Project overview
The JCM 800 pre-amp emulates the tone of the classic Marshall’s JCM 800, using the same circuit schematic that you will find in the most famous British Amps from the ’80s, using JFET transistors instead of vacuum tubes. Try this board and put the intense tone of their JCM 800 amplifier into your
pedalboard. This is a wide-ranging, British-flavored overdrive that can be pushed well into the high-gain territory.
Introduction
This circuit has been developed to recreate all the gain and tone from the famous Marshall’s JCM 800 Pre-amps, replacing the vacuum tubes for the JFET J201. This design’s origin goes back to 2004 by a schematic published by Electric, following the same conversion style as the ROG designs as the Azabache, Britania, Thunderbird, etc.
This version includes five trimmers to bias the JFET according to your taste. It also features pads to use standard through-hole J201 or the more available and reliable SMD version.
- Powered by six J201.
- Five Internal Trimpot to regulate bias of the transistors.
- Designed to use onboard potentiometers. Keep it tidy without using cables!
- The compact format fits perfectly in a 125B enclosure
Controls
- Bass: Tonefor the bass frequencies.
- Mids: Tone for the mids frequencies.
- Treble: Tone for the treble frequencies
- Master: Controls the output gain of the preamp.
- Level: Controls the output volume
- Gain: Controls the preamp gain
For any technical questions regarding this build don’t forget to check out our Facebook Group and our forum at Free Stomp Boxes.
Gregory Kelly (verified owner) –
My all time favorite 800 Emulation! Raw, Clean to Nice breakup, using this as a compliment to combo builds with a, Raw 800 type to, Muff styles (Rams Head) option…I’ll be using this as a foundation for many more Concept Combos.
dimis (verified owner) –
One of the best JCM-800 simulations ever heard!! It sounds so close to the original stuff, that it’s impossible (and I mean it!) to spot the difference.
The build was so entertaining and the PCB is really well-crafted. The GAIN’s spectrum has a range that satisfies every taste, from gently-breaking cleans to high gain paths. All the knobs are very responsive, too. A plethora of interesting and useful sounds!
Can’t go wrong with PGM!!