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Old 7th April 2013, 05:34 PM   #13051
bcmbob is offline bcmbob  United States
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Old 7th April 2013, 06:02 PM   #13052
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I find that the bias voltage tends to rise once the case is all buttoned up. I'd set it to 5.7 or so, then check it after running closed up for an hour.
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Old 7th April 2013, 06:33 PM   #13053
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Old 7th April 2013, 11:26 PM   #13054
Rixsta is offline Rixsta  United Kingdom
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Quote:
Originally Posted by jackinnj View Post
There's a voltage map on the original article --

WRT the feedback resistors -- if you want to vary the feedback you'll need a dual potentiometer of at least 6 watt rating -- unless the potentiometers track perfectly you will need to check the bias and DC offset.
How spot on a comment, so if it did vary DC offset a little could this cause the amp to go to hell ? thanks.
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Old 7th April 2013, 11:43 PM   #13055
Rixsta is offline Rixsta  United Kingdom
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couple more pics of my first F5 Build which was for friend but i was sure i could build it well and well its lasted over 7 months now with no problems, he even left it on for 3 days permanently.
I did under bias but only slightly, i expect its atleast 90% of full bias



It lives at my friends house at the moment but will get it back one day.
Lucky he has Rogers speakers! and audiolab pre-amp which he says sounds nice with it

DSCF1455.jpg

DSCF1453.jpg

DSCF1452.jpg
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Old 8th April 2013, 12:07 AM   #13056
bcmbob is offline bcmbob  United States
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Quote:
Originally Posted by Rixsta View Post
...........and audiolab pre-amp which he says sounds nice with it ]
You are reading my mind. I was just pondering adding one of a couple preamps I have to the new F5. So far I've just used the S/PDIF feed from a computer through a DAC. Are there any precautions, limitations or special considerations for pres with this design ?
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Old 8th April 2013, 12:13 AM   #13057
Rixsta is offline Rixsta  United Kingdom
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Hi bcmbob, someone here should be able to answer that!


I did make a Zen v4 before this and i think it sounded wonderful, i think a made a couple of errors with it tho and it blew up 3 times over few years so on the 3rd fry up i gave up, i presume it was oscillating, what do you guys recon ?

1: Power supply Transformer and caps were in a separate box with 3 pin power lead about a meter long to the amp.

2: leads to mosfets from the board were 4-6" long (probably the worst offender) and if i moved the wires in certain positions hum/noise would come thru the speakers.

3: I built it on Prototyping board although i doubt that's the error as i probably checked my wiring million times.

But to sum up and compare Zen4 to F5 well hmm id have to hear both on the same setup. but its a close one for sure.
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Last edited by Rixsta; 8th April 2013 at 12:20 AM.
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Old 8th April 2013, 12:18 AM   #13058
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there are few threads with F5 and preamplifier in title
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Old 8th April 2013, 12:57 AM   #13059
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Found a few. Thanks for the tip.
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Old 8th April 2013, 12:07 PM   #13060
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Rixsta View Post
Thanks, we have added RF filtering now in the IEC

Thanks Rade95. yes will be adding a bit more than the original PSU capacitance.

Iv'e been thinking about something, is it possible to have a variable resistor with the original feedback resistor so to be able to vary the amount of feedback of the amp ? i like this kind of idea as in theory you could instantly tell the difference. and also if you had not enough volume you could lower the feedback for an extra boost, all be it with perhaps a sonic difference+ more distortion.

I once did this to a B&O beomaster 2400 i think, was quite interesting!
I am surprised no Member replied to this.

RF filtering and DC blocking is on the signal input to the amplifier.
You can also fit RF filtering and DC blocking to the Power input of the amplifier.
These two locations are quite different and require different solutions.

Varying the amplifier gain by changing the feedback also changes the stability margins.
Generally increasing the gain decreases the feedback and this leads to an increase in the stability margins.

Going in the opposite direction and trying to reduce the gain is what can end up with a blown amplifier.

I suspect Pass determined the lowest gain the F5 could be used at, without needing separate compensation components when built using his recommendations.

Increasing the stability margins by increasing the gain can lead to a "flat" sounding amplifier. But since this is a PASS design I suspect there are a range of acceptable gain settings that all sound good.
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