Are there any Mods for MKIV's Lead Channel ?

[Lights Out]

Hi
Im pretty happy with the MKIV's Rhythm2 the Clean is ok too.
But Im not too excited with the Lead Sound , I have experimented with
Different Cabs, Guitars & Amp settings .

It sounds kinda twangy & a little too spongy & not as thick as Id like.
Dont get me wrong its still good . But I would like to improve it somehow.

I have changed the power Valves to JJ 6L6GC's but not the pre Valves yet.

I remember reading somewhere that there are a few mods to the Lead Channel, Does anyone know what they were ?

 

[jackieTHEjokeman]

I'm 99% positive that there are no mods for it. I asked the Mesa store in Hollywood about 3 months ago that same question, unless they just started it. How long have you had the IV? You may need to keep tinkering with it.

 

[Aart]

try a lot of settings with it, i think its the best channel of the amp, but it has a lot of switching options so its not easy to find your sound fast.

 

[Nocki]

I would contact eurotubes and tell him what you want out of your amp.

I contacted drtube in holland and he gave me great advice on what to use. he made my mark IV scremn the way i wanted to!

Nocki

 

[Boogiebabies]

Depending on what version of MK IV you have it is either 100% identical to the IIC+ or 98% on the later MK IV. The only mod I now is to snip out the bright cap on the 270K plate load resistor for the V3B on the MK IV A. It will make it a bit brighter and seem like it has more gain. The MK IV B has this omitted already.

 

[Lights Out]

Thats interesting Boogiebabies..that sounds cute.
Wouldnt snipping the bright cap reduce treble ?

I have owned the MKIV for several months But I have been playing with my Marshalls of late. I was using a rental MKIV for a small tour I was playing on & it got me back in a MKIV Mood

I Have Gotten the High Gain Kit from Bob@Eurotubes . I have only tried the 6L6's so far & I found them a little Brighter & less body than the Sovteks that were in it !!
So I held off on the JJ 12ax7's

I played around with many 12ax7 & at the time settled on a
NOS EI 12ax7 in the V1 slot There similar to Telefunken.
Cant remember what else I put as many arnt labled.

But just yesterday I waked a NOS Brimer in the V1 & it sounded better already.

I guess I underestimated what different the Preamp tubes make in the MKIV.
Being so complex I thought it wouldnt make too much difference.

 

[Boogiebabies]

Cute !! What the heck is cute about that. My kids are cute....


Actually the bright cap on a plate load resistor would reduce highs.

 

[Lights Out]

LOL this thread could go anywhere from here ....
Thanks for the info.

 

[Boogiebabies]

Your right, my Dachshunds are cute too !!!

 

[highroller]

Boogiebabies,

For the mod

What is the cap number you are refering to in the Mark IV V3B schematic ?

When you say sniping out, I assume you mean removing the cap and replacing it with a jumper wire ?

Thanks

 

[Boogiebabies]

What year is your MK IV?

 

[highroller]

1991
(6-26-91 Wa written on the chassis)
Serial IV 2799

 

[Boogiebabies]

C23.


It also sounds like your ghost notes may be a time to start swapping tubes before doing a cap job. I would start with the preamp then the power amp. I have three Boogie's from 1984 and 1985 and they all have the original caps as does my 93 MK IVB and 1992 Dual Rectifier. A cap job on a MK IV would be easy on the main power supply, but a pain on the preamp filters. There on the far right and do not leave a lot of room to de-solder them. It's possible, but just a pain.

 

[highroller]

Thanks for the infos !

I replaced all preamp and power amp tubes and changed the two 220uF/300V caps with new F&T and I ordered three 30uF/500V Atom to replace the old Mesa caps.

See some pics here :
http://pages.videotron.com/heliweb/MarkIV

 

[jargapix]

I got the complete JJ HIgh-Gain re-tube from Eurotubes. I love all the channels but the Lead gives me special goosebumps! It is a bit noisy though!


JA

 

[cnumb44]

what effect were you looking for in changing the caps out? I'm only beginning to get into amp electronics and am just wondering. It looks like you kept the same values on the caps. Was it just a different type of cap which will yield a different sound?

 

[Lights Out]

Depending on what version of MK IV you have it is either 100% identical to the IIC+ or 98% on the later MK IV. The only mod I now is to snip out the bright cap on the 270K plate load resistor for the V3B on the MK IV A. It will make it a bit brighter and seem like it has more gain. The MK IV B has this omitted already.

The only thing I can see that looks like a serial number I can see says ....IV 21 82. Does anyone know what year this would be ?

BTW I just wacked some old Sylvania STR-387's in the middle two slots
& Some NOS Mullards in the outside.
They both measure up about 25ma so I thought they would be safe to use

Im getting a quite different tone. Not quite as punchy
Its alot more Creamier , But i have lost some of the Grainy qualities I like too.

Im getting some interesting results playing around with Power Tubes

 

[Boogiebabies]

It's a MK IV A.

 

[highroller]

I'm thinking of a setup to switch the C23 cap on and off so I can have both the old and new Mark IV lead sound. See pics :

http://pages.videotron.com/heliweb/MarkIV-c23mod.jpg

I found a place to install the switch under the chassis, below the Loop Select switch. I would like to know if such installation could add extra noise, hum or if there is any other issues.

Thanks

 

[Boogiebabies]

Sweet. I tried this on a IIC+ for the bright mod and it worked perfectly.
I used test leads to the switch and decided I may hardwire it in the future and give an hour of play time. You will notice that you can open the treble up to 7-8. Below 7 it is a very fat tone, above it cuts and blends pretty well with the mids and bass. Have fun.