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Have you tried schottkys?
Ivconic - I'm sorry to hear about your experience with TL081.
Here's something that I have wondered about: I remember reading where you said you like to use the transistors/diodes version of the negative voltage converter - instead of using ICL7660. So, have you tried using schottky diodes (1N5817 is what I have in mind) in place of the 1N4148 diodes?
The TL081 uses about 5X more current than the LM308. Using something like 1N5817 should give you almost one more (negative) volt to work with. Maybe worth a try?? It might help the TL081 work better. Of course the problem couldn't be so simple, but still it's an idea... .
By the way, LT1008 (Linear Technology) is a direct replacement for LM308, if that helps. It may be be just as hard for you to come by as the LM308, so that wouldn't be much help - I hope that's not the case. Just two weeks ago, I got LTC to send me two free samples - but I haven't built a PCB yet. I also got LTC to send me one sample of LT1012; it's a possible "dual 308", but I don't have a facility in which to make tests, at this time. (Maybe I should feel guilty about getting freebies, but, naaaa. I don't.)
Because LT1012 is a dual opamp, it doesn't have the "add a capacitor on pin-8" capability, (the 100pF capacitor on LM308-8 adds power supply noise rejection, by the way) but LT1012 might be OK dual, if I can ever get busy.
Thanks for all your test info!Comment
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Hi Ivconic,
The TL081 is considered a general purpose op amp, while the LM324 is a high end op amp with better precision and temp compensation etc. If you find your circuit works better with the LM324, there are even better op amps you can use instead of the LM324. Try reading this: http://thunting.com/geotech/forums/s...ad.php?t=13407
Bese wishes,
J_PComment
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Hi,
yes TGS exist... I've already posted here the PCB assembly, but I repost it again for skeptics
About great performances they are related to BandidoII not TGS. TGS is still prototype no good case , no good tuning, lot of work to do...no real tuning on it , just few tests.
And about 12cm OO coil it exist too... but I've no need of posting here anything of my work.
Why if e.g. Esteban don't want to post his schematic here , I have to post here pictures of my coils ?
To give him some funny argumentation on my coil ?
My coils are nothing special, but they work. That's all.
I've posted in the past cause someone asked me of posting round 8'' before sealing... if remember well I've done. Find it.
DD22 was already sealed at that time and I haven't pictures of the inside woundings.
BTW I have also some mods on bandidoII circuitry. Why I have to show you ?
Now that this is your stupid game I say that:
use your hands and build yourself both BandidoII and coil, and see with your eyes. You have all data you need here and in other threads.
Many folks here have made what I've too, some first of me (PCB, coils) some after me. All with good results.
These are not things from my imagination, but FACTS.
Kind regards,
MaxComment
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My friends were impressed by BandidoII-clone not TGS.Originally posted by Qiaozhi View PostI'm not interested in the schematics, but I was interested to actually see a photo of your TGS. Anyway, you said earlier that your friends were so impressed that they all wanted one. So it thought it must be worth a look.
Also, how about some pics of the coils you have made, particularly the 12cm OO?
Already answered to you.Comment
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Hi,
here are just 2 pictures/part of it... low res
it's BandidoII-clone using Gary's 1st PCB design.
Other parts or higher res or OO coil I'll never show here.
So think what you want!
Kind regards,
MaxComment
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Hi,Originally posted by ivconic View Post
I experimented a lot last few days with TGSL...Bad news is
that i was wrong about replacing LM308 with TL081!
TL081 is working but not that good as LM308?
First time i tried that, was in hurry so i havent noticed
differences. Now, when serious tests performed i am sure
that LM308 is hard to replace.....or...maybe there is good
way to replace it but TL081 is not best choice.
Earlier it was piece of cake to null coill and gain very good
results when LM308 was on pcb and device was used to null coil.
Now it is almost impossible to gain good results and null coil
when TL081 is put on pcb instead LM308??? I gain less distances on
nickel coin and sound is "broken" when reach detection limit..
I tried to achieve good results for over the 2 hours without
success...!? Everything else remained same except those 2 TL081...
I omitted those picofarads on 8. pin of LM308, of course,TL081
not need those...
So...feel like on begining again!?
Havent try to change values of surrounding caps and resistors...
Must be other way to achieve good results without LM308?
With a lot of help from my friends i prepared 4 types of pcbs for
TGSL....even one smd!
Other people draw those pcb's so i am not allowed to post those.
If original designers want to post their draws than let them do that.
I am not post neither one cose simply dont have right to do that...
There is 12x6cm TGSL onesided from my dear Dutch friend, 6x6 from one
Russian brother and small smd from another good friend of mine...
Also very nice coil housings in prepare...Soon to come and post photos
here...
On posted photo there are wounding bodies for two coil sizes;
one is for DD 190mm x 107mm and other 255mmx155mm...
I done some experiments using 0.20mm wire (0.22mm with varnish)..
Body 190mmx107mm;
130 turns=6.4mH =22ohms
125 turns=6.0mH =21ohms
123 turns=5.8mH =20.6ohms constrained=6.21mH
121 turns=5.72mH =20ohms
120 turns=5.57mH =20.1ohms gives frequency 14.9kHz
117 turns=5.38mH =19.6ohms constrained=5.73mH
Body 255mmx155mm;
95 turns=5.07mH=20.1ohms gives frequency 16.18kHz
Wire gauge affect inductance and frequency of course, so it is
obvious that i should use thicker wire to gain proper number of turns,
inductance and needed frequency. Wire should be 0.25mm to 0.28mm...
Since 16.18kHz is a way to high (we need 14kHz) i should wound more
turns, but it would raise resistance of coil to some 28-30 ohms...
Not good, so if i use thicker wire, all will come on right place.
Resistance will stay between 19-23ohms, inductance will be closer to
6-6.5mH and frequency will lower a bit, just arround 14kHz....
Problem is i left out of wire!? #$^@%^&^!!! I have to wait few days
to find proper one...
Only one problem left to be solved; LM308...It is not impossible to find it,
i can...But i am curious to find proper replacement...That's me!
Regards!
you can try with LF351 instead of LM308... not the same but maybe you could find or have already. Other things, of course there are, but are difficault to find and you have to order.
I found it works better than TL081... somehow; they are normally considered equals but they aren't I think !
Now also obsolete parts !
I've found some suppliers of old LM308 on ebay... dip and metal case too (expensive one)... cause it's still in use in e.g. guitars preamps. etc but problem is that one have to make an international order for them...
Kind regards,
MaxComment
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Hi,Originally posted by J_Player View Post
you have lot of confusion about op. amps.
Let's correct:
LM324 is obsolete quad op. amp. ; No good there.
about the link you provided...
the LM394 are junction isolated ultra well-matched monolithic NPN transistor pairs with an order of magnitude improvement...
so matched pairs NPN, not an op. amp.
Kind regards,
MaxComment
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Hi Max,
There is some confusion because I pasted the wrong LM number. Ivconic was talking about LM308, not LM324.
The fact is the LM308 is considered a better op amp. It's a precision op amp with specifications a factor of 10 better than FET amps over the same temperature ranges. I would not expect the general purpose TL081 to perform as well. But the real test is in the circuit.
My opinion is it is worthwhile to spend a little extra money for precision components when they are performing critical functions where an improved overall performance is demonstrated. I wouldn't be concerned if some people call these obsolete. They are readily available in most of the world. Of course, there is nothing wrong with continuing to use the TL081 if that is your preference.
Best wishes,
J_PComment
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Hi Max.
Now i comprend some minor problems with my TGS. I m using TL081.
How good is LF351 instead of TL081?
Have anyone here LM308 for sale. I can send money by mail.
Regards
Nelson
Originally posted by Max View PostHi,
you can try with LF351 instead of LM308... not the same but maybe you could find or have already. Other things, of course there are, but are difficault to find and you have to order.
I found it works better than TL081... somehow; they are normally considered equals but they aren't I think ! Now also obsolete parts !
I've found some suppliers of old LM308 on ebay... dip and metal case too (expensive one)... cause it's still in use in e.g. guitars preamps. etc but problem is that one have to make an international order for them...
Kind regards,
MaxComment
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HI
Hi,
I can find 308,but have to travel 250 km just to buy them.
When I will have to buy some soon,so I can help youComment
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Hi,Originally posted by nelson View Post
using LF351 seems a bit more sensitive 1-2cm with 1eur coin. No big improvements.
Better if you find the LM308 or a modern full-replacement.
Kind regards,
MaxComment
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You can buy LM308 on ebay. Best to buy in quantity to keep shipping costs reasonable. http://search.ebay.com/lm308_W0QQ_trksidZm37QQfromZR40
Best wishes,
J_PComment
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Schematics for Esteban...and other "skeptics"
Hi all,
cause someone here maybe think I've never realized an original schematic by my hands...
I post these two of my designs about PI detectors:
- 1st one is a simple PI that detected in ground 1eur coin at 37cm with a 20cm diameter monocoil, it detects gold too, can use on beach
It's simple and remember somehow underwater detectors.
- 2nd one is just a sheet (of many) of a very more complex PI detector with lot of features VCO/no-VCO etc etc, also this I've made myself and works really good
Handdrawn.
Of course... low-res pictures !
Esteban I don't need your schematics... I made myself.
Difference is that my designs work !
Kind regards,
MaxComment
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LM308
http://www.reichelt.de/?SID=304RFZOK...9ac7d;ACTION=4
Click GO.
Very expensive, .... 4.70 Euro
Best regards.
ApComment
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