Hi-hat design, what do you think?

Hello, i’m trying to designing a Hi-hat module and for that i want to mix, white noise, and metallic sound.
The metallic sound is from here : Logic Noise: More CMOS Cowbell! | Hackaday
(multiples square waves mixing through XOR)

The white noise is from here : Simple White Noise Generator Circuit Diagram
(Simple white noise with non-connected leg’s transistor)

The thing is the metallic sound output 8 Vpp and the white noise output 500 mVpp and for mixing them i need them at the same level.

What do you think is the best ?

A - Attenuate the metallic sound to match the white noise level, and re-amplify the mix to be at modular sound level.

B - Use multiple stage of OP-Amp to amplify the withe noise to match metallic’s sound level ?

C - attenuate the metallic sound and amplify the white noise to get both at the same level ?

D - Something else

Thank you for your time =)


You don’t need multiple stages for a 16× noise gain; common noise generators use anything from 10× to 50× or more (the classic Synbal uses a single 450× stage).

Best I’d say to work with signals that are large enough to be well above the noise floor* but not too large for op amps to handle without clipping, but the latter is more like 20 Vpp. So definitely amplify the white noise. Then if the result is too hot, attenuate it with a voltage divider at the output.

If you take a look at the MFOS Noise Cornucopia the noise source (Q1 etc.) goes through two stages of amplification (U1-A and U1-B) with gains of about 1.5 and up to 50 (adjustable) to get it to 10 Vpp. (The first stage is I think more about filtering than amplifying.) You could do something like that. The circuit you linked already has an amplification stage but obviously not enough for this purpose. You might want to consider the MFOS design and others intended for synth level.

* I know, it already IS noise, but better noise you have control over than noise you don’t.

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Both Synbal and Noise Cornucopia are great circuits and answer to my questions :slight_smile:

Thank you :yellow_heart:

My goal is to make something like this :

But without the levels and the caracter (caracter will be tunable with 6 trimpot on the pcb) and i think also without the FM cv
I’m also aiming for the same sound

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I’m still a noob with OP-Amp, I would like to know if the 2 buffers were not redundant ?

Basically I mix 2 noises, then I clone the signal to send it to 2 VCA driven by 2 envelope generators, one of them generating a longer envelope.
One for the Closed-Hat, the other for the Open-Hat

/!\ Work in progress /!\
***EDIT final schematic
The complete schematics for curious

I reckon you should be able to get away with just a single op-amp follower.

For mixing signal, it’s usual to see 2 x 100K resistors, one from each signal before the mix pot, but i’m not an expert :slight_smile:

Thanks :slight_smile: indeed i forget them, i also have updated the link to the schematic with useful (i hope) comments to understand it (in English, sorry Dud :laughing:) and all the links where i take my inspiration from, PCB design time !

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If this is in reference to the schematic bit posted above then no, you don’t need fixed resistors in series with the signals before the mix pot. Putting them there would mean you can’t reach 0% white noise and 100% metal noise, or vice versa. Which may be the behavior you want, or may not. If it isn’t, leave them out.

I’d agree you don’t need both buffers. (In fact I’m not sure you need one buffer, but I’m not sure you don’t either.)


Yes indeed no resistor, it’s a cross fader not a mixer :grin:

Few comments on your design:

First the op amps for the mix are redundant, the transistors in your VCA act as buffers. I’d be tempted to add a 0ohm resistor to the base of each transistor if you are planning to make a PCB so you can lower the noise gain if required.

Many OH/CH designs simplify to a single VCA and related to this the closed hat usually cancels the open hat. Look at a real drum set and you will see why. :slightly_smiling_face:
I learnt a lot studying the delptronics ldb-2 schematics available on his site.

The last suggestion I have is to add a potentiometer or trimmer to the low pass filter on your white noise generator. This will allow you to taylor your noise if it’s too sharp.

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I will follow you’re advice and try without the two buffers.
Just to be sure 0ohm resistor is just a foot print with a wire going trough both pad that gives me the possibility to add a resistor later ?

The thing is i want an output for each hat
You are right, in my design the closed hat dont cancel the open one, i take a look at the LDB-2 schematics at the beginning I based my EG/VCA on the LDB-1 schematics, I didn’t see that there was a second edition :slight_smile:

In the second edition he use transistors for canceling the EG of the open hat, i will try to keep two VCA for separate audio out, but add a switch for the possibility to cancel the open hat or not.

And i also will try to add the low pass pot (i dont like to have an odd number of pots on panel :grinning_face_with_smiling_eyes: )

Thank you for your precisous advices

Thanks I didn’t really understand the purpose of these two resistors :slight_smile:
Indeed i want to start from 0% white noise

look here: ritmus
and here: Hauptseite
… click onto the green round things … awful design of the page.
This was a commen design in these days before Sampling: AK Drummer
I build this in 1993 and it was a really harsh sound but seems to be a good oscillator for some kind of distored FM.

And I finally recommend this:

or this simplified version:

Fill these up with samples of a lot of Hihats and use the Filter to bring them to “oscillation”.

Best Regards

Yup, that’s exactly it.

Just to be clear, I’m no expert on these things, just someone who started to clone the delptronics ldb on strip board with a bunch of mods added … and brought an RD-6 to mod as I couldn’t be bothers programming my own controller!

That said I’ve quickly become dissatisfied with some of the old school 606 mods and I’ve been planning my own, which should be a new topic here soon.

If you get to the bass drum, toms and wood block before I post about the RD-6 mods, message me and I’ll give you some pointers if you want?

I redid some tests on my breadboard, I definitely need 2 buffer at the output of the mixer (the sound deteriorates otherwise).
And I added a pot on my low pass filter :slight_smile:

I still have to do the tests for the EG/VCA, i definitely want to add a switch to be able to cancel the OH or not.

I already did the kick (the topic is here); I also did a snare but I haven’t ordered the PCB yet, I’m thinking of re-doing both later with what I learned doing the hi-hat.
Also here are my kicad project for the kick, and the snare.
I am still interested in anything that could help me to improve them

Thanks for the links :slight_smile:
Unfortunately ich spreche nicht deutsch (yet ! i lan to move in Berlin next summer), i will try with a translator :slight_smile:
As for the sample, what I like is to look at old patterns, understand them and redo/modify them I’m not necessarily looking for ease.

The closed hat cancel the open one if i want to, i’m happy with it now :slight_smile:

The link to the schemmatic has been edited too