thats true if you wanna take the ground from the home terminal directly but i was talking in general most countries have only 2 electricity feed terminals , 220 and nitre,so the transformers usually have 2 inputs(220 and nitre) and 3 outputs(+ , ground(nitre) , -)

yea sure why not ,as long as the output voltage is more than 9 volt for the regulator IC to output 9 exactly.
but make sure the transformer can provide the current needed by the loads ,should be written on each transformer.
also make sure to connect the circuit ground to the terminal between the positive and the negative terminals in the transformer (the terminal in the middle) they should have noted that in the link u wrote.

thnx 4 the link,, lookslike its got another good softs too

expirementing values using matlab is hard unless you have the transfer funcion.. does SPICE do it easily? and what version are you using?

Quotedecreasing the "sweep" resistor's value. (In "Fender" stack it's R1). You'll have to tweak other values accordingly to maintain proper response.

true but how would i know how to change the other values??
the transfer function for the fender stack is very complicated

yea its a nice program,but the you cant change the resistor/cap values to get better responses,,for example :
the fender response when it boosts the treble there is a gain of -3 db
and when it boosts the bass the gain is about -7db
i would like some resistor/caps values which gives me a gain of almost 0 db at each highest boost,, any idea?

at what frequencies should we boost the bass/treble/midrange in the tone control circuit of a guitar preamp for best tone?
i read somewhere that the midrange should be between 300hz to 500hz
,,is it true?

some important q :
how the heck can we calculate the powerchip voltage gain?
its a lil complicated thing to do.
ill try to get its transfer function n plot it by matlab but it doesnt look easy

and is c11 there to attenuate high freq signals?

QuoteHowever, unlike the drive channel (which already has this limiter) the clean channel has no individual volume control. I suppose you could (similarly to drive channel's arangement) add one to "upper" signal path that goes to SW1b.

isnt that VR1 is supposed to do? its a gain modifier for the clean sound so

QuoteThe schematic displays the component a bit strangely (it should have three pins)

well its 3pins but 2 of em are connected together and to ground,,right?

onething more is that the tone control itself ac couple its input with its output,there is just no dc path . so is it the output cap put there for the dc offset caused by the power chip?
and also wuts the cool thing about having R14 R16?some idea behind having the C12 inside the feedback loop.!!?

some points about the k-20X :
1/ that input configuration R1 R2 C1 C19 , thats a second order bandpass filter ,,well it doesnt make any phase distortion as long as the frequencies it passes are in a very big bandwidth ,,
but still dont know why use this kind of configuration.

2/the cutoff freq of the lowpass C2 R4 is about 225 khz ,,why that much? couldnt it be just about 40khz???

3/ nice configuration for the second op-amp,a third order filter for the overdrive,but, are the switches SW1A SW1B both switch in the same time?

4/ why use a lowpass to couple the tone control with the chipamp??

nice idea about using two different color leds teemuk ,ill try to include it and make a switch for this,,also the footswitch.

QuoteIt still has the same less than unity gain

cant we modify the values of C3 R5 to solve this? and let the pot take lower values than before

QuoteOops. My bad: I should have used a term "less than unity gain", which is more correct. That is prone to instability and opamp manufacturers generally suggest that such configuration should not be used. Why build an active attenuator anyway...

sorry but i dont see any less than unity gain configuration.
do u mean that the vol pot of the second stage can cause a unity gain?
even though ,,at this level the sound would be very very low so it wouldnt affect much.

well anyways i think ill go for the K-20X as long as joecool thinks that its a GREAT AMP...thanks joe and any of you guys wanna talk its circuit? cuz it looks impressing to me.

Quotethe preamp is the problem: Its basically just two gain stages, one with switchable gain and diode clipper. These drive a fender-type tone control circuit. Don't expect any miracles from such a simple arrangement

whats the bad stuff? the negative gain? how about modify that for a positive gain, and modify the resistors values,,would it help?
or the bad thing is the fendertype tone control ?? how about making the tone control an active circuit ,,any better?
i dont wana talk now about protections as much as i wanna talk clean sound,,
about the negative gain again all i know is that it shifts the phase 180 degrees,,so wut distorion would it make if i put two negative gain stages like its included in the design so i have the exact copy of the input signal with positive gain(180+180 = 360 = 0) any wrong with that?

good idea about ac coupling the power amp from the tone control ,lookslike we got rid of the cap this way.nice shot :tu: .

QuoteSince you are obviously after a DIY project that will provide a satisfactory outcome why not do it right from the beginning? Throw away the idea that the amp schematic should look simple.

well i was goin for simplicity cuz its gonna be my first built amp as i told you before ,,and yes nothin wrong to apply mods to the design and i will,like changin some resistors values(filters) and have the midrange pot u suggested and bypassing the op-amps with diodes also ill think of better supply,use the TL074 ,i love this IC's s;ew rate,, <3)lol,thats what i think of now.
,if you suggest me another circuit that sounds better than this and is fine for a first build Please let me know.
maybe i should go for joecool's suggestion,.thanks joe for the notice n thanks teemuk for your mods.

Quoteif you make R8 (5.1K) in the tone control variable you got yourself a "mid-range" control

thats a nice shot,,but im not pretty sure of the base range and the midrange in this circuit as long as the -3db of the highpass of r4/c3 is about 372 hz ,,,why on earth they cut the frequencies below? wouldnt that affect the bass control,,lookslike it needs too much boosting to have base ,,,
same thing for other c2/r4 a lowpass with about 300,000.0 hz as a cutoff ,,why that much? isnt better to make it somthin about 30,000.0 hz ??
you got also the lowpass of the volume control pot with the c6,,the band pass would get smaller or bigger as we vary the volume. wuts the point??protection against high amplitudes at high frequencies?could be?

in general the whole circuit looks fine to me but the cutoff frequencies of the filters look a lil strange as i indicated above.

QuoteHook a similar diode arrangement to the pin 5 of the input opamp and you have yourself an overvoltage protection, which will protect the input stage.

what should cause an overvoltage at the inputs? too much gain?

QuoteAs shown, the headphone out feature is rather useless. You need to wire it in such a way that plugging in the phones will disconnect the speaker. There are phonejacks that come with a suitable integrated switch for the purpose. It is strange that they chose to take feed for "line out" before the capacitor.

yea you are right and i decided to not include this headphone plug at all,about having the feed before the cap ,,mmaybe headphones'speakers have their own protection against dc,,or low dc voltage would do no harm.

QuoteYep, it looks like a very basic, simple and cheap amp. Expect it to sound like one as well.

yea it is but isnt chip amps supposed to sound better than discrete ones?
why would it sound cheap? a chip power amp with an op-amp preamp
,,i guess that should sound fine...maybe using the TL072 would make it better

thnx a lot man, u answered all my questions..
i was thinking to do any modification to the circuit but it looks pretty cool i dont wanna change anything
ill try to omit the c19 and see how does it affect the sound,, i dont think its more than a protection against dc .
since there are q's can be included in a FAQ ,why dont u guys make one? who is in charge here?since it saves a lot of questions its a good idea to go with.
again there are some caps in the circuit thats drawn different like c15
whats that shape means? and are they ufarad/volts ?

here is the amp