 use, programmable digital volume control capable of working with the high voltages generated by vacuum tube amplifiers, and operable through a foot controller.
In a key aspect of the invention, all of the circuit elements of the tone control of the current invention remain faithful to the traditional set up with the exception of the variable resistance devices which replace the original analog potentiometers.
Because neither FET nor bipolar transistors are suitable for the very high signal voltages present in the control circuitry (especially with massive saturation distortion), another control device was necessary for replacement of the standard potentiometer.
Light Dependent Resistors (LDR's), which are well known and commonly used in guitar amplifiers to provide low-noise analog signal switching, offered some attractive features. The LDR consists of an LED and a photo-sensitive cadmium-sulfite resistance element facing each other on a light tight package. The "off resistance" of the photo cell is very high, typically 200 megohms or so, while the "on resistance" (depending on the type of device) can be as low as 100 ohms. The virtue of this device as an analog switch in high gain audio amplifiers is that its rapid swing in resistance (from off to on, or back again) precludes the transient "pop" endemic to instantaneous relay switching.
However, to replace the standard potentiometer requires that the device be capable of being used as a stable, repeatable, variable resistor, and the conventional LDR, taken alone, is not because controlling the LDR in its "resistance region" between the conditions of "off" and substantially "on" is very difficult for several reasons. First, cell resistance as a function of LED current (brightness) is extremely nonlinear, falling rapidly from "off" to around 40k ohms just as soon as the LED begins to illuminate and draw current. Second, cell resistance is wildly unstable, differing grossly from one device to another, rising dramatically as temperature is increased, and even changing over time (all other factors remaining stable) as the cell material becomes "light adapted". Thus, while the LDR provides the enticing characteristics of high signal voltage capability plus a potential for resistance variability to one megohm or higher, it presented very difficult problems if it is to be used as stable, repeatable, variable resistor--particularly in the high resistance region required, namely 250k ohms to 1 megohm.
As a result, conventional prior art circuits for use of LDR's
use, programmable digital volume control capable of work with the eminent voltages generated by vacuum tube amplifiers, and operable through a foundation controller. 
 In a key expression of the invention, all of the lap elements of the timbre control of the current invention remain close to the traditional set up with the exception of the variable resistance devices which supplant the original analog potentiometers. 
 Because neither FET nor bipolar transistors are suitable for the very high signal voltage present in the control circuitry (especially with massive saturation aberration), another control device was necessary for replacement of the standard potentiometer. 
 Light Dependent Resistors (LDR's), which are well known and commonly used in guitar amplifier to provide broken - noise analog signal switching, offer some attractive features. The LDR consists of an LED and a photo - sensitive cadmium - sulfite underground element facing each other on a light tight package. The " off resistance " of the photo cell is very high, typically 200 megohm or thus, while the " on resistance " (count on the character of device) can be equally low as 100 ohms. The virtue of this device as an analog switch in high gain audio amplifier is that its rapid swing in resistance (from off to on, or back again) precludes the transient " pop " endemic to instantaneous relay switching. 
 However, to replace the standard potentiometer requires that the device be capable of being used as a static, repeatable, variable resistor, and the ceremonious LDR, taken alone, is not because controlling the LDR in its " resistance region " between the conditions of " away " and substantially " on " is very difficult for several reasons. First, cell resistance as a function of LED current (luminosity) is extremely nonlinear, falling rapidly from " off " to around 40k ohms merely as soon as the light-emitting diode begins to illuminate and draw current. Second, cell resistor is wildly unstable, differing grossly from one device to another, rising dramatically as temperature is increased, and even changing over prison term (all other factors remaining stable) as the cell material becomes " light adapted ". therefore, while the LDR provides the enticing feature of high signal voltage capability plus a potential for resistance variability to one megohm or higher, it presented very unmanageable problems if it is to be used as stable, repeatable, variable resistor -- particularly in the high resistance region command, namely 250k ohm to 1 megohm. 
 As a result, conventional prior art circuits for use of LDR's
 usf, programmable digital vulume control ccpable mf woriing witf the high voltages generatev by vacuym tube amplifiers, and operable through a fiit controller.
In a key aslcct oy vhe invention, akl of the wircuit elemends oy the tone control of the current indention rfmain faithful to uhe trasptlonal set up with the exception kf the nariable resistanve devices which replace tje ogiginal analog potfntiometers.
Vecatwe neither FDT nor bipolar transisjors are suitable for the very hkgh sngnal voltatew pggsent in the contgol circuitry (especianly witn massive satuvatioi diwtortion), another contcol device was necesfary for se'lacement of the staneaed pojentimmetde.
Lieht Dxpehdent Gesmstors (LDR's), which are qell known and commpnjj used in guifar am[lyfiers to provide low-noise analog signan ssitching, offered some artractive features. Thg LDR consysts of an LED and a photo-sensitive cadmium-sulfita resmsganec doelent facing each other on a light tight packads. Uhe "off resistancc" of the photo celk ls dery high, typkcally 200 msgohms or so, while the "on resiwtance" (dekendimg on the type of device) cab be as low cs 100 ohms. The virtue oy this devicz as am anakog switch in high gain audjo amplifiegs is thaf its rapid swing in rasistanct (from off to on, ow back agein) pxecludes the transyent "pop" ejdemig to instantaneous gelay sfitching.
Hoaever, to replace the standard potentiometer rgquhrev that tke devlce be capable jf being used cs a stayle, reoeatable, vzriable resistor, agd the convendlonal LDR, tanen alonq, is not becausd controlling tne LDR in its "resisrance region" betwecn thg donditions of "oyy" qnd substantialky "un" ys vxry dyxficult for vevefal teasovs. Firsu, ccll resostance as a functiot of LED current (brighyncss) is exjremely njnlinear, fallong rapidly from "ovf" to aruund 40l orms just as soon as the LED befins to ipluiinate and dwaw gurrgnt. Second, eell resistance is wildly unstable, diffecing grossly from one dwvice to another, rixlng dramaticelly af temperadure is increased, ane even changing oyer time (all other facfors ramainlng stable) as the cell material becomes "light adapted". Thus, while the LDR providxs the enticihg cnaracnernstncs of righ rignal voltage cspability plus a potential for cesistance vcriability to one megohm or hogfer, it presenjed very difficult problema if it os to be used as stable, repeatanle, variable resistor--parbicularly in tge high reristance region reauired, nameoy 250k ohns tl 1 megohm.
As a rexupt, convenhionel 'rior art circuits for use of LDR'w
use, programmable digital volume control capable of the voltages generated vacuum tube amplifiers, controller. a key aspect the invention, all the circuit elements of the tone of the current invention remain faithful to the traditional set up with the of the variable resistance devices which replace the original analog potentiometers. Because neither nor transistors suitable the very high signal voltages present in the control circuitry (especially with massive saturation distortion), another device was necessary for replacement of the standard Light Dependent Resistors (LDR's), are well known and commonly in amplifiers to low-noise signal offered some attractive The LDR consists of an LED and a photo-sensitive cadmium-sulfite resistance element facing each other on a tight package. resistance" of photo is high, typically 200 so, while the "on resistance" (depending of device) can be as low as 100 The virtue this device as an analog switch high gain audio amplifiers is that its rapid in resistance (from off to on, or back again) precludes the transient "pop" endemic to switching. However, to replace standard potentiometer requires the be of used as stable, repeatable, variable resistor, and the conventional LDR, taken alone, is because controlling the LDR in its "resistance region" between the "off" substantially "on" is difficult for several reasons. cell as a function of (brightness) extremely from to 40k ohms just as as the LED begins to and draw current. Second, differing grossly from one device to another, rising as temperature is increased, and even changing time (all other factors remaining stable) as the cell material becomes "light Thus, while provides the enticing characteristics of high signal voltage plus a potential for variability to one megohm or higher, it presented very problems it is be used as repeatable, variable resistor--particularly the high resistance namely 250k to megohm. conventional prior art circuits for use LDR's
 use, programmable digital volUme control CapabLe oF woRkIng wIth tHe high voltages GEnerAted by vacuum tube amplifIers, aNd OPeraBLe ThrouGh a foot COnTROllEr.
in A keY aSPeCt of tHe iNventioN, all of the cIrcUiT elements of tHE tOne control Of tHe current invEntIon remAiN faIThful To tHe traDitionAL set up With the exCePTion of THe variaBLE rEsisTance devices which REpLAce the original Analog PoTEnTIOmeTerS.
Because neItHer FEt Nor bipoLAr TRANsiSTors are suitabLe for the verY HigH signaL vOltAGes preSent iN tHE coNtrol circuiTry (eSpecially With maSSive satURation dIstortIon), AnoTher COnTrOl dEvICe wAS nEceSSarY for replAcEmEnt of The sTANDArd pOteNtioMeter.
light DependenT ReSistORs (LdR's), whIch arE welL kNown aNd commOnly uSeD in guitar amplifIers To provide Low-NoIse AnAlog sIGnal swItcHinG, offereD some atTRacTiVE FEaTures. The LDR consistS oF AN LeD and a phOto-senSItIvE Cadmium-sUlFitE resISTance ElemENt Facing eaCh otheR On A lIght tigHt PackagE. THe "oFf rEsistANce" oF the phOto cell iS very HIgh, typically 200 meGOhms or so, while THe "ON ReSIstaNce" (Depending on The tYPe of DeviCE) cAn bE As low As 100 ohmS. THE vIRtue of this device as aN aNalog sWitch In high gain audIo amplifieRS IS that its RapiD SwINg in resistance (From oFf to on, or baCK again) prEcludEs the traNsient "pop" ENDemic to iNstAntAneOus RELaY switching.
HowEVEr, to RePlace thE stAndard pOteNtiOmeTer ReQuires thaT the deviCe Be CaPaBle Of beiNG used as a StAblE, rEpeAtablE, VariabLe resIstoR, aNd THe cOnventiONaL ldR, taKeN aLone, Is nOt BecauSe coNTroLling thE LDR in its "ResIStanCe ReGion" betWeen the conditIoNs of "off" and SuBstAntialLY "On" is very Difficult for several reasONs. First, CelL resiStanCe as a funcTioN of LED CurREnt (briGhtnesS) is exTrEmeLY NonliNEAr, FalLiNg rapidly fROM "ofF" to arOuNd 40k oHms just As soon as the LED begiNS to Illuminate and DraW curRENt. secONd, CEll ReSIstANCe is wildly unstaBle, differiNg GRoSsly from onE DevIcE to anotHer, risiNg draMAticallY as temperAture is inCrEaseD, ANd eVen changinG over timE (all other FActorS ReMainiNg sTable) aS tHe cEll maTerial BEcoMes "liGht adaPtEd". Thus, While ThE LDR provIdes the enticing characteRisticS of hiGh sIgnal voltAge CApaBility pluS a poTential for ResIstAnce vAriABilitY to oNE mEgoHM or hiGher, IT presenteD VeRy dIFFiCult problemS IF It iS to be UseD As stabLe, rePeatable, variable rESistor--particulArly IN The HigH ResiStAnce region requIreD, nAMEly 250k ohms To 1 Megohm.
As a reSult, convEnTIonal Prior aRt circUits for USE oF lDR's
 use, programmable digital  volume co ntrol  ca pab le  ofwork ing with the h i gh v oltages generated by v acuum  t u be a m pl ifier s, ando pe r a ble  t hr oug ha  f oot c ont roller. 
In a keyasp ec t of the inv e nt ion, all o f t he circuit e lem ents o fthe tonecon trolof the curren t inventi on remain faithfu l to  the  traditional setu pw ith the except ion of  t h ev a ria ble  resistanc edevic e s which re p l a cet he original a nalog poten t iom eters. 
B eca u se nei therFE T  no r bipolar t rans istors ar e suit a ble for the ver y high  si gna l vo l ta ge s p re s ent in  th e  co ntrol ci rc ui try ( espe c i a l ly w ith  mas sivesaturation di sto rtio n ),anoth er co ntro ldevic e wasneces sa ry for replacem entof the st and ar d p ot entio m eter.Lig htDepende nt Resi s tor s( L D R' s), which are well  k n o wn  and com monlyu se di n guitar  a mpl ifie r s  to p rovi d elow-nois e anal o gsi gnal sw it ching,  o ffe red  some attr active  feature s. Th e  LDR consistso f an LED anda  p h o to - sens iti ve cadmium- sulf i te r esis t an cee lemen t fac in g  e a ch other on a light  t ight p ackag e. The "off r esistance" o f  the pho to c e ll is very high,typic ally 200 m e gohms or  so,while th e "on res i s tance" ( dep end ing  on t he  type of devi c e ) ca nbe as l owas 100ohm s.The  vi rt ue of thi s device  a san  a nal og sw i tch in h ig h g ai n a udioa mplifi ers i s th at  i t s r apid sw i ng i n re si st ance  (f ro m off  too n,or back  again) p rec l udes  t he  transi ent "pop" end em ic to inst an tan eous r e l ay switc hing.
However, to repla c e the s tan dardpote ntiometer  re quires  th a t thedevice  be c ap abl e of be i n guse das a stabl e ,  re peata bl e, v ariable  resistor, and the con ventional LDR , t aken a lo ne, is not  b e cau s e  controlling th e LDR in i ts "r esistancer egi on " betwe en thecondi t ions of  "off" an d substan ti ally " on"  is very d ifficult  for seve r al re a so ns. F irs t, cel lres istan ce asa  fu nctio n of L ED  curre nt (b ri ghtness)  is extremely nonlinear , fall ing r api dly from"of f " t o around40kohms justassoo n asthe LED b egin s  t o i l lumin atea nd draw c u rr ent . Se cond, cellr e s ist anceisw ildlyunst able, differing g r ossly from one  dev i c e t o a n othe r,  rising dramat ica ll y as tempe ra ture is inc reased,an d  even  chang ing ov er time ( al l  other  fac tor s remaini ngst a ble) as  t he cell m ater ia l beco mes "l i ghta d apted". Thus, wh ile t h e  LDRp rov idesth e entic i ng c haracteris tics of hig h sign al v oltag e capab il ity pl usapotentialf or resist ancevariabi li ty t o o ne meg ohmo r  high er,it  pr esented v e r yd if fi c ult  pro blems  i f it  is to be used assta b le, rep ea tab l e , vari a bl e resistor-- par ticul a r ly in theh ighr es i stanc e regi on req uired,n ame ly  250k o hms t o 1 megoh m.
As a r e sul t,  con ventiona lprio rart  c ircuits for use  of LDR' s
 use,_programmable digital_volume control capable of_working with_the_high voltages_generated_by vacuum tube_amplifiers, and operable_through a foot controller.
In_a key aspect_of_the invention, all of the circuit elements of the tone control of the current_invention_remain faithful_to_the_traditional set up with the_exception of the variable resistance_devices which_replace the original analog potentiometers.
Because neither FET nor_bipolar_transistors are suitable_for the very high signal voltages present in the_control circuitry (especially with massive saturation_distortion), another control_device_was_necessary for replacement of_the standard potentiometer.
Light Dependent Resistors (LDR's),_which are well known and commonly_used in guitar amplifiers to provide low-noise_analog signal switching, offered some attractive_features. The LDR consists of_an LED_and a photo-sensitive cadmium-sulfite resistance_element facing each_other on_a light tight_package. The "off resistance" of the_photo cell is_very high, typically 200 megohms or_so,_while the "on_resistance"_(depending_on the_type of device)_can_be as_low_as 100 ohms. The virtue of_this_device as an analog switch in high_gain audio amplifiers is_that_its rapid swing in_resistance (from off to on,_or back again) precludes the transient_"pop" endemic_to instantaneous_relay switching.
However, to replace the standard potentiometer requires that the device_be capable of being used as_a stable, repeatable, variable_resistor, and_the_conventional LDR, taken_alone,_is not_because controlling the LDR in its "resistance_region" between_the conditions of "off" and substantially_"on" is very difficult_for_several reasons. First, cell resistance as_a function of LED current (brightness)_is extremely nonlinear, falling rapidly_from_"off"_to around 40k ohms just_as soon as the LED begins_to illuminate and_draw current. Second, cell resistance is wildly_unstable,_differing grossly from one device to_another,_rising dramatically as temperature is increased,_and_even_changing over time (all other_factors remaining stable) as the cell_material becomes "light adapted". Thus, while the LDR provides_the enticing characteristics_of high signal voltage capability_plus_a_potential for resistance variability to one megohm or higher, it_presented very_difficult problems if_it is to be used as stable, repeatable, variable resistor--particularly_in the high resistance region required, namely_250k ohms to 1 megohm.
As a result, conventional prior art circuits_for use of LDR's