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 Post subject: Updated Mark III+ Info
PostPosted: Fri Feb 23, 2018 12:18 am 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 65
I'm currently working through all the info I can find online as I'm preparing my Blue Stripe for a DIY III+ mod. It's taken a long time learning how to read schematics, looking at everything I can and calling Mike B to double check. There's a lot of info on the well-known C516, C30 and C27 mods, but little about the other component differences. There's also a lot of confusion because the only schematics for the III easily found are for the Red stripe, even when labelled as Blue.

One big myth is that the Blue Stripe is the same as the Red stripe minus the C30 mod. There are lots of component values that were changed between them. The Green and Blue stripes also have a different resistor alongside the C27 capacitor that is supposed to have as much if not more of an effect than the cap itself, which varied depending on the model from the IIC+ through to the Red Stripe. It's unclear whether or not C27 is 10 or 20pf in these, as simul-class amps were supposed to get 20pf. I've seen conflicting information, my gut says all greens are 20pf, all simulclass through to the reds were 20pf, 60/100w through to the reds were 10pf and blues are all 10pf but I don't know. Another IIC+ component I've only seen mentioned once online is the cap at C36 which works with the 5 band EQ.

I've updated Loylo's Red Stripe schematic with values I've been able to work out with my amp or find in others:

(typo at the unnamed pin cap in the lead circuit; should read 500pf for blue stripe value)

Image

I think the 470k resistor listed above is R153. The R119 mod is one I saw on youtube that someone claims Mike B recommends, although I haven't been able to figure out what effect it has. That part of the amp doesn't appear to be on the schematic, but I may just be missing it. Two things I haven't been able to work out due to lack of schematics and my own knowledge deficit;

Someone with a green stripe said that the "phase inverter" cap on theirs was .1 rather than 0.47 as in the IIC+, however I don't know where to look for this. I'm guessing it's one of the big orange drop sprague ceramics but I can't figure out which cap he's referring to. There are a whole bunch of 0.47 and .1 caps around V5. He's not referring to C516 by the way, which is already a 0.47 in the Blue and Green Stripes onwards.

The 680k resistor after the lead input and LDR in the lead section I can't find for the life of me on my blue stripe. There's no 680k resistor in V3A or V3B when I look at my amp. I can see a 680k resistor near c506, which means it could be the 680k I'm after circuit-wise given c506's schematic proximity to the lead circuit but I'm not so sure, my ability to read these things is pretty rudimentary.

All that said, this took me quite a while to wrap my head around so if anyone else is looking for the Mark III+ mod and can't send it to Mesa to have it done, or just finds this interesting, hope this helps!


Last edited by lions on Wed Jul 25, 2018 4:12 pm, edited 6 times in total.

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PostPosted: Fri Feb 23, 2018 4:09 am 
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Mark II

Joined: Fri Jul 28, 2006 5:58 pm
Posts: 104
Location: Europe
lions wrote:
One big myth is that the Blue Stripe is the same as the Red stripe minus the C30 mod. There are lots of component values that were changed between them. The Green and Blue stripes also have a different resistor alongside the C27 capacitor that is supposed to have as much if not more of an effect than the cap itself, which varied depending on the model from the IIC+ through to the Red Stripe. It's unclear whether or not C27 is 10 or 20pf in these, as simul-class amps were supposed to get 20pf. I've seen conflicting information, my gut says all greens are 20pf, all simulclass through to the reds were 20pf, 60/100w through to the reds were 10pf and blues are all 10pf but I don't know. Another IIC+ component I've only seen mentioned once online is the cap at C36 which works with the 5 band EQ.


The main differences are

(1) the resistor in parallel to C27 which is 2M2 in the Blue/Green and 3M3 in the IIC+ and up to Red. This affects mainly the gain in the clean and crunch (R1 and R2) modes, as it forms a voltage divider together with the 470k resistor to ground. In theory it should also affect the lead mode but in practice this effect is swamped by the lead mode as the gain is much higher there, and

(2) the voltage dividers after the second gain stage of the lead circuit - 470k II 120pf to 470k II 680pf in the Blue/Green vs. 220k II 250pf to 100k II 500pf. This means the Blue/Green has more gain and low end, and a bit less high end, so the missing C30 may be a compensation for that.

lions wrote:
Someone with a green stripe said that the "phase inverter" cap on theirs was .1 rather than 0.47 as in the IIC+, however I don't know where to look for this. I'm guessing it's one of the big orange drop sprague ceramics but I can't figure out which cap he's referring to. There are a whole bunch of 0.47 and .1 caps around V5. He's not referring to C516 by the way, which is already a 0.47 in the Blue and Green Stripes onwards.


There are four .1 caps in the Mark IIC+ and III phase inverters: the input, the grounded grid input and both outputs. The .1 caps on the outputs were standard on the blackface Fender amps which inspired the Mark series so that is nothing special. The .1 cap at the grounded grid side is also a standard value found in every blackface Fender. The only unusual .1 choice is at the input of the phase inverter but you have to see this in conjunction with the grid load resistors of 100k and 150k - the blackface Fenders have 1 meg each.

lions wrote:
The 680k resistor after the lead input and LDR in the lead section I can't find for the life of me on my blue stripe. There's no 680k resistor in V3A or V3B when I look at my amp. I can see a 680k resistor near c506, which means it could be the 680k I'm after circuit-wise given c506's schematic proximity to the lead circuit but I'm not so sure, my ability to read these things is pretty rudimentary.


Look at the lead drive input and follow the connection it goes to - the 680k resistor should be connected to this point as well.

Cheers Stephan


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PostPosted: Fri Feb 23, 2018 8:41 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 120
I have a verified Black Stripe schematic if you're interested? (Minus some of the R2 section as I'm still getting my head around that).

EDIT. Links removed due to old version. Full version below

Cheers,

Jon


Last edited by jrb32 on Thu Apr 12, 2018 9:32 am, edited 3 times in total.

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PostPosted: Fri Feb 23, 2018 9:20 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 120
I've updated my schematic with the loylo red stripe schematic, so hopefully we have a fairly decent Black Stripe and a Red Stripe schematic now:

EDIT. Links removed due to old version. Full version below

I wasn't sure about the R2 channel as we've measured something different so I've left that mainly unchanged but it's not essential to the rest of the circuit.

I wouldn't be 100% sure of values until this can be verified by someone with a Red Stripe.

Quote:
I've updated Loylo's Red Stripe schematic with values I've been able to work out with my amp or find in others:


Could you upload this image to google drive with a shareable link? I can't see the image at all I'm afraid on here.

Thanks,

Jon


Last edited by jrb32 on Thu Apr 12, 2018 9:32 am, edited 2 times in total.

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PostPosted: Fri Feb 23, 2018 9:48 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 120
Blue Stripe schematic (from a low version I found on sloclone forums by McBarry) so is probably very inaccurate (mainly due to my reading skills) but is a start and follows the great info from Stephan! Please update with anything you find on yours :)

EDIT. Links removed due to old version. Full version below

Thanks,

Jon


Last edited by jrb32 on Thu Apr 12, 2018 9:32 am, edited 2 times in total.

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PostPosted: Fri Feb 23, 2018 10:49 am 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 65
Does that work now? There's a typo at the unnamed pin cap, it's 500pf not 500f on the blue stripe!

Image

I'm not sure where to ask this but how important is the temperature coefficient on resistors? When I've been buying from suppliers I've tired to go as close to 0 as possible, but I've had to buy some on eBay as some specific values aren't in stock elsewhere online. Will any metal film resistor be ok?


Last edited by lions on Tue Mar 06, 2018 4:44 am, edited 2 times in total.

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PostPosted: Fri Feb 23, 2018 10:54 am 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 65
darkbluemurder wrote:
lions wrote:
One big myth is that the Blue Stripe is the same as the Red stripe minus the C30 mod. There are lots of component values that were changed between them. The Green and Blue stripes also have a different resistor alongside the C27 capacitor that is supposed to have as much if not more of an effect than the cap itself, which varied depending on the model from the IIC+ through to the Red Stripe. It's unclear whether or not C27 is 10 or 20pf in these, as simul-class amps were supposed to get 20pf. I've seen conflicting information, my gut says all greens are 20pf, all simulclass through to the reds were 20pf, 60/100w through to the reds were 10pf and blues are all 10pf but I don't know. Another IIC+ component I've only seen mentioned once online is the cap at C36 which works with the 5 band EQ.


The main differences are

(1) the resistor in parallel to C27 which is 2M2 in the Blue/Green and 3M3 in the IIC+ and up to Red. This affects mainly the gain in the clean and crunch (R1 and R2) modes, as it forms a voltage divider together with the 470k resistor to ground. In theory it should also affect the lead mode but in practice this effect is swamped by the lead mode as the gain is much higher there, and

(2) the voltage dividers after the second gain stage of the lead circuit - 470k II 120pf to 470k II 680pf in the Blue/Green vs. 220k II 250pf to 100k II 500pf. This means the Blue/Green has more gain and low end, and a bit less high end, so the missing C30 may be a compensation for that.

lions wrote:
Someone with a green stripe said that the "phase inverter" cap on theirs was .1 rather than 0.47 as in the IIC+, however I don't know where to look for this. I'm guessing it's one of the big orange drop sprague ceramics but I can't figure out which cap he's referring to. There are a whole bunch of 0.47 and .1 caps around V5. He's not referring to C516 by the way, which is already a 0.47 in the Blue and Green Stripes onwards.


There are four .1 caps in the Mark IIC+ and III phase inverters: the input, the grounded grid input and both outputs. The .1 caps on the outputs were standard on the blackface Fender amps which inspired the Mark series so that is nothing special. The .1 cap at the grounded grid side is also a standard value found in every blackface Fender. The only unusual .1 choice is at the input of the phase inverter but you have to see this in conjunction with the grid load resistors of 100k and 150k - the blackface Fenders have 1 meg each.

lions wrote:
The 680k resistor after the lead input and LDR in the lead section I can't find for the life of me on my blue stripe. There's no 680k resistor in V3A or V3B when I look at my amp. I can see a 680k resistor near c506, which means it could be the 680k I'm after circuit-wise given c506's schematic proximity to the lead circuit but I'm not so sure, my ability to read these things is pretty rudimentary.


Look at the lead drive input and follow the connection it goes to - the 680k resistor should be connected to this point as well.

Cheers Stephan


Thanks for the info!


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PostPosted: Mon Mar 05, 2018 9:04 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 65
Updated; missed a few values - a recent II+ puts the resistor by the pull deep at 1.5k, an older one at 1k so this appears to have been variable.

Image


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PostPosted: Sat Apr 07, 2018 10:47 pm 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 65
Updated using jrb's verified IIc+ schematic:

EDIT: I think the 10k resistor near the 84-removed cap is wrong here.

Image


Last edited by lions on Wed Jul 25, 2018 4:14 pm, edited 1 time in total.

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PostPosted: Mon Apr 09, 2018 6:18 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 120
That's great thanks! Do you mind if I take this idea and redraw my schematics with the color coded component value for each stripe and upload? I think there are a few errors in Loylo's schematics but I could be wrong! It also isn't complete obviously and misses the power section, EQ supply, reverb etc

Once I get my Black Stripe fully traced (all done now apart from the LDR switching and High Voltage supply!) I will also draw up a layout for the PCB where components are for a III. This way people can check their stripe versions easier to confirm values, or if people can send me high res pics of the board I can do this for you. I don't have access to any other III apart from a black stripe but am basing my info upon what you've said about your blue stripe and people who have traced their red and blue stripes in the past (Loylo and McBarry respectively) and some info on the purple stripe from darkbluemurder.

On your edited schematic the 10K to the relays off the middle pot is actually R126. I'm not sure about LDR1 and LDR6 but that is where the 'Treble Shift' takes place for info. I will double check this.

I'll also check C26 for the EQ and where it should be. I know tracing the EQ section yesterday of my III there were some differences between the IIC+ verified sloclone schematic and my III, but then again that has errors so cannot be sure.

Thanks,

Jon


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PostPosted: Mon Apr 09, 2018 9:04 am 
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Mark I

Joined: Mon Dec 08, 2014 2:00 am
Posts: 22
Okay Guys Listen to this a tell me how close is my iii blue to the IIc++ ? i am still working on the mod.

https://www.youtube.com/watch?v=FC71ciVf2PM

awaiting your comments.


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PostPosted: Mon Apr 09, 2018 11:19 am 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 65
jrb32 wrote:
That's great thanks! Do you mind if I take this idea and redraw my schematics with the color coded component value for each stripe and upload? I think there are a few errors in Loylo's schematics but I could be wrong! It also isn't complete obviously and misses the power section, EQ supply, reverb etc


Yeah definitely, go nuts, these are just to show the differences between the stripes as much as anything as there's a lot of misinformation/incomplete information out there, you'd do them much more justice than my ms paint skills do. I don't know if any parts of the red stripe schematic are wrong as I don't have a reference Red Stripe, just my Blue. He traced his himself so I would imagine it's accurate, it's the best we've got for now either way.

Quote:
Once I get my Black Stripe fully traced (all done now apart from the LDR switching and High Voltage supply!) I will also draw up a layout for the PCB where components are for a III. This way people can check their stripe versions easier to confirm values, or if people can send me high res pics of the board I can do this for you. I don't have access to any other III apart from a black stripe but am basing my info upon what you've said about your blue stripe and people who have traced their red and blue stripes in the past (Loylo and McBarry respectively) and some info on the purple stripe from darkbluemurder.


I would take some photos now for you but my camera is bust, but I will as soon as I can. You're always welcome to come down and have a look at my blue stripe like we were talking about!

Quote:
On your edited schematic the 10K to the relays off the middle pot is actually R126. I'm not sure about LDR1 and LDR6 but that is where the 'Treble Shift' takes place for info. I will double check this.


Cool thanks, I'll amend it asap. Was slightly confused about it. The other difference I noticed was the 10k between the fx return and the grid of v2b which wasn't in the original red stripe schematic.

Quote:
I'll also check C26 for the EQ and where it should be. I know tracing the EQ section yesterday of my III there were some differences between the IIC+ verified sloclone schematic and my III, but then again that has errors so cannot be sure.


I was going from a post on the rig talk forum if I remember correctly. It's where I found out about the c32 placement and a few other things that weren't easily found here without some really intense post trawling.


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PostPosted: Tue Apr 10, 2018 5:19 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 120
Full III Black Stripe schematic for you guys! This has taken ages sorry for the delay.

(well about 95% done technically! Some final things to finish off and double check) Everything with a R, C or D, LDR etc number has been verified and traced by me. This includes LDR supply, EQ etc and should give you an idea about how things work exactly! I also finally understand how the R2 circuit works! Hooray!

I will add the Red Stripe and Blue Stripe info to this and go from there along with Purple and Green stripe info I have. I have some questions regarding a few weird things that don't make sense to me but will start a new forum about this. The main bits that don't make sense are:

R133 and C28 - what do they actually do? These are the only weird bit that seems to distinguish a III from a IIC+ fully. If you removed them, in R1 mode it would be the same as a IIC+ preamp layout wise. I notice that similar things are added to the Quad preamp Channel 2. Perhaps this is the big elephant in the room we're not discussing?

R2 mod - I know people say to replace R130 with a variable resistor or POT, but wouldn't R109 be a better candidate for overall R2 volume for the attenuator? Or would this reduce the overall effect of the R2 channel instead?

Also: LDR1A is only for the Treble Shift, not LDR6. LDR6 should deal with the Lead Master. Anyway it would be good to use the images below instead for full comparison from now on:

EDIT - LINKS UPDATED WITH LIONS CORRECTIONS BELOW

Image
Image
Image
Image
Image
Image
PDF Link https://drive.google.com/open?id=1HwhczDup8EDBPKyCUK4CV19XKAcg0aeT

Thanks,

Jon


Last edited by jrb32 on Fri Apr 13, 2018 6:28 am, edited 4 times in total.

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PostPosted: Thu Apr 12, 2018 5:40 am 
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Mark II

Joined: Wed Jan 31, 2018 8:32 am
Posts: 120
I've also started putting the Red, Blue and some Purple stripe info similar to Lions schematic. It also explains the III Reverb Mod and the R2 mod. See above for info!

However, I have no info on the EQ and Power Sections or High Voltage Supply for any of the other III stripes. This is because I do not own these and need people to verify these. I will get a PCB board layout drawn up soon to make this easier for people to do to find where components are, as currently you have to desolder the component from the board to find the R or C number! However, I can go no further so far.

This means, at least, that I can mod my Black Stripe to a IIC+ for the preamp, lead and EQ sections, (power amp is the same on a Black Stripe apart from presence cap.) while maintaining the R2 channel, especially as I have the early IIC+ transformers in mine. No crazy board mods required! It does involve removing R133 and C28, which I've put a message up about on here, and this could be the big elephant in the room regarding the preamp section we're missing?

For comparison of sections, please see my IIC+ schematic which is as accurate as you will get until one can be traced and verified. However, I have no concrete info on the Reverb or the High Voltage Supply for a IIC+ so cannot compare these at the moment.

I will add these IIC+ values and differences in one image at a later stage:

IIC+ schematic: https://drive.google.com/open?id=1ljGYjZx_34k5PMcLGT97brHIuMjGJ34C

Thanks,

Jon


Last edited by jrb32 on Thu Apr 12, 2018 8:29 am, edited 1 time in total.

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PostPosted: Thu Apr 12, 2018 8:02 am 
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Mark II

Joined: Thu Feb 22, 2018 11:37 pm
Posts: 65
Some of those Blue Stripe values are wrong. The values I entered were taken from my actual blue stripe rather than McBarry's (which is wrong in some places - some values have been written over with red stripe ones).

R153 is 332k on a stock blue
C30 is absent in blue stripes, not .001
C21 is 180pf not 120pf on a stock blue

Keen to see how the IIC+ affects your black stripe.


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