Deluxe Memory Man problem / 9V PSU via LT1054

[robotmonster]

Hey guys, need some help with my Electro-Harmonix DMM EC2002_Rev_D board. It is a later big box / true bypass model with 4 MN3008 chips that runs on 24VDC power supply.

I am just an enthusiast who was messing with the pedal trying to make it work with 9v adapter (1Spot). Plan was to put 9V through LT1054 to get 18V understanding that pedal needs no more than -15v. Basically, I wanted to get rid of the EH 24v power supply and use something more common and easy to replace while on the road, ideally hook it on a daisy chain with my other pedals.

Originally:

PSU section in this pedal was organized this way:

-24V PSU -> 150ohm resistor -> 1N4003 diode -> 7915 regulator -> -15V

I have removed everything before the 7915 and hooked up reversed 18V (doubled via LT1054) directly to 7915 and I am happy to report that this worked great. I was getting -15V on the regulator output pin and pedal was playing beautifully with no noise or any issues. However, I was still not happy because pedal had inverted ground now and could not be used with other effects on a daisy chain only alone with 1Spot.

To try to solve this, I built bipolar voltage doubler to get both +18 and -18v to try to keep the common ground across the pedals in the chain, but I have managed to screw something up in the process, possibly shorted something in the pedal or similar and never got this to work properly. I am pretty sure bipolar voltage double circuit that I built works fine because I have measured the voltages and I have modified my Electro Harmonix 10 band EQ (that had internal AC transformer) to work beautifully on standard 9V psu, converted to +/- 15V.  If anyone wants the stripboard layout for LT1054 bipolar doubler let me know.

Current symptoms are:

When I tried hooking -18v to 7915 from LT1054, output voltage was only -8V, and firstly I thought it is something wrong with LT1054 circuit, so I tried restoring everything back to original and use the original EH power supply with resistor/diode/regulator, but I got the same issue and only -8V on the voltage regulator output. Then I hooked -24v from the adapter directly into 9715 input pin, and then I got -15V on the output!?!  Back to original -8, directly -15, and so on. This really confuses me! Why does the regulator fail now if I power through a resistor and diode per original, but works if I power directly to input pin? I noticed that 150ohm resistor gets insanely hot too if running through it. It is not a bad resistor, diode or regulator because I have replaced all 3 parts only to get the same issue.

Worst thing is that after everything, when I tried to hook the pedal to the amplifier I can't hear any effect coming out even with -15V coming out of 7915, there are no delays coming out. Effect signal is broken and I can only hear dry signal. Please help if you have any suggestions. I am not in USA and would be quite costly to send it to EH or similar for repairs. Would rather do it myself, having some fun in the process, and learning a new thing or two instead.

Thanks!!

[midwayfair]

The resistor is getting hot because the charge pump + delay circuit is pulling too much current. You need a higher wattage if you're going to use it. It's probably not necessary -- you have power filtering before and after the charge pump, right?

The diodes, regulator, and charge pump all lose a little bit of voltage at each step. You may also be losing some elsewhere, not sure.

[robotmonster]

Thanks for the reply. Sorry if my post was too confusing because English is not my first language.

We can forget about charge pump for the moment, because now with everything restored back to original/factory, something is broken and effect does not work. I simply reported that it is indeed possible to run DMM with LT1054 and 9V supply.

I believe I managed to short something while working on the pedal, and component of some sort in the circuit is causing effect to fail.

If I connect the original EHX -24V adapter now, though resistor/diode which is just before the -15V regulator, resistor gets extremely hot. On top of that regulator is unable to regulate things properly and gives -8V output. However, if I hook -24V straight to input pin of 7915 regulator, and bypass the resistor/diode, then I get -15V regulated on the output pin, but effect still does not work and I believe regulator gets very hot. By that I mean, blend knob all the way up = pedal silent, blend all the way down = dry signal only, no repeats what so ever.

What I am trying to understand is what scenarios could cause this behavior, resistor to get hot, regulator to fail to output -15V but giving -8V. Even voltage on the input pin drops to something like -9V from -20V if I run it through the resistor and diode.

If I measure voltage after -24V -> 150ohm -> 1N4003 it is around 20V as soon as I connect this to the regulator it drops to -8V. But If i connect -24V -> Regulator, Then it drops to about -18V at the input, and regulates fine down to -15V. I think something completely different is bugging the voltage around the circuit making that resistor to get extremely hot, and regulator not to regulate.

Again, thanks for any suggestions.

[robotmonster]

Found the solution. Turns out I managed to toast two op-amps in the process.

I removed all 5 from the board, installed sockets, and popped new TL072s in there to try the op-amp mod, and pedal started working good as new.

TL072 is a fidelity improvement, letting more of high frequency through in repeats, but I am still not sure if I want this, or if I should put CD4558N back in there for murky super-dark repeats.

Also not sure if I can still recommend using LT1054 with DMM, because load of the pedal is about 30-40mA, and once connected, the board drops output voltage of the charge pump down to -15 to -16V... Pedal still works, but it may not be enough for regulator to regulate, so If anyone decides to run with this mod, I suggest removing the 7915 and regulating via LT1054 itself, or simply using more advanced charge pump IC which can output more than -17V with pedal connected.

Hope this helps someone in similar situation.

Peace, out.
-robotmonster

[Becktron]

Hi Robotman,

Can you post the stripboard layout for bipolar 15v from LT1054?
I'd like to try running some TL07 op amps in a spring reverb circuit with it.
I have it working with bipolar 9v but would like more headroom.

Cheers,

[Becktron]

I meant "Hi Robotmonster"
Sorry for the mistake.