Author Topic: BSIAB Build Question  (Read 301 times)

SpikeVelvet

BSIAB Build Question
« on: March 16, 2019, 09:54:22 PM »
I built a BSIAB from GGG and I love it. I played my first gig with it last night and it is everything I would think a $200 pedal would be. I play a Peavey Classic 50-410 and an HSS Lonestar Strat. My kit came with all 2N5457 transistors and I left C13 and C14 out of the circuit.

This pedal is great. In the past I have been an "amp overdrive only" snob. I don't currently play the kind of music that would need anywhere near the type of gain that would be described as a "Brown Sound". So, I play with the gain around 1-2 o'clock, even though it seems like a lot of the action is from 3 o'clock to full on. I would describe the sound as more 70's than 80's.

I love the punchy aggressive feel it has even with the gain dialed back. The notes practically jump off the fretboard, chords have a nice ringing articulation and single notes sing with a sweet sustain. The quality that really impresses me is how it cleans up. It seems like I don't lose any volume until I turn my guitar volume down to 3 or 4. So I basically have 6 or 7 different gain levels with just the guitar volume. Keep in mind this was at full stage volume with a good sounding tube amp IMHO so YMMV at bedroom levels with a SS amp.

All of that being said, the pedal does have a few issues:
I originally biased Q5 to 3.4V based on the GGG documentation and the volume didnít reach unity until almost 3:00. Upon reading the forums, I went back and biased Q5 by ear and it improved the sound of the pedal. Now, the pedal still doesnít reach unity until the volume knob is around 1:00-2:00. Iím not sure if this is a problem or standard behavior.
The other issue is that it seems the only useful Contour setting is to have the pot dialed all the way back. Is there any mod that would make the contour control have a different sweep and therefore make it usable?
Lastly, even though the pedal sounds great my VDC readings on the transistors are all over the place. Most are somewhat in the neighborhood but some are vastly different than the values posted on the GGG site.
Or could it be my own mistake?

So basically my question is are these problems I should be chasing? Given that I love the sound do I need to be concerned about the transistor voltages? I would prefer if unity on the volume knob was at 12:00 on the knob but it's not a deal breaker. I would like to improve the Contour control.

Any help would be appreciated. Thanks

Kevin

stallik

Re: BSIAB Build Question
« Reply #1 on: March 17, 2019, 03:19:16 AM »
Welcome Kevin.
You appear to really like the sound you have. For that reason alone, I would leave it as it is.
The inquisitor in me would like to know what the same pedal would sound like if all the reading matched the specs. More than once, I've spoiled the sound by chasing the numbers and have never been quite able to get it back. (I probably have but it never feels like it)
So why not build another to play with? You could always sell it when you're done....
Insanity: doing the same thing over and over again and expecting different results. Albert Einstein

SpikeVelvet

Re: BSIAB Build Question
« Reply #2 on: March 17, 2019, 04:04:10 AM »
Not a bad idea. I'm still going to crack it open and double check all of my values perhaps I misplaced a component. Even though with regards to resistors I measure each one before I slot it on the PCB. One thing that came to mind as I was researching this is, since it's a kit and prone to error in construction how many people have a bad opinion of the BSIAB because they played a faulty unit?
« Last Edit: March 17, 2019, 04:05:48 AM by SpikeVelvet »

Slowpoke101

Re: BSIAB Build Question
« Reply #3 on: March 17, 2019, 04:17:13 AM »
The initial biasing voltage for Q5 (GGG version ) is simply to bias the JFET enough to work - well, sort of work. As you found, setting the bias by ear is the way to do it (perhaps the term; "adjust for maximum goodness" applies here ). But I see no problem with checking your build even if it is just to set your mind at ease.

You must keep in mind that no JFET is the same as another (some are very similar but none are identical). Your voltages will vary. They will be close but not exactly the same.

If you like the way your pedal sounds, that is great. No matter what you did to get that tone that you like, if you like it then it is right....

Building another BSIAB may be fun and educational. Plus it gives you a platform to experiment with without upsetting your original BSIAB - keeping its tone.

..

amz-fx

Re: BSIAB Build Question
« Reply #4 on: March 17, 2019, 09:28:50 AM »
There should be plenty of volume available. However, if the volume pot is a linear taper, it could cause the volume control to be less responsive in the low settings. Be sure to use a log taper pot for the volume.

I would bias Q5 to about 5v to 5.5v.

http://www.muzique.com/news/amp-in-a-box/

regards, Jack

GGBB

Re: BSIAB Build Question
« Reply #5 on: March 17, 2019, 11:40:28 AM »
There are alternatives to the GGG contour mod that can work better or at least differently. One is Jack's AMZ Presence/Body control: http://www.muzique.com/lab/tone3.htm. The other is the Pinnacle variation of the tone stack and contour:



SpikeVelvet

Re: BSIAB Build Question
« Reply #6 on: March 17, 2019, 09:33:13 PM »
Thanks. I'll study those and try to absorb. Specifically, I was wondering if I did something wrong but the value of R7--5k6 (the resistor that is in series with the 100k Contour pot) is correct. Would lowering the value of this resistor change the sweep of the pot?

mth5044

Re: BSIAB Build Question
« Reply #7 on: March 17, 2019, 09:44:03 PM »
GGG stipulates 2N5457ís, but there are quite a few schematics and kits that use J201ís for Q3 and Q4, which I believe would give you more gain, and might help with your volume problem.

SpikeVelvet

Re: BSIAB Build Question
« Reply #8 on: March 18, 2019, 12:21:00 AM »
Thanks, Jack

I've been reading your material for quite some time. I'll double check my pot value

SpikeVelvet

Re: BSIAB Build Question
« Reply #9 on: March 18, 2019, 12:23:46 AM »
GGG stipulates 2N5457ís, but there are quite a few schematics and kits that use J201ís for Q3 and Q4, which I believe would give you more gain, and might help with your volume problem.

I am aware of that J201s can also be used in the BSIAB but gain isn't really my problem. I'm actually keeping the gain dialed back.

GGBB

Re: BSIAB Build Question
« Reply #10 on: March 18, 2019, 09:06:21 AM »
Would lowering the value of this resistor change the sweep of the pot?

Yes, but not very much I believe.