New Headphone Amp Project - Single ended class-A 2 Transistors Head Amp! "DIY"

0 Members and 1 Guest are viewing this topic. Read 1020 times.

adydula

  • Facilitator
  • Posts: 1732
Anand,

This is good news then...I would hate to see the DIY part disappear.

That said, Mark'seffort was aimed at a newbie and to help them get into the DIY area....pretty good project for that.

With the DIY parts shirnking is size its becoming harder for folks to build DIY, with some ot the older larger parts going away.

Anyway its great to see good postive numbers like this.

Alex

adydula

  • Facilitator
  • Posts: 1732
FYI,,,

According to Mark Johnson all his T2 pcbs have been sold.

He is trying to get the diy store to stock these for purchase.

Alex

adydula

  • Facilitator
  • Posts: 1732
The T2 is a great example of simple can be very good if done right.

For old folks like me, having built and heard many very high priced amps and dacs, its a reminder that great audio can be had for a relatively low cost.

Alex
 :D

adydula

  • Facilitator
  • Posts: 1732
Here is a  pix of the Fun and T2.

I actually after many hours of listening favor the T2 slightly with all my headphones.

The clairty and soundstage is just a wee bit nicer to me with the all discrete T2.

The FUN allows swapping of op amps and that adds some change in the overall sound output.

Both are stellar amps, both Class A.

Thinking of building another Class A amp for more comparisons!!

Alex




santacore

Looks like a fun build. Where can I buy the board and plates?

adydula

  • Facilitator
  • Posts: 1732
This T2 project originated by Mark Johnson over at diyaudio.com

Here is the link:

https://www.diyaudio.com/forums/headphone-systems/338435-single-class-headphone-amp-using-transistors-t2.html

Mark has sold all his first set of pcb's and panels. He is working with the DIYstore to have them in stock and sell them.
The link to the store is over at the diyaudio webste.

Presently they are not available.

Mark is thinking about doing a second run of pcbs and panels if the store doesnt have them in the near future.

I would go over to diyaudio, create an account and write a note in the T2 thread and ask Mark etc...

Hope this helps, its indeed an easy project and works so very well.

Alex
« Last Edit: 24 Jun 2019, 02:51 pm by adydula »

santacore

Thanks Alex!

randytsuch

Finally finished wiring up my T2, at least enough to try it.

Initial impressions are its a keeper, but letting it burn in right now.

Caveat: 
My build is not per the instructions, I tend to always deviate, and I have no idea if my version is better or worse since I didn't try the original BOM.
I didn't buy the BOM walwart, and have no plans to buy it, so I will never know how it compares. 

I decided to try a different walwart from Jameco, slightly higher current.  I wanted something else from Jameco so I could combine shipping them.
My walwart is also higher voltage so I added a RC filter stage right after the switch, to drop the voltage down a few volts.
Its a linear walwart, so its output voltage depends on your house voltage, and I've found linear walwarts always run high at my house.
I've done this type of power input filter before for class a amps, since they are constant power and current draw, you can calculate what value resistor you need fairly easily.
I also have a bunch of power resistors in my junk drawer, so was able to do this without having to order more parts.
If you don't have a lot of diy experience, I would recommend sticking with the standard bom, and then you don't have to mess around like I did.

EDIT:  EDIT again:
Wanted to add that I didn't install the input cap at first, and amp was really distorting. 
I checked DC on my inputs, and found something like 5VDC, so I added the input caps and all was fine after that.

I thought there was an issue, but I forgot the pot grounds the signal, so I'm not sure why I have a 5VDC offset, need to figure it out still.

EDIT 2:
Keep thinking of more stuff.
If you use the PWB for the back panel, which is really convenient, there is a flex issue.  Its a long, kind of skinny board, so I find if flexes quite a bit when I install my RCA cables into the input jacks.
My RCA cables are difficult to mate, so this will contribute to the amount of flex.  Right now, I don't have a cover on it, so I can hold the back while installing RCAs to limit flex.
I'm thinking about adding a bracket in the middle of the back, or maybe right next to the input RCAs.  I'm not using the output RCA's, didn't even install them.
Pulling out the RCAs is fine because you can push against the back when to remove so it doesn't flex out.  When you install, if the cover is on, then you can't keep the board from flexing in.
Or you can use the metal back and should be fine, but you have to drill the holes for the RCAs and power input jack.

Also, if you care, my T2 is using 340 mA's.  This is 40 mA above what is consumed by the 150 mA bias current for both channels. 
FYI, 5.1V (voltage set across the bias resistor) / 150 ma = 34 ohms
you have two 68 resistors in parallel to get the 34 ohms, but my resistor values were a little low, and this would add a mA or so to the bias current.
Rest of current is likely consumed by the other parts in the circuit.



Randy

« Last Edit: 26 Jun 2019, 03:29 am by randytsuch »

adydula

  • Facilitator
  • Posts: 1732
Congrats on the build.

I would really be concerned about the 5VDC....would look into that one further, maybe Mark would help undersand that one?

I never really noticed the rear panel flex and I have plugged into them a few dozen times testing for sure. I will take a close look and see
how mine flexs...

If it does I would probably just mark, tap and drill the included case backplate and label...no real problem I have many tools, drill press etc...easy for me.

So let us know how it "listens" and what headphones your using etc..

All the best
Alex

randytsuch

Congrats on the build.

I would really be concerned about the 5VDC....would look into that one further, maybe Mark would help undersand that one?

I'm not  :D

Must be some issue with my source, which is kludged together.  But I do have an output cap on it, so a leaky output cap is all I can think of, or I miswired something.
At any rate, it sounds fine after I install the input cap, so I'm not too worried about it right now. 
I may try to figure it out at some time, but I have other things to look at that have a higher priority right now.

I've retired myself from the diyaudio thread, stopped reading and posting since last week, so don't expect any posts from me on the subject over there.
Since you might ask, for personal reasons, I'm going to leave it at that.

My quick impressions is that its a very nice amp, and it soundstages on my Senn HD800 probably better than I've heard before.
I also tried my Alpha Dogs on it, which are Fostex T50 with custom housings from mad dog.  They are orthos and hard to drive, and t2 was less impressive driving them. 
I'll see if it improves, but right now I like it much more with my HD800s than with the Dogs.

Randy