little Class A headphone amplifier thing i "designed"

[Mooly]

This was my own little Class A headphone amp:

Thread 'GERMANIUM Single ended Class A Headphone Amp.'

2010-02-04 7:21 pm

Presented here is a small Class A single ended output headphone amp, unusual because it uses germanium devices.
Why germanium ? Well I have few of these wonderful old devices, and a heaphone amp seemed an ideal little project. There's another reason too... I am working on a new amp (eventually) and headphones are a great way of evaluating circuitry... so I wanted something good.
To anyone not used to seeing and working with germanium, well it probably looks a bit "all upside down" using a positive earth.

Let me say first off that this isn't by any means a "finished" design... it's...

• Mooly
• Replies: 120
• Forum: Headphone Systems

• 

6.8v single rail and 60ma current draw per channel.

 

[No ideas]

dosent look that simple. but also i have an old pcb with vintage soviet germanium transistors but im scared to touch it becuse of how fragille the transistors seem. two of the transistors seem to be power transistors and even come with an heatsink

 

[Mooly]

Old germaniums are great to play around with 🙂

 

[No ideas]

i also made a less sketchy prototype or even the final version of the amplifier(not the germanium one)

 

[No ideas]

main issue i have is poor bass response, probably due to an bad power supply and input output capacitors.

 

[No ideas]

here is the photo

 

[U102324]

Goodness Mooley, you post a new idea almost daily, do you ever sleep?

 

[No ideas]

now im intrested what capacitors should i use and if an higher value (10uf) electrolytic is better than a 1uf/2.2uf mkt/polypropylen cap.

 

[U102324]

Bigger is better, keep in mind your input capacitor is in series with the output capacitor of the equipment you are connecting too, thus the overall capacitance is less and would affect low frequency response.

 

[No ideas]

thats why i wanted to add a jfet buffer

 

[Mooly]

main issue i have is poor bass response, probably due to an bad power supply and input output capacitors.

10uF input and 1000uF output cap (with 32 ohm load) give a -3db point of below 3.5Hz which is plenty low enough for any headphones.

 

[No ideas]

and how would a 2.2uF capacitor do?

 

[U102324]

Five times worse

 

[No ideas]

now im intrested in what type of capacitor to use. electrolytic or film.
same with the output cap but here im limited to electrolytic so now im intrested if i should use 2 in parallel or a single one. also the brand should i use an shitcon or invest in an brand name capacitor?

 

[No ideas]

10uF input and 1000uF output cap (with 32 ohm load) give a -3db point of below 3.5Hz which is plenty low enough for any headphones.

View attachment 1365604

youre using the 25V version instead of the 15V one

 

[U102324]

Why worry, film cap would cost as much as the amp. All you want to do is improve low end. What if the external equipment has a cheap electrolytic in the output. All you doing is place some expensive component in series with a cheap one, what is the point.

EDIT: scratch in you junk bin, find a 10uF cap and see if your expectations are met.
EDIT2: If you confirm that the external equipment is capacitively coupled, remove your input cap entirely.

 

[nuryev]

Hi Mooly,

Stumbled onto your headphone amp project and decided to say hi. I am in London for the a couple of weeks. I know, still too far for a beer or two!
Good to see you are still creating new projects.

 

[No ideas]

Why worry, film cap would cost as much as the amp. All you want to do is improve low end. What if the external equipment has a cheap electrolytic in the output. All you doing is place some expensive component in series with a cheap one, what is the point.

EDIT: scratch in you junk bin, find a 10uF cap and see if your expectations are met.
EDIT2: If you confirm that the external equipment is capacitively coupled, remove your input cap entirely.

i have acces to both a film cap and an film cap as in i phisically have both.

 

[Mooly]

youre using the 25V version instead of the 15V one

Won't affect the bandwidth 🙂

 

[No ideas]

15V version has a 220 ohm resistor after the capacitor. it makes the clipping more equal.