Name these volume knobs, please (Bassman Micro)

King Fan

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Just "Preamp" and "Master."
Good point, Rob. That's what they do and what they are. As I understand it, the volume pot is a standard Fender volume pot, and just decides how much signal gets out of V1. The preamp MV does the same thing, deciding how much post-buffer / tone stack signal goes on to the PI. My limited understanding is these are both 'gainful' signals in the Bassman….

Rob's nice schematic for those who haven’t seen it.

91107E4A-291B-42F1-AADB-C61D3E144EB4.jpeg
 

D'tar

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I like the terms of endearment approach. However, just like getting a new puppy, I would have to observe each ones behavior before etching a name on the tag!
 

Mexitele Blues

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Thinking about it, I now see what you're going for, literally 'naming the volumes'. Thanks.
It took a couple days but I figured out why some of the responses in this thread were confusing for me. Most are using pre and post in relation to the PI while I was picturing the dirty channel on my delta blues. There the Pre is a gain control but the Post knob is still very much in the preamp, in the stage before the tone stack IIRC. Not much of a master.

Anyway...

I submit Gain/Trim/Level and Huey Dewey & Louie
 

King Fan

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Gain, Level, Master
or
Gain, Volume, Master
Thanks, I'm really starting to see choices like that. If I go with 'Gain,' that darn smart @FenderLover has me thinking about how/where to put a resistor so it won't go to zero. But in any case, your option 1, leaving out 'Volume' altogether, has some appeal. At least from the nice demo above, they can both bring some gain or preamp distortion.

I like the terms of endearment approach. However, just like getting a new puppy, I would have to observe each ones behavior before etching a name on the tag!
Right!!! I'm realizing it will be better to find out how they work *for me* before I make a faceplate. After all, why else do they make Sharpies and masking tape?

Back at the label "Bright Volume," if I'm thinking straight, I now see how that might actually be informative. If you ran a bright cap here (even on a switch), the Fender 'Bright' channel volume knob is also a 'bright defeat' knob -- at max, the bright channel sounds the same as the normal channel. I don't often run Fender volumes at max, but with this pre-amp MV in play, you easily could. Too complicated? You're right; I need some beer. :)
 

rdjones

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Thanks, I'm really starting to see choices like that. If I go with 'Gain,' that darn smart @FenderLover has me thinking about how/where to put a resistor so it won't go to zero. But in any case, your option 1, leaving out 'Volume' altogether, has some appeal. At least from the nice demo above, they can both bring some gain or preamp distortion.


Right!!! I'm realizing it will be better to find out how they work *for me* before I make a faceplate. After all, why else do they make Sharpies and masking tape?

Back at the label "Bright Volume," if I'm thinking straight, I now see how that might actually be informative. If you ran a bright cap here (even on a switch), the Fender 'Bright' channel volume knob is also a 'bright defeat' knob -- at max, the bright channel sounds the same as the normal channel. I don't often run Fender volumes at max, but with this pre-amp MV in play, you easily could. Too complicated? You're right; I need some beer. :)
My MusicMan 50RD uses a 10kΩ under a 1MΩ "Gain" control.
Some versions also have a permanently wired 75pF bright cap.
 

King Fan

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My MusicMan 50RD uses a 10kΩ under a 1MΩ "Gain" control.
Some versions also have a permanently wired 75pF bright cap.

Thanks. Yeah, I think once I look at the scheme again, and measure the minimum pot resistance that lets the amp work, I can figure it out.
 

Len058

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Sorry for being direct but... I get a feeling that if naming a bunch of knobs is such a big thing, you'll never finish building the amp anyway.

Two of my builds don't have labels on the pots. I know what they do so...
 

King Fan

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Sorry for being direct but... I get a feeling that if naming a bunch of knobs is such a big thing, you'll never finish building the amp anyway.

Two of my builds don't have labels on the pots. I know what they do so...
Actually, I finished it yesterday. This thread has been a real help; the knobs work pretty much like the *helpful* replies suggest.
 
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Lancer X

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Forgive me for hijacking a bit, but I've been trying to get my head around the "Preamp Master Volume" in @robrob 's design myself. Hopefully I can clarify my thinking as well without disrupting too much here. Please let me know if I am thinking correctly about these pots:

Bright Volume is only named such because the 5F6A had two channels - Normal and Bright. In the case of this single-channel amp, this is simply "Volume" or "Channel Volume", which really means "Preamp Gain", yes? (Controls how much signal is fed from P1 to P2 and the tone stack.)

Preamp Master Volume was added by @robrob simply to control the preamp out level if one wishes to send the preamp signal out to a PA or other power amp. I am guessing that he never would have included this control if there were no FX loop in the design?? If the preamp were hitting the phase inverter too hard, one could still mitigate that issue via the channel volume, right? (I actually intend to place this pot on the rear of my chassis along near the FX send and return jacks. It's not a control I'd expect to access often.)

Then finally, Master Volume controls power section gain. Allows one to, in combination with the Bright Volume, determine the level of preamp overdrive independently from power section overdrive. Send a clean, unclipped signal to be overdriven by the power amp, or overdrive the preamp and then send that signal to the power amp for unadulterated reproduction - or anything in between?

Am I thinking correctly about the role of these controls? (Naming them is a separate challenge, of course.) Apologies again for jumping in.
 
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King Fan

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Forgive me for hijacking a bit, but I've been trying to get my head around the "Preamp Master Volume" in @robrob 's design myself.

No worries, no hijack, good timing in fact. I'm no circuit analyst, but I'll give you my two cents after playing with 'em a bit:

You're right about the 'Bright Volume' -- just the original pot label on the diagram. I yada about this some above.

Pre MV, though, turns out not to be just about the FX loop. It has a big role in the working amp. The layout isn't your friend here. Look where it sits in the schematic; it's like the outlet gate on everything heading into the PI. On a real 5F6a you need earmuffs to dime the volume and get all the good distortion. But here if you turn Pre MV down, you can turn 'Volume' way up and get more preamp distortion out of the speaker at listening level. For me, this is actually the payoff knob.

Post MV is simpler. Probably due to its Type 3 nature, it mostly just cuts SPL. I tend to run it at max most of the time, and (I think others have noted this above) its main SPL effects start once you turn down about halfway. Mostly a '10PM neighbor pacifier' kind of thing. This I think is why some folks above suggest 'Level' might be a good label.
 
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Lowerleftcoast

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Am I thinking correctly about the role of these controls?
I think you have a fair grasp.
This design is different from other similar designs. The other designs have a cold clipper for the second gain stage. The volume control after the first gain stage can be used to overdrive the second gain stage. Either a clean or clipped signal can proceed through the amp. The pre-MV will have the ability to overdrive the Phase Inverter. The post-MV can be used to keep volume down and/or regulate the power tube distortion.
When the vol/gain controls are used judiciously the amp can provide only power tube distortion, only Phase Inverter distortion, only pre-amp distortion, or a combination of the three types.

The Bassman Micro does not use the second triode as a cold clipper so the volume control may just be a way to have the bright cap have more influence (or not) depending on the position of the volume control.

EDIT: In post #64 I consider the cathode follower can be overdriven so the vol control has more influence than I wrote above.
 
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