sontec 1 RU build thread

[analogica]

the thread seems alive!!!...just a question, is there a MOD for the low end section??? I check on both channels that the pots doesnt affect to the signal so much around 60 HZ....do you khow about it guys????

 

[Kingston]

I did a DOA shootout to confirm several things I had suspected. I used the Igor Sontec and a modified PRR176 compressor that has the same input stage, but with a decoupling cap instead of a servo.

My hunch was that the input de-balancing DOA stage is much more sensitive to opamp changes than the summing/output stage.

So I gathered all different types of DOA's I have and started testing.

gar2520, ppa APP2050, ppa APP2055 (FET input) and ppa's latest APP992. They all measure the absolute same frequency response just as expected. The differences can be seen with high resolution FFT distortion measurements as slightly different shaped distortion spread. The differences are very subtle. I had better success seeing what was happening with square waves and oscilloscope but those results were tainted due to RME sound card band-limiting artifacts.

I wish I had a better way of actually seeing what is happening, because especially when chaining channels where more than one opamp is changed, the difference is very easy to hear on transients especially. And yet the differences between distortion plots are very minimal.

gar2520 is smudgy and had obviously most distortion of all these, even midrange-harsh at times. I guess that's one of the reasons why people want to mix rock through API gear. APP2050 is very similar but more transparent, a good work horse I would say. APP2055 does something interesting to transients and imaging. There seems to be a bit more 2nd order distortion, but this sounds cleaner than APP2050. This is a sound I have not heard from FET input chip opamps. gar2520 sounds even "lofi" in comparison.

Then there's the APP992. This is highest mastering grade stuff. Best opamp I've heard, chip or DOA. It goes beyond the transients and imaging of the fet APP2055 and even adds some bass punch. It's also FET input, but seems just about everything has been improved compared to APP2055.

[edit]

Again, I wish I had some quantifiable method to *show* what is happening. I will get a signal generator one day and redo this test with proper square waves. Guess I should get some more exotic DOA's and see what they do as well. To be honest I did not expect differences this significant.

 

[hop.sing]

I just built the igor 250 Eq for a friend and since we had no discrete opamps available at the time, I used signetics 5534 in the input and output stages (they take +-22v), the EQ and servo stages have LME 47860 installed. After receiving the app992 we where surprised about the differences we heard. The 5534 sounds kind of harsh in the upper midrange compared to the app 992. On our listening chain (mytek conversion and psi 215 speaker), that was very audible.
I could not measure any significant differences, like you, but I trust my ears in this case. It would be very interesting to know what is going on there. Those distortion levels (very close to the noisefloor with levels around +4dBu) should theoretically make no difference.
Tobias

 

[i3j0rn]

Hi! I've just finnished building two units.
Works fine!
Sounds Great!
It was also my first DiY project. So...
Thank you so much Igor. Many thanks to everyone for your contribution to this thread! And thanks Tat for the nice case...

I just have to find some good looking knobs and it will be perfect.

 

[cstella]

Looks great! Congrats! 

 

[sonicwarrior]

Wow, that's a tough beginners project (at least regarding the sourcing of the parts).

 

[i3j0rn]

Wow, that's a tough beginners project (at least regarding the sourcing of the parts).

Fortunately there is a lot of usefull informations around here! 
It was great help.

 

[Igor]

My favorite support thread. The project is very straight-forward, so, I really don't need to do anything here

 

[druu]

Right, I didn't realize those cutoff it's on the IO pcb's were supposed to be used to raise the switches to for a Tat case. Anyway I tried to desolder a switch and two pads lifted (furthest two from the front of the switch). Any ideas what I should do to remedy this? I can't read schems properly yet so any advice appreciated!

I think for the other 3 switches I'll snip off at the legs and replace. :s

 

[ptron]

How many DOA's are neededon each stereo unit? (it seems like every IO board requires 2?)

Also, i thought it did but, bypass, would i need some bypass pcb's for it? I thought it was included on the IO boards too!

 

[ppa]

many thanks for the comments on my DOA's!
Another many thanks go to Igor, because if the my DOA's performed very well is even beacuse  Igor's eq permits to my opamps to do so, being this eq a very nice item.

 

[Majestic12]

Finished mine today....

 

[sonicwarrior]

Impressive. 

Is that a Mu metal shield?

 

[hop.sing]

Looks very professional
But the sheet is not really necessary, even without ours has no measurable hum, just a very low wideband noisefloor.

 

[Kingston]

wow, super clean build! good job.

I have a very similar plastic casing transformer and can't measure any 50hz hum above the general noise floor. That PSU shield looks great but might be unnecessary.

 

[Majestic12]

Yeah propably I wouldn't need it. But usually I put some shield around the power supply just to be on the save side. It's easy and not much work to install the shield when I'm doing the metalwork on the case.

 

[hop.sing]

One thing I notice is, that there might not be enough room for discrete opamps because of the large caps in the servo cirquit, but maybe it is just the angle of the picture. Good opamps make a difference there!
Tobias

 

[Majestic12]

Well, I consider OPA2604 to be "good" opamps, unit sounds great. I don't have the intention to put in any discrete opamp stuff....

 

[Igor]

He, funny 2u2 caps! Actually, there is no need for audiofullery cool types, every polyester or polyprop will work fine.

I found that I always prefer opa604 in summing circuit over 2520, 1731, and 990;
however, the best sounding for me is Forssell 993 or our based on cascode topology discrete op - amp.

 

[Majestic12]

In fact...I just bought the big, round 2u2 caps because they where cheap (something like 0,70 cents) and availiable . I don't care about the "audiophile" printing.

I used 2604 + 604 opamps in this build.

The only things I'm not quite sure about are the 5pF blocking caps on the 2604 and the 150pF on the I/O board. I think you don't recommend them Igor, but I can't measure any difference with or without them.