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gasboss775
 Recently, I've been trying out at least one electronic music related circuit on my many breadboards on most days. Recently it's been drums / percussion. Today it was the turn of the DR55 hihat. I seen in another thread that some people had issues building some of the old Roland circuits, because they required large and difficult to obtain inductors. In the case of LC tuned circuits as in this circuit it is possible to use a smaller inductor, in this case 4.7mH by suitably adjusting the capacitor such that the resonant frequency is close to the original. The formula for the resonant frequency is: F = 1/(2*π*√(L*C)) To recalculate C for a given inductor L: C = 1/(4*π^2*F^2*L) OR. 1/(39.478*F*F*L) Just checked the original values: L1 = 45mH, C3 = 6.8n, so with L1 = 4.7mH, C3 = 68n would actually be closer to the original. It still sounded good with C3 = 47n If anyone wants me to post the white noise circuit also, I can.
gasboss775
 I went back to yesterdays breadboard briefly this morning. I realized that I had actually put a 680n capacitor in the C3 position. I tried it with the "correct" value of 68n and to my ears it didn't sound as good, 680n giving a resonant frequency of approx 2700 Hz gave a better sound ( in my mind 2.7Khz seems more appropriate ) Anyway, it's been years since I heard the original machine, so hard to make a judgement about the authenticity of my clone circuit! Build it yourself and make your own judgement.....
PWM
 This looks great! If there only were more hours in a day..
sixty_n
 Thanks for posting this. I'm working on stripboard drums stuff when I get time so this is very useful. Could you post the white noise circuit too?
gasboss775
 Thanks guys. Here is the white noise circuit:
Cablebasher
 Any pictures?
calaveras
 cool I think I have a bunch of those 549s left over from another project. And I need a hihat!
gasboss775
 Cablebasher wrote: Any pictures?

I could take a picture is you want, but it's just a bunch of components on a breadboard just now! Not sure if I'm going to develop this further for now. I have another 2 hihat circuits that I developed on my own, haven't decided which one to build into a more permanent form yet.
Cablebasher
 Hey Gas It would be great to see some pictures if possible. I am in the process of learning Schematic to breadboarding and any pictures would be a great help. No biggie if not though. Keep up sharing the schematics. Cheers.
gasboss775
 I have made a number of improvements to the circuit today. A better accent control circuit similar to the accent circuit in the TR606 and Tr808 drum machines has been introduced. I have changed the value of the capacitor in the tuned circuit to 100n, this gives a resonant frequency of around 7 KHz and sounds a lot more like a hihat, the 2.7Khz would probably be a good noise filter for use in a snare drum - something I may perdue another day. The inputs for accent and trigger were 12 volt positive pulses, but could probably work with lower voltages. Here is a recording ( not very good quality :( )
gasboss775
 Cablebasher wrote: Hey Gas It would be great to see some pictures if possible. I am in the process of learning Schematic to breadboarding and any pictures would be a great help. No biggie if not though. Keep up sharing the schematics. Cheers.

I took a picture of it, but I don't know if it will be of much benefit. The camera on my tablet is pretty poor as are my photography skills.
Here goes anyway:

I might make up a strip board layout if I decide to use it.

Tomorrow I'm thinking about using a modified version of this to try making a snare drum. The noise through the 2.7Khz filter sounded quite snare like, so will give it a try. I am yet to design a snare drum that Iam really happy with. I made a clone of a CR78 snare drum that I liked but that was just copying someone else's work!
gasboss775
 So today I built a snare drum using the 2.7Khz tuned circuit for the noise part, I used the Shell part of the CR78 snare drum, I also included the option of using the CR78 noise part instead of the new circuit, S1 switches between the two modes. There is a balance control to adjust the snare-shell balance, finally there's the impact control, that basically capacitively couples the attack envelope through to the output mixer, to imitate the striking of the drum. Here is the slightly cluttered schematic.
gasboss775
 I have tidied up the Schematic of the previous post and named it "Multisnare V1.0" I may decide to turn this into a permanent build.
gasboss775
 This was an idea I had floating around for a signal processor. It is a voltage controlled clipper. On one input you have the signal, probably from a VCO and a control voltage that determines the point at which clipping occurs. I threw this circuit together around an lm324 to get an idea of the sound of this effect. I liked it! A real unit would need to have a bit more adjustability and perhaps buffers at the inputs for the signal and the CV. Here is the rough idea:
PWM
 I can't keep up with this..!
Dr. Sketch-n-Etch
 Hey gasboss775, did you know that you can do away with inductors completely with something called a gyrator circuit? Basically, it's an opamp and capacitor circuit that mimics an inductor. Search for "gyrator" on Wikipedia to see a simple circuit for doing exactly that.
gasboss775
Have heard of gyrators. The simplicity of the LC circuit appealed to me also I recently overcame my fear of inductors during a stint of exploring switched mode power supplies.

An interesting thing about inductors is that their inductance varies depending on the DC current flowing through them. I'm sure this can be exploited in some way in a sound modifying circuit.

Karl Pilkington, he's a funny guy, in both senses of the word.

_________________________

 PWM wrote: I can't keep up with this..!

And there's more that I haven't drafted schematics for yet.
Paul Perry
 gasboss775 wrote: An interesting thing about inductors is that their inductance varies depending on the DC current flowing through them.

This is true for one with a magnetizable core, the idea is that the DC current saturates the core & it stops acting as an inductor. There used to be very heavy mains voltage regulators working on this principle.
AndrewHP
 I can't keep up with all this fantastic stuff - I'm still tinkering with the vactrol bass (my first attempt at converting to stripboard) and a massive queue is forming behind it! II think I need to buy another breadboard or two so I can work on more than one thing at once.
gasboss775
 This is another idea, I tried out with an lm324, 3 oscillators and 1 Schmitt trigger. The effect is a bit like ring modulation. Via a high pass filter it makes good metallic noise for cymbals and hi-hats.
gasboss775
 Another variation of the above circuit, the result sounds similar to the last circuit, but not quite the same. I intend to try out these ideas with 6 oscillators built around a 40106 hex Schmitt inverter. I expect the result might be closer to noise.
gasboss775
 I made up the TR606 cymbal/hihats oscillator using a 40106, it is the same as the original 4584 hex Schmiit inverters, but much cheaper and widely available. I fed the six Schmitt trigger oscillators into the above circuit ( with the back to back LED's ) and as I suspected it sounds almost like white noise, though a rather gritty noise like putting clean white noise through a distortion unit. I have still to try it with the Schmitt Ringer circuit. The 470n capacitor is to remove the DC offset from the oscillator circuit.
gasboss775
 Paul Perry wrote: This is true for one with a magnetizable core, the idea is that the DC current saturates the core & it stops acting as an inductor. There used to be very heavy mains voltage regulators working on this principle.

I understand this is the basis of the magnetic amplifier. I seen a video on YouTube where a guy built a very crude audio amplifier using just coils, a battery & loudspeaker ( and a signal source, obviously. ) It sounded shit but was a good practical demonstration of the concept.
gasboss775
 I just remembered that the supply voltage for the hex inverter oscillator in the 606 had a 5 volt supply. As I operated mine at 12 Volts the output frequencies would be different, lower in fact. This oddity can be exploited to "tune" the oscillators. I just remembered that I posted a circuit on here at the beginning of February that exploited the variable Schmitt trigger oscillator, in that case using a 4093. I wasn't that happy with the results, but it demonstrates the idea: Metallic noise circuit
gasboss775
 This is what I've been working on, from time to time in various forms for a long time. It is based on the hex Schmitt inverter circuit from the TR606, but in this case 5 outputs are combined into one using 4 XOR gates in a 4070B chip. XOR chips act a bit like a ring modulator for square waves. The effect of combining the 5 oscillators like this is a complex metallic noise sound, useful for generating percussion sounds. This is just the oscillator, which is tuned byvarrying the supply voltage to the hex inverter and the 4070. This tunes the oscillators. Please ask if you are interested in more details about how the circuit works and I will try to explain as best as I can.
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