Few questions about the F5 amplifier - diyAudio
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Old 11th October 2011, 09:58 AM   #1
diyAudio Member
GentryBa's Avatar
Join Date: Oct 2011
Location: Bavaria
Default Few questions about the F5 amplifier

hi there!

first I must say that my english isn't very well, but I try to do my best.

In the moment I'm assembling a F5 circuit (2xmono in one case).
The PCB's for the amplifier are here now (they are from this site- and VEEERY NICE ones!), and my power supplies are ready, too.

the components I used:
- 2x300VA transformator with both 2x18V/8,13A
- 2x28 capacitors each with 4700F/35V for the DC-side
- one huge heatsink (450x300x50mm or 17,7"x11,81"x1,97") for the mosfets

now I have the following ideas:
- the heatsink is the top from the case
- the sides will be made with wood (to match the loudspeakers)
- for the front I want to use brown plexiglass
- the back will be made with 10mm aluminium to take all the connectors

now I've seen here in the forum, that most of you place the heatsinks on the sides of the case. do you think using the heatsink as top would be ok, too?

can I use CAT5-cables for wiring the in/outputs of the amp?
(or what would you choose, if its gonna be a "cheap"-build? )

do I need any shields for the AC-side? (one of you did, the others didn't)

AAAAND one very silly question, but I'm a bloody newbie:
what preamp should I build when using a simple CD-player or cassette-deck? Is it possible to use the amp without any preamp?

I thought I would go for the balanced zen line stage...

oooh I've got sooo many questions and read a lot about the F5's here in the forum... but it's not so easy finding the answers- because there are so MANY answers...

thanks for reading this, maybe you can answer a few of this questions...

best regards,
matthias from bavaria...
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Old 11th October 2011, 01:54 PM   #2
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Location: Upstate NY
The main issue with the heat sinks on top of the case is air circulation. The center of the heat sinks will be hotter than the edges. Only testing can tell you if horizontal sinks will provide adequate cooling. A fan set up to blow gently across your sinks will improve the cooling tremendously.

If you can keep your AC side far enough from teh signal side you don't need shielding. It won't hurt though.

Cat-5 pairs would be adequate for input signal wiring. You would need many multiples to adequately handle the output and DC power wiring. Get a bit of 12 gauge hookup wire for output and rails wiring. Over here the big box hardware stores have small quantities. Car stereo stores usually carry heavy wire, too.

Keep it Pass - a B1 would be a good choice if you need a buffer after your CD player. Unless your CD player has balanced outputs you don't need a balanced preamp.

Enjoy your project
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Old 11th October 2011, 04:48 PM   #3
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Join Date: Oct 2011
Location: Bavaria
hi BobEllis!

thanks for your answer! ok, I have to learn MAAAANY things, I think. the cd-player doesn't have balanced output- it's a normal one which has got 2 chinch outputs for left/right.
can I use this one FIRST WATT B1 as preamp? it isn't balanced, so must be the right one?

the cooling I have to test, ok.
wiring shouldn't be a big issue then, I will go exactly for your tip!

thanks a lot!
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Old 11th October 2011, 07:46 PM   #4
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Location: Silicon Valley, California
Matthias: If you post some pics of your heat sink (and other parts) perhaps someone can suggest a layout that has better natural convection cooling than fins on top....?
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Old 11th October 2011, 09:40 PM   #5
3GGG is offline 3GGG  Australia
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Consider the heatsink on one side with the fins running top to bottom. The toroid could be mounted vertically to make a very slim tall build, could look very nice.
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Old 11th October 2011, 10:16 PM   #6
ra7 is offline ra7  United States
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The F5 does not have much gain. I have seen people complain that it doesn't go loud enough. So, it would better to build a preamp with some gain rather than building the B1-preamp, which is just a unity gain buffer. Don't get me wrong, the B1 is awesome, I use it everyday, but it is not a good match for the F5. Bride of Zen or the JBOZ (search diyaudio) are good options.

Another option may be the BA-3 front end. You can even get PCBs on diyaudio.
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Old 12th October 2011, 09:41 AM   #7
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Join Date: Oct 2011
Location: Bavaria
hi there and thanks for the answers!

ok, I try to build a tower-designed case with heatsinks on every side.

If I want to use the BA-3 as preamp for my F5, how can I adjust the volume then? I surfed through the forum search function, but there are so many answers and posts and threads and... I'm a bloody newbie.

I bought this potentiometer 100K stereo 24 step potentiometer ladder volume control | eBay .
Is it possible to use it with the BA-3 and if so, where should it sit in the circuit?

PS: pictures are coming soon, in the moment I'm missing a few parts...

best regards,
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Old 12th October 2011, 03:37 PM   #8
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Location: Santa Rosa Beach, FL
If you are kicking around ideas about heatsink location and a wood-sided enclosure, you might want to scan my old thread:

Another F5 build--beautiful music, different drummer
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Old 12th October 2011, 04:08 PM   #9
The one and only
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Originally Posted by ra7 View Post
The F5 does not have much gain. I have seen people complain that it doesn't go loud enough.
The F5 has lots of open loop gain, so increasing the gain is trivial. Just
increase the 100 ohms feedback resistors to a higher value, whatever you
need. 200 ohms will give you 6 dB more for example.

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Old 12th October 2011, 07:38 PM   #10
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Join Date: Oct 2011
Location: Bavaria
@CanAm Man: stunning, absolutely stunning! nice- or how do you say here: fugly?

@Nelson (Papa?) Pass: Hmm, do you think, the B1 will do the job for a normal CD-player when I change the value from the resistors?

It's difficult to sort all those threads and infos, but it's very interesting and I will try to give my best!


best regards,
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