BBE B-Max T gain question

[the bat]

Hello
I have a BBE B Max T that I bought from a TB member a few months ago. When I first got it, the input gain knob would start to get a kind of nasty distorion when I turned it up to about 10 o'clock. Past that it would just be complete nasty distortion. However, below this setting where distortion would start it souned incredible. Plugged in it yesterday and the distortion in input gain is completely gone. Infact after about 12-1pm to the max there isn't any volume increase. Still sounds great though. I changed the tube out with three different tubes, all do the same thing. Any ideas?

 

[timmus]

I have the non tube version of that Pre. When I received it many years ago, I had the same problem when playing an active bass through it. I found out there is a front end mod (pads the signal a bit). I installed it and all of a sudden it was usable. It involves a couple resistor changes. If you're at all handy with a soldering iron, it's an easy mod.

I'll see if I can find the instructions on my computer unless someone else knows the instructions and can post them here quicker than I.


Found it! The mods for mine (non-T) and yours (T) are slightly different

For the BMAXT you have 4 component changes

1) R7 gets changed from a 46.4k resistor to a 68.1k
2) R10 changes from a 46.k to 21.5k resistor
3) C8 is removed completely
4) C9 is removed completely

For the BMAX

1) R7 changes from a 46.4k to a 68.1k resistor
2) R10 changes from a 46.4k to a 21.5k resistor
3) R12 changes from a 6.81k to a 14.7k resistor
4) R14 changes from a 5.62k to a 10.0k resistor

 

[the bat]

I have the non tube version of that Pre. When I received it many years ago, I had the same problem when playing an active bass through it. I found out there is a front end mod (pads the signal a bit). I installed it and all of a sudden it was usable. It involves a couple resistor changes. If you're at all handy with a soldering iron, it's an easy mod.

I'll see if I can find the instructions on my computer unless someone else knows the instructions and can post them here quicker than I.


Found it! The mods for mine (non-T) and yours (T) are slightly different

For the BMAXT you have 4 component changes

1) R7 gets changed from a 46.4k resistor to a 68.1k
2) R10 changes from a 46.k to 21.5k resistor
3) C8 is removed completely
4) C9 is removed completely

For the BMAX

1) R7 changes from a 46.4k to a 68.1k resistor
2) R10 changes from a 46.4k to a 21.5k resistor
3) R12 changes from a 6.81k to a 14.7k resistor
4) R14 changes from a 5.62k to a 10.0k resistor

Thank you. The distortion has disappeared on my preamp, but it used to happen----gone now.

 

[the bat]

Thank you. The distortion has disappeared on my preamp, but it used to happen----gone now.

To be clear, I haven't changed anything. The issue is still there.

 

[timmus]

To be clear, I haven't changed anything. The issue is still there.

I'm confused...is the issue still there or is it gone....or intermittent?

 

[eniac]

Plugged in it yesterday and the distortion in input gain is completely gone. Infact after about 12-1pm to the max there isn't any volume increase. Still sounds great though. I changed the tube out with three different tubes, all do the same thing. Any ideas?

That's how my non-tube version behaves when I'm plugged into the passive input (with a passive PB).

Anyway, real long shot, but try connecting effects send to effects return. Could be the latter jack's switching contacts are slightly oxidized, just enough to reduce overall gain a bit. I wish I had a schematic. Looked all over the Internet, no can find.

 

[the bat]

I'm confused...is the issue still there or is it gone....or intermittent?

When I first received the pre I couldn't turn the gain up past 10 o'clock without distortion. Now for some reason the disrotion is gone BUT when I turn up the gain it never distorts. Also past around 1 o'clock it does not increase the volume at all. Still sound good though

 

[timmus]

When I first received the pre I couldn't turn the gain up past 10 o'clock without distortion. Now for some reason the disrotion is gone BUT when I turn up the gain it never distorts. Also past around 1 o'clock it does not increase the volume at all. Still sound good though

OK...I was just a bit confused by the two posts you posted before my "I'm confused" post, One said it was distorting and the other said it wasn't . I'm assuming you were using the same bass in both instances?

 

[the bat]

OK...I was just a bit confused by the two posts you posted before my "I'm confused" post, One said it was distorting and the other said it wasn't . I'm assuming you were using the same bass in both instances?

yup same bass.

 

[the bat]

yup same bass.

The whole reason I posted is because I'm wondering why it used to be distorted, and now it's not without anything changing. Also why it doesn't increase the gain past noon. It stays the same volume past noon even though the gain knob is turned up higher past noon.

 

[timmus]

The whole reason I posted is because I'm wondering why it used to be distorted, and now it's not without anything changing. Also why it doesn't increase the gain past noon. It stays the same volume past noon even though the gain knob is turned up higher past noon.

Weird...I'll have to find my BMAX (it's in a road case somewhere in the barn) and try it and see if I'm seeing the same thing you are...it may be different though...you know, the apples/oranges thing because yours is a T model and mine is not.

 

[eniac]

That's how my non-tube version behaves when I'm plugged into the passive input (with a passive PB).

Sorry, I meant to say ACTIVE input. A bargain-basement workaround would be a tiny box with a simple voltage divider -- either resistors or a potentiometer -- to knock the signal down before it reaches the input. But I don't use the thing any more except to power it up every few weeks like I do my other retired gear.