Last weekend I finished my first Kosmo VCO. In order to test it, I made a simple attenuator (per the Doepfer DIY page: http://www.doepfer.de/DIY/a100_diy.htm) and connected it to a small speaker I had laying around.
The speaker seems to work as it should, as the speaker is definately giving sounds!
Is the aforementioned setup good enough for me to make a small speaker module for my slowly expanding Kosmo system?
If not, is there another simple way to connect speakers to (or include in) the Kosmo system?
When you say “speaker” do you mean something like a powered computer speaker? Or just a speaker cone?
If the latter then no, don’t try to do it that way. Speakers are low impedance and you’ll fry a chip. You can build a simple speaker driver with an LM386. Take a look at section 9 in the datasheet for some possible circuits.
I connected a front speaker from a surround sound set (Samsung PS-FZ210). I have no idea what type of speakers they are, other than that the sticker on the back says it has an impedance of 3 Ohm. As the two speakers only cost me 2 euros, blowing the speaker up is not a big deal. But as I want to make a simple, more permanent set-up (possibly a small module to include in the final rack), I am interested to hear whether this simple set-up will hold up for a longer time.
I agree 100% that if it works, just do it. However, if people think this set-up has no chance of holding up for long, I do not want to waste my time making a speaker module if it breaks very soon.
It’s not the speaker you need to worry about, it’s what you connect it to. The op amps in the synth are not able to drive such a small impedance and they might be damaged by trying.
Thanks for this info! I had no idea that this could damage the synth. Everything I read thus far, spoke about damaging the speaker…
Could you explain what is happening? in other words: why might an op amp in the synth be at danger from damage, if I connect the synth directly to the speaker, with an attenuator in between?
You added a link to a low voltage amplifier. Is it that the speaker is drawing too much current for the op amp to handle? Irrespective of the amplifier you linked, an amplifier with which specifications is needed for such a set-up, as electronics stores have plenty amplifier boards on the shelfs, so maybe I could use one of those…
Any “analog synth” output doesn’t have enough “power” to drive a speaker.
You need a power amp (even if it’s a small 1W one), power amps are designed for driving speakers, with low impedance, while synth outputs/amps are designed to drive only the high impedance inputs of other modules. You can’t get both from the same circuit.
Just like the engine of a car can be designed to be powerful, or to be fuel efficient, not both.
Synth modules have more or less 100k Ohm input impedance, and a synth output is designed to interface with such inputs, while a typical speaker has 4 or 8 Ohms (yours has only 3 Ohms), that’s more than 10,000 less (33,000 in your case), a synth output just can’t handle that.
If the output OpAmp is a TL07x (90+% of all modules ?), it won’t burn out because it has internal protection against that, but it still won’t work.
Applying one form of Ohms law (P = Vˆ2/R), the -5V/+5V level of a synth output delivers 0.00025 W to a 100k input… that’s the parameters used to design a synth output.
OK, most synth outputs have a 1K impedance, and thus can deliver a whooping 0.025W, you may be able to hear something out of the speaker, if you listing carefully
The VCA is an amp that can only reduce the level of the signal (it’s kind of an anti-amp in fact), and it’s purpose is to process the signal by changing it’s level under the control of another module’s output (instead of tweaking the level pot by hand all the time), not to deliver power.
VCA = Voltage Controlled Amplifier. It is controlled by the voltage of the output of another module, but it’s own output can also just drive the inputs of other modules.
The magical word in the amp you’re looking for is power, even small power, but power.
Look for a small amp circuit. There are several on tindie, bangood, etc that could do what you’re asking. I just did something similar here, but used the amp from one of those little marshal amps. You could likely do something similar with a basic amp circuit or even have the speakers in individual panels.
eric, thanks a lot for all the info! I really appreciate your advice!
Blockquote Synth modules have more or less 100k Ohm input impedance, and a synth output is designed to interface with such inputs, while a typical speaker has 4 or 8 Ohms (yours has only 3 Ohms), that’s more than 10,000 less (33,000 in your case), a synth output just can’t handle that.
Could you tell me what the formula is behind this? I have trouble figuring out why a 4-8 Ohm speaker is more than 10,000 less, while a 3 Ohm speaker is 33,000 less. Should this not be the other way around? Thanks in advance!
Ive been curious about this, im wanting to plug into my guitar amp (line in) and use that as my main source.
Currently I use the aux in on a portable bluetooth speaker when testing.
I assume those work because they have their own amp’s. At a guess… plugging in headphones into the lmnc mixer is a bad idea?
Yes, headphones aren’t as low impedance as a speaker but still much lower than synth modules are intended to drive. You can send it into a mixer or sound interface that has a headphone jack and use that.
@analogoutput: Once more, thanks for all your information! I am a total electronics noob…
I really want to find a way to include speakers in my set-up without an external mixer, as I feel like it takes away from the whole idea of having a dedicated synth case. I cannot imagine I am the only noob trying to achieve this. Therefore, I was very surprised I could not find straight-forward information on this subject on various synth fora (or is it forums in English… ), including this forum. Ofcourse, it could also be that I am using the wrong search terms…
Taking your last information into consideration, let me rephrase my previous badly structured question. What is the formula to figure out the specifications of the amplifier needed to overcome the 100k Ohm of the synth to the 3 Ohm of the speaker(s)?
What you need is any consumer level audio amp. (you could use pro gear, but the price…)
It can be a cheap small board from aliexpress or banggood (check you can power it from the +/-12V of your synth or else you’ll need yet another power supply), or a hifi preamp+amp, or anything in the middle.
A powered PC-speaker is probably the best solution for an all-in solution.
Then you probably need a very simple attenuator to adjust the out-level of the synth to the expected in-level of your amp (which is lower for consumer level gear, about 1Vpp vs 5Vpp for synths)
Something like this : https://www.muffwiggler.com/forum/viewtopic.php?t=2065
(Yes it’s just a single pot… add a input jack and output connection fitting your amp)
Thanks. Based on your initial response with the link to the LM386 circuit, earlier today I already bought a small cheap LM386 amp kit at my local electronics store.
