saint gillis

Re: DMMT3904 matched pair
« Reply #20 on: August 01, 2019, 06:41:04 AM »
Old thread, just to say I tried the DMMT3904 on a minimoog synth filter, thoose little bastards are very noisy, avoid for audio!


JohnRoberts

Re: DMMT3904 matched pair
« Reply #21 on: August 01, 2019, 01:04:35 PM »
2n3904 is a small geometry general purpose NPN switch... not remotely a low noise audio amplifier.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

PRR

Re: DMMT3904 matched pair
« Reply #22 on: August 01, 2019, 03:08:00 PM »
> 2n3904 is a small geometry general purpose NPN switch... not remotely a low noise audio amplifier.

Sheets say "general purpose" and give both amplifier and switch data.

They even give noise data. Not the best, but not bad (IME, typically better than claimed) *IF* working at low current from high impedances. MM phono, step-up mike transformers.

JohnRoberts

Re: DMMT3904 matched pair
« Reply #23 on: August 02, 2019, 10:07:28 AM »
I never found it to be very low noise, but old transistors like the 2n5088 that even called themselves "low noise" were not very... By the late 70s I was buying low noise bipolar devices with 1 dB NF to low Z (not 10kOhm).

Motchenbacher and Fitchen, a classic text about low noise design, wrote up the 2n4403 (another GP bipolar device) for low noise design, using several in parallel (last century).  I am also aware of some low noise design in the 70s-80s using medium power bipolar transistors for their low Rbb, but they had to be screened for acceptable process noise.

I guess its all relative... The constant NF curves are useful design tools for setting current density but even with the 2n3904 dialed in for a MM phono cart you are still leaving a couple dB of noise on the table compared to using modern lower noise devices. I used a low noise JFET in my last phono preamp, also last century. 

In a phono preamp application the 2n3904 could be acceptable to many due to the relatively high surface noise of vinyl, but there were still better options in my opinion and experience (I designed several phono preamps over the decades so melted a lot of solder in that pursuit). 

JR 
 
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.


 

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