Marshall Jackhammer mod

[deaconque]

The Jackhammer is pretty famous for having a muddy unusable distortion setting, here's how to fix that:  All you have to do is change C22 to about 470 pf and switch D4 and D5 from 1N4148 diodes to 3mm red LEDS.  That's it.  The distortion setting now sounds just like the sound clips on Marshall's website, so much better.
Here's a pdf of the schematic
http://freepdfhosting.com/06eb1d9fb6.pdf

[Paul Marossy]

Amazing how changing just a few parts can make such a difference, isn't it? 

[deaconque]

I was really surprised that it was so easy.

[jkokura]

I have one of these. Can someone repost/send me the Schem? I'd love to mod it for TBP also...

Jacob

[deaconque]

http://diystompboxes.com/pedals/schems/JH-1.pdf

[jkokura]

thanks

Jacob

[lucianmbv]

hello:),
first of all i'd like to say that i'm not into electronics and such but a friend of mine that is changed the 1N4148 diodes to 3mm red LEDS and the C22 to a 470 pf one. with the LEDs in place i got no sound at all. after removing the LED and resoldering the old diods back the sound was a bit brighter but i got a loud sqeak with full gain.

any help?

thanx

[CynicalMan]

Yep, that can happen. Only easy solution is not to use full gain. The MXR Distortion III is similar: it's muddy, but if you mod it for a better sound, it squeals at some settings. It's as if the designers felt that users wanted higher gain without squeal rather than a decent sound.

[lucianmbv]

ok, thanks

guess i'll just stick with lower gain, it's way better than putting back the original C22. as for the LEDs i'll give it another try

[lcv]

Hi,
FYI, by  removing  that 2.2n cap  from the Shredmaster also (vey similar design) you transform it in a killer!
Regards,
lcv

[RoyBGood]

Does anyone know of a link to sound samples of this mod? Failing that - and I know it's hard to describe sounds!  - how does the modded version compare to a stock JH1?

Thanks

[lcv]

Hi,
The sound has more mid-high. It cuts through the rest of the band's sounds at lower amp volume settings.
Since the pedal basic sound is very rich (having many clipping stages interacting) , it actually gives  to the following tone controls much more usable  scope.
I'm still  using that modded Shredmaster circuit  to my great satisfaction.
I would suggest you to spend some effort and try it out....

Regards,
Luca

[RoyBGood]

...thanks for that. I quite like the basic character of the distortion, but even with a Strat, it's got that 'blanket over the amp' sound! I think I'll give it a go.

[licho]

Hello, replacing C22 value changes the OD section, not the best thing IMHO.
If you'd like to keep great OD mode unmodified but change the crappy Dist mode, here is the simple but great mod:
- remove D4 or D5 (leave one 1N4148 only)
- disconnect CON8 (it will unplug C27 and R30)
That's all, folks! It will transform Dist mode into OD mode but with asymmetrical clipping that sounds amazing. Try it!
You can also modify C12 to 220nF (to the original guv'nor spec) to reduce bass slightly.

Best regards,
Piotr

[marushio.rima]

The Jackhammer is pretty famous for having a muddy unusable distortion setting, here's how to fix that:  All you have to do is change C22 to about 470 pf and switch D4 and D5 from 1N4148 diodes to 3mm red LEDS.  That's it.  The distortion setting now sounds just like the sound clips on Marshall's website, so much better.
Here's a pdf of the schematic
http://freepdfhosting.com/06eb1d9fb6.pdf

broken link

[diffeq]

The Jackhammer is pretty famous for having a muddy unusable distortion setting, here's how to fix that:  All you have to do is change C22 to about 470 pf and switch D4 and D5 from 1N4148 diodes to 3mm red LEDS.  That's it.  The distortion setting now sounds just like the sound clips on Marshall's website, so much better.
Here's a pdf of the schematic
http://freepdfhosting.com/06eb1d9fb6.pdf

broken link

Here is a working one from reply #4: http://diystompboxes.com/pedals/schems/JH-1.pdf   

[marushio.rima]

The Jackhammer is pretty famous for having a muddy unusable distortion setting, here's how to fix that:  All you have to do is change C22 to about 470 pf and switch D4 and D5 from 1N4148 diodes to 3mm red LEDS.  That's it.  The distortion setting now sounds just like the sound clips on Marshall's website, so much better.
Here's a pdf of the schematic
http://freepdfhosting.com/06eb1d9fb6.pdf

broken link

Here is a working one from reply #4: http://diystompboxes.com/pedals/schems/JH-1.pdf   

diffeq thanks a lot