Replies to Minipulse Plus

[bernte_one]

ok i will take a two kits as soon as available

[eogeo]

Thanks Qiaozhi for all the effort you have put into this project and a first class build manual which will make assembly and testing so much easier. PCB ordered. Also thanks to Silverdog for providing a great service.

There was a mention somewhere else on Geotech, Baracuda thread perhaps, that matching the J113 FET's may improve performance a bit. Is that also the case with this design?

[6666]

Thanks Andy and Qiaozhi, have ordered a PCB.

[silverdog]

OK, I have a limited number of REV-B boards left from the prototype run - I have put 10 in the shop for those awaiting them
I will be making a very small number of kits later in the week - then arranging a further batch of boards

Please thank Qiaozhi for all his hard work on this project, without this kind of commitment we would not have projects to build

[Davor]

Thanks for Ver B, very interesting that you have managed to do away with offset adjustment on preamp.

That's the very reason I'm up to making this particular rig. Differential integrator is the key feature of this gem that is very forgiving. It acts as a balanced detector so even the FETs charge injections cancel each other. Trouble with most detectors in amateur stratum are half wave VLFs and unbalanced PI detectors. This one is a step beyond

I believe this is a nice platform for further improvements, however, I don't expect many of those.

GB will be a nice challenge.

[bernte_one]

so andy please list them in the shop

[6666]

Thanks for Ver B, very interesting that you have managed to do away with offset adjustment on preamp.

PCBs are available from www.silverdog.co.uk

When they are listed I will order a PCB.

[Qiaozhi]

Thanks for the final version B. It is very nicely described, and I'll order my PCB(s) in a week.
I wonder about possible improvements in form of replacing the NE5532 with NJM2068, my favourite op amp of late. It is less noisy (with 1k towards the coil it does not make much difference though), it is faster, and it has better THD. I have no idea how it would do in a PI front end.
BTW, schematics look immensely better in documents when they are placed there in just about any format other than jpeg. Only jpeg makes that ugly artefacts around lines and text. For me gif works the best.

The Minipulse Plus is a design that we (Geotech members) can take further if desired. Please feel free to experiment and make improvements. You might also want to try even higher TX pulse rates, and longer pulse lengths, whatever. In general though, I would like to keep this design simple to build, without lots of extra options and adjustments. I think we should leave the design as it is for a while (at least until the current batch of PCBs is exhausted), with possible modifications scheduled on an annual basis. That would give everyone time to develop new ideas ... such as adding ground balancing, for example.

Regarding the images, I agree. The 3D PCB image on the title page is a GIF, whereas all the others are JPG; except the TX oscillator waveform, which is a BMP (generated by the scope). I'll change these to GIFs when the document next gets updated.

[Davor]

Thanks for the final version B. It is very nicely described, and I'll order my PCB(s) in a week.
I wonder about possible improvements in form of replacing the NE5532 with NJM2068, my favourite op amp of late. It is less noisy (with 1k towards the coil it does not make much difference though), it is faster, and it has better THD. I have no idea how it would do in a PI front end.
BTW, schematics look immensely better in documents when they are placed there in just about any format other than jpeg. Only jpeg makes that ugly artefacts around lines and text. For me gif works the best.

[6666]

Sounding good Qiaozhi.

[WM6]

Great news Qiaozhi, bravo.

Maybe you can post last version of schematic?

[Qiaozhi]

Any Idea of costs for the board yet ?

Andy (Silverdog) says they'll be about £7 each.

I did a bit more on the build tonight, and so far so good.
Power supplies are stable.
TX running at 1kHz with 80us pulse width.
Faster preamp working as expected.
Sample generator creating all the right pulses.
Integrating sampler giving a good signal at the output when a target is placed near the coil.
Just to need to fit final integrator and audio stage, so nearly there.

[WM6]

Thank you for this piece of history.

[lytle78]

Field Test

IMG.pdf

here's a field test of the minipulse.

the 13" depth in air on an old English penny (cartwheel type) is a couple of inches more than my DF PI and about the Same as my TDI with GB on!

[satdaveuk]

Any Idea of costs for the board yet ?