More on two-box, CA3035, etc.

[Dale Seppa]

Taking the earlier quote from Carlos Daniel Fidel, and combining it with a definition found on the web AND after I learned that the spanish word "etapa" is "stage" we have the following description of a replacement for the CA3035:


CA3035 replacement will be: A simple audio amplifier with three stages.


Claus-Peter is wondering what type of meter will be adequate for the receiver in the two box design?


All input welcomed.

[Carl]

Update on CA3035




I finally got around to looking at the 3035 problem in Rake's two-box design. The 3035 is basically a triple gain stage IC, each stage being a wide-bandwidth common emitter stage (see pic). It is NOT a diffamp-based IC like the traditional opamp.


I think all that needs to be done to replace the 3035 is design a high-gain wide-band amp using modern opamps. Rake mentions that the 3035 in his receiver has a gain of 129dB. This exceeds the DC open-loop gain of most general purpose opamps and I suspect that Rakes means 129dB of DC gain, and somewhat less at the operating frequency of 180kHz. So if you try to use a GP opamp with the typical 1MHz gain-BW product you will only be able to get a max gain of 5 or so at 180kHz.


One solution is to get some hotrod opamps. Since I work for Analog Devices and we make hotrod opamps, I've ordered some that should work nicely. The AD8031 (single) and AD8032 (dual) are capable of about 40-45dB (>100) of closed loop gain at 200kHz. Plus, they're single supply, low noise (~15nV/rtHz), and low power (800uA) - almost perfect for any metal detector receiver.


When I get them in I will build up the receiver and check it out. For those who are truly interested I am willing to share a VERY limited number of samples. I think that anyone who wants can order samples from the ADI web site, www.analog.com. I don't know the procedure though, and would be interested to see if any common joe out there is successful with this.

[nelson]

Charles Rakes two box metal detector

Carl, can you help me with the CA3035 replacement?
I´m building the Charles Rakes two box metal detector, but i can´t find the replacement for CA3035.
On January 2007, im living on vacations and i have plans to carry three detector for field test, the clone pi, delta pulse and a two box MD.
So, if you can help i ll really appreciate your suport.
In advance many thanks.
Regards
Nelson

Taking the earlier quote from Carlos Daniel Fidel, and combining it with a definition found on the web AND after I learned that the spanish word "etapa" is "stage" we have the following description of a replacement for the CA3035:


CA3035 replacement will be: A simple audio amplifier with three stages.


Claus-Peter is wondering what type of meter will be adequate for the receiver in the two box design?


All input welcomed.[/QUOTE]

[chemelec]

If you go to this Link, You will find a Descrete Version of the CA3035 using Transistors.
It has been tested and it Functions Almost Identical to the CA3035.

http://www3.telus.net/chemelec/Proje...al-Box/Box.htm

Although I was Not very happy with the results I got with that detector.
************************************************** ******

Carl, can you help me with the CA3035 replacement?
I´m building the Charles Rakes two box metal detector, but i can´t find the replacement for CA3035.
On January 2007, im living on vacations and i have plans to carry three detector for field test, the clone pi, delta pulse and a two box MD.
So, if you can help i ll really appreciate your suport.
In advance many thanks.
Regards
Nelson

Taking the earlier quote from Carlos Daniel Fidel, and combining it with a definition found on the web AND after I learned that the spanish word "etapa" is "stage" we have the following description of a replacement for the CA3035:


CA3035 replacement will be: A simple audio amplifier with three stages.


Claus-Peter is wondering what type of meter will be adequate for the receiver in the two box design?


All input welcomed.

[/quote]

[Carl-NC]

Besides Gary's transitor-level substitute, I posted an opamp-based substitute a while back, click here. And I agree with Gary, this is not a high-performance design.

- Carl

[nelson]

two box md

Hey Carl and Gary, thanks a lot for your help.
By the way, do you have any other two box detector that cab fit my needs.
I really need to build one of this devices to experiment and compare it with delta pulse that i will carry on my next vacations.
In advance many thanks.
Regards
Nelson

[Unregistered]

Here you can still buy the CA3035

http://www.find-ic.com/partlist/CA3035.htm

[nelson]

Thanks a lot for the information.
Regards
Nelson

[chemelec]

Here you can still buy the CA3035

http://www.find-ic.com/partlist/CA3035.htm

YES, POSSIBLY. However you Will Pay a REALLY HIGH PRICE for it.

And PROBABLY you will need to buy a LARGE Quantity, or they won't even Answer your Request.

[JC1]

Thought

Hi Guys,

I would think a good approach to the replacement of 3035

would be a quad op amp with amps in series,

with each amp a simple bandpass filter, with a gain of

say 5 so 5x5x5x5 = 625.

The Q of each stage should be as high as can be practical

without being too selective or temp drift of the center

frequency could occur. Even lower Q after four stages would

result in a fairly sharp filter.

[Geo]

Hi Guys,

I would think a good approach to the replacement of 3035

would be a quad op amp with amps in series,

with each amp a simple bandpass filter, with a gain of

say 5 so 5x5x5x5 = 625.

Hi JC1. From my experience a gain of 625 is low. We need a gain at least 10.000 so when we null the coils with full sensitivity to have a small signal at the output of Op.Amp
Regards

[JC1]

Whoops!

Hi Geo,

My bad !!! I haven't built a two box ever,

or looked at the designs very close.

Ok. Gain of 10,000.

10x10x10x10 = 10,000.

I forget the center frequency on these two boxers,

but could use from 1 kHz to 100 kHz for experimentation.

so for 100 kHz would need gainbandwidth for op amp

of 1 MegaHz. Many op amps could meet this requirement.

so selection of op amp would be for say lower noise.

[JC1]

links

Hi Geo,

I found a couple of links for doing

what I was talking about.

In both of these if you make R2 adjustable

you can "tune" the center frequency and get

everything just right even if the parts are 10%.

http://www.electronics-tutorials.com...ss-filters.htm

http://sound.westhost.com/project63.htm

[JC1]

Free software

Hi Geo,

Here's a link for FilterPro.

You may already have this or something else,

but makes the design process quicker.

http://focus.ti.com/docs/toolsw/fold...upportsoftware

[chemelec]

Hi Guys,

I would think a good approach to the replacement of 3035

would be a quad op amp with amps in series,

with each amp a simple bandpass filter, with a gain of

say 5 so 5x5x5x5 = 625.

The Q of each stage should be as high as can be practical

without being too selective or temp drift of the center

frequency could occur. Even lower Q after four stages would

result in a fairly sharp filter.

I Doubt that Bandpass filters is a good idea.
There will probably be a lot of Phase Shifting, resulting in problems.

The transistor circuit I show effectively gives the same results as the origional 3035 IC.