• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Bearfoot Blueberry Clone overloading

aborgman

aborgman

Jun 12, 2007
4,000
1,158
Ypsilanti, MI 48197
#1
I recently built a clone of a Bearfoot Blueberry using the stripboard layout/schematic from freestompboxes.org

Invalid Link Removed
Link Removed
Invalid Link Removed

It sounds great - as long as you keep the drive WAY low. Anywhere above about "2" on the drive control and it's too much overdrive/fuzz.

After spending some time simulating the circuit, it's pretty obvious why - at the LOWEST gain setting, the 1n4007 diodes in the second stage start conducting at less than 0.2V peaks at the input - due to the minimum of ~5x gain coming out of the first stage.

I'm just looking for the least little bit of grit and touch sensitivity, and thought the Blueberry would be perfect because it is so often described as "low gain"...

So:

1) Does this seem to mirror others experience?
2) Does everyone just run a really weak signal in?
3) Correcting it - lower the gain of the first stage, or attenuate the signal feeding the circuit?
 
#2
I find it better than some other pedals; it handles my high output BB1025X better than the SFT did (which I had to run at 18v to increase headroom). So I'm not feeding it a weak signal by any means, I get a nice mild drive with the gain around 11 o'clock.

Maybe try and compare it to the real deal, in case there's an error either in the schematic, your build, or an off-spec component?

Also the Bearfoot is labelled as safe up to 15V, so you could perhaps try that?

If it sounds great with the drive way low, and too much drive at 2 - do you mean 2 o'clock, or 2 as in '2 out of 10'?
 
#4
dannybuoy said:
Maybe try and compare it to the real deal, in case there's an error either in the schematic, your build, or an off-spec component?
Click to expand...

If I had a real one around, I would...

It could be an error in the schematic.
It's unlikely an error in the build or an off-spec component... because Spice simulations of the circuit exactly agree with what I'm hearing.


dannybuoy said:
Also the Bearfoot is labelled as safe up to 15V, so you could perhaps try that?
Click to expand...

That will change the point at which the jfet starts distorting - but it will have zero effect on the inverse parallel diode clipping circuit, and that seems to be the issue.

dannybuoy said:
If it sounds great with the drive way low, and too much drive at 2 - do you mean 2 o'clock, or 2 as in '2 out of 10'?
Click to expand...

I mean '2 out of 10' (9 o'clock) - by the time I reach 5/10 (12 o'clock) it's full on fuzz.
 
#6
Mosfed said:
You messed something up. My blueberry can run with the drive dimed and not even come close to fuzz or heavy distortion. It's definitely pretty medium drive.
Click to expand...

Possibly - but what I'm hearing exactly agrees with simulation.

The first stage (depending on nature setting) has a gain of ~5x. As soon as the input peaks hit ~100mV, you're looking at 0.5 volts across 1N4007 diode clipper - and it starts conducting and chopping the waveform.
 
#7
aborgman said:
Possibly - but what I'm hearing exactly agrees with simulation.

The first stage (depending on nature setting) has a gain of ~5x. As soon as the input peaks hit ~100mV, you're looking at 0.5 volts across 1N4007 diode clipper - and it starts conducting and chopping the waveform.
Click to expand...

I have no idea of the electronics.

But - I can tell you from my experience with the Bearfoot Blueberry - and I run it with a pretty hot signal from a FEA Opti-Fet with the gain cranked and with an always on Fairfield Barbershop always before it. And its a medium-to-low overdrive pedal. Check out these sound samples of the Blueberry - I posted them on Monday. Those were done with the drive basically dimed.

As you would expect - useless without earphones or decent speakers.

 
#9
aborgman said:
Your dimed blueberry is about what mine sounds like (with my bass and amp) with the drive at 11-12 o'clock... and that is WAY fuzzier than I want.
Click to expand...

So then it has to be the schematic.

@Azure Skies is the guy that traced it, I think. Or sorry - he traced the BJFE version. But he should be able to help, I would think....
 
#10
I would take out the 1n4007 clipping diodes and see if the problem goes away. Chances are you either accidentally put in a schottky 1n5817 in it's place, or you got a bad spec'd 1n4007. You didn't by chance get the parts from Tayda, did you?
 
  • Like
Reactions: DirtyDuke
#11
In addition, I am convinced the 500k potentiometer is way too much gain for this circuit. The original BJFE had a 360K in it, and even that got distorted really fast. I've built a few original BJFEs usng 250k for TBers and I feel like the range of overdrive is just right.
 
  • Like
Reactions: DirtyDuke
#12
Azure Skies said:
I would take out the 1n4007 clipping diodes and see if the problem goes away.
Click to expand...

I'll give that a shot and see what happens.

Azure Skies said:
Chances are you either accidentally put in a schottky 1n5817 in it's place, or you got a bad spec'd 1n4007. You didn't by chance get the parts from Tayda, did you?
Click to expand...

It's definitely a 1n4007... and not from Tayda. I buy 'em cut tape 500 at a time from Mouser/Newark/Digikey. It's certainly possible there is bad part there though.

I'll probably just have to haul it into work and get it on some test equipment - hopefully comparing the Spice simulations with function generator/o'scope results will turn up something if it isn't a bad 1N4007.
 
#13
Check and make sure your R10 is truly 1k. If you put a smaller resistor there then it would increase gain (or if you shorted something, thereby decreasing the resistance). A smaller drive pot will definitely help. This is a big part of why the mad professor variant sounds so...different. They use a 1M potentiometer, and the gain is massive.
 
#15
Azure Skies said:
In addition, I am convinced the 500k potentiometer is way too much gain for this circuit. The original BJFE had a 360K in it, and even that got distorted really fast. I've built a few original BJFEs usng 250k for TBers and I feel like the range of overdrive is just right.
Click to expand...

The BJFE circuit is definitely lower gain - no matter the position of the drive pot.

In the BJFE circuit you're looking at an AC gain (ignoring the 2nd/3rd stage feedback) of 4x (1+ 3K/1K) and maximum of 374x (1+ 373K/1K).
In the Bearfoot circuit you're looking at an AC gain (ignoring the 2nd/3rd stage feedback) of ~6x (1+4.7K/1K) and a maximum of ~506x (1 + 504.7K/1K).
 
#17
JFETs tend to have a large variance in their Vgs. If you happened to get one with a low Vgs, you could be hearing the JFET clip. You might want to try replacing the JFET with a 3 pin socket, and try a few different 2N5952s to see if that solves the problem.
 
#19
Azure Skies said:
JFETs tend to have a large variance in their Vgs. If you happened to get one with a low Vgs, you could be hearing the JFET clip. You might want to try replacing the JFET with a 3 pin socket, and try a few different 2N5952s to see if that solves the problem.
Click to expand...


The jFet is socketed, so swapping it isn't a real big deal... but:

When I first built this last week, I didn't have all my parts in... so I was running it with an LF356 in place of the CA3130 and a 2N5485 in place of the 2N5952. It sounded the same, and the jfet bias was basically identical to what it is now with the 2n5952.


Seems to me you'd need to get >1V at the jfet gate to get it to really distort, and the 1n4007 clipper will never let you get anywhere near that.
 
Last edited:
#20
What bass are you using? The pedal's tone control plays a huge part in the way it clips. If the tone control is counterclockwise, the low end is boosted in the gain stage, making it sound more fuzzy/buzzy.
 

Latest posts

Top Bottom
Back