Single Ended Solid state preamp

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
That appears to be an NPN transistor. To make a one transistor amplifier we would need to know the supply voltage and the gain needed. Also using one transistor means the design will have several compromises such as fairly high output impedance.
 
A simple common emitter stage like in the pic attached will work. The 2n2219 is supposed to be nearly the same as KT603A. The distortion is going to be quite high, 5% at 2 volts rms out. Of course it will require a regulated supply or noise will be an issue as well.
 

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Jay

Banned
2003-02-11 9:02 am
Jakarta
Not an amplifier but an preamplifier

JFET-BOZ is a preamp. It uses NJFET instead of NPN. If you have many NPNs, why do you want a single transistor preamp? NPN/BJT is not suitable for single ended gain stage. There's nothing wrong with two or more transistor, would you think so?

BTW, I always buffer the input of my low power chip amps with NPN-BJT. The chip amp uses single ended supply, so low that very low noise NPN can be used (many of them have maximum Vce of 15V). Schematic topology is similar to what Jerluwoo posted except that output is taken from emitter (instead of collector). My favorite NPN for this purpose is gold plated 2N2222A.

EDIT: For more than one transistor you'll need PNP. Sorry. But eww... they are cheap.
 
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Bonsai

Member
Paid Member
2003-07-25 10:44 pm
Europe
www.hifisonix.com
A simple common emitter stage like in the pic attached will work. The 2n2219 is supposed to be nearly the same as KT603A. The distortion is going to be quite high, 5% at 2 volts rms out. Of course it will require a regulated supply or noise will be an issue as well.

Buffer the output with a current source loaded emitter follower.
 

juma

Member
2005-11-08 11:27 am
Zemun
If it had to be with just one BJT I'd choose one with higher hfe - otherwise the Zin will be too low or the Zout too high.
Proposal in attachment has Zin of about 20k, Zout less than 1k, gain is about 2.5V/V.
THD should be somewhere between 0.01% and 0.1% at 2V_RMS output.
Q1/Q2 run at Ic=15mA, R1/R16 should be 0.5W or more.
All caps should be rated at 35V or more.
Q1/Q2 can be any general purpose NPN BJT with hfe > 300.
Sound of this preamp is slightly on the mellow side...
 

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scholl

Member
2012-12-30 5:07 pm
IXCYS Depletion Mode Fets..

Im looking for an single ended solid state preamp only with one transistor design.

I have looked everywere to see if there is an design with only one transistor
use in an line preamp. does it exist

Take a look at IXCYS 10M90S and 10M45S constant current sourses. These make very sweet little single stage or more complicated preamps. Super simple to use. Just use the datasheets to figure the bias current and a 100-200 resistor usualy sets it up nicely. You can bypass that for more gain or even use two resistors in series and bypass one of them to get a desired gain. Without a bypass cap and a K resistor of 200 and an A resistor of 1000 gets a gain around 5. IT'll drive a 15K ohm input resistance with ease. I use 50V powersupplies you can use most any above 24V but they like a bit more voltage.
 
I wonder why everybody suggests lots of different preamps based in JFets, MosFets, bipolars with Hfe>300, constant current sources:rolleyes: , PNP, etc., when the OP clearly stated
i have a lot of KT603A
.

Which, by the way, is a crappy obsolete Soviet era transistor.:eek:

And anyway he still hasn't answered the very basic questions posted in # 2 and # 13.
Oh well.