New adventures with a pair of McCormack DNA-750s monoamps...my old ones!

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jeffreybehr

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2017Nov13:  Oh my...5-1/2 years later I may be buying these very amps back from the friend to whom I sold them.  Their job would be to drive a pair of Revel Ultima Salon2s next year.  More soon.
Old thread: http://www.audiocircle.com/index.php?topic=104073.0
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2017Nov14:  I believe we'll soon have a deal and I'll end up with 'my' amps.  I plan to remove ALL the old 680uF BG-Fs and end up with, in addition to the 80,000uF of Nichicon Super Through initial PS caps, only the original 8-count of DNA caps.  This time those will be BlackGate (std.) 470/160s plus a total of 4uF of SoniCap Platinum bypasses per amp.  That would total 83,760uF of capacitance, exactly the same as the sum of the original caps.  I've read the old thread completely a couple times recently and am amazed at all the time and effort I and my goodbuddy Pat put in.  I also can't see anything else I need to redo.   :D

Because of the (temporary) low price, I ordered the same type of 2-outlet, plug-in-the-wall-outlet power conditioner I had used previously with the '750s, an Audience aR2p...
https://www.thecableco.com/adept-response-ar2p.html
...the standard version ($200 under RR!), for these amps.  That way I won't have to replace the still-fried-closed power switches AND I'll have some noise filtering and surge protection on them.

Here's a pic from February 2012.  NONE of that equipment but the screen is still in my system. 


Another pic, from December 2012, with one of the amps, finished.  Still V'steen 5A speakers with custom-wound Neotec UPOCC-copper or -silver speakercable.  Still in the system now are the Neotec ICs and Neotec/Furutech powercable.

« Last Edit: Today at 05:13 am by jeffreybehr »

maty

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2017Nov14:  I believe we'll soon have a deal and I'll end up with 'my' amps.  I plan to remove ALL the old 680uF BG-Fs and end up with, in addition to the 80,000uF of Nichicon Super Through initial PS caps, only the original 8-count of DNA caps.

You MUST read:

[French]

http://www.quebecdiy.net/t712p150-amplificateur-ussa-dans-le-ventre-de-la-bete-construction-par-pinnocchio#16727 [pictures]

http://www.quebecdiy.net/t712p150-amplificateur-ussa-dans-le-ventre-de-la-bete-construction-par-pinnocchio#16770

to English with Google

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I let the amplifier work for over a week and a half and listened to lots of music. I wanted to be sure of what I heard. I will also validate with Fab, but so far I “hood” on the sound of my USSA 5!

The power supply in an amp makes all the difference, a huge difference in fact. That’s why you should never be afraid to invest in it. The double bridges of ultra-fast diodes with “soft-recovery”, the Mundorf M-Lytics MLGO condos with low impedance and ripple very high and the layout of the PSU very well done, high quality processors. All that matters a lot. This makes a power supply with lower impedance and a much lower noise in the end.

Result, full of low-level micro-details that were difficult to hear or went unnoticed, improved dynamics, a super silent background (very black) and micro-details that are no longer hidden or washed (washed). It was excellent before but there, as I told Fab, I almost fell off my chair. On some recordings that had a remarkable stage depth, it’s even better, difficult to explain, must be heard. I can stick my ear directly on the tweeter and not even a slight whistling, nothing, enough that sometimes I do not know if the amp is open or closed (I have no switch illuminated forward)!

In short, I am very impressed to hear that with a high quality PSU, the USSA 5 sounds even better. Proof that the PSU is the “bottleneck”. ]

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J’ai acheté 8 condos Mundorf M-Lytics MLGO 33000uF 40Vdc pour mettre dans mes deux nouveaux PSU pour le USSA 3/5. Un ESR de 6mOhm et Ripple de 11.2A

In ALL of my DC & Ripple Blockers I use an expensive and big EPCOS with very low impedance and high current riple too.

[IMG] http://maty.galeon.com/WP-imagenes/hum/ATL-Hi-Fi-DC-Blocker-x4-ME-open-front-side-3.jpg

EPCOS B41505A7189M000 CAP, ALUM ELECT, 18000UF, 35V, CAN

-> http://uk.farnell.com/epcos/b41505a7189m000/cap-alum-elect-18000uf-35v-can/dp/2283916?ost=B41505

-> http://www.farnell.com/datasheets/1680485.pdf

maty

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and https://hoppesbrain.com/2017/11/07/a-tour-of-a-hoppes-brain-gfa-555-restoration/

[IMG] https://hoppesbrain.files.wordpress.com/2017/11/20171103_213808.jpg

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Adcom GFA-555 top view. The power transformer has a null point in it’s radiated magnetic field, and is rotated to align the null with the sensitive input circuitry of the amp.

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Improvements to the input board:

47uF local power supply bypass capacitors are added to provide a local source loop for high-frequency currents. (The main power supply capacitors are separated from the input circuitry by several inches of wire that necessarily has some inductance.) These bypasses are again bypassed with parallel 0.1uF polypropylene capacitors mounted beneath the board. These handle frequencies too high for the electrolytics.

Hand-matched input transistors are installed and thermally bonded in heat-shrink for better thermal gain tracking.

Dale RN55C mil-spec 0.1% tolerance low thermal coefficient resistors are installed in the signal path and feedback loop. The gains of the left and right channels of this amp are matched within 0.01db.

Heatsinks are attached to the four TO-216 transistors to prevent heat stress cracks in their solder joints. (A known issue)

Bourns sealed trim pots installed

For the feedback to ground, a Nichicon Muse 47uF is used. This cap exists in parallel with the original silver-mica 1uF, which I leave alone, as it’s a fantastic capacitor.

Nichicon FG 4.7uF is used for the bias circuit…