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sammichFM


Wilba
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I would describe it as transient noise that comes from the high frequency noise in the DC power output itself. The noise is caused by the high frequency circuity that is acting like an on/off switch flipping the source input on and off rapidly to end up with the output. It's a very efficient process - much more so than linear PSUs. They can also handle a wider range of input voltages because the switching circuits just switch at different rates depending on the input to produce the stable output.

The trade-off is that what you really end up with is a bunch of pulses on the DC signal that look like a certain voltage overall (say 12V). Think of it as a somewhat ugly high frequency square-wave of sorts. The problem here is that the high frequency noise this creates cannot be totally filtered out without using capacitors that are built to dampen HF noise (such as tantalum). These can be both expensive, some say dangerous (I tend to disagree), and a bit of a black art. From what I have read, ceramics can reduce HF noise but this comes at a price. So you have to end up using various different types of caps. In the end, capacitors are not perfect and you may need to use quite a few to remove the noise, or may not be able to remove all of it regardless.

Linear PSUs do not have this problem as the noise they generate is typically easier to filter out and it's usually HF (though I think if you have HF noise coming from the AC side, you may see some of that on the DC - not entirely sure though).

All that said, if you're not hearing the noise, it could be too high pitched for your ears - either because you went to too many concerts without earplugs :) Or because the switching frequency of your DC supply is above the audio range (say 1MHz). In those cases, the noise is likely there but you and your audio equipment can't really pick it up. Some might call that a non-issue but I prefer linear PSUs just because I don't want HF noise of any kind in my audio signal, regardless of whether or not I can hear it. Plus I find them more interesting.

TL;DR If you can't hear it, it's probably ok.

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Did read all :thumbsup: So I plugged in my goobay PSU and listened closly to it. Indeed, it produces some kind of high-pitched, squeeky noise. I consider myself having a good hearing, I never go to concerts without earplugs. But this squeeky noise doesn't appear on the headphones. They are Sony MDR-V500 ones, not the best, but also not the worst. I'm not sure, if the not hearing is due to the headphones. Will check the signal of the audio output with my soundcard. Maybe I can see it, instead of hearing it. Will report later on.

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Yeah a spectrum analyzer may help there. I find myself using the one in Live a lot more, particularly when mastering, so it may show you what's going on. Thinking about it, you could always filter it out with EQ if you don't mind losses in treble but it's generally nice to know that isn't required as a default option, particularly if the high pitched noise is in the audio band enough to affect things (such as noise drums and such).

If you do some searching on the forums, you'll likely find a few flamewars over whether or not switch-mode is really that bad or if it's Satan himself being resurrected through audio. The best advice I can give is do some research (including the audio tests like you are doing) and form your own opinion :) I will say that for the Sammich kits, since the power supply requirements are simple, linear is still probably your best bet.

Switchmode tends to be discussed more in a practical sense for the larger projects that need a series of voltages, such as the MB-6582 or when using SSM filters and other fun things. In those cases, switchmode tends to offer multiple voltages in smaller packages than a linear supply and with a lot less heat. Sort of an aside but I thought I'd mention it anyway.

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Lol'd at the Satan thing. Oh no, flamewars... let the numbers speak. Did some testings with my Terratec Phase USB 26 (24bit/48khz) and the Spectrum Analyzer in Live. First spectrum shows the signals of the shut off click and the signal of the sammich being turned on without ever being played or being shut off via the power switch. Second spectrum shows the signal of the Rhodes Piano played and then the signal of the sammich being stopped playing tunes. There is a slight difference (the -24db peak at 500hz) between the signal being on but stopped playing and being turned on anew. You can see it, but you can't hear it. Has someone an opinion on why this happens? Noticed the same thing with the sammichSID back then.

post-7120-024934800 1309380647_thumb.jpg

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  • 3 weeks later...
  • 2 weeks later...

Thanks m00dawg. It does look nice in the photo. Up close, it's not so great though. It's a bit uneven, and the paint isn't thick enough to smooth over the bumps at the bottom of the engraving, so it looks quite messy, unfortunately. I used acrylic paint, rather than an oil-based gloss enamel, as recommended, which in retrospect maybe wasn't the best choice. Having said that, I'm generally pleased with it overall. The sound is good, too, once you get over how terrible the presets are, and start creating your own sounds. The patching randomising functions are both inspiring and addictive, I've been finding!

Incidentally, I had no problem at all finding a power-supply that worked. I've tried two different cheapo 9v DC wall-warts, and both have worked fine. I'll probable settle on the £7 one I got from Farnell, as I bought a matching set of 4, to power this box, and my 3x Shruthi-1 synths.

a|x

Edited by toneburst
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Batch #3 is being prepared now. Due to cancellations, people deferring to later batches etc. I have only 25 confirmed orders, and still waiting on people to reply to my emails, so chances are good that if you email me to go on the waiting list, you will get a kit from this batch in September.

Based on the low popularity of sammichFM (which I expected, it's not as retro-cool as a SID synth which is comparable to expensive commercial products like SidStation and HardSID), Batch #4 might not happen until December or even January, it might take that long to get 50 orders, and I'd probably want at least 60 because there's inevitably a 30% or more cancellation/postpone rate. SO many people go on my waiting lists and then bail out when it's time to order or pay, which is difficult to manage sometimes, but probably for the best, because then kits go to the people who really want one and know what they're doing ;-)

TL;DR? PRE-ORDER NAO!

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It's a shame (though as you say, predictable) they're not proving as popular. The OPL chip certainly doesn't have the analogue warmth of the SID, but you can get some amazing sounds out of it.

Any plans for other Sammich projects, Wilba? How about a a SammichSEQ, or maybe even a SammichSJ (SpaeakJet)?

a|x

Edited by toneburst
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I love my sammichFM! I've even used the shitty stock GMIDI patches with it, and with good results (namely when that kind of sound is exactly what I wanted). I dig it! It's a bit different to mess with than the SID and I think the full control-surface of the MBSID tends to offer a more versatile synth but I generally agree. If you want a SID, why wouldn't you also want an OPL3 chip :)

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I just got the notification that the thing is coming in the mail and I can't wait! I finished building the sammichSID not too long ago and the thing is a monster.

Few questions Wilba, you said in the email that you were sending 20k pots instead of a 10, will it have much of an effect or just make it so you have to rotate the potentiometer a little less to get a change?

Also, you don't have tracking on them right? Because I'm so stoked to build this one right away, just have to practice doing the SMT soldering.

Edited by Snyderman
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I substituted a 20K pot for the 10K pot used for LCD contrast - it's used as a voltage divider so there is no difference in operation.

I use "registered post" so there is a tracking number of sorts, in case it gets lost, but no real-time on-line tracking. Although I have found that the USPS tracking webpage can tell you if the parcel is in the USA yet, or delivered.

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  • 1 year later...

Hello,

if there are some spares (though I'm afraid i doubt it reading the thread through) count me in as well, I'm lacking a small portable FM synth, the whole MBFM just isn't really well-suited to travel with me by plane :rolleyes: 

Thanks a lot,
freddy

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