S.I.R. 100W SuperLead Schematic pt. II

Everything from original vintage Marshalls to reissues.

Moderator: VelvetGeorge

User avatar
CoffeeTones
Senior Member
Posts: 958
Joined: Mon Oct 11, 2010 9:52 pm
Just the numbers in order: 7
Location: USA

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by CoffeeTones » Mon Jun 10, 2019 1:18 pm

blacklabel wrote:
Mon Jun 10, 2019 12:15 pm
So this is what I should do, replace those 3 blue ones.
For the shielded cable I don't know what to do, but I will also try to add a 33pF or 47pF capacitor welded directly to the valve pin in this way as in the image above. I don't know who suggested it

Image
You are correct on the 470nF cap and 22K resistor. The small blue cap bypassing the plate resistor may be the right value - 2kV is the voltage rating. The number under it should be 221 which is 220pF. It seems to be, but the pic is not 100%.

Small pF value caps from plate to grid, at the tube socket can be used, but the caps will put voltage on the input jack if they short circuit. You'd really need to put a blocking cap at the input to safely use those mods. 15pF to 47pF has been discussed, with 15pF to 22pF being preferred, IIRC.

User avatar
CoffeeTones
Senior Member
Posts: 958
Joined: Mon Oct 11, 2010 9:52 pm
Just the numbers in order: 7
Location: USA

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by CoffeeTones » Mon Jun 10, 2019 1:49 pm

Scratch that idea for now :roll:
Last edited by CoffeeTones on Mon Jun 10, 2019 1:52 pm, edited 1 time in total.

blacklabel
New Member
Posts: 22
Joined: Mon Jan 20, 2014 7:28 am
Just the numbers in order: 13492

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by blacklabel » Mon Jun 10, 2019 1:49 pm

CoffeeTones wrote:
Mon Jun 10, 2019 1:18 pm
Small pF value caps from plate to grid, at the tube socket can be used, but the caps will put voltage on the input jack if they short circuit. You'd really need to put a blocking cap at the input to safely use those mods. 15pF to 47pF has been discussed, with 15pF to 22pF being preferred, IIRC.
So this little cap is used to replace the shield cable 'correct-but unsafe', to have the same effect?
in my case there is the shield cabl, but it's not correct being safe, right?

User avatar
CoffeeTones
Senior Member
Posts: 958
Joined: Mon Oct 11, 2010 9:52 pm
Just the numbers in order: 7
Location: USA

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by CoffeeTones » Mon Jun 10, 2019 2:00 pm

blacklabel wrote:
Mon Jun 10, 2019 1:49 pm
CoffeeTones wrote:
Mon Jun 10, 2019 1:18 pm
Small pF value caps from plate to grid, at the tube socket can be used, but the caps will put voltage on the input jack if they short circuit. You'd really need to put a blocking cap at the input to safely use those mods. 15pF to 47pF has been discussed, with 15pF to 22pF being preferred, IIRC.
So this little cap is used to replace the shield cable 'correct-but unsafe', to have the same effect?
in my case there is the shield cabl, but it's not correct being safe, right?
Yes, to get a similar effect as the hot shield. Your shielded wire is correct for most standard config, but not what #34 was shown to have.

blacklabel
New Member
Posts: 22
Joined: Mon Jan 20, 2014 7:28 am
Just the numbers in order: 13492

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by blacklabel » Mon Jun 10, 2019 2:05 pm

CoffeeTones wrote:
Mon Jun 10, 2019 2:00 pm
Yes, to get a similar effect as the hot shield. Your shielded wire is correct for most standard config, but not what #34 was shown to have.
Now it's all clear!
next Thursday I will make these changes, so I could also change the shield cable to make it like in # 34 (although I don't know how to do it) or leave it like this and add only the little cap.

User avatar
CoffeeTones
Senior Member
Posts: 958
Joined: Mon Oct 11, 2010 9:52 pm
Just the numbers in order: 7
Location: USA

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by CoffeeTones » Mon Jun 10, 2019 2:20 pm

You can do whatever you feel safe with, but the cap from plate to grid is fine with a blocking cap at the input - those are not too hard to accomplish. IMO, the hot shield is not worth it. Most shielded cable of that size is not rated for proper voltage. It's harder to accomplish safely.

blacklabel
New Member
Posts: 22
Joined: Mon Jan 20, 2014 7:28 am
Just the numbers in order: 13492

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by blacklabel » Mon Jun 10, 2019 4:00 pm

Excuse me CoffeeT this will be the last question :D
could you tell me if there is a precise value to buy for this blocking cap and where should I get it soldered to the input?
I should say what to do to the luthier, so I don't know if he knows it. They are generally not even technicians :D

Image
Image

User avatar
CoffeeTones
Senior Member
Posts: 958
Joined: Mon Oct 11, 2010 9:52 pm
Just the numbers in order: 7
Location: USA

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by CoffeeTones » Mon Jun 10, 2019 4:41 pm

Save this because I'll remove it soon. Use .22uF 400V to 630V rated cap. .1uF would work if need be. The 1M resistor must go from the cap's output to ground. https://scontent-atl3-1.xx.fbcdn.net/v/ ... e=5D86DE4F

blacklabel
New Member
Posts: 22
Joined: Mon Jan 20, 2014 7:28 am
Just the numbers in order: 13492

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by blacklabel » Mon Jun 10, 2019 5:19 pm

Thank you CoffeeT, i hope he will understand :toast:

User avatar
CoffeeTones
Senior Member
Posts: 958
Joined: Mon Oct 11, 2010 9:52 pm
Just the numbers in order: 7
Location: USA

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by CoffeeTones » Mon Jun 10, 2019 5:30 pm

Small pF cap would go from pin 6 to 7 not 6 to 8 as shown. I only re-drew the input jack wiring.

Unique
Senior Member
Posts: 136
Joined: Wed Oct 02, 2013 12:48 pm
Just the numbers in order: 13492

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by Unique » Tue Jun 11, 2019 9:37 am

CoffeeTones wrote:
Mon Jun 10, 2019 1:09 pm
The #34, .1uF versus .68uF presence cap is debatable and there's more to that subject than I care to get into again. You are misleading by saying to remove the present pot mounted, 4k7 tail shunt / part of the negative feedback circuit. By doing that, he will not have a proper ground source for the PI and the negative feedback circuit will be incomplete. I see Santiago has the 25k pot wired as shunt on the schematic, but it must be an error. I'll have to dig up the pics.

I have not looked at the pics of the #34 original lately, but it may have had the 5k presence pot / circuit with .1uF or .68uF cap. That 5k pot is wired much differently than the 25k pot circuit, in which case the 5k pot is acting as the 4.7k tail shunt and part of the NFB ratio divider. Anyone building the mod should try both circuits and decide which is preferable for themselves. Check out the 68' Plexi and 2203 schematics or layouts to view the presence circuit differences described above.
I've seen another stock '84 JCM 800 2203, identical to #34 with the exact same big blue presence cap and it was indeed a .1uF. Santiago also confirmed this for me. Then I was able to locate one for myself through a friend.

As far as the resistor on the presence pot goes, I have clear enough pictures of #34's presence circuit and there is no resistor on the pot. I took mine off and presto, there was part of the sound I was missing. Yes, it is possible that #34 originally came with a 5k pot, but since Marshall had quit using those pots some years prior, I seriously doubt it is. Not only that, but with #34's presence pot you can see the old solder left behind on the back of the pot from where the resistor was removed. The sound of my amp after removing this resistor was the confirmation for me that what I see in the pics is true. My #34 modded amp is an '83 JCM 800 2203 that is about 4 months older than #34 and it did not come with a 5k pot and it was equipped with a .1uF presence cap as well. However, my original presence cap looked like what is in the pics above, the box type, and it was also tan in color. Other than that, my amp is identical to #34 in every way as well. The '84 JCM 800 2203 I looked at, did not have a 5k pot as it also had the 4k7 resistor on the pot with the same big blue .1uF presence cap that is in #34. So I'm pretty sure #34's presence cap is a stock .1uF. I tried a .68uF cap and it didn't quite sound right either. It sounded good, but not as correct as the .1uF. So I believe that with my amp and this other amp both having the same presence circuit, and that other amp coming with an identical big blue .1uF presence cap like what is in #34 as stock and a 4k7 resistor on the back of the pot, that this was enough for me to believe that #34's was no different.

I will admit this, we do not know if anything from AFD100 discovery video was staged, but according to Santiago, it was as everyone seen it. He is also adamant that the schematic was exactly as he saw it in the amp. If you look at the schematic, it doesn't show the resistor on the presence pot, but it also looks as if that part was cut off. The pot is listed as being a 25k pot. And with the pics I have of #34, there is definitely no resistor on the pot.

Another thing people have missed on the schematic is that the resistor on the hot-shield is at the input and not the socket. This is also clearly shown in the pics of #34's. You can clearly see the resistor at the input. With my amp, having the resistor at the input does make a difference in the sound compared to having it at the socket.

User avatar
CoffeeTones
Senior Member
Posts: 958
Joined: Mon Oct 11, 2010 9:52 pm
Just the numbers in order: 7
Location: USA

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by CoffeeTones » Tue Jun 11, 2019 11:58 am

Unique, my main point is that simply taking the 4.7k out and not rewiring the 25k presence like the 5k circuit is not a technically sound idea. You refer to the Santiago schematic, so look at it again. The 25k circuit is shown to be configured as the 5k circuit (with a 25k pot), not the 25k circuit with only the 4.7k removed. You mentioned nothing about rewiring the 25k circuit, you said only remove the 4.7k. If you do not reconfigure the 25k circuit wiring to the 5k circuit, retaining the 25k pot, the PI and NFB will have issues. If you reconfigure the circuit to 5k spec with 25k pot, you will have properly grounded the PI and provided NFB, but you now have a 47k (total) tail and 25k instead of 4.7k (resistor)to 5k (pot) as NFB shunt, thereby altering the NFB ratio and PI cathode DC, among other things. I did not say it will not work if wired correctly. Your initial post suggested to wire it improperly. How is it wired in your clear pics of #34?

I didn't say which presence cap value was used as an absolute. If Santiago says it was definitely .1uF, so be it. He is probably the only person who would know at this point. I believe the investigation video of #34 was legitimate. Still, the .1uF vs .68uF is an open question for some people. I know .1uF is the only value that sounds right in #36. I have not done anything with #34 in a while now. I do not like the .68uF in most situations, but it sounds right in some amps such as the RT mod amps you'll find on youtube. #34 is a thinner sounding amp, so someone who wants to thicken the sound may prefer .68uF, although .22uF, .33uF and .47uF work much better depending on the pot value used.

I do wonder which resistor value was used at the PI output grids in #34. I don't recall the details of what that specific amp would have came stock with. That doesn't matter much because any value change could have been made.

How about posting the clear pics you have of #34. I don't see any reason not to at this point.

I am surprised that #34 gets such a great AFD tone in one of those vids. Of coarse Slash was playing but still, the amp was sounding right.
:toast:

blacklabel
New Member
Posts: 22
Joined: Mon Jan 20, 2014 7:28 am
Just the numbers in order: 13492

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by blacklabel » Wed Jun 12, 2019 3:35 am

Are you talking about this?
where is the 4.7k resistance?

with zoom: https://www.mediafire.com/convkey/008b/ ... j2e7zg.jpg

Image

User avatar
CoffeeTones
Senior Member
Posts: 958
Joined: Mon Oct 11, 2010 9:52 pm
Just the numbers in order: 7
Location: USA

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by CoffeeTones » Wed Jun 12, 2019 8:44 am

That is one view. It's not clear enough to say. There appears to be something "brownish" with solder at the bottom, on the right side of the pot and it appears to be connected as the normal 25k circuit. The 4.7k resistor is most often soldered to the buss wire, not the back of the pot. That is where the components are usually mounted in the 25k circuit, but is not a very clear image. Santiago drew it as a 25k pot with the cap connected as in the 5k circuit, or it's a simple mistake in his schematic. One thing for sure, removing the 4.7k and leaving the cap connected as in the 25k circuit, is the wrong thing to do. It will affect aspects of the PI operation. Without the 4.7k and with improper wiring, the PI cathode has no proper ground because the presence cap, as connected in the 25k circuit, blocks the DC from ground. I repaired an amp with this mistake once. Before the repair, the PI voltages were all screwed up and it sounded like poo. Try it all three ways if you want to. Just let us know your thoughts afterward.

Image

Unique
Senior Member
Posts: 136
Joined: Wed Oct 02, 2013 12:48 pm
Just the numbers in order: 13492

Re: S.I.R. 100W SuperLead Schematic pt. II

Post by Unique » Wed Jun 12, 2019 10:30 am

Coffee first let me say that your circuit knowledge is unmatched in this thread and I have learned a lot from you. So I can't really comment on the technical aspects as you do. All I can say is what I see, with the knowledge I have, and speak from my own experiences. I have had this resistor off for about 3 years and have never had any issues and everything works as it should. Although I do seem to go through a lot PI tubes? Could that be the reason?

From my understanding, the resistor on the presence pot is only there to keep DC off the pot with a 25k pot as DC can be scratchy sounding. From my experience, removing this resistor did not make the amp sound that scratchy, more like a bit more 'raspy' sounding. I found removing this resistor is what gives that wah sound some depth and it's woolliness. Something I don't really hear from most #34 mods outside of #34.

When I first noticed that the resistor was not on the presence pot in #34, I researched this as much as I could to learn more about it. From what I could see in the pics, and then compared it to how my presence circuit was wired before removing that resistor in my amp, I seen no difference other than the absentee resistor. From all I read, it seemed to be no big deal removing this resistor other than your allowing for more DC on the pot. I found this to be a key part of #34's sound. Whether it's right circuit wise or not as you say, I'm not sure, this is how #34 appears to be set up as far as I can tell. I'm not saying what you've stated is incorrect, you are probably right. I will have to take another look at the schematic Santiago made. But if I remember, it gets cut off right there and does not show the 4k7 resistor.

As far as the pics goes, I stated them being "clear enough" to see what is what. I do have the same pics of #34's circuit from every angle as anyone else who has went through that video frame by frame. I even spent a lot of time trying to enhance them, brightening them up and sharpening them some to clear them up a little. But they are clear enough to see what is what.

Now here is another mystery that really stumps me. And that is, there is no 150k resistor on the back of the PA pot in #34, neither is there a bright cap. That little brown mark that everyone says is a resistor is actually a burn mark on the green wire, where Frank or someone hit it with the iron. Zoom in on the photo's, enhance the color and brightness, and you will see it clearly. I tried my amp without these two components and it didn't sound too good. I believe without a doubt that they are part of the mod. So why are they missing?

There is three possibilities for this I can think of. One, when they shot the video for the AFD100 vlog, they had taken the components off for whatever reason and did not get them back on in time for the video shoot. I also thought about this for the presence resistor. But it doesn't make much sense that they would be removing components unless they were trying to measure them, or something. Even then, that doesn't really seem like a good reason.

Two, it's possible that Slash had a 150k pot installed for the PA and did not need the 150k resistor anymore. But from what I can tell, the pot looks to be the original. I think a newer pot would show a slight difference in color and age when looking at the pics and would stand out somewhat. I could be wrong, but that is my thinking.

And three, which to me seems most likely, I think that maybe at some point Slash had them removed so he could have more options with setting the PA. In the early days when recording he normally set his PA between 1 and 2 (as per Adam Day). As of late, when you look at the studio track sheets for his first solo album he is now setting the PA between 5 and 7, and you see this also in pics of #34 in studio settings on the web. If you do that with the 150k on the back of the PA pot, it doesn't sound too good, and definitely not like what you hear with Slash's sound at anytime. But the tubes your using definitely can have a huge effect on this. Since he doesn't use any kind of attenuator or PPIMV with #34 he really has no need for the bright cap either. I believe these components were there in the early days, but have since been removed. Frank still continued to implement these in his #34 mods when he did them. But he also did a few things different today than how he did it in #34 from the pics I've seen of Franks more recent #34 mods.

Now here's where things seem to get cloudy. Santiago has stated that Slash told him nothing in the amp has ever been changed since he's got it. So that leaves this a mystery to me. Because without the 150k on the back of the PA pot, the amp loses a lot of it's drive, especially with the lower PA settings, and just sounded kind of flat to me. But this would be the case since that is what that resistor does, lowers the pot's value to achieve more gain at lower settings, correct?

As someone who has worked in studios and understands the recording process, the changes we hear in Slash's sound from the old days to his more current work, there is a difference in the sound of #34. But I believe that most of this is due to how it was recorded, the studio gear used during the process, the mics used, preamps, consoles, ect, and how it was mixed, all plays a part in that. But I also think that the changes in sound is also due to the tubes he used back then compared to what he uses now, the speakers he's currently using in the studio (he tends to favor the V30's now over his usual greenback cab he used mostly during the early days), and how he is biasing the amp. Then you figure in the settings he uses today compared to those that's marked on the front of the amp (there's quite a few more than the obvious big magic marker settings you can easily see). But without the 150k on the PA, none of those settings sounded too good, or should I say correct.

All in all, my mod is exactly like what you see in the pictures with the presence cap removed, except I have the 150k on the back of the PA pot, and a bright cap (that came stock and I left it there), and it sounds spot on. It's only my playing that makes the biggest difference.

Post Reply