Stock Power Supply Load

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robheaton
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Stock Power Supply Load

Postby robheaton » Sun Feb 02, 2020 6:20 pm

I'm debating some upgrades for my QL, but wanted to check the stock PSU can cope!

Here is what I'm thinking of using;
1. Tetroid QL Backplane
2. Tetroid Gold Card
3. Tetroid Disk interface with CF card
4. vDrive

I already have Tetroids replacement voltage regulator installed.

Can the QL PSU cope with all this or am I just asking for trouble?


Current Retro Hardware :-
ZX80 Clone, ZX81 + Chroma + ZXPand + Zeddynet, Just Speccy 128, Speccy 48K x2, Spectrum 128 +2, BB Sinclair QL + Trump Card Clone, Aurora + Super GC + QubIDE.
BBC Model B 32k + Datacenter + Z80 Tube, BBC B+64K, BBC Master 512, BBC Master 128k + Datacenter & 6502 Tube, Risc PC x2.
Amiga 600, Amiga 1200, Commodore 64 x3, Commodore 128, Commodore 128DCR, C64 Ultimate, VIC 20, Sega Megadrive, Mega CD + 32X, Sega Megadrive II + Mega CD II, Sega Saturn.
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Dave
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Re: Stock Power Supply Load

Postby Dave » Sun Feb 02, 2020 10:00 pm

That is well within the regulator's ability to supply. Not a problem at all.

If anything, your system will be cooler than if you had a 7805 in there!

I would recommend putting a 10v or 16v low ESR 47uF capacitor across power and ground somewhere close to the 8301/DRAM area. If that interests you, I'll point out the perfect spot for each issue of PCB.


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robheaton
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Re: Stock Power Supply Load

Postby robheaton » Sun Feb 02, 2020 10:44 pm

Dave wrote:If that interests you, I'll point out the perfect spot for each issue of PCB.


That would be great if you could please Dave.
Forgive me, I’m no expert, but what benefit will there be by doing this?


Current Retro Hardware :-
ZX80 Clone, ZX81 + Chroma + ZXPand + Zeddynet, Just Speccy 128, Speccy 48K x2, Spectrum 128 +2, BB Sinclair QL + Trump Card Clone, Aurora + Super GC + QubIDE.
BBC Model B 32k + Datacenter + Z80 Tube, BBC B+64K, BBC Master 512, BBC Master 128k + Datacenter & 6502 Tube, Risc PC x2.
Amiga 600, Amiga 1200, Commodore 64 x3, Commodore 128, Commodore 128DCR, C64 Ultimate, VIC 20, Sega Megadrive, Mega CD + 32X, Sega Megadrive II + Mega CD II, Sega Saturn.
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Dave
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Re: Stock Power Supply Load

Postby Dave » Sun Feb 02, 2020 10:55 pm

The memory switches with the CPU's cycles, and with the 8301's video scan and refresh function. All of that DRAM switching in unison creates a huge buzzsaw of power demand. This causes ground bounce - which is that the relative value of 5V and ground shifts. This introduces subtle noise into video, into microdrive recordings, but usually not enough to cause functionality issues. The Samsung changes were almost entirely focused at these issues, to pass FCC mandated testing.

A nice cap right near the trouble-spot helps things along quite nicely. So does Tetroid's regulator, which responds a bit more quickly to current changes than the 7805 does.


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robheaton
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Re: Stock Power Supply Load

Postby robheaton » Tue Feb 04, 2020 6:25 pm

I've got everything ordered from Tetroid, now to sit back and wait.. :mrgreen:


Current Retro Hardware :-
ZX80 Clone, ZX81 + Chroma + ZXPand + Zeddynet, Just Speccy 128, Speccy 48K x2, Spectrum 128 +2, BB Sinclair QL + Trump Card Clone, Aurora + Super GC + QubIDE.
BBC Model B 32k + Datacenter + Z80 Tube, BBC B+64K, BBC Master 512, BBC Master 128k + Datacenter & 6502 Tube, Risc PC x2.
Amiga 600, Amiga 1200, Commodore 64 x3, Commodore 128, Commodore 128DCR, C64 Ultimate, VIC 20, Sega Megadrive, Mega CD + 32X, Sega Megadrive II + Mega CD II, Sega Saturn.
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Vyper68
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Re: Stock Power Supply Load

Postby Vyper68 » Fri Mar 13, 2020 1:40 pm

Dave wrote:That is well within the regulator's ability to supply. Not a problem at all.

If anything, your system will be cooler than if you had a 7805 in there!

I would recommend putting a 10v or 16v low ESR 47uF capacitor across power and ground somewhere close to the 8301/DRAM area. If that interests you, I'll point out the perfect spot for each issue of PCB.


Could you point out the best place to put this on an Issue 5 PCB please?


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