Modding a Fender Frontman 15G?

ribolovec2

Member
2009-12-09 6:19 pm
Hello, guys. I have a Frontman 15G but it isn't the best amp you could imagine.. it has no reverb.. the guitar tone is a bit odd and the amp has lots of noise and thermal hiss. I have just opened the enclosure and I saw that the PCB has empty spaces with missing parts and it says 'for reverb models only' .. which makes me think that the PCB for the reverb model (15R) and the non reverb model (15G) is the same.. So maybe i could just add the missing parts.. but I can't find a schematic for the R-version.. could someone help me, please?
Another thing.. about the hiss - the solution is to lower the values of all resistors which comprise dividers and filters (for the filters if i lower the resistor's value n times, i have to raise the capacitor's value n times to keep the same RC constant and therefore frequency response), right? Do you think that all that can be done and is worth it?
 
Assuming it's the exact same board, and you can identify (and obtain) all the parts, then you should be able to add the reverb - but it all depends if you can find what they are, and obtain them (specifically the actual reverb unit - depending what it is).

I must admit I'm dubious about reducing noise and hiss by altering the values, for a start I would identify where it's coming from.
 

wakibaki

Banned
2008-01-08 11:51 pm
Here is the schematic:- http://support.fender.com/schematics/guitar_amplifiers/Frontman_15G_Schematic_68F.pdf

There are multiple copies of the schematic if you just google Frontman 15G. I haven't heard this amp. but I'd agree with Nigel, if there's a lot of noise and hiss it's probably because of a fault. OK, it's solid state, which isn't a big recommend, but Fender equipment is mostly pretty good. So don't go messing with the filters, just fix it before you attempt any mods.

w
 

ribolovec2

Member
2009-12-09 6:19 pm
wakibaki, your schematic can easily be found on the Net, but if you have a close look, you'll notice that it doesn't contain the actual reverb section and the pcb layout has a blank white spot exactly where the reverb components should be. Thanks a lot anyway. I'm not talking about lots of hiss and hum.. with the guitar plugged it's hardly audible, but it is pronounced with the instrument unplugged, when the input is shorted to ground automatically, which eliminates ground hum as an option.. it can only be thermal hiss, I suppose. However, I'm going to add the reverb (or at least see if I can) first and then experiment a bit with the filters and the hiss.
 
wakibaki, your schematic can easily be found on the Net, but if you have a close look, you'll notice that it doesn't contain the actual reverb section and the pcb layout has a blank white spot exactly where the reverb components should be. Thanks a lot anyway. I'm not talking about lots of hiss and hum.. with the guitar plugged it's hardly audible, but it is pronounced with the instrument unplugged, when the input is shorted to ground automatically, which eliminates ground hum as an option.. it can only be thermal hiss, I suppose. However, I'm going to add the reverb (or at least see if I can) first and then experiment a bit with the filters and the hiss.

If it's quiet with the guitar plugged in, but hisses when it's not, then it sounds like the socket isn't shorting out correctly. You would expect any guitar amp to be noisey with an open input (which is why the jack socket is supposed to short out).

The overdrive channel is also likely to be noisely regardless, that's a consequence of high gain and clipping.
 

shanx

Member
2010-12-23 7:15 pm
Quebec
For curiosity sake I tried a 25R out at a music store, and it had much the same issues as the 15G/R. Entry level practice amp with a low price tag so it wasn't really surprising. That was the reason I revisited this thread, because I guess there maybe a few people could be interested discussing possible mods and/or upgrading these things.
I don't know if the OP ever did the reverb add-on and filtering mods or if the project was abandoned and the amp is sitting in a dark corner somewhere...
If there is some interest maybe I should start a new thread?
 

shanx

Member
2010-12-23 7:15 pm
Quebec
Yes I agree that a speaker upgrade would be major tone improvement. Even adding an external speaker jack would be a simple way to make it flexible and try larger speaker, or make it an amp ''head' as I saw some guys doing (which ruins the combo portability )
The thought crossed my mind about the tube champ, but looking at the chassis of this (just a bent sheet of thin steel) I think I would reserve all that good tube stuff for a proper chassis and tweed cabinet!!
The 25R has a very small reverb assembly inside the chassis. The reverb is a problem: it gets really muddy at higher depth settings (over 2 or 3) and maybe a combination of the feedback circuit and lack of a proper 'verb tank.
 
This is what sort of bothers me about a lot of the entry level solid state amps and not just this series. There are these op amp sections with tone shaping, and I am not sure if they are there mostly to compensate for an inferior speaker? This is a noisy amp, there is a bit of an odd tone to it, almost a caricature of an early fender. Clean is passible, but the ''overdrive'' is (to put it mildly) sounding like a really cheap fuzz pedal IMHO. Champs and Princetons did what they were designed to do incredibly well and surpassed their roles as student amps, remaining pertinent after decades.
Sorry I went on a bit of a rant there...but it just bugs me.
So speaker would be a definite. Verb tank too. Redesign of OD and warm up the Clean channel. Big list, more thoughts?
 
Just some electronic ideas:
2 stage FET preamp at input somewhere before channel switch, maybe after 1st op amp
Princeton tone stack (or bassman)
OD channel String of multiple Ge diodes or diode connected Mosfets ( à la Zendrive)
or complementary Mosfets. Add pot across clipper pair and adjust so there is come semblance of not being on or off. The present circuit hits the clipping limit really hard when you bring up the overdrive gain.
 

shanx

Member
2010-12-23 7:15 pm
Quebec
On reviewing the schematics of the Frontman series all the way up to the 212R, I ended up with a lot more questions about the overall designs. Not that I don't understand the basic circuitry, but more questions about ''why is it done that way''? Are the design engineers at Fender content enough tone-wise with the entire preamp and ''overdrive'' that they basically recycled it from same, for example Princeton 112 Plus from twenty years ago?
Why run a tone stack through the clean channel only , but some different fixed network before the ''overdrive'' circuit...(with all sorts of fancy tone shaping post overdrive on the 212R)? That filter pre-contour before the drive is all scooped out and tinny sounding even before it gets to clipping.
There is enough issues here to contend with that if one considered modding it, that a load of stuff would get pulled and redesigned. Is it worth the time and money? I am not quite so sure yet.
Maybe a complete new designed board upgrade at that point, done from scratch...which is where I am probably heading.
 
The Frontman series is an entry level series of products.

What Frontman 15G are you looking at? On both the Mexican and Indonesian versions I see a split after the input stage, branching to the overdrive or the clean, then they merge, and the tone stack is common to both.

But looking at the FM212R, once again the signal path splits after the first stage, the lower branch is the clean and it does have a tone stack going into it. But look at the overdrive channel above. There are clipping diodes and tone shaping for sure, but look just left of the reverb drive, and just right of the mid contour switch, and there it is, another tone stack just for overdrive channel.

Scooped out and tinny overdrive? That is what the kids want in an amp.
 
We must remember that these are marketed as budget amps with little concern about good "tone" when they were designed. Features, cost, and marketability were the top priorities, if you want a practice amp that happens to sound great, buy a Vox Pathfinder, and upgrade the speaker to a Weber. With these fenders, they are best suited as second amps for a budget stereo setup, children's practice amps, or cabinets for tube builds or extension speakers. We would waste more money than it's worth to upgrade these amps, just use them as they are, and maybe upgrade the speaker, but dont try to mod their garbage PCB's and destroy the amp in the process.
 

shanx

Member
2010-12-23 7:15 pm
Quebec
Apologies Enzo, I did not comment correctly on the tone stack. What I should have said was the tone stack(s) only happen post clip, when overdrive is engaged. The pre-shaping filter is ''fixed'' not variable before the distortion circuitry.
You and pbarnell are right, that is why I decided to do a different design-build. I ''pulled the plug'' on buying the 25R, even at $100, as it would only be the enclosure being used (and maybe the transfo). I will focus on ''good tone'' with a bit different approach. Thanks!
 
''why is it done that way''?
Because it works.
or ... you can't argue with success

Or, to qualify these apparently bold statements:
*Natural selection*
which in this case means:
this is a cutthroat competition Market ; whatever you make, if it sells appreciably less than others, dies a "commercial" death.

So the survivors are:
* 10/15W amplifiers (because that's "enough") , as in: 2W amps are too weak and above 20W become more expensive than what kids expect to pay
* SS beats tubes BIG WAY, costwise
* cheap 6" speakers are about the minimum, cheap 8" still affordable and "good enough", cheap 10" are on the edge. Forget a good 10" or any 12" there.
* cabinets should be small/light enough so a kid or teen can easily grab one in one hand, a guitar or bass in the other, put some cables and pedals in his backpack and still be able to travel on public transport or not be a nuisance to somebody who gives him a ride.
*the whole shebang should cost $50/100 , not much more.

Under those strict conditions, it's very hard to deviate from the average beginner amp design.

FWIW those small amps can sound VERY good, problem is that beginners aren't savvy on getting the best out of them.

Just 2 examples:
1) ZZTop ripped the guts of the smallest , entry level Marshall amp, the Lead 12 (a.k.a 3005 or 5005) , mounted them in racks , and used them live and in studio, for thunderous sounds.
Yes, they used the line out to drive huge PA type power amps and lots of 4x12" cabinets .... but didn't touch or modify the circuit, because "it was a power or speakers problem, not an EQ one"

2) here's a clip from a Australian friend.
Believe it or not, the guitar sound you hear comes from an overdriven Fender Squier 15 amp, 8" speaker, close miked with an SM57 and fed to the PA.
The walls of Marshalls are used as props, disconnected .... or it would be impossible to play in that stage, and sound mixing would be chaos:
Beyond Salvation - The Angels - Live 1990 - YouTube