Mark III R2 volume mod?

[timv]

Does anyone know how this mod is done? I have a blue strip mark III and the available schematic online is for some other stripe and it doesn't quite match up. I am an electronics tech and have worked on a lot of amps and built my own so know my way around but wanted to see if I could get some help before I lift the circuit board out to figure it all out. If anyone has one and could take a picture of the mod internally or something, that would be great. Thanks.

 

[Joey707]

Unfortunately I don't have a photo. The info I have says, " Replace R130 with a 250K audio taper pot. I've done it a couple of times. It's pretty easy. You should be able to do the mod without lifting out the board. On the short heads or combos you can put the pot where the direct level control is. The direct level can be preset with a resistor so it will still work but isn't adjustable. You can also get rid of the direct out. Plug the hole where the pot was, and put the R2 master pot where the direct out jack was. The pot will then sit right above where it says "Rhythm 2" on the chassis. That's where the Rhythm 2 footswitch jack is located on the underside of the chassis. So it almost looks stock.
On the long chassis heads you can put the pot where the Reverb control would have been on the back panel if it were a short chassis amp. On the long chassis heads the reverb control is on the front.
If I get any spare time I'll take one of my amps apart and provide more info. But it may be a couple of days.

 

[timv]

Thanks for the info. If you think about it I would really appreciate a picture but I think that info will be enough.
Thanks.

 

[vcamargo99]

If the mod is for helping the clean/R2 volume levels be equal, I would love to find out more info on it. I've done minor mods to my Blues Junior and can swap out resistors and caps, but pics are always make it easier (for me). Please post 'em. Thanks!!!

 

[Joey707]

Ok, I have photos ready. However I don't have any place to host photos so I can't post them here. Send me a PM and I can email them to you. I discovered something I wasn't aware of. The amps I did the R2 mod on are done as described above. The amps that were done by Mike B. at Boogie are done differently. R 130 is removed. One wire from the pot goes to the trace coming from the LDRs that are right next to R 130. The other wire goes to one side of R 131. In the photos the gray wire goes to one side of R 131 and the white wire goes to the area where R 130 was.
The way I was doing this mod was based on info I got from Mike a long time ago. The amp I took the photos of was done about 2 years ago. So I would assume the method described in this post and shown in the photos is the current way the mod is done.
If you want to keep your direct output working but without a level control the resistors used are 22K and 4.7K. The 22K is attached to the white wire that comes from the presence control to the direct output jack. The 4.7K is right beneath it and goes across the jack.
Let me know if you have any questions.

 

[Joey707]

Ok, guys I've sent the photos. If either of you wants to post them feel free to do so. If you have any other questions feel free to ask.

 

[timv]

I got the pictures. Thanks. That point on R131 is the same as the other side of R130 when you remove it. I'm guessing they attach the wire at that point because there is more material to connect it to so a more stable connection. I actually removed the reverb pot on my amp because at some point when it was put in a rack mount case it lost its reverb tank. I don't really use reverb and don't want to spend 250 dollars to get a new head case for it so it is the R2 master volume for now. I will take some pictures of my work to post also.

 

[Joey707]

Yes you are correct. It would be easier and more stable to connect the wire to that point. I was in kinda of a hurry and didn't notice that. I glad you did. Have you tried it yet?

 

[timv]

I did do the mod and it works great. I attached the wires to the points that the resistor was in but I am going to redo it once I get the new wire I ordered in the mail. I might attach to the other point when I redo it just for a better mechanical connection. I will take pictures once I am done and try to post them here. Thanks again for the help.

 

[screamingdaisy]

vcamargo99 sent me the pics.....I'll add them here for future use;

MkIII Rear Panel

MkIII Rear Panel 2

Pot and Direct Out Jack

Resistors on Direct Out Jack

MkIII Chassis 3

Mk III Chassis 4

MkIII Chassis 5

 

[gtrguy06]

Does anyone still have the photos of the MKIII R2 modification?
Thanks,

Dave

 

[timv]

I put the original pictures and some others with notes on my yahoo photos page. You can see them here: http://pg.photos.yahoo.com/ph/tvogelin/album?.dir=537fscd&.src=ph&store=&prodid=&.done=http%3a//pg.photos.yahoo.com/ph/tvogelin/my_photos
I think that link should work. Let me know if you have any questions.

 

[psychodave]

I would love to do this, but I am a bit afraid since I dont know my way around a Mesa. I am only familiar with Marshalls

 

[gtrguy06]

Well, I nipped R130 out and cut out the direct out pot and output and put in a 250K pot on my 1988 MKIII 60 watt combo. I have volume control over R2 now and R1 is good, but the lead channel sounds weak and tinny!

Any Ideas? I'll try putting the direct out pot and output back in and see if I need it for some reason.

 

[JOEY B.]

What is the resistance value of the original R130 resistor?

 

[gtrguy06]

It's a 15K 1% tolerance.

 

[madman6680]

Repost pics please?

 

[AustinK]

here is the threadhttp://forum.grailtone.com/viewtopic.php?t=18520&highlight=

 

[Boogie Woogie Man]

I put the original pictures and some others with notes on my yahoo photos page. You can see them here: http://pg.photos.yahoo.com/ph/tvogelin/album?.dir=537fscd&.src=ph&store=&prodid=&.done=http%3a//pg.photos.yahoo.com/ph/tvogelin/my_photos
I think that link should work. Let me know if you have any questions.

I went to the link but unfortunately, the site has now closed. does anyone have pics of the mod for a blue stripe ?

 

[AJ_Newkirk]

Try clicking on the thread AustinK posted just above your post.