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Old 12th October 2013, 03:00 PM   #13391
labjr is offline labjr  United States
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Quote:
Originally Posted by BobEllis View Post
The boards from the store's last batch include P3 right next to the input jfets and the thermistors connect between Q5 Source and R12 as shown in the article. Not sure when this was incorporated.
Still shows Rev. 2.0 in the store?
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Old 12th October 2013, 03:35 PM   #13392
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My output boards are V3.0, front end V2.2. I guess Jason needs to update the store's page.
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Old 12th October 2013, 03:41 PM   #13393
labjr is offline labjr  United States
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Quote:
Originally Posted by BobEllis View Post
My output boards are V3.0, front end V2.2. I guess Jason needs to update the store's page.
The F5 is only one board. Are you referring to the turbo boards?
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Old 12th October 2013, 04:19 PM   #13394
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Oops, I am looking at F5T boards. Sorry about that.
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Old 12th October 2013, 04:32 PM   #13395
gk7 is offline gk7
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Yes I meant the "normal" (not turbo) boards, there seems to be no P3 and the the
thermistor arrangement I cannot deduce from the photo.
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Old 28th October 2013, 11:41 PM   #13396
Corpius is online now Corpius  Netherlands
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Today I finally hooked up the amplifier boards to the power supply. Biased both channels without any problems. I kept them powered for an hour or so and re-adjusted the bias. That's when I noticed the transformer humming a bit. I tried swapping hot and cold because that was the easiest thing to try. Any ideas how to get rid of it? I'm using a 300W (Amplimo) transformer. Maybe the F5 is just a bit too much for a 300W transformer, because there was no audible hum when I had just one channel connected.
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Last edited by Corpius; 28th October 2013 at 11:45 PM.
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Old 28th October 2013, 11:58 PM   #13397
crcook is offline crcook  United States
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I'm running a 300va 16volt transformer and no humming problems. Check the mounting...
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Old 29th October 2013, 05:49 AM   #13398
WalterW is offline WalterW  Netherlands
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Quote:
Originally Posted by Corpius View Post
Today I finally hooked up the amplifier boards to the power supply. Biased both channels without any problems. I kept them powered for an hour or so and re-adjusted the bias. That's when I noticed the transformer humming a bit. I tried swapping hot and cold because that was the easiest thing to try. Any ideas how to get rid of it? I'm using a 300W (Amplimo) transformer. Maybe the F5 is just a bit too much for a 300W transformer, because there was no audible hum when I had just one channel connected.
Probably DC in your mains 230V....
I had the same problem with Amplimo transformers. Read this: Mains DC and Transformers

I build figure 8 in a separate box and no more hum.

Walter
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Old 29th October 2013, 11:13 AM   #13399
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my guess is, a little loose windings. 300VA is on the minimum side. and the chances for humming caused by loose windings is greater.
i dont belive its DC. then it would hum with only one ch too.
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Old 29th October 2013, 05:31 PM   #13400
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Hello again,

I'm slowly starting to develop the project of building a F5 in my head. I've already come across several problems, some of which I can't seem to solve by reading up on them. I've read the article about grounding by Dave Davenport and did not quite get it. I have huge problems understanding his diagrams.

I understand that for satefy reasons I have to connect the chassis to earth. I've planned on using the schematics for the "First Watt PS 0 R1 Power Supply" which is found in the F5 pdf. Why is the power ground connected to earth and why is a thermistor between them? How do I connect the grounds of the amplifier circuit and the input signal to that ground - a simple wire? I want to have the PS and amp in seperate boxes and since the thermistor between earth/chassis and ground seems to indicate a potential difference between the two I'm wondering if i need to connect both ground and earth with 2 seperate wires to the 2nd box, one going to the chassis and the other going to the ground of the amp circuit.
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