Recapping Yamaha A-720

Hello Guys,

i will Recap in the next time my Yamaha A-720.
For now, only the Electrolytics.
I ordered some Capacitors at partsconnexion and still waiting for it. (Canada -> Germany) takes a while.

I ordered a few Nichicons KZ, 2x Nichicon KG (22.000uF / 80V), 2 Elna Silmic II, and already have Nichicons ES BiPolar.

:scratch2: Is it recommend to change in Step 2, the Polypropylen Film Caps in the P/S and on the Amp Board? And whats with the Mylar Caps, should i change these ones? :scratch2:
Should i glue the new Caps on the Board? (against Mikrophonie Effect) or hat it be done only for easyer manufacturing apects?

I have to say, the A-720 is in an very great Condition, i think it`s never been running in CLASS-A Operation (There are no spurs of any Hot Times in it).
I had luck to become a non-smokers unit

Iam electrician with good soldering skills. But i´am new in the HiFi Business... so i have these questions ;D

i work especially in the High Frequency Range up to 67GHz. (EMI Measurement Receivers & Spectum Analyzers)

When the times comes up with the Project Recapping, i will take some Pictures and will open a Thread.

This is my STEREO Stack, Yamaha A-720, T-1020,K-1000

Wie geht's Herr Shane54 ;-)

I have recapped an A-720. Mine is black, I like the nice silver look of yours. I replaced all the electrolytics except the two big filter caps. I'm listening to it right now, it puts out a very nice sound.

It seems a professional repairman would not replace the polypropylene and mylar caps if they meet specs, which seems likely to be the case. However, as hobbyists, we are free to experiment as we like. Maybe you have access to test equipment that would show a difference if you replace any of these caps?

As I understand it, the glue was used for manufacturing purposes.

If a deal goes right, I might have an A-720 (silver) in a few days for a good price...

Karl vd Berg said:

If a deal goes right, I might have an A-720 (silver) in a few days for a good price...

Click to expand...

Good luck, I hope you get it.

I am going to replace the phono opamps in the A-720, I picked up some Brown Dog adapters and some replacement opamps. I'll report on that here, as I am pretty sure you will be interested in hearing the results (good/bad/indifferent).

39cross said:

Good luck, I hope you get it.

I am going to replace the phono opamps in the A-720, I picked up some Brown Dog adapters and some replacement opamps. I'll report on that here, as I am pretty sure you will be interested in hearing the results (good/bad/indifferent).

Click to expand...

Sure I will. :yes:

Did you replace its relay as well? I'm curious if it is the same as the one I put in my A-520... :scratch2:

Hello ;D

i`am fine (mir gehts prima

Okay, so i will only change those Electrolytics, including the big Black Filter Caps (i choose Nichicon KG`s).
As well, i have to change some Resistors nearby those f... Glue... it corrosive the Resistors...

Yes indeed, i have access to the Best of the Best (Rohde & Schwarz UPV --> http://www.rohde-schwarz.com/en/product/upv-productstartpage_63493-7558.html)

But at the moment, i had a lot of work, and it`s difficult to take the Amp with at Work, and in the other Hand, not possible to take the UPV with me at home --> $$$$$$$$$$.
I think it will be very interesting to take a test of the most prime Specifications before and after, like a comparison .
But is it not more important how it Sound`s for the Human ear? i personally think, when i will love the Sound, some THD (total harmonic distorsion) or SNR (Signal Noise Ratio) or klirr Factor has not the weighting to become more in Love with it ;D

YeZZzz i Love the Silver color, until i buy it, i dont like Silver Electronics (had a Harman Kardon AVR Black as DTS Receiver ) and with the Tape Deck and the Tuner it looks pretty fine. The next thing i will buy to Complete the Stack, is a CD Player ( the New Collection CD-N501 or CD-S700) but sorry, those are not the haptics like the old 80s Stuff.. maybe the CD-S1000 / 2000 / 2100... but these are very expensive..

Karl vd Berg said:

Did you replace its relay as well? I'm curious if it is the same as the one I put in my A-520... :scratch2:

Click to expand...

No, I didn't replace the relay, sorry :-(

I had problems with the class a, tone direct and muting switches, they were scratchy and caused a channel to cut out. Disassembling the front panel gave access, and some deoxit took care of the problem. This made a big difference.
The other switches were OK, but I gave them the treatment as well.

Today i have to go to the custom to pay Noun,... here they are... ready for change

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ließ den Spaß anfangen!

39cross said:

No, I didn't replace the relay, sorry :-(

I had problems with the class a, tone direct and muting switches, they were scratchy and caused a channel to cut out. Disassembling the front panel gave access, and some deoxit took care of the problem. This made a big difference.
The other switches were OK, but I gave them the treatment as well.

Click to expand...

Ok, nice! :thmbsp:

As you're going to open anyway the unit to replace the phono opamps, I'd put a new relay in it. This is a 1985 unit, iirc. All the units from that time I had to replace the relays, soon or later. Including the one in my A-520... :thmbsp:

Shane54, nice big cans!

yes, they are huuuuuge, as big as the original hope the original have also a Solder Lug *i dont know...!?)

39cross said:

ließ den Spaß anfangen!

Click to expand...

ja , ich denke morgen

off course, i think will start tomorrow ;D

Job is done

First listening impressions:

Clear Clear Sound. A little bit Analytic. The Voices are very classy. I dont know if i should like it... i think i have to listen some hours (50+) and wait that everything is grossed (e.g. the Caps) in the first moment, i thought it sounds a lil bit metallic (hope you with me what i mean) . We will see what sounds up ;D

Uhhhm, the old Caps, some are good as well, some are bad.

Rubycon BlackGate F : 1000uF/6.3V -> now: 328uF and a ESR about 0,7Ohms --> rubbish
Some has a good ESR and some are very bad, i think the lower Voltage ones are now, after 30years have done theyre Job.
Rubycons Black Gate F 1000uF / 25V are good...


The Big Nichicon 22000/63V : ---> now: 24,5mF / ESR 0,043 Ohms thats great, i dont had to change these...

Measured with Philips LCR measurement Device.

--Karl - thanks for the advice on the relay, I will get a replacement next time I order some parts.

--Shane54, that is good news, it should sound better when it's been used for a while. Nice that you have a good LCR meter. Do you have another use for the KG's you bought?

I thought it was interesting that Yamaha used Blackgates, I saved mine to measure the ESR someday. I replaced them with Elna Silmics.

One interesting thing, if you notice there is a long run of wire from the preamp section to the accessory jacks in the back of the unit, then returned to the front. I am thinking of bypassing these.