I've been working on replacing the original electrolytic capacitors and have noticed whilst testing the unit that there is an odd fault.
When switching all the speakers off the right speaker on the A channel still plays. Switch the A channel back on and the left kicks in too. (works as it should) Switch the B channel on only and B plays as it should (no sound from A). Both channels work together too without an issue. Both A & B off and headphones in i get sound out of both channels on the headphones but the right A speaker still outputs.
The right channel on the "DISC" input doesn't work either, but that might be down to a cap or dodgy connection. I'm still waiting on the remainder of the capacitors to arrive.
Does anyone happen to have the service manual for this unit? (My dad supposedly had a paper copy stashed in the attic but cannot find it)
This is the unit in question...
When switching all the speakers off the right speaker on the A channel still plays. Switch the A channel back on and the left kicks in too. (works as it should) Switch the B channel on only and B plays as it should (no sound from A). Both channels work together too without an issue. Both A & B off and headphones in i get sound out of both channels on the headphones but the right A speaker still outputs.
The right channel on the "DISC" input doesn't work either, but that might be down to a cap or dodgy connection. I'm still waiting on the remainder of the capacitors to arrive.
Does anyone happen to have the service manual for this unit? (My dad supposedly had a paper copy stashed in the attic but cannot find it)
This is the unit in question...
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What sort of speaker switch is fitted? Is it that odd metal work gizmo btm. RHS?
I'd check it out while you operate the control and see if any parts are loose or just not making proper contact.
If fitted, slider or rotary switches don' last forever either, so locate the "works" and check that the switch
actions are firm and make positivecontact.
I'd check it out while you operate the control and see if any parts are loose or just not making proper contact.
If fitted, slider or rotary switches don' last forever either, so locate the "works" and check that the switch
actions are firm and make positivecontact.
Completed most of the restoration work this evening. Fitted new main filter caps (BHC, 10,000uF 63V) and the rest of the parts replaced with FM/FC. There is a single cap left to replace (behind the volume pot) which should be arriving tomorrow. All of the old caps were measuring a lot higher than their ratings and there has been a fair improvement in sound since changing them. I checked the speaker switch and the wiring and cannot find anything suspect. Gave it a good clean but still no dice.
Back together.
Back together.
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Looks like a cool amplifier. If it stacks up to the models by Leak before it, Im sure its a quality item, I suspect it was high end in its day.
Does it have a way to play music without the tone controls? What happens with the 4 channel matrix switch?
I wonder if its like I read about in some instructions for a Reel to Reel tape deck and its rectified two channel making a quadraphonic amplifier.
You might have a 4 channel amplifier their, and it might be worth making a simple op amp preamp putting in a 4 channel volume control and ignoring all the rest of the preamp, particularly this crude way of multiplexing quadraphonic signals down two channels, it looks cool
Owen
Does it have a way to play music without the tone controls? What happens with the 4 channel matrix switch?
I wonder if its like I read about in some instructions for a Reel to Reel tape deck and its rectified two channel making a quadraphonic amplifier.
You might have a 4 channel amplifier their, and it might be worth making a simple op amp preamp putting in a 4 channel volume control and ignoring all the rest of the preamp, particularly this crude way of multiplexing quadraphonic signals down two channels, it looks cool
Owen
It's quadraphonic, which is analog decoded, 4 from 2 channels, like FM is 2 from 1 channel. The difference is that the licensed trademarks "Quadraphonic" or "SQ4" aren'tused as they belonged to RCA or JVC IIRC. I can't see that there really are an extra 2 channels in these Pics.
The matrix switch will allow different modes of playback in the Phono or Tape modes wich should be bypassed with other inputs like tuner or aux. This was sometimes the only way to avoid those troublesome switches. and the strange sounds that occur when you try Quad playback with a stereo disc. Leave in the off position to avoid problems.
In any event, it's likely the switching of speakers will allow coupling as stereo (parallel pairs) or quad (all separate. These won't be wired in a conventional manner, as you find, so you may have a bit of work ahead sorting the switch wiring out in a manner the suits you. A schematic would help, of course.
The matrix switch will allow different modes of playback in the Phono or Tape modes wich should be bypassed with other inputs like tuner or aux. This was sometimes the only way to avoid those troublesome switches. and the strange sounds that occur when you try Quad playback with a stereo disc. Leave in the off position to avoid problems.
In any event, it's likely the switching of speakers will allow coupling as stereo (parallel pairs) or quad (all separate. These won't be wired in a conventional manner, as you find, so you may have a bit of work ahead sorting the switch wiring out in a manner the suits you. A schematic would help, of course.
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Fitted the last cap that was missing and had another look at the switches. Gave the wires a "wiggle" and checked to make sure none were possibly making contact with another and couldn't find anything at fault. Put it back together and now the speaker switches work exactly as they should. Seems it just needed a prod.
It was the bottom pair of switches on this board.
It was the bottom pair of switches on this board.
Two more faults i've noticed since putting it back together are that the disc preamp (phono stage) has quite a muffled sound to it and there is some hum that gets amplified. The hum seems to be internal as it doesn't matter how i plug in various devices, its still there. Suggests to me that it is picked up in the preamp, since it increases with volume.
At the age of the unit, all electrolytic caps are suspect. At least replace any in the preamp and it should also be configured for stereo, not Quad. mode. I guess you have a conventional MM cartridge of nominal 47k fitted? 'Not sure how these compare to original SQ4 types. It may be worth checking this out.
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All the electrolytic capacitors in the unit have already been replaced. The film/ceramic capacitors are still original, but i doubted that these deteriorate. (although from what i just found with the celestion Xovers, even film caps can be miles out of tolerance too) The matrix mode switch has always been set to off and all filter switches are off. The hum sounds like mains hum.
The cartridge i use is a shure M75ED type 2 with a jico sas stylus. Sounds fantastic via my luxman, which rules out the cartridge being at fault. The rear sensitivity switch doesn't affect anything other than the output volume.
The cartridge i use is a shure M75ED type 2 with a jico sas stylus. Sounds fantastic via my luxman, which rules out the cartridge being at fault. The rear sensitivity switch doesn't affect anything other than the output volume.
Sorry, I realised you changed all electros last time but the hum suggests connection issues with the cartridge i.e. what suits one amplifier need not suit all if say, the cable earths form a hum loop with the chassis ground wire. It's worth checking as there could be a problem there.
Did you ever test the phono operation before overhauling it?
Did you ever test the phono operation before overhauling it?
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