Wednesday, January 12, 2011

Mission 753 Freedom


I finally laid my hands on the infamous unit. Weighting in at about 25kg each, it is a well constructed speaker.
753 without cover. Meridian A500 (with puppet on top), Quad ESL Pro63 in the rear and the Technics Honeycomb 

Upon initial listening using the copper cable transferred from the Technics Honeycomb, the 753 was disappointing - sounding compressed, glimpse of imaging, restricted headroom, with plentiful of flabby bass???

I was driving it using the Leak Delta 30 with only 15W RMS per channel but enough to drive my other well known speakers ... (not tried the Leak on my stored Celestion SL6s and the Pro63 yet)

Searching the internet, there were many comments regarding using an amp of atleast 50W per channel as well as mods to the crossover, etc to get the best from the 753.

What I did note was that the above setup while had plentiful bass and sounding compress, the 753 did convey the details as per my other speakers.

Hence I decided to try a simple experiment before going for the "works". I replaced the existing copper cables with my old QED Silver Anniversary (newer version has less than half the original core size).

Sounds almost top flight via the low wattage Leak Delta 30 using QED Silver Anniversary speaker cables!!! Like night and day by just changing the speaker cables.


Update

On the following week I managed to add a Sansui AU-7900 to my collection.

Tried pairing it with the 753 via the copper cable (since it has more power than the Leak). Bass was respectable but over-emphasized. The treble had the 'behind the veil'effect. Hence I inserted a bypass using a ROE 0.022uF for the 10uF and 6.8uF capacitor. And insert WIMA 0.33uF bypass for the 470uF capacitors. Furthermore added 2 layers of foam padding to the bottom cavity as the original was empty(?).

The cross-over unit looks a bit different from the pix(s) on DIYAUDIO and other websites as this is the Freedom model - without the 1,000uF capacitors and a simplified crossover board.
Original
After adding bypass to capacitors
Different view of cross-overs

Add 2 layers of foam

Speaker cable from the AU-7900 - more than enough 'juice'to drive the 753F

Been an hour and the sound is beginning to take shape ... vocals are sweeter and bass is firmer. Has the makings of a keeper!


Update:

Using the previous setup and copper wires, the 753F seem to slightly warmish. Bass became more firmer, voices were almost "being there" but there seem to be a very light veil still in-place.

Connecting the 753F via QED Silver Anniversary seems to be it. Everything is falling into place, with firm bass!!

15 comments:

  1. Hello WCK,
    I also have some 753 Freedoms and would love to improve the high frequency as they do sound flat compared to other speakers I have heard.
    How much of an improvement did it make?
    I am competent with a soldering iron by have never 'bypassed' before as I know little about about crossovers.
    Is it possible to have a close up photos of the bypass you have done, more importantly to the high frequency side.
    I have clicked the photo to enlarge it but it quite difficult to see.
    Hope you can help.
    Regards, Jon.

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  2. Hi Jon,

    Best to add the bypass to the 6.8uF and 10uF capacitor for non-bass bypass. Otherwise the mid and high will not be "1". It opens up the high and mid, most noticable on voices and instruments. Background details as well after say 30-60min run in.

    Basically just solder the bypass to the leads from the 6.8uF and 10uF capacitor since these are MKT1813 (no polarity).

    Do be careful to ensure your soldering iron does not came into contact any of the cabling etc.

    I used the ROE 0.022uF as these were leftovers from my Quad 33 (#2 - not in blog yet). Looking back maybe I should have use the ROE 0.033uF on the 10uF (for mids as I have leftovers from the Quad upgrade as well!!). Still sounds nice with the 0.022uF there at the moment.

    Currently waiting for the bypasses added to the 470uF's to be broken in. Bass is still changing e.g firming up.

    I was surprise the foam did not produce as much impact as I initially though (upon initial usage after adding them into the lower cavity).

    Will update the item once I have a chance to do more over weekends. And will post a better pix for your reference when doing so.

    Apologies for the delay.

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  3. Thanks for the response WCK, I appreciate the info.
    Looking forward to the update :)

    ReplyDelete
  4. Hi WCK,
    Thanks very much for that.
    Another question...does it matter what the voltage value is of the 0.022uF?
    There are plenty on the web but they all have different values.
    Many thanks in advance,
    Jon.

    ReplyDelete
  5. Hi Jon,

    I used ROE MKT1813 630V as these were leftovers from my 2nd Quad 33 upgrade.

    Since the original electrolytic capacitors are 50V, you should use capacitors of equal or higher voltages.

    ReplyDelete
  6. Hi Jon,

    In-case you did not see the item about the 753F prefers silver cabling. The other sites has similar feedback as well.

    ReplyDelete
  7. Hi WCK,
    Thanks for the info.
    Bypass is now done and there is a good improvement in the top end.
    The vocals actually flow freely now and no longer hit a muffled barrier!
    I'm pretty sure I've got some QED silver cable lying around somewhere so I'll give that a go also.
    Regards,
    Jonathan.

    ReplyDelete
  8. Hi Jon,

    Glad to hear!

    You should try the 0.33uF bypasses on the 470uF capacitors as well.

    The bass firms up and now reproduces drums much more accurately (if you heard live drumming before).

    If you don't like them, these are easily removed as well.

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  9. Hello WCK,
    Like Jon, I also have some 753 Freedoms and would love to implement the mods you have made.
    I am also competent with a soldering iron by have never 'bypassed' before as I know little about about crossovers.
    Is it possible to have a close up photos of the bypass's you have done.
    It's quite difficult to see accurately from the photos.
    Hope you can help.
    Regards
    Tony

    ReplyDelete
  10. Hi Anthony,

    If you place the cursor over the pix(s) and double-click on them you get the full size pix shown.

    ReplyDelete
  11. Hi WCK,
    Thanks for replying. I have done that but still can't quite makeout where the all the legs of the caps across the 470's are actually soldered. If you can be of further assistance I would be extremely grateful.
    Regards
    Tony

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  12. Hi Anthony,

    Apologies but the nature of your questions suggests you should read-up on basic electronics before proceeding any further.

    Otherwise you risk damaging your speakers and maybe even your amplifier if the soldering was not perform properly.

    A more suitable alternative maybe to use silver speaker cables for connectivity between an amplifier and the tweeters while retaining the cooper cabling for the bass - your amplifier can support two sets of speakers.

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  13. FYI

    Been a while since the above and the unit has came on very nicely since.

    When using it for about 8hrs a day during weekends, and looks like the new components was "run in" by mid Apr2011.

    Am now using it with the copper cables I normally use, no the silver cables. Driven using the AU-7900, since it has enough juice for the task.

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  14. Have since sold the 753 Freedom(s) to make room near the stereo cabinet. Must admit it went like grease lightning!

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