PT80 power draw problem

[Marcvv]

The PT 80 should draw around 35 ma afaik. On start up it draws up to 200 ma and then settles to around 49 ma.
I am running the pedal on 18 volt. (I tried two ways: with a voltage doubler (LT1054) and with a regulated 18 volt power supply)

I replaced the 100 uf capacitors after the 5 and 12 volt regulators. No difference.

Any suggestions??

By the way: sound wise the pedal works fine.

Marc

[Marcvv]

The problem is focused on the PT2399 side of the PT80.

The side that is fed by the 78L12 is fine.
If I remove the 78L12 and the NE570 I still have a power draw of 150 ma after the 78L05 that slowly goed down to 50 ma.

I replaced the 100uf elco and the 0.1 cap after the 78L05 as well as the 47 uf elco at the PT80. No difference.

The PT2399 is fine. I have tested it in another build. The same goed for the 78L05. Swapped it with the same result.

Any suggestions?

Marc

[JKowalski]

The problem is focused on the PT2399 side of the PT80.

The side that is fed by the 78L12 is fine.
If I remove the 78L12 and the NE570 I still have a power draw of 150 ma after the 78L05 that slowly goed down to 50 ma.

I replaced the 100uf elco and the 0.1 cap after the 78L05 as well as the 47 uf elco at the PT80. No difference.

The PT2399 is fine. I have tested it in another build. The same goed for the 78L05. Swapped it with the same result.

Any suggestions?

Marc

There's nothing wrong. Tolerances account for the 35-50mA difference, and it's likely that the original measurement was off by a bit anyways. Plus they may have been running at a lower voltage, where the regulators might not have to work as hard to bring it down. Digital chips always take a pretty hefty current draw.

The high current on start up is normal - that's the filter capacitors charging. When you put a voltage across a capacitor that's totally empty, it draws as much current as it can! This gradually goes down as the capacitors reach a steady voltage state, eventually equaling the average current draw it needs to recharge the caps which are being drained by the circuit. It's all totally normal, don't worry about it.

[Govmnt_Lacky]

By the way: sound wise the pedal works fine.

Like I always say.... Ain't no sense in fixin somethin' thats workin'! 

[Marcvv]

There's nothing wrong. Tolerances account for the 35-50mA difference, and it's likely that the original measurement was off by a bit anyways. Plus they may have been running at a lower voltage, where the regulators might not have to work as hard to bring it down. Digital chips always take a pretty hefty current draw.

The high current on start up is normal - that's the filter capacitors charging. When you put a voltage across a capacitor that's totally empty, it draws as much current as it can! This gradually goes down as the capacitors reach a steady voltage state, eventually equaling the average current draw it needs to recharge the caps which are being drained by the circuit. It's all totally normal, don't worry about it.

Thanks for chiming in.
I understand what you are saying and thanks for explaining.
I do have a question:
- I use a powersupply with multiple outlets. All isolated and the supply 10 volt 100 ma each. When I connect the pt80 the powersupply starts humming untill the current draw has lowered to 100 ma. Does this mean that I should use a powersupply that gives e.g. 200 ma?
- the 78L05 gets hot. Should I replace it with one that can handle a higher current??
- I use a voltage doubler with a lLT054 to power the PT80. The LT1054 gets also hot.
(I have used this voltage doubler on other pedals and I have no problem with it. Current draw is then normal with the right voltage readings.)  Usually a MX1044 or &660s is used with the PT80 but that can handle even less current....

Marc

[cpm]

actaully i dont see the need for the 12v. You have enough headroom on the opamps to hard-clip the PT's limits, even at 9v.
but if you for any reason want to stick with it, jut put the 5v regulator outside the doubled power. no need to go from 9 to 18 and then back to 5. Because doing so, a 20mA (for the PT) from the 7805 at 18v is actually +40mA at your 9v supply...

[Marcvv]

actaully i dont see the need for the 12v. You have enough headroom on the opamps to hard-clip the PT's limits, even at 9v.
but if you for any reason want to stick with it, jut put the 5v regulator outside the doubled power. no need to go from 9 to 18 and then back to 5. Because doing so, a 20mA (for the PT) from the 7805 at 18v is actually +40mA at your 9v supply...

Hi Carlos,

I understand what you are sying but this is how the PT80 originally was designed. I will try your suggestion.

[Marcvv]

.

The high current on start up is normal - that's the filter capacitors charging. When you put a voltage across a capacitor that's totally empty, it draws as much current as it can! This gradually goes down as the capacitors reach a steady voltage state, eventually equaling the average current draw it needs to recharge the caps which are being drained by the circuit. It's all totally normal, don't worry about it.

Is there a way to make the capacitors charge slower so they do not draw that high current on start up??

[cpm]

I understand what you are sying but this is how the PT80 originally was designed. I will try your suggestion.

thats fine, on the original design ther is not a voltage doubler. so the suggestion is to use the doubler only to feed the 12v regulator, and keep the 5v regulator on the main 9v supply

Is there a way to make the capacitors charge slower so they do not draw that high current on start up??

yes, a resistor in series with the supply input, before the filter caps. These would limit the inrush current, but also will drop some volts depending on the total current flowing. This is about V=IR

but those regulators will do a good job on filtering the noise on the power rails. Usually you dont need a big cap after the regulator, i think you can go as low as 100n. Also, a moderate cap before the regulator, may be 100uF, plus the limiting resistor as previously noted.

[Marcvv]

I understand what you are sying but this is how the PT80 originally was designed. I will try your suggestion.

thats fine, on the original design ther is not a voltage doubler. so the suggestion is to use the doubler only to feed the 12v regulator, and keep the 5v regulator on the main 9v supply

Is there a way to make the capacitors charge slower so they do not draw that high current on start up??

yes, a resistor in series with the supply input, before the filter caps. These would limit the inrush current, but also will drop some volts depending on the total current flowing. This is about V=IR

but those regulators will do a good job on filtering the noise on the power rails. Usually you dont need a big cap after the regulator, i think you can go as low as 100n. Also, a moderate cap before the regulator, may be 100uF, plus the limiting resistor as previously noted.

Hi Carlos,

Of course you are right that there was no voltage doubler in the original design but there is in the version of GGG http://www.generalguitargadgets.com/pdf/ggg_pt80_lo1.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a.
I will follow your suggestions and see how that works.

[Marcvv]

I was using the PT 80 in combination with the taptation tap tempo chip. It was working fine to a certain point.

That was when I started to notice that the PT80 was drawing too much current. So I seperated the two to find the problem. The result was the I had to fix the high current draw of the PT 80.
That is what lead to this thread.

As the taptempo chipset replaces the delay time pot I had forgotten to put the delay time pot back when I was searching fore the current draw problem.

I suddenly realised that and put it back and voila.... bob is your uncle (as I believe they say) It is working normal again with a power draw of 40 ma.

Thanks for helping me with this.

Now I have to solve the problem with the tap tempo chipset.

Marc

PS

I am still wondering how they can work with a Max1044 in combination with the PT 80 as used in the GGG version. To my experience the Max 1044 can not handle 40 ma??