Greetings! Total newbie here. Is it possible to use my old stereo amp as a bass amp? I figured, I’ve already got some nice Bose speakers and an older (once top-of-the-line) Technics amp. It has the old-style RCA jacks on the back for inputs. TYIA!
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You’ll almost certainly need a preamp. The signal levels coming from a bass (or guitar) are, I think, significantly lower than what is typically expected from an aux input to any stereo amp or active speaker. There are a whole range of preamp options that will do it.
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Would something like a Vox amplug qualify as a preamp?
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yes but it’s so limited. You’d provably want something more like Mustang or Katana Go if you can find one. I don’t know if it would solve your problem though.
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I actually use a Zoom B3n multi-effects pedal which has a choice of several different digital preamps in it and have this plugged into some active studio speakers. This is for when I’m in a confined space; I’m currently in a caravan for a couple of months so my Ampeg amp is a little too big for the space! It works pretty well but I’d be careful of sending too much higher power bass signals to speakers not really designed for it. I have to watch that with mine.
This set up works but a proper amp is just so much better. I also have a small Spark Mini but I don’t find that is as good quality sound.
I’m afraid I don’t know the Vox amplug but if it’s output is designed for headphones is probably good for the aux input of a stereo.
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I’d just say, not advised. If your serious about wanting to play do yourself a solid and buy a small bass amp. Your stereo and Bose speakers are not built for it.
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I’ve played several gigs using a stereo as an amp - we ran our mixer in to it. Works great.
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Then you might want to explain in greater detail how you accomplished it so the OP doesn’t somehow blow up his stereo or speakers just plugging in and having at it.
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In our case it was really simple, mixer master line out to the line in on the stereo amp. Nothing magic or difficult about it. Just be careful with mixer levels and volume on the stereo and it should be fine.
We had a pair of woofers and a pair of normal stereo speakers hung off the amp, worked great.
You’ll need some kind of preamp with a line level out for the bass.
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I asked Vox about this. Their reply: “The Headphones output can be used as a direct line output (such as when going direct to a mixer/PA system, recording device, or audio interface). So, the Headphones Out can be connected to the line-level input(s) of other audio equipment. You’ll probably need to adjust your levels accordingly - both on the amPlug and on the audio equipment you are connecting to. Start with a low volume from the amPlug and gradually increase it until the sound seems to be the appropriate level for the setting of the volume control of the equipment you are playing it through. If the amPlug itself is causing the Line Input and/or speakers connected at the other end to distort (a distortion not produced by the amPlug itself), try reducing the output volume from the amPlug until there is no added distortion produced by the Line Input or speakers.”
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Also, I will definitely spring for a pedal, amp, etc. in the near future. Just trying to make use of some audio equipment I literally haven’t used in a few years. 
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It might be a good idea to EQ a high pass for above 50-60Hz for a “normal” stereo system, depending on the amp and speaker size.
If you don’t have an EQ: turn the bass on the system system down a little. Nobody likes turning down the bass while playing bass guitar, I know. But there is a risk to really damage stuff!
Bass can go very low … and most non-highend stereo systems don’t support very low frequencies without distortion or even blowing up the speaker, especially at higher volumes!
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That’s generally good advice for EQing bass regardless - and especially for recording. I’d say closer to 40-50Hz is fine though. All you want to do is have it rolled off to trim all the low end mud.
In my experience it’s also unlikely to damage any normal stereo speakers even if you don’t do this; ours were fine and there was a lot (A LOT) harder stuff on the low end than bass guitar going in to them - think raw synth sawtooth and square waves. And of course it won’t hurt the amp whatsoever.
We used to joke a lot about chewing up our speakers but there was no actual degradation.
Just make sure you’re running line level outs to line level ins and it should be ok. Note that bass preamp and EQ pedals output instrument level, not line level, so those won’t work as well (tone suck plus distortion is likely). I recommend a mixer.
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Hmmmm, not convinced: maybe @Al1885 or @BozzerWolf can do a little test with their JBL Charge to confirm?
- Connect the JBL Charge to the Boss Katana GO.
- Turn up the Volume on the Katana, Charge and Bass
- Play a very low tuned & bass heavy song as hard as you can.
- Observe
I’m pretty sure that they will reach their breaking point quite soon!?
You can also test this with playing heavy bass through your notebook!
I made a mistake with the output settings of my notebook once and had to replace the little speakers. It was more expensive than I thought.
My point: some stereo systems are simply not made for heavy bass. You better be careful with smaller systems.
Don’t care 
I’m just passing on my subjective experience from doing this, with a 100W stereo amp in to two normal (8"/1") speakers and two woofers (12 or 15", I forget what we did there).
What you choose to believe is your own issue.
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Let’s be honest: your two (!!!) 12" or 15" woofers make the difference!
Most home stereo systems look like this and will surely be destroyed by playing bass guitar through them.
This stuff reminds me of a CD I bought some years back, but a bit of back history is required.
I went to a school run by a Benedictine monastery and they had a new abbey built and wanted to transfer the big bell from the old one. They told the architect the weight and he duly designed the tower for to take it. But when he saw the bell which was intended to be swung not hammered (they had omitted to tell the architect this), he politely suggested they only use it on rare special occasions. One time we were taken up into the tower to see this bell and it measured something like 5m diameter (say 16 1/2 feet) and they weren’t allowed to ring it with anyone standing in the same room.
Anyway some years later (when it was all the craze) they released an album of Gregorian chant in which they opened the CD with this bell being rung. On the CD they had a warning to turn your stereo down as it had sub acoustic vibrations that would easily destroy your speakers! Let’s rock!
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That’s doable. can’t do it the other way around or the speakers will be blown in seconds.
What you get on those bluetooth speakers are mid bass and not really sub bass. It’s ok in a small room but not great with open space and higher volume.
How would you even do it the other way around?
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