Charge pumps a bad idea with 1590As?

[Mark Hammer]

I was building a small FET preamp into a 1590A and thought "Hey, I've got charge-pump chips.  Why not take it to the next levl and double that V+?"  I did just that but the whine from the chip (7660) was simply intolerable.  So I'm wondering if I simply omitted something I should have included (I diduse 47uf caps with suitable voltage ratngs for the supply-voltage bump), or whether the crowding if ins and outs in a chassis that small is just asking for trouble.

[bean]

Did you jumper pins 8 and 1? That puts the whine out of the audio range.

[Rob Strand]

o I'm wondering if I simply omitted something I should have included (I diduse 47uf caps with suitable voltage ratngs for the supply-voltage bump)

You need a good size cap on the input supply.  Those designs slam discharged caps across the input supply.  They need the input cap to hold enough energy to stop the supply dipping/modulating.
Low ESR caps help a lot.   Standard caps are quite variable.

As for a post fix you could add an RC filter to the 18V supply.

Did you jumper pins 8 and 1? That puts the whine out of the audio range.

I think that only works for the MAX1044 (not the ICL7660).

IMHO the lt1054 is a much more suitable device.  It has a 25kHz mode and handles upto 15V

The MAX1044 and ICL7660 are only rated to 10V.  If you connect an unregulated supply to the pedal they can blow up.  Even a new battery is pushing the friendship.  There's plenty of people with stories of these blowing up on the web.

[Edit: There is a ICL7660A which goes to 12V but is ~ 10kHz like the std model].

[EBK]

... or whether the crowding if ins and outs in a chassis that small is just asking for trouble.

I'm going to just boldly and carelessly state (without proof) that a 1590A is not "small" with respect to the things we generally stuff into them, including charge pumps.  A 1590A is (again, being bold and careless in my words) merely "small" with respect to the size of our fingers.

[italianguy63]

The LT1054 needs a 5 to 20pF cap between pins 2 and 7.

The other 2 good ones are the TC1044S and the ICL7660S.  Both rated at 13V.  And both of those need the "boost" jumper installed as mentioned earlier.

MC

[Rob Strand]

The other 2 good ones are the TC1044S and the ICL7660S.  Both rated at 13V.  And both of those need the "boost" jumper installed as mentioned earlier.

Yes, ICL7660S is better than the ICL7660A

Edit: It is highly desirable to use switch frequencies above 20kHz.   For switch frequencies less than 20kHz many pedal will produce an objectionable whine; particularly those using JFET, MOSFET, BJT stages.  These will need additional RC filtering on the supply and good attention to layout.    To avoid problems just use the higher frequency chips.

Risky for 9V:
MAX1044   10V, 5 to 10kHz,  70kHz with boost
ICL7660    10V, 5 to 10kHz

OK for 9V:
ICL7660A  12V, 5 to 10kHz
ICL7660S  12V, 5 to 10kHz,  35kHz with boost
TC1044S   12V, 10kHz normal, 45kHz low noise
LT1054      15V, 25kHz  ; higher current, better regulation   (not the LT1054L)


Corrections accepted.
I've used the nominal max not the absolute max.

Edit:  When using these chips read the warnings in the datasheet.   Particularly those about the configuring the LV pin and BOOST pins.

[diffeq]

If getting LT1054 is troublesome, you could roll your own charge pump, at any higher frequency:
http://www.ti.com/lit/an/slfa002/slfa002.pdf
with Shottky's for lower drop. 555 runs fine from +5V-15V range, fine for pedals.

[italianguy63]

One final bit of wisdom I can pass...

I mostly use the TC1044S in my builds.

In the past I got the TC1044SCPA from Tayda.   Experienced weird problems that plagued me for many months.  Long story.  I started using the TC1044SEPA from Mouser.  No problems ever.  As an added bonus, I checked prices lately, and Mouser's price is substantially LOWER than Tayda (on this component)!  Put that in your pipe and smoke it!

Carry on!
MC

[Rob Strand]

If getting LT1054 is troublesome, you could roll your own charge pump, at any higher frequency:
http://www.ti.com/lit/an/slfa002/slfa002.pdf
with Shottky's for lower drop. 555 runs fine from +5V-15V range, fine for pedals.

The low R1 and R2 values waste a bit of current.  Something like R1=R2=8.2k to 10kohm and C5=1nF
would be a bit better.  Switching roughly 50kHz to 55kHz. 
Maybe a small improvement with a 10uF output cap.

[Mark Hammer]

Just to close the gap here, I was using a 7660D.  I had some 1044S chips in the drawer, but thought I'd save them for a circuit that wanted more current and a bipolar supply.  Clearly the wrong move.

But I appreciate the useful info people have provided here.

[Rob Strand]

With the tiny load of a JFET preamp the 555 option isn't such a bad thing.

[diffeq]

With the tiny load of a JFET preamp the 555 option isn't such a bad thing.

According to the datasheet, 555 can source/sink up to 200mA, shouldn't this be enough for most pedals?

[rankot]

ICL7660A  12V, 5 to 10kHz
Corrections accepted.
I've used the nominal max not the absolute max.

This one is NOT a good choice for 9V pedals, it has VERY audible whining at 10kHz and no boost option. So avoid it for any cost, I had a very bad experience with this IC while making Ampegulator pedal. Replacing it with 7660S cured the problem.

[bean]

Usually I stick with the TC1044SCPA ($1.12 from Mouser) for low current use and LT1054 for anything requiring over 20-30mA.

It gets even more confusing because the MAX1044CPA is the equivalent of the TC1044SCPA.

[italianguy63]

Usually I stick with the TC1044SCPA ($1.12 from Mouser) for low current use and LT1054 for anything requiring over 20-30mA.

It gets even more confusing because the MAX1044CPA is the equivalent of the TC1044SCPA.

Yes.  The TC1044SEPA is also $1.12.  I think only the temperature range is different.  I buy them 25 at a time so only $0.83.  I think Tayda is near $2 bucks.

I quit using the MAX1044 upon reports it was too fragile-- although I never had one of those fail either.

MC

[italianguy63]

I had to look... Tayda is $1.69.

[Rob Strand]

According to the datasheet, 555 can source/sink up to 200mA, shouldn't this be enough for most pedals?

That's the spec but in reality the voltage drops go up considerably above about 30mA. 

If you look at the load graphs in (which is for a CMOS 555),
       http://www.ti.com/lit/an/slfa002/slfa002.pdf
you can see the voltage drop rises with load.     That's at 12V which gives slightly more favorable results than 9V.
I'd say less than 10mA would be a good guide.  Maybe up to 20mA if you can accept some voltage drop.

The charge pump devices often give an output resistance spec.   The 555 has an Ro of 270 ohms. The charge pump devices quote 30 ohms to 60 ohms.   Quite a difference.

[Rob Strand]

This one is NOT a good choice for 9V pedals, it has VERY audible whining at 10kHz and no boost option. So avoid it for any cost, I had a very bad experience with this IC while making Ampegulator pedal. Replacing it with 7660S cured the problem.

Actually good point.  Only some circuits will work OK.
Things with BJT, JFET and MOSFETs are probably going have trouble.

I've added some notes to the post above - thanks.