Explendid amplifier designed by Michael Bittner, our MikeB

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#3,783
Hello! I am newbee at electronics,have a little something assembled by my hands,some basic knowledge and uni-meter(V-A-O meter). I am reading posts here for quite some time and i still haven´t found answer to a question i have... I´ve completed two pcb´s of sym/asym5.3 asuming that i allready have proper supply,but when it came to that i found out that it´s not +/-36 VDC but +/-42VDC. Is it safe to connect sym/asym5.3 to that level of a supply or i will have to make a voltage regulator to decrease a voltage level (if taking off a few rounds from a transformer turns up as inposible)? Sorry for my bad english,i don´t use it or write as much as i am listening to it... Thanks up front!
Aleksandar M
 
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#3,784
44250 said:
...i found out that it´s not +/-36 VDC but +/-42VDC....
Click to expand...

Hello Aleksandar,
a good, simple and cost effective way around it is to use a capacitance multiplier (see attached picture). You'll lose 4V (to get +/-38V) and the sound of your amp will benefit too.
The schematic shows a circuit needed for one channel. MOSFETs can be bought at kelco.rs
 

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#3,785
Thank you very much for yor answer my neighbour! 🙂 I will try to open the transformer and take off a few rounds if it is posible-i haven´t tried yet-and if the primary coil (220V) is over the secondary coil I will do either as You suggested to me,or something that APEX suggested at ES-forum(possible here too) and it looks like this...
 

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#3,786
Yes, series regulator is an option too, but it's made to keep the PS voltage at fixed value. Since symasym is AB class amp the rail voltage will sag depending on the load (output power) and you'll have to set the regulated voltage lower (depending on your transformer's power and elko's quality) to avoid the situation where rail voltage sags too much. Cap. multiplier will always give 4-5V lower rail voltage no matter what is the unregulated input voltage.
 
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#3,787
OK,that sounds like a very good reason,very helpfool text too! I have a 350VA transformer(should be enough for 8 Ohm load,and a bit tight or for a 4 Ohm load) and a bunch of (4 x 2200uF,2 x 4700uF and 2 x 6700uF) capacitors. Should be enough to push two channel of symasym I guess. The transformer I have is not bifilar wounded so it is not possible to decrease output voltage without a lot of work. I will do as You said that it would be smart to do. I will have to make two of capacitor multiplier because... ? IRFP240/9240 has 150Watts of power,and if there is 4V at drain/source,and let´s say 10A drain/source it would be 40Watts of power so I guess the power is not a reason? Thanks!
 
#3,790
The MOSFET's low output impedance may cause a lot of interaction if 2 channels were used with the same multiplier.

The BJT regulator would have less output impedance, but you would have to parallel multiple BJTs to get the same power capability of the MOSFET.

- keantoken
 
#3,792
OK than I ´ll do as you suggested to me. Those were two very good reasons why not to use one,but two capacitor multiplier. Thank you both very much! I beleive that soon there will be some hearing impressions by me and my sample of symasym. I have started to assembling it because i had large enough heat disipator,bunch of capacitors,large transformer(turns up with too high secondary voltage 🙂 🙂 ),box of some old amplifier and enough of time so I said to my self "Why not?" Oh yes,and a friend of mine,Boris from Sarajevo had sent me PCB´s and recomandation to do it,so,here I am... Thanks again to both of you!
 
#3,796
Hello to all,

Is there someone kind enough to point me where the PCB file for symasym5 amp? I am interested to build this amp and I hope Sir Alex MM would be kind enough to make the PCB layout if there's no one available... And please make the pcb layout for lasertoner transfer in pdf.

I hope I'm not asking too much for this...

Thank you so much in advance!

Blueice23
 
#3,798
I am interested in building the Symasym 5.3 using a 25-0-25 transformer (or 2).
After reading the project page and some of this lengthy thread, I am a little confused as to whether this amp can be input from a preamp (with the basic amp circuit as shown on the project page).
Can someone enlighten me if changes to the circuit are required in order to use a preamp?

Thanks
Peter
 
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