The Crank by Mark Hammer

[soggybag]

Here is a build I made of The Crank by Mark Hammer. I'd say it spans the range from Boost to Overdrive tones.

My build got the pot rotation backwards. 🤦‍♂️ I fixed the volume pot with some jumpers but the gain pot is a dual gang which seemed like too much trouble so I left it the way it is.

[antonis]

Is indeed R4 30k mojo E24 series value ..??

[soggybag]

Here is a link to a blog post with more pictures and information: http://www.super-freq.com/the-crank-by-mark-hammer/

[soggybag]

Is indeed R4 30k mojo E24 series value ..??

For build R4 was a standard 30k 1% metal film resistors. Our marketing department has insisted on the verbage: "...uses only the highest quality components throughout, including only metal film resistor for increased tone, sustain, and organic clarity."

I'm not part of that team and have no control over what they do or say.

[antonis]

 

I was kidding about R4 rather "odd" value, in the mean of it's highly unusual to implement resistor values other than E12 series (as E6 for capacitors) in stompboxes circuits..

No implication about build quality or effectiveness!! :beer:  :beer: :beer:

[soggybag]

I was joking myself. I just happen to have a 30k on hand or would have used the nearest value.

[ElectricDruid]

30k was the stated datasheet value in all the SSM2164 example circuits. Quite why they chose that over 33k I have no idea, but ever since, 30k resistors remind me of the 2164!

Incidentally, the newer SSI2164 has increased the currents to get the noise down, so now the example resistors in the datasheet are 20K - still not 22K!!. They do say, however, that anything from 7K5 to 100K is allowable, so maybe I'm just being fussy.

To be honest, I always use E24 values anyway and never limit myself to E12 for resistors, although I'd use an E12 value by preference if it makes no difference. For caps, it's a different story and you're lucky to get E6!

[Mark Hammer]

1) Nicely done!  I salute your diligence and am honoured by it.

2) The 30k value is not special.  It was simply a product of working out the math.  If 30k is not available, use 33k and substitute the 4k7 value in the ground leg with 5k1.  The gain and bandwidth of the first stage is negligibly affected.

[Elijah-Baley]

Well done, Mark.

I have a question, I think I missed something. I see in the schematic a dual gang 10k pot, but in the image on your blog there's a dual gang 25k log pot.
Is there a reason for that?

[Mark Hammer]

Not sure whose blog you're referring to, but it isn't mine.  Use of a dual-ganged 25k pot will affect both minimum and maximum gain, though not by an excessive amount.  Some might even prefer that extended gain-range.

[soggybag]

I have 10k dual gang in mine, maybe that's an error: http://www.super-freq.com/the-crank-by-mark-hammer/

[Mark Hammer]

Not an error to use one.  It's what I drew, and it's what I have in every one I've built.

[soggybag]

I guess the issue I was having is getting a 25k dual gang pot is difficult, 10k dual gang was easy to find.

[Elijah-Baley]

Sorry, it was soggybag's blog!
Thanks for make it clear, soggybag!

[aquataur]

Sublime Greetings, folks.

It happens this unit caught my attention by divine intervention, while I was looking for a unit that mimics the tone of an amp at the proverbial "edge of breakup". A tone shaper as a last instance right before a cleanish amp so to speak.

I like to use fuzzes and the like. Into anything but a smoldering tube amp they sound shrill and unusable. The tubes seem to impress their own sonic signature that masks all that fizz besides compressing heavily.

You all will say immediately, any overdrive can do this, but not if you use the fuzz as it should be used - riding the guitar's volume. By doing so, you hit the overdrive with a signal that is much bigger than they usually expect (once you go up for lead tone), and most of them lose their countenance in this case. This is with its gain set low, so that it normally would be clean. A tube stack would not do that at elevated levels.

I have tried many overdrives, so there are: ROG Thunderbird, Hotcake, Honeybee, CMOS 4069 based, etc., and even the amp`s built in overdrive channel, and all started to sound splatty in this mode, except the Euphoria. I concede that this is probably not what they were designed for.
I kept staring for hours at the schematics until my eyes got sore and did not see what does it.

Now this was the precursor to my question: how does The Crank behave in this respect? Say, with the gain set pretty clean, being thumped down with a huge signal from a fuzz or a rat or whatever? I am not after the boost per se.

Can one of you folks actually try this?

Thanks,
Helmut

[Mark Hammer]

Thanks for your interest.

The Crank does two things not immediately apparent.  One is that it only clips a little, at highest gain, and below that the diodes serve more to limit peaks - i.e.,a wee bit of compression, or at least "dynamic restriction".  The other is that treble is rolled off as Gain is turned up, which is useful for nudging the amp in a better direction of breakup.

It's a pleasing circuit, but not necessarily the solution to every overdrive goal.  Should you want to try it out, but find any shortcomings, I'm happy to suggest mods that might nudge it more in your preferred direction.

[iainpunk]

i don't think its an overdrive you're looking for. most tube power amps (contrary to popular believe) has some pretty hard clipping going on (due to high gain and negative feedback), not to speak of crossover distortion that some power amps impart when clipping (through bias shift of the two halves).

you might want to try something like a DOD250 or Blue Clipper if you want to push it like a tube amp.

cheers

[aquataur]

Thank you very much for your replies.
I realise I should have been opening a new thread. Did not mean to hijack this thread.

@iainpunk I think you are on the right track basically. Just looked up the Mxr D+ (which is a brother of the DOD250) here. It appears this has a huge mid boost, which is not exactly what I want at this point.

Interestingly, the blue clipper looks deceiptively like the Euphoria (a link to the clone  here). It overdrives an OPA with with a small slew rate, which will keep the highs low, and then a series of bounding diodes. Secret recipe of RATs as we know.

The Hotcake does the same btw, (without diodes), and while it sounds useful, it becomes splatty with elevated signals. This has also too little compression for the purpose.

The Euphoria (MDMA) works with or without diodes. The snag with this is, it is not so great for an overdrive tone, funnily. Maybe to adhere to this gain staging scheme, a tube screamer of sorts before it as mid-heavy boost would do the crunchy Marshall bit. Or - the Crank. Not instead, but before...

For the amp simulation bit, I set it absolutely clean as low as possible, and use the OPA mode or the smooth mode. When i dial up its gain, I can hear how sustain increases, where the "amp" starts adding its bit. It bounds the signal really vigorous, it just does not get louder. I use its volume control to set the system volume. I set it totally transparent as outlined here and it does not get any more trebly.

@Mark Hammer, I think I will try The Crank on the breadboard.

[Mark Hammer]

The Distortion+ and DOD250 do NOT have midboosts.  Rather, because they use the ground leg of a non-inverting op-amp to adjust gain, as you turn up gain it trims off more and more bass, leaving lower mids and above.  When the gain on either of them is set low, you have all the bass you need...just not the volume or clipping.  Increasing the .047uf cap, connected to the Gain pot. to something like 0.1uf or higher, will retain more bass at higher gain settings, making the mids seem less the focal-point.

By using two gain stages in the Crank - one using the ground leg for gain adjustment and the other using the feedback loop - I was able to manage bandwidth more strategically.  I deliberately designed it to lose as little bass as possible as gain is turned up.  It does lose a small amount, but not enough to notice; losing more top end than bass as gain is increased.

Here's the principle to keep in mind with non-inverting op-amps.  Think about what the bandwidth of the negative feedback from the output is.  The more negative feedback finds its way from output back to input, the lower the gain will be for those frequencies.  The analogy I like to use is a car designed to run at full speed all the time, with the only way to adjust speed being how hard you press on the brakes.  If there is a capacitor between input and output, that cap is like an expressway for higher frequency negative feedback.  So it steps on the brakes for higher-frequency content, but not lower.  When a cap is in the ground leg (between the "-" pin and ground), that retains negative feedback for any frequency content below a given point.

How can you know where the gain is retained versus lost?  The formula is 1/(2 * pi * R * C), where R is in megohms and C is in microfarads.  So, with the Drive/Gain control on a Dist+/250 set to minimum gain, we have 500k of pot resistance in series with a 4k7 resistor and a .047uf cap.  Plugging 504.7K and .047ufd into the formula, the bass rolloff doesn't start until around 7hz.  Turn up the gain a bit, so that the pot resistance is 100k, and the bass rolloff is at 32hz.  Drop the pot down to 50k and our rolloff climbs to 62hz.  Pot down to 10k, and the rolloff begins around 230hz.  And finally, at max gain, bass rolloff is at 720hz.  The Dist+ was produced during an era when we didn't use clean boosters, apart from drive pedals, so it attempts to cover both bases.  These days, I can find no sensible reason to use a Gain pot higher than 100k or even 50k, and even there do try to use a reverse-log taper, so that the higher-gain settings are not squished into the last 5 degrees of clockwise rotation.

Going in the other direction, let's look at the feedback path in a Tube Screamer, where we have a 500k gain pot in series with 51k resistance and a 51pf cap in parallel with that.  Here, unlike using the ground leg, gain is increased as total feedback resistance is increased.  So, at minimum gain, we have 51pf and 51k in our formula: 1 / (2*pi*.051*.000051).  At minimum gain, there is only a "negative feedback expressway" for content above 60khz, which has no impact on what we hear.  Increase Gain pot resistance to 50k, and that drops to around 31khz.  With Gain pot = 100k, rolloff at just under 21khz and still no audible impact.  Gain pot = 200k, we start to lose a teensy bit of top end (rolloff just over 12khz), and finally when Gain is maxed (500k), that 51pf cap provides enough of an expressway for high-freq negative feedback, that we experience a rolloff starting around 5.6khz.  Not dull or mute, by any stretch, but enough to rein in some of the harmonic content generated by the clipping diodes.

My reasoning was that, if one  only adjusted the ground leg resistance in one stage, and the feedback resistance in a second stage, by a small amount, the total gain achieved could be substantial, with experiencing the big changes in bandwidth when all the gain adjustment is concentrated in one locus.

I hope this little tutorial was useful, and not too pedantic.

[aquataur]

No, that is great stuff. Thank you for the effort. I interpreted the graphs as mid hump. It so happens I have a board lying around, so I will whip up one of them. The symmetric variety seems appropriate. I'll report back when I know more. This may take one or two days.

Your design is on my list too.