Starting a First Watt F3 build and need some help

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#41
Hello all,

I haven't been home yet to tinker with the amp yet but I have been doing some searching on the net for a suitable preamp. I came across this preamp design by Carlos Filipe Machado. The design uses a single 2SK170 JFET per channel and is supposedly capable of powering a 10Kohm input inpedence. Does it sound like a good match? It also runs on a single +46V rail which has me tempted to tap off of the power supply of the F3 clone. Any comments?

http://myweb.tiscali.co.uk/nuukspot/decdun/gainclonepre2.html
 
#42
Hello all. Good news, I decided to switch over to the ZenV9 design as it contained fewer components and was able to get sound out of the completed channel. I have one question though. In the ZenV9 manual it states that the Vds should be set to 2.5V as the third way of selecting R3. Vds is the middle pin of the jfet correct? Is this set at operating temperature or when the amp is first powered up? Thanks.
 
#45
Hello all. I'm back to tinkering with this DIY F3 again. The amp sounds great. I must thank you all for your input thus far. My concern at this point is that I cannot get a stable Vds voltage on the jfet. The voltage runs all over the place. I know that this device is temperature sensitive. Is this necessarily a problem or is this something that is to be expected? I have considered thermally isolating the jfet by giving them each a dedicated heatsink separate from the mosfets. Would this be a good idea or am I worrying too much?

Thanks in advance.
 
#47
It starts at around 3.6V cold and by 15mins I'm down to around 2.9V At 30mins I'm down to 2.7V. Seems most stable after around 2 hours but even then I'm looking at variations of as much as .15V.

Thermoprobe reads a heatsink temp of 50C after about an hour of running.
 
#51
Hello,
Im starting the amp to build as well, I would say Im a total noob on electronics... I have build a few minor amps and now I try this one to be my personal "high end" amp for single driven fullrange speakers.
I have ordered the parts from:
Tech DIY Company Store

Now I have some realy basic questions:
Does the amp need to be started after soldered? Or does he run on first power up?
Did you put any speaker protections in your amps?
Can you recoment me any transformer for European 240v?
 
#52
imagios said:
Hello,
......
Does the amp need to be started after soldered? Or does he run on first power up?
......
Click to expand...

explain exactly what you mean ?

imagios said:
Hello,
......
......
Did you put any speaker protections in your amps?
........
Click to expand...

you don't need SP with F3 - startup is gentle , and it have coupling cap on output , so DC can't reach your speaker .
all you need is some salt between your ears - to prevent overpowering the speaker ...... but that's case with all amps :rofl:


imagios said:
Hello,
......
.....
Can you recoment me any transformer for European 240v?
Click to expand...

I'll pass that one , because I'm not in Europe
 
#58
In a 6 Moons review it made this statement about F4:
"If you've got a low-power SET and want to hear bass, definition and linearity you never knew you could, go humbucker and tie an F4 to its outputs"

As I'm feeling that the F3 is more for my taste.
could I not at a later date, add as above states, a F4 to a F3 if I wanted more volume to drive a wider range of speakers. ?
 
#59
going from 15W/8R to 25W/8R isn't much of progress , taking in account complexity you propose

there is big amount of redundancy , if you realize that Papa meant on tube power amps more in (SS) preamp power category

so - feeding F4 with 3W tube power amp is sane .....
 
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