[MyPants]

Mypants,
Sorry, don't understand your last post is referring to?

Oh I just mean y'all are getting deep into some DIY stuff for some seriously meaty amp designs and it's fun to watch.

 

[MyPants]

Looks like they've made 4 posts in the Headphones For Sale thread, and then a "." in a bunch of other threads.
Wonder what that's all about?

Probably trying to hit the minimum post count required to use the marketplace.

 

[xrk971]

That’s a pretty lame way to bump a thread (worse than people who actually say “bump”). At least add some new info.

I am thinking of offering my Pocket Amp, reconfigured as a balanced input / output amp as a transportable desktop amp. Contact me if you are interested - it will be on a custom ordered basis. It will look similar to this and use the same case. Will have dual 9v batteries in slide out casette trays and also external DC wallwart capability.

 

[SDBiotek]

That’s a pretty lame way to bump a thread (worse than people who actually say “bump”). At least add some new info.

I am thinking of offering my Pocket Amp, reconfigured as a balanced input / output amp as a transportable desktop amp. Contact me if you are interested - it will be on a custom ordered basis. It will look similar to this and use the same case. Will have dual 9v batteries in slide out casette trays and also external DC wallwart capability.

Does it only have balanced input?

 

[xrk971]

No, it will have optional single ended input (which only gives single ended output.). Will follow diagram posted above.

 

[MyPants]

Hey @xrk971 , what happened to the pocket class a kits on your etsy? I was just recommending the kit to a buddy who wants to build one, but it looks like they're not available anymore.

 

[xrk971]

Simply a matter of parts running out of stock - I can order more of there is interest. I will put it back as soon as parts arrive in a week. Or he can preorder.

 

[DBaldock9]

I've begun ordering some of the parts I'll need to assemble the 6 DCA channels I need, for a Balanced (2 boards, 4 channels) and a Single-Ended (1 board, 2 channels) Amp.
This is in addition to the power supply I found on eBay, and the circuit boards and FETs that I ordered from you previously.
Just purchased a set of the 1% 3W 270Ω resistors, from an eBay vendor.

 

[xrk971]

I was wondering when you were going to build the balanced DCA’s. Do you have 6 boards?

 

[xrk971]

Here’s a new spin on this amp. Using an ultra low 117uA bias current in the JFET (via new DC setpoint resistors), the sound is sweeter (lower third harmonic relative to second) and lower overall THD, and more dynamic through higher gain. It seems that the input signal had to control a much lower bias current and this seems to give the sound an immediacy and naturalness that’s close to LIVE sound. It’s an experiment that is turning out superb. It’s what I am listening to at present as my main portable amp.

https://www.diyaudio.com/forums/gro...-pocket-class-headamp-gb-189.html#post5750411

Revised schematic:

This is the predicted FFT for 1.4Vpp into 55ohm headphones (THD is only 0.05%):

Test amp with new resistors and only 117uA of bias current through the input JFET:

 

[DBaldock9]

I was wondering when you were going to build the balanced DCA’s. Do you have 6 boards?

No, just the three boards, and FETs, that I ordered from you previously.
1 board to drive the Left Balanced Channel.
1 board to drive the Right Balanced Channel.
1 board to drive the Left & Right Single-Ended Channels.

 

[xrk971]

New Balanced Drive 2 Transistor SE Class A Headphone Amp with beautiful harmonic profile and ability to drive 50ohm cans.

https://www.diyaudio.com/forums/hea...rive-2-transistor-se-class-headphone-amp.html

Measured FFT for 2Vpp itno 49ohms:

 

[xrk971]

Here’s the new Muscle Amp - uses eight OPA1622 in parallel. Can drive speakers even down to 4ohms. About 10w into 8ohms. Tested T 47ohms and listening with 50ohm HE400i. Fantastic dynamics. Zero noise or background. Powered with 25va 15v trafo through a cap multiplier for low noise power source.

Here is closeup if the OPA1622’s:


Test setup with 47ohm dummy load and 2ppm 1kHz reference source. Focusrite 2i4 interface.


FFT for 2Vpp into 47ohm load (0.0008%THD):

 

[xrk971]

Hi Folks, I haven’t been here for a while but thought you all might be interested in a new project brewing over on DIYA. It’s going to be a new PCA Mk II. This time fully assembled and tested and ready to run (RTR) all SMT design. You just need to install in your own mint tin or 3D printed case. I will provide STL file.

Main features are still SE Class A amp but this time, using hybrid JFET input and BJT output in a complimentary feedback pair (CFP) topology that had better dynamics and lower distortion. Built in 4100mAhr LiPo with battery management and LED fuel gauge, DC-DC step up for stable 18v output, and MOSFET cap multiplier for smooth slow startup to prevent turn on thump. USB charging or 24v wallplug wallwart use. Same compact form factor but improved sound and longer lasting LiPo battery. Still in development stage. Will be a group buy in order to get manufacturing cost for a RTR amp down.

https://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-post5974736.html

 

[DBaldock9]

Hi Folks, I haven’t been here for a while but thought you all might be interested in a new project brewing over on DIYA. It’s going to be a new PCA Mk II. This time fully assembled and tested and ready to run (RTR) all SMT design. You just need to install in your own mint tin or 3D printed case. I will provide STL file.

Main features are still SE Class A amp but this time, using hybrid JFET input and BJT output in a complimentary feedback pair (CFP) topology that had better dynamics and lower distortion. Built in 4100mAhr LiPo with battery management and LED fuel gauge, DC-DC step up for stable 18v output, and MOSFET cap multiplier for smooth slow startup to prevent turn on thump. USB charging or 24v wallplug wallwart use. Same compact form factor but improved sound and longer lasting LiPo battery. Still in development stage. Will be a group buy in order to get manufacturing cost for a RTR amp down.

https://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-post5974736.html

I would like one.