RELIC HAWK

[Max]

Max,
Did you try to short-circuit the RX coil?
Or the opamp inputs untill you find where it enters the circuit
Regards,
Fred.

Hi,
yes, I did but find at U4 the "source" of sinusoidal noise... well... better say I can trace till there.

Maybe it's external noise (almost sure it is cause of the 50Hz frequency)... I still don't know... will try to find the hot spot if I can.

Kind regards,
Max

[Fred]

Hi Max and Fred,look at U11 is it gnd or - on point 12 .Grt Nakky

Hi Nakky,
U11 is reversed, pin 2 is on the other corner , what you see is pin 9

Thanks
Regards,
Fred.

[nakky]

Hi Max and Fred,look at U11 is it gnd or - on point 12 .Grt Nakky

[Fred]

Max,
Did you try to short-circuit the RX coil?
Or the opamp inputs untill you find where it enters the circuit
Regards,
Fred.

[Max]

Hi Max,
That´s strange.reminds me of some wrong ground reference at some place.

You didn´t forget the ground clip at you scope probe?
I will have to wait for the 27m4 and 24m2 Ic´s so i cant try it all yet.
I have populated it with resistor .Look great already
regards,
Fred.

Hi,
yes I put the clip at GND level... and got such stuff... changed ic at U7 and got less "noise" : tested NE5532 that has more CMRR but problem is big and not related only to supply I think... there's something wrong maybe about GND tracks ? Ground loop ?

I don't know... will look for that but it's clear something is wrong if I get such enormous 9Vpp at U7!

The sampler works fine... at least seems work nice on the scope.

Kind regards,
Max

[Fred]

Hi Max,
That´s strange.reminds me of some wrong ground reference at some place.

You didn´t forget the ground clip at you scope probe?
I will have to wait for the 27m4 and 24m2 Ic´s so i cant try it all yet.
I have populated it with resistor .Look great already
regards,
Fred.

[Max]

Updated...

It is becoming very dificult to increase nº of components...

-2X 100K resistor to - from U5 and U9
-1.6M disconnected from +
-U5 power rails fixed.
-Some minor stuff like more separation on some traces/pads.

Please someone verify !

regards,
Fred

Hi Fred,
I had a bad gnd connection at U7... due to solder on top layer... after fixed that device started working somehow but very bad...

1 eur coin at 20cm but sound is very bad... chatters always present ...it's unstable and noisy.

I followed signals but just relevant anomaly is that U7 has on output at pin7 something 9Vpp@50Hz , that's huge amount of sinusoidal noise!

Let me explain... I found that at U4 I can trace the introduction of about 20mV noise at 50Hz that then propagates and is amplified by following op amps along the chain... so I end up with 9Vpp at U7!

Now the problem is... the coils are shielded... and I'm using a very low ripple powersupply... so where's that dang 20mVpp noise enter the PCB ??? Where is it from ???

I haven't fluo-lamps there... I haven't anything that emits strong 50Hz radiations... but my dubt is device is so sensitive that source of noise is probably farther than I expect to be.

Another consideration is about decoupling caps... I still haven't them on circuit... so maybe the problem could be there...

Kind regards,
Max

[Fred]

Updated...

It is becoming very dificult to increase nº of components...

-2X 100K resistor to - from U5 and U9
-1.6M disconnected from +
-U5 power rails fixed.
-Some minor stuff like more separation on some traces/pads.

Please someone verify !

regards,
Fred

[Max]

How many mistakes one can make?

I also found more mistakes, important too: the 100K resistors that connect U5 and U9 pins 5,6,12,13 that goes to (- ) are missing.



Fred.

PS : Pin 3 and 6 of U2 have been corrected before.Pse don´t make it look worst that it is !

Hi,
yes, right ... I'm going to fix them too... also one could use resistors on the switch too though ugly solution... I'll make them fit inside the board or on bottom side.

Kind regards,
Max

[Fred]

How many mistakes one can make?

I also found more mistakes, important too: the 100K resistors that connect U5 and U9 pins 5,6,12,13 that goes to (- ) are missing.



Fred.

PS : Pin 3 and 6 of U2 have been corrected before.Pse don´t make it look worst than it is !

[Max]

Hi Fred,
I have bad news about board... other mistakes:

first you need pin3 and pin6 of U2 need GND connection...cause it's missing

also...

following the signals I found that the 1.6Mohm is connected to the + rail... and that U5 power rails are missing... so you have to cut there at 1.6Mohm and use some jumpers to carry supply at U5.

All I solved easy... with some jumpers and cutting some tracks.

This way I get good signals till the middle of signal paths at U4 outputs.

The circuits seems get fair 50Hz ripple on signal path... that's maybe cause I still didn't mount the 100nF decoupling caps on bottom of PCB.

Kind regards,
Max

[Max]

actually looking at my PCB as posted here it looks like drawn with a pencil.Quite awfull.
Anyway, i think if you have tried with high gain transistors and very fast (RF) ones ,and as Ivconic says it must be a regular type, there is no much more to be done ....I think the 2 NPN together look a bit strange,but this has probably been checked.
The other (RX)coil close to the TX one will modify its inductance, and may help to reduce number of turns (or is it the other way around ),but i doubt it will be enought to make much difference...

Regards,
Fred.

Hi Fred,
well... I'm not totally sure of coils I'm using at now. Board is all populated and I started tracing signals, the device doesn't work for now.

The coils I'm using are 1mH , 20AWG coil for TX, with resistance under 1ohm and another one I've made using 140turns of 30AWG on 137x255dd former... that gave me around 45ohm resistance and 15.3mH inductance once thighted with tape etc

The RX seems very small compared with TX... but this apart I think this set will be good for testing stuff...

The signal I read at RX preamp is clear (ne5534 output) and I can null very nice looking at preamp out. The problem now is that following the signals I found a strange stuff around U3 outputs... and now I'm checking for mistakes there.

I can hear sometimes some cracking sound... the 5Khz signal is scaled down by 4024 to get around 1.25Khz audio tone (f/4)... but I have low sound with lot of noise from 16ohm speaker I'm using... sure the headphones solution is the right one, but I'm doing this way just to check now.

PS: don't worry....though not perfect...you board is good!

Kind regards,
Max

[Fred]

Hi,
I've tried there a 33K but without relevant effects. I think problem is that some components are still unknown... as for the last PNP transistor that's maybe something a bit more special than a BC557 I think. The fact it was SMT say they used something particular... maybe available just as SMT or maybe not... but they want/used SMT any case... so we can expect something exotic will make it work on smaller coils but not or not well with traditional gen. purpose PNPs.

Though the frequency is so low (5Khz) I think the oscillator design is so critical that only the use of right stuff will make it run smooth.

Congratulations! Nice PCB Fred!

I'm doing some measures on coils I've made... found 1mH on the 20AWG... I'm doing also the RX stuff pretty slowly cause I'm doing for 137x255DD former not 30cm round.

Kind regards,
Max

actually looking at my PCB as posted here it looks like drawn with a pencil.Quite awfull.
Anyway, i think if you have tried with high gain transistors and very fast (RF) ones ,and as Ivconic says it must be a regular type, there is no much more to be done ....I think the 2 NPN together look a bit strange,but this has probably been checked.
The other (RX)coil close to the TX one will modify its inductance, and may help to reduce number of turns (or is it the other way around ),but i doubt it will be enought to make much difference...

Regards,
Fred.

[Max]

Hi Max,
Nice papyrus!

I have finally received my PCB´s,this time all went OK.
Not perfect, but OK.So i can continue ...
Did you try to increase the 27K resistor to get better oscillation?


Regards,
Fred.

Hi,
I've tried there a 33K but without relevant effects. I think problem is that some components are still unknown... as for the last PNP transistor that's maybe something a bit more special than a BC557 I think. The fact it was SMT say they used something particular... maybe available just as SMT or maybe not... but they want/used SMT any case... so we can expect something exotic will make it work on smaller coils but not or not well with traditional gen. purpose PNPs.

Though the frequency is so low (5Khz) I think the oscillator design is so critical that only the use of right stuff will make it run smooth.

Congratulations! Nice PCB Fred!

I'm doing some measures on coils I've made... found 1mH on the 20AWG... I'm doing also the RX stuff pretty slowly cause I'm doing for 137x255DD former not 30cm round.

Kind regards,
Max

[Fred]

Hi Max,
Nice papyrus!

I have finally received my PCB´s,this time all went OK.
Not perfect, but OK.So i can continue ...
Did you try to increase the 27K resistor to get better oscillation?


Regards,
Fred.