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Old 1st June 2010, 08:40 AM   #7971
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Hi

I will start building my F5 today and I need to check what the recommended fuse rating should be.

Nelson suggests using a T1.25 fuse if used with a 240v supply. I'm using a single 500VA transformer rather than the 300VA supplied in the production amp.

Would you recommend using a T2A fuse with this larger transformer?

Thanks
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Old 1st June 2010, 09:06 AM   #7972
AndrewT is offline AndrewT  Scotland
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any of 1.2, 1.6 & 2A may work at full output power from the 500VA. try them all.

You will have to use a soft start to attenuate the start up transient current.
two CL60 in series for 240Vac may not be enough for the lowest of these fuses.
either add a third (getting expensive) or swap one CL60 to 10R+10R+10R in series (all 5W)
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Old 1st June 2010, 09:07 AM   #7973
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Quote:
Originally Posted by AndrewT View Post
any of 1.2, 1.6 & 2A may work at full output power from the 500VA. try them all.

You will have to use a soft start to attenuate the start up transient current.
two CL60 in series for 240Vac may not be enough for the lowest of these fuses.
either add a third (getting expensive) or swap one CL60 to 10R+10R+10R in series (all 5W)
Great. Thanks Andrew
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Old 1st June 2010, 12:40 PM   #7974
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fuses worry me... wonder about their sonic contribution(s)... but I may be crazy...


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Old 1st June 2010, 01:38 PM   #7975
AndrewT is offline AndrewT  Scotland
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Bear,
are you really suggesting that we don't fit mains fuses feeding the mains transformer?
I hope not.
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Old 1st June 2010, 03:33 PM   #7976
jleaman is offline jleaman  Belgium
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Quote:
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Bear,
are you really suggesting that we don't fit mains fuses feeding the mains transformer?
I hope not.
Personally, id sacrifice it, if you can hear the difference between having a fuse in your system and not having one, then its pure and simple you are not enjoying your amplifier's sound.

Put it this way, will you still enjoy your amplifier if it burns your house down ?
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Old 1st June 2010, 04:05 PM   #7977
DougL is offline DougL  United States
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Originally Posted by bear View Post
fuses worry me... wonder about their sonic contribution(s)... but I may be crazy...


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Bear,

I would look at this as an opportunity to upgrade your power supply.

Chokes in the power supply, regulation, line conditioning after the fuse could all be possible enhancements. I would look at Nelsons white paper for inspiration on PassDIY. Omiting the fuse is not an option.

Doug
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Old 1st June 2010, 04:34 PM   #7978
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I have a question about a power supply for a F5 amplifier.

In the F5 operators manual, theres is an example of a power supply, but Im not quite sure what the resistors in the schematic are for. The 2 x 2k2 resistors are bleeder resistors? And what are the 8 x 0R47 resistors for?

Furthermore, what about capitance for a supply, how much is needed? Planing on either building a F5 as is or a balanced version.

Whats the best way to make a single ended signal into a balanced? My pre amp doesnt have balanced outputs. Could you use a differential Op-amp? TI has a document about differential op-amps and they show how to use one for exactly that purpose.
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Old 1st June 2010, 04:38 PM   #7979
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Mmmm... DougL are you suggesting that i need to "upgrade" my supply? Nah. (best check my website, fyi) But thanks for the suggestion.

But anyhow, I am just raising the question of the effect of fuses.
Why not a circuit breaker?
How about multiple fuses in parallel?
How about a 10 amp fuse?
An 8 amp?
ok 7 amp... 5?

A 2.5 is a mighty thin bit of wire... so why not just use really thin wire all the time, everwhere?

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Old 1st June 2010, 04:42 PM   #7980
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Neutrality, fyi your questions have been raised before in this thread, and a number of variations and approaches to the PS have been discussed... you might want to search or browse back into the thread?

Imo, the use of an opamp if you have a high resolution system might obviate the benefits of the F5's minimalist approach.

Any means including a single FET as a phase splitter out through a multi opamp "instrumentation" type configuration or a transformer could work.

Others might want to express other ideas or approaches, this is just me making noise...

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