NOON
Well-known member
Hi everybody!
a couple of years ago I picked up the aforementioned line amplifier at a theatre clearance sale in Melbourne, Australia. Haven't had a chance to investigate or play around with it until now, filling in some downtime while recovering from some minor surgery.
There is very little info out there about Murray Amplifiers that I can find in my searching, but it appears to be by Cyril Murray, a well-respected (legendary?) audio designer who worked in the Electrical Engineering Dept at the University of Sydney with the famous Thiele and Small.
This particular unit is a 1980's-made 1U rack unit with single XLR in and out containing a PSU and a Eurocard labelled Murray Australia CD88. The only external control is a pot labelled GAIN and there are three LEDs indicating DC power, audio signal and AGC activity. The board is only 3/4 populated with room for other input stages by the look of it and has 3 blue-coated hybrid modules, one smaller labelled Murray CHD64 at the input and two larger labelled Murray CHD69 at the output. It also has an Allison Research EGC-101 VCA mounted on the EGC-205 eval board and a DBX 2150A VCA. There's a variety of trimpots on the board labelled only with VR numbers. (I'll prob get some photos up later)
I can certainly hear it compressing when I've hooked it up in the studio, but it would be nice to add some T/R/A/R controls to turn it into a full blown compressor. To while away some recovery downtime I've been tracing out the circuit (attached. I only got as far as the VCAs before needing more meds, haven't bothered mapping the output stages as they are hybrid modules and not all that important in this case anyway.) No guarantees on accuracy of the circuit trace, I'm on drugs at the moment.
Now most of it is pretty straightforward and I have some theories to investigate when the grey cells come back online, but in the meantime I'd appreciate the brains trust having a look-see. The input stage is fairly obvious, as is the bypass switch and signal indicator LED circuit. The DBX seems to be set up for external gain control if the board is used in a different unit, it seems to be sitting at 0dB gain with the control port going to an unconnected pin on the Eurocard. I'll probably hook this up as a gain makeup stage.
The sidechain circuit is partly obvious and partly confusing in my current addled state. Anyone want to chip in with suggestions for modifying the circuit for Threshold, Ratio, Attack and Release controls? Any other interesting mods to suggest for this circuit? Any other comments or questions or more info to add about Murray (the man or the company)?
Thanks!
a couple of years ago I picked up the aforementioned line amplifier at a theatre clearance sale in Melbourne, Australia. Haven't had a chance to investigate or play around with it until now, filling in some downtime while recovering from some minor surgery.
There is very little info out there about Murray Amplifiers that I can find in my searching, but it appears to be by Cyril Murray, a well-respected (legendary?) audio designer who worked in the Electrical Engineering Dept at the University of Sydney with the famous Thiele and Small.
This particular unit is a 1980's-made 1U rack unit with single XLR in and out containing a PSU and a Eurocard labelled Murray Australia CD88. The only external control is a pot labelled GAIN and there are three LEDs indicating DC power, audio signal and AGC activity. The board is only 3/4 populated with room for other input stages by the look of it and has 3 blue-coated hybrid modules, one smaller labelled Murray CHD64 at the input and two larger labelled Murray CHD69 at the output. It also has an Allison Research EGC-101 VCA mounted on the EGC-205 eval board and a DBX 2150A VCA. There's a variety of trimpots on the board labelled only with VR numbers. (I'll prob get some photos up later)
I can certainly hear it compressing when I've hooked it up in the studio, but it would be nice to add some T/R/A/R controls to turn it into a full blown compressor. To while away some recovery downtime I've been tracing out the circuit (attached. I only got as far as the VCAs before needing more meds, haven't bothered mapping the output stages as they are hybrid modules and not all that important in this case anyway.) No guarantees on accuracy of the circuit trace, I'm on drugs at the moment.
Now most of it is pretty straightforward and I have some theories to investigate when the grey cells come back online, but in the meantime I'd appreciate the brains trust having a look-see. The input stage is fairly obvious, as is the bypass switch and signal indicator LED circuit. The DBX seems to be set up for external gain control if the board is used in a different unit, it seems to be sitting at 0dB gain with the control port going to an unconnected pin on the Eurocard. I'll probably hook this up as a gain makeup stage.
The sidechain circuit is partly obvious and partly confusing in my current addled state. Anyone want to chip in with suggestions for modifying the circuit for Threshold, Ratio, Attack and Release controls? Any other interesting mods to suggest for this circuit? Any other comments or questions or more info to add about Murray (the man or the company)?
Thanks!
