Keeley Katana Volume Problem

[nation]

Dear All

I'm working through a Keeley Katana and it's very loud. Using a 250k linear pot I get no volume at full CCW. As soon I crack open the volume pot it hits unity almost immediately and just gets louder from there. Virtually unusable. I tried changing to an audio pot and it now hits unity at around 9 o'clock. If I continue increasing the volume it gets way louder and more quickly than the demos of this pedal indicate. Other than leaving off the 4k7 LED resistor and the LED positive I haven't made any subs. The transistors are biased to 9 volts with the trimmers.

Layout and the schematic I assume this comes from are attached. It seems others have had a similar problem with this build but no solution has been provided. Anyone have ideas at what the problem could be??

[Fancy Lime]

Hi "nation",

couple things:

1) If you don't want loud, what is the purpose of building this thing? It's a booster, isn't it? I could be wrong but I think it is supposed to make the signal louder. A LOT louder. Unity at 9 o'clock sounds very reasonable for a booster to me.

2) This thing has, by design, a fairly insane amount of gain. If you are looking for a medium-gain booster, try leaving out one of the stages. Or better yet, use the second stage as a common drain (aka source follower) buffer. This will also mitigate some other problem (see point 4).

3) You definitely want a log pot, not a linear one for the volume.

4) JFETs get loaded down by resistance (or rather the lack thereof) on their output, especially in common source configuration. So if you plug the Keeley into something with low input impedance (certain mixers, audio interfaces... basically anything that actually expects a microphone to be plugged in), the gain of the second stage will change depending on the volume setting. If you plug it into a guitar amp, this should not occur. Making the second stage a buffer may help a bit.

So in summary, I don't think there is anything wrong with the booster itself and what you describe sounds pretty much like what I would expect by looking at the schematic. But the behavior of the volume knob may depend somewhat on the following device.

Cheers,
Andy

[sominka]

There's 151 comments about this build on the site you got the layout.

http://tagboardeffects.blogspot.com/2014/02/keeley-katana-boost-layout-rev-2.html

Have you read through them all? It shows as verified with multiple confirmations.

Cheers

[nation]

Hi "nation",

couple things:

1) If you don't want loud, what is the purpose of building this thing? It's a booster, isn't it? I could be wrong but I think it is supposed to make the signal louder. A LOT louder. Unity at 9 o'clock sounds very reasonable for a booster to me.

2) This thing has, by design, a fairly insane amount of gain. If you are looking for a medium-gain booster, try leaving out one of the stages. Or better yet, use the second stage as a common drain (aka source follower) buffer. This will also mitigate some other problem (see point 4).

3) You definitely want a log pot, not a linear one for the volume.

4) JFETs get loaded down by resistance (or rather the lack thereof) on their output, especially in common source configuration. So if you plug the Keeley into something with low input impedance (certain mixers, audio interfaces... basically anything that actually expects a microphone to be plugged in), the gain of the second stage will change depending on the volume setting. If you plug it into a guitar amp, this should not occur. Making the second stage a buffer may help a bit.

So in summary, I don't think there is anything wrong with the booster itself and what you describe sounds pretty much like what I would expect by looking at the schematic. But the behavior of the volume knob may depend somewhat on the following device.

Cheers,
Andy

Thanks Andy, this is useful info. Understand a booster is loud, just a little surprised as to how quickly this thing gets loud as I rotate the pot. Unity is a lot early than the other boosters I've built (SHO, EP Booster, Naga Viper, Rangemaster). The change to an audio taper made a lot of difference and now actually gives me a usable range before hitting unity at just after 9 oclock but still doesn't seem to operate like the demos of this pedal indicate.

Your point 4 though is very interesting - I've actually been testing this pedal with a S-Gear and a Line 6 audio interface. I'll hook up the pedal to a real amp later today to check.

[antonis]

If you can stand "scratchty" Volume setting, omit 250k pot and replace 4k7 (or 5k) pot for second stage Drain resistor..