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Sansui G-22000, can the pre-amp work without the power amp?

jeromach

jeromach

With sufficient thrust, ducks fly just fine
I'm working on the pre-amp of a G-22000 which has intermittent channel drop outs (I suspect one of the reed relays), but I cannot test it, since it will not go out of protection without the power amp (and that one is not nearby).

I just wonder if somenone knows of a work around to get it to work without the power amp.
 
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It's been a while since I used a 22000 without the Amp. Plug the rear PreAmp Outputs into another Amp or Rec. you have around using the Aux for some sound. The PreAmp will not come out of Protection without the umbilical plugged in but you will find all the functions will work even with the Protection flashing I believe. Just ignore it. For as long as u can...LOL. I believe the relays will still function on/off but will have no effect on sound output thru the PreAmp Outs. You can then check the outputs of the relays or see if they are dropping out. . Do you have a Schematic? There is no way to avoid protection without the umbilical plugged in short of jumping the pins on the cord.
 
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The pre amp/tuner will work fine without the amp attached. The only issue is the protection LED will flash continuously if it doesn't see the amp. It has no bearing on the operation of the pre amp. You can connect any amp to the audio out RCA jacks.

The switches and pots are the most likely source of your channel drop out. There are a hell of a lot of them on this one. They all need to be cleaned. It takes a lot of disassembly to get to them.

- Pete
 
Thanks guys, for so far. The pre-amp/tuner did not work seperated from the amp, although it had been working when still connected, that was why I posed my question in the first place.

Then I found out this; http://i.imgur.com/GNcnP7h.png, these caps belonging in the power supply of the pre-amp. Well, I guess that did not help, euphemistically spoken.

I haven't yet finished working on it, will do tomorrow I hope, I will let you know what happened.
 
To my knowledge, there is nothing in the pre amp that is dependent on the amp to work. The protection circuit has elements in both units and the pre amp supplies power to some of the relays in the amp unit.

When you say it doesn't work when it's disconnected from the amp, how are you testing it? You won't hear anything unless you connect it to an amp but it should drive any amp.

- Pete
 
The problem has been solved meanwhile. I replaced two reed relays and nearly all electrolytics on the PSU board and it plays fine now. Indeed, no necessity to connect it to the power amp part, it plays fine on the Technics SU-3500 that I split for the purpose.

Thanks everybody, for replies and support.

 
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It's a Standard Medex relay, I used DIP24-2A72-21L. The layout is different and I had to piggy back it on the pcb and make some additional wiring, but hey, the originals are the unobtainiumst of unobtainium.

I bought it here in Holland at Conrad, but it is available at Mouser too and I guess at any of the bigger distributors.
 
Nice ! Glad you were able to get where you going with it. Enjoy, now just keep an eye out for the mate. They do come up.
 
Ah, but you misunderstood me I think, the mate is present, only not here, but at its rightful owner's place :).

I gave the power amp a rebuilt already (mainly electrolytics and repairing dry solder joints) and the complete combi played fine when it was here, but when back at the owners place channel dropouts started to happen. So I asked the owner to bring the pre-amp/tuner only, because the set is so very heavy! :).
 
Understood. I give you much praise and respect for being able to get in there and know whats going on . Starting with the small stuff and helping when I can. Perhaps one day i'll have the pins to attempt it. Regards.
 
Nice write up. Good you got it working. Just for the history, there is a tweak you can use , when I find that little paper inside my G22K , which shows what two pins to bridge to take the protection circuit out of the way. If I remember correctly it takes a small resistor of 1kΩ to bridge those pins and it goes out of protection mode.
Anyway glad you did it. Congrats , it's a fine amp generally speaking.
 
There is no "protection mode" for the preamp. The protection LED monitors the amp. It blinks continuously if the umbilical cord is not connected. Although it blinks, it means nothing if the amp isn't connected.

- Pete
 
Well you might be right , but in my G22K the output relay in the preamp doesn't get triggered if the protection doesn't click.
 
You got me curious. Looking at the schematic, there is a relay in the output to the pre out terminals on the side of the unit, next to the connected/separated switch. There is no relay in the output to the main amp. So you won't get sound out of the side pre out terminals if the umbilical cord isn't connected but you will get sound out of the pre out terminals for the main amp.

Not sure why they did it this way. The relay seems to be driven by the same circuit that controls the amp protection circuit but it doesn't shut off the input to the amp. It only shuts off the input to a second amp connected to the side terminals.

- Pete
 
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