Need A Schematic For A BJT Headphone Amp

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Being primarily a Tube/FET guy, I don't usually play around with BJTs. MY question: I am looking to build a small headphone amp for 65ohm/channel JVC headset (or my cheap earbuds) for a small SS regenerative receiver that I am designing. I want use a BJT w/o having to resort to a transformer for coupling the output of the transistor to the headset. I also want to a small, common transistor (2n4401, 2n2222, or similar) which will not draw to much current from the 9V cell that will be powering it- we're talking less than 6mA. So far I have managed to create an emitter follower amp using an MPS5172 with a 470 ohm resistor from emitter to ground and a 1500uf electrolytic in series with the headset. Bias is provided by a 100k resistor from B+ to base. I connected this thing from my Pioneer tape deck. The sound was liveable, there was some break-up. Does anyone have any other ideas/schematics?
 
Keantoken and Bigun,
Thanks for the replies. Bigun, those look like some neat projects, thanks for the link. Keantoken, I have been playing with the circuit that I have and managed to get it to sound better: I put the tape deck output across a potentiometer and linked the wiper of the pot to the base of the transistor by a .1mfd cap. I also increased the value of the bias resistor to 470k. Now I have a volume control for this thing; it seems that before I had been overdriving the thing causing all that nasty breakup. The greatest thing about this arrangement is that I get useable (for what I plan to do) volume at no more than 18mW of power consumption- that is 9V x 2mA max current.
I have a second question: My tape deck seems to be the source of some sort of noise (perhaps motor noise or zener noise). This noise is not heard when the tape deck is connected to my McIntosh C-28 or my own diy triode preamp, nor is it heard when my little headphone amp is donnected from the machine. Is there any way to filter it out?
 
If you like minimalist circuits, here is an even simpler one. The distortion is higher, but stays under 1% for 4mW output into 32ohms (280mV rms). The supply voltage is also higher (3V), and the input impedance is low (~2K). But there are only 2 transistors!
The diode D2 has to be choosen to give a 6~7mA quiescent current (e.g. 1N400x series).
Have fun!
 

Attachments

  • 2TrHPh.GIF
    2TrHPh.GIF
    42.2 KB · Views: 479
If you're a tube and fet guy...searching the wrong place fellow!

beeing this way you will never believe and feel satisfied with junky bgts (this is what you really think about, but will never admit... this does not even goes to your conscience... stays deeply in your system), as you seems to be fet headed or maybe tube headed.... you may love BGTs if you listen without knowing BGTs are playing..if you know...your system will dennie the quality and will search for a defect...normal effects will be understood as defects..something will be perceived as wrong.

I really suggest you to ask for Fets and Tube amplifiers.... because those, even not beeing very good for your ears, will be adjusted and compensated by the brain and will be easier accepted by your pre programed sub conscience.

I could listen a lot of trash made using tubes..and the guy proud smilling thinking they had found the miracle....they found nothing but illusion.... so...better to respect your beliefs to go deep into a nice illusion.

A belief is hundred times stronger than the real thing..you will always be thinking that you're "loosing something" because BGTs....you gonna loose your time.... or will leave with ethernal suspections that could have something even better.

We are much more than supercomputers, we are complex bio chemical processors, with several departments, not only ears..your belief influences a lot..much more than some guys can imagine.

God bless my University... i am now having more clear understanding of psycho acoustics.

regards,

Carlos
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.