Champ for Bass? - yes you read that right.

[holio cornolio]

OK I'm a complete noob so I'm prepared to accept that I'm about to jump in way out of my depth, but here goes: I have a Fender Champ style amp which I built from a Torres kit, and the other day I was tooling about with my P Bass, and getting some very nice sounds out of the Champ. OK, it was clear that the speaker was struggling very hard to keep up, but I found that by riding the P's volume and tone controls (and with the vol on the champ at 12 o'clock - it has no tone stack) I could get all the sounds that I need from SVT style grind, to a nice motowny thump. It's such a simple amp that it seems that you get the true voice of the guitar you're playing. So, I'm thinking, how would I go about building something that could handle the demands of a bass, full time, but with the simplicity of the champ circuit? I'm guessing that simply bolting 4 12ax7s and 4 6v6s into a circuit isn't going to do the trick. Where do I start? Help of all sorts gratefully received.

[Structo]

Well of course the speaker is the main issue.

The bass frequencies cause quite a bit of cone excursion so you should probably use at least a 12'' or 15" bass speaker.

I'm not sure I understand what you are aiming for?

But you should probably try to build a bass amp.

There is more than just the tone stack that makes up a bass amp.
Everything is designed around the bass frequencies.

Also most bass amps that are used to gig with have a LOT of power.
Usually in the 200-300 watt range since it takes more power to make the bass be able to keep up with even a 50 watt guitar amp.

[holio cornolio]

Sorry, I'm not being clear. Most bass amps have a lot of power, because most bassists want a lot of headroom. I don't. I'm comfortably confident that somewhere around 20 - 30 (valve) watts would be adequate for my needs, in terms of volume (currently gigging with 100 watts of solid state power and that's plenty for what I do), and I want something that will overdrive reasonably early too. The champ I have (which is putting out about 3 watts into a 8" cone) has exactly the right level of grit that I want (at about 12 o'clock on the volume knob), but is obviously way too quiet. So I want a way of translating exactly that 'just cooking 6v6' tone, into a bass amp. I don't want any tone controls, I just want to do that stuff from the guitar (bass), and whatever it is about the champ circuit seems to allow for all that without the need for on (or off) board eq-ing.
The champ is perfect for me, it's just too quiet, and the bass will kill it eventually as the output transformer isn't designed to run at those bass frequencies (to generate all that cone movement) and so is probably overloading the old 6v6.... How do I 'translate that tone into something that will work (long term, not just a couple of gigs!) for bass....

[M Fowler]

Check out the schematic for the Fender Bronco bass amp or something like that and go from there with your build. I used to have a small Kalamazoo bass amp that wasn't much bigger if at all. Of course it has two 10 inch speakers. I would run a 15 bass speaker and the volume should increase even with the current champ amp your trying the bass with.

Mark

[billyz]

So why not build the champ circuit and run it into a load instead of a speaker. tap off a line level and into a bigger amp to drive the bigger speaker at the volume you need.

[Tubetwang]

So why not build the champ circuit and run it into a load instead of a speaker. tap off a line level and into a bigger amp to drive the bigger speaker at the volume you need.

Yup! that is what one local band lead guitarist was doing in the 60's.

Lined out champ into twin reverb.

I vividly remember this through this day...

Major Twang

[Stanz]

Sounds like you have the sound you are after, why not mike the speaker into the PA? May not always be an option.

The Champ is single ended. Is that part of the sound? Will any amp you make need to be single ended? Otherwise a 2 6v6 push pull sounds about right. A Fender Deluxe or something along that line. I would definitely try the Champ with a bigger speaker to see if that changes your tone that you have found. I am assuming you will want a bigger speaker for performances.

[holio cornolio]

So why not build the champ circuit and run it into a load instead of a speaker. tap off a line level and into a bigger amp to drive the bigger speaker at the volume you need.

Genius!! That's what I'll do.... Thanks!!!

[holio cornolio]

Check out the schematic for the Fender Bronco bass amp or something like that and go from there with your build. I used to have a small Kalamazoo bass amp that wasn't much bigger if at all. Of course it has two 10 inch speakers. I would run a 15 bass speaker and the volume should increase even with the current champ amp your trying the bass with.

Mark

Hi,

I've been checking out the Bronco schematic for the sake of interest. I'm curious, as far as I can tell, the Bronco is essentially a Champ but with a grown up tone stack in the preamp, and a tremolo circuit - on a bass amp?? Has anyone used one of these? Shoot me down in flames if I'm wrong, but with the treble and bass controls removed from the Bronco, I can't see that much different from the Champ.

I'm in the process of adding a line out and a switchable speaker / load for the champ now, and am excited to see what the results are like. Seems a bit weird to be using an amp essentially as a distortion pedal, but good weird...

Also, spoke to the guy that supplied my output transformer and he seemed confident that it is well up to the job of working with a Bass in such a small amp, although all agree that the poor little 8" jensen 'goin' be good and f*cked up' in no time!! Cheers all for your input

[holio cornolio]

So I've got the line out installed now and it sounds pretty good. It would sound great if it wasn't for the fact that going into another amp naturally amplifies any hum that's present in the first amp. don't know why I didn't think of that before i did it. ah well, if you fix something, you break something else.
I guess long term my best bet is to actually build a gigable valve driven bass amp.

[Wayne]

...or maybe eliminate the hum in your Champ...

[holio cornolio]

...or maybe eliminate the hum in your Champ...

any tips??


thinking about it though - 2 amps, 2 earths = earth loop??? might try disconnecting an earth, but that's kind of frowned upon by the safety conscious....

[Wayne]

Hard to say without being there - it's like trying to give someone a haircut over the phone

Just a couple of quick suggestions, off the top of my head - maybe you could temporarily lift one ground to rule out a ground loop. Also, Champs are single ended. I'm not that familiar with them - never played thru/worked on one, but SE amps are more prone to hum than push-pull. Maybe your Champ could use some more power supply filtering, although that will change the way it feels. If a Champ with a stiffer supply still behaves the way you want it to, you could even look into some sort of regulated supply.

I'm sure other, more experienced folks will chime in with more/better suggestions.

W

[M Fowler]

holio cornolio

Did you get the bugs worked out of the Champ Bass amp project?

Mark

[M Fowler]

I was just looking through my old Fender catolog and spied this small bass amp that you might like to take a look at Musicmaster Bass, 12 watts RMS with 12 inch speaker.