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Old 29th March 2009, 08:21 AM   #301
Nuuk is offline Nuuk  United Kingdom
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Quote:
"How much capacitance do I use in the in the power supply?" its mentioned-----".....and 1000 uF on each pin of the chip amp. " please explain.
It means that capacitors of 1000uF value are soldered into the circuit as closely as possible to the (power supply) pins of the chip.

Quote:
Again,.......is the '35A bridge' used in the chassis grounding same as the bridge used in the rectifier.
Yes, it is the same sort of item.
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Old 29th March 2009, 07:24 PM   #302
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Hi Nuuk,
I intend to use two transformers for powering two amplifiers separately-------- all in the same chassis, can I connect the zero volt lines of both the psu thru te same 35A bridge to the chassis??
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Old 29th March 2009, 07:28 PM   #303
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Quote:
Originally posted by zinblade19
Hi Nuuk,
I intend to use two transformers for powering two amplifiers separately-------- all in the same chassis, can I connect the zero volt lines of both the psu thru te same 35A bridge to the chassis??
In that case I would connect the power ground stars of each channel together with a thick piece of wire and run a single wire from the middle of that wire to the safety earth circuit.
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Old 30th March 2009, 01:41 PM   #304
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Default Thank you

Hi,

this email is just to thank you all and in particular Nuuk, for this great thread. I want to inform you that your efforts are really helpfull.
6 months ago I never did a solder my-self; now I built an integrated amp for my laptop based on the lm1875 chip and a PSU for a VSPS Phonoclone phono pre. They are both working great.

It was not possible without you... and now it is time for my new "reference amp" based on Peter's kit.


Thank you again

Renato
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Old 30th March 2009, 02:28 PM   #305
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Default Advantage of one big transformer

One large transformer will cost less than two small ones for same capacity. Large transformers are more efficient. Simpler wiring. More power is available to the channel that needs it. Get a larger transformer than you need at the minimum voltage you need for your power and you will have better regulation and reduced heat.
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Old 30th March 2009, 08:56 PM   #306
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Default Re: Advantage of one big transformer

Quote:
Originally posted by ted4412wilt
One large transformer will cost less than two small ones for same capacity. Large transformers are more efficient. Simpler wiring. More power is available to the channel that needs it. Get a larger transformer than you need at the minimum voltage you need for your power and you will have better regulation and reduced heat.
Your last sentence contradicts the first. Using a single transformer you will have worse regulation since high output on one channel reduces the voltage available for the other, typically peaks occur on both channels somewhat simultaneously.

In some applications cheaper is good, but we aren't necessarily comparing apples:apples, many people may find surplus transformers or already have something they would use, or find a supplier with good prices but limited choices instead of paying full, premium price from an electronics house which tends to cost more for one large transformer than two not so much smaller ones from another source.

Ultimately if regulation is important enough, one spends the extra money for a power supply stage that drops it's output voltage below the max sag the input stage would ever see from peak load. In other words if an amp would drag transformer X down to 30V at peak output, instead use transformer Y which is high enough above 30V that no matter the load, the output of a regulation stage in a PSU stays at the 30V target.

This way, instead of trying to minimize PSU voltage depression at peak amp output, you are instead reducing peak voltage when there is light load. It is certainly less efficient, but if we cared most about efficiency we'd build Class D or at least use a switching PSU instead.

How fancy a regulation stage in a PSU is, depends on the other project goals and ability of the builder. Relatively speaking it need not be expensive, I recall CarlosFM made at least one that used LM338 which is good for up to 5A if properly heatsunk, and a pass transistor could be added to the reference circuit to get 10A or more, or even simplier if noise rejection isn't important to the builder would be a capacitance multiplier instead of LM338 or a zener/pass-transistor arrangement. All will effectively keep the power rails regulated much better than any reasonably sized transformer choice alone.

Since a capacitance multiplier is a simple concept and CarlosFM has posted various schematics of his LM338 implementation, I'll attach an example of a zener pass-transistor PSU, one that uses two zeners in series to get closer to a target voltage if a supply of zeners for the target aren't readily available (but if they were available then certainly one zener instead of two in series could be used instead).

It is an example only, to go to the trouble and then not make the next step to a true regulator IC doesn't seem logical unless someone were limited in budget and needed to use parts they already had to build something meaning the circuit topology might be similar even if the parts values were changed.
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Old 1st April 2009, 08:25 PM   #307
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Default ac to dc

I was looking at the mur860 most use but its 8amp...being my transformer output has 2 taps, 16v @ a massive 27.5a each,
What would be the best diodes, or bridge rect. to use?
Thanks
James
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Old 1st April 2009, 10:57 PM   #308
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Some experts say to use large bridge rectifiers instead of those little diodes. 400 V or more, 35 amp bridge should work great.
http://sound.westhost.com/power-supplies.htm#rectifiers
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Old 2nd April 2009, 07:25 AM   #309
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Default Re: ac to dc

Quote:
Originally posted by jamesjmcgee
I was looking at the mur860 most use but its 8amp...being my transformer output has 2 taps, 16v @ a massive 27.5a each,
What would be the best diodes, or bridge rect. to use?
Thanks
James

DAMN that is a HUGE transformer !! I'm guessing you got it really cheap (or free) somewhere? What does it weigh, about 50 pounds?

Anyway, you won't use close to even half of that amperage as long as this isn't any kind of crazy frankengainclone. So I'd say the MUR860's at 8 amps should be fine (after all, Nuuk suggests 3A as a good starting point in the article). Although with that big of a tranny, it'd probably be a good idea to put a thermistor such as a CL60 in series with one side of your primaries (in addition to the fuse, of course)

of course, as ted says, a 35A bridge will work fine too (I'd still use the CL60 though)
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Old 8th April 2009, 04:26 PM   #310
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Hi

I have just built a couple of adjustable regulated power supplies for a pair of Pedja's discrete buffers. I have read somewhere that I can put a low value resistor after a single reservoir capacitor to help filter the supply.

Can someone suggest a suitable value?

Thanks

Richard
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