Fender FR-12 preamp mod : The Hissterectomy

WKSmith said:
But buying 12,000 resistors at a time, the cost for metal film was not much more.

Maybe pricing has changed in 10 years though from what I remember. But it was a fraction of 1¢ difference.

I would prefer they save money elsewhere in the design, that actually does kill the hiss. And then buy metal resistors for the audio path , and lower tolerance caps.

For the V2 preamp design, it's on my list of mandatory spec. Because my name is on it.
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Noted. I'll ping you when I'm upgrading my 12,000 FR12s.
 
Their noisy eq has :
12 amp channels 30 resistors & 24 caps

Mine has:
4 amp channels (one is just an inverter)
12 resistors & 7 caps.

The new design will save them
(in just 100 FR-12s )

1800 resistors
1400 film and ceramic caps
300 electrolytic caps
800 amp channels (400 duals or 200 quads)

Imagine these 200 IC sockets were dual opamps
Now imagine twice this amount of opamps and roughly this same pile of resistors and caps.

Fixing the hiss problem is just a bonus.

IMG_1129.jpeg
 
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WKSmith said:
Their noisy eq has :
12 amp channels 30 resistors & 24 caps

Mine has:
4 amp channels (one is just an inverter)
12 resistors & 7 caps.

The new design will save them
(in just 100 FR-12s )

1800 resistors
1400 film and ceramic caps
300 electrolytic caps
800 amp channels (400 duals or 200 quads)

Imagine these 200 IC sockets were dual opamps
Now imagine twice this amount of opamps and roughly this same pile of resistors and caps.

Fixing the hiss problem is just a bonus.

View attachment 128990
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Fender needs to peel off a decent percentage of the savings to help fund your retirement. You're saving them money and would be improving their product.
 
Joe Bfstplk said:
Carbon comp resistors are well known for shot noise issues, especially at higher voltage potentials across the resistor (like in tube amp preamp plate resistors). It's measurable, and even carbon film resistors are less noisy and tighter tolerance. Metal film are even less noisy as well as generally tighter tolerance than carbon film. Certainly any decent engineer would be knowledgeable on the topic of parts quality....
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Who was talking about Carbon comp resistors here?
I mentioned Carbon FILM and Metal film.
Also the circuits that are being discussed are low voltage. So shot noise isn’t a real concern.
 
2204JCM said:
Who was talking about Carbon comp resistors here?
I mentioned Carbon FILM and Metal film.
Also the circuits that are being discussed are low voltage. So shot noise isn’t a real concern.
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I was illustrating that parts quality differs between types of resistors, and has improved over time.

Don't see many carbon comps used lately even in low voltage stuff. Carbon films are quieter, and they are cheap and plenty. Metal films are getting more competitive, price wise, and are a no-brainer....
 
Crosstown said:
Perhaps there are component value tweaks for the 10 vs 12?
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If there's any difference between the FR-10 & 12 preamps is likely on component values the EQ/crossover sections, which appear to be very tailored to the speaker & cab. From those photos, both boards look otherwise identical to me.

EDIT: Yup, definitely the same board, different component selection. My (modded) FR-12 preamp has a bunch of components under the cut knob which are not present on the FR-10, but the board revision code is exactly the same.

PXL_20231029_025939954.jpg
 
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Lysander said:
Woot! Got my first confirmation that OPA4227 works perfectly fine as an opamp replacement for the EQ section, and kills hiss just as well as OPA1604 🙏

https://thegearforum.com/threads/fender-fr-10-fr-12-noise-reduction-mod.3559/post-132389

This is great news for home modders; OPA4227 is a bit expensive at ~$10 a piece, but, it's also available in DIP packaging (part number OPA4227PA). Which makes it much, much easier to install than other SOIC alternatives.
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I need a link for the IC sockets…I have some of these chips on order.
 
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