Elektra Cranker

Stompboxes circuits published in magazines, books or on DIY electronics websites.

Elektra Cranker

Postby snk » 06 Nov 2018, 23:50

Hello
I would like to try to build a pedal based on the EQD Speaker cranker... which is based on the good old Electra Distorsion.
I have already built a SPeaker Cranker, following this layout : http://tagboardeffects.blogspot.com/201 ... anker.html
It works fine, but i want to adjust some values, and try some other component for experimentation purposes.
I enjoy the Speaker Cranker, but i want a more bass friendly pedal (so i upped the input & output caps values).
I want to get rid of the Gain knob - so i have read that i can also get rid of the first 100µF capacitor. I have chosen a fixed value of 3.3K, which should bring me close to half-way of the 5K gain pot, roughly : am i correct ?
I will socket the diodes, and also the transistor, o try with either a 2N3904 or a MPSA13.

Image

My questions are both :
- Is my schematic correct, or is there any eror (it's among my first times using a veroboard :oops: ) ?
- Given that i use a 25V electrolytic capacitor, could this circuit run at 18V ? If not, why (which components would not be 18V compatible ? The transistors ?)

Thank you in advance :)
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Re: Elektra Cranker

Postby Manfred » 07 Nov 2018, 09:41

For further discussions I drew the schematic according to your vero layout.
Swap the LED in your layout, the flated aerea stands for the cathode.
If the circuit should operates with 18V then R1 and R2 must be adapted.

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Re: Elektra Cranker

Postby snk » 07 Nov 2018, 12:48

For further discussions I drew the schematic according to your vero layout.

Wow, wonderful, thank you very much, Manfred ! :thumbsup

At first sight, by looking at the schematic, does it seem correct ?

Swap the LED in your layout, the flated area stands for the cathode.

Doh ! Yes, obviously :slap:

If the circuit should operates with 18V then R1 and R2 must be adapted.

The resistors ? Really ? I knew about the capacitors rating, but I didn't know that one should adapt the resistors values to make them 18V friendly. We keep on learning every day :)
So, in this context, would there is an "universal" resistor value, which would make the circuit equally work at 9V and 18V (if not, i'd rather keep the 9V compatible value) ?
The 2N3904 or the MPSA13 will be fine with 18V ?
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Re: Elektra Cranker

Postby snk » 07 Nov 2018, 15:10

So, i built it, and the output volume is incredibly low :scratch:
Even if i put a LinearPowerBooster with volume at maximum, the sound is far from unity gain...
I don't understand what can cause such a volume drop, as my schematic is not far from the Speaker Cranker one (which i built, sounds great, and is a tad louder than unity gain).

I tried first with a MPSA13, then with a 2N5088, both transistors sound the same.
I then swapped the 3.3K "gain" resistor with a 6.8K : i didn't hear any difference either.
I removed the 1N60 Ge diode : nothing changes. I then added instead a blue led (whic is supposed to sound louder than the Germanium) : no change either :hmmm:
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Re: Elektra Cranker

Postby marshmellow » 07 Nov 2018, 17:20

With 3,3k you only have gain of roughly 2, you need to make it smaller not bigger. By removing the emitter capacitor you also reduced the gain.

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Re: Elektra Cranker

Postby snk » 07 Nov 2018, 17:28

marshmellow wrote:With 3,3k you only have gain of roughly 2, you need to make it smaller not bigger. By removing the emitter capacitor you also reduced the gain.

Thank you, Marshmellow.
Ok, I get it. I will try with a 1K resistor, and add the capacitor back.
How do i figure out the gain ratio, according to the resistor value ?
How much does the capacitor value can change the gain (i mean, i'm trying to understand what's going on under the hood : the Speaker Cranker features a 100µF capacitor. If i put the same value, i should reach the same volume. But does increasing or decreasing the capacitor value affect the gain, too ?)
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Re: Elektra Cranker

Postby Manfred » 07 Nov 2018, 22:45

At first, I got typo in the schematic the type of Q1 is 2N3904 not 2N2904 and a fault too,
the diode D3 got the wrong polarity, the type is 1N4148 and not 1N60.

I run a simulation of the circuit using 9V and 18V power supply without clipping diodes,
the circuit works fine with both supply voltages without any changes.
The only difference is that the clipping of the positive input swing starts at 1.3 Vpeak with 9V supply voltage and at 2.7 Vpeak with 18V supply voltage,
the negative swing remains undistorted.
In both cases the clipped positive voltage swing of the output are so high that the diode clipping starts earlier, the transitor clipping is negligible.

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Re: Elektra Cranker

Postby Manfred » 08 Nov 2018, 08:09

marshmellow wrote:With 3,3k you only have gain of roughly 2, you need to make it smaller not bigger. By removing the emitter capacitor you also reduced the gain.


You are right.
The circuit works as a booster for a positive and negative input swings below 0.6 to 0.7 Vpeak for both supply voltages.
With an input voltage of more than 0.6 to 0.7 Vpeak the clipping starts.

I must take back my statement regarding the adaption of R1 and R2.
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Re: Elektra Cranker

Postby snk » 08 Nov 2018, 11:48

Thank you all for your input, it is very interesting... and i will need some time to understand everything right :)
What i am looking for is :
- bass friendly (full spectrum, no hicut, no low cut of frequencies) ;
- not too much distorsion, just a richer sound with a slight coloration when the input is hotter ;
- output level at least equal to input level (little boost prefered);

I have already built a EQD Speaker Cranker version for a synth, using big value input/output caps, 2N3904 transistor and silicon diodes, and it sounds fine.
I also built another one for an electric piano, using smaller values caps, germanium diodes and a MPSA13 Darlington. It sounds ok on an electric piano, but not so good for a synth (too much coloration, too much bass cut), and i had to put an EHX LPB after it because the output volume was way too low.

Now, my idea is to build another version, with two stacked circuits, for an harmonically rich and boosted signal without loosing too much the original sound.
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Re: Elektra Cranker

Postby snk » 11 Nov 2018, 15:04

Hello,
After some further testings, i found some settings which suit me fine.
Instead of adding a second layer of processing, i tweaked and tested some antiparallel diodes configurations, and i will use a diode switch.
I really like the way this simple circuit can sound by changing the component values, it's easy to customize to taste.
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Re: Elektra Cranker

Postby snk » 11 Nov 2018, 15:56

Here is a layout i tried to make.
The concept is to have a true stereo effect (two circuits en parallel, one for the left channel, the other one for the right channel).
So, i have put the left channel on the top part of the layout, and the right channel on the bottom part. In the center of the layout, i have included a little decoupling circuit.

I have already built the "core" part of the circuit (i mean one channel, for testing purposes), and it works fine.
But i would need advices as i have never built a stereo effect : I guess there is still room for improvements on the layout, and maybe also some errors ?
Maybe the grounding could be simplified ? Also, i don't know it the decoupling is accurate ?

(note : i confess i have been lazy for the diodes layout : i have only shown the way there are wired to the 4PDT, and not their antiparallel wiring. Also, both the filter and gain pots are dual gang, and my picture only show one regular pot, so please don't take this into consideration).

About the hicut filter : I wanted something "smooth" just to cut out a little bit of top end when needed, and i am quite happy with the result. But i used the only dual gang pot i had left, and chose the capacitor value accordingly. Would it give different results if i had chosen a smaller resistance value and a bigger capacitor (or an even smaller resistance value and an even bigger capacitor) ?
(My question is not about the frequency cutoff point, but about other things i may be overlooking, like impedance/load, volume loss, etc)...
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Re: Elektra Cranker

Postby snk » 12 Nov 2018, 21:35

Hello
Little bump :
- Does anyone have an opinion about the quality of the veroboard layout ? Does it make sense ? :)
- About the hicut filter : is it any important to choose a smaller resistance value and a bigger capacitor (or an even smaller resistance value and an even bigger capacitor) ?
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Re: Elektra Cranker

Postby snk » 23 Nov 2018, 20:50

Little bump... Did anyone gave the layout a look ? I am curious to know if the ground connections are correct :hmmm: :D
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Re: Elektra Cranker

Postby Manfred » 23 Nov 2018, 23:55

snk wrote:Little bump... Did anyone gave the layout a look ? I am curious to know if the ground connections are correct :hmmm: :D

At the moment I'm very busy with doing other things.
I will have a look at but it takes time.
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Re: Elektra Cranker

Postby snk » 24 Nov 2018, 11:07

Hi, Manfred, thank you for your reply. I didn't mean to "hurry" anyone in an unpolite way :oops: :D

My concern is that, despite having built dozens of veroboards already, i always followed ready-made layouts, and therefore i think that with this one (which i created), there might be room for improvements.
The idea is the following :
- it's meant to be atrue stereo (stereo in, stereo out) effect, using dual gang knobs.
- So, i took the basic layout of theEQD speaker cranker(based on the Electra distorsion), tweaked it to custom values and with some diode clipping mods (which i tried on a "regular" mono board), and gathered both of them into a single board, along with a decoupling board.
- So, there might have some mistakes, but also some things which might be streamlined further, and i would be curious to have some knowledge from forum members ;)
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Re: Elektra Cranker

Postby Manfred » 05 Dec 2018, 15:08

Hi snk, I drew the schematic according your latest vero layout.
I guess the value of the gain pot is 5 Kiloohms.
Please, complete the wiring of the diodes in your layout.

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Re: Elektra Cranker

Postby snk » 05 Dec 2018, 16:40

Hi, Manfred
Thank you for your answer.
The diodes use the "usual" parallel clipping wiring, like that (wiring done on the upper left serie of diodes, i will update the schematic accordingly).
Image
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Re: Elektra Cranker

Postby snk » 05 Dec 2018, 16:47

I guess the value of the gain pot is 5 Kiloohms.

Yes, that's it : 5K ohms

Please, complete the wiring of the diodes in your layout.

Ok, it's not very pretty, but it should be that :
Image
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Re: Elektra Cranker

Postby Manfred » 06 Dec 2018, 00:16

About the hicut filter : I wanted something "smooth" just to cut out a little bit of top end when needed, and i am quite happy with the result. But i used the only dual gang pot i had left, and chose the capacitor value accordingly. Would it give different results if i had chosen a smaller resistance value and a bigger capacitor (or an even smaller resistance value and an even bigger capacitor) ?
(My question is not about the frequency cutoff point, but about other things i may be overlooking, like impedance/load, volume loss, etc)...


I think the 50kB potentiometer is ok, because its value have less influence on the transistor stage gain
and provides for a low output impredance in respect to a common amplifier input impedance of 1 Megohm.

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Re: Elektra Cranker

Postby Manfred » 06 Dec 2018, 07:59

Hi snk, the double switching of the caps and the diode circuties is not absolutely necessary.

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