Kenwood KT-7500 restomod : blue,green LEDs, power supply upgrade, recap

[hopjohn]

Just another option. I haven't looked at the one I did for a while, but I know I mounted a radial cap there with a dab of rtv silicone and moded the board with a new through hole on the near side of the wide trace you see in the photo. Dunno what Kenwood was thinking with that one. The 7500 layout leaves a lot to be desired. Sure sounds good after mods though.

 

[leesonic]

Adding these pictures here of the last one I did, just so they won't get lost forever. This one had RGB LEDs fitted, with the famous Leesonic "select-a-color" (pat pending) switch on the back panel to set the dial lamp color.

Lee.

 

[leesonic]

Fixed dead picture links.

 

[Spenser]

Edit: Important note: If you are doing the KT-7500 Passive EQ mod as listed on the FMTunerinfo site be aware that when replacing the .15uf caps at C45 and C46 that the new 1uf cap should go first in the signal path (coming from the Low Pass filter). Then add the 10k series resistor to the outgoing leg of the cap toward the opamp. It isn't discussed there and was a source of confusion for me. I've seen photos where this mod was done incorrectly so please be advised.

This old thread is terrific, Lee. So very helpful. Thank you!!!

John, what do you like in the way of polypropylene capacitor for the passive EQ at C45/46 hoping something Mouser carries that would work well in your opinion. I'm thinking maybe WIMA MKP mounted underneath, as I just noticed Ray / Jim's WIMA usage see below linked from FMTunerInfo mods page.

A picture in the MP Barney page shows the wrong configuration for the passive EQ capacitor-transistor combo if it is to be as you so described. Post #9 of this thread of Lee's has the link. C46/resistor add-on needs to be flipped around to the other lead if I am not mistaken. Jim's might be wrong, too, at least the one that can be clearly seen on the mod page. The resistor appears to be on the low pass filter side.

https://www.fmtunerinfo.com/RayModBottom.jpg

At the risk of more Pandora's Box I have two ERSE PulseX (MPX) 1uF250V. Hee ho. They're under a buck apiece. Don't know if they work in this application. SonicCraft online description of their Sonicap or MultiCap offerings says ERSE and others are 'bright and harsh' compared to their caps they say are more 'well balanced.' ERSE says their PulseX totally uncolored +/-3% tollerance. Uncolored would be my druthers anyhow.

 

[hopjohn]

John, what do you like in the way of polypropylene capacitor for the passive EQ at C45/46

Likely use MKP2D031501H00JI00 which should have the longer leads to work with.

 

[DAY4201]

This old thread is terrific, Lee. So very helpful. Thank you!!!

John, what do you like in the way of polypropylene capacitor for the passive EQ at C45/46 hoping something Mouser carries that would work well in your opinion. I'm thinking maybe WIMA MKP mounted underneath, as I just noticed Ray / Jim's WIMA usage see below linked from FMTunerInfo mods page.

A picture in the MP Barney page shows the wrong configuration for the passive EQ capacitor-transistor combo if it is to be as you so described. Post #9 of this thread of Lee's has the link. C46/resistor add-on needs to be flipped around to the other lead if I am not mistaken. Jim's might be wrong, too, at least the one that can be clearly seen on the mod page. The resistor appears to be on the low pass filter side.

https://www.fmtunerinfo.com/RayModBottom.jpg

At the risk of more Pandora's Box I have two ERSE PulseX (MPX) 1uF250V. Hee ho. They're under a buck apiece. Don't know if they work in this application. SonicCraft online description of their Sonicap or MultiCap offerings says ERSE and others are 'bright and harsh' compared to their caps they say are more 'well balanced.' ERSE says their PulseX totally uncolored +/-3% tollerance. Uncolored would be my druthers anyhow.

I am confused by this part of the mod. Does the picture in the MP Barney page show the wrong configuration for the passive EQ capacitor-transistor combo?

 

[Spenser]

Shoot I thought I took that down. Wasn't sure I was right. Does it appear wrong to you? It did to me. I could be missing something though. Been wrong before. Heh. Went topside with the big WIMA's, by the way, instead of putting them on the foil side. After done shipped it off to Punker X for alignment and the improvement was remarkable. I so far have been unable bring myself to take it (and upgraded 7100 integrated), out of service to give the next things their turn in my rotation.

 

[DAY4201]

I have spent more time on this then I ever thought I would trying to figure it out. I guess it comes down to what Hopjohn means by "Then add the 10k series resistor to the outgoing leg of the cap toward the opamp." If he means the "outgoing" trace from the filter then Jim's photo is correct IMO. Otherwise, I would say you are correct. I hope that someone with more smarts than me can clarify this as I am still stuck. I have tried to make some sense of this issue, at least for myself, by creating the attached photos. The red lines are just place holders for R56 & R57 which I have removed to upgrade to 4.7 ohms per Jim's mod.

 

[Spenser]

Hold on I'm trying to find my file on this. I just boxed mine and may pull it out to look see what I did. I can't remember diddly.

OK. Found the file and pulled the tuner. You're right. If the right way is the way HopJohn's research shows, the solder pad you've marked as outgoing is the wrong one. Instead the resistor goes between the capacitor and the op amp. At least that was my interpretation and what I went with. I pulled my tuner and and took this picture. Hope this helps.

John?

Look at these big ass poly pros. I tacked them to each other and to one of the neighboring filters behind with a teeny spot of hot glue. Yeah baby.

 

[Spenser]

I have spent more time on this then I ever thought I would trying to figure it out.

I too spent a ton of time on the reserach and planning on mine. Of course for me, along with my poor memory, I have a mind like a steel trap. Nothing gets in.

 

[David_NC]

Hold on I'm trying to find my file on this. I just boxed mine and may pull it out to look see what I did. I can't remember diddly.

OK. Found the file and pulled the tuner. You're right. If the right way is the way HopJohn's research shows, the solder pad you've marked as outgoing is the wrong one. Instead the resistor goes between the capacitor and the op amp. At least that was my interpretation and what I went with. I pulled my tuner and and took this picture. Hope this helps.

John?

Look at these big ass poly pros. I tacked them to each other and to one of the neighboring filters behind with a teeny spot of hot glue. Yeah baby.

View attachment 1923463

I seem to have gotten lost in much of this thread.... what does this mod improve? I know most have been done to my 7500, but I'll have to check this one when I get it back. It's at the shop getting an alignment.

On another note, have any added the filter to cut down on HD's self-noise? That certainly looks like a worthwhile one, based on how noisy stations with HD can be.

 

[DAY4201]

I seem to have gotten lost in much of this thread.... what does this mod improve? I know most have been done to my 7500, but I'll have to check this one when I get it back. It's at the shop getting an alignment.

On another note, have any added the filter to cut down on HD's self-noise? That certainly looks like a worthwhile one, based on how noisy stations with HD can be.

You raise so interesting questions that I unfortunately can't answer. I just don't have the required knowledge to do so. The only thing I can say about the mods for the KT-7500 (and other tuners) is that they were developed IMO during the "heyday" of FM radio. Being 70 years old I remember when AM stations were the best to listen to all that great 50's and 60's music. Now I only listen to AM for sports. I rarely listen to FM at all but may do more if I ever get through the mods of this tuner. As for HD radio I don't have a clue. Right now if I want to listen to the "radio" I listen to Sirius/XM in my car. Bluesville is the only station I listen to. At this point, my goal for this tuner mod is to finish it and probably sell it.

 

[DAY4201]

Hold on I'm trying to find my file on this. I just boxed mine and may pull it out to look see what I did. I can't remember diddly.

OK. Found the file and pulled the tuner. You're right. If the right way is the way HopJohn's research shows, the solder pad you've marked as outgoing is the wrong one. Instead the resistor goes between the capacitor and the op amp. At least that was my interpretation and what I went with. I pulled my tuner and and took this picture. Hope this helps.

John?

Look at these big ass poly pros. I tacked them to each other and to one of the neighboring filters behind with a teeny spot of hot glue. Yeah baby.

View attachment 1923463

Thanks for taking the time to take and send the photo! You right about those big polys. I don't think they will die in my lifetime.

 

[Spenser]

Ha. That's funny. I laughed. Thank you. Don't do the mod and sell it off. Like Leesonic did. Hi Hi Lee. (that's amateur-radio-speak for laughter in case he does not know)

Get it aligned and play with it for awhile at least. It's an amazing piece especially when it's well tuned. Help preserve (and advance), radio.

There are a couple good threads on radio status. Here's a start.

https://audiokarma.org/forums/index.php?threads/whats-the-future-for-fm-broadcasting.208415/

 

[Spenser]

I still haven't been able to devote the time to learn filter-network-physics but that is what this mod is about. It is part of two or three other changes that all taken together rework the original filter network design. Then again I could be totally full of you know what. Ha.

 

[David_NC]

Adding these pictures here of the last one I did, just so they won't get lost forever. This one had RGB LEDs fitted, with the famous Leesonic "select-a-color" (pat pending) switch on the back panel to set the dial lamp color.

Lee.

View attachment 678243
View attachment 678244
View attachment 678245
View attachment 678246

That reminds me a lot of the 7500 I recently purchased. I didn't get pics of all the colors, though. The colors were much brighter, but the reflection on the front seems to have washed them out a bit.

 

[Spenser]

ha. was wondering. that's great.

 

[leesonic]

That reminds me a lot of the 7500 I recently purchased.

Looks like one of mine.

 

[DAY4201]

Looks like one of mine.

Very nice!

 

[David_NC]

Looks like one of mine.

When it's back from getting an alignment, I'll get an inside shot; maybe you'll recognize it.