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Old 26th September 2009, 10:19 PM   #5011
fritz39 is offline fritz39  United States
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Default F5 on higher voltage?

I've seen lots of debate about the power rating of the transformer for the F5 and I know the right answer is 18V-18V at >300VA.
But has anyone tried a higher voltage? I have a nice big 25V-25V I would like to try.
Thanks.
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Old 26th September 2009, 10:27 PM   #5012
tinitus is offline tinitus  Europe
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And I was thinking about 15V trafos, with raised bias

Wasnt there something with input driver stage being at the limit with the original supply

Last edited by tinitus; 26th September 2009 at 10:32 PM.
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Old 26th September 2009, 11:29 PM   #5013
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I have simulated the circuit with +/- 35 Volt rails, and it runs quite happily.
However you have about 280mW dissipating through each Jfet. I have no idea how long these devices would last, at that level of power dissipation.
The data sheet says they are rated for 400mW maximium each.

Just one more thing I hope you a have a preamp with enough gain to make use of the extra voltage headroom.
Also, you will need bigger heatsinks if you want to maintain the same level of bias current.

If you are prepared to experiment and blow a few jfets, then give it a go.

Last edited by Melon Head; 26th September 2009 at 11:57 PM.
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Old 26th September 2009, 11:38 PM   #5014
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by ichiban View Post
I'm wondering if the F5 would be up to the task of driving Strathearns
one half ohm resistance if the amp only high passed 300-500 Hz ?
First order input filter on F5.

Anybody?
ya teasing as , right ?
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Old 26th September 2009, 11:53 PM   #5015
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Quote:
Originally Posted by thanh1973 View Post
Just one more thing I hope you a have a preamp with enough gain to make use of the extra voltage headroom.
You can always build SY's ImPasse preamplifer which was designed for bridged F4's.

The gain of the F5 can be tweaked up -- I did this when I used lateral mosfets.
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Old 27th September 2009, 12:01 AM   #5016
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So someone got this working with lateral mosfets.
How does it sound?
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Old 27th September 2009, 01:58 AM   #5017
ichiban is offline ichiban  United States
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Quote:
Originally Posted by Zen Mod View Post
ya teasing as , right ?
No, I am not. My thought is at that xvr point and above the
F5 would not be required to output a lot of power, yes/no?

The N.Pass F5 article states
"It will drive a 2 ohm load without burping, and 1 ohm without misbehaving."

Now that would be full range.

If not, then a paralleled set of outputs, or an X'd F5?
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Old 27th September 2009, 03:21 AM   #5018
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Hi ichiban,

I've been lurking here while I start to collect my F5 bits, but your post causes me to write. Have you heard of using autotransformers for speaker impedance matching? Your Stratherns might be well served with these:

http://www.zeroimpedance.com/Zero-New.html

Regards,
John
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Old 27th September 2009, 03:37 AM   #5019
ichiban is offline ichiban  United States
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Quote:
Originally Posted by nerdorama View Post
Hi ichiban,

I've been lurking here while I start to collect my F5 bits, but your post causes me to write. Have you heard of using autotransformers for speaker impedance matching? Your Stratherns might be well served with these:

http://www.zeroimpedance.com/Zero-New.html

Regards,
John
Thanks for the reply. I use the torroidial transformer that came with the Strats for matching to 4 8 16 ohm amp outputs. However, I've read that a direct amp feed, if the amp is up to it, results in better sound. As I recall the Eagle? & the big Thresholds and Krells were said to be up to the current, pun intended, task at hand.
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Old 27th September 2009, 09:56 AM   #5020
AndrewT is offline AndrewT  Scotland
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Originally Posted by ichiban View Post
As I recall the Eagle? & the big Thresholds and Krells were said to be up to the current, pun intended, task at hand.
do they all have multi-paralleled output stages?
I know the Krells have.
The F5 is a single pair.
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