REVIEW: Audio-GD Roc - Page 22

I really felt a major difference in soundstaging between 10.33 and 8.5. I'll give it another sometime, I just didn't have the time to get a good variety of music. I definitely felt the dynamics drop down a bit. After listening again this morning the graininess I felt in female vocals may not have been as drastic as I had originally thought. It might have been in comparison. They still sound very good, but not as amazing as when compared to the "spooky real" feeling I got out of Norah Jones at 13.5.

When originally tweaking these voltages I was concerned that this might cause some damage to the amplifier. Are these worries unfounded?

AFAIK we are safe. Our amps even run cooler.

I am almost willing to bet ( a nickle or two ) that that slight grain is caused by the stock NoVer caps.

 

Elwappo99 give 12.5 V  a whirl with the dynamic cans and 13.75 with the HE-6/LCD-2's.

 

Faudrei....Can the current be tweaked as well ?  I would think a boost in current for the planar cans would help greatly (which is likely why you went with the beefier Fairchild Stealth diodes). What part number are the FC Stealth diodes...I'd like to compare the datasheets of the stock Motorola types with the Fairchild parts. What changes (if any) did the swap to the new diodes bring ? I'm thinking a swap of the stock diodes in the CD7 transport and the RE1 DAC might be a worthwhile finishing touch.

 

Peete.

 

 

 

 

Yes Peete, PSU integrated current limiter can be tweaked too. Roc in stock configuration has constant 0,170 A through his rails limited by "pile of resistors" marked in this picture:

 

 

By soldering additional resistor in those two marked positions you raise constant current flowing through (10 Ω ≈ +60 mA; 5 Ω ≈ +120 mA). But beware, by doing this - amp runs hotter so you should closely monitor the temperatures after you increase the current limit.! Also beware - you should not go lower than 5 Ω.

 

I went for 5,7 Ω that I had on hand so I have ≈ 270 mA current limit which translates into 1,8 W (instead of stock 0,75 W) into 25 Ω impedance of my hardest to drive orthos. The additional power makes nice difference with HE-5.

 

As for diodes, I think A-GD uses On Semiconductor 8A rated ultrafast diodes, which are not bad at all. I went for Fairchild Stealth 4A 600V diodes, but now I wander whether I underrated them - they get very hot without heatsinking. I also can not give meaningful assessment of the SQ change they made because I was doing the recap, bypass and recabling thing in the same time (lifting Roc's board is a hell of a job). What I can say is that the cumulative result was astonishing: increased clarity, effortless SLAM!, "blackness"... but you already know that from your Phoenix mods Peete.

 

All this tweaking and learning along has made me admire Phoenix even more: you can do all this and more to Phoenix... just that tweaks mentioned here must have much greater effect on that dual mono triple stage parallel class A PSU that Phoenix have... not to mention that you can go safely to 0,35 A limit on Phoenix (by KingWa's words)... Eh, if I could just save up some money...

 

Errr... anyone interested in buying "slightly modified" Roc?

Thanks for the juicy details FD........you are correct the Phoenix does indeed use ON 8A UF types....have a look at this link http://www.fairchildsemi.com/sitesearch/fsc.jsp?command=eq&attr1=Maximum+Repetitive+Reverse+Voltage&attr2=600.0&q=50&ia=1&qt=1306936606&vid=%24__visitId__%24&i=part_number&qid=%24__queryId__%24&s1=Product+Volume%2F%2F0&s0=Product+New%2F%2F0&g=Family&a1=Average+Rectified+Forward+Current%2F%2Fv%3A0&a0=AAAFamily%2F%2Fv%3A0&a3=Package+Type%2F%2Fv%3A0&a2=Maximum+Repetitive+Reverse+Voltage%2F%2Fv%3A0&qtid=%24__lastTextQueryId__%24&t=0&c3=e%3A0%2F%2FPackage+Type%2F%2F%3Aeq%2F%2FTO-220AC&c2=n3%3A0%2F%2FMaximum+Repetitive+Reverse+Voltage%2F%2F500..0%2F%2F1000..0&c1=e%3A12%2F%2Fpart_type%2F%2F%3Aeq%2F%2Fg&c0=e%3A0%2F%2FAAAFamily%2F%2F%3Aeq%2F%2FRectifiers&as=1&c4=n%3A2%2F%2FAverage+Rectified+Forward+Current%2F%2F%3Aeq%2F%2F8..0&domains=fairchild_db%3Apart_number&text=

 

Now that is one obnoxiously huge linky if ever I saw one.....the Hyper fast II and Stealth II parts look very interesting. The RE1's diodes are mounted on the underside of the pcb that covers the transformers themselves...it's likely Kingwa has used ON UF (4A perhaps ? ) in this application as well. At any rate I bet the 8A 600V Stealth II's might be a worthwhile upgrade. The CD7 uses the Motorola type (of unknown part number and spec).

 

I'd definitely think seriously about adding heatsinks to your 4A Stealth diodes FD.

 

Peete.

Edited by Pricklely Peete - 6/1/11 at 7:14am