1976 Electric Mistress volume drop - the best solution?

[yeeshkul]

Guys i own a 1976 Mistress and it has an annoying volume drop as expected.
What is the best solution?

I've heard about these so far:
1. A standalone clean boost circuit mounted to the output.
2. The input IC buffer/pre-emphasis can be changed into a slight boost.
3. Some sort of a mod in the circuit.

What would you recommend?

[Scruffie]

For mine I built a vero daughter board with a charge pump to run it off 9V and opamp output boost, works very well, you have to add an extra cap on the back of the PCB to filter some of the BBD input high frequencies to prevent heteordyning with the charge pump but it doesn't hurt the tone IMO, is easily reversible and gets rid of the 'chirping' noise the pedal already suffers from.

I'd suggest it, or just the output boost its self as it's the less invasive of the mods.

The input being boosted does improve the S/N a bit but can also mean the BBD distorts if your pickups are strong and the other popular mod with a cap and resistor (can't remember the specifics) alters the wet/dry mix which leads to a weaker flange so overall, the output boost wins.

[yeeshkul]

I'll try the input boost, and if it gets too much for the BDD i guess i'll add the output boost instead.
Thanks!

[yeeshkul]

Hmm, i tried to raise the 6k8 feedback resistor in the pre-emhasis (second half of the 4558 chip). It indeed did increase volume, but it also overboosted the BBD. Even 6k8 seem to cause a slight distortion with humbuckers.



I am gonna probably lower that to 5k6 and add an output booster circuit.

And yes, that "mod" that is all around the web, where you replace the 13k mixing resistor and the cap in series is a pretty bad idea.

[DrAlx]

The reason they reduced the 6k8 to 5k6 when the EM circuit changed to 9V version is because the BBD bias voltage is lower giving the distortion you describe.

Boosting the the output is definitely the way to go. David Gilmour using an output boost pedal for the EM in his rig.

[thermionix]

David Gilmour using an output boost pedal for the EM in his rig.

Kinda funny.  I had read this thread earlier today.  Then tonight I was watching some recent documentary on DG.  There was a scene at a rehearsal where they showed a brief partial shot of his pedal board.  There was his Electric Mistress, and just to the left was a Boss FA-1 FET Amplifier pedal with "Mistress" written on it.  Ding!

[yeeshkul]

I am pretty sure that ""Mistress" note was a message for us, DIY people. 

[yeeshkul]

Actually, if if you play just ordinary singles (about 0.8 p-p output voltage), it can be adjusted for unity volume and no distortion.
In that case, insert 25k trimpot instead 6k8. Now, you need oscilloscope to proceed.
Feed the input with 0.8V p-p sinus and use the trimpot the get unity level signal in the output.
Then adjust the Bias pot to clean the output signal up. That is the trick, from certain input signal level on, the output signal will not clean up. There is your limitation.
As far as you have a TB switching installed, you need to count on a hair stronger signal input. Just a hair, the pedal has a buffer on the input so it doesn't really bleed that much.

Conclusion
1. A standalone clean boost circuit mounted to the output - the best solution, used by Gilmour, hence blessed.
2. The input IC buffer/pre-emphasis can be changed into a slight boost - yes, yes, less noise but limited by your pickup strength
3. Some sort of a mod in the circuit (especially the 47n/13k mode) - no, don't do it, unless you can cope with changes in the sound.

[Plexi]

I would use a LPB with trimpot at the output.