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Old 23rd June 2013, 11:21 AM   #3641
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Soon enough.
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Old 23rd June 2013, 11:55 AM   #3642
evanc is offline evanc  United States
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Nice looking boards buzz.....
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Old 23rd June 2013, 11:58 AM   #3643
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buzzboards ......

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Old 23rd June 2013, 12:00 PM   #3644
6L6 is offline 6L6  United States
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Buzz - how long are the boards, and can you daisy-chain them if you want more output devices?
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Old 23rd June 2013, 12:05 PM   #3645
evanc is offline evanc  United States
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The output stage is so simple it doesn't seem too bad to build ptp
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Old 25th June 2013, 04:44 PM   #3646
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Quote:
Originally Posted by Navyblue View Post
I replaced the TL431, but it doesn't help.

Since then I tried a lot of stuffs, and finally be able to narrow down the problem, which is at C1. Here are the gist.

- The reason that the DC fluctuation at output symptom is voltage across TL431 isn't as still as it can be.
- When I soldered a 220F electrolytic capacitor at C1, the problem appears.
- Replacing the 220F electrolytic capacitor does not solve the problem.
- Soldering a 47F film cap largely solved the problem, but soldering 220F electrolytic capacitor on it brings the problem back.
- If I connect the 220F electrolytic capacitor through wire with alligator clips, the problem disappears.
- If I clip the leads of the 220F electrolytic capacitor directly without the wire, the problem came back.

So I thought, may be I need the resirtance of the wire. So I tried adding a resistor (1Ω, 5Ω and 22Ω). If I clip the resistor leads directly, the problem remains. If I connect the resistor through wire with alligator clips, the problem disappear.

Why is it that the wire with alligator clips seems to posses magical property? Any ideas?
Btw, just for reference, I think I found the cause of the problem.

As mentioned I did everything that I can imagine around the TL431 with no luck. I got stuck and one thing lead to another, I neglected this project. Then one day I got an epiphany, and true enough the wildish voltage fluctuation went away when the 2SK170 is disconnected. So it's probably fried.
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Old 1st July 2013, 02:12 PM   #3647
pdyn is offline pdyn  Poland
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I've just buid F4. I have some questions:
1. Why C1 i C2 is so big?
2. Can I change JFet N+P Follower with only N+N-fet follower (re-design circuit)?
3. can i drive irfp power follower with BLS Pre, without j-fet follower (re-design circuit) ?
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Old 1st July 2013, 02:24 PM   #3648
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Sorry. missed some questions. These boars are 6" long. THey will allow a bias at my chosen point of .5a/fet for total of 1.5a Iq. The SE bias will be about 1/10th of that. With a bridged amp , we are talking something like 30W class a into 8R, similar to the Firstwatt series. This is mainly a test of the Se bias concept as well as the FE boards that will be pushing it along. AB power will be higher due to available rail voltage. On my expected set of speakers, this will be an exuberant amount of power. That being said i may use more fets in the end.
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Old 1st July 2013, 02:33 PM   #3649
6L6 is offline 6L6  United States
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PDYN -

1) So the AC component (the music signal) moving across the cap is very small, and the cap stays almost completely charged at all times.

2) Yes, you could, but as you say, it would be a re-design of the circuit and hold no resemblance to an F4 at all. Look at the Burning-amp 1 or BA-2 Single-ended output stage for ideas.

3) Yes, you can use the output from a Balanced linestage, and without the input buffer. The F4 was designed to be used as a bridge monoblock when driven through it's balanced input. It will give 100W into 8ohm this way.

You might as well keep the input buffer in the circuit, it's sonically invisible, and acts as a impedance matching circuit, letting the output stage operate optimally.
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Old 29th July 2013, 02:21 PM   #3650
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So does this mean that there is no effect of the electrolytics on the sound?

Last edited by valvesound; 29th July 2013 at 02:23 PM.
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