Thundercheif Build Report

[RDV]

I perfed this one up today, and it went well except I put the 2nd .68uF in the wrong spot. Got that fixed & off we go. A question: Is this circuit supposed to have a lot of gain? This one has about the same amount as the English channel I have. Quite a bit, but from the description at ROG I guess I was expecting a bit more. I also know better than to judge any circuit by listening through a 386 based amp(they lie). I'm looking forward to a "big amp" test, but that's rather difficult in the house.

Anybody got a answer to my gain question?



RDV

[tcobretti]

I haven't built the t-chief yet, but the older marshalls had less gain than you might think.  I had a 50w plexi and my line 6 plexi is the exact same - crunchy, not distorted as hell.

I apologize if I'm telling you stuff you already know.  

travis

[Lonestarjohnny]

Mine sounds about like the mp3 on ROG's site except i backed the gain down on mine, which i copyed the dark channel of the plexi preamp, then i built a bright channel that has a bit more gain, put it on another switch and i play clean through the dark channel and lead's with the 2 combined, smoke's just like my old plexi did when i put the jumper on the input's,
Johnny

[vdm]

i haven't built one (yet :twisted: ) but if you used different JFETs like 2N5457 or MPF102, they have lower gains than the J201s, so that's a thought.

my problem is i can't get the j201's here in OZ.. i guess i'll order some soon...

trent

[Alex C]

Hey RDV, I found myself in a similar situation after I built mine about a month ago.  It's got a decent amount of gain, but I need a booster in front to get it to sound like the "Bond" ROG sample.  Mine's nowhere near as crunchy by itself (even using humbuckers).   Also, mine's got quite a bit of treble, almost too sharp, and tacking on variations of LPFs on the end isn't doing much- it's either muddy or shrill or not enough volume.  Any ideas?  I know they're  probably basic ones, like other types of filtering, or tweaking caps, etc.  Any I should target specifically besides input and output?  Thanks; sorry I couldn't help, RDV, but you're not alone!

Alex

EDIT: I adjusted the trim values extensively to get EXACTLY 4.5V on each jfet, as I assume this is how the sample was recorded, and how the circuit is intended to be biased.  But I subbed in seriesed resistors for the trimpots (I needed them for something else), so I can't easily tweak the voltages.  Will changing the 4.5V increase my gain?  If so, do I want higher voltage or lower?  Thanks

[RDV]

Alright, scratch all that low-gain crap from my 1st post. I had the last JFet back ass-wards, and it was the only one I didn't socket(arrghh). I turned it around and it's got plenty of gain.

Alex C.:

Mine's kind of dark now actually. It sounds like I had the same symptoms as you. You might make real sure about the pinout of the JFets(especially that last one).

Regards

RDV

[Eddie]

I get too much gain from TC.I will try MPF 102.I use high output humbucker. Where do you get the distortion from? Second Jfet?
The real plexi gets the distortion from the poweramp mostly. Thats why I increased the byass resistor at Q2.

I think that that these Lowpass filters compensate the treble addition from the preamp you are using. Try to remove one! LPF too.Another idea is too use 20k trimpots instead the 15k fixed resistors. You could tune it by ear more easily.

You could remove both LPF`s and go straight in the poweramp via effects return.

Eddie