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Yamaha CX-1000U Preamp Refurbish Project

Discussion in 'Yamaha' started by rgbeach, Apr 2, 2018.

  1. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    I'm nearing completion of this project, and thought that I would document it here so others that may want to make the attempt have a reference. I don't claim do have done everything "right", and perhaps I did things that were unnecessary but, for better or worse, it's what I did. If anyone has comments or suggestions, please share; and, of course, if anyone has any questions, I will be happy to answer to the best of my ability.

    At this point, I'm still in progress on the phono board. I've tested all other inputs (both analog and digital - there are a lot of them) using a CD player as the source and the headphone out of the preamp and it sounds very nice. However, since I rarely use headphones I can't say that it's better or worse than before. But, at least it works and it doesn't suck!

    I'm planning on testing with my power amp soon, and I will post the result in this thread. To that point, I think I will just add individual replies to this thread as I document the work. It feels a little easier to write (as well as read) when done that way. Smaller, more digestible chunks.

    With that as an intro, here is how it all started...

    Background

    A couple of years ago, I purchased a Yamaha CX-1000U preamp from a Goodwill in San Francisco for $39! To date, it's my best score ever by far, even if you factor in the $60 shipping cost. I was visiting a buddy and on our way to breakfast one morning I forced him stop at a Goodwill we were walking past. And the rest is history.

    A couple months later, my buddy shipped it to me and I was very pleased to find that it worked without any issues. All I was able to do at the store was power it on, so I had no idea if it functioned. Fortunately it did, and I added it to my system (Adcom GFA-535 power amp) and have been using it ever since.

    It did develop an issue on the phono input, which was part of the motivation to take on this project. It would produce loud hum and I would have to jiggle the interconnect a bit to get it to stop. I knew that the RCA jack just needed to be resoldered (cold solder joints are common on these units). Beyond that, I am a tinkerer, and this thread (audiokarma.org/forums/index.php?threads/yamaha-cx-1000-refurb.689969/) motivated me to go all out and re-cap the entire unit. Well, except for the video board. I have no use for the unit's video switching and given it's only got composite video, I can't imagine a future owner needing them either.

    So, a couple of weeks ago, I pulled the unit from my system and jumped in...


    Here's a picture on the day I purchased it. Nice!
    20150501_174213000_iOS.jpg
     

     

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  2. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    Project Goals

    1. Fix the phono input. As expected, this ended up being the RCA jack losing it's connection with the board due to a cold solder joint. I resoldered back in place, and resoldered ALL RCA jacks, including those used in the digital section.

    2. Replace all aging electrolytic capacitors with newer, "better" versions. The CX-1000U has primarily Elna Dourex throughout, as well as different Elna's and other brands in a few locations. Nichicon Muse in the phono stage. I used Nichicon KZ (Muse) and Nichicon FG (Fine Gold) throughout, with a couple of exceptions. Particularly on the analog inputs: replaced the 1uF 50v Elna electrolytics used for DC blocking with Wima MKS. I did try to be use the right capacitor for the right application (for instance, I used Nichicon KG for the 4 power supply smoothing capacitors), but tended to stay within Nichicon's "high" or "premium" audio-grade lines.

    Of course, there's lots of debate on capacitor replacement, which brands to use, if "designed for audio" is any better than a standard capacitor, and so on. My perspective was, since I was going to be spending the time to replace ALL the capacitors, I was going to use something "high end" - even if all it does is make me feel better!

    3. Replace the NJM2068 opamps in the analog inputs with something "better". Opamp replacement is another area that generates a lot of discussion. The CX-1000U uses these NJM2068 on the analog inputs and mostly NJM5532 elsewhere (such as in the line amp and after the DAC). I had considered replacing ALL the opamps, but opted only for those on the analog inputs. My choice was OPA2134, but I also purchased LM49720 to experiment with. To make replacement easier, especially if I decide to put the 2068s back in, I soldered DIP8 sockets in place.

    4. Replace the 2-prong power cord with an IEC inlet. Probably not necessary, but something that I do in most of these types of projects. For safety, as well as flexibility for power cord swapping (though, I just use whatever I have lying around!). I also removed the 2-prong switched inlet, because I don't use it, and I didn't feel like cutting a bigger hole for an IEC female inlet (and I didn't have an extra one handy).

    5. Learn something!
     
    Bratwurst7s likes this.
  3. Gridslayer

    Gridslayer This and that... Subscriber

    Messages:
    1,134
    Location:
    NE Ohio
    Ambitious endeavor... I have one and really like it. Looking forward to hear if your efforts result in improvements...
     
  4. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    Before you get started...a few words of advice...

    1. Be patient. The CX-1000 is a complex preamp, with several different boards that are accessible from the top, bottom, sides, and sometimes impossible to get to unless you remove another board or a shield plate or something else. There's also ~20 jumper cables running between all the boards and you have to pull all of them in order to get the boards out. There's dozens of screws to remove. It's heavy. There's ~150 capacitors to replace, 300-400 solder joints involved, etc. It's really easy to try to rush the job - at lest for me - and that never works out well. I've found that taking pictures (and even documenting my progress) every step of the way forces me to slow my pace down. For most of us, this is probably not a simple Saturday refurbish job. I ended up focusing on 1-2 boards each evening over the course of a week.

    2. Watch those cables. As mentioned above, there are many cables used throughout the unit to provide power, connect boards, etc. These cables are fixed at one end, which helps you keep track of them, but it's not always the same end, so you have to unplug cables from multiple boards just to get one board out. Fortunately, each jumper cable is numbered on marked on BOTH boards, so you can fairly easily which cable goes where. However, because there are so many, it's hard to keep track of which chassis cutouts to run the cables through. Pictures help here so that you have a reference. The other thing to keep in mind is that the connectors on the boards are old and brittle, and the connections themselves very tight. Be careful when pulling them, because the connectors can crack. Just pull on the cable, as close to the connector as possible, and with a little pressure wiggle I back and forth until it breaks free. Some are easier than others. Lastly, I decided to number each cable using permanent marker on white electrical tape, which made it much easier to figure out what went where.

    3. Have a plan. You don't have to replace ALL capacitors, for instance. Some chose to only replace those in the signal path, some only on a few inputs, some only those that are out of spec, etc. It all depends on your budget for parts, your time, what your goals are and so on. I want to use my CX-1000 for a long time in my main system, and because I got it for such a low price, I was OK spending a bit more on parts. Whatever you decide to do, make a parts list (I will include mine in another post on this thread). It will help with both ordering your parts, as well as using as a guide when you start actually doing the work.

    4. Be careful to not damage the traces/solder points on the boards. For the most part, removing old parts was pretty easy and without issue. (Though it would have been a lot easier if the parts we're numbered in the bottom of the boards!) But, I did encounter a few places where my solder sucker sucked part of the trace/solder point away from the board. It also happened in a few places where I had to wiggle a part out of it's through hole. I ended up using desoldering wick in some spots, lots of rosin, etc. And, in every case, there was not enough damage to cause any lasting problems. Just make sure to use a multimeter to test connectivity from the damaged point to it's nearest connection.

    5. Cold solder joints. Related to the above...When replacing one of the capacitors on one of the boards, I had to slightly move a regulator to fit the new capacitor in place - maybe just a couple MM. When I looked on the bottom of the board, all 3 of the regulator's leads had broken away from their solder points. So, in addition to the RCA connectors, I resoldered all regulator leads on all boards. And, I tried to keep on eye out for other obvious cold solder joints, and reflowed them when and where necessary.

    6. Testing. For the most part, in order to properly test the unit after doing your work, you need to remount all the boards and reconnect everything. That by itself is daunting, but necessary. Be prepared to have to disconnect everything if you encounter a problem. There's really no way to partially remove a board. For example, in my first test the right channel of the CD input, as well as the left channel of the CDV2 input had no signal. I tried to only disconnect a few jumper cables, and lift the board out enough to access the underside. Sorry, doesn't work. Just relax and take the whole thing out and fix the issue. Be prepared to do this multiple times as you find issues. I tested every analog and digital input using a CD player as the source and the headphone output. I verified that the balance and tone controls worked. I verified the Source Direct and mute buttons. Really as much as I could test, I did.

    7. Follow the signal. The service manual is readily available in pdf format, though the schematic is impossible to read when printed and even on a standard computer monitor. I found it better to view on my phone (Galaxy Note 8), which had much, much better resolution and allowed me to zoom in great detail. Anyways, follow the signal path (clearly labeled) in the schematic and figure out what is going on. Start at the CD input and work your way through to the output. It's a great exercise, and it helped me tremendously in understanding the circuit.
     
    Mr. Yamaha likes this.
  5. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    So far so good, at least with the headphone outputs. Though, as I mentioned, I rarely use them so it's hard to say definitively that there is an improvement. Once I complete the phono board, I will test more thoroughly in my main system. I expect great things - even if only placebo ;)
     
  6. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    One other thing...

    8. Capacitor fit. Keep in mind that there are several spots where capacitor fit will be a problem, particularly height, though there are some tight spaces with regards to width. The boards on the top of the unit (digital 1 & 2) do not have room to mount the size capacitors necessary in a vertical position. For example, C478 on Digital 1 is a short and very wide. So, you'll have to mount some horizontally. In my parts list (forthcoming), I tried to indicate where space on the board could be an issue. Just pay attention to the physical sizes of the stock capacitors when you're selecting your replacements. This meant, for me, removing all the capacitors from the boards first in order to measure them - especially the larger ones. Finally, before soldering the new caps in place, try to do a fit check by placing the board in the chassis to verify that it will work.

    Here's a picture of the digital 2 board with the larger capacitors (C486 & C495) mounted horizontally, both sitting on top of smaller capacitors (C492 and C489) also mounted horizontally (you can see C492 under the larger black capacitor).
    20180403_102112.jpg


    Lastly, a quick note about C486...This is a 4.7mF (that's millifarad, not microfarad) 5.5v electrolytic. Your replacement would be a 4700uF of at least 5.5v. I went with a 6.3v.
     

     

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  7. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    For those that just want to jump right in...

    ...attached is my parts list. Nichicon KZ and FG throughout, with a couple of exceptions:

    1) Nichicon ES (Muse BP) for all the bi-polar capacitors - C13-16, C307/308
    2) Nichicon KG (large can aluminum for audio) for the big power supply smoothing capacitors - C24, C34, C35, C37
    3) Nichicon KL (low leakage current, a step below JB which is designed for memory backup, which were too large for this application) for the "battery" on the digital 2/cpu board - C486
    4) Nichicon KW (miniature for audio) for power supply smoothing on the digital 1 board - C478
    5) Nichicon PM 1uF 50v for C467 on digital 1 board - because it's all I had on hand for that value, and I had already placed my Mouser.com order!
    6) Nichicon PX 1uF 35v for C38/39 and C52/53, also because they were what I had on hand - the stock parts were rated at 50v, so I know it's a risk stepping down to 35v. However, I read through the schematic and tested voltages, and these shouldn't see more than 20v. Still, if you replace these make sure to order replacements rated at least 50v.
    7) WIMA MKS for DC blocking on all analog inputs/outputs, replacing the stock Elna electrolytics
    8) WIMA MKS for DC blocking on the equalizer 3 board - C727/728 (these are on the inputs of an opamp in the tone control section)

    Note about #8...there are several places throughout the design where electrolytic capacitors are used for what appears to be DC blocking on inputs and/or outputs of the various opamps. However, many of these are of much higher capacitance and it's not practical to fit in film capacitors in these spaces. For example, C745/746 are 10uF/25v on the output of the opamp mentioned above. A similar WIMA MKS of this value is around 3X the size and would be difficult to fit! I probably could have been (and should have been) more thoughtful about these DC blocking applications and worked harder to find better options.

    Couple of other notes...

    First, I grouped like capacitances together and ordered a single voltage. For example, if I needed 4 10uF/6.3v, 4 10uF/10v, and 4 10uF/25v, I just bought 12 10uF/25v. This got me into trouble in a couple places, with the larger voltages caused a fit issue on the board. In retrospect I should have been more thorough in this area.

    Second, there are 2 places where 10uF/50v electrolytics are used for DC blocking on the analog 1 board: C150/151 which (presumably) blocks DC from the input stage to the follow stages, and C175/176 which (presumably) block DC to the preamp outputs. As mentioned above, film caps would be difficult to fit into these spaces, so I just used 10uF/50v FGs in these spots and bypassed them with 0.1uF WIMA MKPs. Other people have used BP caps in these areas, which I considered (and even ordered, after the fact). I may change these out at some point.

    Here you can see C150/151 and C175/176 with the WIMA bypasses in place:
    20180401_093701.jpg 20180401_093708.jpg


    Third, back to C175/176, these are on the schematic and in series with R279/280 47R resistors. However, on my board there was no spot for C175/176 - they were hacked in there. So, it took a little work to get the resistors, the electrolytics and the bypasses in place.

    Fourth, the boards. Unfortunately, the service manual refers to boards by number and not by function, and the numbers are not on the boards themselves. These are the boards:

    Inked20180402_080234_LI.jpg
    Analog 1 - This is the big boy! Most of your work will be done here. It handles analog input/switching/output, DAC, and secondary supplies. It's the large board in the picture above, and accessed under the bottom plate.

    Analog 2 - This is the line amp and located under the top cover (see picture below)

    Digital 1 - the main digital board. Handles digital input/switching/output and it's own power supply. Located under the top cover and shield plate (see picture below).

    Digital 2 - the CPU, located under the top cover (See picture below)

    Equalizer 1 - the phono stage, it's the vertically mounted board on the right in the picture above. You can remove it without removing the side or back panels. Simply unscrew it from the back panel, and then on the other side of the board there are 2 pins (one on the bottom and one on the top) that you pull out, which will allow the board to come free. Note that this board is connected via a blue ribbon-style cable to the phono input selector at the front of the chassis. So, though board comes free it is limited by this cable. You can detach the control from the front panel to pull it completely free. I did not do this.

    Equalizer 2 - the AC input (see picture below)

    Equalizer 3 - tone controls, balance, headphones, located under the analog 2 board. You need to remove analog 2 to get at this guy. If you want to remove Equalizer 3 entirely, you have to detach all the controls/pots from the front panel. I did not do this, which made it a bit harder to remove/replace components on this board.

    Inked20180403_121856_LI.jpg
     

    Attached Files:

    Last edited: Apr 3, 2018
  8. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    The IEC inlet...

    I decided to mount this in the spot where the original 2-prong cord comes into the chassis. I used this spot as the bottom right corner and then used my chassis nibbler to cut out a space big enough for the IEC inlet.

    20180403_125654.jpg

    You can see that the switched outlet has been removed - I will get a plug to fill that space eventually. I used a drill for the screw holes.

    Here is the inside view:
    20180403_125333.jpg

    Note the ground point on the chassis at the top of the picture. This was the location of a plastic mount for 2 terminals that took the AC in from the power cord and the blue/white leads to the board. I just needed to make the hole a little larger for the bolt. The bolt is secured to the chassis with a washer and nut, then the crimped and soldered ground wire, then another washer and nut. After tightening, I used Gorilla glue on the end of the bolt to keep everything in place.
     
  9. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    Subjective Testing

    I'm waiting for some replacement parts for the phono stage, and the CX-1000U is just sitting there staring at me, wanting to be tested. So, what the heck, let's do it.

    20180403_134517.jpg

    That's my current main system: Adcom GFA-535 (recently refurbished), Sunfire Theater Grand preamp (temporary until the CX-1000U is finished), Sony PS1 (heavily modified) as CD source. The AR-XA turntable was moved to accommodate the in-progress CX-1000U.

    I've been listening to Bill Evans' Complete Village Vanguard Recordings lately, so I decided to start my test with that CD. Couple of immediate impressions:

    - Wider soundstage. I really noticed the left/right separation on this CD. Evans' piano is panned right, while Lafaro's bass and Motian's drums are panned left. What really stood out was the drums. They appeared wider than I had previously noticed.

    - Clarity / detail. At the beginning of CD1 Lafaro is tuning his bass using his bow - it jumped out of the speaker, like he was there in the room with me. Similarly, during the brief intermission I could hear tiny clinks of what were probably fingernails tapping against a glass, the sound of a chair creaking as someone moved in it (presumably), I think even a whoosh of air in the left mic as someone walked past it. I never noticed any of these things before.

    Next I played Norah Jones' Little Broken Hearts. It has a good mix of electronics and acoustic instruments, and her singing is tremendous (as always). On Good Morning her voice was a bit more forward than I remembered and it was like she was "there". The other thing I noticed was the tightness of the bass/bass drum on some of the tunes - definitely tighter and punchier than I remembered.

    Lastly, I played Nova Collective's The Further Side. This is a CDR burned from FLAC files ripped from the vinyl which was played on my AR-XA. Anyways, I definitely noticed the tightness and punch of the bass/bass drum, but the big improvement was the clarity of the full kit, in particular the cymbals. The differences in the various cymbals really shone through, even different sized crash cymbals. They were so clear. The snare drum cut through the mix, and I could hear the buzz of the snare itself during tom rolls, etc.

    Perhaps the preamp is now a little brighter, but I wouldn't describe it as harsh. Just clear and more detailed and spread out. And, as I said, the low end is now tighter and punchy, where before it was big and boomy - or maybe just very "full".

    Anyways, on this first listen of maybe an hour, this is a different preamp!

    Disclaimer: I realize that this was just a very subjective listening test, with no direct AB comparison. I am sure that I'm biased by what I've heard others say about similar projects, as well as my own desire for the result to be "better than I remembered it". Still, the fact that after all this work, it's working correctly and sounds great is very satisfying!
     
    Last edited: Apr 3, 2018
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  10. 39cross

    39cross AK Subscriber Subscriber

    Messages:
    937
    Location:
    Beverly, MA
    Nicely done. Have you tried any opamp swaps yet?
     
  11. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    I haven't yet. I'm really liking the OPA2134 in there so far.

    The priorities at the moment are:

    1) finish the phono stage
    2) replace the electrolytics (with Wima bypasses) on the pre outs (C175/176) and DC blocking to post-input stages (C150/151) with film types

    I'm still waiting on the parts to arrive...
     

     

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  12. Mr. Yamaha

    Mr. Yamaha Not so much Yamaha lately...

    Messages:
    898
    Location:
    Amsterdam Area, The Netherlands
    Great work :bigok: Great inspiration for the CX-1000 that I will be picking up tomorrow.
     
  13. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    598
    Nice work!
    Perhaps you're already aware but Wima make a 10uF/50V MKS2 with a very good form factor (7.2x11x16, 5mm LS).
    They are expensive but there are no other 10uF film caps this small to my knowledge.
    Might still be too big, but the reel version may work.
     
  14. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    Funny you should say that...I ordered those Wima MKS2 caps a couple of days ago :) I hope they fit!
     
  15. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    Thanks! It's a great preamp, and for ~$120 USD and a little time you can make it really, really sing!
     
  16. 39cross

    39cross AK Subscriber Subscriber

    Messages:
    937
    Location:
    Beverly, MA
    You're lucky you have the switch caps btw, they like to come unglued and disappear forever. I have a couple that are missing the caps.
    I look forward to digesting your parts list, I haven't touched mine yet, it's in my main stack.
    Hope those Wima's fit OK.
     

     

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  17. rottalpha

    rottalpha Yamaholic Subscriber

    Messages:
    1,813
    Location:
    Middle of Crook County
    carefull with long leads on those caps.
     
  18. rottalpha

    rottalpha Yamaholic Subscriber

    Messages:
    1,813
    Location:
    Middle of Crook County
    Please do not take this the wrong way, but I think the preamp looked better before. The parts you removed had no negative impact on the sound either.

    Overall, I admire your efforts. This is not an easy pre to restore, as you already figured out, so Kudos on the perseverence and for sharing the progress with the group.
     
    avionic likes this.
  19. rottalpha

    rottalpha Yamaholic Subscriber

    Messages:
    1,813
    Location:
    Middle of Crook County
    :thumbsup: on the sockets
    Changing only the op-amps in many cases will bring no real benefit, unless the circuit they function in, is also optimized (for the new op-amp).

    Edit: A wise bird pointed out to me that there isn't much to the supporting circuit for the op-amps in this CX so swapping the op-amps might not be that difficult, given that you find something suitable.

    I frankly did not look at the schematic of the unit before, but now that I did, I do see that yamaha used a pretty decent op-amp to begin with.

    Please let us know if you find any meaningul gains from the swap
     
    Last edited: Apr 27, 2018
  20. rgbeach

    rgbeach Active Member

    Messages:
    148
    Location:
    Palos Heights, IL
    My chassis skills are not very good, that's for sure.

    Is there no benefit whatsoever to using a 3-prong AC cable? Sonic, safety or otherwise?

    Thanks for your advice!
     

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