F5 power amplifier

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#2,424
Nelson Pass said:
That is our own member Jackinnj. I regard him as trustworthy.

😎
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TNX,

I have had to raise some prices -- I am out of my OLD stock on the IRF/Vishay HEXFET's -- and since Vishay took over IRF's discrete products the prices have really shot up. (Pretty unbelievable if you look at the bomb Intel laid on the market, but discretes is discretes.)

I think 1 shipment may have gone astray over Christmas -- have been away for 2 wks.
 
#2,425
Just got done reading through.....a second time. If we remove TH1/2, does R15/16 need to be removed as well? A builder in this thread somewhere removed the thermistors, and put 5.6K for the resistors and jumped TH1/2. Is this correct?

For the inevitable water cooled version, is there a limit to P1,P2 adjustability to increase bias in its stock form. Does the value need to change to offer larger window? Does the source resistance need to be changed as well? Or will just changing R11/12 to 0.33 allow for proper adjustment?

I ask because it wasn't clearly defined, if it was, I apologize.🙂



-john
 
#2,426
You can just remove the thermistors (you'll just need to adjust P1/P2 accordingly). R16 and R15 won't do anything if the thermistors are not there too.

When I fired up my F5 for the first time I was too lazy to adjust the P1/P2, and something started smoking very fast. Luckily nothing burned, so the amp was fine when I turned down the current. But you should easily be able to double the current just by adjusting the potmeters.

Why don't you want to remove the thermistors?
 
#2,429
Awesome! Thanks for the heads up. I know that when i had emailed Colin Pass about it, he said they hope to be able to offer the F5 boards with matched fets as well (like they are doing with the B1). I'm in no rush to build the F5, the B1 comes first (waiting for the next batch of pcbs), but I was just curious if pass diy would still be selling boards, especially with the group buys and such.

-Justin
 
#2,434
Reuse Transformers?

Sorry for the newb question...

I've got a Zen V4 built which uses a single rail power supply - each channel with a 300VA transformers, each with dual 18V secondary windings. When I built it, I assumed that if I were to build another amp, I'd just get new transformers, but now the cost savings of re-using the transformers looks too tempting.

The problem is that the Zen V4 used the secondary windings in series to give 36VAC, so I trimmed the unnecessary leads really short and then soldered them together. So my question: if I'm to reuse the transformers for the F5, can I use a power supply with just one rectifier bridge like the Zen V4? It would seem that using dual bridges with the windings in parallel gives 2*25VDC = 50VDC, or one bridge with the windings in series would give simply 50VDC. Am I missing something? Er, rather... what is it that I'm missing? 🙂

If I can't use just one bridge, I'd have to unsolder the tied together leads and take the odd step of extending them. oi - heatshrink, I guess.

-j
 
#2,436
Single bridge is ok, but you'd need a center tapped transformer. If you paralleled the secondaries into a single bridge, you'd have + and Gnd, not a dual rail supply.
 

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#2,440
i finished my f5 few days ago.
It was pretty easy to ajust the both sides to 0,6V voltage drop at the source resistors and to almost zero offset.
But:i have a voltage drop on R3/4 for about 4,9V and 5,1 V instead of the recommended (or better: expected) 4,2 Volts.

Still no sweat, or anything unhealthy in that nice little amp?

stefan
 
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