low cost pre amp plans

[doveguy1]

can it be done for $100.00?

 

[fdegrove]

100 BUCKS.

Hi,

Depending on what you want 100$ in not going to give you a 1000$ sound...if at all it can be done.

So, I'll be looking forward to the low-fi goalposts you're going to set.

There are limits,

 

[Sch3mat1c]

Ah, shuttup Frank.. J/K.

Lesse, AES P-T442, 125V 15mA + 12.6V 300mA, enough for two 12AU7s; $17. I have a spare Chicago Standard transformer which is the same except for 6.3V 600mA heater winding, and made a preamp (12AX7 + 12AU7) with it.
What I think is the current schematic, is attached.

Tim

 

[fdegrove]

LIFE IN AMERICA...

Hi,

Amazing what Madonna can do with a 100$...

Hi, Tim...

 

[arnoldc]

well, i made one for just $80

 

[Brett]

One of these?

well, i made one for just $80

 

[arnoldc]

no brett, the one in the picture is far more too expensive

 

[Zen Mod]

Ah, shuttup Frank.. J/K.

Lesse, AES P-T442, 125V 15mA + 12.6V 300mA, enough for two 12AU7s; $17. I have a spare Chicago Standard transformer which is the same except for 6.3V 600mA heater winding, and made a preamp (12AX7 + 12AU7) with it.
What I think is the current schematic, is attached.

Tim

hehe,that must sound like tube ****

 

[Zen Mod]

hehe,that must sound like tube ****

correction-some words are forbidden,so I must refrase that:
"that must sound like tube sheeeettt!"

 

[Sch3mat1c]

Oh you're just mad 'cuz it doesn't have an OPT

Tim

 

[James D.]

...WOT? How about 100euro...

I had an idle 30 minutes at lunch to day and thought I would have a go at a 100 euro preamp with an OPT...


A few compromises are needed but I came up with this parts breakdown...

Hammond 125 PP OPT 12.5k:8R 125C PP www.tubes.it € 18.53 2off € 37.06
Power Xfmr 230V@12omA TRA200 www.askjanfirst.de € 14.99 1off € 14.99
Elec cap 100+200+200uF KON6005 www.askjanfirst.de € 2.67 1off € 2.67
6N6P www.askjanfirst.de € 7.89 2off € 15.78
noval socket www.askjanfirst.de € 1.86 2off € 3.72
BYV26E www.diyparadiso.com € 0.47 4off € 1.88
Ultrapath cap. Audyn 15uF 400V www.diyparadiso.com € 5.80 2off € 11.60
100k log pot stereo carbon Hi-qual. www.diyparadiso.com € 5.00 1off € 5.00
220R 4W metalfilm www.diyparadiso.com € 0.86 1off € 0.86
270R 4W metalfilm www.diyparadiso.com € 0.86 1off € 0.86
470R 4W metalfilm www.diyparadiso.com € 0.86 1off € 0.86
220K 2W bleeder www.diyparadiso.com € 0.24 1off € 0.24
TL431cp www.diyparadiso.com € 0.27 2off € 0.54
68R beyschlag www.diyparadiso.com € 0.10 2off € 0.20
68k beyschlag www.diyparadiso.com € 0.10 2off € 0.20
BC550c NPN transistor www.diyparadiso.com € 0.14 2off € 0.28
220uF 25 V Elna Cerafine www.diyparadiso.com € 3.66 2off € 7.32

Total € 104.06

The OPT is a compromise - but swop it for a Hammond 1609 and add 50 euros to the cost and it should be good. Of course it doesn't include switches input/output sockets or chassis...they are all in the parts box already

ciao

James

 

[dhaen]

Hi James,

Does the second triode provide a bias current for the transformer?
I presume it's grid will go to ground through a resistor.

Cheers,

 

[James D.]

...Whoops!

John.

Thanks - good spot!!!

It does indeed on my sketches but I missed it on the .gif file. I did it all in a hurry today... there are probably other errors as I really rushed it but I thought the idea was interesting enough to post...

The second triode is for bias current - I first wanted to go push-pull so no decoupling at the cathodes but then I remembered that the psu sounds awful - it's cheap but awful so the fix for that was to use full decoupling at the cathode to remove the psu from the signal path.... and since the SE OPT are so expensive I decided to leave the second triode in as dc bias for the PP OPT...

It ain't pretty but it's cheap!!! Should sound nice too...

ciao

James

 

[Sch3mat1c]

How isn't it PP? Looks like you got a LTP there, so the other side will be the inverse of the first.

Tim

 

[dhaen]

Tim, you missed the 220u decoupler.

 

[Colt45]

8 euro for a 6N6P!?

I'll supply them for 4 euro

 

[Zen Mod]

Oh you're just mad 'cuz it doesn't have an OPT

Tim

with or without OPT

it's just too wimpy

 

[fdegrove]

Hi,

Ok, alright already...we'll add a few 150H chokys.

 

[Sch3mat1c]

Tim, you missed the 220u decoupler.

D'oh!

Well why the heck would you have it in then? More power and less distortion...wtf...

Tim

 

[fdegrove]

Hi,

Well why the heck would you have it in then? More power and less distortion...wtf...

Why? Does anyone want more distortion and less power?

The SET guys might...

No, Tim, the idea is to be able to use a PP OPT iso the more expensive SE OPTs.

Cheers,