Help with Sopht Amp

[PurpleTheory]

Hello,
I really want to build a sopht amp http://www.sopht.ca, I have all of the
materials to build it, i just had a few questions, any help would be
greatly appreciated. but i have to warn you that i'm fairly new and
inexperienced in the world of effects, so let me appologize in advance if
my questions are painfully lame  :mrgreen:  

i've really like the sound of the 12AL8 version, so i've been trying to map
out a pcb following that schematic http://www.sopht.ca/schematics/sopht_12al8.jpg
the first question that i had was concerning which pins connect to what, i can't figure out how they are numbered. also, where is says: V4 12V +V, does that mean connect both 12v and pin 4 to that section? Below is the pcb that i started throwing together, does it look right? I've never drawn one before.

at the bottom i tried to map out the voltage regulator from ruby tuby, is that right? Also i read in another post that you could use a 1meg pot and a 2 meg pot to control volume and gain, where abouts would i put those?

thanks in advance,

Matt

[MartyB]

I'm thinking of building this one too.  I found these pinouts for the two tubes used:

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/1/12U7.pdf

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/1/12AL8.pdf

Here's the way I think this fits with Stephane's schem: (sorry for the crappy paint bitmap)

http://www.freewebs.com/martyb/sophtpinouts.htm

I haven't critically looked at your layout yet.

Hope this helps - MartyB

[MartyB]

OK purple theory,

Here's some things I see:

The other end of R5 goes to gnd.
R6 goes to 12AL8's pin 8.
Pin 8 on the 12AL8 should be changed to pin 9, which goes to gnd.
Pin 7 on the 12 AL8 should be changed to pin 2.

What would be cool would be to incorporate the tube sockets on the pcb.  If I get alittle more time this weekend I'll work more on a layout.

MartyB

[PurpleTheory]

Yeah, that would be way cool to incorporate the sockets on the pcb, thanks for taking the time to help me out too, i'm going to rethink the layout a bit with your corrections.

matt

[MartyB]

Okay here's a rough layout using the tube-socket-on-pcb idea.  Scroll to the bottom of the page.  Somebody here want to run with this football - put into express PCB?

MartyB

[PurpleTheory]

Sweeeeeet! I'll see if i can draw it up tomorrow.  

matt

[PurpleTheory]

hey MartyB,
I was drawing this out and I started thinking, what would be the best way to mount the tubes to the pcb? Would you mount the socket and connect the traces to it with wires, or actually solder the socket to the pcb and then mount it on a chassis or something? I'll see if I can find examples of other projects where people have mounted tubes to pcb's.

matt

[coreybox]

How does this amp sound......ive been looking into building a small tube amp. Can you give me something that it compares to? thanks alot

corey

[smashinator]

It's sounds pretty darn good!

go to http://www.sopht.ca there are sound samples galore.

[coreybox]

so how could you add a volume pot on to this? just a normal volume pot...not a fancy master volume

[coreybox]

And what would  be a good output transformer for it?

annnd what woudl eb the best way to power this amp?(i see there is no power transformer..........so im not sure exactly the best way to get 12v?

thanks

[william]

The power supply is a 12volt wall wart.  The kind you use to plug into the wall.  The sopht uses low voltage tubes.  12volts is plenty.

[PurpleTheory]

Okay,
Here's the layouts that i've drawn so far; the first one is the layout without the tube sockets mounted to the pcb and the second one is with. i included the voltage regulator from the ruby tuby schem on both (is that necessary?) do they look right? Thanks again MartyB for the drawing, helped out a lot! Let me know if you see any mistakes, or see any ways to improve the layout.

http://home.comcast.net/~knowitallrocks/temp_images/sopht_help2.png

Also, do you know where to put the pots? I read in another post that you could put one between stage one and stage 2 of the triode, but like i said i'm not too saavy on the subject, so i'm not quite sure where that is :oops: and another between 12U7 and 12AL8, so between...er...uh...not quite sure exactly where either :lol:  What do you think?

thanks,
matt

[mpeg2]

I built one of these (the photo on the bottom of the page is my build). One thing you have to make sure of when figuring out the pinout for the tubes is whether the diagram you have is a bottom or top view (the ones I've seen are bottom view).

I put a volume control in mine by replacing R5 (the 1Mohm to ground between the two stages in the 12U7) with a 1M audio Pot (connect one end of the pot to C1 - the other to ground. Connect the wiper to the 2nd 12U7 stage). You could alternatively replace R6 with a pot - but the other way seemed to make more sense to me.

I'm going to breadboard the 12K5 version soon & try both locations for volume control - when I do, I'll post something.

I've got mine driving a 4x12 cab - kind of interesting to get tube breakup at a volume where you don't bother the kids sleeping elsewhere in the house.

  Rich

[MartyB]

Thanks Rich for the vol control idea.  Nice build!  Yes. The pinouts are for the bottom of the board.
MartyB

[MartyB]

Rich,

  Would this be the way you have your 1 meg pot control wired?

MartyB

[slajeune]

Hi All,

sorry for falling off the face of the earth for a while .  Anyways.

Marty, yes, that's how we would wire a volume or gain control.  You can also place it instead of R8.  This is refered to a master volume.

When I get a bit more familliar with the bias points for these tubes, I might put both controls in (pot at R5 and pot at R8).  That way, we can control the amount of preamp and power tube distortion.

The layout is an awesome idea!  Since I haven't yet revisited the 12AL8 design, I would add 4 placeholders for cathode resistors and 4 bypass caps (an example of a cathode resistor would be R6 and R8 in the 12K5.  The bypass caps would be C3 and C4.

Cheers,
Stephane.

[slajeune]

Forgot to answer the question about the output transformer.  I am using a Hammond 119DA which is available at AES ( http://www.tubesandmore.com/ ).  It is very close to the load that the tubes want to see.

Thanks,
Stephane.