Death Of zen On 15V supply? - diyAudio
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Old 20th August 2006, 11:34 PM   #1
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Default Death Of zen On 15V supply?

Hey, I have built a death of zen and have it running now on 15V supply, but it isnt behaveing very well.. It is more than loud enough.. but the bias pot has to be almost all the way down before i get any music atall and if i turn it any further down it starts to buzz.. also cant get rid of DC offset on output.. end up with like 5V before output capacitor.. So i guess the resistor values need tweaking for use on such a low power rail.. Anyone care to help me? This is the schematic i used.. KSE340 instead of BD139... BC558 instead of BC559... 2N3055 as output..
Even with it running in this state i am still impressed by the sound.. Cant wait to get it running better..
Thanks,
Owen
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Old 20th August 2006, 11:35 PM   #2
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At a guess i'd say R2 needs changeing for something smaller to help me get around the dc offset problem? possibly 47K? Should this make a good starting point?
Owen
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Old 20th August 2006, 11:51 PM   #3
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i dont think that Vr1 is sposed to spark is it? :/ think the leg that goes to ground might be broken.. would deffinatley explain why i have such high dc offset issues.. :/
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Old 21st August 2006, 12:06 AM   #4
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wait a minute.. it has single supply rail so there is sposed to be high dc offset at the output thats why there is an output cap?
just been playing more and if i increase Vr1 then i can turn the bias up more without it starting to humm.. :/ is this normall? or do i still need to do some tweaking?
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Old 21st August 2006, 12:25 AM   #5
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I would suggest doing your math.Using the original schematic and supply voltage find the current needed in each stage and the voltage drops then change values to achieve the same current for your 15 volt supply.
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Old 21st August 2006, 01:44 AM   #6
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The voltage at the output (before the cap) should be 1/2 the supply voltage.

And read this thread: DoZ (P36) Design Problems and Solutions
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Old 21st August 2006, 02:20 AM   #7
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Hi, I have switched to a 40V supply now and it is still behaveing the same.. The heatsinks atleast get warm now though.. My meter still refuses to read ANY current draw though when i hook it up in series between amplifier and power supply.. supply voltage is actually about 39V.. Voltage before C3 is about 19V.. I can turn the bias up the same as before then it starts to humm if i go any higher.. wierd thing is that the amp only starts to play music a small amount before the bias is at the max i can adjust it too.. is this normall or is there somethign not right with my amp?
The amp sounds fantastic! but i cant measure bias current because my meter is refuseing to work properly.. need to get a new one.. way i see it is aslong asd it is playing music and not makeing any nasty humm and isnt too hot it will be fine?
It isnt the transformer that humms on mine.. it is deffinatley comeing out of the speaker...
Owen
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Old 21st August 2006, 02:27 AM   #8
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i'd still expect these heatsinks to be WAY hotter though.. even with a fan! they are just slightly warm to the touch at the moment :S And yes.. The fan is an 80mm fan.. not very powerfull so that the noise is kept down.. i have 4 of those sinks so i plan on eventually building it up into a proper stereo amp in a nice big chassis with two 80mm fans (push / pull) on each pair of heatsinks..
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Old 21st August 2006, 02:48 AM   #9
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hi,

Vr2 sets the idle current at the collectors of the 2N3055 transistors, while Vr1 sets the voltage at the positive end of C3 output coupling cap.

notice however the these two pots have interaction so set Vr2 first them Vr1, a slightly higher that Vcc/2 is allowed, so instead of 20volts, maybe 21 is just about right...

a resistor, perhaps a 1k, 1/w should be connected between the minus side of C3 and ground, this ensures that approximately 0volts is present at that end at all times, (dc sense)
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Old 21st August 2006, 02:54 AM   #10
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ok. so im lookign for about 20- 21V on the + side of C3 then? Ive been tweaking it a bit more.. reseated the 2N3055's on the heatsinks.. one sink is still running cooler than the other though for some reason? but i have put my fingers straight on the 2N3055's and they both feel only slightly warmer than their corresponding sinks so i think one of the transistors is actually running hotter then the other.. :/
I noticed that vr1 and vr2 mess around with each other.. after tweaking the bias setting i find that the voltage at C3 has changed and i reset it...lol.. all good fun though
Must order some decent power transformers.. Theis one is haveing problems keeping up.. rails drop from about 40V to 34V when i crank it up a little... still.. sound sgood
Owen
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