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xrk971 Pocket Class A Headamp GB
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Old 3rd January 2018, 01:57 PM   #1441
schlomoff is offline schlomoff  France
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Default pca

sweet year X, just to tell you that I enjoy with the amp at work as at home with a t40rp fostex or hd25. For those who have a doubt they spend next to a very very beautiful thing and not for dear.Thank you, thank you X for your work
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Old 4th January 2018, 08:59 AM   #1442
xrk971 is online now xrk971  United States
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xrk971 Pocket Class A Headamp GB
Hi Schlomoff,
So good to hear that your amps are working and playing beautiful music for you. Thanks for the feedback. Any photos?
Cheers,
X
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Old 4th January 2018, 01:14 PM   #1443
manniraj is online now manniraj  India
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Hi xrk

A quick clarification please, I have a silent switcher from linearaudio.nl lying idle and I wanted to make a good portable headphone amp for my SE598 cans and none other than your PCB came into mind. Can I use this silent switcher as it can even with power banks to make it completely portable in a small case which I can design?

Thanks
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Old 4th January 2018, 04:43 PM   #1444
manniraj is online now manniraj  India
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Quote:
Originally Posted by manniraj View Post
Hi xrk

A quick clarification please, I have a silent switcher from linearaudio.nl lying idle and I wanted to make a good portable headphone amp for my SE598 cans and none other than your PCB came into mind. Can I use this silent switcher as it can even with power banks to make it completely portable in a small case which I can design?

Thanks
Reading about the output power from the silent switcher it can give +/-15v @ 150mA standard with a 5V 2A mobile charger. But the switcher can also provide +/-15V @ 300mA (double the amps) if using a 9v 2A mobile charger which is readily available.
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Old 4th January 2018, 06:13 PM   #1445
xrk971 is online now xrk971  United States
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xrk971 Pocket Class A Headamp GB
The silent switcher is a nice dual rail supply for dual rail needs and kind of a waste on single ended single supply amp. Look for the MT3608 DC step up board. Under $1 and 1.2MHz frequency and if followed by a cap multiplier is super low noise. The high frequency gets it way outside of audio band and is easy to block.

MT3608 2A DC DC Step Up Power Apply Module Booster Power Module For Arduino-in Home Automation Modules from Consumer Electronics on Aliexpress.com | Alibaba Group

Adjust it to supply the amp with 16v to 18v.
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Last edited by xrk971; 4th January 2018 at 06:17 PM.
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Old 4th January 2018, 08:36 PM   #1446
diyricky is offline diyricky  United Kingdom
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Hi xrk971,

Have just completed a discreet component version to prove I can build it ok and yes it really does sound good, thanks again for sharing !

On your post of the 31st you have specified new resistor values which seem to be better for my 50ohm cans.
The build I made used 470uf Nichicon with 2.2uf on the output plus 2.2uf input.
Should these remain the same for those new resistor values ?

While not into the technicalities of the frequencies etc, when you and others have changed the values of those 3 caps, are you altering eg boosting the frequencies or do they allow them to be extended further ?

While your design is aimed at 18v, apart from power output, would running at 12v cause any detriment to output quality ?

Finally my build went ok apart from that during construction I followed the lower B channel on your circuit diagram, as I discovered, Q1B has been inverted , D and S are shown incorrectly. - not a problem if using your pcb.

Thanks Again
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Old 4th January 2018, 09:37 PM   #1447
xrk971 is online now xrk971  United States
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Diyricky,
That looks way cool! Nice! You have the fat Silmic's on the output - sweet!

Click the image to open in full size.

Q1 and Q2 are n channel JFETs and the manufacturer data sheet says that D & S are interchangeable - so no problem flipping them. It works just like a voltage controlled resistor (it is on with zero gate and pinches off with increased gate). But works in either direction.

I like your little copper tabs and heatsinks. A discrete TH version could be made using an IRF610 (or almost any N channel MOSFET). The performance of the ZVN4306GTA is very good though (almost special).

At lower voltages, the bias setpoint via the resistors needs to be reset for optimal performance but I would say running at 12v will give more distortion (it might sound quite tubey and pleasing to some). It will clip at lower value so dynamic peaks will get lopped off. Use an MT3608 DC-DC step up to boost your 12v to 18v. If building a desktop version, go with the IRF610 and the associated resistor values for 115mA bias current at 20v and have a nice desktop amp capable of driving lower impedance headphones.

IRF610 HPA here:
xrk971 Pocket Class A Headamp GB

Click the image to open in full size.

Click the image to open in full size.
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Last edited by xrk971; 4th January 2018 at 09:39 PM.
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Old 5th January 2018, 02:00 AM   #1448
manniraj is online now manniraj  India
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Quote:
Originally Posted by xrk971 View Post
The silent switcher is a nice dual rail supply for dual rail needs and kind of a waste on single ended single supply amp. Look for the MT3608 DC step up board. Under $1 and 1.2MHz frequency and if followed by a cap multiplier is super low noise. The high frequency gets it way outside of audio band and is easy to block.

MT3608 2A DC DC Step Up Power Apply Module Booster Power Module For Arduino-in Home Automation Modules from Consumer Electronics on Aliexpress.com | Alibaba Group

Adjust it to supply the amp with 16v to 18v.
Thanks, I think I already have the DC-DC boost power supply similar to the one you listed but regarding the cap multiplier something like Jumas then with the heat sink the cabinet size becomes bigger and may not be fully portable. I need to see how to get a simple cap multiplier without the usage of a bigger heat sink.
Or I can use this also if it suits - Capacitance Multiplier

Last edited by manniraj; 5th January 2018 at 02:11 AM.
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Old 5th January 2018, 03:05 AM   #1449
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by manniraj View Post
Thanks, I think I already have the DC-DC boost power supply similar to the one you listed but regarding the cap multiplier something like Jumas then with the heat sink the cabinet size becomes bigger and may not be fully portable. I need to see how to get a simple cap multiplier without the usage of a bigger heat sink.
Or I can use this also if it suits - Capacitance Multiplier
You must have not seen this micro Juma cap Mx by RaptorLighning. It fits on a dime and everything fits the same mint tin.

xrk971 Pocket Class A Headamp GB

He posted Gerbers for it if you want to make it too. Works flawlessly.

Click the image to open in full size.
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Old 5th January 2018, 04:17 AM   #1450
BYRTT is offline BYRTT  Denmark
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Quote:
Originally Posted by diyricky View Post
...While not into the technicalities of the frequencies etc, when you and others have changed the values of those 3 caps, are you altering eg boosting the frequencies or do they allow them to be extended further ?...
Compared to capacitor coupled high impedance inputs think capacitor coupled output is rather complex because of the relative low load impedance and also because real loads (driver voice coil) inside audioband is reactive having a resonance peak at low frq plus it behave as a inductor increasing impedance as frq goes up.

Example of complex is below simulation that is a 3 ohm source as X have simulated for PCA output with a load of flat non complex 50 verse 300 ohms, when amp looks into these two loads via a 470uF capacitor we will get different low frq extension. Some reason to call it complex is because this behavour can under subjective listening test confuse us to conclude that one set of cans have better low end extension than another set, when in reality its because the two set of cans have different load impedance. Some of us users have 2200uF in PCA and this is probably good for use with low impedance cans.
xrk971 Pocket Class A Headamp GB-3000-png

Other thing is a electric stop parameter to control voice coil motion (dampening) is AC output impedance of source amp which is said to be good if its eight times less than load, but when amp output is capacitor coupled we loose dampening the lower the frq and what those numbers are for a 470uF verse 2200uF capacitor can be seen below. If effect is audio able can be discussed but think especially with a DC coupled amp verse AC coupled that its easy to subjective sense better motion control for very low frqs and if one open up cans and look physical at driver motion its also easy to see motion is stiffer with AC dampening as close to DC point as possible.
xrk971 Pocket Class A Headamp GB-3001-png

Third graphs below is simulation with Xsim, 3 ohms output impedance over 470uF capacitor but this time into real reactive load which is blue traces, we can see a little bass ripple and some of it is caused by impedance resonance peak at about 110Hz and also at VHF response starts climbing a very little bit because impedance starts rising up there. Grey curves are much flatter because drivers impedance is compensated with two networks seen in schematic window, so if one linearize with such networks or have cans that is compensated ab fabric (some Fostex are) then response is less sensitive to amps AC output impedance.
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