F5 power amplifier

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#9,301
uvellani said:
Use several RC stages. 0.5 ohm will drop about 1 volt or so. You will need 7-8 of them on each rail. And the resistors will need to be rated 10W or higher. But then all this will probably end up costing the same as a new transformer.
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I have found a variety of these 10+W surplus and from less than a dollar a piece for ceramic case and up to $5 for metal case resistors.

Did you recommend .5 ohm so that the heat dissipation is spread out? There are higher values, like you didn't know, and my guess is they are getting some serious strain turning volts into heat.

Does it make a difference if they are ceramic or wire wound, ect. for this purpose?

It is getting cold and having a nice hot amp at my "sounds" appealing. Especially, while I puzzle out the very cool and complex options that have also been offered.
 
#9,306
My F5

My first F5 up & playing ;-)
PSU type "Sjøstrøm-overkill-pcb" filled with 4 x 47 000 + 4 x 56 000uF + 2x18V -1000VA-trafo
Maybe it does make a difference, as I think it sounds surprisingly strong on not so efficient speakers, with good bass-punch.

Arne K
 

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#9,308
Costly to fill, but worth it.
I used som time to figure out the bias-adjustment, the 2 pots did react quite different.
Running 1,5A now, heatsinks are warm, but not @£$# hot, and I can hold my finger on the mounting-washer for several seconds...(they are %£$# hot).
Chassi used to be a NAD 208

Arne K
 

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#9,309
brucegseidner said:
I was able to pick up a couple Stonehenge size toroidal transformers rated at 500VAC but they have 24v+24v windings. Being of little brain, but knowing that once through the bridge rectifiers, I will be over voltage for the F5, I need direction on how to reduce the voltage to the spiffy blue boards I am set on assembling.

My question is, short of buying 18v+18v transformers, what are some straight forward ways that some kind soul would draw out and I would build. I can solder well, am very handy in a shop and I can read schematics. But mostly I love to listen to music. I have read that "voltage regulation" is not critical for the F5 but frying it with too much juice is likely an important consideration none the less.

I have been reading about linear voltage regulators and they seem pretty straight forward. Is this the way to go and if it is what unit would be most appropriate for my F5 power supply?

Thanking you in advance.
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No need to drop voltage.
Have you considered cascoding front end?
Very easy to do.
 
#9,310
Melon Head said:
No need to drop voltage.
Have you considered cascoding front end?
Very easy to do.
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Is this done with skates? I have really enjoyed ice cascodes when they have come to town. But the sound in those hockey rinks is not great.

Cavemen, like myself, really relate to Beauty and the Beast. Little Mermaid I can do without.

I may not be on the right cave wall. A brief definition and an example would really help. My guess is that this is a popular modification of the F5 which I will explore and thank you for suggesting, cave man humor, notwithstanding.
 
#9,311
You're approaching 30 volt rails, but you can drop a
couple volts off with a CRC power supply filter.

With 0.4 w dissipation max, keep the Jfet current
at 10 mA or below, and from my testing you will see
actual breakdown up around 43 volts, so it probably
won't break.

😎
 
#9,317
brucegseidner said:
What are the dimensions of this handsome beast?
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External: 400x300x100mm (w/o feet)
Internal: 300x300mm

More details:
18+18V 400W transformer
77000uF caps per rail (154000uF total)
I use resistor pairs for R11 and R12 - one 3W resistor is obviously not enough.
temperature is about 50C at FET cases with standard 1.3A bias and 45C with reduced 1A bias (i'm using reduced one becasue the amp will have a shelf on top of it and i need only 3-4W for normal listening)
2x16A relays in protection modules
less than 1mV DC at outputs
 
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