Ibanez Tube Screamer with one or two JRC4558D ICs, what's the difference?

[anotherjim]

I've gathered that the MC1458 is probably the most common and longest lived type of dual 741 op-amp. Previous ones needed more than 8 pins for both offset null connections, such as the LM747. The 4558 was seen as an improved 1458.

[StephenGiles]

"Neckbearded"?   

"neckbearded" - a gender neutral worn beard around the capacitors!!!!!! Have you not seen them??

[Ashura]

The header of this thread asks "What's the difference?".  I'm presuming the implied question is whether there is a sonic difference.

Yes, indeed the question is focused on this. However, I think it would be interesting to know the technological/technical difference between the two ways of doing it. Which, after all, would be better... (?)

[ElectricDruid]

"Better" isn't a term that means anything on its own. It always comes with parameters attached, even if those are only implied. I suspect you mean "sonically", but "lowest cost", "simplest layout", "easiest part availability", "most robust", "lowest current consumption" and others are all valid, along which whatever weighted combination of those you want.

I like simple circuits, so while I'll add parts if it makes a big sonic difference, I won't keep adding bits for marginal gains in quality. Plus "sounds good" doesn't always mean "technically the highest specification". We're rarely looking for 20-20KHz flat bandwidth and distortion figures of 0.01%. So even "better sonically" can be a bit vague!

[Mark Hammer]

"Neckbearded"?   

"neckbearded" - a gender neutral worn beard around the capacitors!!!!!! Have you not seen them??

Only when I look in the mirror after starting a shave, only to find out that the blade is too dull to continue after doing the "easy" parts.

[ElectricDruid]

+1 totally agree with Mark's post.

There's a lot of stuff about different op-amps will show up when you push them hard or beyond their design limits - e.g. into clipping.

But when you use them at unity gain as a buffer? Nope, not so much. You'll really struggle to find measurable tonal differences from one to another for many common op-amps.

I couldn't care less whether the buffers on my tube screamer were transistor or op-amps, as long as they were designed decently.

[thermionix]

"Neckbearded"?   

neckbeard n. - A man whose facial hair grows mainly on his neck and not on his face.

neckbeard v. - To hoard or buy up large quantities of hard-to-find items.  Apparently a common practice among neckbeards.

[Ashura]

I thank everyone who participated in this conversation about the JRC4558D on this Ibanez Tube Screamer pedal.

Changing a subject, but still talking about the same pedal, I would like to know what the function of this diode(D8) W03C in this circuit (?). I imagine my doubt comes from my little knowledge about electronics, but, why is this diode in parallel with the positive and negative tracks? If his function is to protect the circuit from a reversal of polarity, should not he be in series position on the circuit? Being in parallel it seems to me to have no function ... (?!)

[tonight, we ride]

It is there for reverse polarity protection of the DC jack. Plug in the wrong type of jack (negative tip vs. positive tip) and the diode acts as an easier path for current than the rest of your circuit so you don't damage anything further down the line.

You can do a similar thing with a forward-biased diode in series with the positive side of the DC jack, but then your circuit power is a diode drop less than whatever you plug in.

[Ashura]

It is there for reverse polarity protection of the DC jack. Plug in the wrong type of jack (negative tip vs. positive tip) and the diode acts as an easier path for current than the rest of your circuit so you don't damage anything further down the line.

You can do a similar thing with a forward-biased diode in series with the positive side of the DC jack, but then your circuit power is a diode drop less than whatever you plug in.

Thanks @tonight, we ride. Now I understand. So, this diode creates a short circuit situation, right? Is this short circuit situation technically better than placing diodes in series on the positive and negative tracks, which, instead of causing a short circuit, would block the current flow if an inverted polarity source were used?

[sominka]

No not short circuit.
Stops the current flowing the wrong way which will damage the opamps.

Please can the people who understand electronics better than me reply in a way that everyone understands and not get too technical.

Cheers

[tonight, we ride]

It's not a short circuit either way... the diode is there to offer resistance between the two power nodes and drop voltage.

Imagine having the pedal powered as expected: you would have +9V DC on the top node (connected to the cathode - negative terminal of the diode), and ground connected to the bottom node (connected to the anode - positive terminal of the diode). This is normal operation, and creates a situation where the diode is reverse-biased and thus can be considered a HUGE resistance to current flowing through it. Current gets to that point, effectively ignores your diode as a path to get back to ground, and instead continues forward to your circuit.

Now imagine the opposite situation occurring from accidentally plugging in a DC jack that has the polarity reversed: you would have ground on the top node (connected to the cathode - negative terminal of the diode), and +9V DC connected to the bottom node (connected to the anode - positive terminal of the diode). This would forward bias the diode, which means it is more than happy to conduct current until failure. The diode still offers resistance and will drop the typical forward voltage of roughly 0.6 Volts, but in order to maintain that voltage it will pass more and more current until potential failure of the diode. This creates a situation where you are saving your opamp and transistors from potential damage, while potentially sacrificing a diode. Although, your diode will ideally have a maximum forward current rating that will be able to handle whatever your power supply is churning out. Use a 1N400x series diode and you shouldn't have any problems unless your planning on using a power supply that is going to give off multiple amps of current.

Some other people may have further opinions about this, but there's no real advantage/disadvantage to having the diode in parallel with the supply (and reverse-biased) vs. having the diode in series with the supply (and forward-biased). The only notable difference is that if you have the diode in series with the power you will have a constant diode drop worth of voltage lost by the time it gets to your actual circuit, so some people go the parallel route if they are trying to reduce unnecessary power consumption.

[Ashura]

It's not a short circuit either way... the diode is there to offer resistance between the two power nodes and drop voltage.

Indeed. The diode has some resistance, so there is no short circuit. I despised this feature of the component. 

Some other people may have further opinions about this, but there's no real advantage/disadvantage to having the diode in parallel with the supply (and reverse-biased) vs. having the diode in series with the supply (and forward-biased). The only notable difference is that if you have the diode in series with the power you will have a constant diode drop worth of voltage lost by the time it gets to your actual circuit, so some people go the parallel route if they are trying to reduce unnecessary power consumption.

What would be a source of this tipe? Would you have an example of one so that I can study it?

[tonight, we ride]

Here's what the circuit you posted would look like with the series diode arrangement.

In this circumstance you can still trace the current from the most positive point of the circuit to ground.

With the diode in the forward-biased arrangement the current can travel from the 9V DC source to the anode of the diode and on to the rest of the circuit. If, for some reason there is a short circuit past the diode it will potentially protect other points in the circuit by failing as an open circuit if the maximum forward current rating of the diode is exceeded.

If the diode were flipped 180 degrees, with the cathode (negative side) of the diode connected to the positive side of the 9V DC power supply and the anode (positive side) of the diode connected to the top of the capacitor, the diode would then be reverse-biased.  You can no longer trace the current from the most positive point in the circuit to ground without being blocked by the diode, which means no current will flow through the circuit. You will still have the voltage drop across the diode (about 0.6 Volts), but no reasonably measurable current will flow through it, so it is basically an open circuit.

(Sorry about the poor lighting on the photo! Three beers into the night and didn't want to turn the lights back on)

[R.G.]

The shunt diode scheme is, as noted, designed to protect against reversed battery or power supply voltages by conducting so much current that the reversed voltage never gets above one diode drop - about 0.6V to 1.0V if the current it really large.

The series diode scheme protects against reversed battery or external power supply by blocking current flow in the "wrong" direction.

A diode lets current flow only in the direction of the arrow part of the diode sche matic symbol. It blocks current in the reversed direction, shown by the "bar" part of the schematic symbol.

The shunt diode scheme is really best suited to batteries and "smart" external power supplies. The fundamental ideas of what a guitar pedal looks like and acts like was solidified when batteries were the only good option for powering them. Batteries have limited "short circuit" current, something a diode can conduct without damage for a short while. A shunt diode also subtracts zero voltage from a battery in the "correct" direction. So a shunt diode is just about ideal for protecting against fumble-fingered insertion of batteries backwards. Smart power supplies have built in current limits that will not kill a shunt diode, so this is a good solution for them as well. Batteries lose voltage as they wear out, so losing voltage to a series diode can be a real problem to sound quality,.

Shunt diodes are not so good if you connect a not-smart power supply backwards. Simple brute force power supplies can supply so much current to a shunt diode that the diode overheats, then burns open. When that happens, the reversed power supply can start killing capacitors and ICs in the pedal. Transistors may or may not live through this as well.

The worst of all possible schemes for a shunt diode protection setup is to connect an AC power supply to the external power jack of a pedal with a shunt diode. AC power supplies are almost always a simple transformer; this can supply very large currents to a shunt diode, burning out the diode, then killing the rest of the pedal. A pedalboard apocalypse can happen if you have your pedalboard powered by a single power supply through a daisy chain cable and you hook up an AC power supply to the daisy chain. The common AC power supplies for digital effects pedals use a power connector that is similar enough to the "normal" DC connectors to force the AC connector in. When this happens, every pedal is subjected to the AC power, and pedals start dying.

Series protection of some kind is the only good answer for a high current "dumb" DC power supply or AC power supply mis-connection. You lose some voltage, but this is not so bad with a fixed power supply that doesn't drift down like batteries.

Even better is a smart circuit solution to reversed power supply voltages. There are several schemes that actually sense whether the incoming power supply voltage is the right polarity and turn a series transistor on or off depending on the polarity. A series transistor can have a much smaller series voltage drop than a diode, so this almost eliminates the difficulty with the voltage drop of a series diode.

If you have found it yet, there are a number of articles on powering pedals, including reverse polarity protection, at geofex.com.

[phaeton]

I've gathered that the MC1458 is probably the most common and longest lived type of dual 741 op-amp. Previous ones needed more than 8 pins for both offset null connections, such as the LM747. The 4558 was seen as an improved 1458.

Aw shoot.  Here I was thinking I could get all mischievous and nail together a TS-9 circuit with a pair of groady old 741s just to give everyone the heebie-jeebies.  Guess not.

[zombiwoof]

All the versions we have seen (and that have filled hundreds or thousands of posts on this forum and other similar forums) have one IC with two opamps inside it. It is called a "dual opamp." That is like the 4558 or the many chips we substitute. The one you have also has two opamps on one IC, no? What do you mean?

+1 this. Not two ICs, two op-amps. In one chip. Hence the difference between the schematic (2 op-amps) and the pictures (1 IC).

Show me a photo of a tubescreamer with two chips and I'll believe you.

T.

There was a pedal in the short-lived "Master Series" pedals that is considered to be the TS of that series, I forget the name of it but it had 2 dual opamps in it.
Al

[Ben N]

Or is there some "secret" issue of the TS we haven't yet stumbled on?  Stranger things have happened.

No, no, they haven't.

[Ben N]

I told him that it was to comply with EU regulations!!!!!!

You may have to revise your answer post-Brexit.

[Resynthesis]

All the versions we have seen (and that have filled hundreds or thousands of posts on this forum and other similar forums) have one IC with two opamps inside it. It is called a "dual opamp." That is like the 4558 or the many chips we substitute. The one you have also has two opamps on one IC, no? What do you mean?

+1 this. Not two ICs, two op-amps. In one chip. Hence the difference between the schematic (2 op-amps) and the pictures (1 IC).

Show me a photo of a tubescreamer with two chips and I'll believe you.

T.

There was a pedal in the short-lived "Master Series" pedals that is considered to be the TS of that series, I forget the name of it but it had 2 dual opamps in it.
Al

That'd be the STL I think. Its forerunner the ST9 was much the same with the extra opamp used for the mid-boost circuitry. The ST9 had the boost before the clipping stage and the STL after (I may have reversed those so don't take as gospel).