Carvin Legacy JFET emulation

[demym]

Hi,

i have breadboarded this Legacy JFET emulation:




I've used almost all the right values for caps and resistors.. It works, and the sound is nice and, i would say, very Legacyesque...

I only have a doubt; turning the 47k trimmers for third and fourth stage, they don't seem to have a 'central spot' (i mean, they work as a normal pot, from nothing to the maximum); the first two stages trimmers, instead, behave as usual in JFET emulations (bad sound or nothing at the extremes, and right spot while turning to the center);

has anyone tried to build this one ? The sound is good, as i said, only don't understand why those 3 and 4 stage trimmers don't behave as the first two ones (and as other JFET emulations that i have experimented)..


Thanks in advance

[Ripthorn]

I could have sworn there was another thread about this same circuit not too long ago.  But here is my suggestion, try a pot with a larger value.  Most jfet biasing trimpots are 100k.  If you really need to dial in the right spot, you might spring for 25 turn pots so that you can dial in the exact value and then replace with a fixed resistor.

[CynicalMan]

What range of voltages can you get at the 3rd and 4th JFETs' drains with the problem trimpots? Can you get 4.5V?

[demym]

Yes, i can get 4.5V also on stage 3 and 4....

I am used to adjust trimpots by ear first (but always measure voltage after), and on 3 and 4 i do not get the negative kind of biasing... but i can get 4.5V, so i suppose it's ok..

Thanks anyway

[roseblood11]

Hi,

has anyone got a layout (maybe veroboard?) for this circuit?


Immo

[Brymus]

I could have sworn there was another thread about this same circuit not too long ago.  But here is my suggestion, try a pot with a larger value.  Most jfet biasing trimpots are 100k.  If you really need to dial in the right spot, you might spring for 25 turn pots so that you can dial in the exact value and then replace with a fixed resistor.

I remember a Carvin Lone Star thread from a guy in New Zealend his emulation sounded good.

[aziltz]

I remember a Carvin Lone Star thread from a guy in New Zealend his emulation sounded good.

I thought it was the Mesa Lone Star?   

[Auke Haarsma]

I've posted a Mesa Lone star (Lonely Star) project a couple of weeks ago. Don't live in NZ however

[Brymus]

I've posted a Mesa Lone star (Lonely Star) project a couple of weeks ago. Don't live in NZ however

Your right I was thinking of your build  "my bad" IDK about the Kiwi refrence I must be losing my short term memory 

[demym]

I've finally finished the build of the JFET Carvin Legacy. I did it onto a veroboard; sounds awesome ! The tonestack is very responsive, and seems as each control influences the others (or maybe it's just me thinking it...).

I've followed exactly the schematic i posted at the beginning of the thread.

I only have one problem: when i connect the 47uF polarized cap on the gate of Q4, i get indeed more distortion (reaching what i think is the correct distortion amount for the real amp, that, apart from hearing it from the hands of SteveVai for many time every day, i never had the pleasure to play on it); but i also get some oscillation at high gain values (or having the treble pot at max); if i detach the polarized cap, i don't get any oscillation, but the sound is also more raw/dry, and less distorted that what it should be, me thinks.

I don't know if some of you guys have built this one, but, as i  followed exactly the schematic (using the same jfets, 2N5457), what could be the reason for that oscillation ? It happens only when the cap in parallel with the 2.2k resistor is connected, and only if i have gain at max and/or treble pot at max. Having gain at max and treble not at max doesn't cause any oscillation.

Maybe some of you electronics guys can answer this question ?

Thanks in advance, have a nice time