AX-700

[Bratwurst7s]

Looking at the relay as it is in your photo, trim off the middle legs. Hmn. Actually, I guess that they ate the middle legs no matter how that you look at them. Just cut them off flush with the base of the relay and it will work fine.

Cheers,
James

 

[Bratwurst7s]

OK. So I have another of these fine amps on the workbench. A few things that I wanted to post about.



With the last amps for some reason that I can't explain I only removed the phono board to re-cap it with it laid on top of the heatsink. This time around I thought that I'd try to use my brain for something more than balast and pulled both the phono and input boards and laid them on the bench. Duh. So much easier. Also, looking through the schematic again I realized that I had missed that not only are C119 & 120 directly in the signal path (22µF/16v BP), but also C107 & 108 (10µF/16v). So this time around I used Nichicon ES Muse 10µF/25v BP for C107 & 108.

Cheers,
James

 

[Bratwurst7s]

In the past when I used the Elna Tonerex 680µF/100v to replace C331 & 332 I drilled the main PCB to accommodate their snap-in leads (10mm spacing vs the oem 7.5mm lead spacing). More and more, after drilling new holes on a pcb I get the feeling that I've just done something dirty and repulsive. It's a permanent change to a board that can't be replaced except by cannibalism. So I made a vow to not do that anymore starting with my AX-500 when I worked on it a couple of months ago.

So this time I used some old 1mm leads cut off of some other caps and made leg extensions with a 7.5mm spacing. Before attaching them I used side cutters to shorten the snap-in leads to 3mm. The new leads were then tightly wrapped around the snap on leads for a good mechanical connection and then soldered.

When I did a similar leg adaptor to the main filter caps in my AX-500 I cut spacer plates out of 4mm pvc and filed/sanded/drilled them to fit. This worked, but was a lot of extra work. This time I simply found some rubber o-rings to use as spacers. 22mm OD and 3mm thickness (hence shortening the snap-in leads) I glued the rings to the caps with some general purpose rubber cement, and added a few spots of glue to the bottom of the ring when installing them. The whole thing went very quickly, no fuss no muss and no drilling.



Cheers,
James

 

[Bratwurst7s]

 

[Bratwurst7s]

Lastly, and perhaps most importantly, I have finally found some main 18000µF filter caps that can be installed quickly and easily with no drilling or mods to the amp.

United Chemi-Con KMH with 5 leads. Mouser has them for under 15€ each. EKMH800T183BM80T. They are 80v and 105°. Same height and diameter as the original caps.

The only mods are done to the caps and are quite simple and easy. The original caps have 4 lugs (2 are dummies for stability) with 22mm spacing. The new caps have 5 lugs (3 are dummy) and have 25mm spacing. So one only needs to snip off the 5th lug and do some minor bending to the remaining 4. Just bend the entire lug a little bit in towards the center of the cap and then bend the small end section of the lug back to vertical. It was very easy and the cap was a nice snug drop in fit. Again, no fuss, no muss and no drilling.



I'll post some pics of the finished interior in the next day or 3, after I actually get it completely finished.

Cheers,
James

 

[Bratwurst7s]

The capacitor replacement parts list has been updated.

Cheers,
James

 

[Bratwurst7s]

For the front function boards I used film caps. For the 0.33µF/50 I still have a bunch of Panasonic ECQ but because they are no longer available I showed Wima MKS02 in the re-cap parts list. The only down side of the Wima caps is their relatively short leads. There isn't enough space between the function board and front frame panel to mount the 4.7µF Wima's standing up so I had to make lead extensions to mount them at an angle. A spot of glue holds them stable against the other oem film caps.

The original Elna 4.7µF caps were mounted with glops of Sony bond. It didn't damage the nearby resistors but I did have to replace the long jumpers above that spot due to corrosion.




Cheers,
James

 

[Oldsansui441]

Looks like it is coming along well, nice work, will be interesting to see what you think it sounds like compared to original.

 

[Bratwurst7s]

Looks like it is coming along well, nice work, will be interesting to see what you think it sounds like compared to original.

Thanks! No photos today, but tomorrow I should have some to post.

Yesterday I deoxed everything and today turned it on for the first time since re-capping. The left channel dialed in to 10mV with very little gain on the trim pot (perhaps 3 1/2 to 4 turns of the 20 turn pot) and shows a miniscule 3.3mV DC-offset. Measuring idle current on all 4 emmiter resistors in the left channel there is only about a 0.5mV difference).

However the right channel had to be turned up a fair amount to get the idle current at 10mV on the middle of the road emmiter resistor, with about a 2mV spread between the 4 test points. Worse, the DC-offset on the right channel is 10 times higher than the left channel at ca 33mV.

So at the moment I'm stepping back and trying to decide what could be done to get the right channel looking better. I've already re-flowed all solder connections the right channel.

Cheers,
James

 

[Bratwurst7s]

OK. As promised here are a couple of overall shots of the finished interior with the new filter caps.



Cheers,
James

 

[Bratwurst7s]

Recently I recapped a pair of Braun L1030 speakers for a friend and he stopped by to pick them up today. Since he also now has the 1st AX-700 that I worked on and a Denon DCD-1290 it seemed like a perfect time to give this latest AX-700 a sound test. I have another DCD-1290 here so my friend was able to audition his speakers on essentially the same amp and cdp that he will be using at home. We played Rory Gallagher's first solo album.


In spite of the obviously non optimal speaker speaker stands the combo sounds just fantastic. We also changed to mono for a short time and the sound centers perfectly without either channel playing louder than the other. At this point I believe that I'll leave well enough alone and not fight with trying to change anything in the right channel regarding the ca 33mV DC-offset. I do still have to find a rec-out switch to replace the missing one.

Cheers,
James

 

[Oldsansui441]

Great to hear you are very pleased with the results, l bet your friend will be very happy with all of your work .

 

[Bratwurst7s]

Thanks OS441. Yeah it sounded pretty good. There's only one obstacle to the amp moving on to a new owner. That missing rec-out selector knob. But I may have found a pretty good replacement. Not quite perfect but very close to the original in looks and size for a very reasonable price. I'll know in a day or 3.

Cheers,
James

 

[Oldsansui441]

That will finish it of nicely then, yes knobs and buttons aren't the easiest to find unfortunately and if you can find any they are usually expensive.

 

[Bratwurst7s]

OK. Darn knobs. Loose one and deal with the ebay knob Mafia and spend 10% of the price of an amp for a knob. Or get creative.

The faceplate cutout is about 20mm in dia, and the original wing-knob is 18mm in dia. The poti shaft is 6mm in dia and extends to about 1 faceplate thickness less than flush with the faceplate, if that makes any sense. Ok, so it stops just short of the inside edge of the faceplate. That's kind of a problem for finding an aftermarket knob.

I looked around a lot. I could find aluminum 18mm wing-knobs, but they all had 4mm mounting holes and a knob width in the "wing" area of 6mm. So I couldn't just use one of them and bore the hole larger. But I could find 20.5mm OD knobs with a 6mm mounting hole. So I bought a couple of them. Mentor is the brand, P/N 5582-6631. Black powder coated. I bought them from Bürklin at about 1.60€ each.
http://www.mentor-bauelemente.de/en/products/k/aluminium-wing-and-pointer-knobs/?seite=2#startup

I tried at first to take a knob and turn it's od down to fit into the faceplate hole but that looked like shit. But that's why I bought 2 knobs.

Mounting the 2nd knob meant using a shaft extension and barrel clamp. But the length of the poti shaft complicated things. I mean. heck, if it was shorter I could buy a 6mm-to-4mm barrel clamp and a 18mm knob. But that long shaft precluded that. And being the cheep Barstool that I am I decided to McGuyver it.

I found a 6mm long shank screw and cut off the head and threaded section. For a barrel clamp I found a wire terminal barrel clamp that had a 6mm ID and removed the brass clamp section. It needed to be cut down to 16mm to fit, but first I drilled and tapped a new M4 set-screw hole. I filed flats on the shaft where the set-screws would contact the shaft for a nice secure contact. I like set-screws with a ring face better than a point face, they have more contact area and don't leave such a deforming hole where they set.



Cheers,
James

 

[Bratwurst7s]

The results are far from perfect, the white line marking is a bit too much and it looks obviously non original, but at the same time it at least doesn't look butt-ugly, it fits, it works, it's not plastic and was quite inexpensive. It will do until I find an original knob for a reasonable price.

Cheers,
James

 

[Oldsansui441]

Nice fix, sometimes you have to think outside of the box don't you. I know what you mean about knobs on Ebay, l have unfortunately had to fork out for a couple in the past.

 

[ebere]

Folks first time posting on AK although I have been a big fan and read up lots here so thank you all for the posts. I currently own a Yamaha AX700, Sansui AUX501 & Sony F470 to name a few. I am looking for some help as I am a novice at this stuff & hope for your expert advise on the subject. The AX700 & the AUX501 are both depicting the same problem of a scratching sound on one channel and I was hoping you would be able to advise what needs to be replaced. All these amps have been used for years by me and are in original condition. I want to start with the Yami if possible I popped the case but cant really see anything unusual. I cant figure out how to add pics thus lookinf forward to your advise.
Regards from Vancouver
Ed

 

[avionic]

Folks first time posting on AK although I have been a big fan and read up lots here so thank you all for the posts. I currently own a Yamaha AX700, Sansui AUX501 & Sony F470 to name a few. I am looking for some help as I am a novice at this stuff & hope for your expert advise on the subject. The AX700 & the AUX501 are both depicting the same problem of a scratching sound on one channel and I was hoping you would be able to advise what needs to be replaced. All these amps have been used for years by me and are in original condition. I want to start with the Yami if possible I popped the case but cant really see anything unusual. I cant figure out how to add pics thus lookinf forward to your advise.
Regards from Vancouver
Ed

Welcome aboard Ed...

 

[ebere]

Thank you Avionic, looking forward to some advise on how to proceed with the AX700 sort crackle distortion issue for a better explanation.
Regards
Ed