ok i have the fet vulcan on breadboard, ive read through a few threads on it, that were pretty old, but still relevant.
http://diystompboxes.com/analogalchemy/sch/jfetvulcan.html
i was just wondering if there were any updated mods/tone control/ etc etc....its a pretty good hi gainer for a 3 fet (j201) jobby... :icon_twisted:
just in need of a few tweaks i think....ideas?...have you built one?...what were your findings?..preferences?...cheers rob.
IT's super high gain ! !
Tone shaping is subtractive, and requires a certain amount of current drive to work right, a gain=recovery stage post TC can bring the signal strength back up to normal or above normal output/volume.
Calculating the impedance is another matter, if needed add a buffer prior to the TC...a 'lighter load' TC might be another option, 'good' voicing + just a bit of treble control has served well on a number of other occasions [basically gets the 1 sound to be treble compensated as volume changes to help match amp>room>speaker settings/responses.
Hi Rob,
Maybe change the 100 pF right in the middle of the schematic?
Perhaps you like Davissons's BlackFire better. Listen to it at Paul Marossy's site:
http://www.zeta-sound.se/effects_eng.html
You can find the schem at the same place as where you found the Vulcan ( ...analogalchemy/sch)
Maarten
Yes, definitely tweak the 2.2M/100pf values. They have a large effect on the "voicing". For bass changes, the 1uf electro's can be reduced. I like a BMP tone control at the end of these type circuits. There is plenty of output.
Try this: use the 470k/470pf part as suggested and remove the last 1uf electro.
Also measure the bias of the J201's. I found they varied a lot when I tried it. ;)
cheers guys:
this has a heap of output, probably get away with a tone without a buffer i would think...(compared to bypass at the moment anyway)
i'm not a great fan of the bmp tone..its way to bright for my tastes, but i'll have a tinker with it as i have a seperate plugin vero board bmp with socketed caps/resistors.....i'll mess with values etc...
@wgtp: what were your bias voltages?...or rather what should they be?..
i'll mess with those 470k/470pf, and electro's too, it needs tightening up on the low E, definately, to get more of a punchy chug, it definately has great potential to be a
nice heavy and lead sound...
cheers guys!...
ok, been messing around with this a little more....
i'm getting dreadful hum on this..hmmmmmmm....not matter what i do. any ideas...
my bread connections are all ok, using a 9v psu which i have used for all my builds and is fine ,
i think i'll put 100k trimmers instead of the 100k resistors , to get a better bias/sound..
it sounds really flubby on the low end ...with no bite/definition....hmmmmm, time to get those trimmers on there i think....
Bias should be "around" the typical 4.5v with a 9 volt battery. Not sure about the humming. Try a .01uf input cap for tighter bass and reduced hum, experiment with it.
Using a resister between the output and the BMP tone control will reduce the highs in relation to the lows. Start with 10k and go to 100k if needed.
Good luck. ;)
cheers wgtp:
yep!, i just put trimmers on for the 100k's, hum has gone...so ive got to treat it as per dr boogey then really...4.5v, with a bit of tweaking by ear too... ;)
cheers man, i'll let ya know how i get on... thanks again.
I breadboarded this the other night. Ended up changing all the .1 caps to .01s and the middle transistor needed far more than 100k to bias right: I think I ended up at around 220k or so. In the end, I skipped the middle stage altogether! Less gain, but a more useable circuit for me. YMMV and probably will! :-)
Quote from: harmonic on September 01, 2011, 02:44:11 PM
I breadboarded this the other night. Ended up changing all the .1 caps to .01s and the middle transistor needed far more than 100k to bias right: I think I ended up at around 220k or so. In the end, I skipped the middle stage altogether! Less gain, but a more useable circuit for me. YMMV and probably will! :-)
hi cam: yeah gotcha, that middle fet needs way more to bias....god knows how it has 100k on there!... :icon_rolleyes:
this should be trimmers for sure!... 100k/200-250k/100k's...
anyway, i'll try a few other fets in that middle stage and try the .01's and see how it goes....cheers rob.
edit:, ok , ive changed the first 2 100nf's to 10nf's..and left the last 100nf in there.....much better but still lacking definition on the low 'E'
its ok on lead up to the 24th fret, but just gets muddy as you get lower, especially on the neck pickup... ::)
The only demo I've heard of it was Aron in another thread using what sounded like a (very tasty) strat -- single coils anyway. Sounded lovely on that. I have a two humbucker 'super-strat' with a coil-tap on the bridge pickup. It sounded really undefined on the lower two strings, but much better when I went to the single coil. What guitar are you using to test with?
hmmm...i'm not a strat guy...
ibanez rg470...humbuckers....
I can't remember. I know I loved the FET Vulcan. I usually just put in the Shaka Tone Control or for extreme control, a modified VOX tone control.
This was the thread I was referencing:
http://www.diystompboxes.com/smfforum/index.php?topic=67677.0
^ yep thats the clip i heard....it does sound fendery..and it sounds ok on the low end of things...hmmmm..... :-\
edit: heres a clip of what i have at the moment...as you can hear it gets real muddy stiill on the lower stuff......(just into a mixer no amp)..
http://dl.dropbox.com/u/7464107/vulcantest1.mp3
Intense! :-)
Are you using J201s? Whatever, maybe looking through your stock for lower hfe transistors to tone the madness down a little?
Try a .001uf input cap. ;)
Have had a lot of trouble breadboarding high gain circuits (especially with FETs), too much hum and oscillation. Even more so with 4 stages. The actual build should be quieter.
As far as the low-end goes, lowering the cap values would probably help, can always add the bass back in at the end with a tone control. Again the breadboard might be the actual culprit here, only one way to find out unfortunately :icon_mrgreen:
cheers guys:
that clip is with a 10nf input cap :-\, i'll get back on this today... thanks for your advice.. :)
i have made allowances for un-shielded breadboard, i'll try some different fets today n see how that goes... :icon_wink:
right just to report, i changed out the fets for 5485's/mpf102's , sounded a bit better, but its still fluffy.
rebiased all the fet's swapped n changed em round, changed the 100pf/470k/ to other values,
put all 10nf's in there..trimmers on all fets...........hmmmmm....still lacks that bite definition,on the low E, still muddy, its like the sound is 'around the note', rather than
a good pinchy punchy chug defined, ....i'm starting to believe this is just not for me!........i had the same with bsiab2 too.....bad low end.......
i guess that's a hazard of hearing and going by clips, too many variables, guitar/recording/amp/playing etc...........oh well.....boo hoo..thanks anyway guys!... :icon_cry:
Well, to achieve the ACTUAL and stable limiting of the signal voltage on the FET gates, it's necessary to shunt gates to the ground with the 2 MOhm (or so) resistors.
Obsreving signal form on the gate with the real scope shows the limited signal because input impedance of the scope works like such a shunt. But when you take the scope probe away from the gate, the gate voltage becomes not limited at all.
This effect have been caused with the diodes' and other leakages togetger with very high impedance of the gate curcuit.
Change the coupling cap before the Gain pot to 1n.
^ yep thats better..cheers,..its more toppy, but i'm sure that low end will be there if i whack a tone on it... ::)
this is what i have now...still not right, but a lot more defined/better...(with a crappy 1 pot tone on it)
http://dl.dropbox.com/u/7464107/vulcantest2.mp3
Sounds good man. :icon_mrgreen:
Have been working on a four-stage, channel-switching version of the circuit for the past few weeks. The breadboarded versions were completely unusable but fine when soldered together.
FETs are ultra-sensitive and can pick up signals through the air from across the room. Even though the breadboard contacts are insulated they are very close together and the FETs can still pick up signals they shouldn't. A soldered-together build is probably going to perform better.
Might try raising the source bypass cap values if you can't get enough low end from your amp controls. Another idea, the uppermost bias resistor (10M) doesn't necessarily have to go to 9v. You can use a lower value (say 2.2M or even 1M) as long as it goes to a lower voltage source. Possibly less noisy, unsure.
Quote from: Joe on September 08, 2011, 11:02:49 PM
Sounds good man. :icon_mrgreen:
Have been working on a four-stage, channel-switching version of the circuit for the past few weeks. The breadboarded versions were completely unusable but fine when soldered together.
FETs are ultra-sensitive and can pick up signals through the air from across the room. Even though the breadboard contacts are insulated they are very close together and the FETs can still pick up signals they shouldn't. A soldered-together build is probably going to perform better.
Might try raising the source bypass cap values if you can't get enough low end from your amp controls. Another idea, the uppermost bias resistor (10M) doesn't necessarily have to go to 9v. You can use a lower value (say 2.2M or even 1M) as long as it goes to a lower voltage source. Possibly less noisy, unsure.
hi joe: 4 stage one .nice.... dr boogie-ish is it?..
yeah i was looking at those 10M's seem a bit excessive in value, i'll try it, and the caps....
its funny i was going to pull this off my breadboard today, but i'll give it one more shot i think....cheers rob. ;)
edit: ive changed so many bits on this now i'm going to draw up a revised schematic..and post it up..
i tried changing those 10M - 4.7-1M much much quieter even on breadboard...its really getting there..this will be a totally different beast to the original...a lot more bite and 'defined' chug... :icon_twisted:
A little bit modded version just with 2,2 MOhm resistors - pls take a look here:
http://imageshack.us/f/839/jfetvulcan1.jpg/
With the low cut-off voltage FETs (J201 for example, Ucut-off = 0.5V) one can get about 80-90 dB gain with three stages.
So, is it necessary to add the fourth stage? :o
^ thats a heavily modified one eh...: i'd rather keep it to 3 stages too if i can.. :)
anyway heres where i am now..schematic and clip...its getting there!.. no tone control and recorded out of my bread into my mixer / no amp.
i let the note die off , its pretty damn quiet for being on a breadboard...i went with 2n5485's in the end and put the 10M'S back in.., less flabby that the j201's imo...
(http://dl.dropbox.com/u/7464107/vulcan3.jpg)
http://dl.dropbox.com/u/7464107/vulcantest3.mp3
I don't think C4 is really needed.
Quote from: Joe on September 08, 2011, 11:02:49 PMthe uppermost bias resistor (10M) doesn't necessarily have to go to 9v. You can use a lower value (say 2.2M or even 1M) as long as it goes to a lower voltage source. Possibly less noisy, unsure.
Hey Joe ( :icon_wink:) can you further explain what you mean by "lower voltage source"? Thanks.
i'll try it cheers...
Quote from: Davelectro on September 09, 2011, 12:39:12 PM
I don't think C4 is really needed.
Hey Joe ( :icon_wink:) can you further explain what you mean by "lower voltage source"? Thanks.
C4 is needed or the gain pot would interfere with the following stage's bias point.
For the lower voltage refer to the schematic DDD just posted, just a voltage divider filtered with a cap as seen on many opamp circuits.
Quote from: deadastronaut on September 09, 2011, 03:46:29 AM
hi joe: 4 stage one .nice.... dr boogie-ish is it?..
It's similar to the Dr. Boogey. Tried to cop the Orange and Red channel EQ's, and rigged up an fx loop for each channel. Switching is pretty basic, just a single DPDT relay to select gain controls and fx loop returns. Kinda noisy and trebly but working ok, will post circuit when I have time.