Yea...it is a vr...ebay or china have it...price is depends on the quality ofcoz and the resistor...

what is the main different for stepped attenuator vs the vr i have now?
makes a big different if change? just google for it and guess what, it priced almost the same as the T-amp...

http://item.taobao.com/item.htm?spm=a1z09....&_u=n580smne2d5

This is a pretty good buy.

I use the DACT CT-2 for my speaker amp

I'm using entry level alps, this seems like a much better choice.

Just assembled a cmoy amp using the JDS v2.03r PCB, does anyone know where to get a recommended charger for the amp?

I haven't stuffed the device in a tin yet but I'm getting noise when adjusting the volume knob, and there is some noise at loud volumes as well. Is this expected from cmoy amps, and are there any suggestions on how to fix it?

take pics of your build, and list down the components you used.

http://imgur.com/HeyH95h

JDS v2.03R board with all the stock JDS components. May get some opamps from my.element14.com later for comparisons with the OPA2227PA.

Take close up shots, the top and bottom.

I need to see how the work looks like.

Will upload those later once I touch up the PCB. The TLE2426 transistor seems to be defective. Getting a replacement from element14 soon.

Does anyone have recommendations for a suitable high capacity 9V rechargeable battery for the amp?

This post has been edited by yimingwuzere: Jan 6 2015, 04:57 PM

How about 2 units of 18650 or 16650 3.7V Li-Ion battery ??

Google for them ...

LI-ION is explosive.

Not recommended for those with little to no experience in electronics.

I asked John from JDS Labs on that, here's his reply:



Still prefer to get a good NiMh battery though

This post has been edited by yimingwuzere: Jan 8 2015, 02:01 AM

Hi all.

I want to ask some million-dollar question:

I have gone through about 50% of the thread, So I been thinking

Why do you guys need a headphone amps? For high impedance cans, yes understandable. Perfectionists Audiophile also acceptable (I myself can be considered audiophile but with shallow pocket) But how about others?

Even newbies with little soldering experience also want to build at least a Cmoy. Some members here already have decent sound card (X-Fi, etc) also willing to go through hard times building headphone amps. Is headphone amp really that important/significant?

http://www.innerfidelity.com/content/ultim...y-do-i-need-one

http://www.inearmatters.net/2008/12/to-amp...not-to-amp.html

Thanks for the links

Conclusion reading from the links, the inefficient headphones (high impedance ones) benefited the most from headphone amp, while the efficient ones depends on the case. If the built-in amp of portables/computers already good enough, the performance gain is rather small margin.

So how about forumers here. Care to discuss why you need a headphone amp? Probably an hobby? Or just living up the DIY spirit?

For me, if I start to make my own headphone amp than its just for the strong will of DIY spirit

Depends really. There are a lot of crappy devices for sound output around in the market. Let's take Samsung phones for example: try comparing the Galaxy S2 versus the old Galaxy S / Nexus S and the S3... the S2 sounds muted in comparison to the others and definitely requires an amp for any decent music listening unlike the other two.

Another one would be to pair with a DAC with less than ideal output impedance, like the Stoner UD120.

Opamps may also add a bit of colour to your headphone experience. Quick testing of my colleague's Sennheiser Momentum headphones with an AD823 helps a lot with imaging and instrument separation.

Anyway, I already assembled the cmoy I was building. http://imgur.com/Gxxig6x

Tried several paper punchers, none could cleanly punch through the Altoids tin so it now looks a little beat up. Oh well...

Also, does anyone know how to check for amp oscillation without using an oscilloscope? Tried a OPA2228 in the amp, but nothing obvious yet like opamp heat etc. from use, just excellent airy presentation.

This post has been edited by yimingwuzere: Jan 12 2015, 07:21 PM

I see I see... In that case than headphone amp has significant role, especially to provide lower output impedance

Congrats on building DIY cmoy

Hey, I have been thinking, how do you guys power the amp using single battery. Is it just simple resistor divider, which I predict is a rather noisy supply and have limited current capacity, or rail splitter but inherently halve the single power supply for each rail.

So an idea going around in my mind, how about designing a flyback switching power supply which immune to battery voltage swing while providing steady output +9v-0-9v for the headphone amp.. Meaning that a single 9V is usable down to probably 3V of charge remained. Almost like 'joule thief'. This also means that the power supply could be used with a wide range of battery types

I also thinking using discrete components to build the basic smps, but it still take up quite some space though, esp using through holes. Perhaps using integrated controller that already include all smps functionality will be more space-wise, but I dont have much experience with smps integrated controller

Here some example circuit using a integrated smps controllers. Pictures courtesy of Texas Instruments LM1577/LM2577 datasheet



The LM2577-15 in Flyback configuration



Above circuit's input voltage range, showing a wide input range with minimum 4V. Already pretty impressive.

LM2577-ADJ can be used instead to get lower output, say +9V-0-9V.

Yes, I know implementing this kind of power supply is more demanding and complex, not to mention doubtful component availability but the obvious advantages will justify though. Smps are efficient, exceptionally clean (switching freq is above audible range) and a lot longer lasting battery-power

If anyone know where can get LM2577, please let me know
On side note, I only been to Jalan Pasar once so I dont have the specifics about what they have to offer there.

Edit: forgot to ask, I wonder how much voltage is actually needed in typical headphone amp, say a cmoy amp? Perhaps a +6V-0-6V is already enough? Lowering smps output voltage close to actual needed voltage is more ideal, lowering the battery charge level required, thus squeezing more battery juice.

This post has been edited by SilverCast: Jan 13 2015, 02:14 AM

Try my.element14.com or or my.rs-online.com

(For people who can read Chinese)

Hong Kong electronic experiment magazine 無線電製作 ,
they publish all their past magazine online on their website,
some issue publish audio power amplifier article
example issue 251 (dated Feb 2011) 超低失真200W功率放大器

http://www.electronictechnology.com/magazi...l&mid=2&id=3791

but their website required you register an account to free access their magazine (provide your name, company name, address)
I am not with a company so i can't register.

This post has been edited by tanhks: Mar 24 2015, 08:13 AM