Fender FR-12 preamp mod : The Hissterectomy

WKSmith said:
Here are the first amp 2 stages
Click to expand...

Excellent! I began tracing the differential input stage last night, and my schematic looks pretty much identical to yours :D

I'm thinking about focusing on that final 4558 stage going straight to HornOut as a potential noise source. Everything else to the right appears to be related to the tweeter power amp, built around a TDA2050.
 
Lysander said:
Excellent! I began tracing the differential input stage last night, and my schematic looks pretty much identical to yours :D

I'm thinking about focusing on that final 4558 stage going straight to HornOut as a potential noise source. Everything else to the right appears to be related to the tweeter power amp, built around a TDA2050.
Click to expand...
That is another likely culprit There is a HM4850 mosfet under the board too, it may be for switching though.
 
Lysander said:
Interesting. I assume that's under the tweeter amp section? Can't imagine what would need a MOSFET switch within the preamp.
Click to expand...
I bet it's for the amp sense , soft turn on for the amp module

Edit: it it part of the de-pop circuit for the 2050 amp and horn. It is only rated to dissipate 3 watts of power. It switches off the negative (ground) lead of the horn output.
 
Last edited:
This is why i love this forum.

Manufacturers must dread it though. Any time a new product comes out that even looks in Fractals direction, the forum is tearing it apart :tearsofjoy:


high tech car GIF by Audi
 
Romo82 said:
This is why i love this forum.

Manufacturers must dread it though. Any time a new product comes out that even looks in Fractals direction, the forum is tearing it apart :tearsofjoy:


high tech car GIF by Audi
Click to expand...
I'm pretty sure that's where the quality vrs quantity comes into play! I think it's cool that people are digging into things to make them better or to fix what's wrong.
That said I shake my head that one even has to do that especially in the world we live in today when it comes to knowing how things should be done opposed to how things are actually done.
 
Sixstring said:
I'm pretty sure that's where the quality vrs quantity comes into play! I think it's cool that people are digging into things to make them better or to fix what's wrong.
That said I shake my head that one even has to do that especially in the world we live in today when it comes to knowing how things should be done opposed to how things are actually done.
Click to expand...
It's a shame that we have to write the manual for this thing. But it's a really good platform for tinkering!

At least we are gently picking her locks. Uli Behringer won't be easy on the new girl.
 
Sixstring said:
I'm pretty sure that's where the quality vrs quantity comes into play! I think it's cool that people are digging into things to make them better or to fix what's wrong.
That said I shake my head that one even has to do that especially in the world we live in today when it comes to knowing how things should be done opposed to how things are actually done.
Click to expand...

I noted this on a different forum, but i found nothing wrong with how the FR-12 is built, or even its preamp design philosophy. It's made to look and feel like a "normal" guitar combo, down to how the tone controls and high-cut/presence behave. At $500-ish, is also competitively priced.

The only reason i'm going through mine right now is the noise floor, which is IMHO unreasonably high for a FRFR. I've owned similar solutions from other companies which are essentially noiseless without an input; this is not rocket science.

As a side note, i'd like to see someone press Fender reps on why they're advertising this line as 1000W, when the amps are clearly nowhere near that.
 
Last edited:
Lysander said:
i'd like to see someone press Fender reps on why they're advertising this line as 1000w
Click to expand...

Would probably be wasted effort. Pretty sure we'd just be quietly ignored. Their sales guy has already been saying hand-wavy things on TGF and has even told me things that are technically untrue concerning the Tone Master Pro.
 
jellodog said:
Would probably be wasted effort. Pretty sure we'd just be quietly ignored. Their sales guy has already been saying hand-wavy things on TGF and has even told me things that are technically untrue concerning the Tone Master Pro.
Click to expand...
Tell that dude to PM me. I will fix this thing,
And help with the manual.

It would be easy for a company with such history to say.. it's 150 watts and it is louder than many similar products rated at 1000 or 2000 watts.
 
WKSmith said:
It would be easy for a company with such history to say.. it's 150 watts and it is louder than many similar products rated at 1000 or 2000 watts.
Click to expand...

It's a stupid loud amp. I've been wondering if the speaker is unusally sensitive, because i used to own a Powercab 112, which is 250W RMS, and the FR-12 can easily get just as loud - if not louder.

Then again, the PC 112 was silent AF. You could not tell the thing was on without looking at the back panel.
 
Could be peak vs rms? Could also be 1000 at 1 or even .5 ohms. I'm not giving Fender any pass here other than to say power ratings have always been pretty suspect as there's no real standard way to assign a rating.

I always take what the rating says on the box with a grain of salt. I want to know if it can get loud enough with an acceptable amount of distortion.

But more on the mods: @WKSmith , you haven't quite solved the hiss yet, right? Thinking it's gain at some point within the amp stages?
 
Deadpool_25 said:
Could be peak vs rms? Could also be 1000 at 1 or even .5 ohms. I'm not giving Fender any pass here other than to say power ratings have always been pretty suspect as there's no real standard way to assign a rating.

I always take what the rating says on the box with a grain of salt. I want to know if it can get loud enough with an acceptable amount of distortion.

But more on the mods: @WKSmith , you haven't quite solved the hiss yet, right? Thinking it's gain at some point within the amp stages?
Click to expand...
I'm looking at the rating on the power amp module for the 300w spec.

And yes that hiss is likely several cascaded gain stages. It reminds me of the hiss in a K&K pure preamp, which is entirely just a crappy textbook cut and paste baxandall 3 band eq circuit. Just bad design.

I haven't solved it yet. I put in the new preamp and put it back together. I can't quit playing it long enough to open it up again.

The mod really makes my dc30 models have that elusive boutique voxy chime and with lots of touch sensitivity. I never thought I would see the day that I would become a FRFR tone snob, but here we are. 🤣😂
 
Lysander said:
Think you're right here.

I'm considering opening mine up again and replacing all opamp ICs with OPA2134/4134s, and maybe improve decoupling/filtering; that should help... a bit. The noise floor seems to be more a consequence of design than implementation.
Click to expand...
big heck yeah!
PM me your list of the passive parts you need. I have a lot of nice caps and resistors I can send your way.
 
You must log in or register to reply here.
Back
Top Bottom