Volume level

[Filthymidget]

Starting from the 7 o'clock position I've got to turn my volume knob to the 12 o'clock position before i really hear any sound.  Then at 2 o'clock up to 4 o'clock I have high volume.  Is this normal?  I thought I read somewhere that someone turned there's to 9 o'clock and that was plenty loud for them.  I wonder where 0 was for them?  I want my amp to go to 11!!

[Jim R.]

Wellm, if it were me, I'd be glad to have that much range to play with.  However, nobody can really answer your question without knowing what your source is and what the sensitivity/efficiency of your speakers is.

[Filthymidget]

Source is Logitech squeezebox playing flacc and .wav files.  Speakers are 96 db Hammer Dynamics 12's very high efficiency speakers.

[Grainger49]

No volume till 12:00 is not normal or right. 

Check your manual where the instructions for the volume control are.  From the picture on the product page the red wires from the selector switch go on the right most lug of the volume pot.  The black wires go on the left most lug of the volume pot.  The cables going to the 12AT7 have the red wires going to the center lug of the volume pot and the black wires to the left most lug of the volume pot. 

If that is right you need to check the cables at the selector switch and at the 12AT7 as well. 

[Jim R.]

Well, if it were me, I'd almost be glad to have that range of control, but given the source and speakers, I'd say something is not quite right.

Did you have your SB modified such that the output op amps were removed and replaced with coupling caps? 
This typically brings the output level down to 1vrms.  Also, have you checked to make sure that you don't have the digital volume control turned down on the SB, or maybe in slim server or whatever it is they are calling it these days?

When I had an SB 3, it was modified and had a much lower output level than stock, but I never used the digital volume control because at least mine wasn't a proper dithered control.

I  haven't progressed far enough with the construction of my amp to know what else to suggest at this point.

HTH,

Jim

[InfernoSTi]

Not that it is much help, but on my 96db speakers, 7:00 is zero and 9:00 is my normal listening level.  I can actually listen a little lower late in the evening when I need to be a bit quieter.  I don't think I have gone past 12:00 ever....

John

[Filthymidget]

Grainger:  All wiring is correct with good solder joints.  Just seems strange to me, it really is weak until i get the knob turned past 12 o'clock then peters out at around 5 o'clock.  It really seems like i'd more power than what is needed but i don't. 

Jrebman:  My SB has no modifications done to it.  This volume situation is the same with all input devices.  TV and phono w/preamp.

[InfernoSTi]

Have you tried attaching a CD player to it directly via RCAs to see if that is any different?  That might rule out input concerns entirely.

[Filthymidget]

Thanks Inferno, i'll try a cd player.  I have a friend with the same speakers but different bottlehead tubeamp.  He doesn't need to go past 3 o'clock position either.  He thought it odd i had this experience.

[Filthymidget]

Still low volume level until 12 position.  Could it be a bad volume pot?

[InfernoSTi]

Again, I'm probably not knowledgable enough to help, but it seems like you could take some resistance measures at zero, 9:00, 12:00, and 3:00, and full, you could see if you have a "normal" set of readings compared to mine.  Please note I measured twice to get a range since I am only turning to approximate locations. I also only measured one channel (the top one because it was easy to reach) so the range isn't between channels, it is variation in turning to a certain point on the volume.  Here is what my pot measures:

Zero (7:00): 1.6 to 1.7 ohms
9:00: 4.4K to 4.7K ohms
12:00: 14.3K to 14.4K ohms
3:00: 67.7K to 73.6K ohms
Full (5:00): 98.7K to 99.1K ohms

If your measurements are not advancing in a reasonably similar range, that may tell you something.  If nothing else, this gives you something to do this afternoon!

John

EDIT: For clarity, I did this with all speaker wires, RCAs, and power cord removed, as well as the 2A3 tubes removed (I left the 12AT7 in place).  I should have stated this in the post.

[JC]

You know, I have to wonder if you maybe just got the wrong kind of pot.  Some type of Linear Taper instead of a Log Taper or Audio Taper.

It is not unheard of that a pot manufacturer lets a few slip out that are mislabeled.

First thing I'd check is the resistance from terminal 1 to terminal three on each section.  Then, the resistance from terminal 2 (the middle) to whichever end is at ground.  Do that one at all of the "o'clocks", and make a note of your readings.

BTW, you may wish to unplug anything you have plugged into the inputs, as the output impedance of another device may interact with the pot and skew your measurements.

Caveat: I don't own your amp or have its schematic, so I'm just going by a general idea of how the pot is usually wired.


EDIT: Hah!  I see InfernoSTi beat me to it!  Note how his measurements are changing in a non-linear fashion!

[Filthymidget]

Thanks guys!!  I'll try this afternoon to obtain resistance readings.  I'll post the results after.

[Filthymidget]

Ok the first measurements i took were at the pot terminal that has wire going from the potentiometer to the selector switch.

Zero (7:00): 94.4k ohms
9:00: 94.3k ohms
12:00: 94.3 - 94.4K ohms
3:00: 94.1K ohms
Full (5:00): 94.4k ohms

That didn't seem to tell me anything so i took measurements at the terminal that goes from the potentiometer (center terminal) to the power supply.
These were more in line with your readings.

Zero (7:00): 1.4k ohms
9:00: 4.29K ohms
12:00:  12.58K ohms
3:00: 64.1K to 64.3K ohms
Full (5:00): 94.5K ohms

[InfernoSTi]

I think the first set of readings shows the full resistance at any position of the control.  The second one is pretty well in-line with what I have in my Stereomour.  It seems that it isn't the pot (or at least not something obvious). 

I'm sure Paul Joppa will weigh in the next time he checks the boards....

John