Fender FR-12 preamp mod : The Hissterectomy

Joe Bfstplk said:
So the engineers managed to patially win a battle for a change, then?
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...possibly? I've been trying to figure why the preamp (the EQ section, in particular) is based on simple concepts, yet so needlessly convoluted.

My guess is that Fender spent some time dialing the EQ into something that not only plays well with the speaker+cab, but also feels and reacts very amp-like. Definitely the case for me.
 
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Sixstring said:
This is my point! It's Fender that is doing this... their first real push into the world of FR cabs and modeling as we know about it and they come out with a somewhat week impression on quality and execution on both fronts!
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Sixstring said:
Anything worth doing is worth doing right! If @WKSmith only needed $10 extra dollars to fix half of the problems in the amp maybe a little extra can fix the hissy part IDK?
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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.
 
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.
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You nailed it .

It sounds great out of the box and it has a certain backline mojo that was missing in the FRFR world.

I seriously love it.
I just love it more now with some tweaks. There are more cool mods in the works.
 
Lysander said:
...possibly? I've been trying to figure why the preamp (the EQ section, in particular) is based on simple concepts, yet so needlessly convoluted.

My guess is that Fender spent some time dialing the EQ into something that not only plays well with the speaker+cab, but also feels and reacts very amp-like. Definitely the case for me.
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Absolutely needless convoluted eq design !

The eq circuit alone has 12 OpAmp stages! of gyrators and resonators and multiple instances of redundant serial resistance between stages.

My next step is to install some switches to:

1) Mute the amps at the crossover input

2) bypass the eq

3) mute just the compression driver and add a level control

4) cut the 2nd stage gain in half (ish) for +4dB hot inputs.

That will tell the truth about the hiss quickly.
 
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WKSmith said:
Absolutely needless convoluted eq design !

The eq circuit alone has 12 amp stages! of gyrators and resonators and multiple instances of redundant serial resistance between stages.

My next step is to install some switches to:

1) Mute the amps at the crossover input

2) bypass the eq

3) mute just the compression driver and add a level control

4) cut the 2nd stage gain in half (ish) for +4dB hot inputs.

That will tell the truth about the hiss quickly.
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I can't wait to see/hear the results. This seems like fun.

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.

...

I'm not trying to be combative here. I'm just trying to keep things in perspective.
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I agree. I haven't been motivated to actually buy one yet, but that's because my wife works in film....needless gear purchases still aren't high on the priority list yet. The thing was impressive.
 
WKSmith said:
I put the mute switch in. It grounds the input of the crossover. And the hiss goes almost entirely away. It's in the eq 😉👍
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Honestly would be kind of cool if Fender started shipping these with an EQ bypass switch. I would run the bypass on for home playing, where I have time to sit and dial the EQ on the modeler specifically to my room. Then in a live situation where I don't care about the hiss, I can use the onboard EQ for quick venue adjustments.
 
Jkist7 said:
Honestly would be kind of cool if Fender started shipping these with an EQ bypass switch. I would run the bypass on for home playing, where I have time to sit and dial the EQ on the modeler specifically to my room. Then in a live situation where I don't care about the hiss, I can use the onboard EQ for quick venue adjustments.
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For personal reasons, that's what I'm hoping @WKSmith figures out how to do.
 
IMG_1084.jpeg

It works! Eq bypass with one switch, one resistor, and one cap (that I could have skipped)
The level is almost the same bypassing the eq as it is with 12 opamp stages and a jfet stage.

Analysis and charts( and voltage measurements) soon... and maybe a video.

I can fix this hiss, not just for me and those handy with a soldering gun.. I can fix all of them. Using their existing parts, and throwing a lot of them out . Like seriously a lot.

And yes. The hiss is terminated!
 
WKSmith said:
View attachment 128361

It works! Eq bypass with one switch, one resistor, and one cap (that I could have skipped)
The level is almost the same bypassing the eq as it is with 12 opamp stages and a jfet stage.

Analysis and charts( and voltage measurements) soon... and maybe a video.

I can fix this hiss, not just for me and those handy with a soldering gun.. I can fix all of them. Using their existing parts, and throwing a lot of them out . Like seriously a lot.

And yes. The hiss is terminated!
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Want a job at Fender? Because this is how you get a job at Fender.
 
WKSmith said:
View attachment 128361

It works! Eq bypass with one switch, one resistor, and one cap (that I could have skipped)
The level is almost the same bypassing the eq as it is with 12 opamp stages and a jfet stage.

Analysis and charts( and voltage measurements) soon... and maybe a video.

I can fix this hiss, not just for me and those handy with a soldering gun.. I can fix all of them. Using their existing parts, and throwing a lot of them out . Like seriously a lot.

And yes. The hiss is terminated!
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So bypassing the EQ got rid of the hiss? And the only control that works after that is the volume?
 
WKSmith said:
Actually yes, I want to license my eq design and mods to Fender and Hanser , and fix their amp and cut their production cost. I have all that in the works.

This amp is already completely killing the FRFR backline thing without my help.
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mr burns GIF
 
Deadpool_25 said:
So bypassing the EQ got rid of the hiss? And the only control that works after that is the volume?
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The volume is up front in between the 1st (differential balanced in) and the 2nd (gain) stage.
Bypassing the eq connects the 2nd stage output to the last (crossover) stage input ...before the power amps.

If you run balanced +4dB into the front, the volume is ridiculously hot ..and you have to dump all of the 1st stage signal to ground with the volume knob to make it work with the 7.66X gain of the 2nd stage.

That's why it needs a -10dB / +4dB gain dropping resistor in the 2nd stage.
That will give more room on the volume knob, and require less gain (tiny hiss) in the most critical first stages.

But yes, the hiss otherwise, is entirely in the eq.

Edit: I had not modeled the first 2 stages yet in Spice, so I did not account for the -12dB drop after the 1st stage. Bet even with that it still clips wildly at hot +4 signals.
 
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Nice. I'll put this in my back pocket and keep it as an option if I decide I want to mod it. So far the hiss isn't really an issue for me but if it becomes one, I might be revisiting this.
 
Chewie5150 said:
So how do we send our units to you for modding!? hahah. man that's so intense, everything you've done. So cool.
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I really want to see if I can fix all of them. If Fender / Hanser doesn't want a consultant with a eq design pulled out of the ether, then I might make a new PC board anyone can plug into their FR12 and fix them on the back end.

I think both can be done. I don't know how they would address the units we already own as a repair or upgrade with a retrofit part .

...Or it may be a new product tier for a higher end FR... perhaps even with a Co-axial speaker .

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 😉
 
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