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F5 Turbo Builders Thread
F5 Turbo Builders Thread
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Old 2nd March 2020, 02:59 PM   #5941
BigE is online now BigE  Canada
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Quote:
Originally Posted by Zen Mod View Post
nope

if we are thinking about same cap
Thanks Zen Mod!

That would be C3/C4 with value around 1nF.

I will add it to the boards before continuing.

( Need to complete some other work tonight, then back the F5T -- I did a massive rewiring job on it.... for the better???? we'll see. ).
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Old 3rd March 2020, 06:43 PM   #5942
takitaj is offline takitaj  United States
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BigE, there's probably no need but I put 1nf into all 4 boards (C3/C4). I did it as extra insurance against oscillation. (I sleep better) One nf or two isn't going to reduce the bandwidth any appreciable amount. Sleep is important!

TJ
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Old 10th March 2020, 02:28 PM   #5943
BigE is online now BigE  Canada
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Quote:
Originally Posted by takitaj View Post
BigE, there's probably no need but I put 1nf into all 4 boards (C3/C4). I did it as extra insurance against oscillation. (I sleep better) One nf or two isn't going to reduce the bandwidth any appreciable amount. Sleep is important!

TJ
I shall do this shortly. At the moment, I am embroiled with getting an active speaker system equalized -- and adding a tweeter. It's a bit slow going.

As you wrote earlier: I wouldn't worry too much about the 100R from emitter to drain either, unless you find you have an oscillation issue and it can't be resolved by increasing C3 & C4 or increasing output gate stoppers.

Right now, they are the standard 47.5 ohm. What value would you suggest? Would adding a very small inductor help to block the oscillatory frequencies?

When I fire this up next, I will take a look at the outputs on a scope to ensure that there actually is *some* oscillation. I should be able to see something. Recall, oscillation is suspected because the biasing output offset is very different with and without shorting plugs in place. ( Some 300 mV ).

Last edited by BigE; 10th March 2020 at 02:37 PM.
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Old 2nd April 2020, 08:37 PM   #5944
shawnra is offline shawnra  Canada
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I recently bought F5 turbo pcb's (DIY Audio genuine) from someone, they are un-populated. When I got the boards I realized that I have 3 p channel boards and 1 n channel boards. I'm guessing this is irrelevant and that I can just change a p channel into an n channel and make sure the supply voltages and arranged appropriately.

I'm I correct?
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Old 3rd April 2020, 02:07 PM   #5945
Maciej is offline Maciej  Poland
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F5 Turbo Builders Thread
Routing around MUR diodes is not the same due to different polarisation. GND goes to their outer pins on N-board, while on P-board it's connected to pin in the middle.

I had similar issue - got 3 N and 1 P board. Diyaudiostore.com sent me replacement for free.
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Old 3rd April 2020, 09:09 PM   #5946
AudioSan is offline AudioSan  Norway
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It is correct that the P ch and N ch can not be switched. How ever. The pinout differnce is at positive and negative voltage. Not GND.
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Old 5th April 2020, 05:43 AM   #5947
Maciej is offline Maciej  Poland
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You are right AudioSan. Thanks for correcting this.
I need better glasses .
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Old 5th April 2020, 10:21 PM   #5948
shawnra is offline shawnra  Canada
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Thanks for your input. I sliced and spliced and now the P channel diodes are orientated correctly for N channel use.

I doubt DIY Store would send me a new one as I did not buy it direct from there but from someone who bought these 5 or 6 years ago.

It'll do.
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Old 12th April 2020, 05:11 PM   #5949
BigE is online now BigE  Canada
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In trying to finish this, I've run up against a problem... VAC on the positive rail.

The amp power has been *completely* rewired since last year.

Circuit changes: Tea Bag's power supply boards have has the snubber resistors and caps added. Transformer snubbers were removed. The bleeder resistors on the power supply work.

The transfomer secondaries are 30-0-30, with rails at +41.5 and -41.5 VDC.

However, reading with an ohm meter shows that there is 91.5 VAC on the positive rail! 0 on the negative.

There are no shorts from the diodes to the case. I even replaced with MICA insulators to test. Only the right channel is powered, the input and output boards are not connected. ( Thank goodness. )

I cannot imagine what can be causing this. This is true whether or not the 0 volt line on the secondary is connected to the ground lift. ( The way I read the power supply schematic, the ground lift diode bridge/CL-60 creates the audio ground. )

Does anyone have an idea where I can look? I'm a bit nervous about turning it on.

Last edited by BigE; 12th April 2020 at 05:29 PM.
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Old 12th April 2020, 06:03 PM   #5950
thompsontechs is offline thompsontechs  United States
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Dude that sounds like a mains through a resistor or something. Wait for the other guys....
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Last edited by thompsontechs; 12th April 2020 at 06:13 PM.
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