eniam rognab wrote:oh yeah, i asked my trusted professor at school today and here is what he said
he told me that if the booster stage increases the average DC current this, along with the bias voltage will cause the tube to saturate and red plate if there isnt sufficient limiting circuitry, damaging the tube. he also said that my amp would be perfectly fine!
then he told me a bunch of stories about tubes redplating and 1kW audio amps and then i forget.
does this make sense to any of my super smaht internet engineer buddies?
Sure it do. Herr Professor Ingenieur has very little to worry about, you too, because youre pre stage 12AX7 is so current limited that no matter what you send into it, the most that can happen is that it will distort and fuzz buzz like a fly in a bottle. A very small bottle. No worries all around. A tempest in a tea.... no, thimble. Rock on dude & start thinkin' about making your own overdrive & FX boxes. What they charge for a SHO is insane. This sort of thing, they don't teach in a kollij klassroom.
BTW I bailed on engineering after freshman year and changed major to physics, when I found my kooky kollij wouldn't teach me anything about electronics til senior year in engineering but did offer circuits & electronics courses to soph physics students. Also lucky my jolly physics advisor allowed me to take all the EE courses I wanted. Thank you Dr. Eppenstein! So I got what I wanted & life is good. Sort of. And I understand today's physics is tomorrows engineering. Respect all around, for the good ones. And understand, we all have our "blind spots."
"Wicked smaht", my uncle Ernie would have loved to hear you say that. His accent was way Down East, and with a vocational school education, he ran circles around many engineers & scientists & even MD's.
hey thanks for kind words leo!!
i am in my last semester of my A.S. degree. i cant see myself going straight into engineering school, probably find some employer that will work with me on that like five years out or something. we will see how this math class goes i guess...
i have a couple of design ideas brewing right now, i need more breadboards
this is my favorite season back home. i miss it. after the first frost all the bloodsuckers die and its just you, the dragonflies and the pines. you got a pile o firewood in the dooryahd needin splittin n puttin away, gearin up fuh wintah...
Last edited by eniam rognab on Wed Aug 28, 2013 12:44 am, edited 1 time in total.
JazzGuitarGimp wrote:Q1 in the EP booster is drawn as a JFET. I see the J201 are getting hard to find these days (at least from the mainstream suppliers). I've been using the J113 with good success, and it's a tiny bit quieter than the J 201. You may need to adjust the value of the 6K8 resistor in the drain. Ideally, you want to bias the JFET such that you've about 1/2 Vcc on the drain pin at idle.
sweet! thanks for the input! imma get me some J113s!
eniam rognab wrote:i have a couple of design ideas brewing right now, i need more breadboards
this is my favorite season back home. i miss it. after the first frost all the bloodsuckers die and its just you, the dragonflies and the pines. you got a pile o firewood in the dooryahd needin splittin n puttin away, gearin up fuh wintah...
One of the local guitar teachers started buying FX kits a few years back, then got ideas & expanded/modified the kit circuits. He's made a few dozen by now. Not a business but a bit beyond a hobby. Sells a few and dials 'em in right for their users. He sure knows his pedal building by now. Stopped in to pick up his fixed Fargen s/n 007 and while we were having a big jaw wag - earthquake. The one from Virginia, Aug 22 a couple years back. And it was slappin my place around a bit. No big deal in Calif but you don't expect that sort of thing in NY.
Yeah done the fall log stack back when I lived in the boonies, 10 cord on the porch and still ran out by March. Feels good splittin' though - imagine people I don't like under the axe - very amusing. Gets rid of bad spirits. Even in a T-shirt in 10 degree F weather. "Wood warms twice" - Henry Thoreau. House mates always wondered why I had a big smile on when I walked back in after a splittin' session.
JazzGuitarGimp wrote:I see the J201 are getting hard to find these days
It's an obsolete part, and you can look forward to more jfets in general becoming the same. As a device they just don't have a bulk market anymore.
Just the TO-92 pkg. Digikey show over 100k of the surface mount version available from the manufacturer and Mouser has 10's of thousands on hand as well.
Thanks to all for the FET advice.
I got put off FETs when I 'borrowed' a handful of BF244 from my college, 3 decades ago.
They work great, low noise / plenty of gain but add an unpleasant character to the tone. Every so often I revisit them and tweak the circuit, biasing etc but always come to the same conclusion.
I tried a couple of J201 recently and they were fine, but seemed a bit finicky regards biasing.
Any thoughts on the accuracy of that EP schematic?http://s21.photobucket.com/user/reverwe ... c.jpg.html
My concern being that Xotic claim 1M input and 1k output impedance, whereas the scheme posted would seem to be 500k and 8k2 respectively.
Pete
Forum member Sliberty built me one of these not too long ago. It is currently the pedal i use most along with a Geek triple B. As a clean boost it is excellent.
Forum member Sliberty built me one of these not too long ago. It is currently the pedal i use most along with a Geek triple B. As a clean boost it is excellent.
oh sweet! thats the one! i built my SHO in the really small half tall box that i can find at frys. only room for the switch, jacks, one pot, LED and circuit board all crammed in there. no way room for a 9v or any more controls.
schemo looks real similar to the SHO... maybe i can AMZize it
Very timely topic here for me! I apologize if this is a derailment.
But....I am drawing up an integrated clipper PCB for my JCM800 project and have included the AMZ Mosfet Clean Boost circuit to act as a post clip signal recovery stage. The clipping occurs post cathode follower/pre tone stack.
I suspect that I will need to dramatically reduce the input impedance of the Mosfet boost circuit given its location in the overall plan. But....I am not sure by how much. The info at the link indicates it is 10M in the stock circuit.
I don't have an amp with a CF stage currently at my disposal to do some measurements and was hoping that someone might chime in on that.
In leiu of additional information, I was going to stick a 1M lin pcb pot and tweak it on the fly. Maybe that is a good universal approach?
...Any thoughts on the accuracy of that EP schematic?http://s21.photobucket.com/user/reverwe ... c.jpg.html
My concern being that Xotic claim 1M input and 1k output impedance, whereas the scheme posted would seem to be 500k and 8k2 respectively.
...
I have no idea if that schem is accurate to the Xotic unit, but the DC input resistance on the schematic is 1M Ohm and output is 47.1k Ohm. Still not what you said Xotic quotes. Of course, the AC input and output impedances are complex, as in frequency dependent.
...I suspect that I will need to dramatically reduce the input impedance of the Mosfet boost circuit given its location in the overall plan....
That high of an input impedance could possibly present a noise issue. I would be more concerned with the max ratings of the devices in your 'new' AMZ booster. You should make sure they can survive that amp.
