[makasin]

OK guys so I finished my amp, but now when I play music through it, I dont get much sound. I put the trimmers to the minimum resistance and I have to turn it up all the way for my grado sr60s. I put in a 150ohm output resistor. Should I take that out?

 

[makasin]

It sounds pretty decent. There is definately a little bit of hum that disappears when music starts. My only concern is that the volume is WAY TOO LOW compared to my measly creek.
Hopefully removing the output resistors will fix this, but I dont know how much good it will do.

EDIT: ok this fixed it more or less. Still not as loud as my creek but its better.

Now I have much more hum with my setup though

What should I check first?

EDIT 2:
What does it mean if the hum is present regardless of volume? could it be the line?

 

[FallenAngel]

Buddy, check that all your voltages are correct, especially 40V on the plates. 12AU7 has gain of 10 or 12 so it should be pushing unbearable volumes.

 

[makasin]

the 40V were in the 70s without the tube or opamp. I havent checked it with the amp installed though.
If its too low, what do I do? How far away does the transformer have to be from the board in order for it not to hum?

EDIT:

I just checked the lines.
should be/current voltage:

-12V ->12V
+40V ->60V (both)

This is with the tube inserted and the opamp in

 

[FallenAngel]

Ok, let's start with first things, NEVER TEST THE SOHA WITHOUT TUBE, OPAMP OR POT. This is for your safety.

Now that we've got covered, put the tube and opamp in and try it again. Adjust the bias until you've got 40V on the plates.

 

[makasin]

ah ok sounds good, thanks.
Will this fix the volume issue?
or the hum?

 

[FallenAngel]

It's just to make sure things work properly, there might be other issues we didn't see yet

 

[makasin]

This doesnt work, i can only get it down to 60, otherwise it goes to like 68 or something.
Dont I need 40? Is there a special way to bias these, because i have both pots set to highest resistance (i think), to the right

 

[makasin]

Did I wire the transformer wrong or something?
PICS:

http://www.mouser.com/catalog/628/1627.pdf The transformer wiring info, mine is the FP30-400

 

[FallenAngel]

Ok, if you're seeing B+ on the plates, let's check 2 things:

1) Are you getting -12.6V on the heater?

2) What CCS are you using? Is your CCS wirong correct? Double check.

 

[makasin]

I have the LND150 CCS, heater is at -12.56V , the B+ is still 60.

???

 

[FallenAngel]

B+ should be 60V, the plates should be adjusted to 40V each. If they are showing around B+, something might be funky with your or around CCS.

Like... uhm... where are your C2 / C14 caps? Those are not optional and are right beside the CCS

- Oh, I see some big Orange Drops down below.

Take a pic of the CCS section.

Oh, and about the transformer, you didn't need to solder that little black wire across the two ground secondaries, they're connected anyway. This is creating a little ground loop.

 

[makasin]

oh really? is that the reason for the hum?

 

[makasin]

ah I should note, I received the wrong bridge rectifier because the pinouts are different even though they are spec'd the same, so i ran wires to switch two of the points. I dont think this would be it because the voltages of the 12V and -12.6 lines are good.

 

[tomb]

Makasin,
I'm sorry I didn't get to answer your other thread, but your transformer is wired wrong. Get rid of the short green wire bridging the outputs. Then your transformer connections should be OK. (You can get rid of the short black wire bridging the grounds, too - but that won't make a difference either way - they are eventually combined in the circuit on the board.)

You need two, completely separate 15VAC connections for AC1 and AC2 - those are the wires that come from the dots. The two black wires are the grounds, and are correct. Technically speaking, you do not wire the transformer secondaries in parallel or series. You need two independent secondary supplies of 15VAC, each with their own ground.

Strictly speaking, the Digi SOHA board uses a four wire, dual secondary connection. The grounds are eventually combined into the same thing in the circuit on the board (essentially a 15-0-15 center-tapped source), but that's after your transformer connection. In either case, the secondaries are not wired in series or parallel.

P.S. Your primaries are wired in series for a 240V input - I assume that's what you use where you are?