Question: Practice Amp into a Pedal?

[One-Eyed Shaman]

I was testing out a boost circuit I built on my 25 Watt Fender Frontman solid state practice amp - the boost was crazy loud and was overdriving my amp like crazy - and I really liked how it sounded. I really don't know how amplifier circuitry works, but I'd like to see if I could recreate whatever part of the amp was being overdriven and put it into a pedal form.

Maybe someone could take a look at the schematic for the amp and point it out?
http://support.fender.com/schematics/guitar_amplifiers/Frontman_25R_Schematic_653.pdf

Not sure if what I'm asking is absurd or not, but thanks.

[antonis]

Amps are divided in two main sections: Pre-amp (which is Voltage amp + any Tone/Volume/Effect adjustments) and Power-amp (which is Current amp).

Normally, any overdrive/distortion happens comes out from Pre-amp and is simply powered up (same voltage - more current)..

If amp's output is capable to normally drive speaker load there isn't any "extra" distortion (only the one that comes from pre-amp) so you have to recreate pre-amp circuit but this is allready done in many distortion pedals, which actually play the role of Pre-Pre-Amp..

You also have to take in mind the fact that the excisting combination (boost+preamp) works fine with the specific Power amp doesn't ensure it for any other combination.. 

[GibsonGM]

What Antonis says is the reason why there are so many boosts, overdrives, distortions and all the other million things we use to "get the mojo going"!  What would sound really good in pedal form for use with one amp would most likely be unique to YOUR setup, and would fall short for many other users.   That's part of why many players LOVE one pedal, but others say "this sounds like junk with my rig!".   Other factors are of course musical genre, quality/tone of the instrument used....   

You can't really determine ahead of time how much boost, how much low end cut, mid scoop or boost, is needed to get THAT sound.  You can't even build in enough variation in controls* to allow the user to customize your pedal to their rig, either.
*Not very easily or affordably, anyway....

One eyed - I think you just opened the topic "Why do you guys spend all this time tweaking, redesigning and playing with these circuits with your (and others') amps???"     You might be able to (and I bet you will!) make something sorta like what you suggest for YOUR setup, at lesser volumes - so, get busy!     Now that you've heard it,  you know what you are shooting for.

Welcome to the forum...

[antonis]

Welcome to the forum...

 

Sir Mike indeed IS a gentleman..!!!

@One-Eyed: My apologies..

[Granny Gremlin]

There is precident for this, and it is not entirely a bad idea. 

[TLDR]
Back in the 60s, in Winnipeg, an unknown guitarist kept taking his amp into an unknown repair guy  with the input section blown.  Eventually this tech asked the kid what the F he was doing to blow his preamp section so regularly and in the same way.  Turns out he was using a small combo amp as an OD device, unplugging the internal speaker and running the output into his main amp.  After the tech calmed down, he built him the first Herzog; basically a Fender Champ with a different output transformer - for 10K HiZ guitar level output to play nice with a downstream amp vs driving an 8 ohm speaker.  This was the birth of Garnet amps and The Guess Who.  Randy Bachman went on to use the Herzog to create that uber-distorted creamy American Woman lead tone that has often been copied but never quite duplicated.
[/TLDR]

All you need to do (and if you liked how this worked for you, I think it IS worthwhile despite the above comments) is duplicate the practice amp circuit (or mod your existing amp) for an instrument vs speaker level output.  Likely both the preamp and power sections are a part of the tone you were liking and only using the preamp circuit will be disappointing (but it would be easier, both due to smaller build and fewer mods being necessary to get the right level output).

[slashandburn]

If the goal is to build a distortion pedal that loosely resembles how your amps gain pot responds with your booster in front, a crude design would surely be to play with your chosen booster circuit in front of that U2B block of the circuit on your schem, but I'll emphasise the word crude. I'm also certain other responses are more along the lines of what you're asking. This is interesting though. Feeding another power amp the output of a power amp, you say? Doesn't sound like something for the feint-hearted!

[Mike2E]

I have a few amps, solid state Roland cube and valve fender deville hot rod. I wanted to get a valve sound from the solid state, and found this simulator.
http://www.siliconchip.com.au/Issue/2014/August/Nirvana+Valve+Sound+Simulator?res=nonflash
It simulates high fi amps but but is configurable.
I measured the Fender amp response, and then used information in the article to setup the device to copy it. Quite close in sound using the simulator on the Roland Cube 60W vs Fender. It has a few components you change and then controls set clipping and speaker response. The device is stereo, so looping through one into the other channel you can get heavy distortion

[Guitar Poppa]

Hello !

My english is not very good, so I don't know if I exactly understood what you need...
If you are looking for a low power practice amp, stompbox sized, with a credible classic sound, including overdrive, I may have something good for you...

My GeAmp1W has been designed one year ago. Its is germanium amplified, with level control, a special one knob tone control, 2 presets. The silicium preamp is high impedance and low noise. The overdrive [edit : is produced by] the germanium power amp, much more warm and creamy than silicium. All discreet components : not an IC pharmaceutical sound ! It works with any supply 7 to 12V, negative grounded.
The minimum output power is 0,5W with 7V and 8ohms, 1,3W RMS with 12V and 4 ohms.

Here are to pics  from my site :




You can see that product on my Website : http://guitarpoppa.com/?p=2801
The technical sheet is dowloadable on this page.


I also can give you the power amp's schematics, that are the most typical. You'll add by yourself the preamp and the tone control you want.

Waiting for your visit !
Guitar Poppa

[Hatredman]

How do you guys get so many Ge transistor nowadays?

[Guitar Poppa]

How do you guys get so many Ge transistor nowadays?

Hello Hatredman !

Germanium came back fashionable about ten years ago. A little earlier for old folks like me, who began tinker electronics in the sixties... We remenbered of the warm sound and soft clipping that old technology gave to amplification gears... And of its genetic defects (leakage, current shifting caused by heath...)

When vintage stompboxes came back into actuality, I began to buy NOS components. In the 2000's, there were still stocks of original Philips/Mullard transistors in Europe. They got quickly exhausted, but there were other treasures : Huge stocks from Eastern Europe and USSR. French and dutch companies used to subcontract their production to eastern Europe. It's been easy to earn these components, which are good quality. Moreover, russian Ge transistors are very easy to find and buy in Europe. They are often better on the technological level than european and american material, because russians kept on manufacturing them when western countries stopped production in the late sixties : from 1968 to 1988, they had plenty of time to fix or attenuate the genetical defects of germanium.
So I have now hundreds of western Ge transistors and thousands of Eastern ones... I created the Guitar Poppa micro company to exploit my old knowledges and that stock I acquired at the right time ...

More informations on Ge transistors on my Website guitarpoppa.com ...
Best regards