help on line pre-amp

[cm_ls1]

I have a set of Fostex Pm-2 monitors ... they are loud , clear and transparent ....

after i started reading these forums .. i got psyched up to build a tube - preamp , to give my ipod a signal boost and to sweeten that sterile sound the monitors make !

i originally thought the "foreplay preamp" was the go .. but i cant find any schematics (obviously its copyright)

then i heard something about the "wright - 11 " something or other

the i heard about some aikido pre amp

and then there is some guy "FRED" that has his design.

but i cant for the life of me find ... a schematic

which do you guys recommend ? for hifi applications that doesnt colour the sound tooo much , but just gives it nice touch.

and a schematic if possible!

cheers

CM

[lt cdr data]

just use a basic voltage amplifier stage, its the best sounding by far.

use ecc82, 6922, or 6sn7

check the ratings, 300 volts psu.

make anode resistors around 3x the rp,

can't recall cathode resistor, 1meg input grid resistor, or 470k, same at output, 2uf coupling capacitor.

that's it, and it sounds great

CLClC supply, use hammonds say, either ez81 rectifier or bridge.

dc heaters, CLC filter.

one of the best you will find or hear. others will disagree with tubes, but they are common and do sound fine.

afterwards, you can try output transformer, and a battery bias.

check on the

'read it'

section on the lhs here@

http://www.sjselectroacoustics.co.uk/

lots of info there, get you going, superb design

[sreten]

Originally posted by cm_ls1

to give my ipod a signal boost.........

CM

Hi,

An I-pod driving a valve pre-amp ? what is the world coming to ?

/sreten.

Edit : Seriously speaking, the PM2's don't look too bad.

As a studio monitor they are likely to lack baffle step compensation.

The best way of driving them from a portable headphone out is
via a pair of decent signal transformers + a dual gang volume pot.

You could add a passive BSC circuit to sweeten the PM2's.

http://sound.westhost.com/bafflestep.htm

/sreten.

[cm_ls1]

i was wondering what chassis to use for the pre-amp , i found this hdd enclosure at work ( i was only a "dummy case" with no parts inside , made from brushed aluminium and a white plastic top , there is a pinhole led light on the front , and a mount for a fan at the back , it also well ventilated underneath.

its 160mm square , and around 35cm height.


i might attempt an aikido set up , from all reviews it seems like a great pre-amp , it says that it works with various power supplies , can someone point me in the right direction on what psu and rectifier to use ( do i need a rectifier?) , is the a brand and model you could suggest , and maybe a website that sells them ?

i was going to use 9 pin triodes , 12au7 or something similar ?

thanks !

CM

[bibster]

Originally posted by cm_ls1
...
it's 160mm square , and around 35cm height.

Wow! That's a verrrrrry high box indeed....

I think you'll quickly run out of space in there.
But if you happen to have TWO of them.... You could maybe put the PSU in one, and the actual linestage in the other!

JM2C,

Paul

[cm_ls1]

yeah , thats supposed to be 35mm :P

how big are the transformers ?

i need to keep reading damnit...

im a bit of a noob at this stuff but keen to learn

and be very careful from shock hazzards bzzzzzzt

[lndm]

Hi cm_ls1,

I understand that you said

that doesnt colour the sound tooo much , but just gives it nice touch.

and considering that you also said

to sweeten that sterile sound

might I suggest something based on a 12AX7. These are easy to obtain, have a useful amount of gain and add a gentle warmth and roundness to the sound.

[cm_ls1]

i was hoping to fit everything in the chassis .. but i might have to use a second one as the PSU, as was advised , lucky we have another 2 or 3 at work.

so i physically wouldnt fit

this is how i pictured it...

[cm_ls1]

what do you guys think of this - compared to the aikido , as a first project ?

[Original Burnedfingers]

what do you guys think of this - compared to the aikido , as a first project ?

I built one per the schematic you posted and it was ok. I added VR regulators and it improved the sound. To be honest the Aikido will blow it clean out of the water without a problem. Its your money and time. My opinion it to skip the 5687 and purchase some Aikido boards from Bas and have something that performs well the first time out.