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Old 15th May 2009, 06:18 PM   #691
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Hi,

unlikely, I need your help if you can. As I told you in the previous post, yesterday evening I completed my two monoblock amps with the Audiosector premium kit and they worked fine. I switched on-off many times the amps without any problem.

Today the fuses of both amps started to blow on both amps at switch on.

I use 2 trasnsformers 300VA with dual secondaries 25VAC (I am in Europe so the main rail is rated 230V). The fuses I used are 2AT (slow blow).

The only thing different with yesterday I can imagine is a slightly different tension (maybe higher) of the main rail so that the fuses that yesterday were just sufficient now blow.

What is your opinion? Can I slightly increase the ampere rate of the fuses?


Thank you for your help

Renato
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Old 15th May 2009, 06:34 PM   #692
AndrewT is offline AndrewT  Scotland
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Hi,
each 300VA transformer needs a 300 * 3 / 220 ~= T4A fuse.

If you want to use a lower value fuse you must accept nuisance blowing or fit a soft start.

Go with 50ohm soft start, a delay ~300mS and T1.6A fuse to each transformer.
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Old 15th May 2009, 06:40 PM   #693
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Just increase the fuse value and forget about soft start.
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Old 15th May 2009, 08:51 PM   #694
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Hey folks just wanted to say I got my kit built and it is working wonderfully. It sounds fantastic. I did had the RF interference problem the first day. But I managed to solve it with the fix suggested here in the first few pages. The only thing I do not have working is the LED. It is the little things.

Andrew thank you for the math. I will try your example.

I posted some pictures over here....
http://www.diyaudio.com/forums/showt...27#post1828327
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Old 16th May 2009, 03:20 AM   #695
cyxg is offline cyxg  Australia
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Quote:
Originally posted by Peter Daniel


Some of the upgrades have been discussed here: http://www.diyaudio.com/forums/showt...32#post1231532

Hi,Peter

i running my amp over two weeks. But i found the base is slow, i want to make the amp control the base fast.

what can i do?
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Old 16th May 2009, 03:43 AM   #696
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Quote:
Originally posted by cyxg
Hi,Peter

i running my amp over two weeks. But i found the base is slow, i want to make the amp control the base fast.

what can i do?
You may try replacing Panasonics with BG STD 1000/50. If this won't help, the problem is probably somwhere else and not the amp.
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Old 17th May 2009, 05:30 PM   #697
chuck55 is offline chuck55  United States
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Would there be any improvement by using 1500uf / 50 v Black Gates vs. 1000uf / 50 v? These are the standard BG and 1500uf / 50v is hard to find.
Also, I've been doing some reading on TVC (Sonic Euphoria good bass and dynamics, less clear, less linear) vs. resistor (Placette super clean but less bass and worse at the low volumes I listen at), vs. plain Alps motorized pot (a compromise between the other two) . Would 10k be a good value? My CDP's output impedance is 100 ohm.
Thanks
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Old 17th May 2009, 06:22 PM   #698
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STD BGs come only in 1000uf and produce the best bass. There is not much actual difference between 1000uF and 1500uF.

I would suggest 25K pot value; 10K will work too, but I don't see a reason to lower input impedance too much.
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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 17th May 2009, 08:58 PM   #699
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Hi,

this is just to thank you for the previous suggestions, it seems that the new increased values fuses (3A for now) do not blow anymore.

I still did not build a pre, so for now I can just use an ipod as source (using the head phone out), but I am already impressed by the sound.

The sound is clearly much more transparent than what I get by my valve Yarland integrated amp.

Unlikely I am also in the 5% of users with RF interference problems, so I am going to install in the next days the small caps at the amp input pins as suggested by Peter in post #51.

Thank you again

Renato
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Old 19th May 2009, 09:12 PM   #700
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Hi Peter and company,

I have a pair of 16 ohm bookshelf speakers (WR125ST w/ 16 ohm Alnico piezo) and two identical center tapped transformers (35 - 0 - 35). Both are from Pioneer SX-6 amplifiers. One is functional and currently powering the monitors, but they deserve something better.

I would like to build some LM3875 "premium" monoblocks for them without having to buy transformers but I'm totally out of my league here. On the back of the amplifier it has a VA rating is 280; there is also a 12 volt secondary which I'm guessing accounts for part of the 280 ratings.? But that should still be plenty for a single channel.? Can I safely build monoblocks with these if they will always see a 16 ohm load and I use decent heat sinks?

I looked at the spec sheet for the LM3875, but it didn't give me a definitive answer since all the Typical Performance Characteristics graphs only account for rail voltages up to 40 volts with 4 and 8 ohm loads, and I figure my rail voltages will be about 50V (35 x 1.4).

Thanks,
Roger
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