5 ms·

More thoughts on the 1670 modem's weird noises

76 points by kencausey 2y ago

vidarh 2y ago
You know you're an are old nerd when you see 1670 and immediately think VIC-20. I never even owned a 1670 - just lusted over them in magazines.
fdsfad 2y ago
[dead]
cenobyte 2y ago
Sounds like your Vic 20 and/or power supply isn't shielded very well and its making your speakers do weird things.
- kstrauser 2y ago
  Every 1.2 seconds, though?
hermitdev 2y ago
A thought: maybe the pulse could be some sort of link status probing? e.g. "is this thing plugged in?"
NotYourLawyer 2y ago
Sounds like it could be a mechanical relay clicking. Is it actually coming from the speaker?
- alnwlsn 2y ago
  According to this [0] schematic, there is a relay present. Looks like it's job is to be the hook switch for the phone. The recording sounds like the characteristic ping of a reed relay to me, so it seems like it's hanging up and then going off hook again every 1.2 seconds. Not sure why it would be doing this - maybe it's trying to get a dial tone? Is it smart enough for that? 0 - https://www.zimmers.net/anonftp/pub/cbm/schematics/misc/1670-cr-modem-schematics.jpg https://www.zimmers.net/anonftp/pub/cbm/schematics/misc/1670...
  - pjdesno 2y ago
    Yes, I believe so. You can't expect dialing to work until you've received dial tone, and with older equipment [on the phone company side] there might be a significant delay.
pjdesno 2y ago
I'm surprised that you could get a modem pair to connect with a plain wire. An old dial telephone (e.g. a 500 set) was an entirely passive device, relying on power from the central office end of the wire. The carbon mic didn't need an amplifier - it's just a resistor, with resistance varying according to sound pressure; a transformer subtracted out the mic from the combined signal and sent the difference to the speaker. I did a quick search on 1670 schematics and came up with very little. Note however that several sources identify the USR101 chip as a ROM - that's clearly not the case, as a schematic shows no address or data bus, and you can see a line from the coupling transformer to an RC network and several pins on the device. It's almost certainly the analog front end and the modulator/demodulator. If you could find a datasheet for that device you'd probably be able to figure out how the whole thing works, but I'm guessing those were never available to the public and have been lost to the mists of time.
- pjdesno 2y ago
  See https://hackaday.com/2024/11/19/dial-up-internet-using-the-viking-dle-200b-telephone-line-simulator/ https://hackaday.com/2024/11/19/dial-up-internet-using-the-v... for a description of a telephone line simulator.
- timthorn 2y ago
  It doesn't even need a wire - wet string is enough: https://www.revk.uk/2017/12/its-official-adsl-works-over-wet-string.html https://www.revk.uk/2017/12/its-official-adsl-works-over-wet...
  - genter 2y ago
    ADSL works completely differently than audio as described by pjdesno.
  - Cthulhu_ 2y ago
    Kids these days with their fancy copper wire, back in MY day we used CANS and STRING.
- bongodongobob 2y ago
hinkley 2y ago
Sounds a bit like constructive interference between two sound sources that are almost the same frequency but not. Or RC “ringing”. That click stopping the sound makes me curious to see a plot of bytes per second sent and received. Is the modem resetting itself every time it clicks and introducing a small pause or data loss? Or is it completely divorced from the sound. These modems don’t have fans built in right? If you isolate the speaker does it still make the noise?
- einr 2y ago
  That click stopping the sound makes me curious to see a plot of bytes per second sent and received. Is the modem resetting itself every time it clicks and introducing a small pause or data loss? There is no data being sent or received yet when it makes this sound; as soon as it dials and starts handshaking it goes away. You can hear that here: https://www.youtube.com/watch?v=S-ChICic2TA https://www.youtube.com/watch?v=S-ChICic2TA EDIT: actually that's only partially true -- in the video above it's still making the noise when the dialling is happening. It disappears as soon as it detects a carrier from the other modem. This is weird because the click really sounds like a relay and the function of the relay should be to hang up the connection. Obviously, hanging up while in the middle of dialling is not a good idea.
  - hinkley 2y ago
    Sounds (figuratively, not literally) like a feedback loop when the SNR is zero. I'd totally believe a modem from the 80's was lacking a sophisticated Control System for the idle state.
pjdesno 2y ago
It might be trying to detect dial tone, then hanging up and trying again after a second or so - the click would be the mechanical relay you see in the schematic. (note that standard phone lines don't send dial tone until they detect an off-hook condition, i.e. current flowing down the line. Even then, older exchanges had a limited number of "dialers", and wouldn't send dial tone until one had been connected to the line)
- veunes 2y ago
  For me these little quirks of vintage tech are always fascinating
cluckindan 2y ago
Testing for echo? Impedance calibration?
tbotjenkins 2y ago
Sounds similar but very faint to an Atari 800 tape loader (400 baud) tiny data packets with gaps for demarcation.

76 points by kencausey 2y ago

You know you're an are old nerd when you see 1670 and immediately think VIC-20. I never even owned a 1670 - just lusted over them in magazines.

fdsfad 2y ago

[dead]

cenobyte 2y ago

Sounds like your Vic 20 and/or power supply isn't shielded very well and its making your speakers do weird things.

kstrauser 2y ago
Every 1.2 seconds, though?

hermitdev 2y ago

A thought: maybe the pulse could be some sort of link status probing? e.g. "is this thing plugged in?"

NotYourLawyer 2y ago

Sounds like it could be a mechanical relay clicking. Is it actually coming from the speaker?

alnwlsn 2y ago
According to this [0] schematic, there is a relay present. Looks like it's job is to be the hook switch for the phone. The recording sounds like the characteristic ping of a reed relay to me, so it seems like it's hanging up and then going off hook again every 1.2 seconds. Not sure why it would be doing this - maybe it's trying to get a dial tone? Is it smart enough for that? 0 - https://www.zimmers.net/anonftp/pub/cbm/schematics/misc/1670-cr-modem-schematics.jpg https://www.zimmers.net/anonftp/pub/cbm/schematics/misc/1670...
- pjdesno 2y ago
  Yes, I believe so. You can't expect dialing to work until you've received dial tone, and with older equipment [on the phone company side] there might be a significant delay.

pjdesno 2y ago

I'm surprised that you could get a modem pair to connect with a plain wire. An old dial telephone (e.g. a 500 set) was an entirely passive device, relying on power from the central office end of the wire. The carbon mic didn't need an amplifier - it's just a resistor, with resistance varying according to sound pressure; a transformer subtracted out the mic from the combined signal and sent the difference to the speaker. I did a quick search on 1670 schematics and came up with very little. Note however that several sources identify the USR101 chip as a ROM - that's clearly not the case, as a schematic shows no address or data bus, and you can see a line from the coupling transformer to an RC network and several pins on the device. It's almost certainly the analog front end and the modulator/demodulator. If you could find a datasheet for that device you'd probably be able to figure out how the whole thing works, but I'm guessing those were never available to the public and have been lost to the mists of time.

pjdesno 2y ago
See https://hackaday.com/2024/11/19/dial-up-internet-using-the-viking-dle-200b-telephone-line-simulator/ https://hackaday.com/2024/11/19/dial-up-internet-using-the-v... for a description of a telephone line simulator.
timthorn 2y ago
It doesn't even need a wire - wet string is enough: https://www.revk.uk/2017/12/its-official-adsl-works-over-wet-string.html https://www.revk.uk/2017/12/its-official-adsl-works-over-wet...
- genter 2y ago
  ADSL works completely differently than audio as described by pjdesno.
- Cthulhu_ 2y ago
  Kids these days with their fancy copper wire, back in MY day we used CANS and STRING.
bongodongobob 2y ago

hinkley 2y ago

Sounds a bit like constructive interference between two sound sources that are almost the same frequency but not. Or RC “ringing”. That click stopping the sound makes me curious to see a plot of bytes per second sent and received. Is the modem resetting itself every time it clicks and introducing a small pause or data loss? Or is it completely divorced from the sound. These modems don’t have fans built in right? If you isolate the speaker does it still make the noise?

einr 2y ago
That click stopping the sound makes me curious to see a plot of bytes per second sent and received. Is the modem resetting itself every time it clicks and introducing a small pause or data loss? There is no data being sent or received yet when it makes this sound; as soon as it dials and starts handshaking it goes away. You can hear that here: https://www.youtube.com/watch?v=S-ChICic2TA https://www.youtube.com/watch?v=S-ChICic2TA EDIT: actually that's only partially true -- in the video above it's still making the noise when the dialling is happening. It disappears as soon as it detects a carrier from the other modem. This is weird because the click really sounds like a relay and the function of the relay should be to hang up the connection. Obviously, hanging up while in the middle of dialling is not a good idea.
- hinkley 2y ago
  Sounds (figuratively, not literally) like a feedback loop when the SNR is zero. I'd totally believe a modem from the 80's was lacking a sophisticated Control System for the idle state.

pjdesno 2y ago

It might be trying to detect dial tone, then hanging up and trying again after a second or so - the click would be the mechanical relay you see in the schematic. (note that standard phone lines don't send dial tone until they detect an off-hook condition, i.e. current flowing down the line. Even then, older exchanges had a limited number of "dialers", and wouldn't send dial tone until one had been connected to the line)

veunes 2y ago
For me these little quirks of vintage tech are always fascinating

cluckindan 2y ago

Testing for echo? Impedance calibration?

tbotjenkins 2y ago

Sounds similar but very faint to an Atari 800 tape loader (400 baud) tiny data packets with gaps for demarcation.