Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Power supply upgrade

Remember what a stock G68 looks like?

http://www.Meridian-audio.info/viewphoto.php?compid=25&photoid=482

The fan is still fitted in the above picture, but its obviously under the linear PSU. The big smoothing cap is usually mounted in a bracket on the base of the PSU, which is at the top, as seen above. I just moved the mounting bracket 90 deg to the inside of the side panel on the left. You can just see it peeking through on the left, between the PSU and the controller motherboard. That leaves space for the fan to fit between the base of the PSU and the cap. There's not enought height to lift the PSU up clear of the fan, otherwise (tried that at the weekend).

The alternative would be to rotate the PSU 180 deg about the vertical axis so the base of the PSU faces the G68 motherboard. That would be feasible if I removed the mobo support brackets, and it looks like it would give better shielding of the PSU from the electronics. Here's something I tried this evening in a similar configuration.



This is a generic 75W PSU in that orientation. It goes in, but its perilously close to the display board, and I wouldn't have any confidence in that. I'd much rather remove the mobo supports altogether. That doesn't seem to be much of a problem, as the card brackets support the mobo at the top, and this G68 has small metal brackets that secure it at the bottom, so it wouldn't be going anywhere (and you'd probably suppport the mobo when fitting the cards anyway). I'm not sure if other controllers have those brackets - my C61R doesn't for soem reason.

Of course, I could cut a hole and fit the fan in compartment made vacant by the video cards that aren't fitted to the G68J, but what I keep coming back to is a cheap, simple, standard, robust modification. I'm now leaning towards the big HDBB-105W as the ideal solution for all variants of the G68 - what do you think?

Nick

On reflection, what would be useful is to assemble the G68 with the main board supports rermoved completely. You can't chop and change G-series modules like you can with the 8-series; its not that sort of product at all. The hardware is assembled, then it stays there. Apart from the processor cards, the cards are retained by the rear panel, so I doubt there are any issues, as long it can all be assembled OK. This is quite a big "if", as its damn fiddly. I'd rather do it that way, rather than cut the support brackets short, as I'm aiming to keep the mods reversible. I'll give it a go tonight.

Nick

Nick>
Good work. I can't help but think that a re-work using an external PSU might be a lot easier and give more options. So the work might include:
- Replace the existing mains connector with something different (to prevent muppets connecting the unit directly to the mains)
- Wire the existing connection for the PSU to the replacement for the existing mains
- Use an external PSU/box, thus further eliminating RFI within the box and allowing the use of PSU of pretty much any physical size you like

I did consider using an external PSU last year, but I rejected the idea at the time, as I wasn't sure whether linear supplies were worth pursuing at all. If there had been no benefit with an integrated supply, I wouldn't have been able justify the additional effort to make an external supply.

Having heard the benefits though, it may be worthwhile, though I'm slightly slightly sceptical. If the equipment was suffering from PSU interference, I think it would be heard as a hum, but I never heard any of that. Much to my relief.
Ironically, its probably SMPS that have more to gain from fitting in an external box. The amount of radiated noise and interference they kick out must be bad. In the RF world, 50/60Hz is virtually DC, with just a bit of indutive coupling to worry about.

Controller like the 861 and G68 have lots of space to play with, and its probably the players and slimline equipment where a big linear PSU in a seperate box would be most worthwhile.

The downsde to external boxes, though, is the increased power supply output impedance due to the additional cables and connectors. The 5V load at least is not insignificant, and variations in the load will modulate the supply voltage as received. The controller loads are pretty steady, though, so perhaps its not really much of a problem. Players are probably a bit different.

nick

My M system had an intermittent "click" sound since Dec 2011. Suspecting that a bad PSU should be the cause, I decided to modify my G68 with an external linear PSU. Thanks to the valuable information from Nick, Condor CP498-A will be a good choice with over-engineered specification.

A few days ago my CP498A arrived exactly when my G68 started to generate a loud "click" sound when switching on. I cannot use it now and have to speed up my modification work.

Today I have just verified that my CP498A works fine. When the 5V open circuit voltage was set to 5.13V, its output voltage at 2.7A output was 5.09V. I have configured my CP498A to replace the SMPS. Next I will verify that whether my CP498A can solve the problem of "click" sound.

Casey, I'm very pleased that someone else is having a go themselves. I think you've got a good configuration there; do let us know how you get on or if you need any help.

Nick

I think I finally put to bed my lingering concern about the main board supports. I was worried that the main board may not be properly supported when the cards are fitted, or that the supports were there for some reason I hadn't thought of.

I dismantled the G68J and re-assembled it without any of the brackets. That's easier said than done, by the way. G68 is a pig to strip and rebuild; the 861 is much easier.

In this unit, the mainboard is supported at the top by the longitudinal card supports, and at the bottom by three small metal angle brackets. These are quite sufficient to keep the board in place, and there's nothing to stop you holding the board anyway. You need to be static-grounded of course, but then you can't "assemble" the G68 from the outside, in the same way that you can change boards on the 861.



With the brackets out of the way, there are no real problems fitting any of the large linear supplies, and there's enough room round the sides to access mounting brackets round the outside of the supply. I can't say how much that helps fitting. The picture above is the 105W supply, and the 75W supply takes less space than that. The only issue is running the input and output leads, and giving the fan enough space.

On this G68J, the end of the main board was unsupported, but then there aren't any video boards to fit at that end. For the G68ADV etc, the fourth bracket could stay in place, and provide the necessary support. For controllers that don't have the small metal brackets at the bottom of the main board, the plastic brackets could be cut short, so there's only on screw mount at the bottom. That's an irreversible mod, but nothing to worry about.

This removes the doubt about the final question I wanted answering, and I'm happy about what to do with all versions of the G68.

Nick

Great work Nick. It looks like a fabulous fit. Can't wait to hear back how it sounds to your ears when you bench test it.

One final thought for now. I've been quite keen on the FG Elektronic PSUs, but its occured to me that the "old" generic designs do have an advantage. FG supplies have both the transformers and the heatsinks screwed and soldered directly onto the PCB.

The old supplies use the heatsink as the chassis instead. The transformers and the PCB are separately bolted to the heatsinks instead. Its useful to have the PSU chassis bolted directly to the equipment case, for the benefit of heat-sinking. I'd stil like the option to decouple the transformer from the chassis though. This provides the ideal mechanical configuration, where the transformer is decoupled from the case, but the heatsink is firmly coupled.

You can do that with the legacy Condor & Power One supplies, but not with the FG supplies. If you wondered how important decoupling is, take a look at the cooling fan in any recent piece of electronic equipment - that's very likely to be de-coupled with compliant rubber bushes. Just a thought.

nick

And for anyone who wants to get all ambitious and go over the top, I've been looking at the HDCC-150W supply, which is the largest of all in the Condor, PowerOne and Calex ranges. They're not as easy to find as the CP498A, but I noticed one on eBay today, and did a few measurements. The 105W is 362mm long, and fits OK. The 150W is 381mm long, but is also 115mm deep. I reckon it would fit both the G68 & 861.

Nick

I have connected my Condor CP498A to my G68; it works fine. Since I have also updated my DSP6k with latest firmware, the sound quality remarkably improved in terms of sound stage and details.

Now, the loud "click" sound upon powering on disappeared; however, intermittent "click" sound in much lower volume still persists. The occurrence frequency is about once every several hours. I am seeking some help locally. If anyone here knows the details, grateful if you could advise. It looks like some capacitors have a problem.

The hottest spot on the CP498A was about 42 deg C while the ambient 18 deg C. The current drawn by G68 was within the specification of CP498A.

After the problem of the intermitent click sound is solved, I will update the progress here.

Nick: Thanks for your advice

Hi Nick

Any progress updates on your work?

Cheers

George