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Old 12th November 2007, 07:41 PM   #1
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Question Head Unit Amps Off for Sure?

I just went from powering my front component speakers via my Pioneer head unit (22 Wrms - not good) to using a JL 300/2v2 amp (and wow - it really performs!!).

I terminated the speaker leads from the head unit with a thick wrapping of electrical tape on each now-unconnected end. But, my Pioneer head unit is still getting quite warm. Warm as when its amps were driving speakers! No, I didn't create a short-circuit by twist-connecting the speaker leads, hehe.

Does having no speakers connected to the head unit's internal amplifiers turn them completely off or not? I want this head unit to last as long as possible so I want those internal amps off. Cool running is the goal, heh.

Thanks!
Joe
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Old 12th November 2007, 08:26 PM   #2
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It will always be on unless you unsolder the Amp chip in the HU.
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Old 12th November 2007, 09:09 PM   #3
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Wow. That's a bummer... Not that I often use the system at 34 out of 40 on the volume gauge, I was really hoping the head unit wouldn't heat up like it did previously. With the new component drivers and JL amp, it can easily do the 34/40 cleanly but my SPL meter says danger, according to OSHA recommendations, heh. So, I keep it around 20 (or even less).

Maybe instead of the head unit failing completely, the amp chip will be the first to go and then the unit will keep functioning nice and cool, haha.

What IS really nice is that 1980's music, with a much lower average output, can now be played at a level equal to new CD's that are often horribly compressed to the limit. 150Wrms/ch into 125Wrms/ch drivers gives the proper amount of headroom!

Thanks for your knowledge there!
Joe
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Old 12th November 2007, 09:33 PM   #4
grjr is offline grjr  United States
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As stated before the audio amplifiers remain on even with no load connected. They still generate heat, but typically when the audio amps fail they kill the preamp output signal as well. I've removed the audio amplifiers in some of my decks that I don't plan to use without power amplifiers and they work just fine (and cool). I prefer decks without amplifiers anyways since the power output isn't that great.
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Old 12th November 2007, 10:06 PM   #5
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So, if the amp chip dies, the pre-amp signal goes along with it? Arrrggghhh.

I will now consider taking the amp chip out of the loop as you have done. After moving to external power amplifiers, and noting how much the wattage headroom improves the quality of the sound (along with a 108.5dB SNR of the JL 300 amp), I'm not going to be using the internal HU amps again.

I may seem to be preoccupied with this HU (a Pioneer DEH-P8600MP) but it hasn't gone down in value at all over three years! Maybe $50 as it still sells for around $550. Compared to other technology depreciation, this one just doesn't depreciate! I'm sure there are better HU's out there but I really like this one.

Thanks!
Joe
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Old 12th November 2007, 10:32 PM   #6
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All my Pioneer HU's with failed amps the pre-outs still worked normally
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Old 12th November 2007, 10:56 PM   #7
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Hi AudioBahn:

Thanks for that bit of info there! I was thinking of locating the chip, looking-up who made it, getting a pin-out schematic, and then carefully cutting power to it (wire snip with option to resolder if need be, heh). Getting tech info on chips is pretty easy from the ADC and DAC chips I've done research on (AKM for example).

My model 8600 has so many crossover capabilities and other goodies that I really do love it (all functioning at lower than noticeable noise levels). The only thing I wish it could do is read/play a DVD with uncompressed WAV files stored on it (I don't listen to MP3 encoded stuff, not with the amps and drivers I now have). I also have the XM and RB20 aux input boxes, the latter I temporarily connected to a 'car PC' (vacation roadtrip) which stored my entire CD collection in uncomp WAV format (the sound from the PC's WT192X pro-audio card through the aux input was extremely accurate and uncolored).

I guess the one GOOD thing about the HU heating up is during cold Minnesota winters. The warm-up gets the deck's CD bearings up to proper use temperature nicely...

Thanks again all. I greatly appreciate your thoughts.
Joe
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Old 12th November 2007, 11:47 PM   #8
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Correct me if I'm wrong, but I seem to remember HUs that have a defeatable amp. I'm thinking my son's Kenwood Excelon has that feature.

And I remember having some kind of HU back in the '80s or '90s that had a simple bypass switch for the internal amp.
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Old 13th November 2007, 01:05 AM   #9
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I will double-check on that defeatable amp feature but I'm 99.9% sure my model 8600 doesn't have such a feature. I'm nerdy enough to have read the operation manual to the point of knowing it quite well along with all the configuration screens/pages that the HU provides via its display.

It does sound like a perfectly reasonable feature to offer too.

Thanks!
Joe
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Old 13th November 2007, 01:11 AM   #10
ppia600 is offline ppia600  United States
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My kenwood has a defeatable amp, I have it turned off, it makes the preamp signal cleaner according to kenwood.
That is a nice pioneer, but I'm pretty sure that one doesn't have a way to turn the amp off. I would just take it apart and find the lead that supplies 12v+. It will be easy and you can just cut the trace with a razor or desolde the pin(s) and pull them above the board a little. You could also solder two wires, one to the amp ic power pin(s) and another to the 12v+ source and have an external switch connected to be able to use the amp in the future if needed.
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