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Old 26th January 2012, 12:05 PM   #101
CENTRAL is offline CENTRAL  Greece
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How does biasing affect the end (aural) result?

If my speakers are expected to be quite of a load, should I push the bias higher?

Last edited by CENTRAL; 26th January 2012 at 12:13 PM.
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Old 26th January 2012, 12:11 PM   #102
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Originally Posted by a.wayne View Post
Bear ,

You have played around a bit with the F5, what setup worked best for you , as far as quiescent current , type of build parts , dual outputs or cascode version ....
Right. Wayne you asked my question right out of your hands.

Would like to know which one is better for 90 db 8 ohm speakers.

Standard, double output, cascode version.

Thanks
Pandu
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Old 26th January 2012, 01:11 PM   #103
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Biasing does two things with the F5 - this does not hold true for all amps - it alters the sonic presentation and it sets the maximum current which in turn sets the lowest Z load that will still be in class A all the time.

Regarding the sonics, I am sad to report that on this one I am mostly an "armchair general". While I have a complete amp waiting to be built (actually 4) my personal situation had precluded my taking any action. Drat!

However, my audio friend Rick built one pretty early on and showed me what he did. He did it all, but he used my system as the "reference" so we talked about what was what and he brought it over after each change.

That's in another thread that I started on the F5 that would be here:
F5 Listening Impressions Thread

In general terms the amp is something of a chameleon - it comes out differently depending on how it is built. It seems to range from a bit dull and muddy up through a bit bright. However I did personally find that Rick was able to present a version that on my compression drivers had tremendous HF energy but with NO sibilance. Quite a feat.

Pretty incredible for an amp with no parts and that I dismissed early on as another NP "throwaway DIYer design".

Bias, output devices, matching, resistors and power supply all factor in directly.

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Old 26th January 2012, 01:18 PM   #104
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Originally Posted by pdhanwada View Post
Right. Wayne you asked my question right out of your hands.

Would like to know which one is better for 90 db 8 ohm speakers.

Standard, double output, cascode version.

Thanks
Pandu

Makes no real difference into 8ohms EXCEPT that they may sound a bit different.

The cascode version can run slightly higher rail voltages, but that means more heat.

Doubled up outputs may sound different again, and are best for situations where the load drops below 8 ohms (or whatever ur bias point is...). But matching IS important.

There are some boards that permit both the cascode and the double outputs, or NOT (CViller does...). So you can build with whatever options you want to try, or try them all eventually.

This is where ur layout will count in terms of how easy it is to work on it and change things. You can socket the JFets for example...

I would not think too hard about these things.
Just go ahead an build a version.
Don't make the first version the "final" and fancy one, make it so that the amp works, and get a feel for it before you commit to a fixed package.

Rick built his on wood pieces. Looks like hell, works great!
Maybe the "good chassis" will ruin the sound? Dunno, could happen.

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Old 26th January 2012, 01:23 PM   #105
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Originally Posted by CENTRAL View Post
How does biasing affect the end (aural) result?

If my speakers are expected to be quite of a load, should I push the bias higher?

You need to read the original article again, not the thread. First Watt's article. It explains the biasing.

The short answer is that the biasing is going to vary a small amount around a particular current that sets the amp up for Class A operation.

_-_-bear

Quite of a load? If ur speakers are below a particular Z then this amp is not suitable without extensive modifications, in which case it is not an F5 any longer...
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Old 26th January 2012, 01:28 PM   #106
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Quote:
Originally Posted by bear View Post
You need to read the original article again, not the thread. First Watt's article. It explains the biasing.

The short answer is that the biasing is going to vary a small amount around a particular current that sets the amp up for Class A operation.

_-_-bear

Quite of a load? If ur speakers are below a particular Z then this amp is not suitable without extensive modifications, in which case it is not an F5 any longer...
Could you please tell me where to find the original article?

I think it will handle them ok, they're just not super - easy...

(Spendor S8e)
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Old 26th January 2012, 01:34 PM   #107
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Central,

I think this is what he is referring to.

http://www.firstwatt.com/pdf/prod_f5_man.pdf
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Old 26th January 2012, 01:37 PM   #108
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Originally Posted by KatieandDad View Post
Central,

I think this is what he is referring to.

http://www.firstwatt.com/pdf/prod_f5_man.pdf
Right.

I was thinking the magazine article that I can't find anymore...
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Old 26th January 2012, 01:40 PM   #109
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In the DIY world, playing is the game.

Personally the F5 didn't do it for me, that is MY decision and I opted for the more powerful Aleph 4.

If you think ahead you can build both at minimal loss / wastage.

Buy or build a case that is suitable for both and buy heatsinks that can be added to at a later date.

The only expensive components that cannot be re-used are the transformer(s).

You can build the F5 with 63V caps so that they could be re-used in a more powerful amp.

The only wastage is the PCBs and the components - I'm sure if you are not happy with the F5 you could EASILY sell them here. They only cost about 40 Euros to put together. You'd need to sell the transformers too and increase their voltage but again there are lots of F5 fans that would SNAP them up.
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Old 26th January 2012, 01:42 PM   #110
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Thank you for the tips!
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