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KMG SS Poweramps

Started by THChrist, December 28, 2010, 11:02:15 PM

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askwho69

Hi KMG just want to ask what kind of Transformer are you using in Fet PA? i want to make oe for home use amp :D and use my sans amp as preamp :D


thanks



KMG

Which model do you mean?
For some models I use cores of standard transformers from this company
http://www.transled.ru/products/open/
5W - ТПК-15
15W - ТП-30
90W - ТПК-190
40W - old transformer core (don`t know type)
micro PA - TOT60/TOT57
Parameters of these transformers (TOT series) you can find there (unfortunately in russian)
http://milas.spb.ru/~kmg/files/literature/Malogabaritnye_transformatory_i_drosseli.(1985).zip

askwho69

where can i find transformer for micro PA? the 5watts PA? i really want to make one but i dont really understand how the thing works . .  about amps! :D

KMG

#33
Quotewhere can i find transformer for micro PA? the 5watts PA? i really want to make one but i dont really understand how the thing works . .  about amps! :D
For micro PA you can try to use transformer from old transistor radio.
Also maybe this one will match for loading on cabinet.
75mW rating
http://eu.mouser.com/ProductDetail/Xicon/42TL008-RC/?qs=sGAEpiMZZMv0IfuNuy2LUcl0UojJLOKICZc25y8dmyo%3d
200mW rating
http://eu.mouser.com/ProductDetail/Xicon/42TM008-RC/?qs=sGAEpiMZZMv0IfuNuy2LUcl0UojJLOKIC2kkfS0HPnQ%3d

5W PA transformer
Core cross section 20x16 mm
Each half bobbin:
120 turns 0.25 mm (1/4) primary
75 turns 0.5 mm secondary (for 8 Ohm load)
120 turns 0.25 mm (1/4) primary

askwho69

Wow thank you so much! by the way i found an old monitor and found many things there transformer too. . . but the thing is i dont know how to check the transformers specs . . but thanks anyways!

KMG

Quoteby the way i found an old monitor and found many things there transformer too. . . but the thing is i dont know how to check the transformers specs . . but thanks anyways!
If the transformer has a ferrite core, it is not suitable as the output transformer.

askwho69

ohhh thanks KMG for the reply ... very informative :tu:

phatt

Yes unlikely to find the right Xformer in SS electronic gear  :'(

Though a thought just crossed my mind,,, hum thinkin,,thinkin headscratch.

You maybe able to source 100volt line transformers as they have been used with success in Valve rigs and it is likely they could be made to work with KMG's concept.

The OT is the tricky part for home builders.

This is what someone with a deep understanding did with an Oven tray, Line transformer and the odd valve.
  http://www.ozvalveamps.org/ava100/ava101minilamington.htm
Might be worth a look?
Phil.

KMG

QuoteYou maybe able to source 100volt line transformers as they have been used with success in Valve rigs and it is likely they could be made to work with KMG's concept.
110V transformer with center tap (2x55V) seems to be good for versions with 80V supply.
Just select one with suitable secondary voltage.

phatt

Using mains as OT's?? Yes that makes sense :tu:
But I was actually reffering to *line driver transformers* as used in buildings where very long wires are used to link many speakers.

These unit are probably better suited than mains rated transformers and are intended for audio AC not mains AC.

If anyone is interested I'll try to find more info.
Phil.


J M Fahey

Both types *do* work, with some quirks because of their original intended purpose.
Power transformers work very well in low frequencies (they are designed for 50/60Hz with over 95% efficiency, at full power), they couldn't care less above anything over 400 Hz ; it's a miracle that they have any highs at all.
Cheap line transformers expect to run from 2 to 15W into small speakers embedded in ceilings, etc., meaning their response often starts falling below 200Hz.
Main problem, on both, is getting center-tapped ones.
Well, a 110+110V primary will probably work.

KMG

QuotePower transformers work very well in low frequencies (they are designed for 50/60Hz with over 95% efficiency, at full power), they couldn't care less above anything over 400 Hz ; it's a miracle that they have any highs at all.
In my FET PAs I used thin ribbon winded cores from power transformers (but with interleaving primary/secondary windings)
5W loss ~3dB@20kHz

15W loss ~4dB@20kHz

90W loss ~3dB@20kHz

QuoteWell, a 110+110V primary will probably work.
In this case you have twice reduced primary coil current limit, due to thinner primary coil wire.

J M Fahey

Of course.
You took special care to rewind and interleave properly.
What I talked about was off the shelf, straight power transformers, used as-is.
Nice cores you got; all I can find is regular EI cores (although I often get the high quality Russian iron ones, the ones with a mottled yellow-greenish surface), the same I found on some Soldano transformers.
Other times I get the dull grey Brazilian ones, which are also quite good.

KMG


KMG

#44
Samples recorded by my friend DKS from GtLab
Tube preamp UENGO-1 + 5W Fet PA
Midgain
http://milas.spb.ru/~kmg/files/projects/fetpa/mp/samples/JTR_FET_MIDGAIN.mp3 (1,89МB)
Highgain
http://milas.spb.ru/~kmg/files/projects/fetpa/mp/samples/Uengo_Hg8_M.MP3 (1,8МB)