Fender FR-10/FR-12 noise reduction mod

[vtgearhead]

Thank you for the welcome. I've been lurking here for a while, but don't often post because the interwebs often include verbal jabs and barbs that I don't want to deal with. I'm an older guy and learned this lesson in the early 1990s when Genie and Compuserve were the big places for people to congregate. And then when AOL came along, well that was revolutionary! I got into a couple of verbal "scuffles" back then and soon realized that I like peace and equanimity more than trying to "win" a battle of wits (or opinions) with strangers.

Exactly this ^^^. My philosophy of forum discourse is simple: Life is too short for head-bumping. I work hard to avoid posting anything that could even remotely be taken as personal and do my best not to react or respond when attacked. Keeps me sane and content.

 

[Humberd]

We all need more guitar's

 

[LScottK]

We all need more guitar's

Yup - It's a disease.

 

[lolainnb]

@aflynt @Lysander Ok so IF I have two OPA4227PA Do I still only need to replace the 2 IC and leave the first TL084CN alone like @aflynt did with the OPA4228PA?

Realistic-looking photoshop attached to illustrate what I may do

 

[Lysander]

@aflynt @Lysander Ok so IF I have two OPA4227PA Do I still only need to replace the 2 IC and leave the first TL084CN alone like @aflynt did with the OPA4228PA?

If you only have two OPA4227, yes, you need to replace the two rightmost ICs highlighted in your very scientific image That section is where most of the hiss is introduced.

If you can procure another OPA4227 though, replacing all three ICs is recommended for the best noise performance.

 

[aflynt]

I’ve got an OP4227PA and a few 14 pin SOIC chips and adapters arriving today. I’ll see if the 4227 makes a difference hiss or sound wise in that first TL084 replacement position. The 4228 didn’t make any noticeable difference hiss-wise when I had it in that position, but it had some stability issues there so that might be why.

-Aaron

 

[Lysander]

I’ve got an OP4227PA and a few 14 pin SOIC chips and adapters arriving today. I’ll see if the 4227 makes a difference hiss or sound wise in that first TL084 replacement position. The 4228 didn’t make any noticeable difference hiss-wise when I had it in that position, but it had some stability issues there so that might be why.

I expect it would improve the noise floor a tad, but it won't be as drastic as the other two.

Hiss is caused by cascaded opamp stages, so improving the noise floor on 66% of those will have a much bigger impact than the final 33%.

 

[lolainnb]

Thank you @Lysander and @aflynt
I will wait to see Aflynt’s results and I will order the 3rd OP44227 for the first position based on that

 

[aflynt]

I got the OP4227PA in and replaced the TL084CP in the first position. This is with the OP4228PA in the other two positions.

Noise-wise I didn’t measure any real difference. Interestingly, the noise floor seems to increase a bit after it’s been on a bit and played. Measured by the same db meter in the same places on the speaker (taped them off over woofer and tweeter) with the same amp settings after the same amount of time the two chips were within a half db of each other: 33.5-34dbA over woofer and 54 - 54.5dbA over tweeter.

Sound-wise, the TL084CP seems more diffused and bandwidth constrained. Less high and low end. I have no way to verify this with blind testing though so take it worth a grain of salt. It’s very likely that my mind is playing tricks on me.

-Aaron

 

[lolainnb]

I got the OP4227PA in and replaced the TL084CP in the first position. This is with the OP4228PA in the other two positions.

Noise-wise I didn’t measure any real difference. Interestingly, the noise floor seems to increase a bit after it’s been on a bit and played. Measured by the same db meter in the same places on the speaker (taped them off over woofer and tweeter) with the same amp settings after the same amount of time the two chips were within a half db of each other: 33.5-34dbA over woofer and 54 - 54.5dbA over tweeter.

Sound-wise, the TL084CP seems more diffused and bandwidth constrained. Less high and low end. I have no way to verify this with blind testing though so take it worth a grain of salt. It’s very likely that my mind is playing tricks on me.

-Aaron

Thank you for sharing these results. I’m going to leave the first TL084CP in place then

 

[aflynt]

I got the OP4227PA in and replaced the TL084CP in the first position. This is with the OP4228PA in the other two positions.

Noise-wise I didn’t measure any real difference. Interestingly, the noise floor seems to increase a bit after it’s been on a bit and played. Measured by the same db meter in the same places on the speaker (taped them off over woofer and tweeter) with the same amp settings after the same amount of time the two chips were within a half db of each other: 33.5-34dbA over woofer and 54 - 54.5dbA over tweeter.

Sound-wise, the TL084CP seems more diffused and bandwidth constrained. Less high and low end. I have no way to verify this with blind testing though so take it worth a grain of salt. It’s very likely that my mind is playing tricks on me.

-Aaron

Maybe I'm not totally crazy? It's entirely possible I'm doing it wrong, though. I did 5 20-20k sine sweeps with each chip in the 1st "eq" 14 pin slot. All sweeps are identical for each of the same chip, but different by 3 or 4 db in places between the two chips. The mic didn't move at all. I taped the cab feet position on the floor so that was within a millimeter or so at the most.

-Aaron

 

[Lysander]

Maybe I'm not totally crazy? It's entirely possible I'm doing it wrong, though. I did 5 20-20k sine sweeps with each chip in the 1st "eq" 14 pin slot. All sweeps are identical for each of the same chip, but different by 3 or 4 db in places between the two chips. The mic didn't move at all. I taped the cab feet position on the floor so that was within a millimeter or so at the most.

Honestly, those diffs are so small than they can be anything - a few dB of ambient noise, the cabinet not sitting in the exact same position, the control pots being slightly moved... The way the EQ stack is designed makes it pretty much opamp-agnostic, specially given it's only handling audio up to ~20kHz.

Then again, i swear i can hear a slight, but for the better, difference after swapping the input RC4558 with OPA1656, so

I really should get a Bode plot for the preamp when i open mine again, just to rule out the speaker+cabinet as an influence.

 

[Ledvedder]

I'm going to order 3 of the OPA4227PA chips. Do I need anything else for replacing these 3 chips? I keep seeing mentions of IC sockets.

 

[Lysander]

I'm going to order 3 of the OPA4227PA chips. Do I need anything else for replacing these 3 chips? I keep seeing mentions of IC sockets.

Yeah, IC sockets unless you want to solder the new ICs directly to the board.

 

[Ledvedder]

Yeah, IC sockets unless you want to solder the new ICs directly to the board.

Would this work? https://www.mouser.com/ProductDetail/TE-Connectivity/1-2199298-3?qs=fK8dlpkaUMtBOtVI99wRlQ==

 

[Lysander]

Would this work? https://www.mouser.com/ProductDetail/TE-Connectivity/1-2199298-3?qs=fK8dlpkaUMtBOtVI99wRlQ==

Yup! Any socket for DIP-14 ICs will wok perfectly fine.

 

[vtgearhead]

If it's worth buying a socket, it's probably worth getting a machined-pin type. But, that's just me being fussy...

 

[Ledvedder]

If it's worth buying a socket, it's probably worth getting a machined-pin type. But, that's just me being fussy...

What's a machine-pin type?

 

[aflynt]

What's a machine-pin type?

I believe the ones with the holes instead of the slots. Like these.

https://www.mouser.com/ProductDetail/437-1108331441001101

Those are the ones I used. They are working well. Not sure if it makes a difference or not.

-Aaron

 

[Lysander]

Those are the ones I used. They are working well. Not sure if it makes a difference or not.

Nah, as long as the IC fits all options are a-ok. I personally prefer the older style, bent sheet metal socket because ICs with thicker leads sit much better; the main advantage of machined pin sockets is that there's no chance of flux of solder contaminating the contacts.