Bassman Pre-amp build

[Rafael]

I still kick myself for selling my silverface Bassman and my blackface Bandmaster back in the 80s....but my back has thanked me over the years...and recently I gave my back the best gift since I retired ol' number 14 [my birdseye maple Boogie Bodies bass] by switching out my Seymour Duncan 400 for a Carvin BX500 lightweight head....

But at band practice I've been really digging the sound of a Bassman 100 that is set up as the "house" rig, and it has me GASing for that Fender sound once again....

But there's that back thing....

So I got to thinking, why not build a Bassman WITHOUT the heavy transformers required and use it as a pre-amp for my Carvin? The two of them could share a small road case and give me the best of both worlds.

So I started with this:



which is a low-bit multi effect unit I picked up for almost nothing at my local used gear shop.



A few minutes with a screwdriver, pliers and wire cutters and we have this



Okay, a good start. I've been modding tube amps for a while now, so I have a bunch of miscellaneous parts in the old parts bin, plus I put in an order with Weber for some things I'm out of. In addition I had to order something I'm unfamiliar with: A toroidal transformer for the mains......

The plan is simple: Build a Bassman gain section in a 1U case and use it to drive my power amp so I can turn it up for that tube grind, but throw in a few bells and whistles along the way. Heck, when you get a chance to improve on a classic, no holds barred!

First off I want to have a bit more tone control flexibility, so I'm going to add a midrange control.... and while I'm at it might as well add a shift control to the tone stack. Second, I'm going to run a master volume. Plenty of master volume haters in the git-fiddle world, but I think it makes sense in a pre.

In some areas I plan to go high tech, like how I bypass the gain stage's cathodes. But I'm undecided yet on whether to go metal film or stick with the vintage "tone" of garbage resistors...

If anyone has any bright ideas [I'm definitely not the smartest one on the block] drop me note and I'll try to incorporate suggestions in the final design. And if this has been done too many times, excuse me for beating a dead work-horse, let me know and I'll give up! but I tried looking in the thread bank and hadn't seen this done recently....

[dhsierra1]

have a look at this:

Alembic F-2B

[Rafael]

Originally Posted by dhsierra1

have a look at this:

Alembic F-2B

Nice....well, I didn't think I was the first one to think of this...but I hope I can throw in a couple of unique twists to make mine a little bit different!

[dhsierra1]

Originally Posted by Rafael

Nice....well, I didn't think I was the first one to think of this...but I hope I can throw in a couple of unique twists to make mine a little bit different!

like ice cream, there's always room

[will33]

Man, I'm no electronics whiz by any stretch but I can follow instructions and put parts together.......I'm keeping track of this thread.

I love bassmans, my only complaint has been getting loud enough AND keeping the "warm but still somewhat clean" tone (don't want their grit for bass). Hence I relugated mine to guitar duty. It's a later 135 running on 2 tubes. If you can do a blackface (or silverface, I don't care) pre with a couple bells and whistles (like a decent DI that won't get burned by phantom power), I'm in.

Some of the older alembics come close but not the same. Basically a bassman with no power section is where it's at.

[dhsierra1]

Originally Posted by will33

....Some of the older alembics come close but not the same. Basically a bassman with no power section is where it's at.

I've played through (and own) both Showman (the basis for the Alembics) and Bassman (blackface era) amps and love them both, but what exactly about the Bassman pre do you prefer over the Alembics? Just curious to hear your opinion

[Rafael]

The stock faceplate was never going to fly no matter how Frankenstein I wanted this build to be, so for less than four bucks [shipped....thanks Sweetwater.com] I got a 16-gage [yes in metal thickness it's 'gage' not 'gauge' so please no spellcheckerz] powder coated rack blank and as luck would have it, it just jams onto the front of the chassis.



It's getting pretty crowded there since I want the kitchen sink model, but I think it'll go
input/mute/bass/mid/shift/treble/master/presence/logo/LED/power switch
on the rear would be a fuse, bias test points & trim pot, speaker and line output.

I can see potential for a balanced out down the road but for the moment I just need something to drive my Carvin as it has an out of its own.

[will33]

Originally Posted by dhsierra1

I've played through (and own) both Showman (the basis for the Alembics) and Bassman (blackface era) amps and love them both, but what exactly about the Bassman pre do you prefer over the Alembics? Just curious to hear your opinion

Just your basic non-descript terms like warmth and mojo but I'm thinking that probably has to do with being coupled to a tube power section. For whatever reason, it was like 80-90% of a bassman but wasn't all the way there. If there was a such thing as a 200-300 watt tube bassman, it'd likely be the last amp I ever buy. Yes, I know about the Studio or whatever the 200 watt one is but haven't found one. Basically I want the bassman's warm but relatively clean tone at higher volumes.

[dhsierra1]

Originally Posted by will33

Just your basic non-descript terms like warmth and mojo but I'm thinking that probably has to do with being coupled to a tube power section. For whatever reason, it was like 80-90% of a bassman but wasn't all the way there. If there was a such thing as a 200-300 watt tube bassman, it'd likely be the last amp I ever buy. Yes, I know about the Studio or whatever the 200 watt one is but haven't found one. Basically I want the bassman's warm but relatively clean tone at higher volumes.

I hear you, there's something about having the tube power section adding that extra "something". And I really love the Fender sound, no slam on Ampeg or Mesa, just my preference.

That said, have you ever experimented w/any of the mono/stereo tube power amps that've come down the pike over the years, I think Peavey had the Classic 120 (they make a stereo 120 a side one, too) and I believe Carvin makes a tube power amp but don't recall the stats on that but believe that hits triple digits.

I know the PV uses 6L6s like the Fenders and I think the Carvin does as well.

Perhaps those coupled w/what the OP's pre or the Alembic might be a way?

Sorry OP, didn't mean to hijack the thread

[will33]

Carvin's is a 100 watter, not enough, nor peavey's 120. Haven't actually played either but I know they're not enough to get the "warm, sorta clean, and loud" I'm looking for.

[dhsierra1]

ah, perhaps the stereo version of the Classic 120 so you get 120 into each, say, 15" driver if that's your poison? Then you've got 240 watts.

[will33]

Originally Posted by dhsierra1

ah, perhaps the stereo version of the Classic 120 so you get 120 into each, say, 15" driver if that's your poison? Then you've got 240 watts.

Now that could work, sounds nice.

[B-string]

Originally Posted by Rafael

The stock faceplate was never going to fly no matter how Frankenstein I wanted this build to be, so for less than four bucks [shipped....thanks Sweetwater.com] I got a 16-gage [yes in metal thickness it's 'gage' not 'gauge' so please no spellcheckerz] powder coated rack blank and as luck would have it, it just jams onto the front of the chassis.



It's getting pretty crowded there since I want the kitchen sink model, but I think it'll go
input/mute/bass/mid/shift/treble/master/presence/logo/LED/power switch
on the rear would be a fuse, bias test points & trim pot, speaker and line output.

I can see potential for a balanced out down the road but for the moment I just need something to drive my Carvin as it has an out of its own.

I though you just wanted a preamp! You are not going to be able to fit output tubes (reason for bias test points or speaker outs) in that case and the iron transformers, the bulk of an amps weight.

[Rafael]

Originally Posted by B-string

I though you just wanted a preamp! You are not going to be able to fit output tubes (reason for bias test points or speaker outs) in that case and the iron transformers, the bulk of an amps weight.

Will33 read my mind....I've been thinking about the contribution to an amp's sound by the inverter and, for that matter, to the output tubes, so I'm planning a type of amp emulator so you can get the full sound of the amp at the line out.

[B-string]

The trouble lays in the tube output and how it interfaces to a speaker (impedance only one factor, also inductance, it is a reactive load with back EMF not a static load). Otherwise with a small tube amp you like the sound of (with a speaker you like) a speaker to line converter will work (but you will be carrying two rigs). At that point you would be better off miking the one rigs cab?

[dhsierra1]

Originally Posted by will33

Now that could work, sounds nice.

they can be found for around 300 or so clams, not as rare as the 200 watt Fender. I have the 60 watt version and like it very much w/vintage speakers and roll yer own tube pre's. Nice sound IMO.

OP, what are you planning for the power supply? You have a few challenges ahead of you w/a 1U rack mount and whatever add-on's you're planning. Obviously quite do-able based on what's out there, just checking.

[Rafael]

Originally Posted by dhsierra1

OP, what are you planning for the power supply? You have a few challenges ahead of you w/a 1U rack mount and whatever add-on's you're planning. Obviously quite do-able based on what's out there, just checking.

I looked around and decided that given the limitations of the 1U form factor it was going to be a toroid, and the smallest one I found that included a 6.3v tap for the heaters can handle enough current to run way more than I'll need for this setup. I'm not concerned with power supply rail sag like a guitar player would playing a Bassman dimed so the high tension is going to be a full wave 1N1007 array through some large caps....power supply hum is NOT a desirable vintage tone!

[B-string]

Reduce hum? DC filiment supply regulated. Careful on the PS build, too large a cap load before any dropping/filter resistors will cook the trans.

[Rafael]

Originally Posted by B-string

The trouble lays in the tube output and how it interfaces to a speaker (impedance only one factor, also inductance, it is a reactive load with back EMF not a static load).

Which is the theory [and one I don't disagree with] with Weber's power soak, a speaker driver sans cone in a box...all the squishy analog interference we hear as amp/speaker interface tone....

...but I'm not a purist, and I'm not getting THAT freaky with this....tapping into the full signal chain less the drivers is enough of the real thing for me in my application. But even THAT is semi-emulatable [is that a word?!]

[will33]

Full disclosure.......I don't know what all that other stuff you guys just said is but "tapping into the full signal chain sans drivers" sounds mighty nice to me.