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  TS-950sdx AF Unit Mod  





Gotta pre-amp dat VOOODOOOO!!!

If you would like Voodoo-LABS to perform these mods
or if you would like to purchase a unit already modded by us,
Then check out our Price List or give us an email.

But First, Ya gotta read the 'Stuff'....

Difficulty -
First, these mods aren't all that easy if you've never had any SMD (Surface Mount Device) experience.
You run the risk of lifting circuit traces, overheating components, damaging ESD sensitive devices, and such.
Kenwood epoxies there chip components to the circuit boards with glue.
This makes it that much more difficult to desolder and remove these components without damaging the surrounding items.
It takes time, equipment, and patience to do it correctly.

There's also a choice to be made on how you want to proceed with this mod.
They're actually 2 alternatives to the original mods that We did.

Alternative #1 -
There's some Tantalum (Yuk, Spit!) chip capacitors used in this rigs Audio circuits. These could be just simply changed in value.
Also the other chip caps that need to be increased in value could be changed with Tantalum chips.
Kewl! So whats the Problem??
Well, Tantalums sound just plain Horrid...Yuk, Spit!! They are Tubey sounding on the low end and have a high frequency distortion We just don't care for.
They really shouldn't ever be used in any Audio path...anywhere...at any time.
But that is of course just an opinion.

Alternative #2 -
They're now high value ceramic capacitors in chip form that could take the place of some of the Tantalum (Yuk, Spit!) capacitors in leu of the electrolytics.
This'll give you an easier modification but with slightly less audio quality.
Ceramic Chips that big in value have bad Temperature coefficients and change values with temperature.
Some people would probably not be able to hear the difference, but We sure can!
They do sound WAY better then Tantalums (Yuk, Spit!) though!!!

Original Mod -
We chose the path of lesser Audio Evils.
Sure, electrolytics aren't supposed to be used in the Audio Path either, but they're allot better sounding then the first 2 mentioned components!
Especially now since Panasonic came out with there low ESR high grade stuff.
What we did was replace the Tantalums (and some other chip caps) with High Grade Panasonic Low ESR Electrolytic Capacitors.
The problem with that is, since the Tantalums are on the bottom of the boards, there's no room for the electrolytics there.
The solution is to carefully drill holes thru the PC board to allow the leads to go thru from the other side.
This makes the mods more time consuming and dangerous.
You have to be aware of the circuit traces on the other side of the board before you drill.
Sometimes you will be drilling thru the Ground Plane on the opposite side,
this requires counter boring to keep the penetrating leads from touching the ground plane.

Op Amps -
We're firm believers in the Audio differences between Op Amps.
The original Op Amps were upgraded with newer Analog Digital units that have a greater Bandwidth, Slew Rate, and SOUND!!
This is something that is NOT necessary to do in order to get the increased Receiver Bandwidth,
but it does affect the overall depth, resonance, and ambiance of the Audio.

Circuit Description:

AF Pre-Amp Circuit:
The TS-950sdx uses a separate AF circuit for each receiver (Main and Sub-Receiver) to amplify the Audio Frequencies.
The circuitry for each AF amplifier circuit consists of 3ea pre-amps and and a power amp.
We'll go thru it for a general understanding.

The AF unit receives the low level Audio from the demodulation circuits for the start of AF Amplification.
These inputs come from the Digital DSP unit, the AM detector, the FM demodulator, and the Sub-Receiver.

We'll Follow the Main AF Circuit first.
The low level audio is input to the Main AF circuit from the Digital DSP unit for SSB, the AM Detector for AM, and the FM demodulator for FM of course.
All of these inputs are diode switched by IC's according to Mode Selection on the front of the rig.

The low level audio is routed to the first Pre-Amp/Low Pass Filter, IC7.
This is a NJM4558M Op Amp configured as an inverting amplifier with a gain of about 18db.
It is using the feedback loop as a Low Pass Filter by paralleling a 100pf chip capacitor (C301) with R37.
The cut off frequency is around 13.2Kc, so this is acceptable with no changes.
The 1uF electrolytic coupling capacitor (C22), rolls off the low frequencies too much. It will have to be increased in value to 4.7uF.

The amplified AF signal now goes thru the 1uF SMD coupling capacitor (C27), this will have to be changed to 10uF to pass the lows adequately.

The AF signal can now take 2 paths.

Path 1 leads to Q10, which is a Bipolar Transistor amp in a Common Emitter configuration.
This is for amplifying the AF signal for output to the Acc2 Jack.
There is an electrolytic coupling cap that need to be changed here.
C33 is a 10uF cap that needs to be changed to a 22uF.
Q10 also has a 10uF emitter bypass capacitor (C34), which will need to be increased to 47uF.
Both of these caps limit the low frequency response.

Path 2 continues off the AF Unit to the AF Gain Control and then back to the AF Unit.
This was were we found another Ground loop problem which was causing Hum in the Subreceiver Audio AF.
The ground at terminal #3 of CN14 needs to be lifted.
This is accomplished by removing the 0 ohm resister/jumper, (R301).

The signal then goes to the 2nd Pre-Amp/Low Pass Filter, IC8.
This is a NJM4558M Op Amp configured as an inverting amplifier with a gain of about 31db.
It is using the feedback loop as a Low Pass Filter by paralleling a 150pF chip capacitor (C188) with R69. The cut off frequency is around 3.3Kc
This is unacceptable and will have to be modded by changing C188 to a 39pF capacitor.
This will up the cut off frequency to around 12.3Kc while not changing the gain structure of the amplifier.
There are 2ea coupling caps for this pre-amp which will have to be changed, due to their low frequency roll off.
C42 which is a .22uF that needs to be changed to 1uF, and C46 a 1uF that needs to be changed to a 10uF.

The signal then goes by a .0047mf chip capacitor (C48), that is shunted to ground which is rolling the high Frequencies off at around 3Kc.
This cap will be changed to a .001uF cap to increase the cutoff frequency to around 15.9Kc.
Then the Amplified AF Signal leaves the AF Unit and goes to the Control Unit.

The Sub Receiver circuit is almost a duplicate to the Main Receiver circuitry.
One difference is that the 2nd pre-amp is on the Control Unit instead of the AF Unit, but they are essentially the same.

Monitor Circuit:
The Monitor circuit audio is tapped from the Sub-Receiver low level AF Input, and goes thru some diode switching for TX/RX.
It then leaves the AF Unit to goto the Monitor Gain Control and returns back to the AF Unit.
The Monitor signal then goes thru a RC Low Pass Filter made up of R304 and C304. The cutoff frequency is about 3.2Kc.
We will be changing C304 from a .033uF to a .01uF to increase the cut off frequency to around 10.6Kc.
This signal is then injected into the Main AF circuit thru a 3.3K resistor (R64) in front of IC8, the 2nd Pre-Amp.

We've noticed a small low level 60cps hum in this circuit.
This is a combined result of the monitor circuit being injected at a high input level, and the 2nd Main AF pre-amp operating at a fairly high gain.
We found the solution to be to attenuate the Monitor input circuit sumwhat by changing R64 from a 3.3K resistor to a 25K.
This made the monitor level perfect on our rig with the gain control at about 12:00.
If you notice the Monitor level is too low in your headphones, reduce the value of R64.

Yer gunna have to get to the boards and remove them from the radio in order to do these modifications.
The AF unit is located on the bottom of the radio.
To access it, Very carefully turn the TS-950SDX upside-down. The DSP Unit (normally on the bottom) will be on the top now.
Squeeze the DSP Cable connectors and carefully jiggle them while pulling to disconnect them from the back of the rig.
Remove the 14ea countersunk screws from the bottom cover, then remove it.
This will expose the inside of the rig. You will see 4ea circuit boards side by side.
With the front of the rig facing you, the AF Unit is the circuit board on the left, closest to you. See Pic.

AF Unit Removal:
This AF Board needs to be removed.
We found it's best to remove the Cable Connectors and Ribbon cables first, before the screws are removed.
It might be helpful to take a picture of it, or to label the connectors to aid in reinstallation.
To remove the Cable Connectors, it takes a gentle but firm touch.
Grab the wires next to the connector and lightly pull on it while gently rocking the connector back and forth.
Do this while simultaneously holding the printed circuit board down.
Be very careful not to get to rough with them. You don't want to pull or push too hard, this stuff is fragile.
The Ribbon cable connectors have a quick release on them.
There's a ledge on the top of the connector, gently lift up on the ledge and the top will pop up releasing the ribbon cable.
Remove the 8ea screws holding the circuit board in the chassis.
Gently wiggle the board out from under the wire bundles and structure.

Now that the AF board is out and on the bench, ya got all your parts, ya ready to VIOLATE the SDX!
This board is fairly easy to mod.
Most of the components that have to be changed are Electrolytic caps.

Tip #1:
There's a conformal coating on the surface of the PC Board to keep moisture and such from getting to the components and solder pads.
This must be removed before heat is applied.
If it isn't, then you run the risk of it flowing in with the solder and contaminating an otherwise good solder joint.
They're expensive chemicals made just for this application, But we've been using Acetone on a Q-Tip for years with no adverse consequences.
It also works great for cleaning the Flux up after the soldering is finished.

Tip #2:
Un-Soldering can be a real pain in the butt.
They're many special devices just for this.
The thing we use the most of is Fluxed Solder Braid.
This stuff is worth Gold, especially when working with SMD stuff.
We usually fold it in a "V" shape and place it on one side of the SMD solder pad.
Then the soldering iron tip is placed in the "V" and pushed against the solder joint.
Presto...the solder is gone. Then the other side is done.
The SMD will still be stuck there because it is Epoxy Glued in place.
Most of the time when unsoldering the other side of the SMD, while its still hot, you can "flip" it up with the soldering iron tip.
You have to be sure all the solder is gone, cause if it aighnt, you'll lift the solder pad.
One friend of ours says he just takes nippers and crushes the center of the old SMD component while its still soldered on the board, then unsolders the ends.

Solder Braid also works great on the Plated Thru holes in the circuit board. Like were the Electrolytics are mounted.
Take a small bit of solder and "reflow" the old solder joint.
Then make the "V" with the braid, and apply the soldering iron tip. It will suck all the solder out of the hole.
Most of the time...;)

Tip #3:
For soldering we use an ultra fine tip and a thin solder.
This allows us to get in some very congested areas with the minimum of heat and solder to get the job done.
The size of the solder we use is .025" diameter flux core.

The board is marked with both the Capacitor Numbers and the Polarity.
It's really just a matter of unsoldering and removing the old capacitors, and installing the new ones.
The sizes are close to the same so they should fit with no problems.
No surprises here.
Be sure to install the Capacitors with the correct Polarity!!

These are a little more difficult to identify. The board isn't marked for these items.
We have added some pics to help you find them.
Removal and Installation is also a little tricky, especially for beginners.
C27 & C29 are of a special installation and will be described in-depth below.
The other 3 have the same case sizes, so they should fit with no problems.

Trying to identify C304 is rather difficult because the Service Manual X-ray view is of a earlier board Revision and doesn't show it.
See the pictures below for the locations.

Changing SMD Chip Caps C27 & C29:
These are the 2 caps that you have alternatives to changing.
Our way of changing with electrolytics is more difficult and time consuming, but sounds better.
The easy way is to just change them with either the 10uf Ceramic chip or the 10uf Tantalum (Yuk-Spit) chip.
Here are some pics to help if you decide to use the electrolytics.
If installing the Electrolytic or the Tantalum, the "+" terminals must be installed towards Q8 & Q9!!

The board isn't marked for these items either.
So We've added some pics to help you find them.
See the pictures below for the locations.

This mod is NOT required to get a Flat Receiver Response.
It does not have to be performed.
But...
It sure makes the rig sound better.
It gives the Audio more depth, fullness, and ambiance. The Low Frequencies are smoother and more defined.
We're firm believers in the Audio differences between Op Amps.
We've changed allot of them out over the years and they have made a difference each time.
We found that this particular Op Amp had the best Fidelity.
You could try different one's of course to suit your tastes.

Installation is a little more difficult than the caps.
This is due to the IC's being of the SMD variety.
Just take your time, let the solder braid due the work.

C23 is changed from a 47uF to a 100uF electrolytic.
This is to give the DC voltage on the power supply rail of the IC's a little more filtration and storage capacity.
This helps with the Low Frequencies.

OK...
Before you attempt to re-install the AF Unit, take the time to look over the board extremely well.
Be sure all the Flux from your soldering is cleaned up.
Look for any accidental solder bridges that might have happened while you were soldering.
Be sure all the cut leads from the installed components are not "stuck" on the board anywhere.
Give it a good inspection.

AF Unit Installation:
It is basically just the opposite of the removal.
We found it's best to install the screws first before the Cable Connectors and Ribbon cables are reattached.
Use the pictures you took of it, or the labeled connectors to aid in reinstallation.
To install the Cable Connectors, again, it takes a gentle but firm touch.
Line up the connector and gently push down on it until it snaps into place.
Do this cautiously, because if you push too hard, you run the risk of cracking the PC Board.
The Ribbon cable connectors have a quick release on them.
Be sure the ledge on the top of the connector is lifted up.
Insert the ribbon cable, then push the ledge down and bottom it out.