Will a Bassman/Champ preamp work as a dirtortion 'pedal' before my all tube amp?

[carlo]

Hello everyone! I was thinking of building a tube preamp, either from the Fender Bassman(5F6-A model) or the Fender Champ(5F1), to use as a distortion unit before my FBT 500R tube amp. My question is, will it damage the amp? i just got into tube amplification and i find it to be somewhat more delicate than transistor units, hence my preoccupation. im choosing to build a preamp rather than a more traditional distortion as a first step to buildig a complete amp. im using the schematics from this site http://www.classictubeamps.com/preamp.html as a reference, anyway, as i said, im new to tube amps so ill probably have lots more questions coming. thnks a lot in advance for all the advice!!! if there is something thats not clear or for other info just ask! thanks again. Carlo.

[Mark Hammer]

Pretty much anything that provides an input signal in excess of what your amp is expecting from a guitar will serve to generate distortion, and so act like a distortion pedal.  Whether it yields the sort of distortion you want is a whole other matter.

Indeed, many of us here tend to find it ironic when people make requests for "clean boosters", because the unstated goal is often to push the amp hard enough to produce distortion...in which case the cleanliness of the booster doesn't really matter all that much.

Will it damage the amp?  Depends.  Certainly anything that ends up generating too much heat in the speaker voice coil, or the output transformer, can be damaged by applying excessive input signals, but then that's usually one of the very good reasons for including a volume control on most amplifiers. 

I can understand the desire to tinker with tube distortion rather than solid state, if all the anticipated distortion is supposed to come from the tube unit itself.  On the other hand if the intent is to garner more pleasing distortion from a tube amp, especially if the kind you like is power-stage distortion, then the particular technology used to push the amp makes no difference.  Tubes are as good as transistors, analog ICs, or digital emulation.  That doesn't mean there is no reason to prefer a tube-based pedal over a discrete transistor or IC-based one.  rather, one doesn't truly need it to elicit pleasing sound from a tube amp.

[Tubebass]

Try searching  Garnet Herzog.

[carlo]

thanks a lot! i have to admit i have no idea what im looking for or what ts gonna sound like, the idea was to simply to amplify the signal before it runs through to amp(since i have to get it all the way up to 10 to get some distortion). anyway looking at the garnet herzog(Thanks, thats just what i was looking for!) i got the idea of putting an input and an output pot. now the question is, where do i put the input pot so that i can get some distortion from the preamp aswell? taking the Bassman premp circuit in consideraton, my first idea was to make the 68k grid resistor a variable resistor so i can controll the amount of signal going in to the first tube(12ay7). then i saw a sort of feedback loop going from the plate back into the grid of the second triod of the second tube(12ax7) passing through a 100k res. which i could replace with a 100k variable resistor(i was thinking that this way, even if the pot was all the way to 0 it wouldnt completely kill the signal). the first idea is kind of trickier since there are 4 of those 68k res. and i dont really know how to replace it without rewiring the whole thing and maybe leaving out the high gain/low gain inputs. but... if they both work i guess ill put them both in and see what happens .

[lopsided]

Hi Carlo,

I am trying out something similar, with the Vox Berkeley preamp stage. I know that tubes are not magic but I just think it is fun to try to get the touch of different technologies.

The preamp , at least in my case is able to produce very hot signal, so I decided to put a resistor in series with the output cap and a classic volume pot after it. You have to experiment with the best values though.
Here is my original tread: http://www.diystompboxes.com/smfforum/index.php?topic=94289.msg812943#msg812943
And here is one where I am discussing amp safety problems: http://www.diystompboxes.com/smfforum/index.php?topic=94905.0

Have fun with your projects!
J.

[petemoore]

  I'm inclined to beleive that clean preamp is a clean preamp whether it's Mosfet, Jfet, tube...whatever...clean is clean.
   I use clean tube preamps to drive the output stage of my tube amps, I have only build 'standard' types of amplifiers which include preamp tubes. Back to the inclination to move away from tubes...since they're built I'm happy, but if designing a distorting amp [for my druthers] it'd be Output distortion and it seems as long as the 'clean' preamp drives the tubes into non-linear behaviour [regardless of the actives chosen for the job] it'd work as expected...except solid state is more reliable, less expensive etc.
   Also making mention of si or other distorter before the output amp, which 'could' be tube, but having messed about with tube-pre-distorters and reverting back to traditional non-tube type distorters for pre-preamp signal processing.

[zambo]

I made a trainwreck style preamp using 12ax7 tubes and running in starved plate mode at 12 volts. It worked surprisingly well. traded it to a body for a wah. it also works well but thats a different story. try the starved plate au7's and see if you like it. its pretty cheap and very fun without a ton of danger. They also sound good going into the poweramp in of my tube amps. make sure you use a larger size input cap as at low voltage the grids tend to conduct and make scratchy pots etc.

[DavenPaget]

Greg , the 12AU7 draws more current then the 12AX7 . One needs to be careful .

[zambo]

yeah, I always use a onespot power supply thats 1.7 amps so it does the heaters fine and can handle the current draw. you can run 3 12au7's with a smps  off one of those pretty well.

[DavenPaget]

yeah, I always use a onespot power supply thats 1.7 amps so it does the heaters fine and can handle the current draw. you can run 3 12au7's with a smps  off one of those pretty well.

I was talking about the bias resistors .

[zambo]

I been using 1/2 watt. are those to light duty ?

[DavenPaget]

I been using 1/2 watt. are those to light duty ?

That would be sufficient , i believe .

[zombiwoof]

Pretty much anything that provides an input signal in excess of what your amp is expecting from a guitar will serve to generate distortion, and so act like a distortion pedal.  Whether it yields the sort of distortion you want is a whole other matter.

Indeed, many of us here tend to find it ironic when people make requests for "clean boosters", because the unstated goal is often to push the amp hard enough to produce distortion...in which case the cleanliness of the booster doesn't really matter all that much.

Will it damage the amp?  Depends.  Certainly anything that ends up generating too much heat in the speaker voice coil, or the output transformer, can be damaged by applying excessive input signals, but then that's usually one of the very good reasons for including a volume control on most amplifiers. 

I can understand the desire to tinker with tube distortion rather than solid state, if all the anticipated distortion is supposed to come from the tube unit itself.  On the other hand if the intent is to garner more pleasing distortion from a tube amp, especially if the kind you like is power-stage distortion, then the particular technology used to push the amp makes no difference.  Tubes are as good as transistors, analog ICs, or digital emulation.  That doesn't mean there is no reason to prefer a tube-based pedal over a discrete transistor or IC-based one.  rather, one doesn't truly need it to elicit pleasing sound from a tube amp.

Mark, when people talk about "clean" boosters, I think they are really saying one that doesn't color the sound or change the basic tone of their guitar.  Obviously the booster is used to hit the front end of the amp hard to produce distortion, but the term "clean" is used to differentiate the sound of the booster from those that color the sound in a certain way (such as in the case of the vintage "treble boosters" of the past).

Al