PSU Recommendation for GML 8302
« on: April 29, 2020, 04:32:28 PM »
I have a GML 8302 with no power supply. The GML PSU is damn near $1000 after tax and shipping. That's insane!!

I have a spare +28/-28 linear supply from a smaller 1960's Quad Eight console I could use, but I'd have to recap it, test it, and even in tip-top rebuilt shape, I feel like a newer Acopian or Lambda design with current limiting could provide cleaner power, lower ripple, etc. What do you think? Rebuild the QEE supply and use it? Is there a model of Acopian or other you'd recommend keeping an eye out for? Or should I bite the big, fat, overpriced bullet and buy the damn stock GML 8355 for 1,000 doll hairs? Thanks!

PS: I should be clear, wiring is simple, 5 pin XLR, pin 1 = ground, pins 2,3 = +28, pins 4,5 = -28. This is clearly labeled on the actual GML 8355 PSU.


Ricardus

Re: PSU Recommendation for GML 8302
« Reply #1 on: April 29, 2020, 05:05:55 PM »
I somehow love the idea that one of George's designs would be powered by a PSU from a 1960s Quad Eight. I would do that, but hey, some people say I'm crazy.

I somehow even think George would love that idea. I had the pleasure of meeting him at many trade shows over the years. Back in the day, him, Roger Nichols, and Ed Cherney used to run the recording forums that EQ Magazine used to have online, so it was fun being able to interact with them and ask stupid questions. George apparently found my (bad) humour entertaining.
Audio mastering for hire..

moamps

Re: PSU Recommendation for GML 8302
« Reply #2 on: April 29, 2020, 06:29:24 PM »
This power supply looks very simple, 100VA max transformer, small rectifier, only two 2400uF/50V caps and most possibly some reg. ICs mounted on the chassis under perforated plate. So your QE power supply would be ok, IMO.
It would be nice also if you can post some high res pictures of the pre's interior. 

Re: PSU Recommendation for GML 8302
« Reply #3 on: April 29, 2020, 07:01:19 PM »
This power supply looks very simple, 100VA max transformer, small rectifier, only two 2400uF/50V caps and most possibly some reg. ICs mounted on the chassis under perforated plate. So your QE power supply would be ok, IMO.
It would be nice also if you can post some high res pictures of the pre's interior.

Not terribly high-res, but I happen to have this on my phone.

The QEE PSU is pretty smaller, certainly no bigger than the stock GML PSU. It was built for only a 12 channel chassis. But it was a 12ch MM71 with lots of iron. I believe those op amps suck up a lot of amps....so it should have plenty of overhead for the GML. I "upgraded" the QEE console to a massive, way overkill, brand new Acopian rackmount supply. Honestly way more juice than the QEE will ever pull (hopefully) but gives plenty of headroom, allows building a bigger frame at some point, and looks gorgeous (clean white panel with big VU meters).
« Last Edit: April 29, 2020, 07:04:44 PM by jdurango »

moamps

Re: PSU Recommendation for GML 8302
« Reply #4 on: April 30, 2020, 02:29:38 PM »
Not terribly high-res, but I happen to have this on my phone.

Thanks for picture. There is lot of very positive reports about the sound of this preamp. Unfortunately it is too expensive for me. BTW, I don't see how the phantom power is implemented. Is there any sub-board on left side close the power connector?

Re: PSU Recommendation for GML 8302
« Reply #5 on: April 30, 2020, 03:00:34 PM »
Thanks for picture. There is lot of very positive reports about the sound of this preamp. Unfortunately it is too expensive for me. BTW, I don't see how the phantom power is implemented. Is there any sub-board on left side close the power connector?

I was wondering about this. I don't recall seeing a sub PCB, but looks like there's one in this older 8304 on GS:

https://www.gearslutz.com/board/attachments/high-end/116087d1398684623t-gml-pics-img_1716.jpg

Since there's no 48v rail on the PSU, I'm guessing he uses the 56v difference between -28 and +28 regulated down to a +48v rail. I supposed you'd have to establish a new/floating? ground reference somehow. Way above my pay grade....but I don't see a step up transformer, so that's all I can fathom.
« Last Edit: April 30, 2020, 03:12:20 PM by jdurango »

Gold

Re: PSU Recommendation for GML 8302
« Reply #6 on: April 30, 2020, 03:23:37 PM »
There should also be regulators for bipolar 18vdc for the IC opamps.

moamps

Re: PSU Recommendation for GML 8302
« Reply #7 on: April 30, 2020, 04:04:37 PM »
If there is no external board which generates phantom power, most probably each board has a small dedicated DC-DC converter (IC + multiplier, this 14pin chip on the left side maybe).  IC opamps (for servo?) may have local zeners for dropping  power voltage to +/-18V. It is just speculation.   


 

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