Noiseless MOSFET boosters: ZAZEN and QIGONG

[Fancy Lime]

Thanks for the schematics Andy

You're welcome, my pleasure. Very happy to hear that you like them.

I'll post my layouts if anyone wants a stripboard layout.  They are hand drawn too .. 

Yes, please! I really suck at layouting, which is why half the stuff I design never makes it off the breadboard...

Andy

[bluebunny]

I'll post my layouts if anyone wants a stripboard layout.

Good point. I should dig out my vero layout and post it too.

Edit: done - see below.

[bluebunny]

[BetterOffShred]

First layout is Zazen, pretty straight forward, values correspond to the schematic.   Shown in pencil are the changes to make it into board 1 for the Qigong.. not the best idea but it worked fine

Second layout is the 2nd part of the Qigong board. I just used a single piece of strip 11 wide and 15 rows.  Also not ideal but it works great.  See the power and ground jumpers in the built pic. Numbers follow the schematic from the gain knob forward on the Qigong schematic. 

Final note, did not include power conditioning. If desired just use a huminator layout.  Mines quiet as a mouse without it.

Sorry for the numerous inconveniences on the boards, but they work great haha

[Fancy Lime]

Very cool! Thanks guys!

Andy

[Lino22]

May i know why it has 10u and 100n in parallel on the source? Is that some kind of fine tuning?

[ElectricDruid]

May i know why it has 10u and 100n in parallel on the source? Is that some kind of fine tuning?

I think that's mentioned in the first post:

"Film capacitor C4 makes sure that the increasing impedance of the electrolytic C3 toward higher frequencies does not cut highs, while the large C3 ensures not to cut lows."

Electrolytics tend not to work that well at higher frequencies, so adding a smaller cap that is more effective for those frequencies does a lot more than the simple "capacitors in parallel add together" rule would suggest. In some cases, a specific type of cap is chosen too - so a ceramic 100nF in parallel with a larger electro, for example.

[antonis]

Electrolytics tend not to work that well at higher frequencies, so adding a smaller cap that is more effective for those frequencies does a lot more than the simple "capacitors in parallel add together" rule would suggest. In some cases, a specific type of cap is chosen too - so a ceramic 100nF in parallel with a larger electro, for example.

Like in countless supply filtering..

@Lino22: Look also at 220μF/100nF shunting supply rails..

[PRR]

Electrolytics tend not to work that well at higher frequencies, so adding a smaller cap that is more effective for those frequencies...

That's old data. From Murata:
https://article.murata.com/en-us/article/impedance-esr-frequency-characteristics-in-capacitors


A 10uFd Al e-cap made in the last 30 years will come down to 10 ohms in the top of the guitar band *and stay there* (dropping to 5r) until far up in the short wave radio band.

As you see, "better" caps (Ta, film, ceramic) are prone to SHARP DEEP anti-resonant dips around 1MHz. Same if you put one across an e-cap. That's a woo-woo fashion statement, not good engineering. Remember that MOSFETs (and some chips and BJTs) have gain to 1MHz and beyond.

[Lino22]

Paul but i see the ceramic and films are 10-1000 times under the elytes all along. I am not sure how to translate your post ... 🙂

[Rob Strand]

May i know why it has 10u and 100n in parallel on the source? Is that some kind of fine tuning?

As per RG's old post, the reverse ground connection needs good bypassing.  The extra 10nF is a bit of insurance.   The reason is given by Electric Druid.

[Lino22]

Sure, i thought Paul thought it was a hype. Sorry for my being slow

[mzy12]

I've seen a MOSFET Fuzz Face on reddit in the past that I'd like to give a shot at making, but I whenever I see MOSFETs in audio applications, I do worry about the excess noise (funny thing to say when compared to a germanium fuzz face, I know). I wonder what it would be like with BS250s?

I still definitely do not understand why P-Channel MOSFETs would be quieter haha. Very interesting finding!

[Rob Strand]

Don't forget Jonny Reckless's "Moon LNDer overdrive distortion - depletion mode MOSFET pedal design".

That does aim at getting less noise.  It uses N-channel depletion mode MOSFETs so no need to flip the grounds. 
https://www.diystompboxes.com/smfforum/index.php?topic=125775.0

[mzy12]

Very interesting! Gonna give that a shot...

Is there a reason that depletion mode MOSFETs would offer a lower noise floor? Can't seem to find any in that thread.

Also the higher input capacitance/miller capacitance might be beneficial for a Fuzz Face circuit as that is one (of the many) reason(s) that people suggest that Ge transistors are preferred - and also why there are a good few circuits floating around using power transistors to get some of that back in Si transistors.

I will experiment to find out.

[amptramp]

Does anyone have a value for nV/(SQRT Hz) for any of these MOS devices?  I would like to see how it compares to JFET's, especially the JFE150 from TI:

https://www.ti.com/lit/ds/symlink/jfe150.pdf?ts=1702390107280&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FJFE150

I really don't see a need for 0.8 or 0.9 nV/(SQRT Hz) in a world where a TL07X works well, but it is there if you really need it.

[amptramp]

There are also Gallium Nitride transistors that excel at microwave frequencies because the mobility of GaN is about 7 times that of silicon, but they also claim to be low noise.  Has anyone tried them in audio circuits?

[mzy12]

I really don't see a need for 0.8 or 0.9 nV/(SQRT Hz) in a world where a TL07X works well...

I would be of the opinion that the TL07X has unacceptable performance for a design in the year 2023, but that is, admittedly, a very extreme position to take

Does anyone have a value for nV/(SQRT Hz) for any of these MOS devices?  I would like to see how it compares to JFET's, especially the JFE150 from TI:

I have never been able to find any noise figure for any discrete MOSFET. It's probably fair to assume that even the best ones would have good average noise figures but shoot up beyond 20nV/rtHz at the lowest audio frequencies.

For example, the OPA1678 CMOS opamp has great characteristics for an opamp that you could use in a guitar pedal. It's even relatively affordable! But that input voltage noise really starts shooting up below 100Hz. Still a much better chip than a TL07X. Of course, seeing as it is CMOS architecture vs the TL07X's JFET input, clipping the rails as most gain circuits do will more than likely produce a noticeably different sound.

There are also Gallium Nitride transistors that excel at microwave frequencies because the mobility of GaN is about 7 times that of silicon, but they also claim to be low noise.  Has anyone tried them in audio circuits?

I'd defo like to try them. MOSFET noise problems are much, much lower down in the frequency spectrum than microwave though. Not sure how GaN would affect that.

[Rob Strand]

Is there a reason that depletion mode MOSFETs would offer a lower noise floor? Can't seem to find any in that thread.

I think it comes down to the specifics of the device.   The 2N7000/BS170 is a big clunker with a lot of area and potential for surface effects, which cause 1/f noise in MOSFETs.

I'd only judged lower noise floor from loose experience since the small depletion MOSFETs from the 70's used to be OK for noise.  Some of those were targeted at low-ish noise for RF - but RF can side-step the 1/f noise problem.

As far as I understand, the LND150s are not only depletion they are lateral MOSFETs.   You could spend a lot hours researching if that is an important factor or not.

I really don't see a need for 0.8 or 0.9 nV/(SQRT Hz) in a world where a TL07X works well, but it is there if you really need it

I don't expect them to approach low noise JFETs by any means.   I could be wrong but I have seen people stating the LND150's are noisy - it all depends on what your reference is: low noise JFETs or 2N7000's  .   The LND150's are definitely better than the 100's nV/rtHz from the 2N7000's.

[mzy12]

As far as I understand, the LND150s are not only depletion they are lateral MOSFETs.   You could spend a lot hours researching if that is an important factor or not.

I may just bother one my uni professors with that question when we're back in class in January hahah