Serbian pi Gold-Skan

[dbanner]

All things considered( correct layout, wiring, components etc), and assuming you know how to adjust the offset trimmers and properly damp the coil, you can be suspicious of fake op amp chips. Especially, but not limited to the preamp chip.

[fadiashour]

Please, what is the value of the capacitors, is it 16 volts or 25 volts, because I put all the capacitors 16 volts and the circuit works for a moment and then gradually collapses

[Carl-NC]

For 15V lines I would use 25V caps though 16V should still work. Are your caps new or recycled? Did you test things as you assembled?

[dbanner]

Hi Carl.

[fadiashour]

Of course it is new and I checked it before installation, but I will replace it with 25 volts and try

[fadiashour]

Is this the correct way to modify the trimmers?
Is this the correct way to modify the trimmers?

[ZOUjiarui]

Hi guys, has anyone tried running this machine with big coils?

[Op04]

Hi guys, has anyone tried running this machine with big coils?

Before make this, you must understand supply rail and where the signal path goes, also be very careful for timing and know how to measure. Take your time first to understand, or else you be stuck in the end, since too many measurement and synchronize geb and disc, so many variable. For big coil must increase pulse width and everything change with it so hard to guide even some people done with GS5 SD2000 but guide for troubleshoot is time consuming. So take your time first to know each section. Regards.

[ZOUjiarui]

Thanks Op04. it sounds difficult

[haylaz0036]

guys i am looking for the latest and working .lay version and parts list

[ZOUjiarui]

I think it's a static pi, I don't see a resistor connected to j113 (the gs4 has it), it might work with a big coil like a TDI, there's a video somewhere on the forum

[Dean Sarelius]

Hi Everyone
I have been looking at the Goldscan 5 front end and would like to get your feedback on the front end. What I recall from previous posts is that most of the gold signal is within the 15us sample phase of the back emf pulse. In my opinion it appears that the front end of the Goldscan 5 is pinching off the signal by applying 2 x 1N4148 diodes to the second stage refer cct diagram below. In my opinion the second stage is squeezing the signal into the ground sampling region so would welcome your comments..?

[moodz]

There are two transistors connected as "diodes" across the input of the 5534 internally anyway ... not as robust.
If you have a sufficiently fast coil then you wont have a problem with the signal being "squeezed".
This frontend works ... OK.

[Carl-NC]

I don't understand the question. The diodes in front of the first stage protect the 5534 from flyback destruction. Moodz is correct that the 5534 has internal diodes but other opamps may not. The diodes between the stages are intended to limit the overdrive voltage to the second stage and speed up its recovery.

If you are wanting to sample earlier then increase the 1k resistor that feeds the first stage clamp. Try 2k. This reduces the peak clamp current in the diodes which reduces the diffusion capacitance and makes turn-off recovery faster. The downside is that it increases thermal noise, but that may not be a limiting factor. In one of my PI designs I've run it up to 10k and sampled at 3-4 us, but this also requires a really good coil.

Edit: as you increase the 1k input resistor, the feedback resistor (10k) also needs to increase to maintain the preamp gain.

[Dean Sarelius]

Thanks for the feedback this is very helpfull especially regarding the input resistor value and how it improves the speed of the flyback pulse. One other question I have regarding the same circuit is the lack of DC compensation on the first stage. As far as I can see if the first stage is not compensated correctly then the second stage will be unable to centre the flyback signal..?