RumbleFX build and general guidance

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

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edsonmarquezani
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RumbleFX build and general guidance

Post by edsonmarquezani »

Hello, everyone. I built a 18watter a few months ago based on this layout from RumbleFX[1], which seemed to be one of the coolest around (there are so many versions of these Plexi 18w that I had a hard time figuring out which one to pick).

So, besides the VVR, which I couldn't get to work, despite many tries and even help from other forums - I blew up 4 or 5 FET transistors and just gave up on damn solid state crap :P - everything worked fine.

But, I'm still interested in messing around with this build and would like to ask a few things.

1. I've been reading some old threads and no images or attachments are available anymore; so, I also see many MODs being mentioned, from guy X and guy Z - where can I find this stuff? I would like to explore the possible modifications for this circuit;

2. This build has a PPIMV but it cleans up a lot in lower volumes, is it really expected? I guess so, since power distortion plays an important role in this circuit, but just wanted to confirm, since stock Plexi master volume mods are also a common thing;

3. I dared to add a NFB to it, to see what would happen. Weirdly, I couldn't hear any difference until I used a very low resistor value (10k from the 8omh tap, which means a lot of feedback, with a 470R resistor added from PI tail to ground, the NFB going in between). The NFB helped a lot in reducing noise at higher volumes but didn't seem to change my tone much. I'm really not sure about this NFB setup I came up with, does it sound right?

4. I have no reference of the real thing, but I found this one to have such a glassy high-end. Is it really like this? The Plexi tone, I mean. Are there tweaks I could do to be able to tune it more. Maybe a presence control?

Thank you all in advance!

[1] https://www.ramblefx.com/diy
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Bieworm
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Re: RumbleFX build and general guidance

Post by Bieworm »

You’re trying to get a lot of options on an 18 watt. I assume you’re doing this for fun and experiment? When it’s for tonal purposes I would not do all that personally… imho every time you “think” you expand the options on an 18 watt, you’re losing the great tonal goodness of its simplicity.

Look at the Trinity Thor if you want good plexi tone in 18 watt package. That’s a great amp
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"THIS should be played at high volume..preferably in a residential area"

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