|
Author
|
Topic: ST600M stereo playback conversion
|
Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
|
posted August 28, 2008 02:33 PM
This week's diary...
Monday: Settled down to convert my ST600M for Stereo Playback. Had planned this 5 years ago and after spending the last 3 years extending and renovating our retirement home I had at long last been allowed to spend time on a hobby. Stripped the machine down to the bare amplifier and examined it along with the notes I made 5 years ago. Something was wrong; I discovered that I had done the conversion 5 years back .... and forgotten about it!. Put it all back together.
Wednesday: (Tuesday is a day off and the wife insists we go out for the day). Dug out my copy of "June is bustin' out all over" from Carousel (Derrann print, one of my favourites), set everything up through an external power amp and switched on. Didn't sound very Stereo to me! Even through headphones. Switched off, stripped it back down to the amplifier. A few checks; found dead short between the output channels, so I was getting Mono! Remembered that I had discovered that 5 years ago and had put it to one side for investigation.... and forgotten about it!
Thursday: Spent the morning trying to remember what I had done 5 years ago and reconciling it with the notes I made at the time. It turns out that I am not suffering from senile dementia (despite what the wife says), and the fault was a stupid one; one channel's leadout wire was soldered to the wrong PCB land.
Connected it all up again, switched on and... crisp, sparkling Stereo! Useful three days, despite me being so thick.
Now I have a Stereo Elmo and a Stereo (S926) Eumig. Now all I need is the time to compare them to decide which is best. I bet somebody out there can save me the trouble?
--------------------
Retired TV Service Engineer
Ongoing interest in Telecine....
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
|
posted August 30, 2008 09:52 AM
Kevin and Steven,
htt://8mmforum.film-tech.com/ubbpics/ST600M0007.pdf
(as far as I can tell, you will have to copy this address to your web browser to get to the .pdf, and then print it for reference)
Here's the description promised..
The idea arose back in the 90's when I was the proud owner of only two projectors, the ST-600M and a Eumig 824 Dual Gauge. I would have liked a Stereo machine but at that time both new and used machines were out of my budget. When my Elmo motor stopped working, I got in touch with Hanimex at Swindon, who sent me a replacement Motor Control board, which didn't cure the problem. They were very helpful and sent me a complete set of schematics and layouts for the machine, from which I was able to solve the problem...Their new board had been incorrectly assembled! The connection socket had been soldered the wrong way round (pin 1 in the pin 8 position)!
The amplifier schematic (which I hope reaches this post as I have had to upload it as a PDF because of its size) proved interesting as the microphone recording preamp uses half of an IC with two identical seperate amplifiers; only the external components are different. Also, the amplifier of this model has all the switching and connections for the version with Optical sound, only with the exciter lamp and photocell not present ( the boxes on the shcematic identify those). The Magnetic-Silent-Optical switch is there; the Optical position is inhibited by the size of the aperture in the Control panel. A little ingenuity (please refer to the PDF as needed, the mods are shown in red) makes a conversion to Stereo Playback possible.It should be noted that the point of the exercise was to enable Stereo playback; the question of whether recording would still be possible was of secondary importance since recordings of Main or Balance tracks could be made on my other machine if needed.
1. The M-S-O switch aperture was enlarged to allow the switch to access the O position. This makes available some unused switch contacts.
2. The PCB tracks were cut at the points shown with "X". These......
a. makes sure that SW103-1 does not ground the Main Track head in the Play position.
b. isolates IC 101-2 from the main output amplifier, and
c. isolates SW102-3 from the 11V supply.
3. Additional connections were added as per the dotted lines; The first provides a Ground at the two centre contacts of SW102-3, the next one
grounds the common connection of the two heads via SW102-3 in the Optical position, the third replaces the deleted ground connection at
SW 103-1 via SW102-3 in the Magnetic position and allows head switching to revert to normal in the Magnetic position.
The last connects the "hot" end of the main track head to IC 101-2 input, via the Optical position of switch SW102-1.
4. Various component values were changed to make the circuit of IC 101-2 the same as IC 101-1, identified by the large dots...
a. R120 was removed completely.
b. C120 was changed to 680pf.
c. R116 was changed to 56 ohms.
d. R115 was replaced with 150kohms in
parallel with 0.033 uF, both in series wth 3kohms.
5. A 3.5mm Stereo ouput socket was fitted in the rear panel
alongside the AUX OUT socket, and connected to R108 and R127
where shown
by the arrows.
In use the Main-Mix-Sub switch is left in the Mix position and the Magnetic-Silent-Optical switch in the Optical position. Stereo at 30mV level is taken from the Stereo output jack. The internal monitor does not work, neither is there an output to an external speaker.
In the Magnetic position, Mono play back is available in all three modes (Main, Sub and Mix) because of the new grounding arrangements for the heads and SW103-1 via SW102-3. The internal monitor, amplifier and mono speaker output works normally in the Magnetic position.
Obviously, the Microphone input no longer works. The effect on recording (now via AUX IN only) in the various mono modes has not yet been tested but, as said above, it's the playback facilities that are important. There is a full set of contacts available on SW102 in case they are needed (nothing envisaged at present!).
The extra connections appear to be very long in some cases, but the amplifier board is very compact so the actual links are actually very short. The biggest problem is identifying components, switch contacts and PCB tracks, so the job is not recommended for the inexperienced in electronic repair and assembly.
A previous post refers to a simple mod on a basic ST-600 M (or MO) for bringing out a mono signal to a HiFi power Amplifier. To achieve this it is only necessary to cut the connection between J102 and the "R" contact on SW103-2 and reconnect J102 to the two centre contacts of SW102-2. This will enable J102 to be used as an AUX Input on both Record and Playback, and as a low (30mV) level AUX Output during both Magnetic and (in the case of an MO machine) Optical Playback.
Martin
[ August 30, 2008, 11:30 AM: Message edited by: Martin Jones ]
--------------------
Retired TV Service Engineer
Ongoing interest in Telecine....
| IP: Logged
|
|
|
|
Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
|
posted August 31, 2008 03:56 AM
Steven,
Thank you for your comments; if you decide to try the mono conversion contact me first at blagdonian(at)btinternet(dot)com so I can pass on a couple of tips regarding dis-assembly and send you an annotated PC board layout.
General,
My remarks regarding the effect on recording in the last post were precautionary (to avoid egg on my face!), but having fully analyzed what I have done (and no doubt others are checking) I am happy that when the Mode switch is in the Magnetic position all circuitry other than the microphone preamp is effectively back to where it was before the conversion, and will work for both recording on seperate tracks and for playback of tracks 1 and 2 individually or combined.
The only real anomaly with regard to normal Audio Practice is the signal level at the outputs (30mV instead of the more usual 150mV of a "Line" input or output) but this can be allowed for at the external amplifier input. It is strange that Elmo has adopted this level, just as it is strange that they designate the "Moni" socket, which is intended for an earpiece and is part of the final speaker circuit, as (Aux Out) also.
I don't know if this is the case on the ST-600D M/MO, as it has a different amplifier. I do have a copy of the Operating Manual for that machine; there is no circuit diagram and Elmo do not list sensitivities (levels) in their Specifications, another departure from normal audio practice.
Martin
[ March 04, 2014, 08:03 AM: Message edited by: Martin Jones ]
--------------------
Retired TV Service Engineer
Ongoing interest in Telecine....
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
UBBFriend: Email this page to someone!
![[Cool]](cool.gif)
![[Smile]](smile.gif)
Kev.
Printer-friendly view of this topic
