Bassman Micro features and functions -- my experience

King Fan

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Today I plugged in my Timmy and Strymon Flint straight to the input and got some weird hissy noise I'd never heard before. Lessee here, the input volume and pre-amp MV are set pretty high; why not use the FX loop like I've done before? So I did that instead, and suddenly the pedals were glorious -- no extra noise. What a great amp. Huge thanks yet again to @robrob and his wonderful Bassman Micro page.

It suddenly struck me how many features I've occasionally seen left out of builds of this amp, so I just thought I'd write a note to future builders suggesting they leave them in. The FX loop is one example; I liked it the first time I used it but today made me more aware how vital it can be on a higher-gain amp like this.

Even bigger deal: The *two* MVs. These get downplayed some in various descriptions, but I find they're key to getting the full variety of tones out of my amp. And IME they're both vital -- especially the Pre-PI MV. To be fair, the Post-PI MV wasn't super-amazing with the original Type III. A switch to the Lar-Mar Type II Post-PI MV made a ton of difference. (Rob's added this to the plans.) For me, at least in my EF80 version, the Lar-Mar is far more effective and sounds better. (If you already did the Type III and like it, don't feel bad keeping it -- this advice is aimed at future builders.)

A final but less obvious big deal is the Mids/Raw pot. Simple but really awesome. Rob describes it nicely: "An excellent alternative to the Raw Switch is just using a 100KA pot for the Mid tone control instead of the standard 25KL pot. The 100KA (yes, audio taper) pot will allow you to gradually roll on more preamp gain and mid freqs instead of having the all or nothing of a raw switch." This is just a wonderful 'turn here for tone and volume' knob, user-friendly, easy, and effective. (FWIW I used an extra-low 4.7K shunt resistor to give even a bit more mids cut at minimum, a cool idea Rob suggested in a thread somewhere.)

Several other features are less critical, not crippling if left out, but nice to have. Bright switch? Easy, useful, why not? I find both my bright (250pF cap) and normal channels useful for getting different sounds. NFB? Sure, I usually leave it on (mine's 15K). But an NFB switch is nice, too; the no-NFB option is the least critical in my use, but I still like it. And that brings us to Presence. If you were totally out of panel space, I admit you could leave off this control -- long before I'd omit an MV. But it's really cool to be able to shape the character of the NFB tone; not massive, but audible, useful, elegant, a nice thing to have.

As always, YMMV. More details of my build are in threads here, here, and here.

IMG_1901.jpeg
 

King Fan

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Nice looking amp.... It’s on my list once I fully understand what you just explained. :)
Thanks. It's a great build. Don't let me confuse or cloud anything with my comments; a lot of what I'm saying could be boiled down to, "Build it the way Rob drew it; don't start leaving out features."

But still, you're wise to plan and study. I studied this build for 2-3 years before tackling it, and I'm glad I did. One reason: These Micro amps aren't like Grandma's 1957 meatloaf recipe, where you can just do exactly what she did. They're novel designs. When Rob started, they were experiments, and they changed over time. Even when he got them sorted out, you get big (cool) choices: What power tubes? What *kind* of PT? *What size chassis???* But those choices lead to other important questions: What's my B+ target? how do I make sure I can hit it? how does wiring change if I choose output tube A and transformer B?

Then there are lots of lesser options -- that are still important. Rob discusses 'em, but you may be left wondering what to add, "what to leave in, what to leave out." This thread was aimed at some of those questions. I'm *really really* glad I 'left in' the two MVs and the FX loop. I'm really glad I switched to the Lar-Mar (even after the build was done). And I'm really glad I went with Rob's Mid/Raw pot. (Note though: This would probably be great even if you left out my added shunt resistor, which requires re-designing the presence and mids wiring -- in other words if you just built it as Rob describes it).

Then I'm also glad I left in the bright switch and the NFB function. Adding an on-off NFB switch was easy and fun. As was tuning the bright cap by ear. And I haven't even mentioned my headphone jack -- see Rob's 5E3 micro. I don't use it much but it'll be nice to know it's there late some night.

There's no such thing as too much study. My ludicrous long spell of reading and questions here led to other tweaks that IMO eased building or made the amp a bit quieter or safer or prettier. And I still shoulda studied and planned a bit more on drilling holes and making a cover plate for my PT cutout!!!
 

King Fan

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Now that is a cabinet!

Thanks. Most of the credit isn't mine. A great deal of it goes to Reggie at Rawcabs (on e-bay) who listened hard to my goals and asked really good questions to understand my design and dimensions, then custom built it out of pine he selected. His elegant woodwork, perfect fit, and nice pre-sanding meant I just had to do final sanding, a finish, holes, and hardware. Then Sandy at Precision Design helped me get the faceplate into vector format and then shipped it out -- looking perfect -- in a few hours. So I can take credit only for the finish, the hardware, and the basic design. Oh, and the grill cloth imperfections. :)
 

Lancer X

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Great to hear your feedback, @King Fan. I'm smack in the middle of planning my Bassman Micro build - most of the components are in hand or ordered.

I was going to leave out the mid control mod, but I'll be sure to include that after hearing your experience!

I am planning on the following:
* LTP EF80 w/ EZ81 and Type-2 MV
* Combo in custom blackface PR cab w/ 10" Weber AlNiCo
* Bright Switch
* Mid/Raw 100KA pot
* "Poor man's FX loop"(TM)
* 3-Way NFB (5F6A/5E3/JTM45) switch
* Gain Boost switch
* Switched "Lead"/Plexi voicing
* Almost forgot: your cool cap bleeder circuit!
 

Lancer X

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Today I plugged in my Timmy and Strymon Flint straight to the input and got some weird hissy noise I'd never heard before. Lessee here, the input volume and pre-amp MV are set pretty high; why not use the FX loop like I've done before? So I did that instead, and suddenly the pedals were glorious -- no extra noise.

I have a question/comment: so, can I assume you only moved the Flint to the FX loop? (It's the perfect location for time based effects, for sure.)

Reason being, normally you want your overdrive pedals to hit the front of the amp. If you place it in the FX loop, it's not encountering the preamp and only hits the PI and power section.

BTW, I am also a huge fan of the Strymon Flint and a transparent overdrive. I use a JHS Morning Glory (Bluesbreaker type) as a subtle always-on effect into my Deluxe Micro, and it just makes a wonderful amp noticeably better.
 

King Fan

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I have a question/comment: so, can I assume you only moved the Flint to the FX loop? (It's the perfect location for time based effects, for sure.)

Reason being, normally you want your overdrive pedals to hit the front of the amp. If you place it in the FX loop, it's not encountering the preamp and only hits the PI and power section.

BTW, I am also a huge fan of the Strymon Flint and a transparent overdrive. I use a JHS Morning Glory (Bluesbreaker type) as a subtle always-on effect into my Deluxe Micro, and it just makes a wonderful amp noticeably better.

Excellent question. As noted in my original thread about the FX loop, I knew 'time-based' effects were the biggest beneficiary, but I'm no pro at pedal management. And yesterday I wasn't clever enough to move just the Flint, so I can't answer the question directly. You're right, it was almost certainly the Flint that was making the hissy weirdness going into the input jack. For purposes of discussing the loop, I shoulda just mentioned the noise when the Flint ran to the input and its (usual) glorious quiet and super clarity in the FX loop.

How and how much did moving the Timmy make a difference? Does it make *any* sense? Honestly, I may never have plugged Timmy into this amp until yesterday. In my simple mind, it needs an OD pedal like a moose needs a hatrack; it can already drive like Lewis Hamilton. And thanks to the two MVs, it can do it at comfortable SPLs.

So how much was my mostly boost doing after the PI? Heh, I don't know. :) Maybe I can try "all boost no drive" into the input jack, and also maybe see what varying level and drive do -- if anything -- going into the FX loop.
 
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King Fan

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Also, @Lancer X , you bring up another good point. My list of 'what to leave in', and my couple 'what to add' items from Rob, aren't to say folks should do exactly what I did. It's cool to add other features Rob discusses, and there's no rule you gotta stop there. These amps are one-off specials -- you're not trying to clone a classic design. The one thing I tried to do was make sure my personal or experimental mods were made to be defeat-able, or reversible, or easily tuned and adjusted...
 

loopfinding

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If you place it in the FX loop, it's not encountering the preamp and only hits the PI and power section.

which is another tip: if you own amp-in-a-box pedals, an FX loop is totally worth it.

the amp-in-a-box pedals almost always only model the preamp. so sticking them straight to the micro's power amp is not only a cool way to turn them into an actual amp, but also to get some saggy tube power mojo.
 

Lancer X

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These amps are one-off specials -- you're not trying to clone a classic design. The one thing I tried to do was make sure my personal or experimental mods were made to be defeat-able, or reversible, or easily tuned and adjusted...

Absolutely! (Although one of my goals is being able to switch my Bassman to a virtual classic JTM45 and/or 5E3 as well.)
 

Lancer X

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Excellent question. As noted in my original thread about the FX loop, I knew 'time-based' effects were the biggest beneficiary, but I'm no pro at pedal management. And yesterday I wasn't clever enough to move just the Flint, so I can't answer the question directly. You're right, it was almost certainly the Flint that was making the hissy weirdness going into the input jack. For purposes of discussing the loop, I shoulda just mentioned the noise when the Flint ran to the input and its (usual) glorious quiet and super clarity in the FX loop.

How and how much did moving the Timmy make a difference? Does it make *any* sense? Honestly, I may never have plugged Timmy into this amp until yesterday. In my simple mind, it needs an OD pedal like a moose needs a hatrack; it can already drive like Lewis Hamilton. And thanks to the two MVs, it can do it at comfortable SPLs.

So how much was my mostly boost doing after the PI? Heh, I don't know. :) Maybe I can try "all boost no drive" into the input jack, and also maybe see what varying level and drive do -- if anything -- going into the FX loop.

Order of the pedals will make a big difference too. In general, I don't like the sound of a reverb being effected by downstream gain. As such, placing them in the FX loop avoids having additional preamp gain piled on top of the reverb echoes. (Likewise, if your Timmy was placed after the Flint, it would have applied additional gain to the reverb trails.)

There are certainly tone-sculpting opportunities in placing your Timmy before and after the Bassman preamp - there's definitely no wrong answer there, especially considering all the stage controls that @robrob provided to us. But typically, people insert overdrives into the front of the amp.

All that said, if your amp were making some degree of hiss, feeding the Timmy into the preamp would likely increase the severity of the hiss. Like when you slap a fuzz pedal onto a single coil guitar - the noise floor is suddenly an elevator instead. 😆

Agreed that your Bassman and my 5E3 micro have no lack of drive. Still, the Morning Glory into my preamp (even at low settings) creates an additional nuance of lovely, subtle color to what the Deluxe already does so well. Everything is a matter of personal taste of course. (Beauty in the eye of the beer holder, as they say.) 🍻
 

King Fan

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Cool info, thanks. And just to clarify, the amp itself makes no audible hiss. If Timmy or the Flint make noise in normal use, I've never noticed it. Umm, maybe the trem, especially the harmonic trem, exaggerates treble and so hiss -- a little.
 

joulupukki

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Yours is an excellent build @King Fan ! So exceptionally clean & precise inside and out.

My micro seems to take overdrive pedals really well. I haven't saved my pennies enough for a Flint (or other good reverb pedal), but I'm guessing it'd sound good too. These two amps should get together again sometime soon and do a comparison for overall volume (and volume before breakup would be interesting too). I'm still toying whether I ought to switch mine from a 12BH7 to handle a pair of EF80s. ...or to just build a bigger brother with the same pre-amp... maybe like 12 - 15 watts would be stellar with a Type II MV to tame it when wanted. :)

About the only thing I wouldn't do if I built it again would probably be the 3-way NFB switch. I ended up using a fairly low R value for the JTM45 side just to notice some difference between it and the 5F6A setting. There's definitely a difference in "rawness" between the values (including when it's off), but I'd be tempted to just go for a simple ON | OFF NFB switch instead. 99% of the time I leave it on the JTM45 setting.
 

King Fan

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About the only thing I wouldn't do if I built it again would probably be the 3-way NFB switch.

My friend, I appreciate your insights — I used some down the stretch on this project!

It’d be cool to hear from other Bassman Micro builders about what features they like best. For sure the ability to swap tubes to (basically) get a JTM45 Micro is a feature. But I’ll admit I don’t know the NFB story in that amp, or how to repro it here. For that matter, I know the 45 was the 'first' Marshall, but I don’t know how popular it is now compared to the next generation, when (if I understand it) more Marshall tone shaping showed up.
 

Blue82DC63

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King Fan,

Thanks for your threads about your Bassman Micro build. I am in the early stages of building a Bassman Micro EF80 Lar-Mar. You've already answered a couple of questions for me. Your threads have been incredibly helpful. One more quick question, I am planning to use the same Marshall 18 watt chassis you used. However, I will also use a Marshall 18 watt style cabinet which means the chassis mounts on the bottom upside down compared to yours. Rob's website has a Marshall layout for the Micro with north and south reversed. This has caused me to question my spatial awareness because, as far as I can tell, I can use the normal layout as you did and, when flipped over, everything will be in the right place (though the dials and plugs will be aligned in the opposite direction compared to yours). Is this correct? Thanks!
 

Lancer X

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For sure the ability to swap tubes to (basically) get a JTM45 Micro is a feature. But I’ll admit I don’t know the NFB story in that amp, or how to repro it here.

I am so deep in these NFB maths right now…

I’ve got the original 5F6A and JTM45 sorted out now, but for the life of me I can’t rationalize why @robrob selected a 15k NFB resistor for the micro. 1+2=4 and it doesn’t seem to provide the proper amount of feedback at the moment, and it’s making me nuts.

As soon as I can grok what’s going on in the Micro NFB and EF80 math, I’ll post the proper resistors for a switched mod.

(Ditto for the switched Micro “lead”/Plexi mod.)
 

King Fan

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However, I will also use a Marshall 18 watt style cabinet which means the chassis mounts on the bottom upside down compared to yours. Rob's website has a Marshall layout for the Micro with north and south reversed. This has caused me to question my spatial awareness because, as far as I can tell, I can use the normal layout as you did and, when flipped over, everything will be in the right place (though the dials and plugs will be aligned in the opposite direction compared to yours). Is this correct?

Heh, you're asking the wrong guy. :) I almost melted by brain on the upside-down and backwards thing when I was planning. I *think* you're right. I think I asked this same question and someone posted a pic of a Marshall-built combo with front-mounted controls "upside down". But I also bet @joulupukki can tell us more clearly and confidently -- he built his Marshall style.
 




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