DIY Class A Headphone Amp suggestion

[AKSA]

Yes, I always use a LP filter on all preand power amp inputs.
But if you have one you can drop it.
Sometimes a base stopper is helpful to prevent oscillation. You might use around 47R carbon for this role however.
HD

 

[widea]

Yes, I always use a LP filter on all preand power amp inputs.
But if you have one you can drop it.
Sometimes a base stopper is helpful to prevent oscillation. You might use around 47R carbon for this role however.
HD

I always thought this base stopper resistor was to prevent the base of the transistor from being 'overloaded' or something like that, did not occur to me this was to prevent oscillation. Or perhaps overloading and oscillation are related, don't know.
Anyhow, it is probably wise to leave the filter where it is. Thank you AKSA!

 

[Nico Ras]

You will see this filter on many amplifiers and its purpose is simply to prevent RF to be attenuated at the input. Nothing special, only preventative measure. In the past in Europe, people always complained that AM radio bled into their sound systems and I guess it has a historical reason.

 

[merlin el mago]

Long & interesting thread, I want to make the Headphone amp for HifiMan Edition XS 18R 92dBs, could someone link me to the schematic if exist or the mod to use it?

TIA

 

[widea]

Long & interesting thread, I want to make the Headphone amp for HifiMan Edition XS 18R 92dBs, could someone link me to the schematic if exist or the mod to use it?

This is the one you may want to take a look at: 24V version
Also, see
https://www.diyaudio.com/community/threads/diy-class-a-headphone-amp-suggestion.415623/post-7754585 and
https://www.diyaudio.com/community/threads/diy-class-a-headphone-amp-suggestion.415623/post-7754723
for lower power variations.

 

[merlin el mago]

Is the attached schematic?

 

[widea]

Is the attached schematic?

Yes, without R13 and C8, not needed.
It can be operated at 24V supply voltage, but at 19V, Q2, R5, R6 dissipate less heat: 1.3W, 1.3W and 640mW respectively.
At 24V Q2, R5 and R6 dissipate 2W, 2.4W and 1.1W respectively.
Also you'll probably find a 19V power supply from an old broken laptop more easily than a 24V one.

 

[Michelag]

And also R9, which is a fictive load for simulation purpose

 

[widea]

And also R9, which is a fictive load for simulation purpose

True, but it also indicates that it can work with 16 ohm headphones (Merlin wants to use HifiMan Edition XS 18R headphones).

 

[merlin el mago]

What's the pourpose of L1, R11, C5 & C6. Filter the brick SMPS PSU?

What's the total power consumption?

 

[widea]

What's the pourpose of L1, R11, C5 & C6. Filter the brick SMPS PSU?

Polyswitch R11 acts as a fuse, L1 and C6 are for filtering noise (from the SMPS), C5 for stabilizing supply voltage.

What's the total power consumption?

Using a supply voltage of 19V: 3.4W
Using a supply voltage of 24V: 5.7W

 

[merlin el mago]

24V 238mA thanks

 

[merlin el mago]

Could I use other transistor for Q2 TIP42C?

I guess the higher hfe will be better.

 

[widea]

Could I use other transistor for Q2 TIP42C

I am pretty sure you can but others in this thread may have suggestions on this. The original mentions a MJE350.

 

[AKSA]

Yes. Master device (smaller) should be fast (100MHz or more)
and slave device should be slower (less than 70MHz.
This generally minimises oscillation.
HD

 

[merlin el mago]

Thank you guys.

 

[AKSA]

Always a pleasure in a gracious thread!
Hugh

 

[Michelag]

Thanks Nico very good advice.
M, your HPA draws almost 300ma from each channel and typically you would use at least 10uF per ma in the supply.
But test if the supply can cope with 3300uF per channel as many switch mode supplies complain.
Hugh

Ok, cleared now, 3000uF per channel. It has a terrific dynamic range, the little heater 😁

 

[AKSA]

All motorboating is now gone?
Very nice happy ending!

Hugh