Good article on capacitively-coupled output sections. (By Rod Elliott.)

[Artie]

I was just looking at my basket-case Marantz 1060, and its' service manual, trying to decide what to do with it. I've only ever seen good reviews of the 1060, and it's capacitively-coupled. It occurs to me that cap-coupled might be the perfect speaker protection scheme. No matter how catastrophic an output failure your amp may have, the speakers get a loud "thump" at worst.

While searching for info on cap-coupled outputs, I found this article by Rod Elliott. It's a long read, but a good read.

Capacitor Coupled output

 

[HPMguy]

That was interesting, thanks!

After I retire I may actually learn some electronics -- no time for more than a smattering of it now.

 

[egellings]

I was just looking at my basket-case Marantz 1060, and its' service manual, trying to decide what to do with it. I've only ever seen good reviews of the 1060, and it's capacitively-coupled. It occurs to me that cap-coupled might be the perfect speaker protection scheme. No matter how catastrophic an output failure your amp may have, the speakers get a loud "thump" at worst.

While searching for info on cap-coupled outputs, I found this article by Rod Elliott. It's a long read, but a good read.

Capacitor Coupled output

Should the amplifier fail by going into a catastrophic HF oscillation, you may end up with fried tweeters & maybe midranges. Output cap won't help you there. For DC rail-out failures, which are more likely, then the cap definitely works.

 

[Artie]

Should the amplifier fail by going into a catastrophic HF oscillation, you may end up with fried tweeters & maybe midranges. Output cap won't help you there. For DC rail-out failures, which are more likely, then the cap definitely works.

Good point. And I have an old Yammy integrated that had that exact problem. I blew several output sets before I realized the problem. You generally examine the output of an amp with the 'scope set to display audio frequencies. The HF escaped me for awhile. Thankfully, it was a low power amp, (CA-400), so the outputs didn't cost an arm & a leg.

 

[gslikker]

Output caps get about half the DC, up to some 40 Volts on the 1060.
The original output caps are 55V as per specification. Good enough if the amp works.
However, if the amp ever fails in some way one of the output transistors connected to the supply voltage fails shorted or is steered fully open while the fuses do not blow, it connects the cap to the supply voltage and you can get close to 80 Volts over the cap.

So, if recapping anyway and wanting full protection, suggest use 80V output caps.

 

[ConradH]

Per the schematic they used an 80V PS cap and 55V output caps. I always want my output caps to have margin beyond the maximum voltage in the amp. Definitely something to upgrade!

 

[Artie]

I've also heard, (read), that it might be a good idea to parallel a smaller cap with the larger output cap to improve HF response. Can anyone confirm if this mod is legit?

P.S. While we're on this subject, would multiple smaller caps sound the same as one big one? In other words, the 1060 uses a 3000uf for the output. Would six 500uf's react the same? Mind you, I'm not considering this mod. Just curious. (For other projects.)

 

[HPMguy]

Ah, the infamous "bypass cap".

I would not. You really don't want anything past 20kHz going through that cap since speaker killing oscillation is typically around 50kHz. Best to block it

Caps in parallel with widely divergent values can do all sorts of strange things, include signal phase shifts between the caps.

 

[Artie]

Ah, the infamous "bypass cap".

I would not. You really don't want anything past 20kHz going through that cap since speaker killing oscillation is typically around 50kHz. Best to block it

Caps in parallel with widely divergent values can do all sorts of strange things, include signal phase shifts between the caps.

Cool. Thanks for that info.

 

[Lavane]

I was just looking at my basket-case Marantz 1060, and its' service manual, trying to decide what to do with it. I've only ever seen good reviews of the 1060, and it's capacitively-coupled. It occurs to me that cap-coupled might be the perfect speaker protection scheme. No matter how catastrophic an output failure your amp may have, the speakers get a loud "thump" at worst.

While searching for info on cap-coupled outputs, I found this article by Rod Elliott. It's a long read, but a good read.

Capacitor Coupled output

I've restored two 1060's. One I kept, the other I gave to my son.
One came to me as an actual basket case. It came in a box in pieces.
At some point someone tried to repair it by using random resistors and transistors. It was a mess with wiring cut, etc. But well worth restoring. I had to replace every transistor on the amplifier board along with the caps and some resistors and diodes. The 1060 became my favorite SS integrated amp.
It works very well as a preamp also. I use mine sometimes as a preamp for a Marantz model 140 power amp. You still get that nice Marantz tone.

 

[Artie]

It works very well as a preamp also. I use mine sometimes as a preamp for a Marantz model 140 power amp. You still get that nice Marantz tone.

That's what's top on my "may do" list. On the other hand, I may sell it "as-is", because I'm getting old, and have too many irons in the fire. Decisions, decisions.

 

[Lavane]

That's what's top on my "may do" list. On the other hand, I may sell it "as-is", because I'm getting old, and have too many irons in the fire. Decisions, decisions.

I'm 64 and still burning myself with a solder iron.
It took awhile to bring the one 1060 back from the dead, but it was fun.
I took my time, checking the schematic against what was on the boards, sourcing parts and going at it one board at a time. Problems some fall into is to shotgun a bunch if new parts all at once. Then find problems they didn't have before. If they just got the thing working first, then replacing caps and any other old parts that need replacing one board at a time, there would be a lot less frustration. Once you finish a board, and then if you have a problem, you know where to look right away.
But I'm sure someone will take it off your hands pretty fast if you decide to pass it along as is.

 

[Artie]

I'm 64 and still burning myself with a solder iron.

In a few months, I turn 70. Now, whenever I want to mess with my vintage stuff, I grab something that works, and listen to the music. I do still enjoy repairing guitar electronics though.

 

[Lavane]

In a few months, I turn 70. Now, whenever I want to mess with my vintage stuff, I grab something that works, and listen to the music. I do still enjoy repairing guitar electronics though.

I've recently started to mess with tube Guitar amp builds and repairs.
It's a lot different than hifi. Distortion and saturation can be a good thing with guitar amps.

 

[rothwellaudio]

These two replies should be taken together.

After I retire I may actually learn some electronics -- no time for more than a smattering of it now.

Caps in parallel with widely divergent values can do all sorts of strange things, include signal phase shifts between the caps.

No, caps in parallel will not do all sorts of strange things. Phase shifts between caps? If the two caps are in parallel, how can there possibly a phase shift between them?

 

[HPMguy]

Split signal path through two different construction caps. Different plate values, different reluctance, different reactance, different frequency response characteristics.

I wouldn't have had fits with that part of physics if they were simply additive.

 

[arts]

I have always liked the sound of hifi gear that uses cap-coupled output stages, and that's about the only SS gear that I enjoy listening to.

I also absolutely love the tone and response of cap-coupled musical instrument amplifiers, especially when being pushed hard.

The (original) Acoustic Control Corporation made some great sounding and very powerful models using this output design.
I still have Frank Marino's old Acoustic 270 head that I used as a backup for decades

 

[gadget73]

not looking at the schematic, but most cap coupled amps take their feedback after the cap, so whatever it does is compensated for. No special need for bypass caps or anything like that if the feedback is connected to the speaker side of things.

 

[rothwellaudio]

Split signal path through two different construction caps. Different plate values, different reluctance, different reactance, different frequency response characteristics.

That's the point of bypass caps.
Where two components join there can be only one voltage at any point in time. There cannot be a phase difference between anything.