Plexi bright cap

Emiel

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I’ve clipped the bright cap in a 2203 and my 72 Trem; didn’t care for it as it neutered the amp somewhat…immediately soldered them back in.

I agree, I like a 100pf cap if you run the amp relatively clean (2-5). I love the stock 5000pf anything beyond that on my '68 spec 1987!
 
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Marcomel79

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Changed the tone stack to 33k/500pf and tried the amp this morning, very pronounced difference. More mids and less shrill sound. I can even turn up the treble a bit. This amp is a war machine! Aggressive yet very dinamic. Will play with the bright cap one of these evenings, but at the moment im putting the finishing touches on a 212 cab im building. See you on the next episode!
 
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Marcomel79

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BRIGHT CAP UPDATE:

After testing the amp with a 100pf bright cap i decided to take it out and even without bright cap the amp has still plenty of edge and i still need to dial back the treble, almost to zero. I did move the nfb from 16 omh to 8 ohm which gave the amp even more edge. I think ill move it back to the 16 ohm tap. Too aggressive... might play with presence cap a little bit to find a balance. Also i might try a lower gain tube on v1 to see if i can tame it a bit, but im afraid that this is a wild beast.... whoever said that the search for a prefect tone is an endless quest???
 

Derrick111

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Like I said in an earlier post, you should look at the choice of speaker(s) first. It sounds like your speaker choice is on the treble side for that amp.
 

Marcomel79

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Like I said in an earlier post, you should look at the choice of speaker(s) first. It sounds like your speaker choice is on the treble side for that amp.
Right now im playing it through a closed back 212 with only one 16ohm greenback on the top slot, with no grill cloth. The other speaker is coming next monday. Bottom slot is open. I guess once in place, the grill cloth will block some of the high frequencies..
 

Derrick111

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Hmmm... yea, but I would think that this arrangement still shouldn't be causing your perceived overly bright sounding amp. It's really hard to say just what's going on without being there to hear it or having an accurate recording that represents the actual sound so that we can properly make recommendations without just taking logical stabs at it.
 

Marcomel79

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Hmmm... yea, but I would think that this arrangement still shouldn't be causing your perceived overly bright sounding amp. It's really hard to say just what's going on without being there to hear it or having an accurate recording that represents the actual sound so that we can properly make recommendations without just taking logical stabs at it.


I mean, its not overly bright right now, I just thought it would have been much darker without bright cap. But i guess wiring the 47k nfb resistor from the 16ohm tap to the 8ohm tap made the amp a bit more aggressive, so that can be perceived as bright... ill make more tests when i get the other speaker..
 

gregr

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Are you using the normal channel at all and is there a master volume?

In place of R31 and R32 is the obvious candidate. When set at the same ratio it will be as if it isn’t there. Post PI is an obvious choice as well.

London Power Scaling is a lot more involved but it’s pretty damn cool. I once borrowed a guys Suhr Badger 18 and loved it.
 
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Marcomel79

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Are you using the normal channel at all and is there a master volume?
Using the high treble channel only, with the normal channel turned up. No jumpering, no master volume
 

gregr

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Did you try turning the normal channel volume all the way down?

Check this out if you haven’t already.
https://londonpower.com/power-scaling-faq/

Remember Fletcher-Munson: when sound gets louder it’s perceived as having more bass and treble. That could be a big reason why you’re hearing what you’re hearing.
 

Marcomel79

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Did you try turning the normal channel volume all the way down?

Check this out if you haven’t already.
https://londonpower.com/power-scaling-faq/

Remember Fletcher-Munson: when sound gets louder it’s perceived as having more bass and treble. That could be a big reason why you’re hearing what you’re hearing.
Thank you for the link. I was thinking of doing the Rich II mod PPIMV. I did put a type 3 mv in the beginning and worked fine , although after a while it didnt...
 
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Marcomel79

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No grill cloth will make a speaker sound very bright.
Thats what i hope it is. Also im standing right in front of the speaker( at a distance, head level). If i stand in front of it with the speaker pointing at my belly then the sound is very bassy...but yeah i will first have to test the cab before i wrap it in tolex and add the grill cloth
 
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Marcomel79

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Almost any amp or speaker will sound bright if it’s pointed straight at your head.
Agree. Plus with no grill cloth the speaker will definitely sound a bit brighter. Next monday ill get the second speaker which is gonna go in the bottom of my 2x12. Im sure that will change the sound for the better. Fuller and rounder.
 

Derrick111

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Especially if it's a closed back cab... should be punchier and more defined/less flubby.
 

Marcomel79

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Especially if it's a closed back cab... should be punchier and more defined/less flubby.
I will test the cab more when i get the other speaker. I guess what im looking for is that classic AC/DC tone through greenbacks. I dont know the science behind closed vs open cab, my guess was that closed back would give me a bassier sound....
 


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