Question about SL+ JCM800 tone stack mod...

[Chad]

I was just reading about the SL+ JCM800 tone stack mod on Grailtone, then took a look at the PCB layout PDF file for the SL+. That layout already shows R31 as having a 33K resistor....and C14 having a 470pf cap.

Does that mean Randall has started shipping the SL+ modules with the modification already in place or am I misreading something?

Thanks.

 

[metalmm785]

Hey Chad, i was thinking of doing the same mod to mine, however the schematic numbers are not the same as the actual values on my particular module, so you may want to check your resistor value in this page to make sure of what you got http://ourworld.compuserve.com/homepages/Bill_Bowden/resistor.htm
If it's not the same, most likely it needs the c14 replacement cap too.

I just bought the parts and I'm hoping it brings the mids more to the front, as per say, as i always found it a little too dark/scooped for a true marshall sound...

 

[muudrock]

I would do like Metallmm said and check the values first. It's possible Randall has changed the stock values but I haven't heard anything about it. I did the mod over a year ago and I highly recommend it. This mod brings a nice flavor to this module.

 

[Chad]

Thanks for the replies, fellas.

I checked my silverface SL+ and R31 is 56K +/- 5%.

C14 is hard to read. It is blue and I think it says in three lines...

B
221K
1KV

Any ideas as to what that means? From this page...

http://xtronics.com/kits/ccode.htm

...I'm wondering if it is a 220pf cap with +/- 10% tolerance. And 1KV must mean 1,000volts?

 

[Chad]

Where did you buy your caps and resistors? I believe this is the correct resistor....

http://www.radioshack.com/product/index.jsp?productId=2062332&cp=&origkw=33k+resistor&kw=33k+resistor&parentPage=search

But I'm not sure where to find a 470pf 500V+ cap.

 

[metalmm785]

Hey Chad,
A fellow forumite was kind enough to provide me with the part # from this website for replacing the parts on the sl+ mod, so hopefully this helps you out too...
site is http://www.mojomusicalsupply.com/index.asp
and the part number is #5168225 for the cap and #7292045 for the resistor.

Best of luck!

 

[Chad]

Thanks for the link, bro!

 

[muudrock]

Follow that link. I think that's where i got the parts as well.

 

[metalmm785]

I finally modded my SL+ with the replacement parts and the midrange is definately more cutting. Nice improvement and it's definately worth it!
On the other hand, I also realized that i completely dislike the 0.0022 cap. The bass response just doesn't ring to me...I'm a bedroom player so i don't know if maybe it would sound better at louder volumes but i just don't like the Feel of it...It sounded better with the 0.0047 and i had to break it off to get it out since the prongs were non existant
The only remaining cap i have is a 0.001. Hopefully not too dry for a healthy marshall tone.