Joe Davisson's JFET Vulcan has a low output volume?

[gigimarga]

Hello,

I've just finished a JD's JFET Vulcan using this schematic: http://www.diystompboxes.com/analogalchemy/sch/jfetvulcan.html.
I changed the 2.2M/100pF to 470k/470pF, too.
It sounds amazing, but it has a low output volume (I've expected to have a lot of volume)...

It's this OK or not?

Thx all!

[petemoore]

  The Vulcan's are known for high gain and output, there are fixed resistive dividers between stages, the second one [string of two 470k's] 1/2's the signal voltage.
  Jfet pinout re-verifcation is a must for these components, from the data sheet is the best way.
  This has 33k source resistors, I'm familiar with smaller values there, perhaps Joe has adressed some of the 'finicky Jfet' issues with this one.
  I remember some Jfets were stubborn to bias, I tried others, various drain resistor values.
  Because the gain stages are duplicative, the bias, and audio probe should give a pretty good idea of which stages are strong/weak [when audio sampling each gate/input, then the drain/output] and comparing the gain increases of the 3 stages. They of course will have different input levels though, each stage sees an input signal that has been boosted by the previous gain stage. All things such as this taken into account, the audio probe tells tales of strong or weak gain stage performance in any case.
  Read the "Debugging" sticky.

[gigimarga]

Thx a lot petemoore!
It seems strange to me to have a so low output, so I will follow your advice to test it with an audio probe.
I built the JFET Vulcan on a PCB of a Eighteen (which have worked, but I didn't like it anyway), so the J201 are OK.
The bias it's OK with the 100K: 4.5V on the drain Q1 and Q2 and 4.23 on the drain of the Q3 (what was very interesting is that I have 200K trimpots and I've set them at half...and I had from the start right voltages!)

[petemoore]

  Cool, set the trimpots by ear, I'd start with the last one first, tune them for loudest or focused sound.
  Sources above the gates voltage ?

[Joe]

Just remove the 470k/470k divider from the output. I should change those schematics. I think I did that so the volume difference between off/on wasn't quite as extreme.

Using large values (33k/100k) on the JFET's was simply to raise the gain without adding transistors. But you can do lower source/drain resistors, and use 4 or 5 stages, etc.

[gigimarga]

Just remove the 470k/470k divider from the output. I should change those schematics. I think I did that so the volume difference between off/on wasn't quite as extreme.

Using large values (33k/100k) on the JFET's was simply to raise the gain without adding transistors. But you can do lower source/drain resistors, and use 4 or 5 stages, etc.

Thx a lot Joe for all your work!!
I'm very exciting about building almost all of your circuits
ANyway, do you have some soundclips of them?
I saw that Obsidian has over 5 versions...

[Joe]

No sounds, sorry. I think Aron might have some Obsidian samples posted on here somewhere.

I was trying to make a transistor Obsidian for awhile, but scrapped it. The posted version is probably the best because the BS250's really have a lot less noise than BS170's or 2N7000's, if you can deal with the upside-down polarity.

The Vulcan circuits are pretty basic, I never hammered them out very well with tone controls, etc. Use them as a guide for your own creations. I should also mention that I was using EMG's when I designed them, so some boosting may be required for other pickups.

Thanks, and have fun 

[gigimarga]

Thx a lot Joe for your kindness!

I removed the 470k/470k network from the output and now sounds as I expected

Which do you think that it was the best version of Obsidian with BJTs that you built?

What tonestack (except the Big Muff-like) do you think that will be OK after Vulcan?