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Re: Low Noise Transistors: Comparing the ZTX1053A and ZDT1053 (Dual) vs. the ZTX689B and ZTX851

Posted: Fri Apr 10, 2020 7:13 am
by mediatechnology
terkio wrote:
Tue Apr 07, 2020 8:04 pm
What I have in mind is using a matching gig where I insert a resistor in the transitor base to represent the bias resistor that will be used in the final circuit.
There's a lot to be said for simply using the preamp itself as a test circuit which includes the bias resistors.

I would suggest that approach in the MC preamp instructions but it would require socketing the input transistors.
Since I'm not crazy about leaving the sockets in for the final build I suggested testing Vos out of circuit.

Re: Low Noise Transistors: Comparing the ZTX1053A and ZDT1053 (Dual) vs. the ZTX689B and ZTX851

Posted: Tue Jun 02, 2020 7:17 am
by AnalogJoe
You might want to check out this webpage http://www.dicks-website.eu/low_noise_a ... part3.html they compare several transistors, apparently the ones with the lowest noise are the ZTX853 with a merely 1.62 Ohm of base spreading resistance, or 0.22 nV/rootHz.

Your test setup seems to be better thou, in a "Double Balanced" configuration, opossed to the single transistor used in the webpage.

Re: Low Noise Transistors: Comparing the ZTX1053A and ZDT1053 (Dual) vs. the ZTX689B and ZTX851

Posted: Tue Jun 02, 2020 7:34 am
by mediatechnology
Thanks analogjoe.

I did post Dick's link in another thread but somehow missed the ZTX853. https://proaudiodesignforum.com/forum/p ... 496#p11496

Dick's website also has a nice op amp noise calculator: viewtopic.php?f=12&t=1148

I'd be curious to see how the ZTX853 directly compares to the ZTX951 (PNP).

One of my objectives is to find higher-gain low noise transistors in the Zetex series that would serve well in mic preamp applications where the absolute lowest rbb' isn't necessarily required due to the higher source impedance.
Fortunately there are quite a few.
We're lucky we can use these power devices "off-label."

Re: Low Noise Transistors: Comparing the ZTX1053A and ZDT1053 (Dual) vs. the ZTX689B and ZTX851

Posted: Wed Jun 03, 2020 5:55 pm
by AnalogJoe
mediatechnology wrote:
Tue Jun 02, 2020 7:34 am

One of my objectives is to find higher-gain low noise transistors in the Zetex series that would serve well in mic preamp applications where the absolute lowest rbb' isn't necessarily required due to the higher source impedance.
Fortunately there are quite a few.
We're lucky we can use these power devices "off-label."
They are not that cheap thou, the ZTX851 is around a dolar a piece, you can buy a pair of opamps with that!

Re: Low Noise Transistors: Comparing the ZTX1053A and ZDT1053 (Dual) vs. the ZTX689B and ZTX851

Posted: Wed Jun 03, 2020 7:03 pm
by mediatechnology
In 100's the ZTX851/853 drop down to about 67 cents.
Still not cheap but capable of outperforming just about everything out there other than the PNP ZTX951.

I just did a side-by-side comparison and I think they're the same die with the ZTX853 having higher Vce breakdown of 100V vs 60V for the ZTX851.

I hadn't looked at the ZTX953 before but it appears to be the PNP compliment to the NPN ZTX853.

I think Dick's measurement differences between the ZTX851 and ZTX853's rbb' may be statistical since they are so small.

Also looked at the ZTX857/957 300V complimentary pair. Both have significantly lower Cobo than the ZTX851/951 ZTX853/953.