Sunday, November 7, 2010

Musical Fidelity A1X

Regrettably, I had sold my pristine condition British made A1X without taking pix(s) of the internals.

Luckily, these are readily available on the internet. There are many articles on the mods, tweaks and recapping for the infamous unit so I will not go into those in detail.

As per other units in collection, I had recapped the A1X and obtained much improvement. Most noticeable was the definition and strength of the bass once the 4x10,000uf caps were replaced. And I put a bypass of 0.1uf (recycled poly) on the 10,000uf caps.

What I did discover along the way was not mentioned in any blog or website. After completing the above (as far I had searched on the net), I notice the A1X performed much better but was lacking in the ability to resolve details in the background ... it was definitely there but something was holding it back.

I reviewed the schematics (which are plentiful on the net - example below) and noted C15 and C16 are on the signal path.
Since I did not have the original pix of my A1X, I will use the following from the internet to illustrate the caps I am referring to e.g caps with 22 written and indicated by the arrow pointers in red.
sample with arrowed indicators
I replaced these 22pf caps with 33pf silver mica's. When tested, it sounded like a valve unit - warm, full bodied with all the details!!!

When the buyer of my (previous) A1X first heard the unit, he literally "fell head-over-heels" over it. He had previously heard other A1 and A100 units as well as the reincarnation.What more can I say ...

22 comments:

  1. I have the same unit, all original. I'm thinking of doing exactly what you did to the A1-X (Cap change and replacing the 22pf with 33pf. I currently find the unit very hot after 1 hour or so.

    ReplyDelete
  2. Hi Simon,

    The recap will not reduce the heat levels. Even before I recapped, the A1X gets hot after about 20-30min.

    I recapped to obtain best performance possible, and, to remove the slight veil in-place.

    Used to have a fan blowing into one side of the unit. Hot air coming out the other side of the A1X is like openning up the oven door after baking something in it!!!

    ReplyDelete
  3. Hello again,

    Yes nothing will decrease the heat except for a fan. I will proceed to recap the 4x axial 25V 10000uf caps. You mentioned adding a 0.1uf on the 4x 25v 10000uf caps. Could i get more info on the 0.1uf caps? Also, i want to change the 22pf caps for 33pf silver mica's. My question is what is the voltage tolerance on the one's you installed, i can get some at 33pf 500V.

    Thanks
    Simon

    ReplyDelete
  4. Hello Simon,

    The recycled 0.1uF used are the yellow Japanese ones on the right side of http://myoldvintagehifi.blogspot.com/2011/04/polys-normally-replaced.html

    The 33pF silver mica used were 100V. Otherwise the leads may not fit into the PCB. Most older Brit PCB tend to have very small holes for the lead. I purchased them from http://cgi.ebay.com.sg/33pF-100V-10-Radial-Silver-Dipped-Mica-Capacitors-25-/380259563969?pt=LH_DefaultDomain_0&hash=item58893c79c1#ht_1916wt_698

    ReplyDelete
  5. Hello,

    When you say bypass .1uF is it per 10000uF cap or .1uF per side(2 caps)?
    Also can i use PP caps for bypass such as mundorfs? or stick with the recycled poly?

    Thanks,

    ReplyDelete
  6. Hi Carlo,

    Only on each of the 10,000uF for audio.

    You can use more expensive PP such as Mundorfs, but you need to consider the ROI of the Mundorfs vs something 10x cheaper and you can't tell much difference from.

    ReplyDelete
  7. Hello Again,

    I did change the 4x 10000uf caps + changed the 4x 22pf caps with 33pf caps. The amp sounds great, i didn't install the 0.1uf on the 4 main caps (10000uf). Would it make a difference in sound if i do install them?

    Thanks

    ReplyDelete
  8. Hi Simon,

    Glad to hear you like the results.

    The 0.1uF bypass caps only need to be installed on the main audio caps (2x10,000uF)- closest to the transformer on both sides of the "U" plate.

    If you do install them, you will be rewarded with more bass extension.

    If you did used silver mica's for the 33pF, the sound stage would open up e.g more realistic and natural.

    Best wishes!

    ReplyDelete
  9. Hello,

    I did the .1uF bypass on the caps my amp now have a better bass extension.. Thanks to you.. :) Next is to change the 22pF to 33pF also i want to change the original vol pot to alps blue velvet and bigger power cable..

    ReplyDelete
  10. Hello Again,

    If I change the 22pF to 33pF will it make the sound more "fatter" compared to the original?

    Thanks,

    Carlo

    ReplyDelete
  11. Only initially until the new component has been bedded in. I used silver mica's which would also let HF thru. The idea to use silver mica's came about after I last open-up my Accuphase E-203 which pretty much had silver mica's thru-out the unit!!!

    ReplyDelete
  12. Thanks for the reply but I find the MF A1x sound thin.. Will all of the mods make it sound bigger or fatter? Or it's just the amps character?

    ReplyDelete
  13. I remembered the 33pf Silver Mica made the A1X sound richer, especially the bass. Treble became fluid and much clearer.

    The Silver mica(s) do not cost much and if the results are not desireable, you can easily revert to the original components.

    ReplyDelete
  14. use stmicroelectronics tip35c and tip36c.
    dump the 2955 and 3055 in the bin for regulator circuits.
    colin
    cape town
    sa.

    ReplyDelete
  15. this is the hottest i have ever felt an amp run, main top heatsink off and no fan running.
    about to mount a hq mains fan to blow the tunel.
    then i will test and fry some lunch on the top.
    colin

    ReplyDelete
    Replies
    1. The A1X had holes in the side walls for ventilation. Hence all I had to do was put a fan on one side. Air coming out the other side of the A1X was like that from a HOT oven!!!

      Guess it is a great 2-in-1 for hifi fans in cooler regions of the world - hifi and heater all in 1!!!

      Delete
  16. Since a couple of weeks I re-won a A1-X and replaced may capacitors. Mine is in perfect conditions.

    Can somebody tell me if it is possible to lower some gain of the Alps potmeter? After 1 mm turning it get very loud...

    ReplyDelete
    Replies
    1. Did you replace the potentiometer with same value?

      Delete
  17. Hi, I didn't changed the Alps 50K potmeter.

    Ad.

    ReplyDelete
    Replies
    1. My previous unit did not behave so. Suggest checking the resistors leading to the potentiometer or the potentiometer itself to see if they are within spec.

      Delete
  18. Checked values and they are ok. Everyrhing looking ok...
    The A1 looks also hardly used. I have a new Alps 20K which I can try....

    ReplyDelete