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I'm building this, but a put a quarter inch jack where the speaker would go, and the output is tremendous. Like, turn the amp volume all the way down to zero and its still pretty loud. How can I make it quieter?

Just add a volume control, yo.

McSpunckle wrote:Just add a volume control, yo.

what value pot and where? I tried and it just changed the pitch slightly.

the pot value is not that important, because the pot acts as a voltage divider. but you should use a value that is high enough so you have a high enough load. 100k to 500k is what i use.

I usually don't build them with volume controls. but I also don't build them with a speaker output. the kaustic machines APC uses a divide by 3 attenuator. see the 10k and 4k7. the same as a volume control turned down.

So how's it sound, nieh?

nieh wrote:

McSpunckle wrote:Just add a volume control, yo.

what value pot and where? I tried and it just changed the pitch slightly.

Put it right before the 1/4" jack. As Schlatte said, 100K to 500K is fine-- even lower should be fine, really, given that it's designed to feed into a speaker (which is probably why it's so damn loud in the first place).

I'm not familiar with the way the 555 chip works, honestly, but maybe running it off a standard 9V supply instead of the +/- 9V would help? Unless it's one of those schematics that says "-9V" when it really means 0V.

McSpunckle wrote:Unless it's one of those schematics that says "-9V" when it really means 0V.

yep... it's one of those...
the 555 chip is a timer ic... often "misused" as a squarewave synth or something....

McSpunckle wrote:says "-9V" when it really means 0V

the schematic symbol for ground is used. the 555 outputs clock pulse maybe 1v or 2v lower than the supply. when the pulse goes low, it sits at 0v. they are not always %50 duty cycle but most configurations get pretty close to %50. your DC offset would be like +3.5V but after it passes the cap your DC offset is zero. one of the edges is always more square than the other. I'm not sure why but it does contribute to that sweet (or awful) 555 sound.

here's a really useful link for calculating voltage dividers. http://www.raltron.com/cust/tools/voltage_divider.asp

i usually use 10V as an input voltage since it's a nice round number, but anything will do. so for example, if you want half the volume you would input 10V for the input voltage, 5V for the output voltage (half the input) and any resistor size for R1 or R2. hit compute and you get the answer! if you plug in the values from the kaustic machines divider (10k/4.7k) you can see that it attenuates 10V down to 8.246V, which is approximately divided by 1.2 - 100k/4.7k would be a divide by 3.

obviously this calculator doesn't account for impedance, any of the surrounding components, etc so take those things into account as well when choosing the range of values.

also if it's changing the pitch, it may help to add a unity-gain buffer between the output of the 555 and the volume control. maybe.

SS/BS thanks for the calculator. I always thought it was a linear ratio but I can see now that it is not. good to know.

the pitch is a function of the internal impedance + external impedance of the 555. even the power impedance will affect the pitch and duty cycle. I know this cause I have had issues with 555's acting funny. they also consume a lot of power compared to your average CD4000 series logic. on a 556 setup to do two totally independent oscillators, I could never get them to stop syncing. they always snap right back to the closest harmonic, usually octaves. the results where better on two 555's. that proves that the 556 can not do everything the 555 can do in the real world.

also another way to change your output voltage is to run your 555 at 6v. 5v is the lowest operating voltage on the datasheet. you can get SMD versions that run on 3.3v

smallsnd/bigsnd wrote:here's a really useful link for calculating voltage dividers. http://www.raltron.com/cust/tools/voltage_divider.asp

ok using the calculator I get
9.5v IN
10k R1
4.7k R2
3.037v OUT

9.5/3.037 = 3.128 = divide by 3

is that right? I don't know how you got divide by 1.2

I usually just do (10+4.7)/4.7 = 3

or you can write that as Vout = Vin/((R1+R2)/R2)

oopsies my mistake! i did 10k/47k by accident... sorry charlie