fourkidsco
New Member
Greetings all!
I have lurked here for years, working my way through a Kenwood KA-3500 and KA-9100 restoration. Still have the 9100, and love it.
Recently I was offered a KT-7300/KA-7300 pair in excellent cosmetic collection (including original packing in perfect condition). The problem is the amp stopped working a month ago and the absence of the relay click on turn on would indicate that there is a high probability of one or more output circuits being burnt out. Given that these were in use for years, I am not surprised.
So I cruised around and tried to dig up information on a replacement circuit and was unable to find anything definitive. Lots of options/opinions, but nothing definitive.
The most promising one seems to be this:
http://www.suwa-koubou.jp/repair/ka_7500/ka_7500_2.html
(Note the change suggested at AK for this design: https://audiokarma.org/forums/index.php?threads/ta-100w-follow-up-work-around.353919/page-3, post #58)
I had an email exchange with Seiichi Suwa who runs the site and he gave permission for his design to form the basis of a PCB for a replacement circuit. Given that the Sanken devices specified by Seeichi are available at reasonable cost from Digikey, it seems like a good starting point.
I found several other options, including the "Sicman" option (which lacked a current limiter), the link above, and this link from Poland: http://e-hifi.pl/index.php?id=43 (Search the images for the schematic).
Did I miss anything?
My older son can design the PCB layout and we have a location that can produce them...what I need is a bit of input on the community on the final design and on prototype testing. As I recall, while Seiichi's design was labeled "good", or at least "sufficient", it seemed like there were ideas about enhancements. For example, I have wondered why pin 9 is not connected in Seiichi's design, but is connected on the schematics in the Polish design.
My son and I have some ideas for components, layout and mounting of the board to give it a professional and non-hacked look, we just need to finalize the circuit design.
I would do a small run of 6 boards as samples and would look for 2-4 people who would be willing to experiment with the boards and do some testing based on the consensus here. I would mail you 1 board for the cost of postage, probably $2 in the US....I will eat the cost of the board for now. You would need to populate the board but if I order the parts, I could probably provide them at cost+postage. The ideal recipient would be someone who could do some more detailed measurements compared with my capability with an old oscilloscope and Fluke MM.
Ultimately, if this works, I would do a larger run on the final design based on how many people would want them, but that would be at least a couple of months down the road. I am planning on selling the board more or less at cost plus postage, rounded up slightly to cover the cost of the original sample boards.
Note that between my day job and my son's day job, it might be a few weeks before we had a viable prototype submitted for manufacturing, but I figure if I start now we could probably have something by Feb.
Anyone interested in contributing?
I am working on some hand drawn layout examples to show the basic concept and the currently proposed components with a modification to allow an (optional) pin 9 attachment, which would be the first major design post for discussion.
Dave
-----------------
Projects past and future:
Fisher 400
Kenwood KA-3500
Kenwood KA-9100
Pioneer SX-3700
QSC Series III 3500
Fisher XP-1A speakers
HATT MKIII custom bookshelf speakers
Sunn SR410 Redesign/rebuild
Kenwood KT-7300/KA-7300 (?)
I have lurked here for years, working my way through a Kenwood KA-3500 and KA-9100 restoration. Still have the 9100, and love it.
Recently I was offered a KT-7300/KA-7300 pair in excellent cosmetic collection (including original packing in perfect condition). The problem is the amp stopped working a month ago and the absence of the relay click on turn on would indicate that there is a high probability of one or more output circuits being burnt out. Given that these were in use for years, I am not surprised.
So I cruised around and tried to dig up information on a replacement circuit and was unable to find anything definitive. Lots of options/opinions, but nothing definitive.
The most promising one seems to be this:
http://www.suwa-koubou.jp/repair/ka_7500/ka_7500_2.html
(Note the change suggested at AK for this design: https://audiokarma.org/forums/index.php?threads/ta-100w-follow-up-work-around.353919/page-3, post #58)
I had an email exchange with Seiichi Suwa who runs the site and he gave permission for his design to form the basis of a PCB for a replacement circuit. Given that the Sanken devices specified by Seeichi are available at reasonable cost from Digikey, it seems like a good starting point.
I found several other options, including the "Sicman" option (which lacked a current limiter), the link above, and this link from Poland: http://e-hifi.pl/index.php?id=43 (Search the images for the schematic).
Did I miss anything?
My older son can design the PCB layout and we have a location that can produce them...what I need is a bit of input on the community on the final design and on prototype testing. As I recall, while Seiichi's design was labeled "good", or at least "sufficient", it seemed like there were ideas about enhancements. For example, I have wondered why pin 9 is not connected in Seiichi's design, but is connected on the schematics in the Polish design.
My son and I have some ideas for components, layout and mounting of the board to give it a professional and non-hacked look, we just need to finalize the circuit design.
I would do a small run of 6 boards as samples and would look for 2-4 people who would be willing to experiment with the boards and do some testing based on the consensus here. I would mail you 1 board for the cost of postage, probably $2 in the US....I will eat the cost of the board for now. You would need to populate the board but if I order the parts, I could probably provide them at cost+postage. The ideal recipient would be someone who could do some more detailed measurements compared with my capability with an old oscilloscope and Fluke MM.
Ultimately, if this works, I would do a larger run on the final design based on how many people would want them, but that would be at least a couple of months down the road. I am planning on selling the board more or less at cost plus postage, rounded up slightly to cover the cost of the original sample boards.
Note that between my day job and my son's day job, it might be a few weeks before we had a viable prototype submitted for manufacturing, but I figure if I start now we could probably have something by Feb.
Anyone interested in contributing?
I am working on some hand drawn layout examples to show the basic concept and the currently proposed components with a modification to allow an (optional) pin 9 attachment, which would be the first major design post for discussion.
Dave
-----------------
Projects past and future:
Fisher 400
Kenwood KA-3500
Kenwood KA-9100
Pioneer SX-3700
QSC Series III 3500
Fisher XP-1A speakers
HATT MKIII custom bookshelf speakers
Sunn SR410 Redesign/rebuild
Kenwood KT-7300/KA-7300 (?)
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