Vintage Amp Buzzing?

[ComputerWizKid]

I found a Kenwood KA-2000 (Trio for those that remember :sneaky at an estate sale for $3 it is a North American Model (110-117VAC 60HZ 60Watts says the nameplate) and it buzzes out of the speakers only if plugged into a surge protector. My question is why is that? I currently have it plugged directly in a wall receptacle I am using with my computer for audio with a pair of cheap Insignia speakers I bought from BestBuy and at only 13WPC it sounds great (To me at-least as I am no audiophile^_^) was there such a thing as a "Surge Protector" in the 1960's? The amp has a date hand wrote on the bottom of it (I assume that is a date) of 11/67

 

[sdifox]

your ups outputs square waves, the amp is looking for sine wave.


also, amp on ups is a very bad idea.

 

[NutBucket]

Its probably a grounding issue.

sdi, I had never thought about this before....I'll have to ponder it some more as I keep all my gear, vintage a "new", on an UPS.

 

[ComputerWizKid]

I tried it on my UPS and it sounded horrible and I only left it on for a couple of seconds but I am talking about a plan power strip/Surge protector (No battery inside it) and it buzzes with that I have to plug it directly into the wall receptacle to get it to work properly

 

[sdifox]

I tried it on my UPS and it sounded horrible and I only left it on for a couple of seconds but I am talking about a plan power strip/Surge protector (No battery inside it) and it buzzes with that I have to plug it directly into the wall receptacle to get it to work properly

Was it the same outlet? It is probably ground loop.

 

[ComputerWizKid]

Yeah it was the same outlet I used the bottom 1/2 of the outlet now that I think about it, it probably is a ground loop as the computer and the amp are on different breakers.

 

[ComputerWizKid]

Ok I tried it in the same outlet as the computer and it does not buzz anymore thanks

 

[NutBucket]

Oh! Totally missed the bit about being hooked up to a PC. I have to use a ground-loop isolator on the audio cable whenever I hook a vintage amp/receiver up to a TV or computer. Being plugged in to the same UPS/surge strip didn't help.

 

[ComputerWizKid]

OK the buzzing is back this time only in the left channel
could that be a grounding problem also or is it a problem with the amp? It sounds like a 60HZ hum which disappears as soon as I pull the plug on the amp (As weird as that may sound it still keeps playing for about 10 seconds but the buzz is gone then) So I am thinking a grounding issue??

 

[sdifox]

OK the buzzing is back this time only in the left channel
could that be a grounding problem also or is it a problem with the amp? It sounds like a 60HZ hum which disappears as soon as I pull the plug on the amp (As weird as that may sound it still keeps playing for about 10 seconds but the buzz is gone then) So I am thinking a grounding issue??

oh, that could be the transformer vibrating. You have some reserve power in the capacitors after you turn the unit off. Are you sure the buzz is coming from the speakers?

 

[ComputerWizKid]

Yes the buzz is coming from the speaker (only the left one)

 

[Modelworks]

Disconnect all inputs from the amp so it is just the amp + speakers. Turn the volume way up almost to max. You should not hear any buzzing or hum. If it is okay that way then you know the source is external.

If you do hear something with nothing connected then it could be a faulty capacitor , a couple different places will cause that. Power supply (60hz hum), input decoupling(may distort with noise), and output capacitor( changes with volume level) from the internal transistor/fet to the speaker terminal.

The amp is using a half wave setup for the power which means those filter capacitors need to be perfect or you will get noise in the output. Check C10 and C11.


The schematics for the amp are here:

 

[ComputerWizKid]

Yeah I do still hear the buzz with nothing connected I will open it up and check C10 and C11 but what is the value for those two caps? I know it says 1000 30V and 1000 50V but what is the 1000 UF PF?? Also the buzzing does not change volume so I assume it is just the two filter caps

 

[Modelworks]

Yeah I do still hear the buzz with nothing connected I will open it up and check C10 and C11 but what is the value for those two caps? I know it says 1000 30V and 1000 50V but what is the 1000 UF PF?? Also the buzzing does not change volume so I assume it is just the two filter caps

yeah they are 1000uf, I would replace them both with 50V ones if they will fit.
Also check C6 and C7 in the amplifier output stage., they are also 1000uf .

That amp is over 20 years old so it wouldn't surprise me if a few caps are dried out.

 

[ComputerWizKid]

Probably a stupid question since I don't know much about capacitors but what kind of caps are they? I assume electrolytic but what kind as I have found a couple of different kinds of them (Radial Axial) I also have another question how do I go about heating up 33 Year old solder? I two soldering irons (Both Radio$hack) One 15Watt Grounded Tip with a small pointy tip and a 30Watt (Two Prong) gun iron with a giant tip (About the size of an alternator) I really like the way this amp sounds so I don't want to ruin it by messing up the Primitive Circuit board^_^ (PCB) Oh if I can't get the new caps to fit can I solder wires to the cap and then the board?

Thanks

 

[NutBucket]

Don't bother doing that. Just remove the old caps. You'll want radial leads (both leads on one end) vs axial (leads on the axis of the cap, one on each side). Just get some solder wick from the shack to remove the old solder. It'll be easier to remove the old cap.

 

[KGB]

While you're at the Rat Shack, get some of THIS and use it to clean the switches and pots.

I don't see where Shack has radial 1000uf 50V units but instead has axial. Go figger.

 

[alfa147x]

Man I wish I could find an amp for that price!