Convert Haze 40 into JCM 800

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mattnew
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Re: Convert Haze 40 into JCM 800

Post by mattnew » Mon Jul 18, 2016 7:55 pm

I realize it is a bit of a dead thread, but after ~4 years of looking over these mods and not loving my haze 40.. decided to try out the first section of mods.

Couple notes:
C72 -> changed to 1nF . I did this mod and past 5 on the treble knob I would get a whistle coming through the amp. Loud whiney squeak that would go away with treble below 4, however the amp had almost no bass response. I measured the original cap in C72 and found it was a 320pF cap, not the 47pF cap that is shown on the schematic. Not sure what the deal is here but we ended up putting back the 320pF cap.

The rest I did as described, and for the most part it sounds pretty good. The gain is quite a bit more than the original which was my main dislike, and I still have a usable clean channel. I think the only thing I'm not loving is the bottom end is a lot thinner, meaning I can have the bass turned all the way up and it doesn't appear to have much of an effect on the output anymore. I've tried a couple different guitars through it so far, it sounds best with humbuckers, my strats are a bit too trebly through it now though...Clean channel still sounds great...

thoughts?

jessethibes
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Re: Convert Haze 40 into JCM 800

Post by jessethibes » Tue Aug 09, 2016 12:57 am

Man, did you put the 470pF cap in parallel over R88 and R44? I done that, and that was too treble for my taste. If you've done, try to pull off that. Maybe the "too treble" I heard that time (two years ago, I don't remember...) was at really "thin bass?!?" I didn't done the changes for more gain either.

Did you tried another speaker?

mark1198
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Re: Convert Haze 40 into JCM 800

Post by mark1198 » Thu Feb 23, 2017 11:44 pm

Glad to find this forum, finally got tired with my Marshall Haze 40 sound and acted.
1. Changed the tubes out to Tung Sol's (proper Biasing is a must), slight improvement.
2. Changed the speaker to a Celestial 75 watt creamback, slight improvement , then...
3. Simply changed C72 to a 1nF cap (from Radio Shack) and cut C73 out. Big improvement, actually sounds like a Marshall now. It has enough drive for my needs currently, so I stopped the mods there.
Somewhere along the journey I pulled the poorly placed head out and put it into it's own vented box and closed up the back to near factory porting, sans the metal plate for the 1/4" speaker plug.
Question? What about changing C77? would this add some sparkle to the clean channel?
Plastic corners are ordered.
Attachments
Haze Head.jpg
Haze amp.jpg
Cab.jpg

jessethibes
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Re: Convert Haze 40 into JCM 800

Post by jessethibes » Sun Feb 26, 2017 2:42 pm

mark1198 wrote:Glad to find this forum, finally got tired with my Marshall Haze 40 sound and acted.
1. Changed the tubes out to Tung Sol's (proper Biasing is a must), slight improvement.
2. Changed the speaker to a Celestial 75 watt creamback, slight improvement , then...
3. Simply changed C72 to a 1nF cap (from Radio Shack) and cut C73 out. Big improvement, actually sounds like a Marshall now. It has enough drive for my needs currently, so I stopped the mods there.
Somewhere along the journey I pulled the poorly placed head out and put it into it's own vented box and closed up the back to near factory porting, sans the metal plate for the 1/4" speaker plug.
Question? What about changing C77? would this add some sparkle to the clean channel?
Plastic corners are ordered.
Hi Mark!

I had the same feeling when changed C72 and cut C73. The best improvement is right there. Marshall tone from a Marshall amp, finally banana_rasta And yes, the proper Biasing does much difference...

About C77, I didn't tried. I didn't done any change about more gain, because I like as it is. Just thought about putting a 12AT7 or 5751 (don't know if 5751 s possilble) in first-stage preamp, because when the gain is more than 3 o'clock and a good volume, that be kinda "congested" sound, don't you notice it?

Clean channel - on high volume, the bright switch does not solve your problem?

About the speaker, I didn't tried another one. Have a friend that tried the Creamback 75 and hated the results hehe... I'm thinking about creamback 65, or some craziness - Celestion A type hehe... don't know yet.

Anyway, I want to register that I play on stage with a strat, and it's a phenomenal sound. Some pop rock projects (from Pink Floyd to Creedence to Bonnie Tyler hehe), and a jazz blues project, and the Haze goes as a beast. Never used volume more than 5 (what is not a good thing, valves sometimes never get really hot...). Really a great amp, just need some little changes...

Guisoloco
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Re: Convert Haze 40 into JCM 800

Post by Guisoloco » Tue Aug 08, 2017 7:55 am

HI i need help guy.. i tryed to modded my Haze and I messed up!! i modded my haze 40c like a 15 haze and i lost now the original values.. so pls pls any1 can tell me the original values for:
-C58, C59, C53, R15 and C12.

THX A LOT!

Guisoloco
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Re: Convert Haze 40 into JCM 800

Post by Guisoloco » Tue Aug 08, 2017 6:41 pm

[smiley-facepalm]

Pls values for haze 40c...

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Re: Convert Haze 40 into JCM 800

Post by Guisoloco » Wed Aug 09, 2017 12:09 am

i get schematics on an old post.. thx a lot!

Adey
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Re: Convert Haze 40 into JCM 800

Post by Adey » Tue Sep 25, 2018 4:59 pm

Hi guys,
First off, I'd like to say a big thank you to Ach91 and the other people that have contributed to this thread, you guys are awesome! I've visited this thread a few times over the last 3-4 years, but the only mod i've been brave enough try thus far (besides buying a 1985 G12k-85) is to snip C73! As my soldering skills have now improved a bit, I'd like to try some of the other mods.

But I need some advice from you guys if you wouldn't mind. I've looked on Mouser for resistors and caps, but I'm a bit overwhelmed with the options. There are lots of different types of capacitors, but also other specs like, tolerance, min/max temperatures, voltage and watts etc.
Could you guys tell me which type of resistors and caps I need for these mods please? I'm looking at doing the first 'section' of these mods outlined in the first post, just the tone changes, not the AFD hi-gain mods.

Sorry for the necro post BTW, I thought if I posted here, in the future, then noobs like me could have all this info in one place.

Thanks again 👍

Adey

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