The 'Mini-Julius Box'
Credit where credit
is due...
(All Kudos go to Julius/W2IHY)
This 'Mini-Julius Box' now interfaces my "AudioRax" with Both Kenwood TS-870 & TS-2000 H.F. rigs.
Once upon a time... and this is no shit...
I found myself needing to drop the Line Level Output from Both Behringer 802A & 1604A Audio Mixers
from Line Level to Microphone Level before audio Inputs Kenwood 8-pin
Microphone jack Inputs. I also wanted to 'isolate' the Audio Rack from the ham
radio gear to reduce the dreaded R.F. and Ground Loop potential which
lies lurking in most hamshacks…jest Waitin' fer u to hook up some Audiophile
equipment so it can rear it's ugly head!
Being merely a humble ham with only my F.C.C. ham ticket since 1959, I was at a loss as to just where to start... enter my friend Julius/W2IHY , stage left.
After listening to my plaintive cry for help... Julius simply said... "Murf, Give me a minute." He custom designed this little wonder to snuggle between my Kenwood TS-870 Behringer audio rack gear... and... E-mailed it to me in less time than I could make a fresh cup of coffee!
Now I have quite an extensive amateur
radio Junk Box that is over 44 years in the making...
However...
all parts
shown are readily available from your local ChickenShack a.k.a. RatShack store.
COST???
This is the good part...
about Ten Bucks for me and maybe even
less for you! Does all this seem just too good to be true?
Read on BullWinkle...
PROJECT NOTES UPDATED: 08 AUGUST 2004
The variable potentiometer "R2" value (10k) yields a Max. Drop of
about 20db...
by Increasing "R2" to 100k you can increase the drop from Line Level
to about 40db.
Meester Julius designed this circuit around (T1) a Stancor 600ohm, 1:1 Audio
Isolation Transformer.
He "Swept & Spec'ed" it showing -6db points(half-voltage points) well outside 38hz-12khz@1khz
Insertion Loss is only -1.2db
K8GVK/Dave told me he just lifted an audio transformer off an old junk box
computer modem board
(JunkBox Ingenuity!)
Dave built this circuit totally out of his junk-box for his basic TS-870 audio setup.
HOWEVER...
Be very careful about scavenging jest Any ole' transformer & expecting it
to have the same performance as the Stancor transformer Meester Julius
personally spec'd out for this TS-870 circuit.
Julius mentioned various 'audio' transformers were 'swept' with a signal
generator at Constant Amplitude.
Most Half-Power points fell somewhere between 150Hz - 300Hz...
Not that great fer ur 'Pursuit of Amateur AUDIO Excellence'!
A Key difference between this Stancor & a Rat Shack, for example, is Low-End
frequency response.
The Rat Shack Half-Voltage point is 300Hz & the Stancor is 30Hz... Beeg
Difference!
To put it another way...
Put a signal generator on a transformer, look at Output while sweeping the
transformer with a signal of constant amplitude. The frequency where the
voltage drops by half is the Half-Voltage point.
This Low-End frequency measurement shows transformer audio performance.
The final Authority is your Listening public's Receiver audio capabilities
and/or limitations.
They Gotz to Hearz wat ur doing!
* ICOM Front Microphone Input Jack Users
ONLY Please NOTE *
The 4.7mf 'Blocking' capacitor IS required 'cuz ICOM, in their infinite wisdom, 'traditionally'
carries D.C. voltage on their mic. audio line to make their
peripheral devices compatible.
For
example...
Old ICOM factory microphones in New ICOMs (746 - 756Pro - 756Pro2)
So... we gotzta Block da D.C. voltage from affecting da transformer Iffen Yuz Guyz
goez inta da Front!
HOWEVER...
Most ICOM Big-Audio Guyz are Greek... they go inta da Back with Balanced
Line Input... so... No Capacitor and No Step-Down resistor matrix...
Geez...
ENUF of the ICOM stuff already.
KENWOOD Users Please DISREGARD this 4.7mf capacitor... Therefore... it is Not
in These pix!
"GOZINTA"
NOTE: 10Kohm Potentiometer from Junk Box is 'Linear taper' es NOT required. A 10Kohm resistor will work just fine to drip you from Line Level to Mic. Level... I just love Tuning es Tweaking! Also, the 4.7mf capacitor, shown in the Updated schematic, is NOT in the original design pix... itz fer ICOM!
"CUMZOUTA"
Note: The
Resistors are Junk Box 5%, half watt variety...
Yes, I did finish it off with a nice round Knob on the front!
The 'MINI Mini-Julius' Box
Smaller mini-box is 'floating' - 10k resistor replaces 10k pot
Works just as good . . . PFM!
You can do this
project in less time than it took me to publish this page...
Checkout the KD5VHK "KyleBox" VARIANT
5-pin XLR Outputs for Two rigs - PTT - TRS Input... very sexy!
And NOW…
You can even BUY it from
W2IHY…
73 es God bless
MURF/WV4R