Valab stepped att., help with wiring - Head-Fi: Covering Headphones, Earphones and Portable Audio

Oya? · #1 (**permalink**) 07-02-2009, 07:56 AM

Hi guys, I bought one of these attenuators off eBay and I wired it up to my Millet Hybrid. I'm using the 6 terminals that used to have an Alps RK27 in it. For some reason I'm getting almost no sound even when I twist the knob up to max, and there's a lot of hiss. Could someone double-check my wiring?

(I don't have access to my camera so I had to draw it, hopefully it's clear enough)

Did I do something wrong or did I get a faulty pot? Should I be using different terminals? I see alternate pot inputs/outputs on the board.

Any help would be appreciated.

FallenAngel · #2 (**permalink**) 07-02-2009, 08:16 AM

Uhm... the wiring diagram is right in the post

http://i4.ebayimg.com/02/i/000/a5/fa/d004_12.JPG

FallenAngel · #3 (**permalink**) 07-02-2009, 08:18 AM

Check resistance between input and output, sometimes the resistors in those pots get lifted and something worth noting - if you want to resolder those resistors, the contact pad is actually ON TOP, not bottom or side, so make sure you solder the top of those resistors to the contact points, otherwise you get no connection.

JamesL · #4 (**permalink**) 07-02-2009, 08:21 AM

His drawing is consistent with the diagram on the ebay page.
I don't see terminal blocks labeled for LI/LO/LG and RI/RO/RG on either the millet hybrid or max. In either case, I assume you didn't connect the pot output to the amplifier's Lo/Ro

JamesL · #5 (**permalink**) 07-02-2009, 08:23 AM

Quote:

Originally Posted by FallenAngel

Check resistance between input and output, sometimes the resistors in those pots get lifted and something worth noting - if you want to resolder those resistors, the contact pad is actually ON TOP, not bottom or side, so make sure you solder the top of those resistors to the contact points, otherwise you get no connection.

I don't think that's a problem. He's getting no sound on either channels. A lifted resistor would only affect one channel.

Oya? · #6 (**permalink**) 07-02-2009, 09:17 AM

I can't get any resistance readings from the input and output tabs, on both the left and right channels; would this mean that no signal is coming through?

(And sorry I didn't mention that I installed those terminal blocks onto the Alps RK27 pads to make switching pots easier)

JamesL · #7 (**permalink**) 07-02-2009, 10:06 AM

Quote:

Originally Posted by Oya?

I can't get any resistance readings from the input and output tabs, on both the left and right channels; would this mean that no signal is coming through?

That's odd. Even if it was turned all the way clockwise, short-circuits usually read as 0v on a dmm.
Maybe it is a defective pot.
Put the knob position in the middle somewhere. Try to get a 50k read between two of the wires. If you do, the two wires are input and ground.

Turn the pot completely clockwise. You should get 50k between output and ground. 0k between input and output. Vice versa if you turn it completely counterclockwise.

Oya? · #8 (**permalink**) 07-02-2009, 01:36 PM

Apparently I made a really stupid, stupid mistake. I soldered the wires on the input side onto the two blank tabs instead of the start of the circuit that's soldered to the resistors. It was kinda hard to see from the pics on their page so I assumed the blank tabs were the inputs. Everything's all up and working now.

Thanks again for the help, I really appreciate it.

It's a bit hissy at the moment, so I should ground the attenuator chassis to the board right?

keyid · #9 (**permalink**) 07-02-2009, 07:28 PM

lol I did that too and spent hours staring at the diagram and pictures. Try connecting the grounds together (L/R).

Oya? · #10 (**permalink**) 07-05-2009, 03:42 PM

I've got another problem, it seems trivial so I didn't want to make another thread; When I notch up the volume it all sounds silent (the last two or three steps are slightly noisy) and then on the very last notch I just get white noise of sorts. Is this normal?

A non-issue really since I'd never go anywhere near max volume when I'm using it. Just wondering if maybe the very last two resistors are damaged or something.

FallenAngel · #11 (**permalink**) 07-05-2009, 11:09 PM

I REALLY doubt you will (or should) ever get that high in volume, if you are getting close, increase gain on the amp.

rds · #12 (**permalink**) 07-06-2009, 12:07 AM

The last few steps on the Valab are major jumps. You are probably just hearing the noise from your source (or if no source is connected then noise being picked up in the air).

Oya? · #13 (**permalink**) 07-06-2009, 03:09 AM

Quote:

Originally Posted by rds

The last few steps on the Valab are major jumps. You are probably just hearing the noise from your source (or if no source is connected then noise being picked up in the air).

That makes sense.

Thanks!