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Old 9th September 2010, 04:27 AM   #1
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Join Date: Oct 2007
Location: melbourne
Default convert aleph 2 to pre for f4

hi
i have just about finnished building 2 x f4 clones to replace my aleph 2 clones
my question is can the aleph 2 be modified and converted to a pre amp with a volume control added to power my f4

the a2 monos cost a lot to build and it would be a shame to see them not used ,it would be great to convert them into a pre amp with just enough gain and output to drive the 2 f4 clones (daul mono aleph 2 preamp driving 2x bridged stereo f4 cones = heaven hopefully)

the a2 is all standard exept it is run on 25v secondary,s instead of 38v i could drop the supply voltage and lower the amount of output devices no probs but what else would be required to make this work

cheers
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Old 9th September 2010, 05:27 AM   #2
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Drop it down to one pair of output devices
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Old 9th September 2010, 06:46 AM   #3
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Join Date: Oct 2007
Location: melbourne
hi
so one pair per channel ...done
what about supply voltage ? should i keep it the same

also would jfet front end work well seeing as it will only be running the one pair per channel of output devices (i have heaps of j109bl here)

also would a b1 buffer built in to the same cab as the aleph 2 be fine for volume control

cheers
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Old 9th September 2010, 09:54 AM   #4
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Since you already have the transformers you may as well use them.
However you could try a shunt regulator.
You could also replace the input devices with 2 x 2sj74.
I would do these things in steps rather than try them all at once.

It might not be necessay but I would be tempted to put a 10uF cap on the output for safety. It is very important to get the dc offset as close to zero as possible if you are not going to use a cap at the output - I don't think the F4 has an input cap.

Last edited by Melon Head; 9th September 2010 at 09:59 AM.
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