Opening the new DacMagic????

[gvelim]

The AD797 runs hot on U55/U56, U58/59 position however the highs are very detailed, and music sounds much better than other opamps tried, especially complex passages in classical & rock recordings.

Also running a freq sweep from 10Hz-20Khz didn't point any oscillations when measured with my oscilloscope. I recall LM49720 was also hot but cannot recall a "burned finger".

Should I infer the AD797 is stable on this circuit topology besides running hot ?

Re: bypassing, although datasheet recommends bypassing with 0.1uf + 4.7uf, would there be an issue with only the 47nf ECHU bypass cap already in place ?

[evan12]

Originally Posted by bicefalo

Hi Evan,

try UNREG 2 should be better option. Tell us the improvement, if any...

ciao

Hi, i am still waiting on the audio gd clock to be delivered from china! But what do you mean by Unreg 2 is that 7815 reg? I have in the mean time put nichihon es muse series in all bipolar positions, only cost 11 euro. I think this was positive for sound but subtle. Better bass and vocals and slightly better clarity. Hope the clock has some effect?

regards

[evan12]

Originally Posted by gvelim

The AD797 runs hot on U55/U56, U58/59 position however the highs are very detailed, and music sounds much better than other opamps tried, especially complex passages in classical & rock recordings.

Also running a freq sweep from 10Hz-20Khz didn't point any oscillations when measured with my oscilloscope. I recall LM49720 was also hot but cannot recall a "burned finger".

Should I infer the AD797 is stable on this circuit topology besides running hot ?

Re: bypassing, although datasheet recommends bypassing with 0.1uf + 4.7uf, would there be an issue with only the 47nf ECHU bypass cap already in place ?

Have you tried 9v power supply instead of 12 v? I bought one of ebay 9v 2.6A and runs great with dacmagic , alot cooler than before.

regards

[gvelim]

9V AC adaptor doesn't work for me as it causes voltage drop which in turn makes my SRegs not function properly. I have ordered some clip-on TO220 heat sinks to try out. Also I'll get the bypaasing fixed as per datasheet + the feedback cap at pin 7 + 6

[gvelim]

Originally Posted by evan12

But what do you mean by Unreg 2 is that 7815 reg

UNREG2 is the output of R107.

Feeding from R5's output is a much cleaner option with less noise as long as the voltage is good for your purpose. I am feeding from R5 the DACs' SRegulator so that way I avoid overloading the analog +SReg (7815) and improving a bit on heat dissipation.

[bicefalo]

[QUOTE=gvelim;2895410]UNREG2 is the output of R107.

Feeding from R5's output is a much cleaner option with less noise as long as the voltage is good for your purpose. I am feeding from R5 the DACs' SRegulator

Nice idea, I will try it.

About AD 797 : Check their power absorption across R400, if any oscillation is suspected.

Like a guide line, sum the quiescent current ( from data sheet ) and see what you have with no signal ( 50% more or less should be ok ), then try with signal to see if you get an increased value across R400.

ciao.

[evan12]

Originally Posted by gvelim

UNREG2 is the output of R107.

Feeding from R5's output is a much cleaner option with less noise as long as the voltage is good for your purpose. I am feeding from R5 the DACs' SRegulator so that way I avoid overloading the analog +SReg (7815) and improving a bit on heat dissipation.

thanks , unfortunately too late reading your message as my tech installed the audio g clock, used the dexa 7815 output for power and silver cable i bought cheap of ebay. First impressions are good, not night and day but a bit more detail especially on 16bit/44.1 cd rips. sound is clean. Since i changed to 9v adaptor not as much heat as before.

cheers

[gvelim]

Originally Posted by bicefalo

About AD 797 : Check their power absorption across R400, if any oscillation is suspected.

With my R400 at 68ohm I am getting 5.86Vdc which gives me around 86mA for the 4 AD797 + 2 OPA2120 + SReg current. So assuming 16mA go to the 2 OPA + SReg then it will be 17mA for each AD797.

17mA translates to 0.5W which calculates as 86C on the packaging, which resembles reality. The datasheet reads -40 to 80C as normal operating temperature, so what should I infer ?

Since the browndog adaptors are being toasted from both sides, I have put a clip-on heat sink per channel for regulating the temperature.

Otherwise music is sweet, full in midrange and better than before, even when the LM49720s were on.

[bicefalo]

AD797 is a bad beast, looks like yours are oscillating.....
IC adaptors are very bad for stability with hight speed op-amps, no heat transfer to large cooper lines too...
The safe option is to put LM49720s back. In my opinion a couple of silmic II ( 100uf/25v ), at the output of Yours regulators, will give You sweeter HF, creamy mids and strong sub bass, like I have in my dacmagic.

ciao

[gvelim]

I agree browndogs could be the reason for the oscillation so I am planning to fix 2 x 1206 film caps (0.1uf + 0.47uf) per rail on the adaptor to see whether this fixes the problem.

re: Silmic II, I already have super regs installed so would they still make any difference ? also where do you buy them from ?