808 hihats need some help

Hm, not a simple voltage divider to ground. Not sure how to figure that out.

Still, 470R is 10% of the smallest and closest resistor there, so I’d think it’d work.

In fact the normalization doesn’t need to be to 12 V, does it? Presumably the accent input expects a 5 V gate or something? In which case the resistor could be 4.7k or so and you’d still exceed 5 V at R10.


What does this connect to? If an inverting op amp then push button could go into a summing node downstream of R1/R4.

A resistor between jack and R1 presumably would need to be small compared to R1 but large compared to R20, so that seems problematic.


Maybe something like this:


When the push button is closed, voltage at OUT is between 4.5 V and 10.4 V depending on if IN is 0 V, 5 V, or floating.

When the push button is open, voltage at OUT is 4.5 V if IN is 5 V and 0 V if IN is 0 V or floating.

If 10.4 V is a problem you could add a suitable zener to ground at OUT.

(This assumes OUT is floating. Presumably it’s not a low impedance compared to 100k? But if it is, some revision is needed.)


I was thinking a diode on each input as an ‘or’ gate, followed by a pulldown resistor to ground, but I see you already have a pulldown to -12V.


maybe with this sorte of capacitive sensors circuit… I have buy a lot of them but never used that for the moment (never enough time… and the build-list is really so long!) :smile:


I found same things but who looked like the lyra-8’s sensors-switchs. (sorry I don’t remember the link)


Nice project, your mods are looking cool !

maybe you can mod it with this simple diode-clipping distortion active bloc who coming from the Twin-T Kick schematic @Krakenpine


While I really like the krakenpine twin-t, the distortion is a bit too heavy for me :wink: I already distorts quite a bit when I only turn the knob a little bit from full CCW. I would prefer a volume level knob that distorts only in the last third or forth of the rotation. Maybe I can do it by replacing the single diodes with multiple in series?


I don’t know, but play with the value of the 1K resistor to GND, wouldn’t change the game ?


This just came out of my LTspice simulation :wink:

soundcloud link again, discourse can not find the track somehow…

Not too helpful, but every simulation takes 5-10 minutes with the “real” metallic noise.
So for testing I will just use a simple sine wave, that seems to be easier to compute.


Sounds really good. Hope it will be just as good when you build it :slight_smile:


The clipping circuit in the image has a lot of gain. Even though it’s a soft clipping configuration, it will probably even clip guitar signals.

You could try several diodes in series, or led which have a higher voltage drop. You can also put a resistor in series with the diodes

You could also try to increase the resistor from the inverting input to ground, or decrease the value of the pot. It will probably get you better range.

The two resistors on the non inverting input form a voltage divider, i’m guessing you could also try to make the incoming signal smaller to reduce the clipping


Thanks for the ideas for reducing the gain! The difference between using diodes and just driving the opamp over its rails is output level and diodes are a bit softer, right?
I will simulate a bit more, I think!

Seeing the post about Kassutronics wavefolder , I am wondering again if I should replace the transistor VCA in my 808 schematic with a OTA (LM13700), I could then simply use the kassutronics values for getting my clipping :wink: But what else would I get by using a OTA? it’s somewhat cleaner? more “hi-fi”? Do I notice that in a drum module? The mutant hihat does have OTAs, but is it worth it?


Yes the clipping will be ‘smoother’ when the diodes make the signal clip before power rail clipping occurs. But they will always have an influence on the sound if they are in the circuit.

You can also try back to back zener diodes (cathodes or anodes connected together). That way you can choose the clipping voltage. It will be the zener breakdown voltage + 0.7 volts. This sets the voltage that makes the feedback loop clip. Be aware that with the 1k resistor and the 100k pot it will clip into the power rail at very low rotation.

I’m Relatively new on synth stuff, so can’t help you on the ota’s, sorry :slight_smile:


I can really recommend you the DR-110’s open/closed charleston drum’s clone; this is my favorite hi-hat circuit ! These are quite similar to the 606’s circuit.

The mix between the metallic noise with white noise making the sound very realistic and sparkling/shiny !

I just need to adjust the bandpass filter (tune control) and the output level amplifier because we ear a little bit high-frequencies residual noise on audio signal…

This one is the cymbal part:

Here is the post with more details


You are right! It sounds really good!! But I have the panel already planned, there is not space for another sizzle knob!! :joy:


so it will be for your next module… ahah

I have 3 hi-hat in my DIY’s rack :smile:

  • a clone of 808 from eric archer
  • the simple but efficient’s percussive noise’s voice from MiaW
    (I love to playing with CV control of the decay!)
  • and this one based on DR-110

do you mean that it is enough or not??


hmmm maybe I remove the decay for the closed hihat and instead add a knob for the white noise…


great idea !! because decay’s control is really not necessary in a closed hat or I am wrong ? :slight_smile:

maybe that could be interested you:



That is really cool! Now I need to build a clap as well!! xD


This is the VCA, filter and output level section from the 808 hihats (with some adjustments, please ignore the shortcut around C13 and the dangling R72 :wink: ). The core VCA is Q6 and surrounding parts. The original did not have the voltage buffer (U5), but without that I could not get a lot of gain in U3. Can anyone explain why I need this buffer or what else I could do to get more gain? Maybe it’s better to use the OTA approach here, it seems simpler. But then I need to think about how to get the highpass filter (C23, C10, R34, R35, Q13,…) into that design…

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