a friend of mine bought a Matrix M-Stage headphone amp. it was supposed to be 220V version but 120V version was delivered! and needless to say he put the plug in and used it as a toaster! 
gave it to me to fix it... power transformer was gone. the power was Toroidal which melted down ... now schematic, no specification, no nothing. I didn't know what is the working voltage of the circuit so I put it in path of signal generator and oscilloscope and power it with a variable power adapter to find the best working voltage. it was ~12V - 970 milliamperes. I winded a 12V/1Ampere power transformer and put it in... everything is ok and it works but when volume is closed, a hum can be spotted... any idea? 
gave it to me to fix it... power transformer was gone. the power was Toroidal which melted down ... now schematic, no specification, no nothing. I didn't know what is the working voltage of the circuit so I put it in path of signal generator and oscilloscope and power it with a variable power adapter to find the best working voltage. it was ~12V - 970 milliamperes. I winded a 12V/1Ampere power transformer and put it in... everything is ok and it works but when volume is closed, a hum can be spotted... any idea? 
The M-Stage is supposed to be an "improved copy" of the Lehmann Black Cube Linear. I would expect a center tapped secondary as in most any serious headphone amp, so with some dropping resistors I'd expect about +/- 20 V after rectification, so maybe 2x 15 V~ secondary or so, estimated 10-15 VA.
Uh actually you're right. there are two secondary outs with a common center tap. first and center tap go to rectifier to turn into DC and supply whole the circuit and other end goes to earth which is connected to coupling capacitors. so you're telling me that I should try out 2X15V or 2X20V?
Basically, yes.
The BCL clone schematic I'm looking at uses a LM317/337 combo to regulate +/-15 V, so you want about +/- 18 V= or slightly higher für the regulators to work properly. This comes out to about 2x 14-15 V~ secondary.
BTW, the center tap is that one that goes to earth.
The BCL clone schematic I'm looking at uses a LM317/337 combo to regulate +/-15 V, so you want about +/- 18 V= or slightly higher für the regulators to work properly. This comes out to about 2x 14-15 V~ secondary.
BTW, the center tap is that one that goes to earth.
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Uh you're absolutely right there is LM317 which I think is a voltage stabilizer or regulator but I still don't know what is the problem. I connect 2*12V to circuit (total=24v) but noise is still there
I think two separate 12v power transformer will do the justice instead of a toroidal transformer. I think noise is due to the uninsulated EI transformer I winded (I can't isolate it due to the lack of enclosure inner space)Uh my mistake... the center tap is connected to earth. the other leads are connected to rectifier bridge
I finally found out what Matrix did. there is no center tap at all... actually there is a center tap on the Matrix transformer but it is common with one of the main outputs. the earth is connect to one of the AC inputs. I winded two separate transformers one 6VA and one 12VA and isolated them to death. all the noise gone. the amp is working in absolute death silence
one thing interesting! I connected my speakers to this amp and it plays them at pretty remarkable decibels I mean wall-shacking levels... I think about 100db/ 1 meter
thanks everybody
one thing interesting! I connected my speakers to this amp and it plays them at pretty remarkable decibels
I mean wall-shacking levels... I think about 100db/ 1 meter thanks everybody
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