Replies to Minipulse Plus

[josewashere]

I have a friend who has these small adapter boards so that should not a problem.

[KingJL]

There are dip adapters, but fairly expensive: http://www.ebay.ca/itm/1PCS-OPA2211A...item3390bb5205

I believe that this one includes a mounted OPA2211... I would suggest you ask the seller to be sure.

[multieagle]

There are dip adapters, but fairly expensive: http://www.ebay.ca/itm/1PCS-OPA2211A...item3390bb5205

[josewashere]

I will give the OPA2211 a try Thanks!

[KingJL]

GBW (or rather lack of it)!

For an improvement, try the MAX412. I really like the OPA2211, but the available packages make hobby usage extremely difficult. I have used the single opamp version (OPA211) successfully in project detectors (as it is available in SOIC).

[KingJL]

Qiaozhi. Further investigation into using the TL072 in place of the Ne5532. I hadn't noticed this the other day but if you check at longer sampling delays you will find that the detector ignores metal almost completely. Interesting effect!

Anyone have any ideas why this would be the case?

GBW (or rather lack of it)!

[josewashere]

Qiaozhi. Further investigation into using the TL072 in place of the Ne5532. I hadn't noticed this the other day but if you check at longer sampling delays you will find that the detector ignores metal almost completely. Interesting effect!

Anyone have any ideas why this would be the case?

[josewashere]

Yes it could be but it recovers quickly when you remove your finger, maybe too quick to be temp related
Jose

[joop]

I bet it is a temperature effect what you are seeing... VCO drift.

[josewashere]

Yep that is exactly what I noticed here too.
One more thing to think about.. when using the ne5532 if you place your finger on top of u10 vco 555 the threshold will decrease and sensitivity goes down noticeably even if you compensate with the threshold control! When using the tl072 and touching the 555 the threshold rises a bit instead.
When I say touching the 555 timer I mean resting the finger on the top of its case (not touching any pins) Not sure if its a capacitive effect or just coupling extra noise into the 555 but I thought it was a bit strange for a chip operating as an audio vco to behave like this and there could be a bit of gain to be had by reconfiguring this timer layout or components around it?

[Qiaozhi]

TL072 in place of the NE5532 shifts the threshold further up the adjustment pot and really smooths out the threshold. The threshold is far more stable and sensitivity is same to maybe a touch less. The chattiness as you advanced the threshold pot past the slow ticking sound is gone!

I've just tried a TL072 in place of the NE5534, and can confirm that it does smooth out the threshold somewhat, but there is a slight loss in sensitivity. Whereas as TL062 completely smooths out the threshold, and also kills the sensitivity by about 50%.

[Qiaozhi]

Oops, that's a bit of a mystery ... probably the result of some late night working.

C21 in the schematic should not be there! As noticed by CAS, it's not on the PCB, or in figures 3 or 4 of the Build Document. That's another one for the errata list.
C20 is the sync cap, and needs to be added under the PCB. This cap will be added in the next board revision.

Hope that's clear.

In the end there was no need to update the errata list, as the Build Document is not affected. It seems that I must have posted the wrong schematic, which erroneously contained C21.

The correct REV-C schematic is now available for download here -> Minipulse Plus REV-C

[josewashere]

I think I am going to order another board and implement some of these changes of yours. Probably be a 3 or 4 weeks before I have it so hopefully by then you have built yours with these changes.
I do like the SAT though.

[Davor]

You are waaaay ahead of my build, but I tend to analyse things before going to actually building something (I seldom have a chance to do so), so when I do I apply mods instantly.

My Spice sims show that the differential integrator suffers from charge injection spikes originating from the FETs. Faster op amps cope better with spikes, hence TL072 and LF353 are much better choices than TL062. They both have much better noise performance. The most pronounced kind of noise here is 1/f which is indistinguishable from random drift, and it also appears as chatters.

The charge injection is unfortunately not completely symmetric and thus there will always be some offset related to it. Reducing the charge injection effects can be attempted by slowing down gate control voltage transitions. A no-brains solution is simply adding a resistor in series with a FET gate, but the value will depend upon a FET choice. With J113 I'd go with 22k to 47k, and with BF245B (my choice) which is faster and has less capacitances I'd go with ~100k. It reduces and slows down the spikes to ~500ns so that fast op amps may handle them.

The motion compensation as done in Rev-B (C15R29) is IMHO wrong. The spikes are propagated to TL061, again a slow op amp, and its feedback capacitor just can't cope. The original minipulse has a RC LP filter there, and spikes are effectively ironed out. The nature of the integrator in minipulse is so that it actively returns to zero, by way of a slew rate slope (controlled by R22), and not an exponential ever only approaching zero RC filter slope. Hence it is fast and accurate, and it doesn't require any motion filtering. I expect far less masking (better recovery speed) without the motion compensation, and also better stability if it is converted back to a LP filter with ~30Hz corner frequency.

[josewashere]

let me know what you find! If good I will buy a handful to try to get a matching set