Jump to content
Sign in to follow this  
RichP714

mk II count three dozen

Recommended Posts

 
Quote
Excellent work Rich.  I am glad this has been a successful venture for you.  As you know, I am no techie, but i was wondering if you are making improvement tweaks along the way, ie is #36 modded exactly the same as #1?
 
I've changed a couple of things along the way; mostly with the M-1.0t mk II
At first, I had the caps mounted in a cradle, but UPS was able to unfix that; then I tie strapped them down to the mainboard on top of some weatherstripping foam (giving them an absorptive bed to lie in) and that worked, but didn't look very nice.  Now I use the mounting method that RussKall developed for his mk II; it looks much nicer.
 
Also on the M-1.0t mk II I did the 'fulcrum bias pivot' thing; I can't remember which one was the first, but they all get that now.
On the M-500t mk II I reduce the emitter resistor's value (and therefore the needed bias current) to keep the bias point more stable.  Also, I changed the LED driver circuit to accomodate the (often) weak secondary (lighting) transformer.

Share this post


Link to post
Share on other sites

Guest robert
hi; Could you give me the e-mail or phone number of the facility performing the Mark II upgrade. I am not reading the letters correctly from their web sight . Thank you;

Robert

Share this post


Link to post
Share on other sites

Rich, I noticed that they changed optocouplers between the M-500 and the M-500t.  I did a comparison between the two and found that the new one (in the t) passes 63v and the old one passes 80v.  Also, you can get the new one in two versions, one that passes a minimum of 50% of the current and one 100%.  The old one only passed > 50%.  In that they are both available, I wonder why the switch.  Cost?  Reliability?  One is a Toshiba part (new) and one is a Sharp.

Share this post


Link to post
Share on other sites

Quote
hi; Could you give me the e-mail or phone number of the facility performing the Mark II upgrade. I am not reading the letters correctly from their web sight . Thank you;
Robert
 
You can PM me here, or go to the mk II site, contact tab and click on the email link to send; you don't have to read any letters correctly, just click the link.

Share this post


Link to post
Share on other sites

Quote
You mentioned that you changed the input opamp because the NJM072D went unstable with the Mk-II mod.  Without the Mk.II modification would I be safe in changing that opamp to an OPA2134?
 
There's a note in the datasheet on the original opamp that mentions instability under certain conditions.  I noticed that after I'd fixed the oscillation with a feedback cap change.  I went with a higher bandwidth opamp (NJM2082D) I first tried the OPA2134 (a very nice audio opamp) but it was unstable at a different frequency.
 
I'm not sure if it would work or not with a stock M-500t; it should, since you're not changing the output devices (the ones I use for mk II have a higher bandwidth than stock, very nice devices too those Sankens.
 
If you want to give yourself the option to mk II at a later date, the only thing you'd have to do NOW is the PS caps voltage rating and that input buffer opamp; if you are going to stay stock, I'd think the OPA should work fine.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...