JCM-800/2204 Build

[john l]

Alright Miles Ill try to give you a break after this one k. Whats the deal with everybody dropping the screens and preamp filter caps? I have some dual 32ufs and 16ufs to mess around with but I just wanted to understand this a little better before I started swapping parts. If I play heavier stuff would this be something I would want it to do?

[Reeltarded]

Lower filtering feels like it pushes back on your fingers. High filtering stops when you mute like your fingers on a brick wall. That is what it feels like.

I have a 50 with 16 preamp, 16 PI, 16 screens and 32 mains that I love. Another 50 with 50/50/50 that I also love. The one with 50u everywhere likes to be multitracked pretty much straight up. The one that has almost no filtering is fantastic for lead work but not the best choice for 6 tracks of doubling.

The 50u sounds clearer because the mains can keep up with demand. The other a sounds loose because there is a little more demand than it can really hang with.

It's not an easy answer. This is a place to really mess with yourself and decide. Another question to ask is how high is your highest volume? Potential vs demand and balance.

Drop your front end and PI to 16u and leave the screens and mains at 50 is my first thought. Heavy music is demanding on the supply; let it take all it wants. Soften up the front end to let it be a little uncaged. Try that.

[Reeltarded]

John, check your private messages.

[amplifiednation]

Awesome stuff Miles. My head is going to explode

[john l]

Very good stuff indeed. My F&Ts came in so Ive been playing with filtering all day. I first tried just changing the preamp filter to 16/16 and it deffinately made things super stringy as miles said it would but it also seemed to mellow out the amp somehow so Im not sure about it yet. Ive also noticed that ALOT of guys like dual 32s on the screens and preamp so I gave that a try as well and really dug it. Seems like its a good compromise between the touch sensitivity of low filtering and the punch of using 50ufs....
both were very nice.

I ran everything through my Airbrake with the amp almost dimed and couldn't detect any ghosting so its deffinately down to preference.

I really want to try changing all the cathodes to 2.7k/.68s like you said miles

[Reeltarded]

Excellent! Yeah, softwr feeling and it does at least feel like the highs tuck in a bit. I have run 8uF on the preamp without ghosting, but not without swapping back to 16u lol

That feels like playing The Blob at volume.

wub wub wub wub <--- intro to communication breakdown

[john l]

Excellent! Yeah, softwr feeling and it does at least feel like the highs tuck in a bit. I have run 8uF on the preamp without ghosting, but not without swapping back to 16u lol

That feels like playing The Blob at volume.

wub wub wub wub <--- intro to communication breakdown

Ha ha! Funny stuff.
Yeah that's my main concern. Hows it handle at volume.
I think Im going to leave the 32s in and put them through their paces for a while. Definitely don't feel like Im going backwards with it, wish I could make it switchable to AB.

Anything else I should add to the to do list miles?

[Reeltarded]

My best advice, bet ya, is make the amp sound great and play the crap out of it. You can make the filtering switchable but ehhh.

POP

An added tube stage is crazy. You'd like all that.

[john l]

My best advice, bet ya, is make the amp sound great and play the crap out of it. You can make the filtering switchable but ehhh.

POP

An added tube stage is crazy. You'd like all that.

Cool I don't think an extra stage is on the menu yet but I deffinately would like to mess with that in the future on my kit.

Tell me about the 2.7k/.68uf set up. Dropping v1/b that low doesn't buzzy?
I suppose it might not considering your raising the last stage...hmmm.

[Reeltarded]

Everything from 820R ro 3.3k with a .68u in three or four stages sounds good to me.

The 3rd stage of a 4 stage doesn't need a bypass, ever. That is the one to throw a curve ball at. 10k, 27k. Freak out and give that one higher plate load. 180k-270k whatever. I like high plate load on one stage but that is a taste issue like everything else.

Odd that damned near any combination or identical stages even sound good. The changes are about focusing a certain texture in the distortion or defocusing it over all for a thicker nebulous of sound. Identical stages feedback more readily at somewhere different above the knee of the RC. 2.7/.68u is a snarling angry Marshall face.

[john l]

Everything from 820R ro 3.3k with a .68u in three or four stages sounds good to me.

The 3rd stage of a 4 stage doesn't need a bypass, ever. That is the one to throw a curve ball at. 10k, 27k. Freak out and give that one higher plate load. 180k-270k whatever. I like high plate load on one stage but that is a taste issue like everything else.

Odd that damned near any combination or identical stages even sound good. The changes are about focusing a certain texture in the distortion or defocusing it over all for a thicker nebulous of sound. Identical stages feedback more readily at somewhere different above the knee of the RC. 2.7/.68u is a snarling angry Marshall face.

K so your saying to change V1a,V1b and V2a to 2.7k and only bypass the first 2? I might have to go to the parts store today to grab a 3 pole rotary switch to test this bad boy out...

[ampgeek]

I keep chipping away at this as time permits and am at the point where I can see that I need to start moving some of the features off of the main board.

Thinking that the Presonance circuit might do well on an ancilliary board positioned under the pot.

I whipped up the attached as a first shot at it and am hoping that some different eyes could take a look. I followed Martin's design guidance also attached.

Should be a really painless transfer and etch job so I am not too worried about that facet. It will end up being pretty compact at ~1.5" X 1.5".

TIA!
Dave O.

[Bob S]

Hey Dave I really like the Martinizer (presonance).
If it howls at the extremes of pot travel just tie a resistor to the pot.
10% is good.

[Reeltarded]

Dave, I build the res right on the pot with the NFB resistor on it too (res pot) and fly the NFB wire straight across to the output tap.

You can build the tone stack off the board on the pots from the corner of the entrance all the way to the PI cap. It looks beautiful and frees up room for other stuff and junk, not to mention seems to be good practice as far as noise and wire dress goes. A plus.

[john l]

I also started a 2204 build earlier in this thread and have tried all of the things Miles suggested along the way, I haven't implemented all of them quite yet but only because I cant decide where to drill the holes for them to live. Even individually the mods bring good things to the table but together.... they make one hell of an amp, downright scary good 800. Gotta give credit where credits due, of the gazillions of 800s out there this combination is very well thought out. Good stuff miles.

heres a pic. be nice its my first build ever.

[IMG:600:800]http://img.photobucket.com/albums/v299/Johnspics/20130819_162828_zps5e600385.jpg[/img]