Upgrading Meridian G68 Power Supply

kristjansen

Member
2010-12-27 11:11 am
Hi,

I have heard from several sources, that the main difference between the G68 and its higher end brother 861 - is the power supply.

The G68 uses a standard switchmode power supply, and I am looking for some one to help me build a new - and better - power supply.

The current supply is pretty simple and delivers +5, +12 and -12 V (just like any computer PS, I have been told)

I have been recommended to use two small toroidals, one for the +5V rail, the other for the +12/-12 supplies (josep (meridianunplugged.com))

Any good ideas, or perhaps even someone who will help my build this supply ( I will of course pay )

Note: I live in Denmark (we have 230V mains)
 

tatus

Member
2008-06-23 2:05 pm
What is your intention in replacing that SMPS with a transformer based supply? The only thing that I could be worried of is high frequency residuals, but a good SMPS design can eliminate that to a high degree. Plus, the residuals are far beyond the audible range.

Equaling the performance of a good SMPS with regards to PSRR with a homemade transformer supply could be difficulty. I would suggest to use at least a linear post-regulator plus large capacitors. But even with a standard linear regulator you do not achieve excellent PSRR. Mabye have a look at Hypex Electronics BV, it uses a push-pull design.

How do you use the G68? Are you utilising analog inputs or outputs? If you only use digital in/out, the sonic quality cannot be improved through the supply.

Anyway, replacing the +-12 should be sufficient, the +5 will be only for digital supply.
 

kristjansen

Member
2010-12-27 11:11 am
Hi,

Its possible that an upgraded smps would be just as good a soultion.

I use digital in - and analouge out. From what I have heard a better supply will benefint both analouge and digital performance.

ex. The improved 5v supply should affect jitter, and noise beeing led to the digital clock.
 

Yo_Azazel

Member
2008-12-28 9:37 am
Hi Kristjansen et al, "Josep from Meridian HHs" here :)

The 861 uses too a smps, in fact it is probably the same unit used on G-series but it does have an extra board for regulation and better filtering, see here the 861 power supply ensemble...

meridian-audio[.info] | Meridian Boothroyd Stuart

... and here the G68 internals with the same enclosed smps but without the extra filtering (just some smaller cap on the main board:

meridian-audio[.info] | Meridian Boothroyd Stuart

The G-series have also a noisiest display (very big fluorescent) and this with the underfiltered smps is again IMO key to its lower performance side to side to the 861 units (this in itself is subject to debate! YMMV).

So, first try: just upgrade the filtering with some pp capacitors ("supersound" black big boxes seen on the 861 pics, 3uF400V units).

Second try, go all the way and replace the original smps (it does not seem nothing special Tatus, thanks for your comments).

It surprises me a bit no one (Audiomods etc) offers upgrades to these machines... Be aware of MauiMods however, there was some awful stories about them (see the HH forum).

Happy New Year!!
 

tatus

Member
2008-06-23 2:05 pm
The improved 5v supply should affect jitter, and noise beeing led to the digital clock.

Agree. But I doubt that this noise can ever become audible. Consider a typical crystal having a quality factor of 50000, which is in other words the factor at which it will damp all spectra of supply voltage noise other than at its resonance frequency. So it attenuates noise of lets 10mV from the SMPS down to 20nV (nano!).