Tweaking the v1 gain stage

[pbman1953]

I have preamp pedal that emulates a B15n. The unit has 1-12ax7. I like the b15 but Ampeg's for this unit , I'd like to calm down more towards a Fender or Sunn. A bit warmer/smoother through out.




The pedal does have a gain and volume. One similar item to the Ampeg is that there is a 47k resistor on the input on #7. Instead of a cap and resistor combo on pin #8 ,like Fender's and Sunn,  there's only a 5.6k resistor to ground. As used on a B15.


Pin 1 has a .022uf to ground


Pin 6 has a .01uf coming from a tone circuit


The gain connects to pin2


Pin 3 has a 3.3k to ground


Pins 4 & 5 are tied together for the filament & 9 has a filament connection


I know it real hard with out seeing it, but do any parts stand out that could be adjusted to tweak the sound to a what I'm looking for?




Thanks!

[PRR]

> do any parts stand out

12AX7 is NOT a 6SL7. That can be a lot of your not "warmer/smoother through out."

[pbman1953]

Thanks, but I have to stay with a 9 pin tube

[HotBluePlates]

I have preamp pedal that emulates a B15n. ... I'd like ... a ... bit warmer/smoother through out.

... any parts stand out that could be adjusted to tweak the sound to a what I'm looking for?

"Warmer" = less treble?  If so, you can slap a cap-to-ground anywhere to roll off some top end.

Otherwise, folks would need a. schematic of the pedal.  "Emulates a B15N" does not mean "has the circuit of the B15N."

[Carlsoti]

FWIW, the closest 9-pin substitution for a 6SL7 would probably be a 5751. Typically viewed as a drop-in replacement for 12ax7 by guitarists and many/most techs, it'll usually run just fine in any circuit designed for 9-pin 12A_7 tubes. Obviously, you can tweak the circuit for desired performance. You're probably better off tweaking the circuit for lower gain from a 12AX7, as they're considerably more plentiful, than tweaking it for the more rare and expensive 5751.

A schematic of what's there now will be the best thing to determine where to go from here.

[pbman1953]

FWIW, the closest 9-pin substitution for a 6SL7 would probably be a 5751. Typically viewed as a drop-in replacement for 12ax7 by guitarists and many/most techs, it'll usually run just fine in any circuit designed for 9-pin 12A_7 tubes. Obviously, you can tweak the circuit for desired performance. You're probably better off tweaking the circuit for lower gain from a 12AX7, as they're considerably more plentiful, than tweaking it for the more rare and expensive 5751.

A schematic of what's there now will be the best thing to determine where to go from here.

Thanks I do have a GE 5751 that I'll try first on my gig tonight.


The pedal maker will not send me a schematic, product protection probably.


 

[pbman1953]

I have preamp pedal that emulates a B15n. ... I'd like ... a ... bit warmer/smoother through out.

... any parts stand out that could be adjusted to tweak the sound to a what I'm looking for?

"Warmer" = less treble?  If so, you can slap a cap-to-ground anywhere to roll off some top end.

Otherwise, folks would need a. schematic of the pedal.  "Emulates a B15N" does not mean "has the circuit of the B15N."

I'm not worried about treble, that's controllable. I guess I'm looking to soften the Ampegness of this pedal, even though the pedal is what I like. It's the Arkham Oracle, a quality unit.

[bmccowan]

Interesting pedal. I agree with Carlsoti that rolling different tubes is the way to go. I saw on some bass discussion boards that users find a significant difference using different tubes, even 12ax7s from different mfgs will sound different. You likely are not thrilled about buying more tubes, but in addition to the 5751, 12ay7, and 12Au7 with take away some of the punchiness (is that the "Ampegness"?) Within 12ax7s the differences are likely less noticeable, but still there. And do not forget to tweak your guitar's controls - many people forget they are there, but a slight roll off of either or both of the volume and tone controls can make a big difference.

[pbman1953]

I've landed on the 5751 and it seems to be ok. I tried an Au7 and but I run out of a room on the gain pot.


I'd still like to know what factor/parts have influence on the tone.




Thanks to all!