-bye.

    Thanks, but I'm no expert.

    The Neutrik holes were really clean. I use a 24mm knock-out punch, like this: That's the Canadian Amazon site, but I can't imagine there's anything special about it. It's hard work turning it with a big hex wrench, but clamping the back panel makes it doable. (I have a Workmate that grips along the panel's edges.)

    The RCA connector has a big plastic flange that would cover any mistakes. However, the two holes are much smaller and easier to drill, so I did a pretty good job this time.

    The holes for the front panel switches are the bane of my existence. Due to the thickness of the material, it couldn't be punched. My drill press isn't very fancy, so the bit tends to bounce around and chew the hell out of the edge of the hole. You'll notice that the switch looks a bit odd, because I had to add an O-ring to hide the mess.

    I thought using a step bit would make it easier, but success isn't assured. I did do really well once, but I think it's because I luckily used the step bit up until the final size was started. For these two recent front panels, however, I swapped out the step bit too soon, expecting the larger bit to finish the job, but it made a mess. Next time I'll be patient and gradually step up to the final size before switching over.
  5. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    No! hadn't noticed anything and looking again it still looks fine to me...

    Thanks for the tips...and it is certainly easier with round holes. I started my IEC hole with a jigsaw...but don't think i will be carrying on with that!!
  6. S-Man

    S-Man Kinkless Tetrode Admirer

    I was actually thinking about the HCR that somebody was planning to use. However the same applies to the type of R or L filtering you mention.
    Whether there is any audible difference, I don't know.

    I don't know TBH. It's a long time since I had NCC200s and although I owned them twice I could never understand what all the fuss was about.
    However since then I have realised how important the power transformer is to the sound of the amp (which brings us back to what's measurable and what's audible).

    My NCC300 is now somewhat modified to my own tastes (fb cap, driver stage, regs) so it's no longer the authentic Avondale flavour :)
  7. gavreid

    gavreid pfm Member

    Here's a painful warning for you guys - after using Les's amps for nearly 20 years the lack of speaker protection finally caught up with me - expensive repair to follow. As for the remains of an almost new Qudos board - luckily I was on hand

  8. Chops54

    Chops54 pfm Member

    How did that happen Gav?
  9. gavreid

    gavreid pfm Member

    Just randomly putting the stylus down on a record with the volume up a bit...
  10. Chops54

    Chops54 pfm Member

    There has to be more to it than just putting a record on with the volume up a bit. I’m always wary with my Qudos of the bias running away with itself so I have it set on the low side. My NCC300s have big heat sinks but my Qudos Voyagers only have the casework to dissipate the heat. I’m contemplating rebuilding them with heat sinks across the back panel. There’s not much more you can do with a shoebox unfortunately.
    gavreid likes this.
  11. gavreid

    gavreid pfm Member

  12. eddie pugh

    eddie pugh pfm Member

    Sounds a bit like how I blew one of my NCC200's a while back. I was playing with Jez's upgraded CA phono stage and was really enjoying a fairly loud listening session when my Technics SL10
    ran up to the end of the LP groove and the auto cartridge lift and back traverse activated. I'm convinced that the relatively high listening volume and the slight thump of the autolift or the cartridge hitting the end groove caused enough low frequency bump to take one channel out of its safe operating area. Result was a bit of a loud screetch Blew output trannies and fried a couple of resistors but speakers survived!!

    Good bit was it prompted me to upgrade to NCC220's but I must add some speaker protection for my NS1000's

    torstoi and gavreid like this.
  13. gavreid

    gavreid pfm Member

    That's what I was doing too and with Jez's amp - maybe that's too much of a coincidence???
  14. eddie pugh

    eddie pugh pfm Member

    Wow that is a hell of a coincidence !! Dare we ask Jez for a comment.
    I put it down to extended low frequency boost on the modified CA phono but I would add that I had been using the SL10 with a standard CA640 phono for years into my NAC 252 and Avondale modded NAC250 with NCC200 boards for years with no fireworks!!

    gavreid likes this.
  15. gavreid

    gavreid pfm Member

    I'm not pointing the finger at Jez (or Les for that matter) but Jez is aware of what happened - he's no fan of the Avondale amps!
  16. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    As I've explained to gavreid it's nothing to do with my phono stages. I don't fit subsonic filtering and it extends all the way to <1Hz. RIAA eq dictates 10X as much gain at very low bass than at mid range frequencies. If you are playing loud and don't do the normal and sensible thing of turning it down or muting when taking the stylus on or off the record there could be a thump that could drive the power amp into overload. I've explained likely issues to gavried (in PM's) with the Avondale amp that probably caused it but will leave it there for public consumption for obvious reasons.... although IIRC I've publicly speculated about these issues in the past.
  17. laverda

    laverda pfm Member

    'its nothing to do with my phono stages' ?? Not once but twice!!! Over the past 25 years I've build many, I mean many Avondale amps (amp8, 200's, 220's, 300's and others) in various configurations and never have I had one blow up, let alone like that in gavreid's photo.

    Just saying.

    This is now getting off track ..back to the NCC300 builds.
  18. S-Man

    S-Man Kinkless Tetrode Admirer

    IMO it's not wise to run amps without any protection (other than a mains fuse).
    SOA limiting and fuses after the main smoothing caps do minimal or no damage to the sound, but if you are going to run an amp without them then fit a dc offset protection circuit.
    laverda likes this.
  19. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    So I started to do the check of mA vs V and stopped very quickly!!

    With the Les recommended 120mA the voltage was 1.669

    [​IMG][/url]2021-07-31_11-11-53 by rock solid, on Flickr

    So I twiddled the bias and .... by the time I got to 1.693v the mA were already over 260 !!

    [​IMG][/url]2021-07-31_11-11-40 by rock solid, on Flickr

    Surely I must be doing something wrong with the check? it would be well past half an amp by the time I got to 2v Im guessing?

    could someone pleas confirm the voltage test points as I cannot believe the above can be right
    [​IMG][/url]2021-07-31_11-11-02 by rock solid, on Flickr

    The points I tested from marked with red slash
    [​IMG][/url]2021-07-31_11-26-20 by rock solid, on Flickr

    or dots are clearer?
    [​IMG][/url]2021-07-31_11-28-56 by rock solid, on Flickr
  20. S-Man

    S-Man Kinkless Tetrode Admirer

    Voltage measurements for the bias generator are one step removed from what matters.

    Just measure the voltage across all 4 emitter resistors. Then I =V/R, so I go for 11mV across each each 0.22R resistor to give ~50mA per device.
    By doing it this way you can determine the current sharing of the output devices as well as the correct bias.

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