Personal computing discussed
Moderators: renee, Captain Ned
Captain Ned wrote:Wasn't, actually. Haha. Hmm.Well, the one EBay review talks about a weak or dead left channel. I'm assuming that was you.
Captain Ned wrote:Yeah, I guess so. It still sounds better than my old Kenwood KA-3500 that my dad gifted me. :) I guess I'll keep it and just live with the issues.120WPC (with no distortion spec) at 4Ω for under $100 does not speak well of the components in the box.
auxy wrote:Captain Ned wrote:Wasn't, actually. Haha. Hmm.Well, the one EBay review talks about a weak or dead left channel. I'm assuming that was you.Captain Ned wrote:Yeah, I guess so. It still sounds better than my old Kenwood KA-3500 that my dad gifted me. I guess I'll keep it and just live with the issues.120WPC (with no distortion spec) at 4Ω for under $100 does not speak well of the components in the box.
I should probably fiddle with the speaker wires; I noticed last night that rather than cranking up the volume, I can mess with the speaker wires and it seems to make the left channel come back on. Kinda strange.
ludi wrote:The "wiggle the wires" problem, especially at low volume levels, usually means the speaker wire isn't making good contact inside the jack. Sometimes this can happen when the speaker wire is getting old and has excessive corrosion. The other thing to watch out for is that those speakers may be old enough to have breakup in the woofer surrounds.
auxy wrote:"In the woofer surrounds"? If I'm understanding you correctly (and I'm probably not), wouldn't that affect the audio quality more than the volume or functionality (i.e. working at all)?
Captain Ned wrote:It would affect both. Seems that your speakers started life as an acoustic suspension design (superior design to my way of thinking) and ended up as a bass-reflex design. Not sure where your pair falls on that line. If yours are suspension-loaded, failure of the woofer (right, 4" is not a woofer) surrounds would break the air seal in the box and really trash the sound.
If you really like the speakers, finding someone to put new surrounds on the woofers isn't that hard. Paper and foam surrounds die quickest, while rubber surrounds tend to last a lot longer. Been down that path at least twice that I can remember.
ludi wrote:Per the manual, the PTA4 is rated 20Wx2 @ 4-Ohm, 1% THD @ 1kHz; 32Wx2 @ 4-Ohm, 10% THD @ 1kHz; or 120W "max," whatever that actually means. Should be plenty good enough for a pair of PRO-7AVs, though.
ludi wrote:Oooh. That's just what he told me. ¦3cI doubt your Optimus PRO-7AVs are as old as the 1970s. RadioShack sold several variations of a speaker in that format, but IIRC still had "Realistic" branding on all of its audio gear well into the 1980s. The "Optimus" branding picked up sometime in the late 1980s or early 1990s.
ludi wrote:Maybe! I still have it. I got the Pyle to replace it, and it does an okay job. I decided I'm probably going to keep it.The Kenwood amplifier, on the other hand, is definitely a vintage piece. Probably needs a good internal cleaning and some capacitor changeouts by now.
auxy wrote:It actually does still work decently, but the volume control knob is really scratchy, and if you don't put it in just the right spot, the left channel cuts out. Also, if you turn the volume up much, the audio starts to break up really bad.
Captain Ned wrote:Eheh, well, I did that, actually; it didn't help. And then I got all in there with tuner cleaner (helped a little) and a few weeks later, DeoxIT (did nothing). ¦3cviolently swing the volume knob through its range. In most cases this is sufficient to kick out the chow getting in the way of the electrons.
Captain Ned wrote:Hehe. The nerds in Freenode ##electronics were suggesting I replace the potentiometer altogether, but I haven't bothered to do so yet. Like I said, it gets real crackly and the audio breaks up a lot when you turn it up even modestly, so I think there's something else more severely wrong; even if I replaced the volume potentiometer, I think it might neeed more work.If this doesn't work, it's time to desolder the knob from the mainboard, take it out of the case, and have a party with some canned air.
Captain Ned wrote:Are you sure? I mean, you know way more about this than me, I have zero doubt -- I'm not questioning your knowledge or judgement at all! -- I just think I haven't quite been clear explaining what I mean.The crackly and break-up isn't a sign of larger things. It's just 30+ years of crap keeping the slider on the volume knob from directly contacting the underlying coil.
auxy wrote:Captain Ned wrote:Are you sure? I mean, you know way more about this than me, I have zero doubt -- I'm not questioning your knowledge or judgement at all! -- I just think I haven't quite been clear explaining what I mean.The crackly and break-up isn't a sign of larger things. It's just 30+ years of crap keeping the slider on the volume knob from directly contacting the underlying coil.
The volume control is real crackly and noisy when you turn it, but if you get it to the "right" spot, the sound is very clear. However, if you turn it up a bit, even once you get it to the "right" spot, the output is broken-up and staticky, especially on bass-heavy music or any low sound (rumbling in video games). It only does this on the speakers; headphones are clear as day.
That's why I was thinking it might be some other problem.
Captain Ned wrote:See, that's what I thought! It's happening at just like 2/10 or maybe 3/10 of the volume dial, tho. Maybe the amplifier is just old and worn-out?Simply put, you're asking for more power than the amp can deliver.
Captain Ned wrote:Nooo, they're 8-ohm. It says "8Ω 40W MAX POWER 80W" on the back.If the speakers are of 4-ohm impedance (it should say on the back by the terminals) there's a good chance that that old receiver simply wasn't designed to deal with 4-ohm speakers. The industry standard is 8-ohm impedance. 4-ohm speakers require twice the current (amperes) to create the same effective wattage. Old '70s receivers most likely don't have the oomph (highly technical term there) to push enough current to 4-ohm speakers.
auxy wrote:Captain Ned wrote:Nooo, they're 8-ohm. It says "8Ω 40W MAX POWER 80W" on the back.If the speakers are of 4-ohm impedance (it should say on the back by the terminals) there's a good chance that that old receiver simply wasn't designed to deal with 4-ohm speakers. The industry standard is 8-ohm impedance. 4-ohm speakers require twice the current (amperes) to create the same effective wattage. Old '70s receivers most likely don't have the oomph (highly technical term there) to push enough current to 4-ohm speakers.
Heeyyy, since they're 8Ω, could that be why they're so loud with my PTA4? It's rated for 2x120W with 4Ω equipment...
Captain Ned wrote:Oh. Argh, impedance is really confusing.Nope. As the impedance increases current delivery decreases. Since watts = volts*amps, less current means less watts.
auxy wrote:Captain Ned wrote:Oh. Argh, impedance is really confusing.Nope. As the impedance increases current delivery decreases. Since watts = volts*amps, less current means less watts.
Captain Ned wrote:So impedance = resistance. So you have voltage, current, and resistance. V=IR. Or, I = V/R, so assuming the voltage is constant, then as the resistance (or impedance) increases, current drops, and since the power P is equal to volts V times current I (P=VI), then as current drops, so does delivered power. Which you said. Basically.Impedence=resistance. The higher the impedance (in ohms), the more resistant the speaker's internal electronics are to the incoming signal. Back in the early days of hi-fi (i.e. '50s and '60s) most speakers had 16-ohm impedance as it was a whole lot easier and cheaper to build an amp that can push out voltage rather than one that can push out current. It's why truly high-quality amps are all physically massive. Delivering current to low-impedance loads (4 ohms & under) requires so much current delivery capacity that the power supply transformers and capacitors in the amp must be epically large on their own.
auxy wrote:So that means you need MORE current with a high-impedance device, right? Then why does it take so much current to run low-impedance loads? I've read this before and it's always confused me.
Captain Ned wrote:It would affect both. Seems that your speakers started life as an acoustic suspension design (superior design to my way of thinking) and ended up as a bass-reflex design. Not sure where your pair falls on that line. If yours are suspension-loaded, failure of the woofer (right, 4" is not a woofer) surrounds would break the air seal in the box and really trash the sound.
Captain Ned wrote:It's much easier for an amplifier to increase its voltage output than its current output.
Captain Ned wrote:THIS. This is the part that always confuses me. 4-ohm speaker, okay -- so if we're trying to reach 2.83v, then it's 2.83v divided by 4 ohms, or 707mA, and with a 16-ohm speaker it becomes 177mA... I just realized I've had the math backwards in my head the whole time. :lol: :math101: I'm an Asian who's bad at math, sue me. x3A 4-ohm speaker will require 4 times as much current compared to a 16-ohm speaker to induce the same voltage level through the crossover and voice coils.
just brew it! wrote:Captain Ned wrote:It's much easier for an amplifier to increase its voltage output than its current output.
To a point. On any amp that doesn't use transformer coupling of the output stage, your voltage swing is going to be limited to the voltage of the power supply rails.
Captain Ned wrote:It's also the rare solid-state amp that has output transformers, unlike tube amps where the rarity is a non-transformer output (seen a couple and they're bizarre beasties).
just brew it! wrote:I'm having a tough time imagining how you'd even make a transformerless tube output stage -- what do they do, use high-current radio transmitter tubes or something?