Realistic STA-90 receiver questions
Comments
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mhardy6647 wrote: »The DC offset comments have nothing to do with the lamps -- and everything to do with the health and suitability of the receiver's power amplifier to use with a pair of (presumably) valuable speakers :- )
I apologize for being too subtle when I changed the subject!
The bottom line is that the lamps are cosmetic; the performance of the "active" electronics is mission critical.
http://audiokarma.org/forums/index.php?threads/amplifier-distortion-dc-offset-and-you.5634/
I've had it hooked up to a test speaker already and I know both channels are good. I'm going to be hooking it up to my Nova 8B speakers and my Fisher XP-77KC Speakers. I run all 4 since the Novas are good in the low end and the Fishers in the high end. Im also going to do a sound comparison to my current STA-77A receiver. It seems that it's just old age that some of the lamps are out.
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"Good", I presume, in the sense that they make sound, and they both probably sound fine, but all may or may not be well on a four-ish decade old component.
That is why I'd still advise you check for DC on the outputs, to minimize risk of damage to your speakers. If there's any significant DC present on either channel's output signal, it is adding a constant load to the woofer's voice coil and generating heat. If there's enough DC present (polarizing voltage, so to speak) long-term use could easily fry a woofer's voice coil. They're not made for continuous DC polarization.
Normal DC offset is typically 10s of millivolts.
It is very cheap insurance (with respect to your loudspeakers)... and I'll leave it at that.
Indeed, the failed lamps are most likely just due to age (time turned on and lighted).
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mhardy6647 wrote: »"Good", I presume, in the sense that they make sound, and they both probably sound fine, but all may or may not be well on a four-ish decade old component.
That is why I'd still advise you check for DC on the outputs, to minimize risk of damage to your speakers. If there's any significant DC present on either channel's output signal, it is adding a constant load to the woofer's voice coil and generating heat. If there's enough DC present (polarizing voltage, so to speak) long-term use could easily fry a woofer's voice coil. They're not made for continuous DC polarization.
Normal DC offset is typically 10s of millivolts.
It is very cheap insurance (with respect to your loudspeakers)... and I'll leave it at that.
Indeed, the failed lamps are most likely just due to age (time turned on and lighted).
Will do, what's the best way for me to test the DC from the outputs? -
Just a digital multimeter set to DC voltage. One channel at a time; red lead to plus, black lead to ground/minus and check the DC voltage. Should be 100 mV (0.1 VDC) or less -- for most components, much less. Oh, you'll want to check for both positive and negative DC, since the OCL amplifiers have "bipolar" power supplies (both a positive and negative DC "rail" supply voltage).
Check the AK link I posted before for far more information.
There are two issues:
One is DC balance, which can generally be adjusted (although this isn't for novices without, at the least, a service manual for the component in question).
The big problem -- which you don't have, thankfully, is the result of the failure of a transistor; typically a shorted output transistor. This can put the full DC rail voltage (on an amp like that, it's probably + or - 40-ish volts DC) onto the speaker output! This will cook most woofers' VCs instantly. Been there, done that.
Fortunately, you don't have the latter problem -- still good to ensure that there's minimal DC voltage on either channel's output, though.
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mhardy6647 wrote: »Just a digital multimeter set to DC voltage. One channel at a time; red lead to plus, black lead to ground/minus and check the DC voltage. Should be 100 mV (0.1 VDC) or less -- for most components, much less. Oh, you'll want to check for both positive and negative DC, since the OCL amplifiers have "bipolar" power supplies (both a positive and negative DC "rail" supply voltage).
Check the AK link I posted before for far more information.
There are two issues:
One is DC balance, which can generally be adjusted (although this isn't for novices without, at the least, a service manual for the component in question).
The big problem -- which you don't have, thankfully, is the result of the failure of a transistor; typically a shorted output transistor. This can put the full DC rail voltage (on an amp like that, it's probably + or - 40-ish volts DC) onto the speaker output! This will cook most woofers' VCs instantly. Been there, done that.
Fortunately, you don't have the latter problem -- still good to ensure that there's minimal DC voltage on either channel's output, though.
Thanks! I will be. Going over this with my father as he's got more knowledge into this stuff than I do and I will leave the results. -
Radio Shack used to carry stuff like this in the back if their stores.
Now good luck trying to find one that is still open. They didn't close them all,but they shuttered a LOT of them. -
Our local R/S survived the kerfuffle all the way through 2015 and then found out after Christmas that they were closing in Feb. 2016... they're gone now.
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mhardy6647 wrote: »Our local R/S survived the kerfuffle all the way through 2015 and then found out after Christmas that they were closing in Feb. 2016... they're gone now.
Yes I've been meaning to get to my local Radio Shack if they aren't gone yet either, I want to pick up a few things.
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UPDATE!!! I forgot to test the outputs, although I did rewire my speakers and I hooked up the STA-90 and it sounds like no other! No wonder they claim its a sound you can't describe!
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We'll assume "it sounds like no other" in a good way.
;-)
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mhardy6647 wrote: »We'll assume "it sounds like no other" in a good way.
;-)
For sure! Otherwise it would be saying the STA-77A sounds better lol
