Upgrade Output Transformer and add a choke (with pics)

svdijk · **Posted:** Sat Sep 06, 2008 3:09 pm

Admin: We have made this thread a sticky as the choke mod is pretty popular here, please note that it doesn't have to be
a Mercury Magnetics choke ...

I finaly did it, upgraded my JVM with a Mercury Magnetics choke, the MC-10H, and a Mercury Magnetics output tranny, the MAR-JVM100-O!
Here are the pics:

There goes my warranty!!
The choke goes instead of the R106 resistor.

Here you can see the difference of the two tranny's.

Almost ready!

The tranny didn't fit exactly, had to change the hole's!

Here are the wires from the choke.

Up and runnin' again!!

Good things:
The amp is smoother now, and reacts much better!
The mids are sweeeeeet!!!
The amp sounds bigger, because of the bigger and tighter lowend.
And the lowend-thump is unbelievable.
More harmonics.

Bad things:
Tranny didn't fit in the original holes.
Drilling for fitting the choke.
It's heavier now!
Warranty is gone.

hotthands · **Posted:** Sat Sep 06, 2008 5:40 pm

I can deal with the "bad" 'cause it seems like the "good" outweighs the "bad" plus I love to tinker, may have to look into this.

banana_rasta

Todd Zila · **Posted:** Sat Sep 06, 2008 5:57 pm

Cool, and you did it yourself. [smilie=gt-happyup.gif]

I am clueless on what is on the inside. I like what you describe as the end result though. banana_rasta

Are you planing on bypassing the heater rail fuses?

How much did the parts cost you?

tripwire · **Posted:** Sat Sep 06, 2008 6:42 pm

Yes...more info! And was it worth it to you to do it?

Sound must be great cause I love mine now!
[smilie=gt-happyup.gif]

hotthands · **Posted:** Sat Sep 06, 2008 6:47 pm

OT is about $265, choke about $35 didn't look at the PT, probably another couple hundred so it ain't exactly cheap but probably worth it...GAS it never ends!

banana_rasta

tripwire · **Posted:** Sat Sep 06, 2008 7:02 pm

No doubt. It never does...lol

Todd Zila · **Posted:** Sat Sep 06, 2008 7:09 pm

Hothands, if you do, I would love to hear it! [smilie=icon_wink.gif]

The Pup · **Joined:** Sun Dec 02, 2007 7:39 pm **Posts:** 1415

tall6f · **Joined:** Mon Dec 03, 2007 1:24 am **Posts:** 105

Nice job. Pics are great ! Thanks

LG · **Posted:** Sun Sep 07, 2008 9:37 am

svdijk, great post here for those interested in these mods. I've got a Dual Rec that has a Mercury tranny and choke here waiting to be installed. Along with an NOS RFT and NOS Mullard on the way. I'm very interested in the Voodoo Amp mods for the JVM and it looks like you've got that covered for the most part. You're description of the results sums up what I am seeking in the amp. To combine that aggresive EL-34 tone with the increased low end you've described seems to me to be an absolutely killer combination. Possibly similar to the effect of me using my JVM in conjuction with my Dual Rec. Great job here! [smilie=gt-happyup.gif]

svdijk · **Posted:** Sun Sep 07, 2008 10:47 am

The JVM is a very service-friendly amp, so it wasn't that difficult to do the mod!
I thought of bypassing the heater fuses, but it worked oké for 1.5 years, so I leave them for now.
The output tranny was 225,- euro's and the choke 24,- euro's.
And for me it was really worth it!!!

The reasons why I did the mod, was that I was looking for more lowend in the OD1 and OD2 channels, and a thighter bass-response in the crunch-channel.
And the feedback of the amp was not very musical to my ears.
All those things are solved now for more then 100%!!
Even the OD2 channel is awesome now, and reminds me of a Mesa Mark 4, but with a thighter lowend!!

I was very used to my good old JCM800 2210 (alsow with MM ot and choke!), and missed some things in my JVM, like the nice feedback, and very big sound, but now the JVM can sound like that amp, and do a lot more then the JCM800!!

Don't get me wrong, I always liked the JVM from the beginning, just tweaking it, like I did 21 years ago, when I bought my first Marshall, the JCM800 2210, that I still own!!

hotthands · **Posted:** Sun Sep 07, 2008 2:11 pm

Todd Zila wrote:

Hothands, if you do, I would love to hear it! [smilie=icon_wink.gif]

Soon as I recover from my latest spending spree I'm going to do it!
Keep you posted.

banana_rasta

RachelMorgan · **Posted:** Sun Sep 07, 2008 3:12 pm

I might do this in say June 2010. But I'd really like to hear a modded one side by side with an unmodded one and see if you can get the unmodded one to sound close with something like an EQ or KT77s (I think that's the tube sub????) first.

Andy · **Posted:** Sun Sep 07, 2008 3:51 pm

RachelMorgan wrote:

I might do this in say June 2010. But I'd really like to hear a modded one side by side with an unmodded one and see if you can get the unmodded one to sound close with something like an EQ or KT77s (I think that's the tube sub????) first.

In the pix svdijk has KT77's in already ... so svdijk did you try the modded amp with Kt77's and EL34's to try both ?

I guess you did the mods at the same time but I just wondered how much difference the choke made too as that's a cheap mod to do ?

Finally are you sans c83 on this amp too ?

cheers

Leperclown · **Posted:** Sun Sep 07, 2008 5:58 pm

Hey Svdijk, fabulous work!

Not being a technical person, I have a couple of queries.

1. It looks like the JVM has 2 transformers (1 on the left and one on the right). Is this the case?

2. In simple terms, what is a choke, and what is its purpose.

Looks like a great mod that is worth considering.

Cheers

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Upgrade Output Transformer and add a choke (with pics)

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