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Old 16th February 2013, 02:05 PM   #11
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by jerluwoo View Post
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.
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Old 16th February 2013, 04:01 PM   #12
juma is offline juma  Serbia
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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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Old 16th February 2013, 04:40 PM   #13
JMFahey is offline JMFahey  Argentina
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Before jumping into such an undefined project:
1) what will drive it?
2) what will you drive with it?
3) how much gain do you need?
4) what supply voltage is available?
1 to 4 are somewhat interactive, but it's better to answer all.
Otherwise, answering is futile.
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Old 16th February 2013, 05:06 PM   #14
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Yes, I've also thought about a one-transistor-preamp. A IRF610 for example connected to a supply voltage of about 50V. You could simply take the supply voltage of the power amp.
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Old 16th February 2013, 05:55 PM   #15
scholl is offline scholl  United States
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Default IXCYS Depletion Mode Fets..

Quote:
Originally Posted by Jempie View Post
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.
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Old 16th February 2013, 06:43 PM   #16
JMFahey is offline JMFahey  Argentina
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I wonder why everybody suggests lots of different preamps based in JFets, MosFets, bipolars with Hfe>300, constant current sources , PNP, etc., when the OP clearly stated
Quote:
i have a lot of KT603A
.

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

And anyway he still hasn't answered the very basic questions posted in # 2 and # 13.
Oh well.
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Old 16th February 2013, 09:15 PM   #17
Jempie is offline Jempie  Indonesia
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Voltage 12 up to 35 volt
Gain 10
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Old 16th February 2013, 09:20 PM   #18
Jempie is offline Jempie  Indonesia
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Sovjet transistor I have 8 pcs
Not ok to use name me one that's better
It must be simple
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Old 16th February 2013, 10:53 PM   #19
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Mooly View Post
Why would you need a PNP to use more than one transistor ?
I wasn't sure what the OP wanted so I focused on what I wanted

One transistor! It cannot sound without other parts. Most likely will have to go to electronic shop anyway. So why one BJT transistor?? Just because having owned 8 BJTs? I have thousands that I think I will never used.
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Old 17th February 2013, 03:23 AM   #20
JMFahey is offline JMFahey  Argentina
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Try this:
Click the image to open in full size.
Gain: 10X
Zin: around 40K
Z out: 4K7
Transistor: BC546B or C
Or any general purpose low signal NPN, Hfe around 300.
Fed from 20 to 30 V single rail.

This is what's normally achievable from a single transistor without stretching the envelope.
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