Fender Bassman Ten tone mods

[The Kirbster]

Hi all, newbie here. Bear with me, please.

A dear friend GAVE me a `72 Bassman Ten. He bought it trashed, replaced the speakers (w/120 watt QSL woofers), re-tubed, sat the bias (it's been "blackfaced", so it does have a real bias knob in it). It never suited him, as he couldn't get it to overdrive, and I begged him not to hack it up.

I use it with my Boss GT-6, running the left output to channel 1, the right to channel 2 The best sound I can get out of it is with ALL the pre-amp knobs dimed, bright switch on, deep switch on, & regulate the volume with the master volume. I LOVE the deep, percussive bass, but I really have to tweak the EQ on the GT-6 to get sufficient highs from it. Yeah, I know, turn the bass down on the amp...but when I turn the bass down, or even turn off the Deep switch, it loses something that I really like. I'd like the option of plugging in straight, without my pedalboard, and just jump the 2 channels together.

My warped idea is, change the caps on the normal channel to brighten things up, & leave the bass channel bass-y. Since I use both channels, I THINK I could blend the 2 together to get the sound I want.

Any thoughts, warnings, other ideas? It's SO CLOSE to being perfect, if it just had some more high end cut. It IS perfect if I stack my Hot Rod Deluxe on top & back it's bass off, but that's a lot more to haul, and it's harder to keep a lid on the volume with 2 amps.

[Gibsonman63]

Changing the coupling caps doesn't really add highs, it takes some of the bottom out of it, but it may still give the desired result. Have you considered changing out a couple of the speakers? It could be that your speakers are really bassy. A couple of brighter speakers may balance things out.

[The Kirbster]

Considered that, but sometimes I mic the amp-depending on the gig. It'd be a pain to use 2 channels on the board, 2 mics to capture "the sound". I even considered adding a horn, but that's even more problems. This amp needs to be versatile-I use it unmiked with a Blues-Rock band, then mic it & run it VERY VERY quiet with a Classic Country Music show. I even occasionally use it as a bass amp, at low volumes. I ask quite a lot from it, and it ALMOST gives it to me. Seems the louder it gets, the more highs it needs. At least it doesn't have the "farty bass" problem I have with the Hot Rod Deluxe.

[Steve Conner]

Well, maybe change all of the speakers. If they're woofers, as opposed to speakers meant for guitar use, they might not sound too good with guitar. Did he get them from Parts Express? What QSL part number are they? Maybe you can download a spec sheet with the frequency response, and see if they lack high end.

Or, you might consider adding a presence control if it doesn't have one. That can really spice up the high end.

[The Kirbster]

The first thing I considered was changing speakers. I hate to, just because the sound is SO close, almost there. The presence control sounds more attractive to me. As long as I use my pedals, everything is fine, I can EQ around the problem (which tells me the speakers ARE capable of reproducing the highs). I'd just like the option of using it without the pedals & EQ. Fact is, for most blues, rock, it's fine as is. I just need extra cut for Roy Nichols-type licks on the country stuff. Already using a Tele w/phase reversal switch, so there's PLENTY of highs going to the amp! It'll squeak, but I can't make it quack like the duck I KNOW she is!

[Gibsonman63]

Presence control is fairly easy to wire in. If you haven't grounded the amp, install a three prong power cord, clip out the death cap and use the ground switch hole to mount your presence control pot. By all means, do not drill holes in the amp. I don't remember off the top of my head, but the values for the presence pot and NFB resistor should be easy to find.

JM2C, but even if the amp sounds perfect, when you mic it through the PA it will never be the same. The microphone colors the sound, the mic placement colors the sound, the channel strip on the PA, your PA equalizer, your PA speakers, the room, etc.. color the sound. I wouldn't worry about mic'ing more than one speaker even if they are vastly different. Unless you are playing really large venues, your PA is only there to amplify the singer and for sound reinforcement for the rest of the instruments.

[The Kirbster]

Well, maybe my amp is newer than I was told, `cause it sure looks to me like a factory grounded plug, and no ground switch. No worries, I will NOT drill the chassis. I'll wire in the presence pot, adjust it to suit me, wrap it all in some kind of insulator, and just leave it inside the chassis. If anyone has more specifics on how to do this presence control mod, I'd appreciate more details!

Yeah, didn't even think about the mic coloring the sound. Guess I'm sweating details too small to worry about. Just `cause I hear it doesn't necessarily mean everyone else does!

[The Kirbster]

My mistake, it DOES have the ground switch.

I've had the process for adding a presence control described to me on another forum, but I'm not very technologically advanced. At least, I'm not advanced enought o follow his directions. Schematics are not much help, `cause even if I find the part on the schematic, I usually can't find it in the amp.

I'd LOVE to have a presence control, but I'm afraid I'd have to have pictures of the process in order for me to do it. Guitar amp techs are (1) scarce, (2) expensive, and (3) known to cop your vintage tubes, caps, etc. and replace with crap here in rural ARkansas.

Anyone willing to walk a poor uneducated Arkie thru a mod? It'll take patience, but I DO know how to drain a cap, and I always stand on rubber mats when futzing around inside anything electric.

[Steve Conner]

Post a high resolution picture of the guts and we'll see what we can do. Do you know how to solder?

[The Kirbster]

Sweet! I'll get the pics when I get off work tonight.

[The Kirbster]

OK, here's 9 of 12 pics of Bassman Ten guts!

[The Kirbster]

Here's 3 more pics of Bassman Ten guts. The shot of the faceplate didn't come across-musta been the dead camera batteries.

This is the model with the mid tone control on the Studio (Normal) side. I was not sure just exactly which part you needed pics of, so I shot everything except the underbelly of the beast.

Or maybe you're just a Bassman Voyeur? God knows I like to look, even if I don't know much about what I'm lookin' at!

Let me know if there is something you need a better shot of. Thanks for your help!

[The Kirbster]

Yes, I can solder, been patchin' my own cables for the last 45 years. Played my first dance at 10, was snuck into bars almost every weekend `till I got old enough to get in on my own. I've been playin' so long, I no longer brag about it, `cause you'd think I'd be better at it by now! I've always maintained my own guitars within reason-I don't know how to re-wind pups, never tried a refret-yet. Always built my own speaker cables, always TRIED to maintain my amps. I just was never around anyone with the knowledge to keep me from hurtin' myself or messin' up my gear. Now with the internet, I feel like I have some (hopefully) new friends to question.

[tubeswell]

See the attached jpeg for my crack at it (from the pics).

(FYI - a pot wired as a 'variable resistor' is when you wire the wiper lug to one of the other lugs on the pot. And if my scaling of these values is correct (and I don't know if it is or not), then you would probably have to use an electrolytic cap for the 20uF cap. These types of caps have a '+ve' end and a '-ve' end, and if you put them in the wrong way around, they can explode!)

The 20uF cap should go at the junction of the 100R cap with the blue resistor and the big orange cap. The '+ve' end of the e-cap points towards that junction. One of the end-lugs (doesn't matter which) on the 250R pot/variable resistor, is connected to the other end of that 20uF cap, and the other lug end of the pot is connected to the opposite end of the 100R resistor (to the eyelet where that other wire is coming off the board).

Somebody will berate me if I've got it bass-ackwards. (I'm only half-guessing at my suggested scaled values: something about using a 250R pot in series with a 20uF e-cap is bucking my intuition, but I can't put my finger on it)

[Steve Conner]

Oh, this is the silverface circuit where they use really low values for the NFB resistors. That makes life harder

Tubeswell, a RC circuit with 100 ohms and 22uF gives me a breakpoint of 72Hz, that seems a little low. I'd try 2.2 or 4.7uF. If it were me, as a first attempt I'd forget the pot and just tack the capacitor across the 100 ohm resistor for a hefty non-adjustable presence boost.

PS, thanks for the effort editing the picture and figuring out which was the right resistor.