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The Legendary Tones Caswell Mod brings the HEAT to the Studio Plexi and JCM800!

2.6K views· 80 likes· 24:07· Mar 30, 2026

🛍️ Products Mentioned (16)

0:00 - About the Caswell mod 2:39 - Stock Marshall SV20 4:47 - SV20 with the Caswell mod 7:23 - Bite switch on 10:36 - Thump switch off 11:31 - A/B Comparison 12:08 - Stock JCM800 13:20 - JCM800 with the Caswell Mod 14:50 - Bite switch on 16:25 - Bypassing the JCM800 bright cap 18:53 - Drop tuning 20:56 - Final thoughts ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ If you like my content, feel free to use the links below to purchase gear and help support my channel! 🤘 Check out the Legendary Tones Caswell mod! https://legendarytones.com/caswell-1987-mod-bringing-back-the-spirit-of-39/ Ceriatone JCM800 https://ceriatone.com/british-style-jcm800-2203-hw/ Marshall Studio Plexi https://www.zzounds.com/a--3989488/item--MSHSV20H Splawn Amps https://barrztrading.company.site/Splawn-Amps-and-Cabinets-c41630011 Scumback Speakers https://www.scumbackspeakers.com/h_series.html Charvel San Dimas https://www.zzounds.com/a--3989488/item--CHA2965801?siid=367708 Cables D’Addario Cables https://www.zzounds.com/a--3989488/item--PTWPWAMSG Ernie Ball Flat Ribbon Cables https://www.zzounds.com/a--3989488/item--ERNP06221 Strings StringJoy Mark Morton set https://stringjoy.com/guitarstrings/strings/artist-series/mark-morton-artist-series/ Camera Setup Lighting Equipment https://amzn.to/3CXBcp3 Camera Gear https://amzn.to/41f9s7i Rode Lav System https://www.zzounds.com/a--3989488/item--RODWIPRO Rode Lavalier II Pro https://www.zzounds.com/a--3989488/item--RODLAVALIERII SM57 https://www.zzounds.com/a--3989488/item--SHUSM57LC Sennheiser E906 https://www.zzounds.com/a--3989488/item--SENE906?siid=33423 Follow me on Instagram for some behind the scenes action! www.instagram.com/fastredponycar https://www.instagram.com/fastredponycar?igsh=MXdvODNjMWt3bXl3OA%3D%3D&utm_source=qr Check out my N-DSP captures on the Neural Cloud https://cloud.neuraldsp.com/cloud/u/FastRedPonyCar Email me for capture pack info fastredponycar@gmail.com

About This Video

In this video I take a quick look at the Legendary Tones Caswell mod—Tim Caswell’s flavor of “that” hot-rodded Marshall thing—except it’s a plug-in module that drops into a preamp tube socket. I’m not getting deep into install here (I’ve got a separate video for that), so this one is straight to the point: before/after tones, real settings, and what actually changes when you add the module. For a limited time, these were shipping with an upgraded NOS Phillips 1287 tube, which is normally a paid upcharge. I demo it first in a Marshall Studio Plexi/SV20-style setup, guitar straight in (Charvel San Dimas with a Suhr Aldrich bridge), no boost, and I keep the amp in that “stage usable” middle ground where you still have room to hit it with an OD later. With the Caswell, I’m mostly living around 9:00 on the module gain—thump on, bite off—and it just brings the heat: tighter, more aggressive, and more powerful than simply cranking the amp’s loudness controls. The bite switch adds a big upper-mid spike the amp can’t really do on its own, so it’s a balancing act. Then I move to a Ceriatone JCM800. The 800 already has gain, and with the bite on + stock bright cap it can get a little too messy, but once I bypass the bright cap the bite becomes a really useful, different kind of cut. Bottom line: if you want more gain/thump/cut without soldering, paying a bench fee, or permanently modding a valuable Marshall, this is a solid, reversible way to supercharge the amp.

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