Determining correct potentiometer

Posted by Habanera Hal on January 18, 2012 at 5:02pm

I purchased some 2-watt amp kits from Qkits.com (FA602).  These come with a "set it and forget it" trim pot for the volume (VR1- 10K).  I want to have a volume control on the boxes I'm putting them in so I'll wire in a pot through the speaker lead and turn the trim pot up full, but how do I determine what value pot to use?  Do I use a 10K like the trim pot, or use something else?  I'm powering the amp @12V, using a 6" 4 ohm speaker.  I want to be able to have full-range volume control.

Also, any way to add a tone control to this?

Here's the schematic:

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Replies

  • Mama Mojo January 19, 2012 at 10:12am

    that diagram makes my head hurt....

    • petey twofinger > Mama Mojo January 20, 2012 at 2:25pm

      you can ohm out a pot too , if you put the probes on the far pns it should tell you the total resistance of the part , if you do not know hat the value is .

      check this out , been wanting to try one of these circuits :

      http://www.beavisaudio.com/techpages/BigMuffToneControl/

      as far as that schematic goes :

      the triangle represents the chip (the active piece in the circuit , the amp) looks like it prolly has 8 pins .

      the saw tooth squigles are resistors .

      c1 and all like it are electrolytic caps (capacitors) cause it lists polarity (positive) so ya know which way they "connect" .

      c3 c5 c6 are non polarized caps , or ceramic disks , those lil orangies . 

      the speaker goes on the left , the lil plus and minus ,the big plus and minus on the left is the battery .

      i dig that wine crate amp hack Hal !!

  • Bob Lumpkin January 18, 2012 at 9:24pm

    Hi Hal:

     I've used several of these. If you're starting with the kit, just leave off the trim pot & solder 3 wires in it's place (different colors so u can keep them straight) Use a A10k audio pot in it's place. Be sure to keep your wires straight. If you need more info, just e-mail me & I'll send you some drawings, can't do it tonight. 

    Good luck;

    Bob

     

    • Habanera Hal > Bob Lumpkin January 18, 2012 at 10:42pm

      Thanks, Bob.  I purchased the already-assembled kits, but did unsolder the trim pot on the first one and replaced it with an A500k pot I had laying around.  Wasn't happy with the result, so I'll pick up some A10k's at Radio Shack tomorrow.

      Is there any reason not to just wire it in to the speaker line?  Lots less soldering.

      Since you have some experience with these units, maybe you can tell me if there's a simple way to add a tone control.

    • John W > Habanera Hal January 19, 2012 at 6:03pm

      You can't wire it in to the speaker line because the resistance of the speaker is so small compared the the resistance of the pot.  You may be able to buy a rheostat at radioshack and use that for a volume control on the speaker line. 

      As for a tone control, with this circuit I've tried to add an integrated tone control and haven't had any luck yet.  The datasheet on the TBA820M seems to indicate that it is possible but when I wire up my test circuit I don't get any change in the tone whatsoever.  So your best bet is to put a passive tone network in front of the entire amp.

This reply was deleted.