Some Mods for Marshall Class 5

[NXC1978]

Originally Posted by db3266

Has anyone got any before and after sound clips for these mods?

I've been real tempted to go buy another one and make a vid with my A/B box.

[Floyd Pink]

Hmm, I'll to try to record a few clips. Don't expect anything soon though. Got a pretty tight schedule the next couple weeks and I'll need to order some parts.

[nightwulf1974]

Hey all,

I have a parts on order for this mod (less switch and choke) which will be here tomorrow and I am modding the amp then. I also have on order a scumback H-75 with FBI so that should change the character a ton, along with some pretty dang good tubes to experiment with including..
2 - Jan GE 5751
2 - Mullard 12xa7 RI
1 - Gold Lion EL84
1 - Jan EL84

I will be uploading an A/B by this weekend hopefully. Nothing of super quality but using my home vid cam which does a pretty dang good job for what it is. Hopefully there will be a noticeable audible difference. I can't wait to get this thing modded..

~ Night

[db3266]

Lyle - does your first post still represent the full list of your suggested mods?
There are several pages of dsicussion so I just want to be clear that nothing has changed from your first post.

Can you explain what a choke is and what it does?

Thanks.

[NXC1978]

Originally Posted by db3266

Lyle - does your first post still represent the full list of your suggested mods?
There are several pages of dsicussion so I just want to be clear that nothing has changed from your first post.

Can you explain what a choke is and what it does?

Thanks.

Mods still remain the same but I'd read and re-read all the discussion pages before doing anything to your amp. I did and took notes! Here's some info on "chokes" that I found when I asked myslef the same question...
Mercury Magnetics -- The Guitar Amp Transformer Company

[db3266]

I've had an idea.

Can keysandguitars update his word doc and then Lyle could add it to his first post, then all instructions are in the first post (easy for someone then to refer an amp tech to the first post and save them reading through 7 pages). This thread is getting very long and could get confusing with all the Q&A going on.

[nightwulf1974]

Originally Posted by db3266

I've had an idea.

Can keysandguitars update his word doc and then Lyle could add it to his first post, then all instructions are in the first post (easy for someone then to refer an amp tech to the first post and save them reading through 7 pages). This thread is getting very long and could get confusing with all the Q&A going on.

Good idea, if Lyle would not mind, that would be great for many!

[oharadan]

Hi,

This is my first post to this cool site, and also i think this thread is great. I also are not totally satisfied with the tones from my class 5 , esp with my strat. So im thinking of doing these mods.

My soldering skills are good enough to do the mods, but i just have a little worry about discharging the caps. I have done alot of reading and I know to use my discharging tool to clip first to the earth (chasis) and then to v1 pin 1. But the thing with the pcb is that i cant see how to read the value of the caps after that without having to take the pcb out out chasis, and i dont want to do that without knowing the caps are discharged. Dont want to somehow electrocute myself

I guess my question is , is it safe to do the procedure above and then go ahead and remove the pcb and then measure the caps , or is there another way to measure the caps. Thanks for any replies, i want to be safe, and maybe taking it to a tech is the best idea, but i want to build my own amp at some point, and I got a lot to learn.

Thanks

[Lyle Caldwell]

By "read the value" do you mean the capacitance value of the caps or whether there is any voltage in the caps?

The capacitance value of the caps is printed on them.

Voltage is measured with a meter and you can read it without removing caps.

[oharadan]

Yeah sorry about that what i wrote was confusing. I realise I sounding pretty dumb here but this new to me... I know the uf value of the filter caps , what i meant was I want to measure the voltage that are on the caps before i start working on the amp, and since i cant get to the leads of the caps to measure them without taking the whole pc board out (because the solder connection is on the bottom of the board) how do i measure the voltage on the caps?

Hopefully that is less confusing for you. thanks in advance.

[Lyle Caldwell]

Just measure DC voltage at pin 1. Start with your meter at its highest DC setting, then down a notch, then down until you find a measurement.

So if the highest is 600V you may not measure anything. Then at 200V you may not measure anything. At the lowest setting you may measure 8V - that is safe.

If the amp is unsafe you will measure over 100V at pin 1.

[db3266]

Originally Posted by nightwulf1974

Hey all,

I have a parts on order for this mod (less switch and choke) which will be here tomorrow and I am modding the amp then. I also have on order a scumback H-75 with FBI so that should change the character a ton, along with some pretty dang good tubes to experiment with including..
2 - Jan GE 5751
2 - Mullard 12xa7 RI
1 - Gold Lion EL84
1 - Jan EL84

I will be uploading an A/B by this weekend hopefully. Nothing of super quality but using my home vid cam which does a pretty dang good job for what it is. Hopefully there will be a noticeable audible difference. I can't wait to get this thing modded..

~ Night

[db3266]

Originally Posted by nightwulf1974

Good idea, if Lyle would not mind, that would be great for many!

Hi Lyle, is there any chance you could attach a simple instruction set to your first post?

[Lyle Caldwell]

Honestly, between the detailed description, the suggested parts list, and the schematic, if someone needs more help than that, they don't need to be messing around in an amplifier yet.

[F#m7]

Well, I just finished everything up this morning. I gotta say, I'm not really liking the change. The cleaner sounds are a little better, but as you crank it, the aggressiveness I liked about ti before is gone.It also doesn't seem as tight. Seems to have lost some volume too. ??? Tough to tell at home though. To be fair, I need to play it live. But, I might be going back to stock values. I'm still playing around with the master volume. I installed a pot in the back. I found this really old mil-spec pot that is really cool. I'll have to post some pix later. Don't get me wrong, the amp doesn't sound bad, I just don't think it sounds better, at least not cranked. Or maybe I have tin ears.

[Lyle Caldwell]

Part of the "aggressiveness" in the stock circuit is that it rolls off everything below about 130Hz, but it does it after the initial gain stage and the tone stack. Kinda weird.

The modded amp, if you did the cathode bypass cap switch suggested, gives you a choice of a highpass at 33Hz or at 180Hz, before the initial gain stage and tone stack. This gives a choice of a very full sound (Hendrix clean) or a more typically "Marshall" midrange emphasis, which is more aggressive to my ears than the stock amp.

If anything, the modded circuit has a little more gain than the stock circuit, as it removes a pointless voltage divider and adds the "Marshall" 470K/470pf pair for an upper mids emphasis.

First, make sure all the mods were implemented exactly as suggested before judging them.

Second, that's why there are so many flavors of ice cream - we don't all have to like the same thing. You may just not care for it.

[F#m7]

Originally Posted by Lyle Caldwell

Part of the "aggressiveness" in the stock circuit is that it rolls off everything below about 130Hz, but it does it after the initial gain stage and the tone stack. Kinda weird.

The modded amp, if you did the cathode bypass cap switch suggested, gives you a choice of a highpass at 33Hz or at 180Hz, before the initial gain stage and tone stack. This gives a choice of a very full sound (Hendrix clean) or a more typically "Marshall" midrange emphasis, which is more aggressive to my ears than the stock amp.

If anything, the modded circuit has a little more gain than the stock circuit, as it removes a pointless voltage divider and adds the "Marshall" 470K/470pf pair for an upper mids emphasis.

First, make sure all the mods were implemented exactly as suggested before judging them.

Second, that's why there are so many flavors of ice cream - we don't all have to like the same thing. You may just not care for it.

That's exactly right. Also, things sound much different in a live mix. I'll reserve final judgement on what I've done so far.

[F#m7]

AGHHH! Master volume pot isn't doing squat either. Double check me, do I ground lug 1?

[Lyle Caldwell]

Are you putting in a regular master or is this the "headphone mod" we discussed?

[F#m7]

Headphone mod.

[Lyle Caldwell]

No lug of the pot is connected to ground. You use lugs 2 and 3, making it a variable resistor. This in conjunction with the stock 2W resistor makes a voltage divider (same thing a volume pot does). Double check my instructions earlier.

[F#m7]

10-4. Error corrected. I gotta leave for a show in Birmingham, so I'll have to play with it later. Thank you very much for your help Lyle. Very cool of you.

[John R]

How does the tone with this set of mods compare with the mod that FJA does? (

YouTube - FJA modded Marshall Class 5

YouTube - FJA modded Marshall Class 5

)

I dig the tone of that FJA modded amp, but he charges $250 for the tone mod and $100 for the master volume. Plus he recommends swapping in a different speaker, so that's another $120 or so (in the video, he starts with a 4x12 and then switches to the stock 10"). I only paid $330 for my Class 5, so doing $470 in mods is just too much money to "invest" in the amp and he doesn't offer DIY instructions, kits, or schematics.

[Lyle Caldwell]

Dunno. I mod amps as part of my professional services, but I won't do expensive mods on the Class 5 or the Vox AC4 or other economy amps. Makes no sense. If someone wants to put $1000 into an amp there are better starting places. Part of what I do is to consult with clients to get them the tones they want at their realistic price points. I won't steer someone in the wrong direction - I live by my reputation.

That's why I came up with these "$20 mods" for the C5.

[Don]

Originally Posted by F#m7

Well, I just finished everything up this morning. I gotta say, I'm not really liking the change. The cleaner sounds are a little better, but as you crank it, the aggressiveness I liked about ti before is gone.It also doesn't seem as tight. Seems to have lost some volume too. ??? Tough to tell at home though. To be fair, I need to play it live. But, I might be going back to stock values. I'm still playing around with the master volume. I installed a pot in the back. I found this really old mil-spec pot that is really cool. I'll have to post some pix later. Don't get me wrong, the amp doesn't sound bad, I just don't think it sounds better, at least not cranked. Or maybe I have tin ears.

My amp actually has more gain, is more aggressive and seems louder with the mods.

[oharadan]

Hi Lyle,
Thanks for your help, i finally had a chance to do the mods yesterday, sounds great ; I like the 1uf setting of the cathode bypass cap, it sounds better now with my boogie bottle rocket, and the clean sounds sound better to me overall.

Have to wait until i can turn it up louder at band practice, its too loud to do that at home. Which brings me to the point if you could please answer this, how do i install a gain control. Is it possible to replace r24 with a 500k log pot? Do r24 and r 25 act as a voltage divider and with r24 at 220k, is that like having the pot at 220k on the dial? Hmm not sure.

Thanks
Daniel

[Lyle Caldwell]

Daniel,

R24 and R26 form a voltage divider. They are the equivalent of having a 1M volume pot turned down to about 8 (out of ten). But this is serving as a master volume, not a "gain" control in the normal sense. R25 is the grid resistor for the output tube.

The "gain" control is the Volume pot, ala a Plexi.

R14/R11 is another voltage divider, limiting the gain between preamp stages.

[oharadan]

Thanks for your answer and explaining it to me, ahh I see, when i think gain for some reason i always think distortion, but it's just a gain or amplification of a signal (volume pot).

So one more question if thats ok, to give this amp a master volume (distortion at lower volume), i should remove r24, put in a 1m or 500k pot, then i can control the level that is given to the grid of the EL84. For example then i can max the original volume pot which feeds of V1a and turn the r24 pot down, or vice versa..

This is all still new to me, but am I correct in my thinking?
Thanks again, and your pedals look great, will keep it in mind and pass the link along to some of my guitar mates who are always looking for new pedals.

[Lyle Caldwell]

Yes, you could put a 1M pot there for a MV (500K will work but you'll lose low end). You will lose the sound of the output tube being driven hard, so all you'll have is preamp distortion, but that is an acceptable tradeoff for practice levels.

And thanks!

[time pieces]

I own a Carvin Vintage 16 and would love to A/B it against this little Marshall!