Build Your Own Clone Message Board

As discussed in a recent thread, I present the SuperLectra. It's an Electra Distortion with independent Bass and Treble tone controls and a post-tonestack JFET gain-recovery stage. So basically I took a very simple circuit and made it needlessly complex. I also have another version with a single tone control called the MediumLectra, but it's not finished yet.

The tone stack does have a fairly prominent effect on output volume. This may or may not be a big deal to you. I'd appreciate it if FF_Pedals and tonmann would take a look at the tone stack and JFET stage to make sure I have it connected properly.

As usual, feel free to play around with the cap/resistor values in the tone stack. I used Jack Orman's evolved BMP tone control:
http://www.muzique.com/lab/atone.htm


Note: I left the value of C5 off the layout for some reason. It should be 1uf. It is listed correctly on the schematic.





PCB Layout (print at 166 dpi):





And here's the schematic:

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Yes. Yes. Yes.

So the loss of volume issue is completely gone with the JFet gain recovery stage?
Did you compare the overall volume to a stock Electra?

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Oh, and it will fit in a 1590A!

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Yes. No volume loss at all. In fact...


It's definitely got more output than a stock Electra.

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Layout is correct - nice one !

Hopefully you've read my last Heavy Darling post - your ability for layouts was never in question.

I didn't take it negatively. And if I didn't want criticism, I wouldn't post these things online!

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A man after my own heart. The first motto I've borrowed from this board is:

"Assume Nothing"

Hopefully I can use:

"And if I didn't want criticism, I wouldn't post these things online!"

as my second.

May your sparging manifold never rust !!

It won't if you use copper but then again, a little rust in beer is good for color...

Mine is, indeed, made of copper:






No!!! That's what Crystal 60 is for.

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Yum...I haven't brewed in 10 years. Gave my mini-brewery away to my nephew and he occassionaly supplies me with freshness.

Where are we going ?
BYOC - Brew Your Own Concoctions

Very nice CJ! This one looks fun.


I'll add it to the never ending list

What's the issue in the tone stack? Do you need it simulated?

I just think maybe I've overlooked something regarding the JFET buffer. I put that in for two reasons: 1) so output volume after the tone control would be decent, and 2) because I read that it would prevent the adjusting the tone control from have a noticeable effect on volume.

As it is now, adjusting the treble/bass controls has a quite palpable effect on the volume level.

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We can divide the circuit into four stages:
1st stage amplifier (everything to the left, and including C2)
The two diodes
The tone controls (junction of R5/C3 to the junction R6/R7)
2nd stage "amplifier" (everything to the right, and including R8)

Adding one stage at a time and doing a few "pencil and paper" calculations:

1st stage amplifier will give you a gain of about 35dB. The back to back diodes (made both Si diodes to make things simpler) will clamp the signal to somewhere around 500mV - any input signal under about 10mV won't be "fuzzed" with the fuzz effect being more pronounced (read looking more like a square wave) as the input signal rises. The amplitude of the fuzzed signal remains the same - about 500mV.

Adding the passive tone controls (passive means the output signal at junction R6/R7 is always less than the input signal at junction R5/C3) looses you at best about 12 dB. This does two things:

It affects the amplitude of output signal from the 1st stage. With both bass and treble controls on full , the tone control stage looks bass predominant i.e.higher frequencies are cut more than bass frequencies. A 20mV input signal at some high fequency will be reduced to under 10mV at the first stage output and won't be "fuzzed" by the diodes. This is minor to what comes next:

The main effect of the tone control part of the circuit is that it conditions the fuzzed signal. Turning the treble down will round off the corners of a square wave, reducing the bass will lower the flat part of a square wave. this will look like it is creating spikes at the leading edge of a square wave. The amplitude of the signal at the output will never be greater than the amplitude at the input - as you turn either one or both controls down, the amplitude will fall.

2nd stage "amplification" is...... no amplification. The FET is configured as a source follower - the output is taken from the source instead of the drain. The characteristics of a FET source follower are:

Input impedance: high - in this case about 1MΩ
Output Impedance: low - about 10kΩ
Gain: slightly less than 1

With the volume pot at 100% you won't get out more than you put in.

Turning down the bass and treble will reduce the amplitude of the signal at the input of the FET, turning down the volume control will reduce the signal even more.

I hope my ramblings have answered your problem as to why the bass and treble controls affect the output volume.

I would be more than happy to suggest some mods. The main question is do you want to influence the frequencies that are fuzzed or do you want to influence the fuzzed signal ?

Or if it sounds right and you just want more volume, use a common source instead of the source follower.

I know that tone controls do have an effect on output volume, and before now I kinda-sorta understood it. Now I really understand it. Thanks!

But my original main reason for adding the FET stage was to prevent exactly what is happening and what you described. It works fine on a Rat, for example. The "Filter" tone control on the Rat has very little impact on the volume. That's what I was shooting for, but I suppose with the way I've set it up that's not going to be possible.


By all means, please do. Whatever will make the circuit better or more versatile or whatever is surely a good thing.


Originally, the latter. But now I'm thinking it would be cool to be able to do both.

I think that influencing the signals that are fuzzed would be very useful in a Fuzz Face or Tonebender.

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The Rat tone control (100kΩ pot in series with 1.5kΩ resistor, 3.3nF capacitor to ground) is a low pass filter, it removes high frequencies from about 470Hz (pot wiper to the right) to about 32kHz (pot wiper to the left). Using a sine wave as the input signal, the signal appearing at the left of the 100kΩ pot will resemble a square wave signal with rounded shoulders - a slight simplification as this is dependant upon (amongst other things) the sine wave frequency, the gain from the op amp and the type of clipping diodes. The low pass filter will round the shoulders of the wave - more so as the wiper is turned to the right. The maximum amplitude (between the shoulders) is, by and large, not affected. Thus the "tone" (high frequency content) will change but the signal amplitude won't.

If anyone is really interested in how this works please ask, although I warn you learning to play "Stairway to Heaven" is probably easier. (You need to know how resistors in series, resistors in parallel and voltage dividers function).


Mods to the circuit:

1. Beaten to it by FF_Pedals. Make up the gain by taking the output from the drain instead of from the source.

2. Change the passive tone control to an active tone control.

3. Add a high pass filter before the clipping diodes - lower frequencies won't be clipped/less clipped resulting in a less "muddy" fuzz (unless this is intentional).

4. Add a switch between D1 cathode or D2 anode and ground for a second type of asymetrical clipping.

Thanks again, tonmann!!

This is definitely food for thought on revamping this circuit. I'll probably do a different version, as this one does sound good (just not what I intended).

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How much does changing the tranny affect it?

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some of the worse mistakes I have made in life have been haircuts-Jim Morrison

Probably not a whole lot. I've tried a few different types and couldn't tell a big difference either way.

Is there one you have in mind to substitute?

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