I did read that already somewhere on diyA and echoed it, but someone
else on diyA with apparently a Philips history claimed that diffusion was only
here in Hamburg, Germany in the old Valvo fab and in Asia was only post production.
I have moved to ON CPH3910, but still ~150 BF862 in the drawer.
No noise tests for the 3910 yet. Should have ~30 Hz corner from the data sheet
and very small capacitance.
The 3910 spice model has no 1/f.
else on diyA with apparently a Philips history claimed that diffusion was only
here in Hamburg, Germany in the old Valvo fab and in Asia was only post production.
I have moved to ON CPH3910, but still ~150 BF862 in the drawer.
No noise tests for the 3910 yet. Should have ~30 Hz corner from the data sheet
and very small capacitance.
The 3910 spice model has no 1/f.
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I have built the ribbon mic amplifier from AOE3, or really half of it, i.e non-differential
with ZXTN2018, and only 16 transistors instead of the 64 of the diff version.
The ZXTN2018 has SMD code 851, wich probably means that it's the same chip
as the FZT851, only sot-23. It delivered the promised 70 pV/rtHz, but needs
low input impedance because of noise current.
I wanted it for a chopper post amplifier, so the input capacitor is not an issue.
Hey, the chopper transistors are GaN, 1 square millimeter with 4 bumps, no case. 🙂
I could solder that but first must flush my pipeline of uncompleted things
b4 continuing.
The GaN-FETs are the small dots between the huge SOT-343 clock drivers on
the left and the 4 coupling caps.
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Low input impedance? Did you mean low source impedance?
Mind you, if you need an amplifier with noise levels the equivalent of 0.3 ohms, you probably have low single-digit ohms of source impedance anyway, so 100 ohms would still be plenty high enough.
One thing I will note is that the 2.4V reference comes up a bit short -- around 2.1V -- probably not enough current to drive Vf to 0.6V
Got that fixed.
Here's an FFT -- I also experimented with a DMOS CCS -- much worse as illustrated below. Incidentally, the FFT and the Analog Bandpass method yield results within a very small percentage error.
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Here it is in one of the smaller cookie tins -- I have found that the heroic measures taken by Linear Tech don't seem necessary -- no need of a mu-metal canister, just the cookie tin, and the smaller tin is better for the waist-line:
I must say that Jan's "Silent Switcher" makes the Lithium batteries exhaust themselves in about an hour's worth of work.
I must say that Jan's "Silent Switcher" makes the Lithium batteries exhaust themselves in about an hour's worth of work.
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Be careful with fuse-less lithium cells!
Mine did melt their holder in less than a second.
I have locked them now in an aluminium cast Hammond box
with fast fuses.
Mine did melt their holder in less than a second.
I have locked them now in an aluminium cast Hammond box
with fast fuses.
You should get yourself a decent Powerbank or two. I have two from Varta, 10,400mAHr, so I always have one charged. They're about $20 this side of the pond.
Jan
Someone mentioned JFETs being hard to get, has anyone tried these:
NSVJ6904DSB6T1G ON Semiconductor | Mouser
NSVJ6904DSB6T1G ON Semiconductor | Mouser
It was me.
They were diffused on 4” only in Nijmegen and never anywhere else.
Assembly was in a HK for many years and then at a second site at the Guangdong assembly centre from about ‘96. The HK assembly centre was closed down in about 2002/2003 IIRC. I can’t recall what the assembly centre markings were unfortunately.
Hamburg was always only bipolar small signal - never FET products.
Why 4” ? Because that’s what they were developed on back in the day with some other RF parts and once you have an RF process running smoothly you don’t mess with it.
They were discontinued in 2014/2015 (who needs discretes anymore?) but sold off reserve stocks for a year or two. I think Mouser showed them as obsolete in 2016/17.
I have 1000 private stock.
Yes, thanks for freshing up my fuzzy memory!
Can't we persuade the Hamburg folks then to make
more BFT93, BFG31 or other fast-ish PNPs?
No more folded cascodes for RF or my NIST based
isolation amplifier that needs both sexes! :-(
There is NOTHING left!
Can't we persuade the Hamburg folks then to make
more BFT93, BFG31 or other fast-ish PNPs?
No more folded cascodes for RF or my NIST based
isolation amplifier that needs both sexes! :-(
There is NOTHING left!
Sorry Gerard - unfortunately I left in 2015.
The business - like any semi business - has to be brutally focused on what makes money so there’s little incentive to keep parts in the portfolio that have marginal sales, or that won’t payback quickly if a fab transfer is involved. I remember trying to explain this to Charlie Hansen. It’s a totally different world to consumer electronics, Audio etc.
A lot of the guys I knew have moved on - that business was split off about three years ago and is run as a separate independent entity now (with power mosfets* and some RF stuff now on 8”).
*high performance stuff for auto and telecom
Anyway, enough - let’s get back to low noise opamps!
The business - like any semi business - has to be brutally focused on what makes money so there’s little incentive to keep parts in the portfolio that have marginal sales, or that won’t payback quickly if a fab transfer is involved. I remember trying to explain this to Charlie Hansen. It’s a totally different world to consumer electronics, Audio etc.
A lot of the guys I knew have moved on - that business was split off about three years ago and is run as a separate independent entity now (with power mosfets* and some RF stuff now on 8”).
*high performance stuff for auto and telecom
Anyway, enough - let’s get back to low noise opamps!
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I built a version of the HP403 high impedance buffer using ZTX951. It was indeed very low noise (couldn't really come up with a number, but with the IF3602 amplifier it didn't increase the noise level more than a squiggle). Nevertheless, I couldn't get the input impedance above some 10k Ohms, whereas HP specified Zin of 2Meg.
I don't want to lead this thread astray, perhaps a more generalized LNA thread.
I don't want to lead this thread astray, perhaps a more generalized LNA thread.
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Some fodder -- I used a 60 Ohm resistor on the input -- first image has the top on, second with the top off. amplifier housed in a Oreo cookie tin, powered by Jan's "Silent Switcher" and Sam's low noise current source and 2.4V reference:
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I was at Xiaomi 5yr. ago and we toured the company store and the 10.4's were $7 so I wanted to load up but they would only take a CC from a Chinese bank so my host gave me two.
I have two power banks, take them with me when I travel all the time, and as you both suggest will switch from the 18650's -- I have been advised by one of my sons to watch some of the videos.
One issue with the Varta's is that when the load is very light they switch themselves off. A small test circuit with one or two opamps does that. Can be frustrating, I didn't notice it until only recently.
Are other brands similar? The giveaway is probably a pushbutton on switch.
Jan
Are other brands similar? The giveaway is probably a pushbutton on switch.
Jan
All powerbanks switch off when the current falls below the useful charging current for a phone LiPo, which makes them essentially useless for low power circuits.