Modding my 900! (All tube, with clips)

[iron broadsword]

Still lovin this thing.. and I just ordered a weber mass 200 to pair with it. I'll be sure to do some proper cranked clips once I get it.

Also, that link changed so reposting it for posterity. http://www.ghostsauce.net/random/KATLOOPZ.mp3

 

[wakjob]

Yep, I think I'm done. Only thing that would make this amp better is a second channel A, but I can live with that.

Really?

I thought after disabling the pre-tone stack on channel B, they sounded pretty much the same.
Channel B having more saturation on tap of course.

I was thinking that an "integrated quad" consisting of two EL34's & two 6L6's
would rock hard in a 4100.

 

[iron broadsword]

Um, well I could be wrong but no I'm pretty sure they do still sound different. It's been a long time since I messed with the controls though, I set it up to roll for cleans and use chB as a lead tone / boost and it just stays at my church. I guess I might've just thought they were different because I never set the gain levels the same and did a real comparison.

An integrated quad.. interesting idea. Wouldn't going to KT66's be sort of the same effect?

 

[ddaxe]

I had no idea I was such a sloppy player.[/QUOTE]

I too have a 900 4100 DR... and I've had it under the gun (soldering) trying for that "clear" sound... and I have done some of what has been mentioned... my 900 is so "clear".. that yes.. you don't realize how sloppy you are until your faced with such clear definition ... it really made me play better.... My amp will feed back beautifully when you hold a note that little bit extra.. and will sustain forever... for bigger shows.. I pair it with my original 2555 Jub.. and the 2 together are tonal heaven... IMO... I have chased that "clear" sound for quite awhile... which drove me nuts... until my brother in-law (who is an electronic tech & guitar nut) sat me down and we went through every aspect of what I was looking for.. reading tons of stuff on different mods.. until we finally hit upon it.... I love my 900 & would never get rid of it... it's such a workhorse.... sorry I don't have a clip (though we are doing a bigger arena show in 2 weeks) I'll try to video it and post for your thoughts... Great thread.. btw... it was cool to see someone who has been chasing a similar quest as I was.. and nailed it!! On a side note.. few years back.. Gino Scarpelli of Canadian band Goddo was using 2 full stack 900's at a show of theirs I attended... and I was floored how "clear" his sound was...(was then my quest began) and the only pedal he had on the floor was a DS1 for clean boost on the solos... it was ALL 900 coming out of the cabs... So I knew the 900's could be tweeked to sound clear... it was just finding the path to attain it....

 

[iron broadsword]

I think the stock amp will kinda get there if you run the master full up and the gain low, but unless you attenuate then chances are you can't really do that. So yeah, that clear sound like you describe has gotta be tweaked into it. Tschrama ftw for his help with this thread, I've been living the dream.

Also, the mass 200 has been really great with this.

 

[Kelia]

Now for some further mods options you might like:

5] Change C9 (220nF) to 100nF, or even 47nF. Lower the pre-clipping bass response, to prevent mud at huigh gain settings. 100nF or 47nF completely depends on you pickups and playing style.

6] snipe one leg of R17(100k), bend it upwards and solder a 4n7 cap in series between the leg of R17 and the bit open spot were you sniped R17 off. This is a fixed depth mod. As the 4100 doesn't have a lot of feedback (at least mine doesn't, warn tubes?) , the effect is subtle. More deep bass, and a more giving, elastic, organic feel.

7] Pickyback a 4n7 over R38(10K). This shaves a bit more fizz. This is subtle, but welcome I think. This trick I got from the JMP-1.

8] If you did 4], but find the gain too low, consider putting a 4u7 to 22uF cap piclybacked over R2 (1K5). This increases gain and give more overdrive. Might introduve some fizz, so 7] might be very good in combination.

Good day everyone !!
This is my first post ever here and what and interesting Thread !!......Thank’s to Iron for all your answers on your Youtube channel !.........really appreciate !

So I bought last week a mint 1991 4500 head with EL34’s and did this easy mod I found on
GearPage ,
Applies to the 4100 and 4500 models.

1. Remove R7 and R43.
This disables a hardwired tonestack on the gain channel. This tonestack scoops mids, changes the low end and makes the amp sound harsh and sterile.

2. Place a jumper wire over D10.
This will give a smoother, warmer and more organic distortion on the gain channel. It increases the clipping a bit.

3.Jumper C27. Restores the low end.

It really changed the tone in a better way but I’d like to bring it to the tech for those mods , my question is for Tschrama , I love a chewy spongy feel tone-wise and I see that on your number 6 mod , it seems to bring some elastic and organic feel to the amp , could you elaborate please ?.......tx

Cheers !!

Lou

 

[mk2 steve]

I tried those mods listed above (remove r7, r43 etc) out of curiosity a while back, and didn’t like them at all. It didn’t sound bad but robbed the amp of its character. It actually made the amp sound more neutered and weak.

I’ve seen the clip on YouTube as well and it sounds good on there, but in person, meh.

 

[Kelia]

I tried those mods listed above (remove r7, r43 etc) out of curiosity a while back, and didn’t like them at all. It didn’t sound bad but robbed the amp of its character. It actually made the amp sound more neutered and weak.

I’ve seen the clip on YouTube as well and it sounds good on there, but in person, meh.

Strange !!.........mine sounded more woody with some Kossoff tones !

Did you try the mod in this thread ?

 

[Kelia]

Tschrama ?!

 

[tschrama]

Not familiar with that mod... but I amagonna have a look at it.

 

[tschrama]

6] snipe one leg of R17(100k), bend it upwards and solder a 4n7 cap in series between the leg of R17 and the bit open spot were you sniped R17 off. This is a fixed depth mod. As the 4100 doesn't have a lot of feedback (at least mine doesn't, warn tubes?) , the effect is subtle. More deep bass, and a more giving, elastic, organic feel.

Pretty standard Depth mod. Just do it!

But if you want truly sensasional JCM900 4500. Do my mods like mr. Iron did.

 

[Kelia]

Pretty standard Depth mod. Just do it!

But if you want truly sensasional JCM900 4500. Do my mods like mr. Iron did.

Thank’s Tschrama for your reply !
Appreciate !!

So if I understand after reading everything, those below are the “Tschrama” mods that Iron did except mod *8 which he passed.
Plus he also added after spoking or chatting with you the Liam’s R15 bass mod for more heavy bottom thump , but don’t think I’d need this one as I don’t play Heavy Metal.

So with these mods , channel A & B have the gain coming from V1 but just dialed differently on each channel ?!
Also , before I do those mods , is the effect loop ok on this amp or should something be done to it also ?
Tschrama ,have you ever added an extra 12ax7 for channel B or tried the amp with big glass KT66 or better yet have a rectifier tube for a nice fat JTM50 ?
Going crazy now with all those possibilities !!

Question for Iron if you ever read this ,
where the heck are your great clips posted on page 7 that seems to have everyone’s jaw dropped !?......haha!
........................................................


1] C27, (4n7)snipe one leg off
This removes the weird, post-overdrive, pre-EQ, shaving off some of the fizz, restoring mids, and giving a subtle bass boost. It doesn't do anything for more gain or more articulation. It does help the tonestack to react more like a traditional marshall.

2] C35, (220pF) to 100pF
Restoring some of the treble response, pre-overdrive. Better for pince-harmonics, articulation and tone in general. Subtle but worth it.

3] R42, (10k) piggy back another 10K over it. This provides more gain, especially over 500Hz. Great for more saturation, without making it muddy.
4a] D10, (diode) snipe one leg off:
-Prevent the diodebridge to clip the signal to +/- 2 Volts. This alters the clipping threshold, loosing some overdrive. It lowers perceived gain. Could make the opamp clipping more audiable.

4b] R60, (470k) Pickybag 47K over it
-Lowers output signal to the FX-send, and downstream components. Tweak this if perceived volume is too low or too high.

4c] R13, (220k) snipe one leg off
-Removes global feedback around the tube-gain-stage. Now this tube is driven very hard (4a) and acts as a traditional gain stage in vintage Marshall's. It makes the tonestack act like a traditional Marshall tonestack, and its clipping behavior is like an old marshall. But since the clipping treshold of this tube-stage is HIGHER then the diodebridge, you will loose overdrive. It lowers perceived gain.

I never did 4] myself, I only described it could be easely done. So you, mr Iron, are the expert on this mod ,Consider skipping this one!
Now for some further mods options you might like:

5] Change C9 (220nF) to 100nF, or even 47nF. Lower the pre-clipping bass response, to prevent mud at huigh gain settings. 100nF or 47nF completely depends on you pickups and playing style.

6] snipe one leg of R17(100k), bend it upwards and solder a 4n7 cap in series between the leg of R17 and the bit open spot were you sniped R17 off. This is a fixed depth mod. As the 4100 doesn't have a lot of feedback (at least mine doesn't, warn tubes?) , the effect is subtle. More deep bass, and a more giving, elastic, organic feel.

7] Pickyback a 4n7 over R38(10K). This shaves a bit more fizz. This is subtle, but welcome I think. This trick I got from the JMP-1.

8] If you did 4], but find the gain too low, consider putting a 4u7 to 22uF cap piclybacked over R2 (1K5). This increases gain and give more overdrive. Might introduve some fizz, so 7] might be very good in combination.

 

[tschrama]

#8 Yeh.. I never liked the sound of a bypassed last cathode resistor. Skip that one if you dont need the gain.

-The loop is fine, no need to mess with it. Just be sure to include #4b

-Extra 12AX7.. yeh I did that, when I completely remove the preamp PCB and put in a turretboard. But to make the 4100/4500 sound good, that is not nessecery.

-Preamp Circuit Design has far more influence on the sound than any particular brand or type of component. Exchanging power tube types costing 50-100$ can only bring subtle tone differences at best.. which can be duplicates with a 10ct resistor.

If you have the time, do the mods. If you have experince with soldering it sjould be hard to do in a couple of hours. I was very pleased with them, and put some large hours in them to design and verify, both in CAD simulations and in real life.

And post some clips

 

[Kelia]

#8 Yeh.. I never liked the sound of a bypassed last cathode resistor. Skip that one if you dont need the gain.

-The loop is fine, no need to mess with it. Just be sure to include #4b

-Extra 12AX7.. yeh I did that, when I completely remove the preamp PCB and put in a turretboard. But to make the 4100/4500 sound good, that is not nessecery.

-Preamp Circuit Design has far more influence on the sound than any particular brand or type of component. Exchanging power tube types costing 50-100$ can only bring subtle tone differences at best.. which can be duplicates with a 10ct resistor.

If you have the time, do the mods. If you have experince with soldering it sjould be hard to do in a couple of hours. I was very pleased with them, and put some large hours in them to design and verify, both in CAD simulations and in real life.

And post some clips

Awesome Tschrama !!!

Thank’s so much !............will report back when I get the time to do this or
have my tech do it for me!..

 

[Kelia]

#8 Yeh.. I never liked the sound of a bypassed last cathode resistor. Skip that one if you dont need the gain.

-The loop is fine, no need to mess with it. Just be sure to include #4b

-Extra 12AX7.. yeh I did that, when I completely remove the preamp PCB and put in a turretboard. But to make the 4100/4500 sound good, that is not nessecery.

-Preamp Circuit Design has far more influence on the sound than any particular brand or type of component. Exchanging power tube types costing 50-100$ can only bring subtle tone differences at best.. which can be duplicates with a 10ct resistor.

If you have the time, do the mods. If you have experince with soldering it sjould be hard to do in a couple of hours. I was very pleased with them, and put some large hours in them to design and verify, both in CAD simulations and in real life.

And post some clips

Hi again Tschrama !

One more question I have before doing the mod , do I undo what was done previously so it does not mess with your mod ?

Here again below is what was done last week,

1. Remove R7 and R43.
This disables a hardwired tonestack on the gain channel. This tonestack scoops mids, changes the low end and makes the amp sound harsh and sterile.

2. Place a jumper wire over D10.
This will give a smoother, warmer and more organic distortion on the gain channel. It increases the clipping a bit.

3.Jumper C27. Restores the low end.

 

[iron broadsword]

Question for Iron if you ever read this ,
where the heck are your great clips posted on page 7 that seems to have everyone’s jaw dropped !?......haha!

They're the same tones heard in the video, I think. Cheers, bud

 

[Kelia]

They're the same tones heard in the video, I think. Cheers, bud

Hey Thank’s Iron !...Still Rock your 900 ?

Also , what’s the best bias for this mod ,
got some new EL34 JJ’s .

 

[Oculophilia]

They're the same tones heard in the video, I think. Cheers, bud

Iron broadsword, the link to your video seems to be dead. It says file not found.

 

[tschrama]

yeh... undo these other mods.

 

[Kelia]

yeh... undo these other mods.

Thank’s !