Alembic F2B! (PCB and Layout)

Tube or solid-state, this section goes to eleven!
darkglass
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Post by darkglass »

Hello Everyone!

Started this project about a month ago, started doing some research before designing the PCB and stuff.
Used moosapotamus' schems (for both preamp and PSU with slight mods)
Just did the first tests and it sounds really really good. I'm testing it straight to my Ampeg SVT's Poweramp and I'd even dare to say that I like it better than the Ampeg's tube preamp.
This baby is really soft, warm and tubey, but it's also got lots of punch, ideal for every style basically.

So, here is the %&+*!:

Image
Image

PCB: http://rapidshare.com/files/201834589/A ... B.pdf.html

Some instructions:

-Pads labeled with numbers correspond to the 12AX7's pins.
-Both stages cathode bypass caps (C3, C5, C10, C11) are 50uF as appears in the schem, but had some troubles finding some quality caps for that value here in chile so I designed the PCB for using 2 Axial 25u Sprague Atom in parallel, also elft the pads for using normal radial 47uF Caps.
-Bright Switch wired as shown, Low pot must be wired upside down!
-Use Shielded cable for input.
-I left the grounds separated according to each "stage" of the preamp following RG's instructions in his great Star grounding article. All the ground must be indeed wired to the chassis using a single node (or "star"), which should be as close as possible to the input (it shouldn't be so far away from the PSU either)
-I used a 250V AC for High Voltage and 6,3V AC for heaters.

Values:

Resistors:

-R1, R2, R3: 1.5k 2W
-R4, R5: 100R 1/2W
-R6: 470k/2W
-R7: 68k 1/4W
-R8, R14: 1M 1/4W
-R9, R12: 1.5K 1/4W
-R10, R13: 100k 1W
-R11: 100k 1/2W

Caps:

-C1, C2, C4: 47uF/450V
-C3,C5 / C10, C11 : 25uF (Can be replaced by 47uF)
-C6 250pF 300V(?) (I used a Silver Mica with high voltage tolerance, 500V I think)
-C7, C12: 100nF
-C8: 47nF
-C9: 100pF

Some useful Links:
http://www.moosapotamus.net/IDEAS/F2B/alembic.htm
http://www.geofex.com/article_folders/s ... targnd.htm

Warning: Project as this preamp have voltages than can be lethal, please be careful and don't do it if you don't have enough experience with this kind of circuits!

Enjoy!

Greetings from Chile!

Douglas

darkglass
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Post by darkglass »

oooops, didn't realize that the layout pic is too big for fitting the forum's "screen", if you press "view image" or "downlaod image as" you'll get the whole thing ;).

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Post by fosnal1950 »

Hi Darkglass,

Great work there, I've always wanted to try one but never got to it.
Could post me the pdf file ; it could only be downloaded 10 times and I was too late.
Could I pm you with my e-mail address ?

Alf

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Post by darkglass »

Damn it, do you know any better freeupload sites?
I'd be glad to send it to you by email meanwhile.

Regards

D.

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moltenmetalburn
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Post by moltenmetalburn »

PCB pdf hosted here for all to download, enjoy!

http://www.redhillmetal.com/uploads/Alembic%20PCB.pdf

thanks again douglas! :applause:
"The Humans Will Never Destroy Us"

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Post by fosnal1950 »

Thanks guys !

Regards, Alf

darkglass
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Post by darkglass »

Hello!

Here are some pics of my preamp completed!

ImageImage

Regards

D.

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premiumplus
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Post by premiumplus »

Very cool, darkglass, good work.
Are you playing bass or guitar through this? I've read that David Gilmour used to use Alembic preamps, and I'm guessing that this is the one? And what / where do you get the stepup transformer, T2?
Thanks!
Vinyl rules.

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Post by darkglass »

I built it for a Bass Player... I'm a bassist as well, it's unbelievable on bass. Really really great sound...I own a Mesa and an Ampeg bass hybrid heads and this was as good as the preamps on those 2 amps!
Really nifty having in mind that this uses just 1 12ax7.
And yes, David Gilmour uses this preamp with Hiwatt poweramps ;). It sounds amazing on guitar as well!

I used just one custom made transformer. And it's inside the same chassis.
With 250V, and 6.3V taps.

Regards

D.

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Post by moltenmetalburn »

Beautiful work Douglas!
"The Humans Will Never Destroy Us"

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Post by briggs »

Super! I shall build this preamp into the next valve junior I get my hands on - got an 18 Watt to build before then though!
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Post by Krinkle »

Rumor is Gilmour's preamp has modifications. An extra tube, cap value changes etc. It's somewhere on the net.

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Post by lolbou »

- Are you a mod or a rocker?
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Post by Barcode »

hmm, can't seem to fins those horizontal tube sockets anymore :(

I guess I'll have to build it with the tuobe showing :)

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Post by lolbou »

May this help? The tube bracket is well thought!!

http://www.diyguitarist.com/DIYStompboxes/ST1590BB.htm
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Post by borislavgajic »

original schem......and guts

:thumbsup
boris
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borislavgajic
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Post by borislavgajic »

enjoy :block:
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Post by lolbou »

:applause: :applause: :applause: :applause: :horsey: [smilie=a_yumdumdoodledum.gif] [smilie=eek2.gif]
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Post by nixandpavo »

Wow that rocks boris!!! :applause:

Thanks a lot!! :thumbsup

borislavgajic
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Post by borislavgajic »

you are welcome :thumbsup


boris

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