Fender FR-12 preamp mod : The Hissterectomy

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 bi-polar and filtered design. But adds a reflicted charge pump pair of transistors to inflate the opamp supply voltage from 24v to 37.2V entirely removed in the final V2 pre design.

The input is true balanced, and can take +4dB.
Most of it. 😉

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 fair 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 .
 
Last edited:
I mentioned in the eq thread that the notch in the high frequency was likely the crossover. It is, and here is why.

The bottom chart is the spice sim for the crossover circuit.
Blue is the class D amp out for the 12"
Yellow is the horn amp out for the compression driver. I believe I can tune the low pass a little higher and fix that too.

Screen Shot 2023-10-17 at 12.50.22 PM.jpegScreen Shot 2023-10-23 at 9.42.34 AM.png
 
Last edited:
I believe you said your Mute switch "mutes the amp at the crossover Input." Can you explain this concept? What exactly is that muting and why?

(Edited)
 
WKSmith said:
I mentioned in the eq thread that the notch in the high frequency was likely the crossover. It is, and here is why.

The bottom chart is the spice sim for the crossover circuit.
Blue is the class D amp out for the 12"
Yellow is the horn amp out for the compression driver. I believe I can tune the low pass a little higher and fix that too.

View attachment 128439View attachment 128440
Click to expand...
Change 2 capacitor values and it does this
 

Attachments

  • Image 10-23-23 at 10.28 AM.jpeg
    Image 10-23-23 at 10.28 AM.jpeg
    70.4 KB · Views: 45
Deadpool_25 said:
I'm probably nitpicking here, but I don't think the FRs are weak in any way. I actually think it's quite a strong entry into the FRFR market. Saying "it only took $10 to fix half the problems" means that there were problems to fix (and it implies numerous problems). Although it sounds like @WKSmith may have improved a few things that doesn't mean those needed to be improved.

If I understand it correctly, he was attempting to address the little bit of noise. In that attempt he changed out some components for better quality ones. Again, if I understand correctly, that didn't have a significant impact on the hiss, but did end up making the FR sound a bit more musical (I believe this but I think it needs verification as well).

I think the single "issue" identified so far is the hiss and there's been no solution yet. Actually that's not true. There is a solution: turn the Cut knob up a little. Although I'd personally argue that ideally you wouldn't have to do that, I could easily argue the counterpoint that turning that knob up a little is preferable regardless of the hiss.

I'm not trying to be combative here. I'm just trying to keep things in perspective.
Click to expand...
That comment is just me looking at something that was improved upon by someone that doesn't work for Fender! And both the FR cab and their modler have placeses that can be improved on one of which has been pointed out here!

In short Fender has this vast pool of knowledge that is out there in the world of modeling and FR! If they had just looked a little deeper they could have hit a home run with both of their products! That's all I was trying to get across if it seems a little snarky it wasn't meant to.
 
Deadpool_25 said:
I believe you said your Mute switch "mutes the amp at the crossover Input." Can you explain this concept? What exactly is that muting and why?

(Edited)
Click to expand...
The mute lets me ground everything before the crossover to see if it killed the hiss, or if the power amps were involved.
It mostly killed the hiss so I can leave the power amps alone and focus on everything in front of the crossover .. which is the eq, and the input stages I already tweaked.

Maybe I should call it a stand by switch.
 
Last edited:
Sixstring said:
That comment is just me looking at something that was improved upon by someone that doesn't work for Fender! And both the FR cab and their modler have placeses that can be improved on one of which has been pointed out here!

In short Fender has this vast pool of knowledge that is out there in the world of modeling and FR! If they had just looked a little deeper they could have hit a home run with both of their products! That's all I was trying to get across if it seems a little snarky it wasn't meant to.
Click to expand...
Cool cool. I'm just saying they already hit a home run with the FR. WKSmith is just making that HR travel 500 feet instead of 400 lol.
 
WKSmith said:
The mute lets me ground everything before the crossover to see if it killed the hiss, or if the power amps were involved.
It killed the hiss so I can leave the power amps alone and focus on everything in front of the crossover .. which is the eq, and the input stages I already tweaked.

Maybe I should call it a stand by switch.
Click to expand...
Ahhhh got it. Makes sense. More of a testing tool and not meant to be in the "final version" then I guess.

Seems like it might be a fun project. I'm not great at soldering, but I can get it done. If I was able to solder up the fx loop mod on my Vypyr 60 with its SMD stuff, this should be relatively easy.

Thing is, I actually like having the EQ available on there. Sounds like you've started considering a way to have a quieter EQ section?
 
Deadpool_25 said:
Ahhhh got it. Makes sense. More of a testing tool and not meant to be in the "final version" then I guess.

Seems like it might be a fun project. I'm not great at soldering, but I can get it done. If I was able to solder up the fx loop mod on my Vypyr 60 with its SMD stuff, this should be relatively easy.

Thing is, I actually like having the EQ available on there. Sounds like you've started considering a way to have a quieter EQ section?
Click to expand...
I love the eq! But I want to try tuning my quiet eq design to those same frequencies in the stock eq.
The tough part is putting these mods on switches so I can flip it back to the stock wiring to compare.
 
Deadpool_25 said:
So far you're kinda working on two separate mods?

Musicality Mod
Hissterectomy Mod

Is that about right?
Click to expand...
Yes, but I am using sockets for the BurrBrown amp stages. So I can drop in the ones that they use stock. And compare.
That and some metal resistors and box caps are the musicality bit .. just while I am in there.


And yes if I can tune my eq to these stock eq bands and not lose any mojo.. the hiss will have its exorcism.

Also maybe fix the notch in the crossover point with an a/b switch with stock values. So I know that notch isn't part of the magic.

And drop the gain on amp stage 2 for +4dB with a switch.
 
WKSmith said:
I will fix them either way. I just don't want to run a production line in my garage again. I'm old. And busted. 😂

But I still have some friends in Shenzhen and 10's of thousands of passive parts in storage. So there's that 😉
Click to expand...

So....I obviously respect you for what you've done and value your time on this. But...that has me curious. I don't have a clue who you are. What are you talking about here?
 
You must log in or register to reply here.
Back
Top Bottom