Any decent JCM800 in a box, for pretty high gain stuff?

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

Have you built this one Erik? Seeing some problems with guys getting the transistors dialed in and that it's "bright"?

Would seem weird running another Marshall preamp into a Marshall preamp also? No?

I've breadboarded part of it. Ran out of JFETs...lol. It does have that characteristic bright JCM800 sound but changing or removing the 470p cap between gain stages will help. That was a common mod on those amps back in the day to take away some of the brightness. Dialing in the bias of the JFETs is just a matter of having enough to pick through to get dialed in. They're all different as you know.

What a better OD for a Marshall than a Marshall. It might sound weird but it works. When I finally get around to putting one together for use, I'll probably leave the tone stack off for that "All on 10" sound.

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

P'S that emulator looks like a good piece, anyone got soundsamples??

Thanks. I've been trying to get sound samples for months from folks who have built it but no luck.

 

[STRATDELUXER97]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

I've breadboarded part of it. Ran out of JFETs...lol. It does have that characteristic bright JCM800 sound but changing or removing the 470p cap between gain stages will help. That was a common mod on those amps back in the day to take away some of the brightness. Dialing in the bias of the JFETs is just a matter of having enough to pick through to get dialed in. They're all different as you know.

What a better OD for a Marshall than a Marshall. It might sound weird but it works. When I finally get around to putting one together for use, I'll probably leave the tone stack off for that "All on 10" sound.

Erik....One of the best ways "also" to remove alot of highs on the 800 series was getting that darn .001 off the preamp volume pot! :smack: Those 470 pf caps need to stay across the 470k mixers because you lose gain without em..I've modded quite a few 800 amps...Mostly just the 2203/2204 basic models..

As you know the 1987/1959 series Marshalls had the 470k/470pf combination before the 800 series,though I much prefer the earlier series Marshalls(As you already knew)...:laugh2:

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

Erik....One of the best ways "also" to remove alot of highs on the 800 series was getting that darn .001 off the preamp volume pot! :smack: Those 470 pf caps need to stay across the 470k mixers because you lose gain without em..I've modded quite a few 800 amps...Mostly just the 2203/2204 basic models..

As you know the 1987/1959 series Marshalls had the 470k/470pf combination before the 800 series,though I much prefer the earlier series Marshalls(As you already knew)...:laugh2:

Oh yeah, that stupid treble bleed cap. I hate that thing. Notice it's not on the emulation. I forgot that 470pf cap changed the gain too. A few have put a 220pf cap in it's place with good results. I guess the gain change helped the brightness some as well. It all works together.

 

[STRATDELUXER97]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

Oh yeah, that stupid treble bleed cap. I hate that thing. Notice it's not on the emulation. I forgot that 470pf cap changed the gain too. A few have put a 220pf cap in it's place with good results. I guess the gain change helped the brightness some as well. It all works together.

Pulling the cap off of the 470k does help tame the brightness,but it also changes the eq flatter and removes gain...A switch to add or subtract that cap is cool...:13:

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

Pulling the cap off of the 470k does help tame the brightness,but it also changes the eq flatter and removes gain...A switch to add or subtract that cap is cool...:13:

Ohhh, good idea. I never thought about that (switching it in/out). :13: Thanks for the tip. If you do that and it works out OK, I'll had that to the mods list on my page (with your name next to it).

 

[STRATDELUXER97]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

Ohhh, good idea. I never thought about that (switching it in/out). :13: Thanks for the tip. If you do that and it works out OK, I'll had that to the mods list on my page (with your name next to it).

:smack: LOL.....Ok buddy! :dance:

I think I should take the BSIAB 2 board out and mount the Matchbox circuit into that instead,as it already has the switch,jacks,and power supply stuff....The BSIAB 2 doesn't impress me anymore these days after the Plexitone was added...

I need to finish the Matchbox one day soon and see how that sounds?

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

:smack: LOL.....Ok buddy! :dance:

I think I should take the BSIAB 2 board out and mount the Matchbox circuit into that instead,as it already has the switch,jacks,and power supply stuff....The BSIAB 2 doesn't impress me anymore these days after the Plexitone was added...

I need to finish the Matchbox one day soon and see how that sounds?

LOL....you have no idea how many times I've reused an enclosure and just swapped the board out. I have one that started out as the diystompboxes beginner circuit, then the ROG Fetzer Valve and now it has the AMZ Mosfet Boost in it.

 

[STRATDELUXER97]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

LOL....you have no idea how many times I've reused an enclosure and just swapped the board out. I have one that started out as the diystompboxes beginner circuit, then the ROG Fetzer Valve and now it has the AMZ Mosfet Boost in it.

It's cheaper,otherwise I Lack another project box! :smack:

All the pot holes are drilled etc...All I need to do is swap for the right pot values and then mount and re-wire to the other board..

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

It's cheaper,otherwise I Lack another project box! :smack:

All the pot holes are drilled etc...All I need to do is swap for the right pot values and then mount and re-wire to the other board..

Cheaper is good...LOL. I have one project box left undrilled, a 1590BB, and it's reserved for the JCM800 Emulation. Luckily a majority of what I have boxed up requires only 1 pot...LOL.

 

[75lespaul]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

Money is an issue with the forum member though! :yell:

:smack: Oops! Didn't see post #20. I was wondering why nobody brought up the PT.

Sorry Pierre.

 

[Pierre]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

How in a circuit do I tell which diodes clip? I'm guessing they're the ones on the signal chain, in between FETs and in the tone circuit right?

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

How in a circuit do I tell which diodes clip? I'm guessing they're the ones on the signal chain, in between FETs and in the tone circuit right?

Yup. Although ones in the tone circuit may not be for clipping but for other means. Depends on the type used and where it's placed. Direct in the signal path to ground (known as hard clipping) or in the feedback loop of an opamp (soft clipping). If it's connected from the power supply to ground it's a reverse polarity protection diode.

 

[Pierre]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

So D6, D4, D5, D3, D1, D8, D2 as well..? Not so sure about a couple of those...

Any values I should aim for in LEDs?

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

So D6, D4, D5, D3, D1, D8, D2 as well..? Not so sure about a couple of those...

Any values I should aim for in LEDs?

What circuit are you looking at? Schematic?

 

[Pierre]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

It seems to be an official Boss one. It's a JPEG and not a link, let me upload it first.

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

It seems to be an official Boss one. It's a JPEG and not a link, let me upload it first.

Well, which one specificially? Distortion? Super Overdrive? LOL

 

[Pierre]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

Ohhh sorry haha it's a DS1. I bought it a couple of days ago, it was the pedal I was talking about for a while

 

[ErikH]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

Ohhh sorry haha it's a DS1. I bought it a couple of days ago, it was the pedal I was talking about for a while

Oh, ok....then there are two clipping diodes. I think they're D4 and D5 located near the middle of the board facing opposite directions (look for where the black line is on each one) right next to one another. I don't have the original schematic handy to tell what the others are for but I can guarantee that one of them is for reverse polarity protection.

Can't remember what the forward voltage of the LED's I used are but they are small. Not much larger than the one used for the indicator on the pedal. Probably about 1.2v or so.

 

[Pierre]

Re: Any decent JCM800 in a box, for pretty high gain stuff?

D4 and D5 haha The ones I thought were it at first. I'm guessing this also changes clipping from symmetrical to assymetrical if I swap one of them out in the other way?