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Old 15th June 2010, 07:39 AM   #1
Kuro is offline Kuro  Hong Kong
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Default +5V high current low noise regulator?

I'm currently using LT1085 with bypass cap on the ADJ pin to provide low noise output.

I wonder if I can be better than the LT1085 in terms of noise department. The current requirement for my digital circuit is 2.6A.

So far I've not seen any super reg with high current output yet.
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Old 15th June 2010, 08:09 AM   #2
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Curious to know what digital circuitry you have which requires such high current at low noise?
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Old 15th June 2010, 08:13 AM   #3
Ipanema is offline Ipanema  Malaysia
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How about a low noise bandgap driving a low noise opamp driving a power MOSFET in non-inverting configuration.
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Old 15th June 2010, 04:18 PM   #4
Kuro is offline Kuro  Hong Kong
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I'm trying to power my entire TacT room correction preamp. I notice the sound is much better when I change the SMPS to a LPS I built using LT1085. Now I wonder if I can improve this further.
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Old 15th June 2010, 04:31 PM   #5
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how about using pre-reg configuration?
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Old 15th June 2010, 11:56 PM   #6
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Quote:
Originally Posted by Kuro View Post
I'm trying to power my entire TacT room correction preamp.
You might find this thread interesting then. I certainly did

Quote:
I notice the sound is much better when I change the SMPS to a LPS I built using LT1085. Now I wonder if I can improve this further.
It looks from that Slimdevices forum that there are major EMC issues with including a TacT preamp (or perhaps only with a Squeezebox) in a system. So perhaps the lower noise of the linear power supply is a secondary issue. I'd experiment with putting a mains isolation transformer in the input to the TacT (low capacitance, i.e. not a toroidal) preceded by a line filter. Also try this in whatever source you're feeding to the TacT. Also try using cables with very good quality screening (braid and foil together) between components. Since I guess your issue is a system issue, simply lowering the noise on your regulator probably won't have much impact on the sound.
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Old 16th June 2010, 01:24 AM   #7
FuzzyM is offline FuzzyM  Australia
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Default Try an LM7805

Try an LM7805 with a current increasing transistor, as shown on page 23 of the LM7805 datasheet (the pdf on this linked page).

LM7805 Datasheet pdf - 3-Terminal 1A Positive Voltage Regulator - Fairchild Semiconductor
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Old 16th June 2010, 01:43 AM   #8
iko is online now iko  Canada
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Quote:
Originally Posted by Kuro View Post
So far I've not seen any super reg with high current output yet.
Search for the Salas shunt regulator. Several people have been running it at high current too.
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Old 16th June 2010, 03:31 PM   #9
Kuro is offline Kuro  Hong Kong
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Quote:
Originally Posted by abraxalito View Post
It looks from that Slimdevices forum that there are major EMC issues with including a TacT preamp (or perhaps only with a Squeezebox) in a system. So perhaps the lower noise of the linear power supply is a secondary issue. I'd experiment with putting a mains isolation transformer in the input to the TacT (low capacitance, i.e. not a toroidal) preceded by a line filter. Also try this in whatever source you're feeding to the TacT. Also try using cables with very good quality screening (braid and foil together) between components. Since I guess your issue is a system issue, simply lowering the noise on your regulator probably won't have much impact on the sound.
I'm using the Transporter (TP). The SB3 has no comparison to the TP, and AES output of the TP beats the crap out of SB3. Noise is not an issue with TP, as soon as I've reduced the jitter and noise of my TacT preamp, the system sounds better. I've done several iterations of jitter and noise reduction on my TacT preamp, and the system keeps on sounding better, so TP is not the limitation here.

FWIW, I do have a pretty advanced system. I've a balanced isolation transformer with Faraday shield (custom made by Toroid). This feeds my PS Audio PPP AC regenerator. It then distributes power to all my hi-fi gear with critical components not sharing the same bank of AC outlets as PPP provides AC isolation.

The noise floor of my system is already very low. I've also done hard core mods to my TacT 2.2xp preamp, the crystal oscillators driving the ASRC chips have been replaced with low jitter, low phase noise ones. I've also added many Sanyo OsCon caps on each IC chip I can find on the digital input and output boards, to further reduce noise.

Previously, I made an external LPS using a LinearOne LPS. It sounds a lot better than the SMPS it replaces, but my latest creation is a high efficient internal LPS, IMHO, sounds a hell lot better than the external LPS.

I'm using LT1085 to provide the +5V rail to my TacT preamp. The noise output on the unloaded +5V rail is less than 200uV peak-peak when measured on my digital scope. When it is loaded, the noise is just slightly above 2mV.

Today, I changed the LT1085's output cap from a Panasonic "Pureism" 470uF to a Panasonic FM 2200uF low ESR cap. The noise on the +5V rail went down to 1.2mV when system is loaded and running. I guess the 2200uF cap improves the transient response of the regulator. With this mod, I get even more reverbs and ambient from my music. I don't know if bigger output cap will further improve things, I'm doubtful on this, as I did the same on the +/-12V rails and see no futher noise reduction with a bigger cap. I'm really into the "golden ear" stage, so I'm looking at improving the last little mile.

I'm just wondering if there is anything better than what I'm doing now.

I did measure the +5V rail across the ASRC chip on the digital input board, and there is a 7.5mV ripple with 750Hz riding on it. So it looks like I need bigger and better caps to replace the decoupling caps that are already on the main board.

Perhaps I should use a super regulator on the digital input/output board and reduce this 7.5mV ripple to less than 1mV...

Last edited by Kuro; 16th June 2010 at 03:43 PM.
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Old 16th June 2010, 03:36 PM   #10
Kuro is offline Kuro  Hong Kong
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Quote:
Originally Posted by Ipanema View Post
How about a low noise bandgap driving a low noise opamp driving a power MOSFET in non-inverting configuration.
What sort of noise figure am I looking at when driving a 2.6A load?
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