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Can anyone identify what power supply i need for an old mixer/pre?
Old 3 weeks ago
  #1
Here for the gear
 

Can anyone identify what power supply i need for an old mixer/pre?

Hey!!

Can anyone help me work out what power supply this unit needs? I scored this old mixer a couple of weeks ago but i cant work out what power supply i need to test it. It's a homemade unit so the only information i have is the small B+ thats printed above what looks like a 5 pin din connector???

I've attached some photo's of the unit but can upload more if needed.

Any help with this would be great! Thanks in advance!
Attached Thumbnails
Can anyone identify what power supply i need for an old mixer/pre?-dscn0318.jpg   Can anyone identify what power supply i need for an old mixer/pre?-dscn0321.jpg   Can anyone identify what power supply i need for an old mixer/pre?-dscn0350.jpg  
Old 3 weeks ago
  #2
Gear Nut
 
Clive Banks's Avatar
 

Looks like it needs a split power supply.

In the third pic you can see three wires that are connected to the 5 pin din socket.

Red would most likely be +V , Black would most likely be -V and the green one is the earth and chassis earth.
Follow these wires to find the corresponding pins in the socket.

I would start with +/- 12VDC . Make sure you have the correct polarity going to the relevant pins otherwise you may damage something.
I would also consider taking the cards out before you inject power and confirm the polarities are right after you connect the power supply with a multimeter.
If all looks good then load up the cards.
Hope that helps.
Old 3 weeks ago
  #3
Here for the gear
 

Thanks Clive! You're a legend! Really appreciate your help mate!

Ill post an update here once i source the power supply. Have a great day buddy. I owe you a beer haha!
Old 3 weeks ago
  #4
Lives for gear
Which op amps does it use? That would be a good place to start to see what kind of voltage they need. It would also tell you their pin outs, from there you can trace the power rails back to confirm clives wire colour guesses. You really don’t want to make a mistake with power, doing so will blow the whole thing.

Getting the numbers off the transistors will also give you some more info about what they need and can tolerate.

Very cool looking mixer. I bet it sounds amazing. If it were mine, I would mod it so that 2 of the channels went only to direct outs, and the last channel stays to the main mixer out. This way I could record a stereo pair (or kick and snare) on the direct outs and then a room mic on the main mic out (likely the main mix out will be louder and have more character in its sound).
Old 3 weeks ago
  #5
Here for the gear
 

Thanks for the info enginefire! I'm not sure about the op amps, i'm pretty green to this kind of stuff. Just a muso who's getting into recording and trying to learn as i go! All your info/advice is awesome though, really appreciate it. Thanks for your help! Would love to mod this to do exactly what you said! I'm a drummer so that was the reason i bought this unit. I'm looking at producing my first EP so i've been collecting gear to use and i picked this up for $25!!! This is a learning experiment for me, so all the help i can get is great! Your a champ for that info, will definitely be taking it all into consideration as i work out how to get this running! Will post updates here as i find out more info about how to get this going! Just don't want to blow it up, so i'm trying to be as careful as possible. Thanks again mate!
Old 3 weeks ago
  #6
Lives for gear
Op amps circled in red
Transistors in blue
The green circled things are caps, likely tants

Getting the numbers from the op amps will give good info.

If you are serious about this piece, I think you would get a pro to fix it the way you want, it will give you time to do music with it instead of trying to mod this. It looks like a great preamp.
Attached Thumbnails
Can anyone identify what power supply i need for an old mixer/pre?-281b38b8-cebc-4002-b3e0-3f0883040209.jpeg  
Old 3 weeks ago
  #7
Here for the gear
 

Ahh that's really nice of you enginefire! You're a good man!

Thanks for your advice! It's a steep learning curve haha!
I'll make sure i find a pro who's able to mod it and get it running.
Old 3 weeks ago
  #8
Here for the gear
 

Just an updated pic so people can see the numbers on the op amps. Thought this might be useful to anyone who's interested!

Looks like SG301AM / 7233 (or 7232 - a bit hard to read)

749 / LM /301AN

SGSG / 4501N / 8216

Thanks again to everyone who's helped with this!

EDIT: also here's a link to a previous thread where i was trying to identify this mixer (with more pics)
Help identifying Magnecord Mixer
Attached Thumbnails
Can anyone identify what power supply i need for an old mixer/pre?-dscn0337.jpg   Can anyone identify what power supply i need for an old mixer/pre?-dscn0339.jpg  
Old 3 weeks ago
  #9
Lives for gear
 

7233 and 8216 are almost certainly date codes for when the chips were manufactured: 33rd week of 1972, and 16th week of 1982. Quite a spread; it seems to have been made with parts that happened to be at hand, or were new old stock parts, or perhaps it was repaired/reworked at some point. That doesn't really matter at all for your questions--it's just interesting.

LM301A opamps are rated with an absolute maximum supply voltage of +/- 18V; +/- 12V or +/- 15V might be typical supply voltages in this sort of use.

SG4501 is a dual voltage regulator, and it may be what is clean power for the opamps. If that is its purpose in the circuit, then the system supply voltage might not be particularly critical. It may also have some other unrelated use for all I know, such as perhaps regulating the supply for the discrete transistor circuitry.

If I were working on this, I'd sketch out a schematic of the circuitry to work from. It shouldn't be particularly difficult to follow the traces on the boards; they appear to be basically single sided (with a ground plane on the top side) with not at all narrow pitch traces.
Old 3 weeks ago
  #10
Lives for gear
 
Geoff_T's Avatar
 

Hi

This might be a silly question... but isn't this a power transformer?
Attached Thumbnails
Can anyone identify what power supply i need for an old mixer/pre?-transformer.jpg  
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