Surf PI gain modification

[ApBerg]

Hey Apberg,

I tried your 5k pot for the 3K3. I does seem to give a bit more depth. I adjusted the 5K to max out sensitivity to some small gold jewelry and saw that my larger gold rings did indeed show a nice increase. Probably about an inch or so I'm guessing. Nice easy mod. Good job!

Thanks,

Bob

Hello Bob.

Nice you have success with it ! ... and that extra inch can make the differents.

Best regards.

Ap

[Sean_Goddard]

I have been trying to resist posting any more hints on how to get more depth out of the SM PI for the following reasons;

1) Some people JUST DON'T GET IT!

2) Most of the replies seemed to hint that people knew what they were talking about, and I'm afraid they didn't.

3) NO ONE who read that thread could get it through their heads that NOISE is the PI's BIGGEST enemy when seeking to gain depth, and I don't mean an inch or so, I mean SIX INCHES or MORE!!!

People seem hell bent on adding PIC's, AVR's and DSP's which, unless you use spread spectrum clocking (which you can then quantify and account for in your filtering software) throw up so much noise you LOSE depth, not gain it.

I have done a LOT of research regarding this subject and have made some pretty good discoveries so I think I know what I'm talking about.

As one last ditch attempt to point people in the RIGHT DIRECTION please look at this; http://www.jsts.org/html/journal/jou...me08_01_11.pdf and deduce what I'm trying to tell you regarding the MAIN source(s) of noise in a MONOCOIL PI (without breaching patents).

If no one "gets it" now, then I give up!

[ApBerg]

I have been trying to resist posting any more hints on how to get more depth out of the SM PI for the following reasons;

1) Some people JUST DON'T GET IT!

2) Most of the replies seemed to hint that people knew what they were talking about, and I'm afraid they didn't.

3) NO ONE who read that thread could get it through their heads that NOISE is the PI's BIGGEST enemy when seeking to gain depth, and I don't mean an inch or so, I mean SIX INCHES or MORE!!!

People seem hell bent on adding PIC's, AVR's and DSP's which, unless you use spread spectrum clocking (which you can then quantify and account for in your filtering software) throw up so much noise you LOSE depth, not gain it.

I have done a LOT of research regarding this subject and have made some pretty good discoveries so I think I know what I'm talking about.

As one last ditch attempt to point people in the RIGHT DIRECTION please look at this; http://www.jsts.org/html/journal/jou...me08_01_11.pdf and deduce what I'm trying to tell you regarding the MAIN source(s) of noise in a MONOCOIL PI (without breaching patents).

If no one "gets it" now, then I give up!

Ha.. ha.. never give up...

better 1 inch more for real ....than 6 inch more in thin air....

I have for the surf ca. 30 cm for 1 euro...20 cm coil..
If you know what you are talking about...tell us how to make that 6 inch more...for the surf ... no bla.. bla... but just facts please.. so 18 inch, 45 cm, for a 1 euro , 20 cm coil...
O yes for electronics I do not have a degree… just a good willing hobbyist ...that shares his know how here..

Best regards.
Ap

Oopss..to much peper in the chinees food I think.......no hard feelings Sean...

[plumabob]

Wow Ap...Laughing my arse off!!!!!!

[golfnut]

I think sean is trying to say filter away out of band noise - with a filter.

Im off, incoming!

[golfnut]

Fet switching noise

Oh, plus the FET noise - read, separate Tx and Rx coils

S

[Lefizz]

Would replacing the NE5534 with something a bit more modern help. I have loads of decent opamps from when i used to build audio kit. I was thinking of trying a OPA134 seems like it would drop in fine

[TH Jim]

Greets all,

Now that Carl has posted the official Whites schematic of the Pro we can see it is the same as the above posted by John. I've moved my gain control from the 1 meg on the 5534 to the 358 stages and it works nice so far but havent tried it on RF hell beach yet.

Had a thought about the parrallel caps - maybe the 100n can't soak up HF noise as well as 100p can???

Cheers, Jim

[golfnut]

where is carls post of pro Pi?
S

[Qiaozhi]

where is carls post of pro Pi?
S

Look in the Schematics forum.

[6666]

OPA134pa 8nV/rtHz
OPA134PAG4 8nV/rtHz

NE5534p 7nV/rtHz

NE5534ap 5.5nV/rtHz


wouldn't the ne5534ap be a better choice ?

[Davor]

At what source resistance? On this schematic it would appear as ~1k and at that value LT1115 fits the bill.
The key is in finding optimum source resistance, which is calculated from the specs voltage and current noise performance (Vn and In ->Ropt=Vn/In). With NE5534 you get Ropt at ~9kohm, while with LT1115 you get Ropt at ~750ohm. Hence, LT1115 is better.

OPA134pa would have Ropt ~ 1800ohm, and it means that above that source resistance noise will bi dominated by resistor noise only.

Check "Voltage Noise vs Source Resistance" for further ideas.

[Tepco]

First thing to consider here is to remove offset adj. trimpot (R10+R11) from internal adjustment pins and replace whit "generic" offset adjustment to noninverting input, like done in HHd. Adding internal offset adjustment components will in most cases contribute to ckt. noise more than difference between two low noise amps. I never tested LT1115, but i suspect it will be bit slow in recovery (5534 is on it's limit too).