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Old 21st November 2010, 07:27 AM   #9201
cviller is offline cviller  Denmark
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If you are using the drawings to measure something during your build, I will recommend using one of these drawings (letter and a4):

http://viller.eu/audio/2009jan_gbf5/...ntassembly.pdf
http://viller.eu/audio/2009jan_gbf5/...ntassembly.pdf
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Old 21st November 2010, 12:25 PM   #9202
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Thanks.

Do you happen to have anything with dimensions on it? I'm going to transfer it right to a cad drawing.
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Old 21st November 2010, 12:28 PM   #9203
cviller is offline cviller  Denmark
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The size is 10x5cm
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Old 22nd November 2010, 01:55 PM   #9204
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Has anyone come across an illuminated switch for the F5 with 2 led outputs?

I was hoping I could find a switch that would allow me to light up 2 sides of it, independently from the power. I'd just connect the led outputs from the output boards to each side of the switch (instead of drilling out additional holes for them on the front panel of the chassis).
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Old 22nd November 2010, 08:22 PM   #9205
frags is offline frags  Canada
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I've just finished building first channel of my F5. During the test phase I observed the following:
1. It tends to oscillate (about 1MHz) with high capacitive load even if no input signal is provided (0.33uF used and input shorten to the ground).
2. It tends to oscillate with square input signal with fast rise/fall times (100ns, 4Vpp input signal) . As well with such sharp square signal it gets significant overshoot if 2Vpp signal is given for example.

So, to solve these problems I've added 150pF capacitor from JFET gates to the ground.
No overshooting and oscillations and the bandwidth did not reduce for listening purposes.
Adding more values in gate-stoppers did not help at all.

Any comments?

Last edited by frags; 22nd November 2010 at 08:24 PM.
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Old 22nd November 2010, 09:31 PM   #9206
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I think it's public knowledge that you don't hook a capacitor
directly across the F5 outputs.

If you wish to tame your square wave response and you are
willing to introduce a capacitor to the circuit, the best place
is across the 50 ohm (two parallel 100 ohm) feedback resistors.

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Old 22nd November 2010, 10:24 PM   #9207
frags is offline frags  Canada
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Thank you, Mr. Pass.
But my second test (an oscillation and overshooting with fast rise/fall square signal - 1kHz, 100ns edges) was done w/o any capacitive load (only 8Ohm resistor).
You said that adding a few pF capacitor to JFET gates would solve the overshooting issues, but it looks like it was not enough (typical JFET input capacitance is about 100pF at zero Vgs).

Last edited by frags; 22nd November 2010 at 10:27 PM.
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Old 23rd November 2010, 12:25 AM   #9208
nar is offline nar
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Quote:
Originally Posted by frags View Post
Thank you, Mr. Pass.
But my second test (an oscillation and overshooting with fast rise/fall square signal - 1kHz, 100ns edges) was done w/o any capacitive load (only 8Ohm resistor).
You said that adding a few pF capacitor to JFET gates would solve the overshooting issues, but it looks like it was not enough (typical JFET input capacitance is about 100pF at zero Vgs).
As a cure for oscillation problems, you could also add some series resistance with the gates of the jfets - Q1/Q2 - (100 to 221 R for example) and try to get higher resistor values for R13 - R14 (maybe 100 / 221 and perhaps as high as 1k, with tradeoff regarding absolute bandwidth)

Hope this helps

nAr
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Old 23rd November 2010, 12:43 AM   #9209
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Installing small decouping electrolytics on the board rails can also lead to oscillations.
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Old 23rd November 2010, 01:31 AM   #9210
frags is offline frags  Canada
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nAr,

I'll try JFET gate resistors on my second channel. Increasing R13-R14 (330Ohm) value did not help at all.
Looks like the source of oscillation is JFETs, not MOSFETs. The oscillation happened only with high level square signal with sharp edges.
Anyway, adding 150pF capacitor to JFET gates cured the problem.

bobodioulasso,
I have no decouping electrolytics on the board rails.

Thank you, guys.

Last edited by frags; 23rd November 2010 at 01:35 AM.
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