New Project: Alembic F2B Preamp (Layout and PCB)

[zencafe]

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 %&+*!:




PCB: http://rapidshare.com/files/201834589/Alembic_PCB.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/stargnd/stargnd.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

[sjaltenb]

Oh my!!! I am sooo glad you posted this with the layout!!!!!!

I have been wanting to build this for a long time now, just havent wanted to go through all the trouble. Thank you!!!

What type of enclosure is it meant to be mounted in...looks a bit wide to fit in a 1u rack space. Nice work !!!!

[zencafe]

Thanks for posting!
And is not that large at all... I actually fitted it in a large hammond box (way smaller than a 1U rack), you should print the PCB and check the size!

Greetings!

[sjaltenb]

Great! I'll just expand out the pots. And you say all the GND points go to star, and it also looks like you left some ground pads for the shielded wire, such as near the input and output?

Thanks!

[zencafe]

Exactly, actually for the input's ground there's one extra gnd pad, cuz you can use the same shield as ground connection for the jack.

[Ripthorn]

This is pretty cool.  I have built the thing with jfets and I think I might try it with submini's first, but I think I may have a go with 12ax7's since the board is so nice and compact.  Where are you in Chile?

[RedHouse]

Can you post the PDF somewhere else? your rapidshare account has reached it's limit of 10 downloads.

[zencafe]

Sorry, here's a new link!

http://darkfinn.googlepages.com/AlembicPCB.pdf

Regards

Doug.

[bent]

yeah!!!!   

a completed alembic F2B preamp project.....

thank's

bent

[zencafe]

Hello!

I just wanted to share the pics of the finalized preamp!


 


Regards

Doug.

[sjaltenb]

that is beautiful!!! I've still got your project in mind, I cant wait to build it!


thanks again!

[zencafe]

Thanks!

You gotta build it... at least on bass it rocks... I own an SVT and a Mesa Boogie, both hybrid Bass Heads... and the Alembic was as good (if not better) as the preamps on these 2!
I think that for guitar must be great as well... is really sparkly clean.

[sjaltenb]

yeah i've heard it is simply great. I will admit I want to build it because it is the preamp Dave Gilmour used during the PULSE tour infront of his Hiwatt power amps. His clean tone is beautiful during that tour.

apparently his had a tube cathode follower to lower the output impedance to work better with the hiwatt. I doubt it will be a problem but I may try it just for kicks..

[zencafe]

Mhh, I used it in Both Heads Poweramps (both Mosfet powered) and It sounded freaking great!
I'd love to hear it in a Tube Poweramp... (specially with 6L6 or 6550!!) I'm also thinking on building a 2 channel rack version, this as channel 1, and for the other channel a Mesa Bass 400 Preamp. They´re fairly similar... my idea is to mod the Mesa to add more gain (3 stages probably) tu use it as a bass dirty channel, and the alembic for clean.

Regards!

Douglas.

[sjaltenb]

that would be pretty cool! I just printed out the layout, I think i'll just lay this board flat in the 1u rack and have a small satellite board sit vertically behind it to hold the large filter caps and tube parallel to the top and bottom of the rack.  should be a piece of cake.

did you notice any noise issues? i think i'll build mine to look like the original but probably just throw some dummy knobs on the 2nd channel and leave it un-built, for the time being at least. i don't see any reason I would need it.

any pics of the inside? i'm lovin the logo.

[zencafe]

Sorry, didn't take pics from the inside... It was quite neat though, since I designed the PCB according to the room I had in the small chassis... building it in a rack should be way easier.
To avoid noise I used Star grounding (thanks again RG!!).
I located the ground node close to the power supply and input ground pads... and then wired the rest from the pcb to it.
It was pretty silent... for heaters, used 6.3V AC, with the 100 ohms resistors to ground. You could try 12.6V DC for heaters as well... for that you could do a separated PCB, and regulate it with a LM317.
B+ used 250V AC... which rectified and filtered must have been around 350V DC (gotta be careful!!!) I got shocked by a second and it wasn't quite pleasant hehe.

Could you record some guitar samples once you've built it?

Best Regards

Douglas.

[delaystomper]

hi very beautyful job , i would like t build one i tried the links that you posted but it only shows the pcb pdf
can you add the rest of the docs like schematic and parts placement ? it would be awesome if i can finally build one of this i been searching every where
thanks