atheybey@bloom-beacon.MIT.EDU (08/21/87)
Repository: PTT Originating-Client: flower I just bought an ASDG 8M/2 board (8Mb board w/ 2 Mb installed), and a Mini-Rack C. Sometimes, the board chirps (for lack of a better word) when it is accessed. For example, when I hold down the "more" gadget in Facc, it chirps in time with the increasing number of buffers. When I run something out of VD0:, it chirps (slightly differently). The loudest noise I have heard is while the "executing out of fast ram" part of ASDG's memory test is running. It sounds vaguely like a cricket in the distance. The board has worked fine (for the three days that I have had it). As long as nothing is broken, I don't mind the noise. However, I was under the impression that memory boards have neither moving parts nor anything else that makes noise (except RF noise, of course). Incidentally, I (temporarily) have two 8M/2 boards in the rack, and it doesn't seem like the other one chirps. Mine chirped even before the other one was installed. Any answers? (Perry?) Andrew Heybey atheybey@ptt.lcs.mit.edu
mwm@eris.BERKELEY.EDU (Mike (My watch has windows) Meyer) (08/22/87)
In article <8708211723.AA10752@THYME.LCS.MIT.EDU> atheybey@ptt.lcs.mit.edu writes:
<I just bought an ASDG 8M/2 board (8Mb board w/ 2 Mb installed), and a
<Mini-Rack C. Sometimes, the board chirps (for lack of a better word)
<when it is accessed.
<The loudest noise I have heard is while the "executing out of fast
<ram" part of ASDG's memory test is running. It sounds vaguely like a
<cricket in the distance.
I installed and tested an 8M/4 in a Mini-Rack C last night. No
chirping whatsoever. Since I was auditioning a new subwoofer in
another part of the room while that was running, I would have noticed
any chirping.
I'm preparing some commentary on the Mini-Rack & board to post
(probably next week). But I like the subwoofer better.
<mike
--
How many times do you have to fall Mike Meyer
While people stand there gawking? mwm@berkeley.edu
How many times do you have to fall ucbvax!mwm
Before you end up walking? mwm@ucbjade.BITNETjesup@steinmetz.steinmetz.UUCP (Randell Jesup) (08/23/87)
[ In response to question as to 'chirping' noise from ASDG ram board in Mini-Rack C ] I have a Mini-Rack C and 2 Meg ASDG board, and have the same chirping. It is believed to come from the power supply, not the board. The power level required changes when the board is accessed, and this causes a change in the frequencies in the PS (or some such, I'm not an EE). Randell Jesup jesup@steinmetz.UUCP
cheung@vu-vlsi.UUCP (Wilson Cheung) (08/24/87)
Why chirping noises?
The mini-Rack C has a very simple power supply just sufficient to support
a majority of Zorro-I type boards without drawing power from the Amiga. When
any device accesses the address lines of the Amiga all power sources will
experience brief Mhz type power surges as digital gates switch on and off.
A more expensive power supply wont reflect these surges too much as noise.
As to why Mhz type surges produces audible Khz type sounds you'd have to
refer to Mr. Fourier Series and Transform for the accurate answer.
Wilson Cheung
dillon@CORY.BERKELEY.EDU (Matt Dillon) (08/25/87)
>Why chirping noises? >The mini-Rack C has a very simple power supply just sufficient to support >a majority of Zorro-I type boards without drawing power from the Amiga. When >any device accesses the address lines of the Amiga all power sources will >experience brief Mhz type power surges as digital gates switch on and off. >A more expensive power supply wont reflect these surges too much as noise. >As to why Mhz type surges produces audible Khz type sounds you'd have to >refer to Mr. Fourier Series and Transform for the accurate answer. > Wilson Cheung The digital switching has nothing to do with it. Not only are the frequencies five orders of magnitude higher than we could hear, but the bypass capacitors handle the spikes before they get anywhere near the power supply. I don't have a mini-Rack, but I can guess it's got a switching power supply. Switching power supplies work by gating power through an inductor and capacitor. You simply wait until the current in the inductor reaches maximum, then gate the power off. An inductors is analogous to momentum.... the current keeps on flowing even when the power is cut... right into the capacitor charging it and bringing up the voltage at the node. By switching the power on and off at some frequency, you can build up the voltage to (theoretically), infinity. Realistically, the capacitor can only hold so much before it arcs between the plates. In anycase, switching power supplies are used for two reasons: (1) no transformer, (2) they can regulate up (as in step up the voltage), (3) they are usually extremely efficient... as in 85% typical. Oops, that's three reasons. So what does this have to do with chirping? Simple... the frequencies used to switch are quite low, and with sufficient load can get down near 60hz or even lower. With all that power going between the capacitor and inductor you hear it quite well. Switching power supplies are notorious for being noisy, especially when loaded down. Typical switching power supplies oscillate at around 20-30Khz when not loaded terribly, which is beyond the hearing of most people. Well, I've said this much, I might as well finish. The drain reason the frequency goes down when the power supply gets loaded is an artifact of the way it works.... ALL the power a switching power supply uses comes directly from that capacitor (or capacitors). The more power you pull from it, the faster the capacitor drains (causing the voltage to go down a little... a couple of mV), and it must oscillate slower to build up more current in the inductor... Well, a simplistic explanation anyway. -Matt
blgardne@esunix.UUCP (Blaine Gardner) (08/25/87)
in article <8708211723.AA10752@THYME.LCS.MIT.EDU>, atheybey@bloom-beacon.MIT.EDU says: > > I just bought an ASDG 8M/2 board (8Mb board w/ 2 Mb installed), and a > Mini-Rack C. Sometimes, the board chirps (for lack of a better word) Mine also does this, but you're a little bit off the track, it's the power supply, not the RAM that is chirping. (I've got a fully stocked 2 Meg board in my Minirack C, for the record.) The chirping really bugged me when I first got the expansion, and I talked to Perry about it. He told me that it would diminish as the power supply burned in, and it has. The chirp is barely audible now, or maybe I'm going deaf. :-) Chirping from switching power supplies isn't new to me, some of the machines at work really "sing" when there is some heavy-duty video updating going on. (I guess this means that the Amiga is just like the big boys now! :-) When the chirp was loud enough to irratate me, I took the time to isolate the source of the noise, and it was the large transformer on the power supply. During heavy accessing of Fast RAM, the transformer would resonate, and cause the chirping sound. You needn't worry about your RAM, my ASDG expansion has worked flawlessly for about 6 months now. P.S. Using the TimeRAM program that was posted a while back, the 2 Meg ASDG board clocks 18% faster than Chip RAM. -- Blaine Gardner @ Evans & Sutherland 540 Arapeen Drive, SLC, Utah 84108 UUCP Address: {ihnp4,ucbvax,decvax,allegra}!decwrl!esunix!blgardne Alternates: {ihnp4,seismo}!utah-cs!utah-gr!uplherc!esunix!blgardne seismo!usna!esunix!blgardne
grr@cbmvax.UUCP (George Robbins) (08/25/87)
In article <8708211723.AA10752@THYME.LCS.MIT.EDU> atheybey@ptt.lcs.mit.edu writes: > Originating-Client: flower > > I just bought an ASDG 8M/2 board (8Mb board w/ 2 Mb installed), and a > Mini-Rack C. Sometimes, the board chirps (for lack of a better word) > when it is accessed. For example, when I hold down the "more" gadget > in Facc, it chirps in time with the increasing number of buffers. > When I run something out of VD0:, it chirps (slightly differently). > The loudest noise I have heard is while the "executing out of fast > ram" part of ASDG's memory test is running. It sounds vaguely like a > cricket in the distance. The chirping is probably the power supply's reaction to a sudden change in the load when the DRAM duty cycle goes from low to almost 100%. This can represent a pretty big jump in power consumption. It's also possible that there is some kind of contention which would cause even nastier problems, but the ASDG folks are probably more clever than that. Do both boards seem to chirp when used one-at-a-time? If so, then I wouldn't worry about it. If one chirps and the other doesn't, then I'd give ASDG a call and see what they say. -- George Robbins - now working for, uucp: {ihnp4|seismo|rutgers}!cbmvax!grr but no way officially representing arpa: cbmvax!grr@seismo.css.GOV Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
perry@well.UUCP (Perry S. Kivolowitz) (08/25/87)
The power supply in the Mini-Rack-C vibrates some internal part when the power supply is new. The sound will vary with the amount of power used by the memory board. Actually, this can be a feature. Like when you want to read a manual until a certain computation is finished :-) No really, the sound is very low and can't be heard if there are other sounds in the room. Even the sound of typing keys is enough to mask the rustle. (It sounds more like a rustling than a chirp). The Mini-Rack-D and the 2000-and-1 will not make this sound as their power supply technology is different. Perry S. Kivolowitz ASDG Incorporated (201) 563-0529