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Old 12th January 2007, 09:17 PM   #1
student is offline student  Austria
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Default gainclone power supply

hi

i only wanted to ask for the right size of the power supply for a gainclone (mono platine).

i've planned a 20-30.000F supply for each channel.
but i heard that the sound of the lm3886t would decrease extremely if i use such a large supply.

can some 1 confirm this rumor ?
which size would be alternatively the best one ?
____

does the size of the transformator (i want to use 250-300 VA each channel) influence the sound performance of the gainclone in the same way as the capacity of the power supply ?
can i unconsidered use such a oversized transformator ?
____

i also heard that the lm3886t prefers for 4 ohms use 18V than more V.
which voltage would be the best one for a 4-8 ohms use ?
____

sorry for my technical incompetence
and thanks for your effort
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Old 12th January 2007, 11:00 PM   #2
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Default gainclone power supply

Most people use way larger supply's then are needed.
lets say your LM3886 used with 4ohm load and a 30 V+/- supply will put out 67 watts at 60% efficiency so the amp will need at least 107 watts or 107VA transformer, so now lets look at sag in the supply your little LM3886 can put out a PMPO of 120watts if you try to draw that the supply will sag createing a large voltage drop on the supply making the amp less linear adding distortion ect..... so now take that 60% efficiency figure and apply it to the 120watt peak so now you need around 200 watts per chip. If you want you could add another 20% saftey net, but I think it would be over kill
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Old 12th January 2007, 11:28 PM   #3
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halo0925

What would you suggest for cap size to drive a 8 ohm load?

I used a pair of 12,000 mfd caps on my Chipamp.com power

supply board to power two channels. I consider this to be overkill.

I also played around with the bypass cap size in the power supply

to arrive at a more pleasing sound. Maybe you could help explain

why some are using 1,000 mfd caps on the amp channel board

and if this large a cap is really needed.

Thanks
Joe
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Old 12th January 2007, 11:34 PM   #4
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Default caps on bridge

I am a firm believer in more is better one of my large BPA amps uses 12- 4700uf per channel, I also always bypass with smaller low ESR film caps 1uf to 10uf.l
caps can make the difference in dynamics
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Old 12th January 2007, 11:40 PM   #5
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Default Re: gainclone power supply

Quote:
Originally posted by student

i've planned a 20-30.000F supply for each channel.
but i heard that the sound of the lm3886t would decrease extremely if i use such a large supply.

can some 1 confirm this rumor ?
which size would be alternatively the best one ?
____

does the size of the transformator (i want to use 250-300 VA each channel) influence the sound performance of the gainclone in the same way as the capacity of the power supply ?
can i unconsidered use such a oversized transformator ?
____

i also heard that the lm3886t prefers for 4 ohms use 18V than more V.
which voltage would be the best one for a 4-8 ohms use ?
____
1. Yes, I can confirm that rumour, I wouldn't use more than 2200uF per rail. If your speakers need more, build different amp.

2. 300VA transformer is rather conservative size. The quality and size of transformers are approx 50% of the caps influence.

3. I did some testing with Variac connected to PS, and the panel of listeners preferred the higher voltage supply (up to 40V per rail) even wiith 4 ohm speakers. Some will still claim that 18V sounds better, but those people also prefer more soothing and less alive sounds
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Old 12th January 2007, 11:46 PM   #6
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Default PS

Let get realistic, a power supply with an AC transformer can only be so clean, does a gainclone sound better powered by batteries?? is pure DC better? is regulation better? sound quality is in the ears of the person listening try larger caps you might like the sound someone else might not, sound is subjective.
IMHO the cleaner the supply the better this means more capacitance bypassing ect........
Do what sounds good to you
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Old 12th January 2007, 11:50 PM   #7
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Default Re: PS

Quote:
Originally posted by halo0925
Let get realistic, a power supply with an AC transformer can only be so clean
... as your mains supply.

I was using GC with batteries for more that a year, in the end I switched back to AC as I find it sounding more realistic.

The big caps kill what GC has best to offer: the freshness of the sound, few other amps do it better, don't kill it with the big caps
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Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it. - JC
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Old 13th January 2007, 12:14 AM   #8
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Peter,
Most of my amps have all been very large BPA amps, I heard all this and that about chip amps and gave it a shot, I didnt expect very much because I had a bad taste for chip amps like the original STK modules.
Built my first chip useing your schematics, by the way your patek is pure art work
I was amazed but, I was useing two carver 4.0 t's bridged for the bottom end and my KSA250 for the top so the little chip was out classed. So I went on a quest and about 10 BPA units latter I found got a circuit that maintains the sonic signature of a single chip, but the power to drive my setup, and it uses a large amount of capacitance, it may be different for a single chip I used 1500uf fine golds on my original single chip based on your circuit.
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Old 13th January 2007, 07:22 AM   #9
Nordic is offline Nordic  South Africa
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Default Re: gainclone power supply

Quote:
Originally posted by halo0925
lets say your LM3886 used with 4ohm load and a 30 V+/- supply will ...
...not burn out your chip....
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Old 13th January 2007, 09:01 AM   #10
KT is offline KT  United States
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Default Re: Re: gainclone power supply

Quote:
Originally posted by Peter Daniel ...I did some testing with Variac connected to PS, and the panel of listeners preferred the higher voltage supply (up to 40V per rail) even wiith 4 ohm speakers. Some will still claim that 18V sounds better, but those people also prefer more soothing and less alive sounds
Peter, Some time ago I took apart the power supply (Humpty) of my original 47 Labs Gaincard. I don't remember exactly after all this time, but the huge transformer inside was set to output something between 34V and 36V or somewhere in between. It's interesting to me that you're finding some sound improvements at the higher voltages. I always wondered why the Humpty was rated at the higher voltage when talk among gainclone builders was generally of voltages of between 18V and 24V. Best, KT
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