STK 4191v question

kaushama · 13th December 2005, 03:56 PM

I have two STK 4191ii amps and thier THD is typically 0.4%. I have managed to find couple of pin compatible STK 4191v which has THD of 0.08%.

The STK 4191ii circuit has out with only snubber [4.7R + 0.1Uf].
Although pin compatible 4191V circuit has 3 MicroH coil parralel with 4.7R in addition to the snubber. Data sheet says it is to block ocsillation.

My PCR does not have room for new coil and R!!! Are they essential?
Can i omit them?
If not how can I wind a 3 microH coil? Please advice me!

Thanks in advance!

4191ii schematic

kaushama · 13th December 2005, 03:59 PM

This is the schematic for the 4191V taken from the data sheet.

anatech · 13th December 2005, 04:05 PM

Hi kaushama,
Just break the trace and install the resistor with the wire wound around it. If you don't, the circuit may possibly oscillate depending on the load. You do not want that to happen.

-Chris

kaushama · 13th December 2005, 04:09 PM

Thanks! But how long a wire and what gauge should I use to get the specified inductance?

anatech · 13th December 2005, 04:23 PM

Do you have any enameled wire? Look at another amp and do something similar. I don't think the value is very critical.

A 20 GA should do it, 18 GA would be okay too. Solder one end to the resistor and wind the wire so each turn touches the previous one. Solder the other end.

-Chris

Edit: the added resistor should be about 2 watts.

kaushama · 13th December 2005, 04:32 PM

Hi Chris
I have 18 enameled wire. So if I wind the wire ariound the resistor without giving much notice to the value is it OK?

This inductance calculator gives mere 3cm long coil with the diameter of 1cm using 18 gauge wire for the amount of inductance! With some 28 turns!http://www.oz.net/~coilgun/mark2/inductorsim.htm

I thought of adding the coil outside the resistor parralel to R. Is it OK to wind the coil around the R?
Thanks

kaushama · 13th December 2005, 04:51 PM

Further within the size allowed by the resistor I can get more inductance if I use smaller GA wire like 24 or 28 Ga which I have.

Please tell me whether the winding around the R is OK than putting air core coils! I have not seen this LC topology in the amps I examined as I am a newbee!

TKS

anatech · 13th December 2005, 04:56 PM

Hi kaushama,
You will often see the wire wound around the resistor. It makes as good a core as any. You can increase the winding diameter and go for two layers too. I've seen that before.

-Chris

kaushama · 13th December 2005, 05:00 PM

Is it OK to use smaller Gauge wires? I have 24 and 28 GA wires!

anatech · 13th December 2005, 05:02 PM

Hi kaushama,
I don't think those would be thick enough. You are passing all your output power through there.

-Chris

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13th December 2005, 04:05 PM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi kaushama, Just break the trace and install the resistor with the wire wound around it. If you don't, the circuit may possibly oscillate depending on the load. You do not want that to happen. -Chris

13th December 2005, 04:09 PM	#4
kaushama diyAudio Member Join Date: Aug 2005	Thanks! But how long a wire and what gauge should I use to get the specified inductance?

13th December 2005, 04:23 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Do you have any enameled wire? Look at another amp and do something similar. I don't think the value is very critical. A 20 GA should do it, 18 GA would be okay too. Solder one end to the resistor and wind the wire so each turn touches the previous one. Solder the other end. -Chris Edit: the added resistor should be about 2 watts.

13th December 2005, 04:32 PM	#6
kaushama diyAudio Member Join Date: Aug 2005	Hi Chris I have 18 enameled wire. So if I wind the wire ariound the resistor without giving much notice to the value is it OK? This inductance calculator gives mere 3cm long coil with the diameter of 1cm using 18 gauge wire for the amount of inductance! With some 28 turns!http://www.oz.net/~coilgun/mark2/inductorsim.htm I thought of adding the coil outside the resistor parralel to R. Is it OK to wind the coil around the R? Thanks

13th December 2005, 04:51 PM	#7
kaushama diyAudio Member Join Date: Aug 2005	Further within the size allowed by the resistor I can get more inductance if I use smaller GA wire like 24 or 28 Ga which I have. Please tell me whether the winding around the R is OK than putting air core coils! I have not seen this LC topology in the amps I examined as I am a newbee! TKS

13th December 2005, 04:56 PM	#8
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi kaushama, You will often see the wire wound around the resistor. It makes as good a core as any. You can increase the winding diameter and go for two layers too. I've seen that before. -Chris

13th December 2005, 05:00 PM	#9
kaushama diyAudio Member Join Date: Aug 2005	Is it OK to use smaller Gauge wires? I have 24 and 28 GA wires!

13th December 2005, 05:02 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi kaushama, I don't think those would be thick enough. You are passing all your output power through there. -Chris

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