HI all,
I'd like to share some experience on this amp. This is my first DIY project, and the first successful one. I then went through a great length to get the most out of this circuit.In the process I gained a lot of experiences, skills, and interests in DIY.
Let's start with my first built. This amp really sounds good and I had a lot of fun. However I think the hiss is quite unbearable once opamps are changed. So I started thinking about how to improve it.
Then I went through a series of builds and settle with this. You can see I got some jump wires linking to something beneath the board. It is a Super Regulator board. This board is a fantasic regulator and can turn the switching PSU to a high performance PSU. You might also noticed that I got a small black block sitting next to HP jack in place of ua78m33cks LDO. That is a tarco TRS DC buck converter.
In the original design, when OPAMPs are changed, background noise would very likely to be strange. I have tried a variety of opamps. Opamps like LT1354, AD8065, etc would produce a constant "wooooo" sound. That's probably a character of the LDO.
With Traco, that "wooooo" goes away but hiss is a tiny bit stronger (depending on the opamps you use). However the benefit is huge here since the range of usable opamps becomes wider. And Traco really runs cool. It is not warm at all after running for a whole day.
To address the hiss Traco introduces,
I think 2 things might work: 1) use an opamp whose PSRR is higher (closer to 0), like AD8055 and HA5002; 2) swapping out the 10uf grounding cap with a larger cap, such as ZLH, then bypass with a MLCC.
I think the SuperReg is overkill, if I am to build a new one I won't use it. In Pete's original design, filtering caps for the power section is too small. If you don't want to build a new PSU reguator as I did, at least consider putting in a 1000uF cap in the place of C1 or D1 (in Parallel).
I actually plan to add a few more jump wires to the bottom and put more filtering caps into the output of traco.
This is a really fun project.
[Update] I use jump wire to hook up 4 extra caps to increase the 10uf grounding capacitance to a totally around 370uf (Traco's maximum load capcitance is 470uf). I used a ZLH 120uf, a EPCOS 41858 220uf, a epcos c0g, and a vishay 0.1uf MKP film cap. Now noise floor is really low (AD8055) and barely noticeable with audio-technica LS70 iem. In fact my Ha21 has the same level of hiss when used open frame. If you use less sensitive headphones or put it in a case, I think hiss will be completely gone. I am quite happy.
[Update 2] OPA209 works better to my taste than other opamps I have tried, including SS3601.
