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KMG SS Poweramps

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

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KMG

If you have a problems with the definition of the parameters of the transformer core ("Bm"), you can use the following trick. Not exact, but good enough.
If you use a power transformer as the "donor" for the output transformer, count winding turns while unwinding primary coil. So you will know the ratio of turns per volt for the lower frequency equal to the mains.
Voltage on output winding equals U = sqr(Pout * Rload)
Using turns per volt ratio you can calculate turns in the output coil.
Now start PP calculator, enter parameters (lower frequency = mains frequency of the transformer). Change "Bm" untill you`ll get calculated output coil turns.

J M Fahey

Hi KMG, thanks a lot for your links.
I have no problem with Bm, turns-per-volt, current density, etc., have been designing and winding my own transformers for over 40 years.
Anyway, *every day* I learn something new, and I'm grateful for that.
I'll read them thoroughly.
As a side note, I'm now using Russian EI laminations, the bright greenish ones. Very high quality.
I can routinely push them to 15KGauss with absolutely no overheating problems.
A former University pal visited Russia years ago , as part of an official comission to evaluate and buy Russian railroad equipment; maybe they visited your Company too!!
I'll ask him next time we meet.
Thanks again.

phatt

Hi KMG,
           If I may make a constructive critik point about your wonderful work.

I feel that some/most of the folk would be detered from building some of your circuits as it's Suface mount Double sided stuff.
Not something that the average hobby type is likely to have access to.  :'(

In my humble opinion, It would be a smash hit build if it where presented as a single sided board layout.
Just a thought. :tu:

BTW, thanks for the maths short cut about OT and I have no doubt it would sound good even if it was not exact.

Besides some of the best sounding Valve Guitar Amps had crap transformers,, i.e. badly matched to output Valves.
Cheers, Phil.

KMG

QuoteI feel that some/most of the folk would be detered from building some of your circuits as it's Suface mount Double sided stuff.
Not something that the average hobby type is likely to have access to.
Double sided assembly, not PCB.
All of my designs use single-sided PCB (no problems to make them DIY).
About SMD, in Russia, it is often easier to find SMD than through hole components. Except maybe the high-voltage electrolytic and film capacitors and some semicinductors that has only one package version.
For example Mouser offers wide range of SMD compoents.
http://www2.mouser.com/Passive-Components/Resistors/Surface-Mount-Resistors/Thick-Film-Resistors/_/N-7h7yz?P=1z0x6frZ1yzvlks
http://www2.mouser.com/Passive-Components/Capacitors/Tantalum-Capacitors/Tantalum-Capacitors-Solid-SMD/_/N-75hr4?P=1yztnms
Otherwise you can take my schematic and make your own layout for components you can buy.
I just wanted to give my version of the tube emulation using semiconductors.

askwho69

are you related to Einstein? ;D :o  or came from another planet? YOURE GENIUS! your project is super impressive!

Steve Conner

Yes, I agree. No reason to be scared of SMD nowadays. Annoyed maybe, scared no. :)

For these circuits, wouldn't a mains transformer be close enough to use as an OPT? The type with two 120V primaries and a low voltage secondary.

Toroidal ones have pretty low leakage inductance, but they're awfully sensitive to DC imbalance, and saturate more suddenly than EI transformers, which gives harsher distortion. The EI type with chambered bobbins probably have too high leakage inductance.

gbono

I have been "trained" to populate proto SMT PCBs using a pre-heater and a heat gun - the paste is dispensed with an old Madell dispenser and manual "pick & place" with an aquarium vacuum pump. I need a microscope to see what I'm doing  :( Same station does rework

J M Fahey

Quote from: gbono on February 15, 2011, 02:24:45 PM
I have been "trained" to populate proto SMT PCBs using a pre-heater and a heat gun - the paste is dispensed with an old Madell dispenser and manual "pick & place" with an aquarium vacuum pump. I need a microscope to see what I'm doing  :( Same station does rework
I'm impressed !!!!!!!!!!!!  :o :o :o :o :o
Please tell us something about this.
Pictures would sure help; a short film even more so.
Wow!

KMG


joecool85

Quote from: KMG on April 25, 2011, 06:22:02 AM
How about this sound? ;)
http://milas.spb.ru/~kmg/files/projects/fetpa/micro/reamp/1.mp3

Sounds great.  Especially love the first 1/3 of the clip - great tone and playing.

**edit**
Are you planning on selling these amps at all?  Or kits to build them?  At least a preamp maybe?
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

KMG

You will be laughing, but it is the sound of this baby:
http://milas.spb.ru/~kmg/microfetpa_en.html
I simply changed transformer to different one, to match 4x12 cabinet impedance.
Output power is about 70mW, but it really hear with the correct sound of full powered amp head.
It is very suitable for "night playing" when you do not want to disturb sleeping children.
Sample recording path:
E-MU Tracker Pre->Fet JCM800->Micro Fet PA->4x12 Cabinet->Sennheiser E906->E-MU Tracker Pre
QuoteAre you planning on selling these amps at all?  Or kits to build them?  At least a preamp maybe?
Only one item is now planned for production - 5W fet PA

I already received boards & transformers for it.

THChrist

Why not a convertible version? 5w/15w/30w? or something like that? lol
i love the sound you get from those fets!

KMG

The main problem with other PA versions is availability of transformer cores, suitable for sound applications.
5W version uses a standard core, which easy to order.

KMG