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Old 15th June 2011, 08:07 AM   #151
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Default temperature and bias

Hello

It takes a while listening to the F5 and it is fantastic. The combination with the B1 is very quiet.

Compared to my usual amp, a Musical Fidelity A308 (dual mono) note that:

- The timbre has improved considerably. The voices I instruments are closer to reality and sound more natural. This is the biggest difference with the A308.

- The scene is a little deeper. The voices sound a little more advanced and instruments have some more "air" between them in the z-axis

- There is more information on "environment." I suppose they had not previously heard harmonics. Some of this has to do with the "fast recovery", right?

- The upper end is softer. With the A308 is very "fluid" and analytical, for some issues and others would rather brilliant.

- The overall sound is warm without being voluptuous.

- The combination b1 + F5 has ZERO noise. the combination b1 + A308 (operating mode amplifier) ​​has a very slight hiss in his ear in twitter.

- The frequency response is very balanced regardless of the level of spl. with the A308 if you pot up the sound became a bit hard and rough, especially the midrange. With f5 does not happen, his gentle nature is constant. I must say that I have enough spl with the F5. The listeners have not risen to -10 dB and always around to -13 db. My speakers have a sensitivity of 90dB and a nominal impedance of 4 ohms, with a minimum of 3.2 ohm.

- The woofer sounds almost the same or I do not see changes, perhaps a tad thinner, but I'm not so sure.

Seeing what F5 has cost me and what in his day was worth the A308 (2850e.) the value for money is unbeatable.

In general, you could say it's a different sound, more natural than "hooked" but to listen. No ear fatigue.


Now I'm trying different bias settings. Currently I have it at 0.65 V but the sink can get very hot, about 53 degrees (room temperature 29 º). The mosfets are working on the 92 th. I think it's too much and I will lower it.


with 0.65 V the bass is round!. Better than the A308. There is a little more soundstage and mid-bass is more "hot."

I would like to have the maximum current without suffering the mosfets. What is an optimum temperature of operation for the mosfet?.

Br

I hope I understand, my English is very bad
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Old 15th June 2011, 11:13 PM   #152
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Hola Alberto

Sorry I did not see this post (busy in the loft) till now
You have PM

As on PM sink at 53 with ambient at 29 is fine and it will be perfect in the winter.

Main worry is the actual mosfets temperature.

Could you measure the mosfets case temperature?
There is a graph on the mosfets data sheet that shows the relation between the case and Junction temperature.

As you I have 4 Homs speakers but with poor 87 dB so half as loud as yours so I went for the best possible cooling I could in order to increase the current.

If you worry about the mosfets temperature there is quite a bit that can be done
Maybe a start would be to use Kerafol red. Loads about this on this tread....

Another thing you could do is to use a small computer fan for when summer proper came and ambient temperature gets up to hi 30.

I have a symple fan controler that works quite well and is made up with the same parts you use on the F5 you can skip the LM317 part if you use 2 12 V fan in series.

Just stick the thermistor to the heat sink and get the fans to start turning slowly at 50 C the hotter the sink get the faster the fans turn.

I will send you same 100 homs for you to try next time i get to Post office (next week).
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Old 20th June 2011, 03:05 PM   #153
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Look like Albetro got the F5 going and got no more time for us.

Hows the holcos sounding?

Just got my copy of Linear Audio and got to read Ed Simons article about resistor distortion.

Realy interesting stuff and so far it look like one be better off getting its own copy before spending to much on Nudes when RN65 do quite well.

This is Instrumentation wise nothing to do with listening impressions.
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Old 22nd June 2011, 06:09 AM   #154
dazed2 is offline dazed2  Canada
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albertob : I've biased mine to about 0.790 V with a rail voltage of about 21.0V
my heatsinks are about 55C and the top of the mosfet is about 65C.

Dunno if that is ok but it seems ro run fine.

I do have a question for those that have built the F5 though.
I was poking around today with the unit off for a day. So in other words the unit is Ice cold. Anyways, I turn it on, and the thermistor just before the transformer is burning hot! Note I only have the CL60 thermistor on the hot line and not the neutral line.
I think its been running like this since the beginning, as I have never reached in to feel the thermistor until today. I have a 2.5A fuse and it hasn't blown since i put the unit together.
Question to you folks out there, is your thermistor hot as well? or am I doing something wrong?
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Old 22nd June 2011, 07:48 AM   #155
Zen Mod is offline Zen Mod  Serbia
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I hope you touched NTC while amp mains cable is disconnected ;

in contrary - it's nice have you still around to type silly questions .

NTC working temperature is hot - it's resistance , with current flowing through ; that's the reason why you see them in pro gear with long extended and isolated leads , or mounted on ceramic holders
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Old 22nd June 2011, 08:01 AM   #156
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I replaced the insulating sil-pad of the mosfet. I placed mica and thermal grease. What a difference!

The sinks are now over 54 º and 63-64 º MOSFET. Silpad I have not worked well. I have now biased at 0.65 V.

I have not placed the resistors Holco kindly offered me BK. When the place I will post my impressions.

regards

AL
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Old 22nd June 2011, 11:50 AM   #157
6L6 is offline 6L6  United States
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Yes, the CL-60 thermistors get hot.
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Old 22nd June 2011, 04:34 PM   #158
Cassiel is offline Cassiel  Libya
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Quote:
I placed mica and thermal grease.
Hi albertob, this is Alvaro (another Spanish guy ) I was going to use only mica but after reading this.... A couple of questions: where did you get the CL-60 (clueless faces in a big electronic store when I asked for a thermistor), is it Ok if I use a resistor from ground to chassis ground? and what type of wire did you use from the mosfets to the PCB board? My construction technique is similar to yours.
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Old 22nd June 2011, 05:19 PM   #159
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Did we had conversation about Thermistors before
Yours truly uses ceramic purpose made posh insulators and or Glass beads from her theater jelwery box

Please do not tell.
A yess main thing leave thermistor leads long and be prepared to resolder in 6 months time.


Ok Nice to get Alberto back on

And most gougeous F5 monoblocks up and running properly.

Did Uncle Zen give him a fugly?
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Old 22nd June 2011, 05:47 PM   #160
Cassiel is offline Cassiel  Libya
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Just to clarify: I have a ZETEX ZRA6045F in the PS. I only "need" the CL-60 fron PS to chassis ground. I was hoping to finish this beast before weekend - I don't want to order one. Can I use a resistor instead?

* Not in the best mood for silly jokes. Damn, I hate chassis work.
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