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Old 17th March 2009, 10:26 AM   #521
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Quote:
Originally posted by Peter Daniel
Of course, don't forget about the fuse and use slow blow version. With 300VA transformer and no soft start, at least 4A rating is required (with 115V mains). In some instances even that blew occasionally so I normally use 5A SB fuses.

For 230V regions that would be half the fuse value.
Hi Peter,

I'm a little confused (pardon the pun) about the fuses for 240v supply. Half meaning 2 or 2.5 Amp or half meaning 8 or 10Amp?

Many thanks
Lucas
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Old 17th March 2009, 04:47 PM   #522
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Default Amplifier Interference

Also, I have a problem. I have built one of Peter's kits. It sounds great, but I am getting the exact same oscillation through my speakers I got from my old amp (which I thought was buggered). Even without a source connected. So, I thought, hmmm, the speakers? the speaker cable? So unlikely? this is a computer-like oscillation. It turns out that I have these British Telecom Broadband socket communicators, that basically use mains electricity to communicate with each other, and put a horrible and quite loud computer-ish cricket chirping noise into my mains electricity. It's really pretty loud by anybody's standards. How do I get rid of such oscillation in my power supply? Bigger capacitors? I have some 4700uf 63v caps, designed for Hi-fi applications. Should that resolve things?

Many thanks
Lucas
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Old 17th March 2009, 05:03 PM   #523
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Try to install a small cap as described here: http://www.diyaudio.com/forums/showt...22#post1516522

With higher mains voltage, the current is lower, so fuse value should be reduced.
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Old 17th March 2009, 09:40 PM   #524
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Quote:
Originally posted by Peter Daniel
Try to install a small cap as described here: http://www.diyaudio.com/forums/showt...22#post1516522

With higher mains voltage, the current is lower, so fuse value should be reduced.

Thanks Peter. I'm not talking about pops and switch noise though. This is quite a severe computer-like noise caused by intentional mains noise by my broadband/digital tv provider. Will a snubber system work to help reduce this problem, and if so, what do you recommend?

Regarding the fuses, I ask because the 2.5Amp fuses have been popping every other time I switch the amp on!!! (2x20v 300VAC) I will order some 3.15Amp ones then...

Many thanks
Lucas

P.s. I can hear that the amp is very alive and "youthful" sounding. Thanks for putting the kit together!
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Old 17th March 2009, 11:31 PM   #525
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You may try Zobel, checking the small cap wouldn't hurt either. As to Zobel, it is 2R7 and 0.1uF.

If the fuse is popping, try larger value.
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Old 18th March 2009, 09:46 AM   #526
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by LucasAdamson
the 2.5Amp fuses have been popping every other time I switch the amp on!!! (2x20v 300VAC) I will order some 3.15Amp ones then...
transformers and motors require the fuse to be rated at about
VA * 3 / 240, in the UK.
For 300VA that comes to 4A.
It may start repeatedly on a T3.1A fuse.
Both these fuse values can pass double their rating for many seconds, even minutes, before rupturing.
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Old 18th March 2009, 01:40 PM   #527
CFT is offline CFT  United States
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Hi Peter.

In my active system, I use 1,000F FCs for the GCs and they sound great.

For the mid/high channel, I have been thinking of using 100 uF BG N at the chip and some 1,000u F at the power supply side instead. Would you say that will give a greater improvement, in what way, worth it?

Thanks!
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Old 18th March 2009, 10:44 PM   #528
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Hello CFT, I experimented with some capacitors value too.and what I found out was: using big caps on the power supply will give more bass.I try 4.7uf,10uf,1,000uf,2,000,10,000uf and 20,000uf. Right now I am using 20,000uf per channel and the sound is fantastic.some people say putting more capacitance will loose some tonal specially on the midrange frequency. I tell you, I must be loosing some hearing because I only hear improvement (bass) using more capacitance.The best way to hear the difference is using "alligator clips" and start testing capacitors (start from small to big values).maybe you like the sound with small values. Good luck.
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Old 18th March 2009, 11:31 PM   #529
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Maybe they give more bass, but there are many aspects to the quality of the bass and IME big caps never worked well, of course that is also system dependant.

As to small caps at the chips, I only experimented with BG N 100/50 and they worked much better for mids and highs comparing to larger caps: more immediacy, purity and refinement.

See some of my comments from the past:

http://www.diyaudio.com/forums/showt...431#post574431

http://www.diyaudio.com/forums/showt...230#post581230
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Old 19th March 2009, 12:49 AM   #530
ppapcro is offline ppapcro  Canada
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Hi Peter

Would there be any problem (in terms of grounding/hum) with a
3-chassis setup like this:

center- patek style power star ground layout for amp boards
left- 300 VA TR into rec. brd. then out umbil. to L amp inputs
right- 300 VA TR into rec. brd. then out umbil. to R amp inputs

with the ground wires from L & R psu's connecting to the thick copper star joining the amp boards
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