Uher 'Automatic Start Switch' - UK Vintage Radio Repair and Restoration Discussion Forum

TonyDuell · 20th Dec 2017, 4:41 pm

The user manual for my Uher CR210 mentions an 'Automatic Start Switch', type K839 that you plugged into the Accessory socket to cause the machine to start running in 'forward' mode as soon as it got power. The idea was so that you could start the whole thing with a normal mains time switch.

Unfortunately the manual gives no details of what this actually was, and I can find nothing about it on the web. Thinking about it, it could have been a DIN plug with a couple of pins linked, a capacitor (and diode?) circuit, right up to a multi-transistor thing. Does anyone know?

julie_m · 20th Dec 2017, 9:32 pm

Uher sold an accessory device for thheir 4000-series reel-to-reel machines called the "Akustomat". This was a sort of voice-controlled start/stop switch, which started the tape running in response to sound above a set threshhold level. Could your mystery device be like that?

TonyDuell · 21st Dec 2017, 6:10 am

I don't think so.

The CR210 has an odd drive system controlled by a discrete transistor flip-flop (for reversing) which is only powered when the tape is moving. When you turn the machine on, the tape does not start. You have to flip the control switch to one of the (momentary) '1' (forward) or '2' reverse positions to start it. Flipping to 'pause' stops it, it is then restarted by '1' or '2' as appropriate.

What this means is that if you just power up the machine (e.g. by using a time switch to control the mains to the mains adapter) the tape doesn't start. So you can't do timer recordings that way -- without this 'automatic start switch' accessory.

All I know about it is that it connected to the 'accessory socket'. This is a 6 pin DIN socket carrying :

A couple of grounds

The top end of the track 4 head winding (used for a slide synchroniser, and irrelevant here)

+9V power

Remote pause switch (this stops the tape when grounded and re-starts it in the direction it was running in when left floating, it is not the same -- quite -- as the pause function on the control switch)

The signal to start the tape in the forward direction.

It's possible this 'automatic start switch' was just a plug that linked +9V to 'start in the forward direction'. But that might cause problems is it was fitted and the control switch was manually moved to '2'. Or it might have been some kind of timer circuit (maybe just a capacitor, maybe add a discharging diode, maybe a couple of transistors as a monostable) to apply a pulse to the 'start in forwards direction' pin after the +9V line comes up.

I can experiment and see what works, but I would like to know what the original consisted of.

julie_m · 21st Dec 2017, 8:02 pm

Ah, right.

One of my old AKAI mechanical cassette decks had a button which released the pause aftet a short delay, for timer-controlled recordings: the deck would be placed in RECORD / PAUSE, the timer's override switched off and the timer button depressed. Now the pinch roller would be held clear of the capstan until the latter was rotating; and as long as the timer was set to stay ON for longer than the tape would last, would be disengaged again by the automatic stop before the power was removed.

A device that plugged into the socket as you've described it probably would contain a monostable to deliver a pulse to the "start forwards" line and then leave it in its idle state. This probably would have consisted of just two transistors and a handful of passives in the original; I'd probably use an 8-pin PIC microcontroller nowadays, just because they're so cheap.

The Uher "Akustomat" suffered from the common disadvantage of all tape-based voice-conttolled recording devices, i.e. the sound that triggered it has already been made by the time the tape is up to full speed, so the first part of the first word of the sentence is missing or distorted. The only way to get around this is digitally, by having a buffer of RAM which is continuously being written and overwritten and which gets dumped to the SD card in full, including a faithful reproduction of the triggering sound, when the recording starts in earnest.

Still, you could replicate this functionality on your CR210 using the remote pause input, if you really wanted to; you would need a re-triggerable monostable which unpaused the deck for a set period on detecting a sufficient voltage at the input, and restarted the timeout every time the thresshold was exceeded.

TonyDuell · 21st Dec 2017, 8:09 pm

Quote:

Originally Posted by julie_m

A device that plugged into the socket as you've described it probably would contain a monostable to deliver a pulse to the "start forwards" line and then leave it in its idle state. This probably would have consisted of just two transistors and a handful of passives in the original; I'd probably use an 8-pin PIC microcontroller nowadays, just because they're so cheap.

I will do some experiments when I've got the machine back together and basically working.

The device might have been a capacitor (say about 47uF) between +9V and the 'start forwards' line with a diode from there to ground to discharge the capacitor at power-down. Or it might, as you say, be a couple of transistors as a monostable.

To use a PIC you would (a) need some way of powering it from the 9V line (either resistor and zener or 3 terminal regulator) and (b) some way of shifting the output to pull the (normally floating) 'start forward' line up to around 9V (a couple of transistors). At which point the discrete component monostable looks attractive. Fortunately I do not belong to the school of 'design' that thinks no problem can be solved without at least one microcontroller!

TonyDuell · 14th Jan 2018, 5:57 pm

I've had a go at this and come up with something that works. Far from needing a microcontroller, I have a working device in 3 passive components :

Diode 1 (1N4148), Anode to pin 4 of the DIN plug

Diode 2 (1N4148), Cathode to pin 2 of the DIN plug

22uF capacitor, +ve side to pin 1 of the DIN plug

-ve side of the capacitor, cathode of diode 1, anode of diode 2 all joined together but not to any pin of the plug.

Experimenting showed that 4u7 was not enough, 10uF was fine, too high and the manual or auto reverse was affected. So 22uF for a margin of safety.

The components fitted inside a 6 pin DIN plug with no problems.

If anyone is interested, I will try to draw up a readable circuit diagram.

20th Dec 2017, 4:41 pm	#1
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Uher 'Automatic Start Switch' The user manual for my Uher CR210 mentions an 'Automatic Start Switch', type K839 that you plugged into the Accessory socket to cause the machine to start running in 'forward' mode as soon as it got power. The idea was so that you could start the whole thing with a normal mains time switch. Unfortunately the manual gives no details of what this actually was, and I can find nothing about it on the web. Thinking about it, it could have been a DIN plug with a couple of pins linked, a capacitor (and diode?) circuit, right up to a multi-transistor thing. Does anyone know?

20th Dec 2017, 9:32 pm	#2
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Uher 'Automatic Start Switch' Uher sold an accessory device for thheir 4000-series reel-to-reel machines called the "Akustomat". This was a sort of voice-controlled start/stop switch, which started the tape running in response to sound above a set threshhold level. Could your mystery device be like that? __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

21st Dec 2017, 6:10 am	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Uher 'Automatic Start Switch' I don't think so. The CR210 has an odd drive system controlled by a discrete transistor flip-flop (for reversing) which is only powered when the tape is moving. When you turn the machine on, the tape does not start. You have to flip the control switch to one of the (momentary) '1' (forward) or '2' reverse positions to start it. Flipping to 'pause' stops it, it is then restarted by '1' or '2' as appropriate. What this means is that if you just power up the machine (e.g. by using a time switch to control the mains to the mains adapter) the tape doesn't start. So you can't do timer recordings that way -- without this 'automatic start switch' accessory. All I know about it is that it connected to the 'accessory socket'. This is a 6 pin DIN socket carrying : A couple of grounds The top end of the track 4 head winding (used for a slide synchroniser, and irrelevant here) +9V power Remote pause switch (this stops the tape when grounded and re-starts it in the direction it was running in when left floating, it is not the same -- quite -- as the pause function on the control switch) The signal to start the tape in the forward direction. It's possible this 'automatic start switch' was just a plug that linked +9V to 'start in the forward direction'. But that might cause problems is it was fitted and the control switch was manually moved to '2'. Or it might have been some kind of timer circuit (maybe just a capacitor, maybe add a discharging diode, maybe a couple of transistors as a monostable) to apply a pulse to the 'start in forwards direction' pin after the +9V line comes up. I can experiment and see what works, but I would like to know what the original consisted of.

21st Dec 2017, 8:02 pm	#4
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Uher 'Automatic Start Switch' Ah, right. One of my old AKAI mechanical cassette decks had a button which released the pause aftet a short delay, for timer-controlled recordings: the deck would be placed in RECORD / PAUSE, the timer's override switched off and the timer button depressed. Now the pinch roller would be held clear of the capstan until the latter was rotating; and as long as the timer was set to stay ON for longer than the tape would last, would be disengaged again by the automatic stop before the power was removed. A device that plugged into the socket as you've described it probably would contain a monostable to deliver a pulse to the "start forwards" line and then leave it in its idle state. This probably would have consisted of just two transistors and a handful of passives in the original; I'd probably use an 8-pin PIC microcontroller nowadays, just because they're so cheap. The Uher "Akustomat" suffered from the common disadvantage of all tape-based voice-conttolled recording devices, i.e. the sound that triggered it has already been made by the time the tape is up to full speed, so the first part of the first word of the sentence is missing or distorted. The only way to get around this is digitally, by having a buffer of RAM which is continuously being written and overwritten and which gets dumped to the SD card in full, including a faithful reproduction of the triggering sound, when the recording starts in earnest. Still, you could replicate this functionality on your CR210 using the remote pause input, if you really wanted to; you would need a re-triggerable monostable which unpaused the deck for a set period on detecting a sufficient voltage at the input, and restarted the timeout every time the thresshold was exceeded. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

14th Jan 2018, 5:57 pm	#6
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Uher 'Automatic Start Switch' I've had a go at this and come up with something that works. Far from needing a microcontroller, I have a working device in 3 passive components : Diode 1 (1N4148), Anode to pin 4 of the DIN plug Diode 2 (1N4148), Cathode to pin 2 of the DIN plug 22uF capacitor, +ve side to pin 1 of the DIN plug -ve side of the capacitor, cathode of diode 1, anode of diode 2 all joined together but not to any pin of the plug. Experimenting showed that 4u7 was not enough, 10uF was fine, too high and the manual or auto reverse was affected. So 22uF for a margin of safety. The components fitted inside a 6 pin DIN plug with no problems. If anyone is interested, I will try to draw up a readable circuit diagram.