[Elecraft] K2 Audio-Hi Cur-Low P signs and wonders

[Tom Hammond NØSS]

Daniel:

>Last night I rewound all my torroids on the base K2 after L33. Meaning 
>every torroid from L33 to RFC3.

Whew... you WERE on a 'mission'...

>I have already checked on the speaker being shorted, and my speaker audio 
>via that check is alright.
>
>But according to friends who have K2s; I should be getting more audio. The 
>reality is that with AF and RF knob at MAX and Pre-Amp ON, I still have to 
>cup the internal speaker with my hand, so that someone standing 2ft away 
>from me can hear it.

How about the SIDETONE? Can you hear it loudly? Or is is just RECEIVED audio?

UNplug the speaker plug from the RF board and use a couple clipleads to 
temporarily connect the two pins of the speaker header (on the RF board) to 
either a 4-Ohm or an 8-Ohm speaker... (better, a pair of 8-Ohm headphones). 
THEN see if you have ample audio output (something around "ample" should be 
the sidetone set to about 50 and decently loud in the headphones). If you 
CAN get adequate audio, then the problem is probably in your speaker wiring.

If you canNOT get ample audio, CAREFULLY remove C29 (Control Board, 220uF 
'lytic, R20 and pin 6 of U9, the LM380N-8). Use any long-leaded 
electrolytic above about 100uF and connect its "+" lead to the junction of 
R2 and U9-6. Then, attach a cliplead to connect between the "-" lead of 
this cap and one side of a 4-8 Ohm speaker. Use another cliplead to connect 
the other side of the speaker to a GND connection on the K2. This will 
isolate the AF OUTPUT of the LM380N-8 from all other (following) connections.

If you CAN get decent AF output this time, then you have a problem between 
U9-6 and the speaker/headphone jack.

If still you canNOT get decent audio, then suspect your soldering in and 
around U9.

>I had wound them with the wrong size wire. I have passed a note along to 
>Scott to include in the new rev. of the K2 manual to denote that all 
>torroids except for L33 should be wound with #26 AWG wire (red and/or 
>green)and L33 is the ONLY torroid to be wound with #28 AWG wire.

Yeah... they should have builders wind L33 FIRST, to get it (and the #28 
wire) out of the way... so you can place the remaining #28 wire somewhere 
you can't readily get to it... <G>

>So this is what I need to do to get more audio and at the same time figure 
>out why I keep getting HI Cur warnings. (Which Scott explained to me over 
>the phone.)
>
>1. Rewind all torroids in the Low-Pass Filter area of the board.
>2. Do the VCO Linerization according to the pamphlet that came
>    with the K2 Firmware REv. 2 chip. And not according to the
>    book on I believe page 60.
>3. Go back to the book and do the IF Amp alignment, etc.
>
>But ONE thing on the CTRL board that stumps my thoughts is the LM380N-8 AF 
>Amp(audio).  The VAC going in to the IN1 and IN2 are higher than the OUT 
>line. Why is it that way??? I thought that if it is an amp that it is 
>supposed to increase the voltage going out.

Depends upon what the INPUT and OUTPUT LOADS look like!!!

If the INPUT LOAD is high impedance, as it is on this audio chip, you might 
well have a higher voltage (but very little current) input. If the OUTPUT 
LOAd is very low, like 4-8 Ohms, then you may well have low voltage, but 
much more current available to drive the speaker. If the output is 
(essentially) shorted, by virtue of some wiring error or a solder blob 
somewhere, the output voltage could be nearly ZERO.

>   And what does 'N-8' signify for the part name "LM380N-8"??

I believe the "N" indicates the type of covering body used to enclose the 
chip, and the "8" indicates that it is an 8-pin package.

73,

Tom Hammond   N0SS