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Galaxy DX86V mods

Handy Andy

Do Your Research First, Then Decide...
Apr 23, 2018
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Careful is showing off your work @Shadetree Mechanic - you'll find yourself with a lot of buyers wanting a piece of you...

R.f8baf6d0a78078e569b1190a3f1bbb1a
 

Shadetree Mechanic

808 On The North Side of Dover
Oct 23, 2017
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Careful is showing off your work @Shadetree Mechanic - you'll find yourself with a lot of buyers wanting a piece of you...

R.f8baf6d0a78078e569b1190a3f1bbb1a
Maybe by the time I retire in 12 years, I will know enough to be able to make some pocket money by doing this. Sure beats selling firewood, which is what I used to do.
 

WECSOG

Sr. Member
Jan 1, 2020
754
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Just had a nice ragchew with a couple of locals on 38 lsb, and got good reports on the DX86V. I tried an Astatic 636L, RD104, and a ProComm power mic. Reports were that the two Astatic mics were similarly punchy, good for DX. Of course the RD104 was louder because it's amplified.
The ProComm was reported to give a fuller, richer sound; better for ragchewing.

One of the guys I was talking with was running a 5555 with Astatic 636L. He definitely had punchy audio.
 

Shadetree Mechanic

808 On The North Side of Dover
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Just did the mic gain mod. The R176 resistor gets changed from 270k ohms to 330k ohms. My resistor kit did not have a 330k, so I stuck a trimmer in there. I set it with my meter and then cut the extra leg off, and it dropped right in. Then adjusted it while listening to myself on my monitor radio. I turned it all the way down, and then slowly back up. It got to the point where I keep turning, but wasn't getting much louder, so I left it there. It was right about where I had set it with the meter. Now the Astatic 636L is back in action.


IMG_20211116_211517.jpg
 
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Handy Andy

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There is an Upper limit to the level of amplification the thing (the 4558 chip) will produce then it's nothing but acting more and more non-linear and nearly digital - the 4558 is originally a comparator - made analog by the feedback loop you're "toying" with...

Curious to know what you felt that limit was by ear, and what that pot measured out to be?

My guess is close to that 330K - anything higher just "pinches out"
 

Shadetree Mechanic

808 On The North Side of Dover
Oct 23, 2017
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There is an Upper limit to the level of amplification the thing (the 4558 chip) will produce then it's nothing but acting more and more non-linear and nearly digital - the 4558 is originally a comparator - made analog by the feedback loop you're "toying" with...

Curious to know what you felt that limit was by ear, and what that pot measured out to be?

My guess is close to that 330K - anything higher just "pinches out"
Thanks for all your help Andy. The audio with the 500k pot turned all the way up, did not sound bad or different, its just that when I was turning it up, it got to the point that turning it more didn't make it sound any louder. So it left it at that point and I would bet that it is at 330k or really close. This will be a handy adjustment to play with, after I figure out the audio limiter.

Using the schematic for the 979, it seems that the 86v has all the same parts, at least in the audio section. Going by the information you already gave me, it looks like I can make the value of R186 bigger, or put a resistor across D64. Maybe a trimmer at R186?



IMG_20211117_054247074.jpg
.
 

Handy Andy

Do Your Research First, Then Decide...
Apr 23, 2018
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Using the schematic for the 979, it seems that the 86v has all the same parts, at least in the audio section. Going by the information you already gave me, it looks like I can make the value of R186 bigger, or put a resistor across D64. Maybe a trimmer at R186?

Didn't I already discuss something like this in another time - place or world?

Not sure - "Visions Of CB Tricks" comes to mind...Woof...

Making R186 "bigger" can only go so far, you'll need to "drain off" once restricted (just limits current) - else it will still fill up that pool on the other side of the circuit towards the Limiter.

upload_2021-11-17_7-4-32.png

So on some realms this was discussed earlier...


upload_2021-11-17_6-49-8.png


Look Familiar?
upload_2021-11-17_7-5-53.png

GOOGLE Translate...
(...Not Really but it tends to need interpretation...)
[...From My Mind To Yours...]
upload_2021-11-17_7-35-55.png

Starting at R186

R186 = R172
C157 = C132
D64 = D68
C156 = C131
D61 = D67
D62 = D69
C160 = C135
R178 = R190
What you can try and see to some success is to install two resistors - one across D64 as you said, but also you might want to REDUCE the drive it detects by placing a resistor from the JUNCTION of C157 and R186 (start with 1K) with the other lead to foil board ground.

Why?
  • - R186 then becomes part of a divider (Source side) to reduce this "peak" detectors ability to "peak" - the other resistor - the 1K then takes the output of R186 BEFORE it goes into C157 - and reduces it by offering the signal a choice to go into the cap or to ground - the divider process.
    • why such a concern?
    • - dealing with diodes you can run into a problem of their "valve" action as they tend to only work DC in one direction
    • - it will tend to build power in the circuit with the audio getting rectified, any audio
    • - even weak presence of air blowing from a fan, gets sent in to this circuit
    • - and begin to hold onto a rather high charge to force the Q39 Limiter to not only turn on - but stay on too long and you miss the effect of peak clipping versus RMS as this circuit tends to do.
  • Note the Cap C157 - only provides one exit - into the Diode "doubler".
  • IF you take a strong signal into this portion of the circuit, the Resistor value needed to OVERCOME the diodes ability to rectify the signal that the cap now has turned into an AC presence at the ANODE end of the diode - both the negative and positive side of the signal into a P-2-P DC (or positive going) component needs to be much lower
    • - the filter cap C156 "holds" that charge because it can't drain off past D61's Cathode end
    • - it's PN junction is oriented so it blocks it from doing so - so it (your audio signal power) has no choice but to flow thru D62 - towards Q39
  • - many people miss this. This is similar to the HV section of some older CRT Tube TV sets only with fewer stages.
I have to make this somewhat challenging...

So good luck!...

upload_2021-11-17_8-30-14.png
 

NZ8N

Sr. Member
Dec 25, 2017
415
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D64, D61 and D62 are the Positive peak sensing feedback loop for the Mic Amp. When installing Ta opGun CP1, they instruct you to remove the feedback resistor and replace it with their module, and remove D61.

This is what I used to do, assuming the Mod limiter circuits (AMC/ALC) are intact: Do not remove D61 as above.

C158 is your "Sample and Hold" capacitor for where the AMC sense and ALC sense tie together, to the rest of the AMC/ALC circuit. Solder a 22k (10k?) across this capacitor. This allows the capacitor to react to, and hold on instantaneous peaks, but release a whole lot faster. The value depends on the model of radio. On RCI2950's (pre-DX), I used 10k, on 2970's, I used 22k.
On SSB, using an Oscilloscope, readjust the peaks to just under rail-to-rail, you want curves, not flat tops. Instead of a triangular sideways Christmas tree pattern, it becomes a much fatter Christmas tree pattern. On AM, same goes for that, on positive (no flat tops) and negative peaks (no gaps or 0 RF). This makes it a quasi syllabic speech compressor.
 

Shadetree Mechanic

808 On The North Side of Dover
Oct 23, 2017
4,900
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The First State (Delaware)
What you can try and see to some success is to install two resistors - one across D64 as you said, but also you might want to REDUCE the drive it detects by placing a resistor from the JUNCTION of C157 and R186 (start with 1K) with the other lead to foil board ground.

I tried two, 1k trimmers in these locations. I am having a hard time quantifying any difference. Maybe I don't have enough audio to cause any clamping action to begin with? I will go back and verify that I am on the right spots.

IMG_20211118_212551232.jpg
 
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Handy Andy

Do Your Research First, Then Decide...
Apr 23, 2018
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I tried two, 1k trimmers in these locations. I am having a hard time quantifying any difference. Maybe I don't have enough audio to cause any clamping action to begin with? I will go back and verify that I am on the right spots.

Yes, the "clamping" is not "clamp" but "clip" and in flattopping - "scrunch" distortion moments are more the effect.

If you had done any work to the Limiter section - this may be a moot point...

Because what you are trying to determine is if any more attenuation / limiter action is needed. Action being the Limiter - is it hitting the audio still too hard? Doesn't appear to be - you're margin seems to be more towards compression than peaking.

So if the results are little to no effect - then the circuit is balanced the best you can make it and you can just continue on.

Balanced being that the input TO the circuit and the output FROM the circuit is low enough so they any effort you're doing to make the radio "louder" this section is not causing the "squeeze".

Placing a power mic on this? IT's the only other way to check - which again, because of the work you've already performed - by observation - the limiter needs the higher output in order to have any impact - so if no true results can be heard. So the work being performed by you as you go - doesn't seem to impact as much as if it was in it's stock form.

I would like to know if you're checking this in other modes like FM and SSB?
 

Shadetree Mechanic

808 On The North Side of Dover
Oct 23, 2017
4,900
7,840
623
50
The First State (Delaware)
Yes, the "clamping" is not "clamp" but "clip" and in flattopping - "scrunch" distortion moments are more the effect.

If you had done any work to the Limiter section - this may be a moot point...

Because what you are trying to determine is if any more attenuation / limiter action is needed. Action being the Limiter - is it hitting the audio still too hard? Doesn't appear to be - you're margin seems to be more towards compression than peaking.

So if the results are little to no effect - then the circuit is balanced the best you can make it and you can just continue on.

Balanced being that the input TO the circuit and the output FROM the circuit is low enough so they any effort you're doing to make the radio "louder" this section is not causing the "squeeze".

Placing a power mic on this? IT's the only other way to check - which again, because of the work you've already performed - by observation - the limiter needs the higher output in order to have any impact - so if no true results can be heard. So the work being performed by you as you go - doesn't seem to impact as much as if it was in it's stock form.

I would like to know if you're checking this in other modes like FM and SSB?

I checked in AM and SSB. (no FM) With the audio feed back mod, it makes it tricky to use the power mic. But I did try it, and it still didn't seem to make a difference while I was keeping it clean. So maybe the big audio Galaxy was already good to go in this area. Its really sounding good with the 636 mic.
 
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Shadetree Mechanic

808 On The North Side of Dover
Oct 23, 2017
4,900
7,840
623
50
The First State (Delaware)
D64, D61 and D62 are the Positive peak sensing feedback loop for the Mic Amp. When installing Ta opGun CP1, they instruct you to remove the feedback resistor and replace it with their module, and remove D61.

This is what I used to do, assuming the Mod limiter circuits (AMC/ALC) are intact: Do not remove D61 as above.

C158 is your "Sample and Hold" capacitor for where the AMC sense and ALC sense tie together, to the rest of the AMC/ALC circuit. Solder a 22k (10k?) across this capacitor. This allows the capacitor to react to, and hold on instantaneous peaks, but release a whole lot faster. The value depends on the model of radio. On RCI2950's (pre-DX), I used 10k, on 2970's, I used 22k.
On SSB, using an Oscilloscope, readjust the peaks to just under rail-to-rail, you want curves, not flat tops. Instead of a triangular sideways Christmas tree pattern, it becomes a much fatter Christmas tree pattern. On AM, same goes for that, on positive (no flat tops) and negative peaks (no gaps or 0 RF). This makes it a quasi syllabic speech compressor.

Just put a 10k across C158, initial testing sounds great. Getting ready to put it on the scope in the shack.

IMG_20211126_190235.jpg magnifier_20211126_190138.jpg
 

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