New BSIAB build advice

[grs149]

Hello,

After a 10+ year hiatus, I am back building guitar stompboxes, so I thought I'd throw my hat in the ring with this forum. In the mid-80's-early 90's, there were no online communities for sharing ideas, so we had to rely on books, magazine articles, and personal experimentation to figure things out. On that note....

I recently competed a build of the BSIAB II and, while it has an amazing sound, I have run into a couple of problems. First, the available gain seems incredibly high, ranging from heavy overdrive to absolutely blistering distortion. Is this what I should expect from this pedal? Second, it tends to go into self-oscillation (even with the guitar unplugged) at higher drive settings, which I'm pretty certain is not normal.

I compared the voltage readings on my build with the ones quoted at General Guitar Gadgets and noticed that the Source readings for Q1 and Q3 were well below spec (10-20% of specified value). I should point out that I used all J201's for this project, because I had no 2N5457s on hand.

My initial idea was to increase the values of the Source resistors for Q1 and Q3 to get the voltages closer to spec. I also thought about buying some 2N5457s, so that I can build the circuit as-designed. Is there a big difference in the operating parameters of these two devices?

Any advice would be appreciated.

Greg

[troubledtom]

hello, welcome,
   did you shield the input and output wires and ground one side of each?
        peace,
           - tom

[grs149]

did you shield the input and output wires and ground one side of each?
        peace,
           - tom

Nope, no shielding. The whole works is spread out across my workbench. Are you thinking that shielding will get rid of the oscillation problem?

-Greg

[kojjum]

Yes, Im' quite sure it will. The usage of 2N5457 will also contribute to a more silen t circuit. I believe tje J210 is higher gain than the 2N5457. I've tested the NTE247 as well. That's way to much gain. Best combo I think is the one in the original scematic, 32n5457 an 2xJ201.

In my builds I've used shielded cabels from jacks to circuit board. That solved all my problems.

//j

did you shield the input and output wires and ground one side of each?
        peace,
           - tom

Nope, no shielding. The whole works is spread out across my workbench. Are you thinking that shielding will get rid of the oscillation problem?

-Greg

[Ed G.]

Hello,

I compared the voltage readings on my build with the ones quoted at General Guitar Gadgets and noticed that the Source readings for Q1 and Q3 were well below spec (10-20% of specified value). I should point out that I used all J201's for this project, because I had no 2N5457s on hand.
Greg

That's why you have too much gain. It's worth the wait to try out the 2n5457's, they are lower gain, and have a tigher more focused response.
Once the circuit is boxed, it should be very quiet for a high gain device.