EHX - Clockworks EH5385 [schematic]

[e45tg4t3]

Ok thank you, i just never have seen this type of output boost.. Every Day something new to learn ..

Also Attached a Quick View of the first Version of the Clock-Section Board.

I´m gonna make this Modular so i don´t end up with a giant board, and also because the Divisor Sections are all the same...

Ben

[JuliaDee]

Awesome, Ben! Good luck and please let me know how it works out.

julia

Ok thank you, i just never have seen this type of output boost.. Every Day something new to learn ..

Also Attached a Quick View of the first Version of the Clock-Section Board.

First View.png

I´m gonna make this Modular so i don´t end up with a giant board, and also because the Divisor Sections are all the same...

Ben

[e45tg4t3]

So... i finished it some time ago, but never had the time to Upload it. It is NOT verified and i would be lucky if someone of you could look over it. Files are Eagle-Format.

Best Regards

Ben

[DiscoFreq]

Wow, great, I tried to buy a Clockworks several times, but it was always too expensive...

(I do have 2 Drum Sequencers, 1 with and 1 without trigger outs).

[jaidee]

Hi Julia

Thanks for the great post.

I'd still be interested in seeing the original PCB artwork if you can find the time to scan and post it.

[JuliaDee]

Hi Julia

Thanks for the great post.

I'd still be interested in seeing the original PCB artwork if you can find the time to scan and post it.

Here 'tis - COPPER side.

Julia

[jaidee]

Julia, thanks for taking the time and trouble to dig out and post the schematic.

Amongst all the postings on this board this is a fairly unique pedal and circuit, so I feel that we're privileged that you, the designer, have had the generosity and good grace to share the details!

[JuliaDee]

Julia, thanks for taking the time and trouble to dig out and post the schematic.

Amongst all the postings on this board this is a fairly unique pedal and circuit, so I feel that we're privileged that you, the designer, have had the generosity and good grace to share the details!

Thanks, jaidee. I haven't laid hands on a Clockworks in 20+ years, but just the other day I was reverse-engineering a commercial e-drum brain, trying to establish the exact level at which it triggered. I got it just on the threshold, and there it was - the Clockworks effect! sometimes it would fire and other times it wouldn't, but always in sync with the master clock I was feeding it, making nice polyrhythms. It was so soothing I left it on at a low level all day while I worked, and it reminded me why the Clockworks is so cool. I really should build one sometime...

julia

[jaidee]

My attempt to tidy up the PCB artwork - component overlay removed, through-holes redrawn, contrast/brightness improved, cropped, resized and converted to JPEG.

[JuliaDee]

It was recently brought to my attention that the schematic I posted a few years back has an error - the charge pump diodes are backwards. A corrected schematic is attached; I apologize for any inconvenience caused.

Julia

Clockworks Schematic corrected.pdf

(85.65 KiB) Downloaded 324 times

[Wiseblood]

Really cool to have such a brilliant engineer such as yourself to offer up a schematic and some insight to one of your creations. Clockworks is an underappreciated design imo but I know there are some people on here who are stoked to see this and appreciate it, myself included! Thanks JulieDee!

[2BABat]

Hello

New to the forum and pretty new to diy effects. I’m really interested in trying to build a ehx clockworks, but I’m a little confused by the little power schematic on the left side of the page. Did the original clockworks plug into the wall? And could I use a 15 v wall wart to power it?

Any advice would be greatly appreciated!

[JuliaDee]

Yes, the original Clockworks had a built-in power supply and plugged into the wall. You could certainly power it with a 15V wall wart, it probably needs about 200mA.

[ruebezahl]

Hello,

first post here, but i had an eye on this project for some while already. I finally want to attempt to build it. But there are two points where sourcing the components proves a bit tough. So i hope to be able to get some help here, and hopefully also learn something on the way.

1. The 15uF capacitor, like someone mentioned before, are a rare breed, especially when combined with the properties "Low-leakage" and "low tolerance". Like my local electronics store has specific low leakage caps, but can not tell me what tolerance they are, and also don't have 15uF. Online i can find some 15uF but either the tolerance is not stated or 20%, and as for low leakage, that seems to be a property omitted by most datasheets (or i don't know what to look for). On mouser i can find specifically low leakage caps and 15uF, but they are 20% tolerance and also i would have to buy a ton of other stuff before justifying an order on mouser...
For now i will probably combine a 4,7 and 10uF of the low leakage kind and would just try several of them until i am happy with the results.
But before i try maybe someone can explain what would happen if a) the caps are too far from their actual value and b) if the leakage would be too high.
Perhaps this information would make my troubleshooting more efficient, since i honestly don't understand this circuit too good

2. The transistor pair 2n6111 and 2n6290 - I just can't to find the specified Transistors, so i looked up their specifications and tried to find a suitable replacement. To be honest it's quite tricky, since i am not sure for what specific properties i should look out for, as in i don't know exactly what is happening in this part of the circuit and what properties of the transistor should be as close as possible and what is more like a rough estimate will do.

As i understand it the two transistors are part of a series of complimentary NPN and PNP, with the 2n6290 having a little higher max voltage, not sure if that is on purpose or just what the designer had on hand? Anyway, apart from that they are mostly identical, including the HfE, that seems to range from 30-150 for both devices.

So i found a pair of transistors that seem to be an okay replacement here, the TIP41C and TIP42C: the HfE is specified as 30-75, the voltage is much higher with 100V, and the max current close with 6,0A max. Since i am not sure what exactly are those transistors doing here and what voltage and current they can expect, i hope someone can give me green light, and perhaps btw explain what is happening.

Juliadee mentioned before that it is boosting the current of the output, but i suppose the current is still far from 6A. If i gather it right, they are boosting the current of the clock signal, so since it is not about the voltage, the HfE is not too critical, right?

I hope someone can shed some light, and i will definitely post some video if i succeed in getting it running, Thank you!

[JuliaDee]

Mouser currently has 40 different 15UF 16V MLCCs in stock, 4 of which are ±10%. MLCCs are inherently low-leakage, but they do suffer capacitance reduction with DC bias, so use the largest package possible and X7R dielectric to minimize this effect. There are also many 15UF tantalum caps available.

It is the ratio between the 1UF charge-pump input caps and the 15UF staircase caps that's important. Each step of the staircase on the 15UF cap will be Vclock * 1UF/15UF.

In reality, it will still work if the ratio is off or the caps leak, you just might not get evenly-spaced divider ratios or the full range of division on the divisor pots.

The clock buffer transistors should not be too critical, but they should have a decent current rating, especially if low-ESR caps (MLCCs) are used for the 1UF current-pump input caps, since the instantaneous current required to charge and discharge all the caps may be rather high. Their beta needs to be such that multiplied by the clock opamp's output drive capability the output current is sufficient to make a decent square wave when charging and discharging all those caps.

[ruebezahl]

Mouser currently has 40 different 15UF 16V MLCCs in stock, 4 of which are ±10%. MLCCs are inherently low-leakage, but they do suffer capacitance reduction with DC bias, so use the largest package possible and X7R dielectric to minimize this effect. There are also many 15UF tantalum caps available.

It is the ratio between the 1UF charge-pump input caps and the 15UF staircase caps that's important. Each step of the staircase on the 15UF cap will be Vclock * 1UF/15UF.

In reality, it will still work if the ratio is off or the caps leak, you just might not get evenly-spaced divider ratios or the full range of division on the divisor pots.

The clock buffer transistors should not be too critical, but they should have a decent current rating, especially if low-ESR caps (MLCCs) are used for the 1UF current-pump input caps, since the instantaneous current required to charge and discharge all the caps may be rather high. Their beta needs to be such that multiplied by the clock opamp's output drive capability the output current is sufficient to make a decent square wave when charging and discharging all those caps.

Thank you so much for your detailed answer! It's really helpful to get this circuit laid out in such detail. To be honest i still can not completely grasp exactly what happens, but i am getting closer hehe Might also have to read up on charge pumps and such.

I had trouble with the search tool of Mouser before, it seems to work again, and i see the caps you mention but since postage to where i live is kind of expensive and i need to meet a certain minimum order, i decided to try another way first. But actually in a local shop i saw 15uF Tantalums, i somehow thought Tantalums are bipolar and that could be a problem, but now i realized that's not true. Would there be any reason to not use Tantalums here? Otherwise i will just get those next time i go to the city.

Since i managed to obtain all the other parts besides 15uF Caps, i decided to just give it a go first. I breadboarded one of the tracks, using a 10uF and 4,7uF in paralell and it works! Happy! But then i realized that the divisor pot is really off. I guess it could be the caps, but it is really extreme! I measured and basically if the voltage goes below 7V on the voltage divider, it won't work anymore, the output will just be constantly on. And if the voltage at the divisor pot is above 13.4 it just turns completely silent. So through replacing the 1k resistor to ground with something like 200k, i could get somehow a range that i could work with, but still far from perfect. And also that's definitely far from how the circuit should behave.

So i wonder can this really be just due to the capacitors? Like since they are just random cheap caps, their ratings might be off a bit, but that is a bit extreme. For the transistors i used TIP41C and TIP42C, with an HfE of 30-75, could that be too little? Apparently the original transistors have a rating of HfE 30-150. I actually thought HfE is talking about voltage gain, not current gain, since i am not sure what current is "sufficient to make a decent square wave when charging and discharging all those caps" i just figured it might be enough, but duh, might have to search for some with a higher Beta Value. I guess it can't be too high? the bigger the better, right?

Thanks again! I am grateful to have you here helping me.

[JuliaDee]

When the circuit is working, there should be a staircase waveform on the 15UF cap. Assuming the clock is roughly 15Vp-p, each positive transition of the clock should pump the staircase up 15V * 1UF/15UF = 1V. When the staircase on the 15UF cap reaches the threshold set by the pot, the comparator flips high, charging the 10NF cap going into the "reset" comparator's positive input. This has no immediate effect on the staircase, but on the next falling edge of the clock, the diode going from the clock to the 10NF reset cap (I'm really regretting not having put reference designators on the schematic, sorry) discharges that cap, causing the reset comparator's output to go low, discharging the 15UF cap to ground to start a new staircase.

You say that when the divisor pot voltage is 7V or less, the "output is constantly on" - do you mean the output of the comparator? That would suggest that the reset circuit isn't working - are you sure you have the reset diode going from the clock to the reset comparator's input capacitor?

[ruebezahl]

That makes sense, i feel like i can more or less grasp how the circuit is working now

You say that when the divisor pot voltage is 7V or less, the "output is constantly on" - do you mean the output of the comparator? That would suggest that the reset circuit isn't working - are you sure you have the reset diode going from the clock to the reset comparator's input capacitor?

What i mean is that the status LED instead of blinking on every X step of the clock, is just constantly on. I double checked the diode (and any diode for that matter), and i am sure it is just like on the schematic. I checked two places in the circuit with my scope and attached photos

this is measured at pin 2 of LM339, the output of the reset comparator. It kind of works as described, but instead of discharging to 0V, the lowest value there seems to be around 7 V, which explains why the divider is only working in that range.

This is at the positive input of the reset comparator, pin 5. so basically most of the time it's close to VCC, with short spikes down (that's whenever there is a trigger out and the yellow LED is blinking). Kind of fit's your desciption, i only wonder why the spikes seem to be different length, following some kind of pattern. I'd expect them to be the same depth.

So i guess the main question is: Why is the 15uF capacitor not discharging to 0V, but only to around 7V? I played around with different caps, to see if the tolerance could be the issue, but even if i just let one cap dangle, the stairsize changed, but the bottomline remained the same

[JuliaDee]

Yes, the reset comparator is not fully discharging the staircase back to 0V as it should. The reset pulse should be about 5ms wide (10NF x 470K); I can't see from your scope trace what the width actually is. Is the clamp diode at the reset comparator's noninverting input going the right way (cathode to the positive rail)? What does the clock signal look like? Its falling edge is what triggers the reset comparator.

[ruebezahl]

I just finally saw your answer, so it gave me some new motivation to check the circuit again. And... it works!

What was the trouble? Well turned out i trusted a faulty pinout diagram for the 2n4087 and reversed it. The diagram is even contradicting itself, but i guess i missed that. That's it... Duh!

Anyway, thanks so much for your help, without it i probably would have just give up. And all this double and triple checking of the circuit combined with your explanations helped me a lot to actually understand this circuit!



One thing i am wondering. I was curious and swapped the whole clock section for a CD40106 oscillator(cap+resistor) and added one simple NPN for supplying a bit more current. And it works as well (although the divisions are a bit off, but i guess that should be possible to tweak with the resistor values). I mean I only powered one Divider-stage, and the circuit drew like 50mA. When supplying the whole set, a bigger transistor might makes sense.But why is it necessary to use this transistor pair of NPN and PNP, and this seemingly more complicated setup of them? Trying to learn