[akiroz]

Thought I might share some results of the community project I've been working on for the past half-a-year

We call it [Project-H] and it's funded entirely by 9 Head-fiers. (See sig for details)
 

Panel Design
 

Assembled unit front
 

Assembled unit back
 

9 assembled units, 2 with custom laser engraving.

 

[joeyjojo]

Of those two I could only find Cordell's paper "a MOSFET power amp with error correction" (1982). It's impossible to compare them as the test equipment used in the Cordell amp is way better than the audio interface used by Kan (e.g. you can forget about THD/noise measurements for the B22 as it's just the loopback signal).
 
Don't forget the B22 can match the Cordell for power into 8 ohms if you build the bridged variant (50 Wrms), though clearly not for current (it can only put out an amp or two as the MOSFET packages are so small - I wonder how Cordell solved that one).
 
It's interesting to see some of the principles used in the B22 coming from this 30 year old paper. Really they aren't so dissimilar - the B22 just uses more cascoding throughout and runs entirely in class A. My bet is it does have better specs, but obviously this is at the cost of parts. In the end the differences are probably inaudible

 

[miceblue]

Quote:

Thought I might share some results of the community project I've been working on for the past half-a-year

We call it [Project-H] and it's funded entirely by 9 Head-fiers. (See sig for details)
 

Panel Design
 

Assembled unit front
 

Assembled unit back
 

9 assembled units, 2 with custom laser engraving.

Nice! I saw that project in bowei006's sig. I haven't read the details about it, but is it just an O2 with modified parts and enclosure? Too bad it isn't available for us mortals. XD

 

[Talgarius]

Hello.
This is my music listening headphone + amplifier system.
 
Made by P87, show stats:
 
•80 mW into 600 Ohm, 0.00014% THD + N
•Greater than 120 dB of Dynamic Range
•SNR of 120 dB
•Output Voltage Noise of 5 μVrms
•1300 V/μs Slew Rate
 
The core operational amplifier is TPa6120A2 (http://www.ti.com/lit/ds/symlink/tpa6120a2.pdf) and second amplifier is LM6172.
 
Pictures (I cant insert these ):
http://imageshack.us/photo/my-images/826/p87amp01.jpg
http://imageshack.us/photo/my-images/543/p87amp02.jpg

 

[akiroz]

Quote:

Hello.
This is my music listening headphone + amplifier system.
 
Made by P87, show stats:
 
•80 mW into 600 Ohm, 0.00014% THD + N
•Greater than 120 dB of Dynamic Range
•SNR of 120 dB
•Output Voltage Noise of 5 μVrms
•1300 V/μs Slew Rate
 
The core operational amplifier is TPa6120A2 (http://www.ti.com/lit/ds/symlink/tpa6120a2.pdf) and second amplifier is LM6172.
 
Pictures (I cant insert these ):
http://imageshack.us/photo/my-images/826/p87amp01.jpg
http://imageshack.us/photo/my-images/543/p87amp02.jpg

Nice case!
 
Who's P87?
 
Keep in mind that the specs of the op-amp is usually far from the entire amp's specs

 

[akiroz]

Quote:

Nice! I saw that project in bowei006's sig. I haven't read the details about it, but is it just an O2 with modified parts and enclosure? Too bad it isn't available for us mortals. XD

Thanks, It's actually a DAC + O2

 

[Talgarius]

Nice case!

Who's P87?

Keep in mind that the specs of the op-amp is usually far from the entire amp's specs

The P87 a person from Prohardver.hu, He did to me from my specs. Btw you know an usb dac diy for this amp? I saw Musiclands and Fiio but.. Not good rly. If maybe I can use for my smartphone would be best. (USB OTG).

 

[crispchicken]

So, today I got my package from Fred_fred with Cmoy boards and some on/off clicky pots. I put this together this afternoon, happy to say it was only about 40 minutes of work, and it worked perfectly the first time through. A bit of confidence, and only a couple of small audio projects under my belt, seems to be helping immensely with this, its a great feeling to be able to tell you're improving, especially considering the amount of time I spend per day reading about audio electronics!
 
This specific amp is a gift for my father's birthday tomorrow and I'm stoked I managed to get the boards and parts before then! All I have to do tomorrow is find a nice enclosure for it and get some better quality connectors to replace then temporary ones I'm using.
 
Here's a picture of my handywork...
 
http://iforce.co.nz/i/2i1qty0k.vpa.jpg
 
What really blows me away about this little one compared to my stripboard cmoy (that I've been logging some serious hours of use on in the past week or so), is the low noise floor and overall sound quality improvement, while using the same supply and exact same opamp chip(Yeah, it's damn expensive here in nz for a decent audio opamp. I paid 13.95 for this single one in Jaycar! It really adds to the scariness factor when your rather expensive ic's might produce the magical $13.95 smoke that smells so sweet, with just one little wiring mistake... yeah right...  
 
The only difference between this and my other Cmoy was choosing slightly higher quality/better choices of components. Instead of polyester greencaps, I used 474pF polypropylene rectangular ones (if someone could enlighten me as to what the correct name for these are, I'd be grateful) There's also a small low-ESR electrolytic that I added between the two rail splitter caps and ground, I'm not really sure what it even does, but I suspect it might have something to do with the improved sound quality, and who am I to question the markings on the board?! Finally, I also managed to scrounge a couple of 1000uF 15v Sanyo electrolytics out of an old car amp, which according to everyone I talk to, should beat the crap out of "Suntan" caps in quality... the last one I built had 220uF caps in the place of these, and I can definitely hear an improvement in bass "boom" with the much higher rating.
 
My dc offset is only 0.6 on one channel, and 4.5 on the other. This is with an opa2134pa, would that be considered within spec/safe range?
 
peace ya'll!
 
chris

 

[akiroz]

Quote:

My dc offset is only 0.6 on one channel, and 4.5 on the other. This is with an opa2134pa, would that be considered within spec/safe range?

Congradz!
 
$13.95 for a OPA2134? What currency is that??
I got my OPA2134's for around that price in HK$ which is around US$1.8
 
With 4.5mV you'd hear a click with IEMs. It should be safe though

 

[n_maher]

Quote:

And TBH, toroidal transformers provide some degree of self-shielding in the first place, the electromagnetic radiation coming from the transformer is probably very small compared to other current-carrying wires in the system.
 

 
There's been some pretty unproductive discussion in this thread in the last few pages.  I freely admit that I'm not around anywhere near enough anymore to try and fix it.  That said, your comment regarding the potential interference of a toroidal transformers and the beta22 is not correct based on my direct experience.  I was one of the first few people to build a beta22 years ago and my one box build definitely had trafo-induced noise.  I went to great lengths to squash it and in the end the only solution was a (relatively) massive amount of shielding around the transformer. 
 
Here's the amp

 
Inside the small black box in the upper left corner is the trafo.  At first I tried just the steel box to add additional shielding, it was insufficient to kill the noise.  Next I added mu metal banding around the outside of the trafo, again, not enough.  I then added layers of shielding above and below and that was finally enough to make the noise inaudible with my IEMs.  No simple task and directly the fault of the proximity of the trafo to the signal wires.
 
Now, to get this thread a little more back on track here's the KGSS that I mostly finished last night.
 

 

[akiroz]

Quote:

That said, your comment regarding the potential interference of a toroidal transformers and the beta22 is not correct based on my direct experience.

It's simply a speculation of mine based on theory.

I've already said I have no empirical evidence backing that up.

 

[crispchicken]

I stay in new Zealand, where electronics as a hobby is already pretty unusual. Audio electronics being a subset of that... Yeah there's basically just not enough people in the scene to get OK prices.

I was intending to get myself a selection of useful ICs off of aliexpress soon, perhaps someone can suggest a better source.

Recently I've been dumpster diving behind this store that repairs TVs and home cinema gear, and have managed to find a lot of pcbs with assorted useful components on them. More power amp ics than you can shake a stick. it shocks me how bad most of the op amps these receivers from reputable brands are running super low end crapola. I do have some working dual opamps that I tend to use to test before I stick in an expensive one!

Chris

 

[yuujin]

hi n_maher, is that a stepped attenuator?
what brand is that? looks pretty neat.

 

[n_maher]

Quote:

hi n_maher, is that a stepped attenuator?
what brand is that? looks pretty neat.

 


Yes it's a stepped attenuator.  It's a first generation Khozmo that I picked up used.  They don't build them like this anymore so the current ones aren't nearly as neat looking but I think are more mechanically reliable.  I don't tend to volume hunt much, rather set it and forget it, so I think it'll do ok for me in the long run.  I've never liked standard, 24 step units that I've used and had high hopes for Khozmo when they first came out a few years ago.  They had issues initially that I think they've corrected but do your homework before making a selection (if you're in the market). 

 

[elliottstudio]

This is my recent build:
Here's a prototype headphone amp / linestage that I built for my brother. I is a two stage design using 12au7a's and output transformers, Quam 70V 4W speaker transformers in fact. The gain is 1.5 using the 2W input tap. There are 3 stereo inputs, a headphone output and defeat-able line out jacks. It is a pretty simple design but sounds very transparent and punchy. The basic circuit could be adapted for many functions, it could be a full function line stage if I added a mute switch and balance pot and a few more inputs. Or you could separate out the volume pots and add mic input transformers and make a nice two channel mic preamp.
 
For more details go here: LINK