MPX 100 capacitor upgrade

[paulrichards7]

Ive just picked myself up a MPX 100 and am interested in doing these upgrades

I bought this unit for $70 dollars, and wasn't pleased with it. The effects sounded thin and tanky. After one reviewer talked about upgrading the caps, I went ahead and did the same. WOW! It totaly transforms every effect. The reverb, echo and chorus are now full and smooth. I replaced the caps with sprague orange drop. The input caps are .22 and are undersized. I replaced them with the gigantic .47 orange drop caps. I had to file the leads until they were thin enough to go through the holes. The other caps I replaced with the same values. So for $6 dollars worth of caps, you can transform this thing into an inexpensive quality sounding effects unit. Why didn't lexicon do this? With their bulk discount these cap upgrades would have probably cost $2. Why would they risk their reputation on a couple dollars?

AND

The input and output caps are awful and undersized, and this causes a lot of the complaints about 'tanky' sound: they're eating all the bass authority which gives rooms a convincing size and weight, and they sound cheap. I replaced these parts with big .39 polypropylene film caps and the sound became _much_ bigger and better.


Inside pic
http://i390.photobucket.com/albums/oo34 ... 010752.jpg

Now, I can see the 2 input caps on the bottom left of picture, but what are the other caps they are talking about?
Thanks
for your help
Paul

[Jim Williams]

I use a pair of those I bought new years ago. The main problem was the input gain was set too high for analog console +4 dbu levels, the front end clips. I removed the 330 ohm gain shunt surface mount resistors on the input opamp stage connected from the - input to ground. That returned the gain to unity so I can hit it harder without clipping.

[paulrichards7]

Thanks for that Jim, i will try and locate that without schematic
So you dont recommend also, changing those caps?
Thanks again
Paul

[Jim Williams]

Yes, do the rest. The front end dual opamp is a super small sot sized surface mount so replacing that is problematic. The output opamp is standard SOIC so that can be swapped. I would try a BB OPA1642 as it's very clear and quiet without the mondo current consumption of most of the parts I use.
On my pair I swapped the PSU main caps with Nichicon HE's and added 470 uf 25v Panasonic thin case FM's after the regulators. There is also a set of .01 uf white box mylar caps used for a noise reduction scheme, I used Wima MKP-2's and that helps the top end. Usually I will use a Wima or stacked mylar film for the .22 blocking caps. The mylars are bypassed with polyprop Wimas.
I use these for delays, or echos if you like. I use the echo settings as it emulates tape echo with degeneration of the tops on each repeat. I find that to be more natural without those nagging 20k hz repeats. Reverb is saved for other Lexicons and the Bricasti that do a much better job.

[paulrichards7]

Thanks so much Jim
Have you ever thought of putting a book together listing all of your great wisdom/experience in modding?
Also what about a dedicated book to audio electronics and what makes a really great processor
Thanks again
Paul