Best way to convert 18V electric mistress to 9V...?

[tj7]

Want to ensure I go about having my 1970's 18V electric mistress flanger converted to 9V the right way, otherwise it could get a volume drop (and it already has one!), the effect might be half as pronounced or the effect might not work at all.

Is the best way around this to install a voltage doubler inside the pedal? ie Hit it with 9v, through the chargepump and out comes 18v....
Any other suggestions...?

I intend to have the existing volume drop fixed.  the old 'mistresses all have a terrible volume drop when the effect is on.  i can't find an internal trimpot to adjust this, the two pots i can adjust change the modulation of the effect, not volume.  Otherwise the volume could be replaced with a new one of the same value, or a larger value.
What about putting another resistor in series -  with the volume pot could open the pedal up volume wise.  I am wary of having a boost circuit installed as i don't want the tone of the effect changed.

[Fender56]

Hi,

Bringing the pedal down to 9V will not fix the volume drop. Neither the trimpot, which are for voltage biaising and to control regeneration. I "think" that the power section can be damaged by playing with the trimpot... If it sounds good, better to leave them as is.

There is a mod to fix the volume drop. Check this video:

http://www.youtube.com/watch?v=4XqEeJbHcXg

You have to put a capacitor and a resistor in parallel to the existing one in the loop that goes around the SAD1024. In fact, it let pass more unaltered signal to the output. The flanging effect is then a little bit weaker, not very much. But there is no more volume drop.

Look for the 47nF and the 13K placed in serie that surround the SAD1024:

http://sites.google.com/site/electroconducive/EHXElectricMistress18vFactoryEH-5100.jpg

Put a 10K in parallel with the 13K, and a 0.22uF in parallel with the 47nF as said in the video.

Good luck!

[tj7]

In fact, it let pass more unaltered signal to the output. The flanging effect is then a little bit weaker, not very much. But there is no more volume drop.

thanks, very useful video.
have to ask – is there any way of fixing the vol drop without weakening the flange effect...?
cheers

[cpm]

have to ask – is there any way of fixing the vol drop without weakening the flange effect...?
cheers

yes. before the SAD theres an opamp stage, you can change the resistor values to get the bit of extra gain you need.

i also put a voltage doubler from 9 to 18v, then a 15v (or it was 12v?) regulator. That would get rid of the funky power stage on the original.

also added an additional filter at the output of the SAD to get rid of the noise, this was a particulary noisy unit.

[tj7]

yes. before the SAD theres an opamp stage, you can change the resistor values to get the bit of extra gain you need.

i also put a voltage doubler from 9 to 18v, then a 15v (or it was 12v?) regulator. That would get rid of the funky power stage on the original.

also added an additional filter at the output of the SAD to get rid of the noise, this was a particulary noisy unit.

thanks. did the filter you installed affect the tone of the effect...?

[cpm]

thanks. did the filter you installed affect the tone of the effect...?

it depends on the frequency of the filter. In my case a 4th order butterworth around 5~6khz was a good compromise.

if doing a voltage pump, i had to use the LT1054 (which has more current output that the usual MAX...). Also, care must be taken on using an external board far from the main circuit, and neat wiring, to minimize heterodyne frequencies (interaction with the clock HF)

[tj7]

thanks for all the volume drop help.
still after advice re: the 18V to 9V conversion though!

[2tone]

I have been looking into ways to run my Morley MOD-DDB on 9v as well. If you look at the build instructions for the PT-80 delay on the GGG site, there is an example of a charge pump using the MAX1044. I was going to consult one of my E.E. buddies about building this circuit in a little project box and putting it in line between my 1 Spot daisy chain and the pedal. This way I don't have to modify my pedal and I would also be able to use it with other 18v pedals.

[Processaurus]

Consider the LT1054 over the MAX1044.  The Maxim chip is wussy.  10v max input, 10mA max current out.  I've had them break.  The 1054 is rated to 100mA I believe, and higher supply voltage.  There should be a circuit for voltage doubling in the app notes.