RELIC HAWK

[Max]

Hi,
Max.
I am very glad that you are finaly here.
Have you checked this last schematic?Why there are 3 X 393?In yours there is only one 393?
Now I have some "idea" about that TR.Could it be this?

Hi,
really not... cause had no time to read here in past weeks... not that now I have much more time.... just today is special.

Anyway, in which page is that schematic ? I'd like to see it.

Kind regards,
Max

[robopatt]

Hi,
Max.
I am very glad that you are finaly here.
Have you checked this last schematic?Why there are 3 X 393?In yours there is only one 393?
Now I have some "idea" about that TR.Could it be this?

[Max]

the R28 mistery....

Here's something I don't understand. It looks like all that U5B does is output -2.5V and then draw 25mA through R28.

WHY?? What possible useful function does this perform?

Ummh, besides being a 62.5mW space heater?

Maybe it is supposed to stabilize ground. If so then it seems to me like an inefficient way to do so. You won't find me copying that scheme. It's wierd. WIERD. (Arrgh.)

Hi,
it's tricky , I see. And ugly also...at first. Seems it increase the universe's entropy stuff... and nothing more....

Uhm... let make it clear, if we can.

The U5b it's a not-inverting op-amp there.... so... let consider negative reference the -5v and we see the reference is at -2.5 (so 2.5v up the -5v).

Now look at the gain of a non inverting op amp: gain is = 1+Rx/Ry... in our case 1+(100k/100k) = 2

Then if we put +2.5v (think respect the -5V, absolute negative voltage there) you get vout = +2.5*2 = +5V

In other words the vout of U5b is exactly +5V above the absolute negative voltage (-5v , aka -Vee).

Now... that's actually the GND level in the circuit, that's cause we indicate that for gnd and the two opposite -2.5V and +2.5V respect to that GND, used for e.g. references in trimpot section.

Why that ? Simple... RH needs that, needs a floating GND level with two simm up and down voltages, very stable (lm336 is temperature compensated) probably cause it's required for correct alignment by trimpots: remember that whole gain of chain if fairly high there in RH, so voltages must be VERY stable respect e.g. to thermal variations.

Now... you probably were misleaded by all that voltages... you suppose there were 2.5v drop at R28 with big waste of power....+62mW... resistor will be hot! actually isn't so hot, though the resistor is there for a reason.

The reason have to do (probably) with impedance required. You know ... at gain=2 the op amp has very low closed-loop apparent output impedance (that's a good case for us in general) but what about that ?

The current the op amp must provide to the rest of circuit is a factor, the noise propagation is another factor and so on: the resistor is there cause THEY WANNA MAKE an higher impedance separation between the op amp output stage and GND rail.

Why that so ? I think good explaination is about noise propagation : at some frequencies the noise can play a role in op amp gain variations , with potential effects on stability. Think about e.g. some digital noise that will enter inductively the GND tracks... it will be picked-up by op-amp closed loop too and will affect stage gain a bit (small variations but relevant if md whole gain is high such in RH). A solution I saw in e.g. audio hi-fi amplifiers is separate output of op amps from next loads by increasing impedance between stages : that keep noise back propagation harder and let amplifier chains gains be fairly stable vs noise, also at higher gains.

So the answer is maybe a single word.... stability.

Kind regards,
Max

[Max]

I agree with you.But they can't produce 10000 units with trail and error?Just we need to find what is still missing.And oscillator will work from the first switch on.
I have some ideas on this unknown TR now.But problem is elsewhere.Because every TR can be changed with similar.
I will draw my conclusions and will post them so I can hear your opinion.

Hi,
sorry for latency... too busy these weeks.
No you misunderstud.... I mean trial and error for us, homebrewers that don't know exact recipe... e.g. tolerances required and selected gain they use, nor we know the exact e.g. transistor they use there etc.

Sure once you have the exact recipe and quality checks, and also the selected gain well you can make even 1 billion of them all the same. Now... ML has military grade parts, checks , instruments , plants etc.... no homemade md will match ever the ones produced in that industrial heaven!
That's a fact we must face everytime we feel furstrated by some lazy homemade oscillator.

Other stuff.... is by the book... quite easy, like digital parts nothing special.

Kind regards,
Max

[robopatt]

Ok.
We will wait for help to came.
Until then just some ideas.On max schematic there are 3 x 4066.
When I think one is for switching allm/disc other two to determinate s/m/l.
Am I right for this?
So you see my point.See U9 on max scheme.You have used only U3.

And the use of 339.This must be the fast shutdown.

[ivconic]

Tend to agree 100% with you Porkluvr.
More help will come soon here... i am just waiting original device to come.
Week or two more...
Until than

[porkluvr]

That's not good, and I don't have any good news.

What do your + and - supplies measure? If there are no regulators, then the capacitive voltage divider would split the battery roughly in two. It would not be a nice and neat regulated +/-5V that is easier to work with. But that is not important issue... .

Ignore what I said about a 2.5V output from U5B. I don't see that today. I don't know why I had it in the first place, and I may or may not figure it out. But I think it has to do with the fact that there is no negative feedback around U5B (U10B in Max's drawing).

Looking again at the circuit; IF U5B were a perfect opamp, having exactly equal gain on both the + and - inputs, and IF you had a perfect -2.5 input on both + and - inputs (cough, cough), then you have 0V output. If. But that is not going to happen.

U5B is not a perfect opamp. Without NFB a real world opamp's output is not predictable unless you predict it to be either HIGH or LOW. Any in-between condition will be accidental and will change with temperature, resistor tolerance, loading, power supply voltage, and maybe even the phase of the moon! Very tempermental, and practically useless - except as a comparator.

So, I don't know what I did to have a -2.5V output before, but it may have been an accident, or my mistake. I am no closer to figuring out what purpose that opamp sub-circuit serves.

I cannot hope re-engineer this circuit because all I have to work with is second hand information, and no physical lab.

TL272 and LF442 are not same as TL27M2. They're all amplifiers, but have different characterics. But I don't think this is your problem, there is probably something else.

Without an oscilloscope you have very slim chance of figuring out where errors are because you seem to be only person building this detector. You probably need more help than I can give you.

[robopatt]

Do you see 2.5V at the top of R28?
Nope 4,95!

I have try TLC272 and LF442 on this 393 place and they only made the sound worst.

Interesting is that U7 is 393.And on previous schematic its TS27M2.

A simple test could be to install TL27M2 or TLC27M7 and see what happens. If you don't have those, TLC2262 should work.

If you don't have either of those, maybe a LM358 or LF442 would work but they could NOT be considered best choice replacements. If your detector works good, great. If it doesn't work so good, you should obtain one of the first three amps listed or do some research for a good substitute from another manufacturer.

Install a socket if you think you might need to experiment with U7.

You could possibly remove R28 and save battery power, but only MAX or somebody with RH could know it there is an error. Do you see 2.5V at the top of R28?

One problem at a time.

[robopatt]

Interesting is that U7 is 393.And on previous schematic its TS27M2.
Why?Its it mistake or some mod?
I have noticed that 339 is missing.And this IC is part of the sound section.But maybe its vital to use this one there.

Porkluvr,
Do you think that if we remove this R28/100R/ the problem will be solved?
I will try remove this but its elsewhere.
Its there on max schematic,but there is used with 074 for s/m/l.And now only S with 071.But its still compensating something.

[porkluvr]

Ivconic,
I'm not meaning to throw stones at you, Max, or anybody, and I don't want to wear on your patience. It takes a lot of time and effort to RE one of these things and I'm grateful to all who do so. I'm not intending to belittle anybody's effort.

If it's a mistake, then it probably won't hurt to remove the resistor and possibly save some battery juice. If it's for real, then maybe somebody will divulge its purpose.

I saw it and wanted to point it out for what it's worth, because it's confusing (to me) and MAY be a mistake, but I don't know. I'm not well educated and there are all kinds of tricks that I would never think of that some folks have up their sleeve!

[ivconic]

Ask Max, it is redrawn from schematic he posted a while ago.

[porkluvr]

space heater

Here's something I don't understand. It looks like all that U5B does is output -2.5V and then draw 25mA through R28.

WHY?? What possible useful function does this perform?

Ummh, besides being a 62.5mW space heater?

Maybe it is supposed to stabilize ground. If so then it seems to me like an inefficient way to do so. You won't find me copying that scheme. It's wierd. WIERD. (Arrgh.)

[robopatt]

Porkluvr.
You should look this one.
As you can see there are diferances.

[robopatt]

Yes,
You get it right.
But you are using realy wrong schematic.
You should use last posted here.
And on this its R68 470K if I understood you right.But I cant see this capacitator.
Now its more stable.
Still a lot of work before field test.