Darlington Pair wrote:Evanc521 wrote:Nate Dort wrote:tarandfeathers wrote:Nate Dort wrote:Evanc521 wrote:I don't understand the purpose of the voltage divider in the power supply... nothing appears to be connected to the half point.Ground (technically the zero-volt reference) is connected to the half point. This effectively creates a +-4.5VDC bipolar supply for the 4558. Fairly common in pedal designs. The alternative is to bias the signal to +4.5VDC at the input of each opamp with a high-value resistor and run the opamp at 9VNo idea what a real one is like but that schematic is drawn with two batteries, so the supply is +/-9VDC.You're right. Double the numbers I wrote up there.I'm pretty sure they're wired in series, so it'd be 18V.The batteries are drawn in series, but I'm pretty sure that just like most of the other EHX pedals that use two batteries, it's +/- 9V also the center of the power supply is earth which also says bipolar. The rest of the power supply is drawn for bipolar and it shows pin 4 of the 4558 connected to the negative side of the power supply, which would be earth if it were a single 18v supply. It's confusing because it's drawn wrong.Okay that makes a lot more sense... I'll try and draw up a corrected schem

endofanera wrote:Evanc521 wrote:Okay that makes a lot more sense... I'll try and draw up a corrected schemI don't have the knowledge or experience to get in the middle of this, but before you draw up a corrected schematic you may also want to read Nate's comment that followed the one you quoted.Nate Dort wrote:No, it's drawn just fine. 9VDC below "ground" to pin 4, 9VDC above "ground" to pin 8. +/-9VDC bipolar, or 18VDC between pins 4 and 8. It will work as drawn.The alternative is to connect the series junction of the two batteries directly to ground rather than using a voltage divider. The problem with that is if one battery has much lower voltage than the other, then you don't get a matched bipolar supply. The voltage divider always divides the total voltage by two (since the resistor values are the same), so the +/- swing will be equal above/below "ground".My mistake was missing that there were two batteries in the drawing, not one. Therefore, the voltages I originally stated need to be doubled.Yeah, he's right, I was looking at it wrong. Usually EHX does their bipolar power supplies like the Black Finger, which are not 18 volts of batteries with a voltage divider for +/- 9v, but batteries wired +/- 9v

anybody know what the impedance for the speaker is? I found one for cheap and it sounds super cool but I m not sure how long that speaker will last.

the finger genius wrote:Not exactly the same but I took the back off my dirt road special to check and it looks like 8 ohms.Also, I may try my hand at the preamp pedal before I try the Sunn clone. Dr Tony (or anyone else who was working on this) are any known problems with the layout or schematic before I dive in?Thanks!No clue on the Preamp Pedal. I was working on using the preamp from the actual amp (theyre different) as a pedal, but the tone control wasnt working and i never got around to messing with it any more.the finger genius wrote:Also, early dumb question, it looks like the switch is hooked up to output jack and power (I assume so power is disconnected when no plug is in?) - which type of switch should I be looking for for this (and the output jack would be different from input jack then I assume?)On the original there was a separate power switch to turn the power on/off. It wasnt connected to the stomp switch, and you dont use the stomp to turn on/off power. In any pedal from the last 40+ years the power is switched by plugging a cable into the input jack. You need to use a stereo jack for this, and the output can just be a normal mono jack.For the stomp switch, the original just switched the output from the effect out and the input. This can introduce some loading and "tone suck" and anything modern would either use true bypass switching or a buffered scheme. For this, id use true bypass. To do that you'll need a DPDT stomp switch, or a 3PDT if you want to add an on/off LED.

the finger genius wrote:llllllllllllllllllllllll wrote:anybody know what the impedance for the speaker is? I found one for cheap and it sounds super cool but I m not sure how long that speaker will last.There's also thishttps://reverb.com/item/9155063-electro ... m-spaeakerGreat! Before I buy it-Is it common for the speakers in this amp to be kind of farty, like certain Fender or Traynor speakers? If it is I won t need to replace it with the same one , however, if the speakers, when working properly, usually hold up to a regular guitar neck pickup signal when pushed I will jump on this.

Not exactly the same but I took the back off my dirt road special to check and it looks like 8 ohms.Also, I may try my hand at the preamp pedal before I try the Sunn clone. Dr Tony (or anyone else who was working on this) are any known problems with the layout or schematic before I dive in?Thanks!

Also, early dumb question, it looks like the switch is hooked up to output jack and power (I assume so power is disconnected when no plug is in?) - which type of switch should I be looking for for this (and the output jack would be different from input jack then I assume?)

llllllllllllllllllllllll wrote:anybody know what the impedance for the speaker is? I found one for cheap and it sounds super cool but I m not sure how long that speaker will last.There's also thishttps://reverb.com/item/9155063-electro ... m-spaeaker

the finger genius wrote:Evanc521 wrote:A few things:I don't understand the purpose of the voltage divider in the power supply... nothing appears to be connected to the half point. I'm sure there is a good reason for it, but I don't understand the purpose of the parallel resistors (circled in red). The volume control is fairly un-orthodox (circled in green)Not sure of the value of the "mystery pot{ (circled in blue).I'm going to throw this on the breadboard tonight or tomorrow to see what I can figure out. ...And here is an unverified vero layout from the schematic. Does any kind person want to walk me through this section by section (eg input, power, volume, tone, output, trim, etc...) and explain a little bit about what the different components are doing to someone who's just getting started? I'll buy you a beer at PRF NYC Also, I was checking the layout and think maybe the 10uF cap to the furthest right should actually be 1uF, assuming the schematic is right.I can do my best....what specific questions do you have?

Caps store a charge, sure, but that is only one application of them and for most pedals thats barely used except for some power supply smoothing. the other two main things that come to mind are decoupling and tonal control. Decoupling is filtering DC out of the signal. Caps only pass AC voltage, and not DC voltage. If you look at the top leg of the 2n5087 transistor in that schematic (the emitter), there will be DC voltage on that leg from the power supply, but also AC voltage in the form of the amplified input signal. The 1uF cap connecting that leg to the rest of the circuit filters out the DC (or "decouples" the stages) so that only signal voltage carries down.Caps can also be used for tone control as different cap values pass different signal frequencies. So you can use caps to drop highs or lows to ground, etc.One amazing site that you might wanna binge on is ElectroSmash. They have these circuit analysis posts that walk you through some classic circuits. Check it: https://www.electrosmash.com/mxr-distor ... s-analysis