Fender FR-12 preamp mod : The Hissterectomy

The salesman is back at the FR thread on TGP. He said he's got info from a senior engineer at the big F and stated:

From Fender's longest tenured amp engineer:
  • Line Out is protected by blocking capacitors, safe from phantom power.
  • XLR Input to XLR Output maintains phase.
  • XLR Input to speaker should be in phase as long as no one tinkered with the speaker wiring (white wire connected to + speaker terminal).
We've already seen that, even if he's right about the project, then there's a quality control problem at the execution since some units have phase anomalies at different degrees.

But what caught my attention was his statement about the phantom power protection.

Can those capacitors really offer adequate protection against phantom power? Maybe Fender added those to the newer fixed unit after all the buzz about the lack of protection, but then it would be necessary to compare an older pre-factory fix unit with a more recent one.

I know nothing about all this electronic stuff so I can't judge, but maybe Liam, Lysander and some other folks here that had full access to the early pre-factory fix PCBs could share some more insight about this.
 
davi_ssilva said:
The salesman is back at the FR thread on TGP. He said he's got info from a senior engineer at the big F and stated:

From Fender's longest tenured amp engineer:
  • Line Out is protected by blocking capacitors, safe from phantom power.
  • XLR Input to XLR Output maintains phase.
  • XLR Input to speaker should be in phase as long as no one tinkered with the speaker wiring (white wire connected to + speaker terminal).
We've already seen that, even if he's right about the project, then there's a quality control problem at the execution since some units have phase anomalies at different degrees.

But what caught my attention was his statement about the phantom power protection.

Can those capacitors really offer adequate protection against phantom power? Maybe Fender added those to the newer fixed unit after all the buzz about the lack of protection, but then it would be necessary to compare an older pre-factory fix unit with a more recent one.

I know nothing about all this electronic stuff so I can't judge, but maybe Liam, Lysander and some other folks here that had full access to the early pre-factory fix PCBs could share some more insight about this.
Click to expand...
Here is the input board:
IMG_2003.jpeg

Phantom power protection needs more than a pair of electro caps.

1st these polarized caps are not reverse biased to block any DC coming in the XLR out jack. They are configured instead as coupling capacitors from the XLR in to the XLR out.

2nd there are no 6.8k resistor pairs to ground to render phantom to 0V. Those ^ are 100k

3rd there are no diodes (needs 4) to the V+ and V- rails from each cap to shunt the ESD from the caps .. to keep them from discharging directly into the IC.

typical F-corp response. Gaslight. Their response is from a salesdood press release, not an engineer.

Look up phantom power protection for balanced inputs. Elliot sound, TI white papers, not hard to find.

It's 2 6.8k resistors, 2 22uf electro caps (reverse biased) and 4 fast diodes at a minimum. Audio engineers all know this. They believe we are dumb enough to just believe their response. ..Like the hiss compared to Moms sedan press release? Don't buy the sales pitch.

The XLR out is indeed in phase with the XLR in. No one has stated otherwise. Pretty easy to find pins 1,2,&3 on the xlr jacks. ... there salesguy.

The speaker out is in phase on the hissy FR-12 and there is a nasty phase lag on the factory fixed FR-10.

Glad they are having to respond to this foolishness. I won't be expecting a Christmas card from F-corp this year. 🤣

They really need to fix this. The phantom menace isn't just for the first FR IC but it can also be present on the xlr in which is connected to our modelers.

The only way to block phantom on the FR xlr out is to use a transformer based DI ... or a revised input board.

A quick and dirty fix is to push in the ground lift switch. It will at least keep the caps from charging up instantly to +48V DC when phantom is present.

F-Corp can still license this far superior design, but the price just went up. There is room in the budget if you fire who ever is writing these dumba$$ press releases and official statements.
 
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WKSmith said:
Here is the input board:
View attachment 144755

Phantom power protection needs more than a pair of electro caps.

1st these polarized caps are not reverse biased to block any DC coming in the XLR out jack. They are configured instead as coupling capacitors from the XLR in to the XLR out.

2nd there are no 6.8k resistor pairs to ground to render phantom to 0V. Those ^ are 100k

3rd there are no diodes (needs 4) to the V+ and V- rails from each cap to shunt the ESD from the caps from discharging directly into the IC.

typical F-corp response. Gaslight. Their response is from a salesdood press release, not an engineer.

Look up phantom power protection for balanced inputs. Elliot sound, TI white papers, not hard to find.

It's 2 6.8k resistors, 2 22uf electro caps (reverse biased) and 4 fast diodes at a minimum. Audio engineers all know this. They believe we are dumb enough to just believe their response. ..Like the hiss compared to Moms sedan press release? Don't buy the sales pitch.

The XLR out is indeed in phase with the XLR in. No one has stated otherwise. Pretty easy to find pins 1,2,&3 on the xlr jacks. ... there salesguy.

The speaker out is in phase on the hissy FR-12 and there is a nasty phase lag on the factory fixed FR-10.

Glad they are having to respond to this foolishness. I won't be expecting a Christmas card from F-corp this year. 🤣

They really need to fix this. The phantom menace isn't just for the first FR IC but it can also be present on the xlr in which is connected to our modelers.

The only way to block phantom on the FR xlr out is to use a transformer based DI ... or an Archangel V2 / V3 replacement preamp. Period.

F-Corp can still license this far superior design, but the price just went up. There is room in the budget if you fire who ever is writing these dumba$$ press releases and official statements.
Click to expand...
Man, I'm really pissed of by this $hit... I mean, wtf... He could just remained in silence, but he chose to come back and throw this sales pitch bs again. That's messed up...

If you don't mind, may I quote or paraphrase your last post on that thread? I'm feeling almost obligated to do it because now it's clear they are genuinely lying to their consumer base. It would be unethical from my part to let him get away whit this and do nothing.
 
davi_ssilva said:
Man, I'm really pissed of by this $hit... I mean, wtf... He could just remained in silence, but he chose to come back and throw this sales pitch bs again. That's messed up...

If you don't mind, may I quote or paraphrase your last post on that thread? I'm feeling almost obligated to do it because now it's clear they are genuinely lying to their consumer base. It would be unethical from my part to let him get away whit this and do nothing.
Click to expand...
You can post it in its entirety if you wish. Post the pic too. I am sure they have already seen it... or will by 9:00 Arizona time.


This isn't an opinion, this is how you block phantom. And if their most tenured amp engineer really believes that rubbish, that is very concerning.
 
davi_ssilva said:
Man, I'm really pissed of by this $hit... I mean, wtf... He could just remained in silence, but he chose to come back and throw this sales pitch bs again. That's messed up...
Click to expand...

It's annoying and super frustrating; but I'm willing to give him the benefit of the doubt and accept that he may only be believing what he has been told by the actual engineers. I will generally accept what my doctor tells me because I'm not a doctor, for example.

It's entirely possible that he believes what he's saying and isn't deliberately lying, isn't it?
 
jellodog said:
It's annoying and super frustrating; but I'm willing to give him the benefit of the doubt and accept that he may only be believing what he has been told by the actual engineers. I will generally accept what my doctor tells me, because I'm not a doctor, for example.

It's entirely possible that he believes what he's saying and isn't deliberately lying, isn't it?
Click to expand...
Absolutely. They believed the hiss was normal until it wasn't.
 
jellodog said:
It's annoying and super frustrating; but I'm willing to give him the benefit of the doubt and accept that he may only be believing what he has been told by the actual engineers. I will generally accept what my doctor tells me because I'm not a doctor, for example.

It's entirely possible that he believes what he's saying and isn't deliberately lying, isn't it?
Click to expand...
I agree with you. But at the end of the day, it still sucks for us consumers... Because then we would have to choose between two really bad "hypothetic" situations:

1) That senior amp engineer actualy doesn't know how to protect a balanced output from phantom power (oh my... I don't even want to go that way).

2) That senior amp engineer actualy knows that there's no real protection, but is gaslighting the salesman and, therefore, also the whole public that follows that thread.
 
davi_ssilva said:
I agree with you. But at the end of the day, it still sucks for us consumers... Because then we would have to choose between two really bad hypothetic situations:

1) That senior amp engineer actualy doesn't know how to protect a balanced output from phantom power (oh my... I don't even want to go that way).

2) That senior amp engineer actualy knows that there's no real protection, but is gaslighting the salesman and, therefore, also the whole public that follows that thread.
Click to expand...
or 3) it's just marketing BS trying to clean up their mess that is now common knowledge thanks to forums like this one.

If intelligent people push back against this kind of PR ..it will force another preamp board revision. If not one of my pres, they will at least have to re-design theirs. It's gonna cost them $$$$$ anyway.

They could have saved themselves a lot of embarrassment and money. Now they have scaled up this foolishness for mass production.

How you F-corp suits doing this morning? These Fractal folks are a little smarter than the BS you are putting out.
 
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WKSmith said:
Absolutely. They believed the hiss was normal until it wasn't.
Click to expand...
Clash Royale Yes GIF by Clash
 
WKSmith said:
Not sure yet. They are on the way along with another (bigger and higher wattage) titanium driver. I will share details soon.

Pairing the bigger compression drivers with this waveguide:

View attachment 144773

Here is the stock driver

View attachment 144774
Click to expand...
It has begun.

Prediction: Within six months, you’ll be contacting Parkinson’s-free builders about fabricating a cabinet. :p
 
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