I have an old stereo amp. I guess it is about 30 years old. It has served me well over the years and I hate to part with it, but I am wondering if it is time to say goodbye?

I am getting a bit of hum out of the speakers. Yes I know bad filter caps.

The problem is that it looks like they used custom caps. Two cans encased in a molded plastic holder. Each can is 22K ufd. 69 WV.

There are a number od caps of various sizes scattered about the main board.

My concern is that I could find a filter cap in the dimensions needed to fit in the case. And if I did find the right cap in the dimensions needed, I am not certain I would be able to mount it safely given the existing custom mount.

Am I right in my assessment to just replace the amp?

Good news is that it has a nice size power transformer. Hopefully it's windings are marked.

 

You didn't tell us the make, model, power or what, if anything, is special about this old amp.

 

Nothing special about it. It is a Yamaha A-700. I probably paid a significant percentage of my income back in the day.

 

The hum is not super loud but audible at low volume with no other input. I have been doing some checking and apparently this is a popular amp.

 

Mine is black

 

Given 30 years the odds are you will find that new capacitors with greater voltage and uf values will probably be smaller and will easily fit where the old ones sat all while having superior ESR numbers as well.

 

Given 30 years the odds are you will find that new capacitors with greater voltage and uf values will probably be smaller and will easily fit where the old ones sat all while having superior ESR numbers as well.

What about mounting them? It is an odd configuration. Looks to be custom.

What about the 4 terminals on each can. I did not trace it out to see if the wires go to the same place.

What about all of the small electrolytics? Should they be replaced too? Seem like a big job. I am even dreading trying to get the volume control out. It needs to be cleaned or replaced. A bit scratchy. PCB it is mounted to has a ton of other controls too.


Wonder if it is worth trying to sell since the amp seems to be sought after?

 

I'm going to do what you doubt. I have a 1978 Onkyo that is starting to hum. I have no doubt that I can get a couple of, "Computer Grade" cans that will fit right in the old metal mounting brackets, have more capacitance, and lower ESR than the 36 year old originals ever had. One, "on/off" LED and a can of contact spray and it will be good for another 10 years, maybe 20.

You see, it's MINE. It has always been MINE. I never run it to its melting point because my ($800 each) Cerwin Vega H15 speakers can do 103 db @ 1W/1M. I can shake the closet doors and notify the neighbors if I want to, but I don't want to. You literally can't stay in the same room with it cranked up to the edge of distortion.

I don't want to buy a new amplifier with tiny momentary buttons that won't last 10 years and a microprocessor that will do anything except be repairable. I do want to keep the RIAA pre-amp for my vintage vinyl on my direct drive turntable, and several extra input channels for my TV, CD player, DVD player, multi-preset FM tuner, and an effects loop for my graphic equalizer.

It has everything I want and it's repairable.
Consider how many of those aspects your amp has and make your decision.

 

ps, glue has been invented. The capacitors will stay where they belong as long as you don't try to play basketball with it.

 

Two sides to every coin.

You just can't get a clean sounding amp these days and everything has a dSP chip in it. Even when dsp is turned off I am not sure if it is really off or it is just simulated stereo sound that an engineer from Pioneer or denon created for me with digital magic. It just doesn't sound as good as my old onkyo tx5000.

In any case, you might also be tired of fixing things and need something new. Go ahead, stimulate the economy and buy something new while selling your old one to make some collector happy and have something to tinker with.

 

I am wondering if I found the source of the hum. I am using the amp from my TV. I have a XBMC setup.

I added one of those new power strips that shut off when the TV is shut off.

I did some searching on hum and learned other devices can cause hum other than the amp itself.

I plugged the amp into a different out;et and the hum is gone. I did not get a chance to switch back as it is late here.

Hard to believe that a 30 year old amp would have no hum.

What is really strange is the scratchy volume control is gone too. I did try running it back and forth a couple of times while it was on the bench but I have done that before and it never cleared the problem before. But now the noise is gone. Very strange.

I do have an associated problem with the spdif output of my TV but I think I will post another thread on that. Maybe in the Computing & Network forum.

 

There are a few people who rebuild old ham radio equipment, I am one of these. some like to rebuild so it looks like the exact parts inside. They actually open up the old caps and put newer ones inside so the radio looks the same inside. One other way is to just put the newer caps under the chasis, and disconnect the old ones.

 

"Old Amp worth saving?"



Personally, I'd save it. Cannot beat the build quality.

I have an old Harmon Kardon stereo amp/receiver, that just needs a new lamp for the display.

Also have two other old amps/receivers, that need a good cleaning.

 

the reason I like to rebuild the older radios is that they sound better. Newer radios have lots more bells and whistles, but the older radios do not have pll's or any digital logic in them. Newer radios dont seem to have the low noise floor of the older radios. Digital circuits have lots of harmonics that can leak and radiate, increasing the amount of noise heard on fweakere signals. Also, the newer radios wont keep your cofee warm.

 

What about mounting them? It is an odd configuration. Looks to be custom.

What about the 4 terminals on each can. I did not trace it out to see if the wires go to the same place.

What about all of the small electrolytics? Should they be replaced too? Seem like a big job. I am even dreading trying to get the volume control out. It needs to be cleaned or replaced. A bit scratchy. PCB it is mounted to has a ton of other controls too.


Wonder if it is worth trying to sell since the amp seems to be sought after?

scratchy pots are easy to fix with control cleaner spray. You can usually do them in the unit just pack some tissue around it so the cleaner doesn't go every where. Spray it into an opening in the pot case and rotate the control.

As for shotgunning out the electrolytics: probably not that big a deal as long as you can get to them. use a solder sucker and solder braid to unsolder the PCB connections without damaging the traces. Mechanical mounting may be annoying but you can probably kluge them in. It won't have to survive military shake table once installed.

 

I am wondering if I found the source of the hum. I am using the amp from my TV. I have a XBMC setup.

I added one of those new power strips that shut off when the TV is shut off.

I did some searching on hum and learned other devices can cause hum other than the amp itself.

I plugged the amp into a different out;et and the hum is gone. I did not get a chance to switch back as it is late here.

Hard to believe that a 30 year old amp would have no hum.

I have a 40 year old Akai that doesn't hum.

 

scratchy pots are easy to fix with control cleaner spray. You can usually do them in the unit just pack some tissue around it so the cleaner doesn't go every where. Spray it into an opening in the pot case and rotate the control.

Yes I have done that before. The problem with this one is where it is mounted. Not sure I can get to the opening.

Mostly what I have done in the past is to pop them open and clean them.

But the scratch is gone! Maybe it took just a few more fast wipes to get whatever gunk was in there to clear.

 

I have a 40 year old Akai that doesn't hum.

In my post above I think the hum was actually coming from another source other than the amp.

 

In my post above I think the hum was actually coming from another source other than the amp.

Sounds like you had a ground loop.

 

In my post above I think the hum was actually coming from another source other than the amp.

Maybe it's a funky interconnect cable or dirty ground surfaces the RCA connectors on the device.