ELF RM - swapping amplifiers for sound capabilities

[Jacob Watkinson]

Hi everyone, quite a specific question here.

I have the ELF RM 16mm projector with the optical and magnetic sound capabilities in good condition but the amplifier has blown: I noticed sparking when plugging it into the computer and now cannot get any sound (I now know this was stupid), I believe the issue was with voltage and I have blown the amplifier or some other internal component.

I have been gifted an old model of the projector with only optical sound capabilities - my question is, can I transfer the amplifier (or relevant component) from this old projector into my new one and achieve the ability to do both magnetic and optical sound playback?

Thanks as always for your thorough and helpful answers!

[David Strelitz]

Might be worth contacting Kevin Browne in Nottingham to see if he can repair the amp.

[Jacob Watkinson]

I was hoping it wouldn't come to that as I know he has retired but may very well be best to get his thoughts, thanks!

[Maurice Leakey]

I am not too sure, but I believe that the RM model has one, or maybe, two fuses.
If so, check them out before doing anything else.

[John Burgess]

Hi Jacob, if you swap your amp over to an optical only one you will lose the ability to play mag film, as Maurice says check fuses. Good luck !
John

[Nantawat Kittiwarakul]

Just for extreme case, when all else failed.

It's possible to directly tab the output from both the solar cell and the magnetic head, then feed it to any amplifier with microphone input. You'll need to figure out how to power the exciter lamp for optical sound however. But since it's nothing more than linear regulated psu providing 4vdc output so it shouldn't be too difficult.

And the sound quality would probably not perfect - far from that. But at least you'll get passable sound.

[Iain Warner]

Jacob, I've got an RT2 projector that looks like it has been hauled out of a skip. The paintwork on the frame is bubbling with corrosion and the drive belts have all disintegrated and there is no front cover. Having seen your posting I plucked up courage and plugged it in. The pilot light came on, the motor runs and when I switched on the amp I got crackling noises out of the speaker as I turned up the volume pot.
I believe the amp in the RT2 is the same as the RM2. You are welcome to have the whole thing if it is any use to you. Send me a PM if interested.

[Maurice Leakey]

Very commendable, Iain.
But I hope Jacob doesn't plug his gift into his computer. The service manual for the RM under NO SOUND says (among other things) a speaker connection must be 8 ohms or more.
By connecting a computer to the DIN speaker terminal would probably burn out part of the projector's amplifier output circuit. (As it previously seems to have done.)

[Brian Fretwell]

I would hope the computer input resistance would be much more than 8ohms, more like 100k ohm. High resistance would give a problem with valve amps low with transistor ones so I assume this is a transistor amplifier.
I wonder if the jack on the computer shorted out the plug as it was inserted.

[Jacob Watkinson]

Thank you everyone, some very helpful responses here. It does seem that Brian and Maurice are correct, I have definitely shorted the device and I think this was by plugging the jack cable into the mic input on my PC. I had no idea at all that it would be a problem, especially having not had a problem for quite some time via that method.

My understanding is a new amplifier must be installed though I will absolutely check the fuses and I've definitely learned my lesson.

Following this and my hopeful acquisition of the projector from the lovely Iain, how can I safely transfer sound through my PC. Do I need some kind of ohm conversion box?

[Maurice Leakey]

[QUOTE=Jacob Watkinson;....How can I safely transfer sound through my PC. Do I need some kind of ohm conversion box?
[/QUOTE]

Yes, you need an item known as a High-Performance Passive DI Box, available from Amazon.

[Phil Clark]

Bit late to the party on this one but ...

The amps on the Eiki S, R and N series projectors are interchangeable providing you change like for like, i.e. in this case you'd need another amp that supports both mag and optical sound. There were various improvements on the N series amps but they will work in R and S machines.

Natch the optical only and combined mag/optical amps are internally different and cannot be swapped around.

The amps do usually have two fuses, one is for the exciter lamp supply (which is provided by part of the amp board) and one is for the amp power supply.

The boards are also usually repairable if you can get hold of a schematic.

HTH
Phil

[Lee Mannering]

On ebay £2.19 Fwaeh FH-103 Handy Impedance Converter Item no: 143502942824
I had used with Elf machines for some time before I replaced with the Digital Optical board. It has two pots in so you can adjust the levels you require coming out of it.