Superlead bright cap selection and gain boost

Matthews Guitars

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I've decided to do some expermenting with some component values in my rebuilt '69 Plexi. One of which will be the bright cap.

The one in it now, which is the same one that was there when I got the chassis, is 130 pf. I know that's not a standard value.

I want to give this amp a big kick in the pants, making it a lot more sensitive and gainier overall. What new bright cap value range would you suggest I start with?

I'm also looking at best ways to add another tube gain stage. Since this chassis was pre-punched for a fourth preamp tube, that preamp tube socket is already in and wired in to a new perf board, components already on it, just waiting for me to connect it in. I have two triodes available to add, but will likely only put one triode into the circuit. At least at first.
 

junk notes

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I use a 5000pF in my 69 as I do not play at low volumes!

@ricksdisconnected posted this back in March when the video was published. Take a look and see what you like as @Jon Snell suggests.

Pete is a cool guy and a great player!


Sorry I am of no help with adding another tube gain stage, but perhaps tryong out different values with the tone stack.
 

nickfox

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I got a 6 way switch for my 71 superlead. You can see the values in the picture. I checked out two different types of caps, ceramic and silver mica.

I have three main guitars. My strat and 335 really like the 120pF and my lp really likes the 5150pF NOS sprague.

16.jpg
 
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playloud

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If you play at lower volumes, pick something from a 100-250pF range. If you play it loud, try the 5nF. That came stock on my '71 JMP50 and it's great for that classic aggressive Marshall sound.

But if you play it really loud (10), no need to worry about the bright cap!

There's a handy calculator here which shows the frequencies that bypass the volume pot: https://www.ampbooks.com/mobile/amplifier-calculators/bright-boost/calculator/

Basically, the higher the value, the broader the range of bypass frequencies.
 

Matthews Guitars

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I figured, why bother with foreplay? Put something big in there and see what happens. I can always back it off.

So I stuck in a 5600pf silver mica I had lying around.

And yeah, now I know what that's about. :eddie: The gain boost is comparable to kicking in the Tube Screamer that I usually use
as a clean boost pedal. But I get it about "this is what you do if you play loud" because it added so much gain, it basically doesn't DO quiet anymore. That's fine with me. If I want to play quiet I have plenty of choices that will do that.

The only reason to plug into a Superlead is to play loud. And I do.

I may play with other values but I think I'll end up back with this 5600 pf capacitor after it's over. It's giving me what I want.

Overdrive starts with the volume on 2...maybe a bit less.
 

Browneyesound

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How do the channels interact if you connect the inputs with the big cap on the volume? Any differences compared to how they interact with a small cap?
 

neikeel

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How do the channels interact if you connect the inputs with the big cap on the volume? Any differences compared to how they interact with a small cap?
The normal channel does sound duller and you get some channel bleed into normal channel if you crank the bright channel even if you are no plugged into it.
But realistically who plugs into channel 2 on a Superlead.:shred2:
 

william vogel

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I figured, why bother with foreplay? Put something big in there and see what happens. I can always back it off.

So I stuck in a 5600pf silver mica I had lying around.

And yeah, now I know what that's about. :eddie: The gain boost is comparable to kicking in the Tube Screamer that I usually use
as a clean boost pedal. But I get it about "this is what you do if you play loud" because it added so much gain, it basically doesn't DO quiet anymore. That's fine with me. If I want to play quiet I have plenty of choices that will do that.

The only reason to plug into a Superlead is to play loud. And I do.

I may play with other values but I think I'll end up back with this 5600 pf capacitor after it's over. It's giving me what I want.

Overdrive starts with the volume on 2...maybe a bit less.
Your volume control for that channel now is a bass/low mid control with the other frequencies fully bypassed and full throttle. Man those things are incredible too like that. The only disadvantage is the hiss at idle but my opinion is play it don’t idle. I usually run the volume on 6-7 and make my ears bleed.
 

playloud

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The normal channel does sound duller and you get some channel bleed into normal channel if you crank the bright channel even if you are no plugged into it.
But realistically who plugs into channel 2 on a Superlead.:shred2:

Didn't Clapton do that? Possibly why he ended up leaving the Marshall club in the end (the traitor!)
 

Matthews Guitars

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Don't get me going on Clapton. The only phase of Clapton's career that I like at all came to an end when he stopped playing a Les Paul through a Marshall.

As for this bright cap mod, this Marshall is now giving me all that I love about a Superlead, and more of it. MUCH more. I still have all the tonal control I want, but it's at a higher basic gain level.

I run jumpered and use Channel 2's volume control to fatten up the bass. It can get pretty thumpy if not actually thunderous. LOVE IT.
 

Matthews Guitars

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With futher playing I see that 5600 pf is just too extreme. The amp is brutal but it's hairy in the top end and way too susceptible to near ultrasonic oscillation. To turn up the volume means turning down the presence and/or treble in order to keep it stable.

I'll back down the cap values until I find that happy medium where I've got that big gainy sound but the amp is stable under any reasonable operating condition. And look at ways to adjust it internally to keep it quieter as well. Test lead dress changes and also look at adding a few shielded signal cables.
 

neikeel

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Test it by turning volume to 7-8 that is where the cap effect runs out.
The main kick of a 5nF bypass cap on the pot is 0-2 on the volume pot. I find that if you want any clean sparkle at lower volumes (ie using the amp as pedal platform) a cap of 120-180 seems to work best with humbuckers/Tele type guitar (my 2c). If you want full aggression 1nF to 5nF is the zone.
 


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