Building my Boss SD-1 PLEASE HELP!!

[Rock_on]

I saw an easy schematic Boss SD-1 and a slightly complicated one

right now i dont know what to choose.. the easier or the complicated?

i asked it here cause im afraid there would be a big difference in tone or anything...


what do you think guys?? can you tell me the difference?

[crane]

I'm sorry mate but there is no way we can tell the difference between those schematics if you don't show them to us.

[Rock_on]

I'm sorry mate but there is no way we can tell the difference between those schematics if you don't show them to us.

sorry i forgot

[crane]

and the "complicated one" is the original boss sd-1 schematic? If so then the main difference is that original schematic has all the bypass buffer on it. This one shows only the effect circuitry. If you care to compare it with the "complitaced one" - I think the will be 99% the same.

[Rock_on]

and the "complicated one" is the original boss sd-1 schematic? If so then the main difference is that original schematic has all the bypass buffer on it. This one shows only the effect circuitry. If you care to compare it with the "complitaced one" - I think the will be 99% the same.

ok.. so you mean it is the buffer which is different?

well i'll just make an easy one...

thanks.. but answr my last question

[crane]

What exactly is the last question - is it gonna differ in sound? I'm not sure if the original one uses 1N916 as clipping diodes. Those diodes are responsible for distortion.
Take the schematic and layout from the easy version (I assume you want to build it true bypass) and check the values with the original schematic.
On the other hand - why do you want to build SD-1 anyway? I know this is a DIY forum and it's fun to build stuff but I usually try to build things that are expensive/hard to get/bad quality. You can get used SD1 dirt cheap and mod the s**t out of it.
Nevemind the last paragraph - build it and have fun
Happy New Year as well

[Rock_on]

Happy New Year!! same to you my friend. hahaha


i man, do you mean the only difference is the buffer?

[crane]

The MAIN difference is the buffer. There might be some minor part value differences as well. I'm not sure if I'm supposed to do all the work
Ignore the bypass buffer and compare yourself
http://www.hobby-hour.com/electronics/s/schematics/boss-sd1-super-overdrive.gif

[Kipper4]

I dont mean to butt in or hijack the thread (newbie )
In the above schematic the +9volt appears to be going direct to the transistor or am i missing something.
Wouldnt the voltage be too high for a transistor?

[R.G.]

In the above schematic the +9volt appears to be going direct to the transistor or am i missing something.
Wouldnt the voltage be too high for a transistor?

Yes, the power supply voltage goes to the transistor's collector directly, as well as to the + power supply pin of the opamp. Yes, this is correct.

No, it's not too high for a transistor. Transistors can be made to withstand as much as 1kV or more, depending on the design of the silicon inside. Each transistor has a maximum breakdown voltage rating for the collector-to-base and collector-to-emitter.  It is unusual for a modern transistor to have a collector-to-emitter breakdown below 30Vdc.

That does not mean that you can simply connect power voltage to a transistor any way. The details of how parts and power are connected to the transistor determine how it works and amplifies signal. This particular circuit is inteneded to be an emitter follower, with a gain of about unity, and the connection of +V to the collector is OK for this circuit design.

[R O Tiree]

@ Rock on - You're going to have to include the few circuit elements that will enable you to apply the 4.5V bias that is required for some of the connections shown in your "simple" version. Look at the link provided by crane, and you'll see the ones you require are R18, R19 and C11.

@ Kipper - Have a look at the datasheet for a 2N3904, which is a very common TO-92 package transistor used in a lot of effects circuits. Check the absolute max ratings on the first page. Max voltage between C and E (V_CE) is 40V and max Collector current is 200mA. Well, 9V is well inside that max limit in any case and the Emitter is separated from GND by that 10k resistor, which means it will sit about 1 diode drop below the Base voltage. The 470k between the bias voltage and the Base will cause the reading at the Base to be somewhere around 3.5V or so, putting the Emitter voltage at around 2.8V. So, total V_CE is a shade over 6V - massively inside that 40V limit. Lastly, given 2.8V at the Emitter, connected to a 10k to GND, that puts the current at 0.28mA or so. I_E is only a few µA above I_C, so that 0.28mA is only about 0.14% of the max allowable I_C - again, no problem. Hope that helps.

[Kipper4]

Massively thanks.
Everyday i learn something new here. I love this forum.

[roseblood11]

Posted by IvIark over at the forbidden forum:



He has a simplified version without output buffer (but with clipping diode switch) on his blog as well:

http://tagboardeffects.blogspot.de/2012/02/with-switch-to-change-between.html

Offboard wiring for both versions:
http://www.aronnelson.com/gallery/main.php/v/Toneys-Album/Wiring.png.html?g2_imageViewsIndex=1

[Rock_on]

buffer? ok im right,,

can i make another more simpler buffer and connect it there??

look at this


what's the purpose of R18, R19, and C11???

[Rock_on]

When I follow the link directly, I see the image.
It looks like the main difference between the two schematics is that the more complex schematic includes a switch (the 2*2sk30A transistors) to select between the unmodified and the modofied input signal for output via zhe 2sc732 transistor.
This switch is controlled via the monoflop at the bottom (2*2SC1685 transistors) which in turn is toggled by the ON/OFF button at the lower left of the schematic.

It's up to you to decide whether that's an improvement in performance.

i asked this question on electronicpoint.com

that's what he said... i thought the buffer is the difference? unless buffer and the thing he is saying is the same...

[R O Tiree]

No... A buffer is a small circuit that can be used to present a very high (or low) impedance to an incoming signal and/or to separate 2 parts of a circuit so that what happens in one bit doesn't affect what happens in the other and vice-versa. In this case, it's the transistor and its associated resistors and caps on the left-hand side of the diagram you've posted at Reply #2 of this thread.

Taking a look at the schematic that crane linked you to, you can see that this buffer still exists in exactly the same format around Q5, at top-left of that diagram. You can see a very similar one around Q6 at the output of the circuit (at top-right). This one is there to provide a low impedance output to either the amp or the next pedal in the chain and to tidy up the signals from the switching circuitry, which I'll cover at the end... You'll notice that it doesn't exist in the schematic that you are using because it's not needed - that schematic assumes that you're going to use TB switching. Have a look at the various schematics for TubeScreamers and you'll see that they are very similar in concept and layout to the Boss SD-1 "cut-down" schem, with the exception of the TS-10, which is very similar to the full schem.

As to R18, R19 and C11, the 2 resistors act as a voltage-divider, so the junction between the 2 sits pretty close to half the supply voltage (4.5V, in this case).  The capacitor helps to keep that reference voltage smooth and stable. If you omit these components, you will have no means of injecting the required reference voltage (V_bias) into the relevant points in the circuit.

OK, the switching circuit... Have a look on crane's schem at Q3 and Q4. This is called a flip-flop. When you first power the circuit up, one of those 2 transistors will be "on" (passing a current) and the other will be "off" (not passing a current). If the transistor is not passing any current (because its Base is at a low voltage), then its Collector will sit at very nearly 9V (in this circuit). Press the footswitch and that criss-cross arrangement of caps and resistors will flip the Base voltages around, so the 2 transistors change state. More importantly, they will stay in this new state until the footswitch is pressed again, at which point the circuit "flops" back into its original state. Google "multi-vibrator" for more info on how they work.

Moving on to the 2 FETs, Q1 and Q2 (the chap at electronicpoint mentioned two 2SK30A transistors)... These are used to route the clean and distorted signals around to the output buffer (Q6, etc). FETs are pretty odd beasties, difficult to make consistently but with a variety of uses, from amplification stages to signal switches and many others. Hugely useful... In this case, they're being used as switches. FETs have 3 terminals - Drain and Source (the signal passes from one to the other) and Gate. The voltage at the Gate determines whether the signal passes through, or not. With N-channel JFETs (which these are - you could tell with a higher-definition picture because the arrow points iN), if you lower the voltage at the Gate compared with the Source voltage sufficiently, then the internal resistance goes up to an insanely high level, so no signal can pass through. If you raise the voltage at the Gate, the internal resistance gets very low indeed, so signal passes through freely. Now, have another look at that flip-flop and you'll find that the Gate of Q1 is connected (via a large resistor and a diode to "soften" the switching) to Q4's Collector. Q2's Gate is connected (via an identical arrangement) to Q3's Collector. Remember I said that, in a flip-flop, one side is held high while the other is low? That means that one of the FETs is passing a signal while the other one blocks... Press the footswitch the flip-flop changes over and the 2 FETs switch state as well. OK, so the signal from Q5's Emitter goes into C2 and also C9. From C2, the signal passes through the "core" of the distortion circuit finally appearing at pin 2 of the "Level" potentiometer and into Q1's Drain terminal. From C9 we get to Q2's Drain terminal. Both paths end, via their 22k resistors, at C8 and onwards through the output buffer (Q6).

Hopefully, I've shown how only one FET at a time can pass any signal, thus achieving the object of the exercise, and also extended your knowledge of the various sections of this circuit, which you'll be able to recognise in other circuits.

I suppose the big question, now, is "Why?" What's so good (and bad) about True Bypass? Exactly the same question can be asked about too many buffers in your signal chain.

Every time a signal travels through an amplification stage (even if it's unity gain or less) then noise is added (as well as a certain amount of frequency dependent phase-shift which you won't notice). Lots of buffers sitting between your guitar and amp could lead to excess noise, therefore.

A badly designed buffer circuit can alter the tone and/or volume of your signal.

Read this article by Pete Cornish, who makes bespoke pedal boards for a great many musicians. Having read that, you might think that TB is something to be avoided at all costs. Some really old pedal designs, however, do not play well with a buffer ahead of them as the guitar pickup is an integral part of the circuit's dynamics (rare).

A single-pole push-to-make switch is a single point of failure. That said, you have a slightly bigger board and only 2 wires to your switch instead of the usual rat's nest of wiring around a triple-pole double-throw (3PDT) switch. Arguably, any one of those 3 poles in a 3PDT switch could fail and would cause a similar failure in any case.

This list is not exhaustive and I'm sure a search of these forums will turn up several threads about the various switching systems in use. The jury is still out on this issue... Personally, I think a mixture is probably just fine.