[time-nuts] Re: DMTD Questions

[ghf at hoffmann-hochfrequenz.de]

Am 2026-07-09 23:59, schrieb Attila Kinali via time-nuts:
> On Thu, 9 Jul 2026 12:40:25 +0200
> Attila Kinali via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>> There has been also discussions using the ZTX951, which potentially
>> could offer better noise performance due to its low base spreading
>> resistance. But I have never seen any measurements. I believe
>> they have a modern SMD variant of the ZTX951, but I can't currently
>> find it.
> 
> The SMD variants of the ZTX851 and ZTX951 are called
> FZT851 and FZT951.

Just seen:  Last Time Buy Date: 10/28/2026 for the version with wires.
<  
https://www.digikey.com/en/products/detail/diodes-incorporated/ZTX851/92590 
  >

There is also the ZXTN2018FTA in the small SOT-23 case.
It has the laser marking "851", probably for a reason.

In "The Art Of Electronics" ed.3 is a page-long table of
interesting transistors. (Paul Horowitz & Winfield Hill)

They also have a balanced preamp for ribbon microphones
that features a noise density of 70 pV/rtHz. With
reasonable constraints, you cannot do much better.
I have built a single ended version of this with only
16 ZXT851 instead of 2*32 and it works like promised.

<  
https://www.flickr.com/photos/137684711@N07/44311358915/in/datetaken/lightbox/ 
  >

If you need an input coupling capacitor: It must be much
larger than just to dictated by your wanted f-3dB