[peranders]

My overkill headphone amp works! Today I tested the last part, the BJT output stage. The amp is tested with the cute MOSFET's IRFD120 and IRFD9120, small DIL-4 package. I'm surprised that they can dissipate so much heat. I have tested 250 mA = 120 deg C hot!

200 mA = 70 deg C

Can drive any headphone in class A!

 

[Xecter]

try cooking a egg on it?


my friend cooked an egg on this PC, im sure we can arrange a AMP cooking event of some sort.

 

[Tomo]

Heehee,

Mosfet Abuse.

T

 

[peranders]

Quote:

Originally posted by Xecter try cooking a egg on it?

Do you have so small eggs? 6 mm/ 1/4"!

 

[ServinginEcuador]

...but how does is sound peranders? That's always the question here. If it sounds good, and sells for a decent price, we'll buy it.

I guess we should say like MarkL a few weeks ago, "Welcome to Head-Fi peranders, sorry about our wallets." Man, the choices for good amps seems to go up daily.

 

[peranders]

It sounds good, can't give you any more precise description. It sounds even good in pure class B! Very little difference. If you don't know what class the amp runs in you can hardly tell the difference.

The amp isn't adjusted for any market. I made it just for fun and it's quite crazy. An OPA2134 is quite sufficient but not equally fun as this monster.

The step response is clean and the slew rate is 100 V/µs. The temperature stability is excellent.

I like the very small BC847BS/BC857BS, works very well.

 

[ServinginEcuador]

Quote:

Originally posted by peranders The step response is clean and the slew rate is 100 V/µs. The temperature stability is excellent.

You gotta be kidding. Wow. 100 v/ microsecond is incredibly fast. Man, even the expensive Burr Brown OPA627 only has something like 35v/ microsecond.

Maybe you should sell it as a kit or preassembled amp.

 

[peranders]

Quote:

Originally posted by ServinginEcuador You gotta be kidding. Wow. 100 v/ microsecond is incredibly fast. Man, even the expensive Burr Brown OPA627 only has something like 35v/ microsecond.

If you increase the gain a bit the slew rate can be increased to 250 V/µs!

The slew rate is rather much if we talk about discrete designs but if we talk opamps, we can have 2000 V/µs or more!

 

[peranders]

I have taken more pictures of my project but the pictures don't have any text yet so these links are "secrets" for most people.

What do you think of the cute BC847BS? They are very good and also very cheap.


http://home5.swipnet.se/~w-50674/hif...0_overview.jpg
http://home5.swipnet.se/~w-50674/hif...p_polyprop.jpg
http://home5.swipnet.se/~w-50674/hif...ompcap_cer.jpg
http://home5.swipnet.se/~w-50674/hif...ias_mosfet.jpg
http://home5.swipnet.se/~w-50674/hif...0_bias_bjt.jpg
http://home5.swipnet.se/~w-50674/hif...r0_bc847bs.jpg

EDIT: These pictures have text nowadays.

 

[peranders]

Deleted, duplicate

 

[KTpG]

The amp I am currently working on/designing uses three chips, two of which have slews of 1700 and 2000 v/uS.

It sounds quite good and is biased into class A. Unfortunately, it wasn't *just* class A, I had to bias it...

I like the sound, though. If I had the money, I'd build it, but I can't afford to. It is supposed to have dual mono power supplies, with grounds tied together only at the ground of the output jack. Each PS is around $60. So, we are looking well over $300 easy once I buy all the chips... I want to build it so very badly...

 

[peranders]

Deleted...

 

[PinkFloyd]

Looks nice mate

Keep up the good work.

Pinkie.

 

[KTpG]

Hmm... to tell the chips or not to tell... I guess I might as well. It really isn't a huge secret. Well, one is BUF634. ha Maybe you didn't see that coming.

The other is an OPA658, which is a very fast (900MHz) chip with 1700V/uS slew. Oddly enough, you would not think a really fast chip feeding a BUF634 would be stable and sound good, but it really does... and there is absolutely NO hiss at all, unlike when using a META configuration. (I get hiss, maybe some don't...) When I can get stuff about the amp online, I'll post a link if you all promise not to laugh at me and say I am stupid.

 

[Tomo]

Hey,

Quote:

It sounds good, can't give you any more precise description. It sounds even good in pure class B! Very little difference. If you don't know what class the amp runs in you can hardly tell the difference.

I agree. I use a single opamp headphone amp (output stage is AB or B.) I am hearing no apparent distortion. In fact, its sound is superb. Modern opamps are no longer bad for audio.

This amp uses THS4022. 470V/usec, 350MHz, 100mA nominal. It is incredibly powerful tiny opamp. (Special SMD version can deal 2.14W!) Also, it has very low 1/f noise which is remarkable for opamps for this type. Many High Speed High Bandwidth opamps are designed to be operated at high frequency so 1/f noise is fairly high.

I just wrote to tell you I tried this one too. I might try others later. May be we should make a new list of opamps to try.

Just one word of warning. When you use this type of high speed high bandwidth and high power opamps, you better make sure you use snubber-like circuit or feedback filter to kill oscillation at RF. You may not hear oscillations, but you may be disrupting TV or radio signals. In fact, THS4022 can disrupt TV signals if you make it oscillate. (by removing bypass-to-ground resistor and making the opamp input float etc etc.)

Tomo

P.S. Some inaudible RF oscillation can heat up chips a lot.