Cascoded F5

[thor61]

Hello Everyone : I just purchased a set of the Cascoded F5 pcb's. Please advise me as to how to construct this amplifier ! Any help would be greatly appreciated !

 

[Russellc]

Hello Everyone : I just purchased a set of the Cascoded F5 pcb's. Please advise me as to how to construct this amplifier ! Any help would be greatly appreciated !

Where did you get them from? That's where you should start. If from the DIY store, check Civler's blog explaining them.

Russellc

 

[Russellc]

http://www.diyaudio.com/forums/blogs/cviller/191-gb-f5-guide-pcb-version-2.html

 

[Andersonix]

Start with selecting the heat sinks and work backward from there.

 

[tinitus]

no, first get hold of all transistors
and make sure they are genuine
too many frauds around

 

[AudioSan]

where to start depends on what is most important to you.
but in any way. you need the genuine J-fets. h_a and spencer on this forum can help with that.
next is price, power, size, heat.

 

[Andersonix]

I was trying to be too clever: All else falls into place once the HS are selected, because to choose a HS, one must first have decided power output, number of output devices, and bias point, which combined decide the PS size. Also, the HS sets most of the cost and influences the construction type (appearance).

 

[thor61]

Can a 400Va 2 x 18v transformer be used ? I understand the blog says 2 x 22v what can be expected from using a lower voltage ?

 

[Zen Mod]

yup

 

[flg]

Using 18VAC secondaries takes the "need" to cascode away. You can just use a few jumpers on the PCB and not use the cascode hardware. The original F5 was built with 18VAC secondaries without cacodes. However, for more output power you probably want higher voltage secondaries and a cascoded input.
There is also the possibility that cascoding could give better sound? There is no reason you can't use the cascode with your 18VAC secvondaries.

 

[tinitus]

......what can be expected from using a lower voltage ?

maybe less demands on heatsinks, and safer for driving 4ohm speaker
but if you plan to drive more inefficient speakers......

 

[dimkasta]

The single best place to start reading is the First Watt site.

Download and read the F5 manual. It explains in large detail how it works and how it can be configured.
The cascoded part is nicely described on the F5T article that again can be found on the First Watt site.

 

[tinitus]

I guess the 'F5 Turbo' article is the best 'summary' of it all

 

[thor61]

Hey guys take a look at this and tell ne what you think

Sjostrom Audio RFB02 Rectifier Bridge

 

[tinitus]

.... tell me what you think

that you should try and learn to wire them yourself
after that you are free to buy it 'readymade'

Dantimax.com boards
at Mikkel's prices can afford to use two boards per channel
though Im not a fan of those screw teminals
and 10A may be a bit on the low side

 

[thor61]

Thanks, but already ordered 2 of the above

 

[tinitus]

in the forum store here you will also find a 'universal power supply' board

 

[thor61]

Tinitus, I have the universal power supply board, it has several things I don't really care fore 1) rectifier section, 2) power-supply caps if using 8 are 30mm diameter and 3) the screw mounting holes are to close to the caps so now a 25mm almost becomes your max diameter. Ideally I would like to see something like the "Chipamps.com" Aleph psu boards but with 8 caps @ 40mm..... This is what I'll probably end up doing >

 

[thor61]

Bump Wrong pic

The above was for The F4 the F5 cascode will a 2 x 22v transformer in a similar fashion !

 

[tinitus]

now you have bought bridge kits, why not mount caps on proto martrix board, and wire it with solid core copper wire ?
most likely even better