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PostPosted: Sat Apr 28, 2018 4:42 pm 
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Joined: Tue May 05, 2015 9:07 am
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Finally dropped off the Mark lll at the UPS store. $142 to ship it from Chicago. Should get there next Friday. I guess I’ll just have to use one of my c+’s until I get it back. :(


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PostPosted: Tue May 01, 2018 9:20 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 92
So I finished off my Mark III Black Stripe to IIC+ conversion over the weekend, modded to have switchable ++ (I changed a lot of R2 stuff to do this but still kept the R2 mod balancing the level). It sounds RIDICULOUS! I can't stop playing it! Saying that my original III had some minor issues which I fixed in the process and sounded really great to begin with but nothing like this! I am hooked and won’t be changing it back! Whether it can compete 100% with a IIC+ side by side I won’t know until I can get my hands on one (extremely difficult here in the UK) but it really is the business! Really made me fall in love with my playing again. I also LOVE pulling the R2 channel and getting that little extra ++ grunt that just makes everything sing that little bit more!

I drew up a table of what I changed. This is for a Black Stripe. Other stripe versions have differing components and a later board revision so will take a bit of thinking and tracing for anyone wanting to do this if you’re looking for a step by step guide for any other stripe version. Not for the faint hearted (close to 40 steps!):

Image

I left R201 at 1.5K for increased gain and haven’t done any of the reverb mods yet. I’ve also left R126 as it was to increase gain on the tone stack when the R2 channel is pulled by lifting the ground slightly on the tone stack. This is mainly because it’s so hard to get to. I also left R106 at 3.3M instead of 2.2M (2.2M will increase gain even more) because I feel I definitely do NOT need any more gain after doing all the other stuff!

I used Silver Micas on the 1KV disc capacitors I replaced including the two tone stack ones, T110 Kemet upgrades all around for the cathode caps (I used 22uF instead of 15uF as 22uF was there originally. The .047uF caps were already Kemet, the lead ones were upgraded to a 2.2uF AND .22uF Kemet). I used metal film 2% 1/2W resistors on most things as per the originals.

Other minor things I did was replace the 470 Ohm resistors on the Output Valves, R119 because it burns anyway (were lovely black scorch marks under the original!) and R104/R141 for the filter caps with higher W wirewound resistors – I think I used 6W or higher or something stupid, the highest I could get where the resistor was still small enough to fit!

Schematics and some overall board pics here (forgive my hot glue gun work!)

https://mega.nz/#F!HZAAgRLS!g1V-9NWuStE3uW2O7MKZKA

All components were lifted off by one leg at some point to get the component number off the board to trace schematics so it’s not the cleanest looking board in the world. Also you’ll see where the board had burnt during its time with a previous owner. They’d done a bodge repair with an integrated bridge rectifier badly and I had to replace all the bridge rectifier diodes and rebuild the circuit using trace wire. It was fairly simple but took a while. The only difficult section was in the EQ in adding an extra 10uF 63v axial cap and changing the orders of some components, lifting up a couple of the .1uF 400V 715Ps for the EQ section and sticking a component or two in from of them. Elsewhere it was simple component value swaps :)


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PostPosted: Tue May 01, 2018 9:25 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 92
Quote:
Finally dropped off the Mark lll at the UPS store. $142 to ship it from Chicago. Should get there next Friday. I guess I’ll just have to use one of my c+’s until I get it back.


Looking forward to how it sounds!! I dread to think how much overseas shipping would be from the UK! I'd definitely have to send just the chassis not the whole amp if I ever needed anything done (I've got my eye on an SRG IIC Export at the moment but would need to send to Mike B to do his + magic...)


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PostPosted: Tue May 01, 2018 10:16 am 
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Joined: Tue May 05, 2015 9:07 am
Posts: 134
Good to hear you’re happy with how the Mark lll conversion turned out. Wish I could check it out. I bought a Mark lll DRG Black Dot combo on Sunday night from a Guitar Center in California. It has Gain Boost instead of Pull Deep on the faceplate. Don’t know if it has the 105 yet. Should get it on Friday.


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PostPosted: Wed May 02, 2018 10:07 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 92
Quote:
Good to hear you’re happy with how the Mark lll conversion turned out. Wish I could check it out. I bought a Mark lll DRG Black Dot combo on Sunday night from a Guitar Center in California. It has Gain Boost instead of Pull Deep on the faceplate. Don’t know if it has the 105 yet. Should get it on Friday.


You're a buying machine!! Is it a 15XXX serial? Guessing you're gonna keep it stock?

For reference I have a late 1985 571100 power transformer in mine (the UK version of the 561100 which is apparently the same as the C+ X101) but gives out 485V plate voltage so I'm not complaining!! :D

It also has the T100-152019 100W output transformer dated 1982.

I'll try and borrow an SM57 off a friend and get some decent audio recording done or do a video at some point. As others have mentioned it's not so much how an amp clinically sounds it's how it feels and responds that's the important bit. I can definitely get that IIC+ sound and definitely has that 'feel' I understand now. It also has none of the mushy treble shift issues that have been reported on the Red stripe and later IIIs if anyone is interested.

Looking forward to hearing what you think of the + mod once it's back! I'd love if you could pm me some pics of the circuit boards on both once they're with you if you ever take the chassis out - really curious as I'm trying to document the circuit board and component changes between the different stripe versions and what Mike B does for the + mod - but no problem if not :)


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PostPosted: Wed May 02, 2018 10:57 am 
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Joined: Tue May 05, 2015 9:07 am
Posts: 134
The Stripe is #1555x, the Dot 1523x. If I like how the Stripe turns out I’ll send the Dot back to Mesa. I’ll send pics of the boards when I can. I can also send pics of my 1988 Carvin x100a. Maybe you can come with a conversion for it too. :)


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PostPosted: Thu May 03, 2018 8:13 pm 
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Mark III
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Joined: Tue Mar 10, 2009 7:13 pm
Posts: 248
That’s great to hear that you’re happy with your results!

I’m not sure if I could add anything to this thread, but I own a Mark III+ Coliseum that shares the same transformers with the Mark IIC+ Coliseums, but it’s a no-stripe (which came out just before the black dots).

As far the sound goes, it’s about as close to a IIC+ as you can get, while not being a IIC+. The only discernable difference between the no-stripe Coliseum and a non-upgraded IIC+ is the Coliseum has this “thicker” sound to it, almost like there’s an extra fundamental note coming through the cab. This could be an attribute of the Coliseums, or could be chalked up to the difference between wattages.

As we as the feel goes, I couldn’t tell any difference between the “bounce” of the Coliseum compared to the IIC+, and the tightness/urgency of the Coliseum was right on par with the IIC+s. Feel-wise, I actually liked the Coliseum better, just because it was still tight, but tonally thicker.

All of this to say that on the Mark series timeline, I think the Coliseums bridge the gap between the IIC+s and the IIIs a little close than the 60/90W Marks. Maybe it has something to do with the transformers, but I’m a little skeptical of this because my Blue Stripe Coliseum is much more brash and angry, and makes the no stripe seem a lot smoother. To get the Coliseums dialed in similar, I’d need to jump the Presence up from 4-ish to around 8 to get it in the ballpark.

YMMV, but I like my III+ as it is, and would recommend checking them out if anyone ever has a chance. They’re in the same family as their 90W brothers, but they’ve got a lot more lower range without sacrificing any of the immediacy or “attack” of the Mark series.

_________________
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Mark III Coliseum KDRG | Mark III+ Coliseum KDRG | Mark III DRG | Mark IV (Head) | Mark IV (Combo) | Dual Rectifier Revision D | Dual Rectifier Revision G


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PostPosted: Fri May 04, 2018 10:44 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 57
Nice one Jon! You've basically got a IIC+ now, as close as anyone is going to get. What led you to keep R126 out of interest? And hard wiring C47 etc to ground?


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PostPosted: Tue May 08, 2018 4:12 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 92
Quote:
Nice one Jon! You've basically got a IIC+ now, as close as anyone is going to get


Thanks! Now to concentrate on my playing a bit more... :cry:

Quote:
What led you to keep R126 out of interest? And hard wiring C47 etc to ground?


I kept R126 because it will increase gain slightly when R2 engaged but nothing major. Also it's REALLY hard to get to without removing the relay (something I did to trace the board but I am NOT doing again unless I can find a replacement relay as I needed to use hot air and damaged some traces in the process I had to rebuild).

I hard wired R105/C47 to ground because I wanted that to remain to ground when R2 engaged. This is because I want the R2 channel to engage C214 ON/OFF and nothing else for switchable +/++ to get an extra boost. I experimented with replacing R130 with a trim pot but in the end removed it all together as it was a bit muddy for my liking. Removing it made a massive difference! Now I get a slight boost with R2 pulled which you can really feel on the lead channel, but R2 is no longer a distinct channel, which I don't mind as I never used it anyway.

Are you getting any further with your Blue Stripe to IIC+ conversion? I think it's pretty safe to remove LDR6 and the corresponding diode and resistor - it basically forces treble shift to be on in R2 mode as far as I can tell and can be removed if you don't want this.

Another thing I noticed is that I tried the reverb mod (adding a 110K or 120K 2W resistor from R116 to ground) and although it made the reverb really strong, it made the overall amp a lot muddier and I really didn't like the result. I removed it and BAM back to the sound I loved. I ended up putting R242 around R131 which increased the swell without changing the sound of the amp. I have the reverb on about 3-4 now and any more is a bit overpowering.

Just something to note for anyone reading this (yours is a non reverb model though right so wouldn't apply?)

Cheers,

Jon


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PostPosted: Tue May 08, 2018 6:31 am 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 57
jrb32 wrote:
Quote:
Nice one Jon! You've basically got a IIC+ now, as close as anyone is going to get


Thanks! Now to concentrate on my playing a bit more... :cry:

Quote:
What led you to keep R126 out of interest? And hard wiring C47 etc to ground?


I kept R126 because it will increase gain slightly when R2 engaged but nothing major. Also it's REALLY hard to get to without removing the relay (something I did to trace the board but I am NOT doing again unless I can find a replacement relay as I needed to use hot air and damaged some traces in the process I had to rebuild).

I hard wired R105/C47 to ground because I wanted that to remain to ground when R2 engaged. This is because I want the R2 channel to engage C214 ON/OFF and nothing else for switchable +/++ to get an extra boost. I experimented with replacing R130 with a trim pot but in the end removed it all together as it was a bit muddy for my liking. Removing it made a massive difference! Now I get a slight boost with R2 pulled which you can really feel on the lead channel, but R2 is no longer a distinct channel, which I don't mind as I never used it anyway.

Are you getting any further with your Blue Stripe to IIC+ conversion? I think it's pretty safe to remove LDR6 and the corresponding diode and resistor - it basically forces treble shift to be on in R2 mode as far as I can tell and can be removed if you don't want this.

Another thing I noticed is that I tried the reverb mod (adding a 110K or 120K 2W resistor from R116 to ground) and although it made the reverb really strong, it made the overall amp a lot muddier and I really didn't like the result. I removed it and BAM back to the sound I loved. I ended up putting R242 around R131 which increased the swell without changing the sound of the amp. I have the reverb on about 3-4 now and any more is a bit overpowering.

Just something to note for anyone reading this (yours is a non reverb model though right so wouldn't apply?)

Cheers,

Jon


I can't even see R126 on my board. :lol:

Mine is a non reverb you are correct. It's mostly already finished, the mods I've currently got on it are generally just matching component specs to the IIC+ rather than removing the III circuitry. here's what's left to do on my notes:

R1 ++ V1 deletion
Delete R133
Delete C28

R2 ++ V2 restoration
Delete R130
May require deleting R126 [replace with bus wire]
Delete LDR6 circuit entirely [check if safe/effects]

Miscellaneous
Swap R125 (1K) and R204 (1.5k)
C506 0.047 -> 0.01 [some IIC+ puts this at 0.047, verify effect on voicing]
Hardwire C47 & R105 to ground?

Lead
R224 22k to 15k [will only affect pull bright on the lead master]

EQ [tertiary priority]
R263 1M to 470k
Wire 1M resistor before C504 (use OG R263)
Add 10uF 63V Axial polarised capacitor before C503
Add 10k resistor before C503
Remove 56k resistor around LDR7A

Mods to consider if too dark/mushy/grainy
C27 10pf to 20pf [lets more treble through as per simulclass IIC+ & studio pre]
C30 delete [lets more treble through as per simulclass]
C30 500pf [lets more treble through, less pronounced than omitting entirely]


I'm considering leaving LDR6 in and basically turning my amp into a super red stripe, but I can't help wonder if its affecting the tone anywhere else and as I said in that thread, I really never ever use R2 as it is currently voiced as a separate channel, having it as a switchable ++ would only increase its usefulness. I'm 70/30 towards deleting C30 and swapping C27 for 20pf. The amp as it is has great tone but the attack transients aren't where I want them to be, along with the treble shift weirdness. If I was doing these mods myself I'd remove all the III circuitry first and see how it is then, but I'll likely just get it all done at once.

When I get my amp back in a few weeks I'll put up a full list of what I changed, how I went about it, how I perceived the sound changes etc. Plus some clips, maybe even a video.

How much of an effect would you say the EQ mods have had? I'm not really sure if I need them, unless they affect the voicing of the amp rather than the way the EQ works. How did you go about wiring C47 to ground? Does the stock wiring bypass the C47 circuit in R2 mode?


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PostPosted: Tue May 08, 2018 8:00 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 92
Quote:
I can't even see R126 on my board. :lol:


Yeah just leave it! Should be tucked right next to the relay hidden below some wires to the Middle pot.

Quote:
C506 0.047 -> 0.01 [some IIC+ puts this at 0.047]


C506 is 0.1uF (definitely not 0.047 or 0.01!). Definitely. 100%. Schematics that say 0.047 are wrong. viewtopic.php?f=27&t=40649&start=0#p292545

Quote:
Remove 56k resistor around LDR7A


This is just for EQ switching so really no need to remove really.

Some other mods to consider for the lead circuit:

"Replace .22 cap on Pull Bright on Lead Master with Kemet T110 Hermetically Sealed
Replace 120pf cap for Lead Drive input- Dipped for lower Microphonic Noise
Replace 1000pf cap for Lead Drive Output- Dipped for lower Microphonic Noise
Replace 1000pf cap for Lead Drive Plate Resistor- Dipped for lower Microphonic Noise"

Dipped for lower Microphonic Noise = Silver Mica. These steps are from a IIC+ repair and maintenance that was done by Boogiebabies viewtopic.php?f=9&t=49710

I did these to mine when I was doing the conversion.

Thanks,

Jon


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PostPosted: Tue May 08, 2018 4:24 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 57
Cool, how did you wire C47 to ground? Got any photos?


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PostPosted: Wed May 09, 2018 2:56 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 92
lions wrote:
Cool, how did you wire C47 to ground? Got any photos?


Yeah check the mega link above for pics you should see the C47 wire. I basically used the excess metal wire you get after you cut the ends off resistors to fit and used that to short C47 to a ground point just below C506 like a bridge going over nearby traces to avoid them. Easy!

You can see the EQ work done as well with the added axial cap in the pics. I would say the EQ circuit affects the voicing of the amp definitely. I can't say how much of an effect it had though as I didn't do an A/B comparison before doing it. Also with mine I had .047 EQ caps and yours has 0.1. so I think that probably made the most difference. Yours might be negligible but you may as well do it. I think it's the Mark V manual which mentions the extra cap they forgot about which, supposedly, made a huge difference to the sound?

My experience on changing the caps to simulclass values is that the simulclass amps are a lot 'darker' sounding than the 100W/60W amps, even when they are in non simulclass mode.

So if it's a brighter sound you want I think changing these won't work. But if you want to darken the sound then go for it! I could be wrong though.

Thanks,

Jon


Last edited by jrb32 on Tue Jul 31, 2018 9:21 am, edited 3 times in total.

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PostPosted: Wed May 09, 2018 9:21 am 
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Joined: Tue May 05, 2015 9:07 am
Posts: 134
My simul c+’s are brighter than my HR’s. Mike B. is going to reduce the brightness on the Black Stripe so it will be the same as the HR’s.


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PostPosted: Wed May 09, 2018 9:26 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 92
Ah cool my mistake I must have got them the wrong way round in my head. Thanks for clarifying!


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