Simple Headphone Amp

[Nico Ras]

I have done a little more work on the head phone amplifier for those who may be interested and added transistor Q3, increasing the gain of the VAS and Q6 as CCS.

R5 is a 2K multi-turn pot and when playing around a little while making distortion measurements, I could trim the current for optimal performance.

The THD is a respectable 0.006% at 200 kHz and predominantly 2nd harmonic with 0.5V input while still providing more than adequit drive for even low impedance headphones.

Should some-one care to simulate this and provide some comments as to how it may be still be improved while keeping it very simple, I would be very interested.

Should anyone like building the amp I will post a layout as well as have some professional PCBs done in our PCB shop.

I have been listening to this amp with the modifications for the last two days and I am extremely pleased with the outcome.

A jazz musician friend of mine compared it to his current commercial head-fi last night (his costing around $ 1000) and became my first customer

I guess I need to commercialse it now so it looks the part as well and some input from the forum members would also be most welcome.

 

[Gordy]

Hey Nico, are you sure you want to go commercial? The last time I checked the market already had the following, and there may be many others that I didn’t find…


Amity HPA5 and 4
Antique Sound Labs SR Head
Aqua Audio Head
Art Music 001
Audio Innovation Design HD1-L
Audio Technica ATH HA-2002, HA-5000
Audio Valve RKV Mk11
Audiotrak Dr Head
Benchmark DAC-1 with 'phones output
Berringer HA4700
Block Head
CEC HD53
CI Audio VHP-1
Ear Max
Edgar SH-1
Ergo Amp1
Firestone Cute Beyond
Fuchs Zeus
Harmony Design EAR90
Headroom (multiple models)
Izo iHA-1
La Rocco Head Code
Luxman P1
Maple Tree Audio Ear+Purist
Micro-ZOTL is the first product from the David Berning Company
Moth Audio Si2A3
Musical Fidelity X-Cans 2
Naim Headline
Opera Audio
Model: Cyber 30/Signature
Perreaux SHX-2
Precide ERGO Amp 1
Pro-ject Head box
Ray Samuels (multiple models)
Rega Ear
RudiStor NX-33 and others
Single Power Maestro ZR
Skorpion HV-1 OTL
Space tech Laboratory SE-6BQ5 SE-6AS7G
Stello HP100
Sugden Headmaster
Talisman Audio T-3H
Vincent Audio KHV-1
Wheatfield HA2
World Audio Design HD83


Also consider the hassle of homologation requirements (...CE marking in Europe for example) and differing power supply requirements worldwide.

Going commercial may be an interesting venture, and certainly an ego trip, however I guess that it is unlikely to enhance your retirement fund.

 

[Gordy]

Hey Nico, are you sure you want to go commercial? The last time I checked the market already had the following, and there may be many others that I didn’t find…


Amity HPA5 and 4
Antique Sound Labs SR Head
Aqua Audio Head
Art Music 001
Audio Innovation Design HD1-L
Audio Technica ATH HA-2002, HA-5000
Audio Valve RKV Mk11
Audiotrak Dr Head
Benchmark DAC-1 with 'phones output
Berringer HA4700
Block Head
CEC HD53
CI Audio VHP-1
Ear Max
Edgar SH-1
Ergo Amp1
Firestone Cute Beyond
Fuchs Zeus
Harmony Design EAR90
Headroom (multiple models)
Izo iHA-1
La Rocco Head Code
Luxman P1
Maple Tree Audio Ear+Purist
Micro-ZOTL is the first product from the David Berning Company
Moth Audio Si2A3
Musical Fidelity X-Cans 2
Naim Headline
Opera Audio
Model: Cyber 30/Signature
Perreaux SHX-2
Precide ERGO Amp 1
Pro-ject Head box
Ray Samuels (multiple models)
Rega Ear
RudiStor NX-33 and others
Single Power Maestro ZR
Skorpion HV-1 OTL
Space tech Laboratory SE-6BQ5 SE-6AS7G
Stello HP100
Sugden Headmaster
Talisman Audio T-3H
Vincent Audio KHV-1
Wheatfield HA2
World Audio Design HD83


Also consider the hassle of homologation requirements (...CE marking in Europe for example) and differing power supply requirements worldwide.

Going commercial may be an interesting venture, and certainly an ego trip, however I guess that it is unlikely to enhance your retirement fund.

 

[Zen Mod]

I have done a little more work on the head phone amplifier for those who may be interested and added transistor Q3, increasing the gain of the VAS and Q6 as CCS.

R5 is a 2K multi-turn pot and when playing around a little while making distortion measurements, I could trim the current for optimal performance.

The THD is a respectable 0.006% at 200 kHz and predominantly 2nd harmonic with 0.5V input while still providing more than adequit drive for even low impedance headphones.

Should some-one care to simulate this and provide some comments as to how it may be still be improved while keeping it very simple, I would be very interested.

Should anyone like building the amp I will post a layout as well as have some professional PCBs done in our PCB shop.

I have been listening to this amp with the modifications for the last two days and I am extremely pleased with the outcome.

A jazz musician friend of mine compared it to his current commercial head-fi last night (his costing around $ 1000) and became my first customer

I guess I need to commercialse it now so it looks the part as well and some input from the forum members would also be most welcome.

nice looking ;

what I would do is using two bjt CCS both in LTP tail and in output CCS


but I can't tell in any case that with these sound will be better ;

if you leave it as is - route zenner resistor from + rail, not from gnd

 

[Nico Ras]

Hey ZenMod,

will route to positive and check if it makes a difference, I am not sure if it will as there should theoretically be less noise on the ground than on the positive supply that is being modulated by the top power transistor. But hey if its better, then its better.

 

[Nico Ras]

Hey Nico, are you sure you want to go commercial? The last time I checked the market already had the following, and there may be many others that I didn’t find…

Hello Gordy,

When I said commercialise, that is what I meant, make it look neat for my mate. I will probably be bullied or bribed into making a few more free of charge, but that is where I draw the line.

To even consider entering into the audio market is rediculous. Although I have done several commercial audio designs over the past 30 years, it remains purely an addiction. There is little money to be had unless you enter the high volume market.

A lot of these so-called high-end audio companies are little more than kitchen table or garage based operations employing between 1 and 10 people and can survive from a few hand made products per year.

Regarding homologation, this is nothing new to us as we have been supplying the world market with specialised electronic products for almost 50 years. This past year we homologated 28 new products at both MIRA and SGS in the UK.

In fact I very much doubt if there are many high-end audio product has ever seen the inside of a test laboratory, besides safety, I do not have any knowledge regarding legislation or European/International standards committee for audio.

If there was you would find a lot less of the "high-end" products in the market as few of them could afford testing and certification costs for a single product let alone a range of products.

I know of only one "high-end" manufacturer , claiming EC certification, but on closer inspection this certificate relates only to being harmonised to EC requirements regarding houshold electrical appliances.

On the other hand to place CE marking on a product is really a joke, almost every other Chinese product boasts self certified CE compliance not worthy of the ink used to print CE.

Anyway, that is a differnt matter altogether and probably not of any interest to this forum.

 

[Nico Ras]

nice looking ;

what I would do is using two bjt CCS both in LTP tail and in output CCS


but I can't tell in any case that with these sound will be better ;

if you leave it as is - route zenner resistor from + rail, not from gnd

Hi ZenMod,

agreed two transistor CCS reduced the noise floor by 13 dB. Wheter bias is from ground or +V makes no difference at all. Adding a 100nF cap on the pass transistor in the CCS reduced noise by another 6 dB. 19dB lower noise floor is great!

Kind regards

Nico

Well done guy!

 

[Zen Mod]

Hi ZenMod,

agreed two transistor CCS reduced the noise floor by 13 dB. Wheter bias is from ground or +V makes no difference at all. Adding a 100nF cap on the pass transistor in the CCS reduced noise by another 6 dB. 19dB lower noise floor is great!

Kind regards

Nico

Well done guy!

well - that's boiled water ....... there is no any contribution of mine ......

regarding biasing from other side - I think that in dynamic conditions CMRR of stage will be better .......

you tried two bjt CCS in output only?

did you tried it in LTP tail? with multiturn pot in base of lower bjt , you can tweak offset easily .

I know that you know, but just in case - look at my Babelfish schematic ; if nothing else - it's handy

 

[Nico Ras]

what I would do is using two bjt CCS in LTP

Done, that on a previous amplifier and now here some moments ago.

Very interesting. The CCS in the long tail pair reduces overall THD significantly, but all the odd (3rd, 5th, 7th, 9th...) now pops up from below the noise floor. I would conclude it reduces the third order intercept point by introduction of a finite current.

I use a switch to select CCS or resistor and listening is most revealing:

CCS in the long tail pair reduces measured THD significantly but also changes the sound character very much from "smooth mid/highs" to "crisp mid/highs" if you get my drift.

On first impression I personally prefer the sound that includes predominantly second harmonic while there is no odd order products.

Let me live with it a while and report back - this was a very noticeable change in the character of the sound, it does not sound like a class A anymore for a lack of a better description.

I am of the opinion that multi tones will produce many high order products as well using the CCS in the LTP and may also contribute to the different character of the sound. I run test in the morning.

I am not sure that this modification improves the sound quality eventhough it makes a measurable difference in THD. This is one of those instances when science and sound does not make logical sense.

Kindest regards

Nico.

 

[Nico Ras]

Okay ZM, I must admit that I kept the current in the LTP the same in both instances.

I will adjust the current in CCS just to make sure that what I am saying is applicable globally not just for this instance.

Ciao

 

[Nico Ras]

Found a 2m length of nice tubular heat sink for my mates head-fi. Will have it anodised and have a brass face and back plate cut. It would be aesthetically pleasing (I hope)

 

[Nico Ras]

Did a PCB that slides into the heat sink and transistors bolt to sides. It is 95 x 68 mm and contains stereo amp and regulation. Transformer will have to be external.

I will have this done tomorrow and by the end of the week present my mate with his new head-fi.

Sorry picture had to be reduced to grey scale to post, but it is double sided throughole plate with earth planes on both sides.

 

[Zen Mod]

Found a 2m length of nice tubular heat sink for my mates head-fi. Will have it anodised and have a brass face and back plate cut. It would be aesthetically pleasing (I hope)

nice looking chunk

what happened with CCS "issue"......

I'm curious about your findings ......

 

[Zen Mod]

Did a PCB that slides into the heat sink and transistors bolt to sides. It is 95 x 68 mm and contains stereo amp and regulation. Transformer will have to be external.

I will have this done tomorrow and by the end of the week present my mate with his new head-fi.

Sorry picture had to be reduced to grey scale to post, but it is double sided throughole plate with earth planes on both sides.

for later ......... if nothing else more complicated........ you can always try cascoded LM317 shunt reg , from W. Jung's AE article ( don't know where, but google for jung2778.pdf and jung2779.pdf) ).

in my book - shunt regs are worthwhile improvement over series ones

 

[Nico Ras]

for later ......... if nothing else more complicated........ you can always try cascoded LM317 shunt reg , from W. Jung's AE article ( don't know where, but google for jung2778.pdf and jung2779.pdf) ).

in my book - shunt regs are worthwhile improvement over series ones

I have done just that (LM317) with a previous MOSFET design, was nice but again my projects end up in someone elses listening room before I can really get into it.

You may notice, I opted to keep the dual transistor CCS. I am not sure which one actually sounds.... not better different.

I will now have two versions and the easiest way to test it is to live with both. If I am fatigued after a six or eight hour session then I know.

With the resistor load, I pushed eight and more hours every day for some weeks and still love its sound.

We shall see how this goes. Get the idea I love having my music while working. Don't ask me what I do!

 

[Zen Mod]

 

[Nico Ras]

Hi Zen Mod,

just some feed-back on the findings. After living with these three methods of output loading, I can hear absolutely zero difference in any of the methods.

At first I thought there was a difference, but I think it is because I wanted to hear the difference. I am becoming more and more convinced that differences in certain aspects exists only because we want them to exist.

 

[Nico Ras]

To those interested in the PCB, the gerbers are in the attachment.

 

[Nico Ras]

And those who wants a pdf containing the final circuit....

 

[Nico Ras]

PCB top copper