[Heathkit] HW-8 Audio Output

[Jeramy Thibodeaux]

Mark,

Congrats on finishing the board.

The diagram below will work but.  This is technically not mono to 
stereo.  This is mono to multi mono (Mult).  The resistors values listed 
will help balance the left and right channels but expect that they will 
slightly change the audio tone a bit.  Also, the signal level at each 
channel will decrease by about half (-6dB) of the single mono channel.  
If you find that the signal output from the kit is not strong enough to 
drive a left and right speaker then you will need to refer to the kit 
manual and install the components for the Optional gain loop (C5 & R1) 
to increase the gain. You will need to revisit the board alignment 
procedure provided with the kit after installing these parts.  If the 
1.2K resistor (R1) does not improve the gain enough, then reduce the 
value down using standard value resistors until you reach a satisfactory 
level (trial and error).  I would absolutely not put a shorting wire in 
place of R1 for maximum gain as the kit manual states.  If you get to 
this point of considering this, then you will need to look at other 
options (more costly).

A gotcha to watch out for is inadvertently adding ground loops in the 
audio chain thru the speaker wiring.

Good Luck!

73
JT
KG4AZT



On 6/25/25 7:23 PM, Mark K3MSB wrote:
> Hi Jeramy and others...
>
> Got the new audio board installed.... easy build.... and fun!
>
> When going from mono to stereo,  I see there are two ways of doing 
> it.  One way is just to directly the L/R channels together the other 
> way is :
>
> image.png
> Any particular benefits or concerns with either?
>
> 73 Mark K3MSB
>
>
>
>
>
>
> On Mon, Apr 21, 2025 at 9:26 PM Jeramy Thibodeaux 
> <kg4azt at earthlink.net> wrote:
>
>     This should work!
>
>     https://kc9on.com/product/hw-8-lm386-audio-board/
>
>     Several people on the heathkit groups.io <http://groups.io>
>     reflector have endorsed this to
>     fix the low impedance speaker issue.
>
>
>     73
>     JT
>     KG4AZT
>
>     On 4/21/25 5:53 PM, Mark K3MSB wrote:
>     > Thanks everyone;  I admit to being lazy Ken and I didn't look it
>     up but I
>     > figured it couldn't be much.
>     >
>     > I'm repairing one for a friend and told him he could not use an
>     8 ohm
>     > headset, so I was looking for a matching transformer or line
>     transformer.
>     > Lots out there to choose from.
>     >
>     > I think the Radio Shack 273-1380 should work.
>     >
>     > 73 Mark K3MSB
>     >
>     > On Mon, Apr 21, 2025 at 5:26 PM Ken Gordon
>     <kgordon2006 at frontier.com> wrote:
>     >
>     >> On 21 Apr 2025 at 15:38, Mark K3MSB wrote:
>     >>
>     >>> Does anyone know what the output is rated in Watts?
>     >>>
>     >>> 73 Mark K3MSB
>     >> Well, Mark, according to the manual, the audio output
>     transistor is an
>     >> MPS-A20.
>     >>
>     >> Specs say that maximum collector current is 100 mA at 4 VDC, which
>     >> works out to 0,4 watts.
>     >>
>     >> Does that sound about right to you?
>     >>
>     >> BTW, if you have not yet found a copy of "The Heathkit HW-8
>     Handbook 2
>     >> ed 2008 " in PDF format, you may find that book to be of interest.
>     >>
>     >> Ken W7EKB
>     >>
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