Fender FR-12 preamp mod : The Hissterectomy

WKSmith said:
@marsonic I built acoustic preamps for several years. I still have a lot of parts.

and a fair bit of experience having PC boards made, sourcing parts, and assembly/wave soldering.
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That was some good detective and diagnosing work.

I like my PXMs for their form-factor and think their sound meets my needs but I definitely understand that some speakers sound more musical and some have an analytical sound. For recording I preferred the sound to reveal the mistakes and for performing I want a prettier, more musical, sound.

I’d switch over to Fender’s offerings if I felt they would meet my form-factor goals, though I’d get a 10” and a 12”, and I’d definitely want to have the circuits fixed, either from the factory or aftermarket.
 
WKSmith said:
I'm going to say this after getting deep into this thing.

1) It sounds great. Already.

2) It has a cabinet behind me singing mojo. Like damn near spiritual. It's got something going on there.

3) It works so (&$&#%) great with my Fractal presets!!

3) the balanced power supply has a goregeous bi-polar and nicely filtered design. With a low-z buffered ground plane. Really. Nice .

The input is true balanced, and can take +4dB.
All of it. 😉
..Seriously the Fractal out set to +4 and the knob all the way up kind of +4 balanced in.

Parts tho ... Meh

4) they used an old school full size post-thru-hole pcb! Shut you mouth! Old analog sauce.
No programming bi-quads in digital. No latency. .. It's just dang resistors and caps, and amp stages.
I seriously Love them for that!

I love it. It's badass.

..... and it has a tad* bit of hiss.


*Which could be eliminated with a reference quality eq design. And by throwing out 9 amp stages and several dozen resistors and caps .
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this has me thinking. How is everyone setting their outputs on their fractals. If i recall there's a difference between say FM9's and the AF3. REason I'm thinking this, and I could be wrong, is I have Austin buddy's presets and in his instructions I believe for FM9's to run outputs full on vs Axe Fx III to gain stage bit differently like have it around noon/1'oclock ish. I'm vaguely remembering. I have my AF3 on +4 setting and running XLR direct to the F12's. I have my output 1 pretty low...only about 9/10' o'clock. Im only needing moderate volume but signal to noise ratio/optimal signal and all that jazz...should I change that? Like higher output coming from AF3 and just lower the volumes on the cabs be better?
 
Chewie5150 said:
How is everyone setting their outputs on their fractals. If i recall there's a difference between say FM9's and the AF3. REason I'm thinking this, and I could be wrong, is I have Austin buddy's presets and in his instructions I believe for FM9's to run outputs full on vs Axe Fx III to gain stage bit differently like have it around noon/1'oclock ish. I'm vaguely remembering.
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The FR-12 and FR-10 can handle +4dBu at the input, so you can't easily overload it.

With this in mind, I'm running the output from my FM9T fairly hot. Output 1 is at roughly 75% in +4dBu output mode.
 
IMG_1096.jpeg

Here is the new eq design. 4
Make that. 3 clean filters.

One fixed filter to set the stock house curve (the magic sauce) with a bypass switch for true flat response.
Edit: the house curve is not in the eq except for the taper of the pots boosting bass and cutting treble when set to 5.

3 Eq bands tuned almost exactly like the factory eq

Perfectly in phase. Ultra low noise. Ultra low impedance. Low parts count . 12 resistors, 7 capacitors, 4 amp stages. )

Now to order a couple of components 🙂
 
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WKSmith said:
View attachment 128485

Here is the new eq design. 4 clean filters.

One fixed filter to set the stock house curve (the magic sauce) with a bypass switch for true flat response.

3 Eq bands tuned almost exactly like the factory eq

Perfectly in phase. Ultra low noise. Ultra low impedance. Low parts count . (16 resistors, 9 capacitors, 4 amp stages. )

Now to order a couple of components 🙂
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Wait, you‘ve already gotten a replacement PCB designed and fabricated? :openmouth:

-Aaron
 
aflynt said:
Yeah the spacing of the pots on the PCB should have given this away. :)

-Aaron
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It's just the right size to put in an enclosure to sit on top of the FR-12. That way I leave the stock eq intact and can switch between them.

If it doesn't sound exactly like the FR-12 does now, it's not worth putting in a mod. It's not worth the effort if it means losing even 1% of the amps mojo for a tiny bit of hiss.
 
WKSmith said:
Here is the new eq design. 4 clean filters.
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Count Me In Rick And Morty GIF
 
This is all very amazing and much appreciated. While I love the design idea of the FR12, I have no clue how to do the brilliant mods you guys are describing. Will have to wait for Fender to hopefully release rev 2 of the FR12 with little to no zero volume hissing. Unless if used in a live band setting the hiss would be a non-issue.
 
JustCuz said:
This is all very amazing and much appreciated. While I love the design idea of the FR12, I have no clue how to do the brilliant mods you guys are describing. Will have to wait for Fender to hopefully release rev 2 of the FR12 with little to no zero volume hissing. Unless if used in a live band setting the hiss would be a non-issue.
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In a band setting the hiss is not really an issue at all. It's only in a quiet room that it becomes evident.

I am hoping Fender will revise the eq circuit if my design works as expected.
 
JustCuz said:
This is all very amazing and much appreciated. While I love the design idea of the FR12, I have no clue how to do the brilliant mods you guys are describing. Will have to wait for Fender to hopefully release rev 2 of the FR12 with little to no zero volume hissing. Unless if used in a live band setting the hiss would be a non-issue.
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Well, based on this....

WKSmith said:
First pic is stock, 2nd pic is modded,
View attachment 128211View attachment 128212View attachment 128213
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and some assumptions, if you did want to mod it and if WKSmith actually produces boards, it looks like it could just be a couple plug-in connectors and un-attaching the pots from the chassis....which isn't too much for a lot of people and would be easy for an amp tech.

But maybe I'm making incorrect assumptions.

@WKSmith the scoop that someone (maybe you) measured....do you know if that's from the EQ not being flat with the knobs set neutral or from the EQ actually being neutral and the scoop coming from the speakers?
 
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