New Amp Build Thread- Modulus Marshbar

[bfool]

I had the same thing with the picklist on the Marshbar kit. Same as yours I think they went with an older version as I was missing a couple things and had a couple left over components that weren't on the layout. It wasn't a big deal for me and no need for Modulus to ship one resistor halfway across the globe. I either already had stuff on hand or grabbed out of the Frankentone kit and will replace later on my next mouser order.

Cool - I’m in the UK so getting Modulus to post a resistor doesn’t seem unreasonable - but yes shipping one to the US is a bit excessive! As far as I can tell that 220k was the only error on the Frankentone list - I do have a couple of extra components but I think that is because they are made obsolete by the 65/68 mod I included…

 

[MadAsAHatter]

Sorry for the snag.. it will be interesting for a newb like me to find out what turned out to be the issue and how you figured it out.

Something is shorting B+ to ground and probably took out a rectifier diode in the process. That’s my assumption. Outside the obvious that the tubes are all in working order.

@glpg80 You were spot on about the B+ going to ground. Other than the HV fuse popping it didn't take anything else out.

I just got word back from the amp tech (Rob DeAntonio). Turns out the core culprit was an error on the layout. Rob said the layout showed an extra wire that was grounding out the B+ and audio signal. So I followed everything as the layout showed, but what was shown had an issue.

All that needed to be done was snip that ground wire out and replace the fuse that popped. Rob said while he was in there he slightly redid the general grounding so it would be quieter. The layout has everything being grounded near the input jacks. He split it so the preamp & PI side went to the input jack side and the power amp portion now grounds on the opposite side of the chassis.

I'm happy it was something simple, but don't feel too bad about missing what was going on. I don't have enough experience to have known that wire shouldn't have been there in the first place. At least I was able to make it as far as figuring out the problem was on the power amp side.

On a high note Rob gave me really positive feedback on my work. He said everything looked really tidy and all the solder joints were well done. He said if he had to get really nitpicky on critiquing my work; wires on the tube pins were fine, but could have been snipped a little more flush to be 100% they wouldn't make accidental contact with something.

Looks great... Does Modulus provide plenty of wire?

Sorry I missed this question from earlier in the thread. Yeah, Modulus provided plenty of wire.
When running the wires I try to leave them long enough to give enough room to trim back, but not so long to where I'm wasting a lot of it. Doing that left me with probably enough wire to use for a second build.



For anyone who may give this build a try...
1. I'm not sure which wire was drawn in error on the layout. I don't have anything in front of me right now. Once I get the amp back to compare I'll post it.
2. Rob noted the way the presence is designed, it has DC on the presence pot. He said Marshall did it this way on some amps back in the 70's and a few builders still do it too. He said when you turn the presence knob it may crackle a bit like when you have a dirty pot, but this is 100% normal. So nothing bad, just something to be aware of.

 

[jchrisf]

I'm glad you got it resolved @MadAsAHatter and it wasn't anything you did wrong. I'm looking forward to hearing it when you get it back. I've always been a little leery of Modulus and I think I will steer clear of them after reading of your troubles. Their amps look interesting but I've never heard much completely positive about them. In the end you'll have a great amp but it's been a little trouble getting there. With Mojotone, everything was exceptional for me... think I'll just stick with them.

 

[DanTravis62]

@glpg80 You were spot on about the B+ going to ground. Other than the HV fuse popping it didn't take anything else out.

I just got word back from the amp tech (Rob DeAntonio). Turns out the core culprit was an error on the layout. Rob said the layout showed an extra wire that was grounding out the B+ and audio signal. So I followed everything as the layout showed, but what was shown had an issue.

All that needed to be done was snip that ground wire out and replace the fuse that popped. Rob said while he was in there he slightly redid the general grounding so it would be quieter. The layout has everything being grounded near the input jacks. He split it so the preamp & PI side went to the input jack side and the power amp portion now grounds on the opposite side of the chassis.

I'm happy it was something simple, but don't feel too bad about missing what was going on. I don't have enough experience to have known that wire shouldn't have been there in the first place. At least I was able to make it as far as figuring out the problem was on the power amp side.

On a high note Rob gave me really positive feedback on my work. He said everything looked really tidy and all the solder joints were well done. He said if he had to get really nitpicky on critiquing my work; wires on the tube pins were fine, but could have been snipped a little more flush to be 100% they wouldn't make accidental contact with something.



Sorry I missed this question from earlier in the thread. Yeah, Modulus provided plenty of wire.
When running the wires I try to leave them long enough to give enough room to trim back, but not so long to where I'm wasting a lot of it. Doing that left me with probably enough wire to use for a second build.



For anyone who may give this build a try...
1. I'm not sure which wire was drawn in error on the layout. I don't have anything in front of me right now. Once I get the amp back to compare I'll post it.
2. Rob noted the way the presence is designed, it has DC on the presence pot. He said Marshall did it this way on some amps back in the 70's and a few builders still do it too. He said when you turn the presence knob it may crackle a bit like when you have a dirty pot, but this is 100% normal. So nothing bad, just something to be aware of.

Man that would drive me nuts that the diagram they provided was non-working

I'm so stoked this thing is up and running, that head shell is unbelievable aesthetically pleasing

Once you get it plugged in let's get some clips man!

 

[glpg80]

@glpg80 You were spot on about the B+ going to ground. Other than the HV fuse popping it didn't take anything else out.

I just got word back from the amp tech (Rob DeAntonio). Turns out the core culprit was an error on the layout. Rob said the layout showed an extra wire that was grounding out the B+ and audio signal. So I followed everything as the layout showed, but what was shown had an issue.

All that needed to be done was snip that ground wire out and replace the fuse that popped. Rob said while he was in there he slightly redid the general grounding so it would be quieter. The layout has everything being grounded near the input jacks. He split it so the preamp & PI side went to the input jack side and the power amp portion now grounds on the opposite side of the chassis.

I'm happy it was something simple, but don't feel too bad about missing what was going on. I don't have enough experience to have known that wire shouldn't have been there in the first place. At least I was able to make it as far as figuring out the problem was on the power amp side.

On a high note Rob gave me really positive feedback on my work. He said everything looked really tidy and all the solder joints were well done. He said if he had to get really nitpicky on critiquing my work; wires on the tube pins were fine, but could have been snipped a little more flush to be 100% they wouldn't make accidental contact with something.



Sorry I missed this question from earlier in the thread. Yeah, Modulus provided plenty of wire.
When running the wires I try to leave them long enough to give enough room to trim back, but not so long to where I'm wasting a lot of it. Doing that left me with probably enough wire to use for a second build.



For anyone who may give this build a try...
1. I'm not sure which wire was drawn in error on the layout. I don't have anything in front of me right now. Once I get the amp back to compare I'll post it.
2. Rob noted the way the presence is designed, it has DC on the presence pot. He said Marshall did it this way on some amps back in the 70's and a few builders still do it too. He said when you turn the presence knob it may crackle a bit like when you have a dirty pot, but this is 100% normal. So nothing bad, just something to be aware of.

Awesome that I nailed it and glad you got it figured out and working! Great job on the assembly!

In the future I can provide a helpful tip. Anytime you’ve completed a circuit and before turning it on, always, and I mean always, check with an ohm meter resistance from your source to ground. You don’t have to disconnect anything besides unplugging the amp and making sure caps are discharged - but just check it with a meter. You should always read open circuit or out of range from source to ground.

If you knew this before turning it on you would have seen a near zero short or numbers changing oddly and immediately known something’s amiss. From there you start lifting B+ connections in sections to isolate exactly where the fault exists until you find it.

Glad nothing else was damaged in the process. I probably would have replaced all of the rectifier diodes even if they measured good with a meter myself - typically they dont like the flyback of the PT when a fuse lets go. I’m not criticizing or critiquing just stating my own opinion as to why.

 

[MadAsAHatter]

I'm glad you got it resolved @MadAsAHatter and it wasn't anything you did wrong. I'm looking forward to hearing it when you get it back. I've always been a little leery of Modulus and I think I will steer clear of them after reading of your troubles. Their amps look interesting but I've never heard much completely positive about them. In the end you'll have a great amp but it's been a little trouble getting there. With Mojotone, everything was exceptional for me... think I'll just stick with them.

I think overall you'd be fine ordering from Modulus if you wanted something specific from there. There were a few hiccups, but nothing more than what I've heard about other companies. I remember at one time hearing Mojotone had some issue with their layouts. I guess the thing you have to remember is a lot of these kits aren't made for beginners. Most say up front that documentation is minimal and assumes/is best you have prior experience. I saw Modulus put out a couple new Class A amp kits. After the Frankentone I that might be my next project. That or I'm eyeing the Pig 100 from Ceriatone.

Man that would drive me nuts that the diagram they provided was non-working

I'm so stoked this thing is up and running, that head shell is unbelievable aesthetically pleasing

Once you get it plugged in let's get some clips man!

It's a little annoying the whole issue came down to an error on the layout diagram. If I knew more I probably could have spotted it rather easily, but it's all part of the journey of learning. That and I was happy to get positive feedback from a pro tech. That lets me know I'm not completely fucking up these builds.
Amp should make it back to me one day next week. I'll post a clip or two when it's back home and situated.

Awesome that I nailed it and glad you got it figured out and working! Great job on the assembly!

In the future I can provide a helpful tip. Anytime you’ve completed a circuit and before turning it on, always, and I mean always, check with an ohm meter resistance from your source to ground. You don’t have to disconnect anything - just check it with a meter. You should always read open circuit or out of range.

If you knew this before turning it on you would have seen a near zero short or numbers changing oddly and immediately known something’s amiss. From there you start lifting B+ connections in sections to isolate exactly where the fault exists until you find it.

Glad nothing else was damaged in the process. I probably would have replaced all of the rectifier diodes even if they measured good with a meter myself - typically they dont like the flyback of the PT when a fuse lets go. I’m not criticizing or critiquing just stating my own opinion as to why.

Yup, you were right on the money. Maybe one day I'll get to that level of troubleshooting.
I appreciate the compliment on the assembly. It means a lot coming from someone who knows what they're doing.
And thanks for that tip. I'm adding it to my amp startup notes.

 

[bfool]

Great to hear it is up and running and turned out to be something simple!

I just finished my Frankentone build (sounds awesome) - and I had to query a suspicious wire on the layout diagram. Turned out that Modulus had a screw up on their file server, and the version I had was one Michael had created for another customer to help troubleshoot a build and shouldnt have been on the website. They responded to my email and fixed the layout in about 5 mins which was good. So maybe a similar issue with yours? Be a good idea to let Modulus know if the layout on the website is still the same as the one you used... I'd also receommend downloading the latest layout before you start your Frankentone!

Interested to see how Rob modified your ground layout.... Do you know if he powered the amp up before he made that mod and how much quieter it made it?

Cheers

Dom

 

[MadAsAHatter]

The Marshbar made it back yesterday evening. I was able to give it a once over and quick test run when I got home from work today. The ground wire that was amiss was the one going from the middle coupling cap to the two 220K resistors (the blue line in the picture below). That wire was snipped out.

As far as the change in grounding scheme goes, I'm not 100% sure what Rob did. Most of the ground wires are under the turret board so I can't tell exactly what was moved. Overall I can tell he separated the coupling cap grounds and such from the preamp side then ran a wire from where the choke wires are on the board to the chassis. On the picture it's the brown & red wires to the left of the 47uf cap.

So that's the technical stuff. Now to the big question; how does it sound?

First off this is not a bedroom amp. It goes from zero to take your head off in an instant. Just my kind of amp. I was able to turn the volume up a bit, but really didn't get to fully let it open up and breathe. I'll probably be able to do that this weekend. The amp lives up to the description on their website.
Plexi mode sound like you'd expect a hot rodded plexi to sound. Nice thick saturation. This is probably my favorite mode
800 mode is a JCM 800. I was expecting a little more saturation out of this mode. It was more light crunch and I was hoping more for a heavy crunch. Regardless the tone is there and it sounds good.
SIR 34 mode I really can't compare since I never played an Marshall with that kind of mod before. I can say it sounds like a hot rodded JCM800. I suspect that's about how it's supposed to sound.

I'm happy things turned out to be a small error on the layout and not something I completely fucked up.
Overall I'm very pleased with the design and tone of the amp.

 

[Floyd Eye]

Looks great brother but I think I’ll wait for the wisdom from our residential expert before I buy one. I mean I could smoke the tranny if I hook the wrong speaker up to it.

 

[311boogieman]

Glad you got it sorted and thanks for the update. Can't wait to hear this beast.

 

[S̷͖͑m̵͎͂á̵̺s̸͚̈́h̴̬̑]

Thing looks beautiful. Can't wait to hear it

 

[bfool]

Nightmare! I think I see how that error occured - that wire is legitimately on the 20 Watt version, so probably a cut and paste error when the design was upscaled to 50W. I have a copy of the 50W layout I downloaded 1st April and that wire isnt on there - so Modulus have had it fixed for a while: presumably straight after the first time someone powered one on, since it had no hope of working! Feel for you - think only someone with a serious amount of experience would be able to spot that error - no way I would have...

Great you have it working now though - and also nice to have had it reviewed. It will be awesome when you get to crank it!

No question these 50W marshalls are flippin loud though. I can recommend the JohnH attenuator as another light project. The frankentone sounds good through the one I built - although as designed there is still not enough attenuation when the amp is dimed, so I had to build another -14db stage to go after the main attenuator it to get it down to bedroom level.

 

[The Polish Hammer]

Looks great!
No cupholder? Did you triple solder?

 

[MadAsAHatter]

Nightmare! I think I see how that error occured - that wire is legitimately on the 20 Watt version, so probably a cut and paste error when the design was upscaled to 50W. I have a copy of the 50W layout I downloaded 1st April and that wire isnt on there - so Modulus have had it fixed for a while: presumably straight after the first time someone powered one on, since it had no hope of working! Feel for you - think only someone with a serious amount of experience would be able to spot that error - no way I would have...

Great you have it working now though - and also nice to have had it reviewed. It will be awesome when you get to crank it!

No question these 50W marshalls are flippin loud though. I can recommend the JohnH attenuator as another light project. The frankentone sounds good through the one I built - although as designed there is still not enough attenuation when the amp is dimed, so I had to build another -14db stage to go after the main attenuator it to get it down to bedroom level.

I can see that single wire being an easily overlooked mistake translating things over from the 20 watt version. I went back and looked at my copy and what's currently on their site. My copy say Rev1 the website has Rev2 with that wire removed. When the tech was going over things with me he didn't spot it right away and had to trace things back on the layout. So no way I have enough knowledge to have figured it out on my own. This is where I do wish Modulus would also provide a schematic with the layout. I'm decent enough at being able to compare a schematic and layout and maybe could have caught the error. But sending it off to a tech wasn't a waste. This was a step up from my other builds so it was worth it to have a pro look everything over too and make sure I didn't make any mistakes.

I have a Fryette PS100 Powerstation I can use for attenuation. I like playing loud and base "bedroom volume" for me is minimum 90-95dB. I'll see how things go with and without attenuation and decide from there if I want a dedicated attenuator.

Looks great!
No cupholder? Did you triple solder?

No sissy cupholder here. I spill my beer on the amp like a man.

 

[Mike Oxhuge]

Sweet build, love the available tones. You should get a hot mod to compare to the SIR setting. Glad you got it sorted and that headshell is fucking baller!

 

[Wayniac3]

Nice looking build. Congrats on getting her up & running
Enjoy!

 

[MadAsAHatter]

Sweet build, love the available tones. You should get a hot mod to compare to the SIR setting. Glad you got it sorted and that headshell is fucking baller!

I was thinking about that. Or this might be a good candidate for @RedPlated (Jeremy/GroundZero) add a stage mod. The chassis already has an extra preamp tube hole to use; though it might be a little tight for the board. Of course I'll play it as built for a while before I really think about any mods.

 

[The Polish Hammer]

No sissy cupholder here. I spill my beer on the amp like a man.

 

[bfool]

I can see that single wire being an easily overlooked mistake translating things over from the 20 watt version. I went back and looked at my copy and what's currently on their site. My copy say Rev1 the website has Rev2 with that wire removed. When the tech was going over things with me he didn't spot it right away and had to trace things back on the layout. So no way I have enough knowledge to have figured it out on my own. This is where I do wish Modulus would also provide a schematic with the layout. I'm decent enough at being able to compare a schematic and layout and maybe could have caught the error. But sending it off to a tech wasn't a waste. This was a step up from my other builds so it was worth it to have a pro look everything over too and make sure I didn't make any mistakes.

I have a Fryette PS100 Powerstation I can use for attenuation. I like playing loud and base "bedroom volume" for me is minimum 90-95dB. I'll see how things go with and without attenuation and decide from there if I want a dedicated attenuator.



No sissy cupholder here. I spill my beer on the amp like a man.

Well if you have a Fryette already, then you are golden! The JohnH is for those of us who are a) to cheap to buy a fryette or b) too old to dream of being a rockstar and spend more time playing with soldering irons than actually playing the guitar or c) all of the above!

 

[MadAsAHatter]

Couple of quick cell phone clips. Each one goes Plexi - 800 - SIR. Only thing that changed between the 3 clips was the master volume. I started on 2 then 2.5 then 3. Master on 3 was getting close to band volume and getting a little too much for my ears in a small room at maybe 4 feet away from a 4x12 cab. Speakers are a mix or Weber Grey Wolf and Silver Wolf; the GW on top and SW on bottom. I don't know if it comes out in the clips, but in the room you can definitely hear the 800 mode start opening up and get more saturated as the volume was turned up.