Crackle OK ??? - No Crackle far better!!!

    Re: Crackle OK ??? - No Crackle far better!!!

    I can usually tell what experience a person has by what they complain about. People complain about the "crackle" of this circuit topology. The truth is circuit design is about give and take. In this case the designer felt the advantage of this style of gain control out ways the disadvantage of the noise that is cause for a moment. Can the circuit be designed with the advantage of being "crackle" free ? Yes but at the disadvantage of a performance loss that some users may not like.

    The circuit is not bad, the creator simple made a choice to fit their design goals that may not suit your needs. Lets not bad mouth the circuit or designer for that. If you do not like their choice you can use another circuit. Pretty simple I think.

    BTW, why don't people just use a simple non-inverting opamp gain stage for a boaster ? I still don't understand that. ::)

    Andrew

    Re: Crackle OK ??? - No Crackle far better!!!

    Sorry Andrew
    You may be a talented designer BUT you have completely missed the point.
    A simple non inverting opamp is just that - simple.
    The Super Hard On, or the Box Of Rock input and boost stages are considerably more complex than they appear at first sight.
    As I and others have mentioned earlier in this thread, the crackle (sorry backward gain) control adjusts the bias voltage and therefore the operating characteristics (including the dynamic headroom and degree of asymmetry ) of the mosfet.

    To reiterate - at low settings the mosfet is biased for a very clean undistorted output. As the gain is steadily increased the bias point shifts AND 2nd harmonic distortion is gradually generated along with an increase in output level.

    This is a very musical sounding and clever circuit, even though it appears simple to the uneducated novice ;)
    What we need is some way of generating this gain dependant 2nd harmonic generation without that annoying crackle ::)
    I'm sure you and I both know who will be commercialy using the results if we succeed.
    Are you ready for the challenge? Or did you just come here to flame!! :*

    Ich liebe dieses Forum, und mein Name ist Steve von Neuseeland

    Re: Crackle OK ??? - No Crackle far better!!!

    Zitat von bajaman


    In other words it is not just a gain control but a harmonic distortion level control as well - quite effective as many have noticed

    Also, the input impedance varies as gain is adjusted. At unity gain it is about 5M and the impedance decreases as gain increases.

    Re: Crackle OK ??? - No Crackle far better!!!

    Zitat von bajaman

    A simple non inverting opamp is just that - simple.
    The Super Hard On, or the Box Of Rock input and boost stages are considerably more complex than they appear at first sight.

    Have you seen the schematic of the internals of a good opamp ? ;)

    I guess I should have been more clear. If one wants to attempt to design out the issue while still maintaining nearly the same circuit response then well have fun as that doesn't interest me.

    If one wants a simple and excellent performing boaster then I'll stick with the opamp. That is what the opamp comment was about.

    Andrew

    Re: Crackle OK ??? - No Crackle far better!!!

    Hi Andrew
    Yes , I've seen the internal schems for most opamps - all that gain and nowhere to go!!
    You do mean Booster, don't you??
    Having worked with op amps, transistors, fets, mosfets and vacuum tubes for many years, I think I know how most of these devices work thank you. ;)
    But if you don't want to help, then please don't hinder other folk's efforts - leave this thread and go back to your opamps :* :*

    Ich liebe dieses Forum, und mein Name ist Steve von Neuseeland

    Re: Crackle OK ??? - No Crackle far better!!!

    Zitat von bajaman

    You do mean Booster, don't you??

    Yes. Sorry for that.

    Zitat von bajaman

    But if you don't want to help, then please don't hinder other folk's efforts - leave this thread and go back to your opamps :* :*

    I don't believe I was hinder anyone's efforts. Most of the suggestions I would make that would work would defeat the simplicity of the circuit. I just don't understand people trying to reinvent the wheel of sorts. I thought the opamp suggestion might suit user's needs better but if this simple a matter of having fun with design then I won't stand in anyone's way. Enjoy.

    Andrew

    Re: Crackle OK ??? - No Crackle far better!!!

    Hi Andrew
    I appreciate your comments, and because the SHO circuit is in the public domain - at least I have been led to believe it is okay by ZVEX to post it over on Aron's site, I thought we might be able to improve (remove crackle) while still retaining it's good features as mentioned in my previous posts. This circuit and Jack Orman's mosfet booster are very similar at first sight, however there is a major difference - the bias shift and consequent harmonic distortion which varies with gain. If you look at Jack's circuit, he is only changing the AC or signal gain - the bias is unchanged - it gets louder thats all - a very nice clean boost. The Super Hard On is more like a well biased germanium fuzz face in operation - as the signal gain increases so does the harmonic distortion which is mainly 2nd harmonic.
    Unlike the germanium fuzz face though, the mosfet is nowhere near as temperature dependant.
    If you can achieve this type of operation with op amps, then you will become a very rich man :D
    If we are successful in our quest, then who knows where it may take us all :D

    Maybe we need to look at the crackle problem from a different angle - perhaps a way of moving the ground instead of the voltage :)

    Well after 1:30 am here - I'm off to bed - take care all :)
    peace
    Steve

    Ich liebe dieses Forum, und mein Name ist Steve von Neuseeland

    Re: Crackle OK ??? - No Crackle far better!!!

    Zitat von bajaman


    Hi Andrew
    IIf we are successful in our quest, then who knows where it may take us all :D


    Steve

    problem solved! ;)

    no - it`ll not bring me to noseyland or whine,
    but the schemo will go to 2wincity...

    ;D

    Re: Crackle OK ??? - No Crackle far better!!!

    Zitat von markm


    Funny, the crackle never bothered me at all.
    I mus be in the minority once again. ;D

    I've the same thought. I don't turn the poti while playing. I set it once before, maybe the soundcheck/... and then I let my fingers off of it. So there's no crackling while playing.

    But for sure, a non-crackling-pot would be an improvement. How necessary it is ... uhm ... I don't know ;)

    Give me enough knobs, and I can control the world. -Z. Vex

    Re: Crackle OK ??? - No Crackle far better!!!

    Zitat von puretube

    problem solved! ;)

    no - it`ll not bring me to noseyland or whine,
    but the schemo will go to 2wincity...

    ;D

    das Problem (für einige, offenbar), ist gelöst.

    wo uns/mich das hinbringt?

    mich nicht nach Noizyland oder Wein,
    aber die Schaltpictures in die Zwillingsstadt...

    [Übersetzung/translation]

    Re: Crackle OK ??? - No Crackle far better!!!

    I don't see a reason why you simply can't replace the pot with a CA3080 or another OTA wired into the "current controled resistor to ground" configuration?

    To control the OTA a simple pot + resistor as current limiter is sufficent. Adding a small cap at the Iabc input will supply the input with control current while the pot crackes.

    That will get rid of the crackle at the expense of a bit of headroom loss (the OTA can't really simulate a zero ohm resistor, and it will always be a diode drop or two above ground). All this however can be compensated by raising the supply voltage a bit.

    Nils

    Re: Crackle OK ??? - No Crackle far better!!!

    what's the problem with the cracle at all? who's turning the knob during a recording session oder in front of an audiance?
    normaly your pedalboard is preset or maybe you adjust it at the soundcheck. so, who's caring about some cracle in this situation?
    ok, if you like to control the pot with an expressionpedal it might be annoying, but show me someone, who's doing this with a SHO...

    Re: Crackle OK ??? - No Crackle far better!!!

    Hi Aetschi
    The pedal gain control was something I was planning on trying if...... 8)

    Ich liebe dieses Forum, und mein Name ist Steve von Neuseeland

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