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Old 25th May 2006, 03:01 PM   #1
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Question Schematic Reading Help

Hello everyone, i'm trying to make a dicontinued effects pedal but am having trouble reading the schematic. I have a fair knowledge of electronics, but struggle with some things. Before I ask anything here's a link to the effect:

http://www.schematicheaven.com/effec...ifier_dist.pdf

I Know the 4 opamps are actally 2 dual opamps, (each with a shared power supply). But each opamp is labelled strangely. EG:

The first KA4558 is labelled at it's + Power input (I think it's the posative) U22B, the other KA4558 is labelled at it's + Power input (Again I think it's the posative) U24A. Dual opamp 1458 makes more sense because it is labelled U25A & U25B.

Q1 Surely if this is a dual opamp both KA4558 opamps would have the same Code for the power supply?

Q2 Are all opamps just grounded?

The 4007 Cmos chip used for switching is probably confusing everything as i have not seen it in any of my past DIY effects.
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Old 25th May 2006, 03:27 PM   #2
Netlist is offline Netlist  Belgium
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Hi orson and welcome.
This is a single supply design. VCC only, VEE is ground.
IOW, pin8= VCC, pin4= ground.
U22B and U24A are probably a small error in the schematic.
To me it should read U24A and U24B indicating the two halves of the opamp.
The label U23-6 and U23-8 however have corresponding points in the schematic. (R53, R54, R55...) There might be more.

I like the name: Punkifier

/Hugo
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Old 25th May 2006, 03:35 PM   #3
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Q1: Yes, both parts of KA4558 should be marked with the same symbol. Unless they used two KA4558 and used only half of each of them. Maybe the design of the printed board forced them to do so.
Q2: Yes, I don't remember which pin is it. Maybe pin #4 - you have to check it.
CMOS 4007 is not that unusual. Maybe it is not used in analog effects but it is used in many other electronic devices.

If you have problems with the schematics, I advise you to check effects for which printed boards are available. You can check www.tonepad.com

Marek
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Old 25th May 2006, 03:59 PM   #4
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Yeah sadly, this is quite a rare pedal (relatively), it's an effect that does sound synthetic and crazy, so it's unlikly that anyone would have bothered with this one. Purists believe everything should sound warm and anything that doesn't is bad, this is why this wasn't very successful. A lot of experimentalists & pro guitarists love this effect like Graham Coxon of blur etc as it is quite different.

So, how could i simplify, eg remove the cmos 4007 and use a mechanical bypass? I've never had anything to do with gates and would like to read up about them and add it later, it's just to test the basic circuit first.
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Old 25th May 2006, 03:59 PM   #5
Albertb is offline Albertb  United Kingdom
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You have a U25A and a U25B there. Note the pins are 1,2,3 for the A and 5,6,7 for the B. This shows that they are part of a twin opamp package, 4 and 8 are the power pins. You will find its data sheet here: http://www.fairchildsemi.com/ds/KA%2FKA4558.pdf

Your U22B and U24A will also be parts of a dual package, (along with U22A and U24B), and the other parts will most likely be used for other functions within the full original circuit, which are not shown here. This may be for nothing more than convenience of routing on the PCB. Power supply pins will be on 4 and 8 of the package feeding both opamps. This is a standard arrangement so on schematics the power supply pins are not shown or are just briefly mentioned. This is the case in your own diagram. Just take them as read and decouple from pin 4 to 8 with a small electrolytic at each package. (Paralleled with a faster smaller cap if you choose to follow modern practice).

There is no reason why you should not layout this unit around 2 dual opamps which will give you the 4 needed for the schematic you have.

The 4007 is an array of 3 MOSFET n/p pairs and once you can set out which is connected to what, it should not confuse you at all. You can easily find its pinout on the net but basically the first pair use pins 1,2,3,4,5 with their gates sharing pin 3. The second pair are at 6,7,8,13,14 with gates commoned on pin 6. (Pins 8 and 14 are termed Vdd and Vss on your schematic because internally they are used as references for other areas on the chip.) The last set are using 9,10,11,12 with gates on pin 10 and a pair of commoned terminals on pin 12.

Punk, Menace, Slam, and Spikes seem to suggest this circuit works by utilising the actions of a new family of sub-atomic particles. Care to suggest which names are still to be discovered?
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Old 25th May 2006, 05:14 PM   #6
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Rip, Regurgitate, Puke, and Nude Skipping

( These were probably the second choice of dod pot labels, and probably would have made more sense )
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Old 25th May 2006, 05:57 PM   #7
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I cant seem to find the 1458 opamp any suggestions for an equivelent?
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Old 25th May 2006, 07:54 PM   #8
infinia is offline infinia  United States
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Hi

MC1458
http://www.digikey.com/scripts/DkSea...=70276&Site=US


MC4558
http://www.st.com/stonline/products/...181/mc4558.pdf

CD4007
http://focus.ti.com/lit/ds/symlink/cd4007ub.pdf
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Old 25th May 2006, 09:25 PM   #9
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A couple of points:

U25A looks like it's connected in a slightly unorthodox manner. I'd connect 1 & 2 (output & inverting input) together for a classic unity gain buffer, and then provide a DC path from Vbias to pin 3 to bring it into a predictable operating point. 1 Mohm should do it.

The output transistor (Q60) has no DC bias, so it would probably clip rather badly, although that may be intentional...

Rune
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Old 26th May 2006, 04:23 AM   #10
Albertb is offline Albertb  United Kingdom
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"I cant seem to find the 1458 opamp any suggestions for an equivelent?"

Virtually Anything! Cheap, common and cheerful rules here. As long as your design stays within the opamps' parameter range what difference will actually BE HEARD in amongst all of the effects you are incorporating? Can you genuinely hear the sonic difference between the current fashion trend opamp and its predecessor when you are just using diodes to slice God knows how many percent off the top of every cycle of the waveform fed through the unit?

U22B is simply a follower so should be working in its linear region with no overload effects to even consider. Neutrality near as dammit!

U25B has 2 paralleled diodes after it, what can it offer to overall tonal quality?

As Runebivrin has pointed out, U25A seems to be missing bias components. At first I thought that, as transistor Q60 (?) on the output is in the same state, it just looks as a though the guys who put together the schematic had spent too long listening to the result at high levels! Then it occured to me that, if the circuit is correct, this may be intended to actually be taking a sort of digital derivative of the 2 previous clipped signals and squaring it off via positive feedback comparator action. Doesn't work as it is drawn though, the input would only be about +-0.6V. (And I can't imagine what it would sound like, ie WHY?) More bias components would be needed for that. I lean towards the incorrectly drawn follower until someone wiser tells me otherwise.

U24A gets what it squirts out, that is after the signal has been repeatedly decapitated and changed into something which would look more at home in an unhealthy phase locked loop circuit! It seems at first glance to perform some sort of partial integration maybe removing the most severe high frequencies from the square wave and softening it? Spikes and Menace? Again there would seem to be no need to make use of any special properties to do this.

Me, I'd use TL072s and wait for the barrage of criticism!

PS Same applies to transistors in this case as long as their voltage and gain is reasonably high. This 'aint a top flight Naim hifi amplifier!!!!
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