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Old 18th September 2011, 01:10 PM   #11021
udailey is offline udailey  United States
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Davidd, your Heatsinks will cool better on their side. This allows airflow across the fins which is not happening right now .
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Old 18th September 2011, 01:13 PM   #11022
udailey is offline udailey  United States
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Originally Posted by kacernator View Post
So I want to have lower bias because of lower heat - thus class AB operation. I do not need more power (I am fine with 30W-50W into 8 ohms), but I need to lower the distortion in class AB mode(bias). How can I do that if I do not want global feedback from output back to preamp? Thats why I was thinking adding additional gainstage between preamp and buffer and making close loop of NFB within buffer and added middle gain stage - F5. Can it be done to lower closed loop gain of F5 - thus increasing NFB to say 5db or better to unity-gain without stability problems and lowering the overall distortion in lower bias mode?

I am not an electrical engineer, just had this idea.

Thanks.
you know that the f5 is only a 25 watt amplifier right ?
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Old 18th September 2011, 01:47 PM   #11023
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Originally Posted by udailey View Post
you know that the f5 is only a 25 watt amplifier right ?
Yes, but you probably didnt understand me.
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Old 18th September 2011, 04:38 PM   #11024
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Originally Posted by udailey View Post
Davidd, your Heatsinks will cool better on their side. This allows airflow across the fins which is not happening right now .
Darn...... I should have done my heatsinks like David did...... gives me a place to keep my cup of coffee hot...... or maybe cook my "Hot Pockets" for breakfast......

Nice job on the construction......!
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Old 18th September 2011, 09:40 PM   #11025
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Davidsailor.

Must say realy nice build.

I was wondering if you are using diode bridges like the one I have (PB3509 in my build)
those tend to get hotter than standard square block and may need a bit of heath sink.
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Old 18th September 2011, 11:14 PM   #11026
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Default F5 Monoblocks

The horizontal heatsinks work fine and you can leave the palm of your hand on them for as long as you like (so coffee would be tepid). They are Conrad MF35 151.5 types rated at 0.21 degree C/W. As an afterthought I may drill some holes in the side plates to let some air get in and out just to keep the electros happy although the whole case acts as a heat dissipator anyway. They are 105 degree type caps.

The bridge rectifiers are GBJ2004 types, 400V @ 20A's and there is one bridge used on each rail. They are no warmer than the surrounding components.

I forgot to mention in my original post that I have a WIMA 10uf on each rail as well. They seemed to give a little more dynamics to the mids and high frequencies. Buoyed with that success I have ordered 48 PETP 22uf Russian caps and will put 12 on each rail (hopefully they will all fit). Whatever they do, I'm sure it won't be bad.

I listened to a CD last night "Bits, Bytes @ Pipes" produced by Organ Grinder Recordings. This CD features the Wurlitzer at the Organ Grinder Restaurant in Portland, Oregon. Track 13, Warsaw Concerto, has bass extension almost to DC whilst still pushing out plenty of higher pitched instruments at the same time. There was absolutely no sign of the highs being squeezed out by the low notes. My osborn speakers feature 4 x 13" Focal drivers at 92db efficiency so it goes without saying that the listening experience was awsome. Sorry to rabbit on so much but I love the F5's.

David.
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Old 18th September 2011, 11:42 PM   #11027
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Aaahhh..... tepid--that's just how I like my coffee....!

Kidding aside, I'm running the same Conrad heatsinks in my amp, with the fins running vertically. If I have any problems, it's that my heatsinks (and therefore, probably the MOSFETs) are running too cool.

(I would, though, put some ventilation holes in the cabinet, to give the internal components a little air....)

Ken
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Old 18th September 2011, 11:56 PM   #11028
6L6 is offline 6L6  United States
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David - Beautiful build! Very attractive. I'm glad that you are pleased with the sound.
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Old 19th September 2011, 01:43 AM   #11029
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Quote:
Originally Posted by daviddsailor View Post
The horizontal heatsinks work fine and you can leave the palm of your hand on them for as long as you like (so coffee would be tepid). They are Conrad MF35 151.5 types rated at 0.21 degree C/W.

David.
Hi David

I am plan to build one , still collecting parts , if I use half of the heat sink ( ie MF35-75 ) can you imagine how hot it is , may be not too bad for Sydney summer , or may be I should go for MF35-100 , my space in the rack is limited

Very nice built David .

Regrads
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Old 19th September 2011, 01:49 AM   #11030
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Originally Posted by Meganinja View Post
Hi David

or may be I should go for MF35-100 , my space in the rack is limited
The issue might be then: not, how hot it is in the room--but rather, how hot is it in your limited rack space?
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