Salas DCG3 preamp (line & headphone)

[jimk04]

Good to see that you have it working James. Enjoy.

Thanks Keith. Maybe we have a comparison of systems some time.! Thanks again for the rectifier boards.

 

[Salas]

I am puzzled

Before comparing anything, run loopback on your Focusrite boxes first to have a reference of their output to input loop. Use the same test cables you connect your preamps under test.

 

[alexkosha]

Like Salas has pointed out, I am puzzled by the H2/H3 profile differences of the L from the R channels, especially since the THD and THD+N numbers are identical.



Were the measurements taken when hot? Perhaps I missed this but at what input and output voltages were the plots done.

Thanks. nash

The unit warmed up prior test and I did not measure Vin/Vout to compare R/L. The only think that I used is a reference method (means that same condition is used for "before" and "after"). Do not forget, and Salas mentioned that, that recording was done with consumer grade gear and I did hit its absolute limit. That 3H difference can be related to my noise PC, Focusrite 2i2 itself or my cables/connectors/adapters and etc.. As Salas mentioned, next time I’ll use same channel setup gear to measure L and R on Arta. I have my second unit to tune now and I use this experience to bring it up to my expectations. It is total mess there now started with GND loop.

 

[jimk04]

My '18v' transformers seem to be at 24 volts even when loaded onto the DCSTB. And this is on a day of not particularly high incoming grid. Rectifier diode sinks are a little more than warm but comfortable to touch for as long as you wish. Is this ok?

 

[Salas]

They could have been made closer to nominal AC but they obviously aren't. Are they 230V labeled, and how high mains you got on average?

The sinks are for the pass transistors in the regulator sections and those TO-220 semiconductors have no problem with some more heat due to enthusiastic transformers.

From the moment there will be a lid on, extra heat could be accumulating inside the box though.

Drill ventilation holes over the sinks area if there will ever be a perspex lid or other.

Did you listen to more music by now? Going well?

 

[jimk04]

Thanks Salas. Yes it course my mistake. They arent the diodes.

It sounds fantastic! My system has never sounded as good. I thought my small chassis and tight wiring may cause issues but it would seem not.

Thankyou again for a superb design.

 

[Salas]

You are welcome

 

[Salas]

What is your average mains voltage?

 

[jimk04]

It was 240 tonight when I measured 24v secondary but it is often higher than 240. 245 probably average. 248 max I have seen

 

[Salas]

The transformers are surely high but the mains don't help either. What is the model?

 

[alexkosha]

I replicated issue with 3 harmonic. It is bad connection via 1/4 to RCA adapter to audio interface. My 2nd generation Scarlett 2I2 in general has flimsy input and output connectors and might it make sense to change these for something more robust.

 

[Salas]

Use bit of Deoxit maybe?

Those adapters sometimes pick hum also when the RCA doesn't grab them well.

 

[jimk04]

The transformers are surely high but the mains don't help either. What is the model?

Hi Salas. They are ILP brand. A now defunct British brand.....alas. I did Google the model when i recieved them but no info available. They are now buried in my encapsulating cans and I didn't make note.

I may look to replace them at some point.

 

[Salas]

If the build will be well ventilated and the extra heat from their enthusiastic secondary voltage not ever creating a real problem, the higher voltage drop across the DCSTB actually brings benefits to its semiconductors leading to a small performance gain.

 

[thimios]

I replicated issue with 3 harmonic. It is bad connection via 1/4 to RCA adapter to audio interface. My 2nd generation Scarlett 2I2 in general has flimsy input and output connectors and might it make sense to change these for something more robust. View attachment 794182

All this is for the trash!
I don't know any available from a good manufacture.

 

[Salas]

See loopback differences of my little old EMU tracker box with bad RCA contact double cable and good separate cables.

 

[thimios]

See loopback differences of my little old EMU tracker box with bad RCA contact double cable and good separate cables.

What is the sample rate?
Is it the headphone or the line out?

 

[Salas]

44.1kHz ASIO Windows 10. Its own drivers with bit less THD & noise are obsolete, good for Windows XP only. Its the EMU's line I/O looped to itself.

 

[thimios]

44.1kHz ASIO Windows 10. Its own drivers with bit less THD & noise are obsolete, good for Windows XP only. Its the EMU's line I/O looped to itself.

Thanks, so it's a soundcard loop test not DCG3 measurements.
I have a DCG3 new measurement, the best(lower THD) up to now.
I will post latter.

 

[Salas]

Alex was right for saying he was measuring his DCG3 at the limit of his Focusrite in his RightMark report. My audio interface box measuring itself gave bit worse THD+N and IMD SMPTE than his own with the DCG3 in the loop.