Short sound clip of the JCM800 Micro. It's a 1 watt Marshall JCM800 using a single 12AU7 power tube in true push-pull. Layout diagrams, schematics and other details can be found here: robrobinette.com/RR2104_Maste...
This amp has turned out pretty well. Keep in mind it has several changes from Rob's original design, but it isn't a whole lot different. I used a Mojotone 1580 output transformer so I could have an impedance switch and a 12BH7-A output tube. It is a single input and I have two master volumes installed. One is Rob's and the other is a traditional pre PI like in a 2203. I built this thing before Rob added the 65v elevated heater center tap, so I don't have that installed. Most everything else is per Rob's diagrams.Thanks for your comments. I also built a Plexi version of this thing that turned out well.
@@TheGuitaristChannel Since this video was done, I removed the PPIMV since it was messing with the presence circuit. The preamp and tone stack are bone stock Marshall. The output section has been adapted to accommodate the 12BH7A. I can send you a schematic if you’re interested. I just got done playing for the last two hours on this amp. It’s the best low volume amp I’ve built, but it can still easily hit 100db.
It doesn’t look like it’s mentioned anywhere that there is a mild overdrive in front of the amp. That may be why there seems to be more gain. I think I had a Analogman Prince of Tone back then.
Love your work Rob. Thanks for sharing your builds and providing us the resources to build your amps. I built the Bassman micro and I absolutely love it. Im looking forward to building the JCM800 micro soon, cheers.
Wow! That sounds HUGE! Gotta give this circuit a try. So Great to see some vids from you Rob! Your site is an invaluable resource for us DIY-ers! Thanks for all you do for the community, you rock!
Rob, just found your site and wanted to say thank you, so very much. Never built an amp before but I'm gonna have a go at it. Thanks for taking the time and the effort to put the site together and share it
Thanks for the comments. This amp turned out well and the plexi version turned out well also. It has several changes from Rob's design, but he got me started on it. Playing it through 2 Marshall 1960BV cabs really thickened it up.
grazie Rob! mi hai insegnato tutto quello che volevo sapere su come funziona un amplificatore per chitarra, spero di riuscire presto a costruirne uno, grazie!
Hey Rob, love your stuff. I comb your site regularly :) On the topic of master volume, what inclined you to use the PPIMV setup that you did? As much as I like LTP distortion, I have heard (both first and second-hand) bad things about using a variable resistor between both phases as a master volume, especially at low volumes. Would a dual-gang A1M pot work instead, with each pot wired as a voltage divider for each phase? I feel like that would get rid of the harshness I've heard at low volumes.
I agree, a Lar-Mar or Type-2 master volume usually works better than the Type-3 used in the JCM800 but the Type-3 works better than most think and it's simple and transparent at max master volume.
@@TheFrozenDesert I'm not using a distortion pedal, just a mild overdrive set around noon. I typically use a Tube Screamer 808 clone I built to help the bottom end of Marshalls. I haven't done a video of the amp with no pedal since I never run any of them that way. I'll run the tube screamer in the normal way with the volume on 10 and the drive on 0. Any future videos will be with the TS vs the Prince of Tone used in this video. Since this video was done, I've switched from a JJ 12BH7-A to a taller version by TAD. The JJ was noisy at idle and the TAD is much cleaner.
@@td317 Three years later...it would be helpful if you edited the video description to include the fact that you're running an overdrive into the front of this thing.
@@tmx63 This is actually on Rob's channel, not mine, so I can't edit it. It's in the description on my site. It's just a Prince of tone run with little gain and volume about half if I remember correctly. It's been awhile. I run it now with a Klon or a TS808 and there are new versions on my channel.
@@robrobinette pretty good after doing some tweeks to the bypass caps and I increased to 220k grid stoppers to the power tubes. I just finished a "gotta get rid of some scrap parts" amp using the ac15 ef86 preamp, ltp and your 1 watt power section. The power transformer is scrapped from a home theater sub amp (90vac and I used a voltage doubler to get 260vdc no load) and the output tranny I got in a huge lot of random stuff from an estate sale it had a CT primary with a 50:1 ratio so with an 8ohm speaker its pretty close. I'm gonna post a video when it's done I'll let you know. Hey thanks for sharing all your amazing knowledge.
John, I can send you a schematic if you want. I haven't made any significant changes since this video was made other than removing the PPIMV that was causing issues with the presence like most PPIMV's do. The main tweaks were using the Mojo output xformer to provide impedance changing capabilites, I only slightly upped the CT voltage as opposed to Rob's 65 volts, I'm running a 12BH7A vs Rob's 12AU7. I was burning up tubes with the original cathode resistor on the power tube and bumped that up. I think Rob's made some of those changes to his latest schematic. I need to find replacements for the power transformer and the choke since they are Classictone parts that are no longer available.
@@paulrico317 my heaters dont have a CT, where do i put the 100ohm resistors? at the end of the heater run? Edit: Rob had posted somewhere the 100ohm resistors aren't grounded but connected to the elevated junction point 65V
Hello Sir! I would like to thank you personally for all that I was able to learn on your website about amp building! I made the 5e3micro and the 5f1micro thanks to you! I apologize in advance for my English. I have a question could you please give us a 1w 1959plexi micro. once again thank you for the quality of your work.
Just jumping in here. The amp in this video is mine and I've since built a Plexi version of it. I've tried numerous configurations and settled on a 69 plexi with a bass tonestack and I'm pretty happy with it. It's got a linked input that ties the two channels together or they can be used separately like a normal plexi. The output stage with the 12BH7A power tube is the same as this amp except it has a PPIMV. I've add an effects loop to both amps. I'll be posting a video soon of it and an updated version of 800 micro on my St George Amplification youtube channel. The plexi cleans up really well as expected. Both amps can get crazy loud and easily hit over 100DB.
@@paulrico317 hello sir i find layout of the jtm1 50th anniversary with 12au7 output power it s incredible and i actually work on jcm800 micro of rob. Your plexi must be crazy with the 2 input. Bravo for your building. I apologyze for my english i am french but thanks a lot for you repply
