If the output caps dry up, bass will disappear then the volume in general. No good way to test them except a $120 peak ESR meter. Dried up ecaps tend to increase a little in capacitance, so cheap capacitance tester tells nothing. My speaker cap amp, I change the output caps the same time as the main rail cap needs it. If it fails short, you'll get ~25v DC on speaker, which can damage the speaker. Depends on price of speaker I suppose. After my $300 ea SP2-XT were stolen, I carried home two three way speakers for $5 from charity resale shop. Not too worried about protecting those, no bass or high treble anyway.
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Doesn’t really depend on the price of the speaker, more on the power hanging capacity. I doubt the whole 25 volts DC could do a thing to an SP2.
If you’re wondering if an output cap is dried out, temporarily bypass it with a brand new 10 uF. If it gets noticeably BRIGHT sounding, then the original cap has developed enough ESR that it should be replaced. If you just don’t notice a change, the cap is ok for now.
If you’re wondering if an output cap is dried out, temporarily bypass it with a brand new 10 uF. If it gets noticeably BRIGHT sounding, then the original cap has developed enough ESR that it should be replaced. If you just don’t notice a change, the cap is ok for now.
For this type of circuit, is it OK to use a larger value, say a 2700uf/35v?
I just don't enough about this type of design.
Thanks
Bigger output capacitor gets you more bass, which increases the current on the output transistors. Depends on how much soa you have in the output transistors, that were designed before soa rating was invented. I have 3300 uf output capacitors on my 1966 design ST120, but it had 40636 output transistors, selected versions of the pretty tough 2n3055. Die that nearly filled the TO3 case. Copper heat pad that was the same circumference. Those were the days my friend, we'd thought they'd never end - - -
The bigger the cap value, the lower the cutoff frequency of the high pass formed by the cap and the speaker. Whether you want that or not really depends on your speakers. If a speaker can’t handle low bass without overloading there isn’t any point in force feeding it any. For a small speaker in a sealed box or some open baffles, the cap can cause some *peaking* of the bass response right near the speaker’s fundamental resonance, giving a bit of bass extension. Doesn’t work well with vented boxes, and if mistuned doesn’t really help anything. I usually put in bigger ones if I have them, unless it’s something with a built in speaker where the cap definitely is part of the tuning.
So I replace those 1000uf/35v caps with Panasonic 1000uf/35v caps and doing so introduced hum in both speakers. I did replace some of the others that are circled in the pic. I ended up putting back the original 1000uf caps and the hum disappeared. Dead quiet! Sounds very good with plenty of bass and treble. Very clear.
I'm giving it back to the owner as is. Hope he's happy. Not touching the turntable, He can rebuild that. 😀
Thanks for all the help and info on this very old stereo. I would have never known about those speaker output caps.
I'm giving it back to the owner as is. Hope he's happy. Not touching the turntable, He can rebuild that. 😀
Thanks for all the help and info on this very old stereo. I would have never known about those speaker output caps.
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Were those 1000uF the actual speaker coupling caps?
If so and replacing them introduced hum then that is a sign the originals are very deteriorated indeed and not passing the low frequency content... which in turn leads to the obvious thought that the hum is probably originating from similarly deteriorated caps in the power supply.
If so and replacing them introduced hum then that is a sign the originals are very deteriorated indeed and not passing the low frequency content... which in turn leads to the obvious thought that the hum is probably originating from similarly deteriorated caps in the power supply.
Those almost have to be the output coupling caps. There is a very obvious zobel network connected to the negative side of each of them. The big clamp mounted cap is the power supply cap. Another potential reason for getting a “hum” all of a sudden is if something started oscillating at a super high frequency above audio. That can cause power supply hum to become audible when it otherwise isn’t. Most amplifiers actually produce a power hum when driven hard - but it’s usually masked by music that is also playing loud at the same time. When you can’t hear that “music” you will hear the hum. Hard to imaging changing the output caps causing that but I suppose anything is possible. Do those two 10 ohm carbon comp resistors near the caps (in series with these green “chicklet” caps) warm up when this is happening?
I really appreciate all the info on this thing. I'm sure there is allot more work I could do to it. It would take some time to replace all those 50 year old electro's on all the other boards. I'm going to leave it as is. Not getting paid for it except parts and this thing is not fun to work on. 😀