Bassman Micro LTP build

Discussion in 'Shock Brother's DIY Amps' started by Dannebrog53, Mar 16, 2020.

  1. Dannebrog53

    Dannebrog53 TDPRI Member

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    Hey everyone I'm new to the forum and have read about some of your builds. I came across robrob's home page while looking for some general building info on the net and started reading about the Bassman Micro he's designed and was hooked. My compliments robrob and a BIG thanks for sharing your designs and knowledge and to the others on this forum for doing the same. That's why I've joined. I've got a few amps, all too loud for playing cranked or even at half volume in the house, so the idea of a lower powered amp that has the 59 Bassman tone that can also give you the JTM45 tone really got my attention. I've started getting the parts together and have most of them. I'm looking at what I want to incorporate in my build. I like how a few of you have added an extra tube socket and switch so you can select the Bassman tone or the JTM tone. I was also wondering if any of you have added the 3way negative feedback switch mod. My plan is to build as a 2X10 combo (Tweed Super) with a switch so I can select a Fender Tweed style speaker or a more Brit/Marshall sounding speaker. Thanks in advance for your comments and feedback.
     
    robrob and 82LesPaul like this.
  2. printer2

    printer2 Poster Extraordinaire

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    Welcome aboard. You haven't said if you have made any amps before or if you have any electronic experience, not asking any basic questions I am assuming you do. The best thing to do is put in the extra sockets and components you think you would want to put in and build up the basic Bassman. Then when you got it up and running do modifications to it. Getting fancy with a new build if you don't know your way around can lead to loss of hair.
     
    tubedood likes this.
  3. Dannebrog53

    Dannebrog53 TDPRI Member

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    I owe you all a little more background. I'm probably one of the older and maybe oldest on this forum at 66. I have built a couple of low wattage single ended amps many years ago (1969-1971). My dad was an electrical engineer and after graduating college he started his own business. One of his first jobs was building a PA system for the soccer stadium in his home town of Esbjerg, Denmark. Back in 1969 he walked me through amp design, what all the components did, calculating resistance, transformers, preamp and power tubes etc. I'm certainly not as knowledgable as many on this forum when it comes to the actual designing of amps so I've been doing a lot of reading, both on this site and amp books that I have. I'm well aware of the hazards involved, discharging caps etc. and have very good soldering skills. I always err on the side of caution and make sure I fully understand what I'm doing before I jump in and sparks start flying. Now that I'm retired I have the time to get back into it relearn what I've forgotten and build an amp. As for loss of hair that started years ago (comes with age). I prefer simpler amps and rigs and don't use very many effects. I like the simplicity of my Tweed Champ and Princeton and my Marshall 1987 50 (too loud for home use). As for effects pedals, Rangemaster and Brian May treble booster clones that I built, Dunlop wah pedal and Fender spring reverb. Excellent point putting the sockets etc. in during initial build, I'll definitely do that.
     
  4. printer2

    printer2 Poster Extraordinaire

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    I kind of got the feel there might be something more to the masked stranger. No worries then, also easier to discuss thing given a frame of reference. There are a few elder gentlemen that hang around here from time to time. I will be hitting 60 in a number of months so no concern about the loss of hair. I do a lot more with pen and paper (or drawing program) rather than melting solder but I have had an experimental workstation of sorts and have listened to some changes to circuits. I can't help much with mods of the Bassman circuit, just made a 12AB5 (9-pin 6V6) single channel version with a pentode up front. Nothing much different from the schematic. Turned up into Marshall territory had the pentode singing on its own, never got around to modifying it, was thinking of putting a 12AX7 in its place. But since my playing is in its infancy I really have no use for stage ready amps. (why build them? why is the mountain there?)

    I hate to direct you away, but the Marshall take on the 12AU7 powered amp seems to have made many smile, well maybe more like grin.

    https://ampgarage.com/forum/viewtopic.php?t=24671

    And since you have time on your hands.

    https://www.google.com/search?client=firefox-b-d&q=jtm1+schematic

    The first group that tried to re-engineer the amp were from France from what I gather, but others took the ball from them. Might make some good reading over a coffee or two.
     
  5. Dannebrog53

    Dannebrog53 TDPRI Member

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    Thanks for the quick reply printer2, I think I might have led you astray on my goals. I really love the Fender Bassman sound and I'm not planning on modding the circuit much. I was interested in robrob's comment on his circuit that by switching the 12AU7 out for a 12AX7 you get almost the exact same preamp as the JTM45 and with it the Marshall vibe, sort of an added bonus, 2 amps in one. Based on robrob's comments on the nfb resistor I was thinking the 3 way switch might be a nice enhancement when going for the Tweed or Marshall tone. It took me almost 50 years to figure out that smaller amps were better for me. In the late 60's when I started going to concerts Cream, Hendrix, the Who etc. were all using multiple Marshall 100 watt stacks. When my wife and I went and saw U2 the Edge was playing through a single VOX AC30 mic'd through the arena's PA system. Things have changed. I noticed you're in Canada, I was born in Hamilton and lived in Toronto and Dundas before moving to the States.
     
  6. tubedood

    tubedood Tele-Meister

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    Nice choice on the amp project Dannebrog53. Those micro builds have interested me also.
    The Bassman micro looks great, I might try RobRobs JCM800 style micro... that era of music always makes me smile.

    That is as soon as I find my Members Only jacket and zebra striped bandanas hahaa. I loved the 80's!
     
    robrob likes this.
  7. Dannebrog53

    Dannebrog53 TDPRI Member

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    Good to hear from you tubedood. That era really refined the "crunch" tone. I like any amp that's not overly complicated with controls, where the tone for the most part is designed into the amp, like Ken Fischer's Trainwreck amps. You control the sound with touch and and the tone and volume on your guitar. I'll have to look at robrob's JCM build. It doesn't take that much power to become so loud you can't really hear all the great tonal qualities of your amp, plus there's the distraction of stuff falling off the shelves.
     
    robrob likes this.
  8. Dannebrog53

    Dannebrog53 TDPRI Member

    Age:
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    I've officially begun my bassman micro build. I've populated the board and added the jumpers, I'd appreciate if you guys could take a look at and give it a look before I start soldering it all and adding the leads on. I followed the recommendations by some of you and written down the actual values of the resistors according to my meter. I'll clip the "pigtails" off just before I solder the leads to the components, I left them on to old the components in place.
    IMG_8284.JPG IMG_8285.JPG IMG_8288.JPG
     
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