Jump to content

Sansui TR-707A + Heresy III / KG1


Recommended Posts

In the fall of 2019 my Father-in-Law dropped off a Sansui TR-707A Transistor Stereo Tuner Amplifier as one channel was very weak knowing there was a chance I'd be able to diagnose and fix whatever fate this amp suffered.  Over the past two years I'd occasionally open it up, chase down a lead, and then give up when a more interesting/less challenging project came along.  It was always hanging out in the back shelf of the workbench, looking at me with sad puppy dog eyes but knowing it would be a possibly pointless road to go down I hesitated.


Fast forward to six weeks ago when a friend dropped off his NAD C356BEE which was DOA - he fried a few resistors/diodes/capacitors due to a speaker short.  Once I had it up and running again I hooked it to the Heresy IIIs in the main system and was duly impressed.  I was a little too close minded running my Elekit TU-8200 to think solid state could sound so nice!  So I took it upon myself to consider the Akitika kits before realizing I might get the 34 pound beast in the basement working for much less money and have a good story.


A little background gleaned from the internet and my wife's recollection of childhood stories came to a reasonable conclusion: my father-in-law purchased the unit from the base PX in Vietnam and the serial number appears as a 1965 date code so it matches up.  From the on-line manual this is an 18WPC Class AB transistor amplifier and apparently was the first transistor amp that Sansui exported (it also has a really interesting (to me) topology but that isn't my strongest knowledge so feel free to read up on that.


My troubleshooting discovered that there was no signal reaching the outputs so I started working backwards reflowing solder points.  As the pots were scratchy I took out the can of DeOxit and sprayed down the pots which addressed the scratchy sound on the working channel but I was still left with a single channel amp.  I began playing with signals and determined that the offending channel was working, again, nothing to the output.  I even pulled the power transistors and determined all four were in spec - I was happy to find that as the transistors are long since out of production and there aren't any easy replacements or NOS units available that I can easily find.


Going on a whim I checked a handful of capacitors and found one on the offending channel was reading as an open circuit.  I'm not an electronics whiz in the least, but I like buying stuff to feed my audio addiction and who doesn't like assembling a bill of parts and getting stuff in the mail?  I assembled a list of 74 capacitors for the pre-amp, amp, tone control, and power supply circuits and 22 hours after ordering from Parts ConneXion the box arrived.  I pulled the replacement caps for the one that read open (and its channel twin), the iron, and....SHE SINGS!


I've since gone through and replaced about a third of the caps on the pre-amp board and a handful on the output side.  I'm doing this piece meal - one cap per channel per operation, then plugging everything in to check.  The workbench system consists of a CD player and KG1s (rebuilt crossovers in those).


How does it sound?

I really like it.  The bass control offered is out of this world.  The treble is clear and well defined and reveals a few details I had not heard in music previously, although it seems to be hot - I have it turned down slightly on the tone controls.  Channel separation is as expected given the specifications (abysmal by today's standards) and imagining is fairly poor to non-existent.  The hiss during song breaks is noticeable.  Even the tiny little KG1s have great bass weight and extension to them.  I'm really impressed with this beast.


Future work:

1) Finish the preamp recapping project, move on to the output recapping, and the power supply recap (power supply is first on the list to be honest).  I also have capacitors for the tone controls and might get to that.

2) Replace the speaker terminals.  Currently uses a slotted screw which accepts spade connectors, I'm replacing with 5-way binding posts.

3) Replace the RCA jacks.  The built in RCA jacks have a flare, pushing out the sleeve of any connector attached.

4) Replace the non-polarized power cord with either a polarized two-prong cord or a grounded IEC cable.  There isn't enough room to mount an removable plug so I'll hardwire the IEC power cable.

5) I've been unsuccessful in tracking down a replacement knob cover for the balance pot; my back-up plan is to slide the volume knob over to the balance pot and go with an aftermarket knob for volume that is consistent in appearance of the unit.

6) Replace the rubber feet on the outside of the case which have deteriorated due to age.

7) Trouble shoot the lights - while all lighting is functional it is not very bright.


As much as I like this amp, if my father-in-law wants it back I'll let him have it.  But I really hope he doesn't.




  • Like 5
  • Thanks 1
Link to comment
Share on other sites

Thanks for the kind words, and @jcn3 - more guts shots for you.


Last night I decided to put this back on the bench and do some more work.  I'm old enough to know my eyes aren't great in the evening after looking at screens all day so I decided to focus on some of the bigger caps on the output side.  I'm always impressed with how small modern capacitors are - for example, the pre-amp circuit has a dozen or so 30uF caps in voltage ratings 6V, 10V, 16V, and 25V that for simplicity in the Bill of Materials are all now 25V rated (and for future consideration, are all 33uF as good luck finding a 30uF cap).  The output side has a handful of 500uF / 25V caps (now 470uF/25V) and 200uF / 25V (now 220uF/25V) axial caps that are spanning between terminal strips that now look comically small and have resulted in using some hook-up wire and heat shrink tubing on leads.


I looked further at the speaker terminals - my parts bin had a "ganged" set of binding posts (red/black) with 3/4" spacing that was too narrow to fit; but in a "light bulb" moment I realized that the L/R binding posts were spaced vertically 3/4" - so the binding posts were disassembled and will be installed in a black/black and red/red pair (speaker terminals are mounted on plastic and the gang holding the posts is plastic.


After doing the output section I decided to do some work on the pre-amp section.  I thought to myself "I shouldn't do this - my eyes are tired and I can't focus and even the 3.0x magnifiers aren't cutting it" [I'm in my late 40s so yeah, getting old sucks] but I did it anyways.  After doing one cap on each side with much difficulty (I was heating the wrong solder point - first sign of I should have stopped) I powered up to static only to realize I hooked up audio cables wrong when rearranging the workbench.  But even on fixing it I got some "pumping" in the audio chain so....I stopped.  I had been heating a B378A transistor pad so I was worried I fried one, but....Before work this morning I powered up the system to just check the pumping sound and it was gone....so who knows.  Maybe the transistor overheated and took some time to cool.  Might have a long meeting at work today that I can shop around for either NOS or replacements (looks like an AC152 or AC153 might do the trick).


I also need to get some hot glue sticks.  My kids used it to make their Halloween costumes this year and apparently got glue happy. - but I need to put some dabs down to hold some of the new caps in place. I also plan on revising the install of the two blue caps.  Going to leave the monsters they replaced in the board, but hot glue them down and heat shrink the leads. 



  • Like 2
Link to comment
Share on other sites

I'll add more in the future, identifying what changed and why.  One of the two blue caps were the culprit in the non-working channel.  Sorry that single photo stinks!


I'm sitting in my office listening to a Yamaha A-400 two-channel amp with a rebuilt power supply section and Bowers & Wilkins DM12 speakers (acoustic suspension, similar to the KG1s) and this system has none of the bass weight of the Sansui and KG1s.  This 34 pound beast has some serious mojo going on.

Link to comment
Share on other sites

Weekend update:

Upon powering up the beast on Saturday morning the pumping was gone so the suspected damaged transistor was only an overheated transistor.  Emergency avoided.


Worked on the tone control section: this was a tangled mess of layered wires and leads with cloth sleeves protecting the leads - where I could I reused the cloth sleeves to maintain the visual continuity of the amp.  As parts of this has paper-in-oil or film caps that were on the last days of their lives, I reworked this area.  I had some Amtrans and Dayton Audio caps lying around so tossed those in where needed, otherwise I used some Orange Drops or Cornell Dubliners depending on what was available when I made the parts order.


There was a monster 500uF, 400V cap to ground I just tossed in Rubycon cap I ordered for another project in which it didn't fit.


At this point I'm holding off until next weekend.  I'm hosting a Cub Scout event on Engineering for one of my kids on Sunday and I figure I'll open the amp and show what can be done with old electronics (going to teach kids how to hold a soldering iron, tin wires, solder to a board, etc) and might get some free labor with someone with better eyes than me.  Both of my kids (7th and 5th grade) can solder PTP and to a board pretty well so I can always count on their steady hands to do the work even if mom insists on using non-leaded solder for them despite the irony of this amp being all lead.  🙂


Yesterday afternoon I decided that since I liked the bass so much, but the mid- and highs were less than holographic I'd go the biamping route with the Elekit TU-8200 (heavily modified) taking on the non-woofer duty with the Heresys.  After about a bazillion missteps involving hook up, running the Sansui in Mono, swapping channels and other confusion, I came away duly impressed.


I offered the amp back to the my father-in-law and he is grateful for the repair and has unfortunately accepted it back.  I have three more weeks with this amp so while I have yet to find a good parts unit for a reasonable cost I still have time to locate a useful knob, replace the rubber feet, and clean up the insides.  In the meantime I'll likely order either the Akitika pre-amp / power amp combo or try to negotiate down on a "needs work / one channel has feedback / broken glass" Pioneer SX-737 currently listed for $100 near me.



  • Thanks 1
Link to comment
Share on other sites

2 minutes ago, billybob said:

How is the phono section sounding with Fleetwood?


I actually haven't tried it yet  - I just ran it through Aux section via a Bottlehead Reduction.  I think I listened to one side and then switched back to digital files since I'm lazy.

  • Like 1
Link to comment
Share on other sites

5 minutes ago, billybob said:

Cool, know where a couple of vintage besides my integrated are located that need something. Guess though you are busy enough. Forgot where you are located anyway.





I'm in the Boston metro area - if you know of anything that needs work and is a low enough price I'd be interested to add to the collection.

  • Like 1
Link to comment
Share on other sites

  • 2 weeks later...

Last update: replaced the RCA jacks on the rear (required drilling to make openings larger), replaced banana jacks with different ones that fit better (and moved the old ones to my KG4s), finished the recap on both the phono pre and the main preamp. Replaced the knobs wife found the missing knob in the basement (!) I just haven't updated the photo, and the dried out but leave a mark everywhere rubber feet.


Burned in the system overnight, and listening now through the KG4s, this amp loves these speakers. Doesn't match the midrange of the Heresy's but the Sansui pairs so well that I'd be very happy with this system if I could keep it.


My father in law is over the moon with joy right now and is picking up the old Sansui in Thursday.  But eff me, the vintage solid state bug has bit me hard.  Found an Harman Kardon 430 needing work locally so am planning on picking up a new project...thanks for reading!


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...