MAX1044 max voltage: paranoia?

[moro]

I'd like to use the MAX1044 in a couple of pedals.

The maxiumum input voltage on the MAX1044 is 10V. I'm reading 9.4V on my 1SPOT. So, I'm thinking of putting a resistor between the +V and the MAX1044 to drop the voltage to about 9V. Is this unnecessary? Am I being silly?

Thanks.

P.S. I know that there are similar ICs that are rated for higher voltages but none seem to have the cool frequency boosting feature that the MAX1044 has.

[markusw]

but none seem to have the cool frequency boosting feature that the MAX1044 has.

The LT1054 has 
And you can feed it with up to 15V!

Markus

[moro]

The LT1054 has 
And you can feed it with up to 15V!

I was looking at the spec sheet for that yesterday and got excited when I saw that Pin 1 was labelled FB/SD, thinking it stood for "frequency boost / whatever." But apparently, it stands for feedback / shutdown.

Oh, but now that I re-read the spec sheet, I see where it says you can attach a cap to Pin 2 (CAP+) and Pin 7 (OSC) to raise the frequency. Is that what you mean? They don't seem to say how much of an increase you can get.

[soulsonic]

You could always add  a 78L09 regulator to the circuit and rest assured that the voltage will never exceed 9v. It will also do much to remove any potential noise generated by the 1Spot.

[Andre]

You could always add  a 78L09 regulator to the circuit and rest assured that the voltage will never exceed 9v. It will also do much to remove any potential noise generated by the 1Spot.

I'm afraid this won't work since all "78xx" type voltageregulators inputvoltage needs to be at least 3 Volts higher than the regulated output voltage.

André

[soulsonic]

I suppose you're right... but of course you could always use a zener diode with a small resistor. OR a battery! Or a decent power supply and not one of those crummy 1Spots.

[remmelt]

You could always add  a 78L09 regulator to the circuit and rest assured that the voltage will never exceed 9v. It will also do much to remove any potential noise generated by the 1Spot.

I'm afraid this won't work since all "78xx" type voltageregulators inputvoltage needs to be at least 3 Volts higher than the regulated output voltage.

André

Really? Or what? Unspecified behaviour? Will it drop to 6V? I seem to remember using a 78L05 in a LIRC serial module (http://www.lirc.org/receivers.html).

78L05 regulator takes 3-4 mA current all the time and needs at least 2V voltage drop

Hmmm, it seems you're right. I wonder what it does when the serial port's voltage is 6V.

[remmelt]

those crummy 1Spots

Could you specify what's wrong with a 1spot? I was about to buy one...

[Auke Haarsma]

Regarding the 78Lxx: According to specs you are right, but from practice I know it does work sometimes with a lower voltage gap (say 1 Volt).

keep in mind btw that the MAX1044 can only provide ~10mA for your pedals. Fuzz/dist etc will be okay, but modulation pedals often require more.

1spot is a great adapter btw. Never had probs withit, and plenty of juice with 1700mA

[R.G.]

The maxiumum input voltage on the MAX1044 is 10V. I'm reading 9.4V on my 1SPOT. So, I'm thinking of putting a resistor between the +V and the MAX1044 to drop the voltage to about 9V. Is this unnecessary? Am I being silly?

Not silly, just cautious. The 1Spot is very tightly regulated, so the voltage is very unlikely to go the additional 0.6V up to 10V. You're probably fine as is.

However, you could put in a silicon diode like a 1N400x in series with the +9V output. This will drop it to about 8.8V. You probably want to put a 22uF - 47uF cap after the diode. That should take care of any possible issues.

There exist low dropout regulators which can regulate with only about 0.5V across the regulator. That could be put onto a 1Spot and produce regulated 8.9V. Under low current conditions some of the LDOs can regulate with only a 0.1V drop, so for single pedals you'd get regulated 9V from the 1Spot's 9.4.

You could always add  a 78L09 regulator to the circuit and rest assured that the voltage will never exceed 9v. It will also do much to remove any potential noise generated by the 1Spot.

That is possibly true; however, the noise generated by the 1Spot is already low enough that we have never had noise complaints except when it's used to power a pedal which has a digital switching power supply inside. The 1Spot is noiseless to the ear even with high gain distortion pedals and chains of them.

those crummy 1Spots

Could you specify what's wrong with a 1spot? I was about to buy one...

I believe that was humorous. I don't know of any performance or reliability issues with the 1Spot when used with normal pedals.

[snoof]

1spots are great adapters.  ignore the derogatory comments...

[soulsonic]

I don't like AC adapters in general.... I'm a battery man all the way!

[moro]

Thanks for the great info, everyone.

keep in mind btw that the MAX1044 can only provide ~10mA for your pedals. Fuzz/dist etc will be okay, but modulation pedals often require more.

Hrm. That's worrying. I was going to use the MAX1044 on a Flanger 301. In fact, Tonepad recommends it.

However, you could put in a silicon diode like a 1N400x in series with the +9V output. This will drop it to about 8.8V. You probably want to put a 22uF - 47uF cap after the diode. That should take care of any possible issues.

Thanks for the tip. I just tried this with a 1N4007 and it dropped the voltage to 9.12V. I think I'll go with that.

[soulsonic]

The MAX1044 will have no problem providing 20mA in its standard configuration.
If you are in doubt, you can breadboard the circuit to verify exactly how much current that particular circuit will draw.
Looking at the Flanger 301 circuit, it looks like that would be a little steep for the MAX1044 - you'd be getting close to it's limit just powering the opamps, and then you'd have to deal with the BBD chips and also the loss from the 12v regulator. This looks like a circuit where an 18v AC adapter will probably be the best choice (oh no, now I'm a hypocrite!  ).

[R.G.]

I don't like AC adapters in general.... I'm a battery man all the way!

Nothing wrong with that. But for those who do want to use AC adapters, the 1Spot is the only such that I know of that can run a large number of pedals and was designed for quiet operation specifically with pedals from the start. If you know of a systemic problem with the 1Spot, please let me know.

The MAX1044 will have no problem providing 20mA in its standard configuration.
If you are in doubt, you can breadboard the circuit to verify exactly how much current that particular circuit will draw.
Looking at the Flanger 301 circuit, it looks like that would be a little steep for the MAX1044 - you'd be getting close to it's limit just powering the opamps, and then you'd have to deal with the BBD chips and also the loss from the 12v regulator. This looks like a circuit where an 18v AC adapter will probably be the best choice

The other thing you can do is to put more than one MAX1044 (or other charge pump) in parallel. They work fine this way. You need to drive the oscillator of any secondary ones from the oscillator of a master one to avoid making beat notes aliased down into the audio from non-synched oscillators, though. You can keep adding 10-20ma units with more charge pumps.

[markusw]

The LT1054 provides up 100 mA. So it might be an alternative...

Markus

[soulsonic]

I agree.

[moro]

The LT1054 provides up 100 mA. So it might be an alternative...

Like I said above, there's the issue of the frequency boost. I'd prefer to go with the LT1054 if I could find out what frequency it runs at (and what effect the capacitors have).

[markusw]

The LT1054 provides up 100 mA. So it might be an alternative...

Like I said above, there's the issue of the frequency boost. I'd prefer to go with the LT1054 if I could find out what frequency it runs at (and what effect the capacitors have).

The data sheet says it runs at 25 kHz without an additional cap. With a cap of 5-20 pF you can increase the frequency.
I simulated it once in LTSpice to check the oscillator freq with external caps. Will check when I'm back home. If you have access to a scope or freq counter you could adjust the freq to 30-40 kHz .

Markus

[markusw]

IIRC, according to the simulations 5-7 pF raise the frequency to 35-40 kHz (which should be fine I suppose).
Will confirm when I'm at home.

Markus